US20150130277A1 - Dc micro-grid - Google Patents

Abstract

Systems and methods are provided for creating and operating a Direct Current (DC) micro-grid. A DC micro-grid may include power generators, energy storage devices, and loads coupled to a common DC bus. Power electronics devices may couple the power generators, energy storage devices, and loads to the common DC bus and provide power transfer.

Description

CROSS REFERENCE TO RELATED PATENT APPLICATIONS
• This application is a Continuation of U.S. patent application Ser. No. 13/533,593, filed Jun. 26, 2012, and entitled “DC Micro-Grid”, which is a Continuation-in-part of U.S. patent application Ser. No. 13/295,527, filed Nov. 14, 2011, and entitled “Fuel Cell System with Grid Independent Operation and DC Microgrid Capability” which claims the benefit of priority to U.S. Provisional Patent Application Ser. No. 61/413,629, filed Nov. 15, 2010, and entitled “Fuel Cell System with Grid Independent Operation and DC Microgrid Capability”. The present application also claims the benefit of priority to U.S. Provisional Patent Application Ser. No. 61/501,604, filed Jun. 27, 2011, entitled “DC MICROGRID.” The contents of all three applications are incorporated herein by reference in their entirety.
BACKGROUND
• Electrical power systems can be used to provide electrical power to one or more loads such as buildings, appliances, lights, tools, air conditioners, heating units, factory equipment and machinery, power storage units, computers, security systems, etc. The electricity used to power loads is often received from an electrical grid. However, the electricity for loads may also be provided through alternative power sources such as fuel cells, solar arrays, wind turbines, thermo-electric devices, batteries, etc. The alternative power sources can be used in conjunction with the electrical grid, and a plurality of alternative power sources may be combined in a single electrical power system. Alternative power sources are generally combined after conversion of their direct current (DC) output into an alternating current (AC). As a result, synchronization of alternative power sources is required.
• In addition, many alternative power sources use machines such as pumps and blowers which run off auxiliary power. Motors for these pumps and blowers are typically 3-phase AC motors which may require speed control. If the alternative power source generates a DC, the DC undergoes several states of power conversion prior to delivery to the motor(s). Alternatively, the power to the motors for pumps, blowers, etc. may be provided using the electrical grid, an inverter, and a variable frequency drive. In such a configuration, two stages of power conversion of the inverter are incurred along with two additional stages of power conversion for driving components of the AC driven variable frequency drive. In general, each power conversion stage that is performed adds cost to the system, adds complexity to the system, and lowers the efficiency of the system.
• Operating individual distributed generators, such as fuel cell generators, both with and without a grid reference and in parallel with each other without a grid reference is problematic in that switch-over from current source to voltage source must be accommodated. Additionally, parallel control of many grid independent generators, utility anomalies, and/or non-critical load reflections can be problematic.
• To address the mode-switch-over issue, a double-inverter arrangement may be utilized. This allows one inverter to be used in grid tie and a second inverter to be used with the stand-alone load. An exemplary double-inverter arrangement with a load dedicated inverter that is located internally in an input/output module of a solid oxide fuel cell (SOFC) system is described in U.S. patent application Ser. No. 12/148,488, filed May 2, 2008 and entitled “Uninterruptible Fuel Cell System”, which is incorporated herein by reference in its entirety.
• Another approach is to drop power for 5-10 cycles to switch modes. If a single inverter is used, a time of 5-10 cycles would be required to drop grid tie and establish voltage mode control.
• Yet another approach is to use frequency droop to control the amount of power sharing in grid tied export or in load stand alone output control.
DESCRIPTION OF THE DRAWINGS
• FIG. 1A is a block diagram illustrating a system according to an embodiment.
• FIGS. 1B to 1K illustrate the system ofFIG. 1A in various modes of operation.
• FIGS. 2 and 3 are block diagrams illustrating a DC micro-grid according to an embodiment.
• FIG. 4 is a block diagram illustrating an IOM comprising an inverter that is configured for “bi-directional” operation according to an embodiment.
• FIG. 5 is a block diagram illustrating an IOM comprising an inverter that is configured for dual mode functionality according to an embodiment.
• FIGS. 6A-6E illustrate various modes of operation of the system of the type shown inFIG. 1A to provide power to an electric vehicle (EV) charging station according to embodiments.
• FIGS. 7-10 are block diagrams of DC micro-grids according to the various embodiments.
• FIG. 11 is a block diagram of an embodiment high reliability DC module.
• FIG. 12 is a block diagram of a DC micro-grid according to an embodiment.
DETAILED DESCRIPTION
• Referring toFIG. 1, a fuel cell system according to an embodiment includes a uninterruptible power module (UPM)102, an input/output module (IOM)104 and one or more power modules (i.e., power generators)106. If there is more than onepower module106, for example six to tenmodules106, then each power module may comprise its own housing. Each housing may comprise a cabinet or another type of full or partial enclosure, for example the cabinet described in U.S. patent application Ser. No. 12/458,355, filed Jul. 8, 2009, and entitled “Fuel Cell System with Quick Connect Components”, which is incorporated herein by reference in its entirety. The modules may be arranged in one or more rows or in other configurations.
• The UPM102 includes at least one DC/AC inverter102A. If desired, an array of inverters may be used. Any suitable inverter known in the art may be used. The UPM102 optionally contains an input rectifier, such as aninput diode102B which connects to the output of aDC bus112 from the power module(s)106 and to the input of the at least oneinverter102A. The UPM also optionally contains aboost PFC rectifier102C which connects to the output theelectric grid114, such as a utility grid, and to the input of the at least oneinverter102A.
• The IOM104 may comprise one or more power conditioning components. The power conditioning components may include components for converting DC power to AC power, such as a DC/AC inverter104A (e.g., a DC/AC inverter described in U.S. Pat. No. 7,705,490, incorporated herein by reference in its entirety), electrical connectors for AC power output to the grid, circuits for managing electrical transients, a system controller (e.g., a computer or dedicated control logic device or circuit), etc. The power conditioning components may be designed to convert DC power from the fuel cell modules to different AC voltages and frequencies. Designs for 208V, 60 Hz; 480V, 60 Hz; 415V, 50 Hz and other common voltages and frequencies may be provided.
• Eachpower module106 cabinet is configured to house one or more hot boxes. Each hot box contains one or more stacks or columns offuel cells106A (generally referred to as “segments”), such as one or more stacks or columns of solid oxide fuel cells having a ceramic oxide electrolyte separated by conductive interconnect plates. Other fuel cell types, such as PEM, molten carbonate, phosphoric acid, etc. may also be used.
• Fuel cells are often combined into units called “stacks” in which the fuel cells are electrically connected in series and separated by electrically conductive interconnects, such as gas separator plates which function as interconnects. A fuel cell stack may contain conductive end plates on its ends. A generalization of a fuel cell stack is the so-called fuel cell segment or column, which can contain one or more fuel cell stacks connected in series (e.g., where the end plate of one stack is connected electrically to an end plate of the next stack). A fuel cell segment or column may contain electrical leads which output the direct current from the segment or column to a power conditioning system. A fuel cell system can include one or more fuel cell columns, each of which may contain one or more fuel cell stacks, such as solid oxide fuel cell stacks.
• The fuel cell stacks may be internally manifolded for fuel and externally manifolded for air, where only the fuel inlet and exhaust risers extend through openings in the fuel cell layers and/or in the interconnect plates between the fuel cells, as described in U.S. Pat. No. 7,713,649, which is incorporated herein by reference in its entirety. The fuel cells may have a cross flow (where air and fuel flow roughly perpendicular to each other on opposite sides of the electrolyte in each fuel cell), counter flow parallel (where air and fuel flow roughly parallel to each other but in opposite directions on opposite sides of the electrolyte in each fuel cell) or co-flow parallel (where air and fuel flow roughly parallel to each other in the same direction on opposite sides of the electrolyte in each fuel cell) configuration.
• Power modules (i.e., power generators) may also comprise other generators of direct current, such as solar cell, wind turbine, geothermal or hydroelectric power generators.
• The segment(s)106A of fuel cells may be connected to the DC bus,112 such as a split DC bus, by one or more DC/DC converters106B located inmodule106. The DC/DC converters106B may be located in theIOM104 instead of thepower module106.
• The power module(s)106 may also optionally include anenergy storage device106C, such as a bank of ultracapacitors, batteries, or flywheels.Device106C may also be connected to theDC bus112 using one or more DC/DC converters106D.
• TheUPM102 is connected to an input/output module (IOM)104 via theDC bus112. The DC bus receives power frompower modules106.
• The fuel cell system and thegrid114 are electrically connected to aload108 using acontrol logic unit110. The load may comprise any suitable load which uses AC power, such as one or more buildings, appliances, lights, tools, air conditioners, heating units, factory equipment and machinery, power storage units, information technology (IT) loads, security systems, etc. The control logic unit includes aswitch110A andcontrol logic110B, such as a computer, a logic circuit or a dedicated controller device. The switch may be an electrical switch (e.g., a switching circuit) or an electromechanical switch, such as a relay.
• IT loads, (i.e., devices operating in an IT system) may include one or more of computer(s), server(s), router(s), rack(s), power supply connections, and other components found in a data center environment. As described herein, an IT load (i.e., devices operating in an IT system which may include one or more of computer(s), server(s), router(s), rack(s), power supply connections, and other components found in a data center environment) and IT system are distinguished from devices, such as computers, servers, routers, racks, controllers, power supply connections, and other components used to monitor, manage, and/or control the operation of DC power generators and DC power generation systems in that IT loads do not monitor, manage, and/or control the operation of any DC power generators or DC power generation systems that provide power to the IT loads themselves.
• Control logic110B routes power to theload108 either from theUPM102 or from thegrid114 usingswitch110A. The at least onefuel cell segment106A andstorage device106C frommodule106 are electrically connected in parallel to the at least onefirst inverter104A in IOM and to the at least onesecond inverter102A in theUPM102. The at least onefirst inverter104A is electrically connected to theload108 through theelectrical grid114 usingswitch110A in the first position. In contrast to the circuit shown in U.S. patent application Ser. No. 12/148,488, filed May 2, 2008 and entitled “Uninterruptible Fuel Cell System”, which is incorporated herein by reference in its entirety, thegrid114 inFIG. 1A is directly connected to theload108 through thecontrol logic unit110 without passing through a bidirectional inverter. The at least onesecond inverter102A is electrically connected to theload108 with theswitch110A in the second position without using the electrical grid114 (i.e., the output of thefuel cell segment106A does not have to pass through thegrid114 to reach the load108).
• Thus, thecontrol logic110B selects whether to provide power to the load from the electrical grid114 (or from thefuel cell segment106A through the grid) or through the at least onesecond inverter102A. Thecontrol logic110B may determine a state of the power modules and select a source to power theload108 based on the state of the power modules, as described below.
• Asecond switch116 controls the electrical connection between theIOM104 and thegrid114.Switch116 may controlled by thecontrol logic110B or by another system controller.
• By way of illustration and not by way of limitation, the system contains the following electrical paths:
• A path to theload108 from theAC grid114.
• A path from theAC grid114 through theIOM104 tostorage elements106C of power modules106 (for example, ultracapacitors, batteries, or flywheels).
• A path from thestorage elements106C of thepower modules106, over theDC bus112 to theIOM104 and theUPM102 in parallel. The DC bus delivers DC to the inverter in theUPM102. Theinverter102A in theUPM102 orinverter104A inIOM104 delivers AC power to theload108 depending on the position of theswitch110A.
• A path from the power modules106 (which may include power from the fuel cell segment(s)106A and/or thestorage elements106C of the power modules106), over theDC bus112 to theIOM104 and theUPM102. The DC bus delivers DC voltage to the inverter in theUPM102. Theinverter102A in theUPM102 delivers AC power to theload108. Power in excess of the power required by theload108 is delivered to the AC grid through aninverter104A in theIOM104. The amount of power that is delivered to theAC grid114 will vary according the demands of theload108. If the amount of power required by theload108 exceeds the power provided by thepower modules106, the additional power demand may be supplied by theAC grid114 directly to theload108 throughswitch110A in the first position or to theUPM102 with theswitch110A in the second position. The grid power is rectified inrectifier102C inUPM102 and provided to theinverter102A in theUPM102 and converted back to AC for powering theload108.
• FIGS. 1B-1K illustrate various modes of operation of the system shown inFIG. 1A. While the embodiments described below illustrate aload108 which requires 100 kW of power and the fuel cell segment(s)106A which output 200 kW of power in steady state, these values are provided for illustration only and any other suitable load and power output values may be used.
• FIG. 1B illustrates the system operation during the installation of the system and/or during a period when theload108 receives power from thegrid114. As shown in this figure, the fuel cell segment(s)106A and theenergy storage device106C are in the OFF state, theIOM104inverter104A and theUPM inverter102A are both in the OFF state and thesecond switch116 is open such that there is no electrical communication between the IOM and the grid. Thecontrol logic switch110A is in the first position to provide power from thegrid114 to theload108 through thecontrol logic module110. As shown in the figure, 100 kW of power is provided from the grid to the load through the control logic module.
• FIG. 1C illustrates the system operation during IOM start-up and charging of the energy storage device (e.g., bank of ultracapacitors)106C from thegrid114 while theload108 receives power from thegrid114. As shown in this figure, the fuel cell segment(s)106A are in the OFF state while theenergy storage device106C is in the ON state. TheIOM104bi-directional inverter104A is in the ON state and theUPM inverter102A is in the OFF state. Thesecond switch116 is closed such that there is electrical communication between the IOM and the grid to provide power from thegrid114 to theenergy storage device106C through theIOM104inverter104A and theDC bus112. Thecontrol logic switch110A is in the first position to provide power from thegrid114 to theload108 through thecontrol logic module110. As shown in the figure, 100 kW of power is provided from the grid to the load through the control logic module.
• FIG. 1D illustrates the system operation during UPM start-up following IOM start-up. UPM functions by receiving power from theenergy storage device106C. UPM provides the power from theenergy storage device106C to theload108. As shown in this figure, the fuel cell segment(s)106A are in the OFF state while and theenergy storage device106C is in the ON state. TheIOM104bi-directional inverter104A is in the ON state and theUPM inverter102A is in the ON state. Thesecond switch116 is closed such that there is electrical communication between the IOM and the grid. Thecontrol logic switch110A is in the second position to provide power from theUPM102 to theload108 through thecontrol logic module110. As shown in the figure, 100 kW of power is provided from thegrid114 to theload108 through therectifier102C andinverter102A of theUPM102 and then through the control logic module. Some power may also be provided to theload108 from theenergy storage device106C via theDC bus112,UPM102 and control logic module.
• FIG. 1E illustrates the steady state operation of the system. In this mode the fuel cell segment(s)106A is in the ON state to power theload108. The segment(s)106A may provide 200 kW of power in a steady state mode (this may be the designed power output or a maximum power output). As shown in this figure, theenergy storage device106C is in the ON state to act as an emergency backup power source. TheIOM104bi-directional inverter104A is in the ON state and theUPM inverter102A is in the ON state. The 200 kW power output is split between thegrid114 and theload108. Thesecond switch116 is closed such that there is electrical communication between the IOM and the grid to provide 100 kW of power from the fuel cell segment(s)106A to the grid. Thecontrol logic switch110A is in the second position to provide the other 100 kW of power from the fuel cell segment(s)106A in thepower module106 through the DC bus passing throughIOM104 and through theinverter102A of theUPM102 and then through thecontrol logic module110 to theload108. Preferably, this 100 kW of power does not pass through theIOM inverter104A and/or thegrid114 to reach theload108. While a 200 kW power output split 50/50 between the grid and the load is described above, different power outputs may be used as needed, such as 25 kW to 1000 kW, which may be split 10/90 to 90/10 between the grid and the load.
• FIG. 1F illustrates operation of the system during a relativelysteady load108 increase from 100 kW to 150 kW (i.e., when the load requires more power than prior steady state operation). In this mode, more of the power output of the fuel cell segment(s) is provided to the load and less of this power output is provided to the grid than in the stead state mode described above. If desired, 100% of the power output may be provided to the load and 0% to the grid. The fuel cell segment(s)106A is in the ON state to power theload108. As shown in this figure, theenergy storage device106C is in the ON state to act as an emergency backup power source. TheIOM104bi-directional inverter104A is in the ON state and theUPM inverter102A is in the ON state. Thesecond switch116 is closed such that there is electrical communication between the IOM and the grid to provide 50 kW of power from the fuel cell segment(s)106A through theIOM inverter104A to thegrid114. Thecontrol logic switch110A is in the second position to provide 150 kW of power from the fuel cell segment(s)106A in thepower module106 through the DC bus passing throughIOM104 and through theinverter102A of theUPM102 and then through thecontrol logic module110 to theload108. Thus, the power output of the fuel cell segment(s)106A is preferably split between the grid and the load in this mode. Preferably, the power does not pass through theIOM inverter104A and/or thegrid114 to reach theload108.
• FIG. 1G illustrates operation of the system during asudden load108 spike which requires more power than the fuel cell segment(s)106A can generate at that time. For example, the load spike is from 100 kW to 225 kW while the segment(s)106A can only generate 200 kW of power in steady state or in maximum power mode. The fuel cell segment(s)106A is in the ON state to power theload108. As shown in this figure, theenergy storage device106C is in the ON state to act as an emergency backup power source. TheIOM104bi-directional inverter104A is in the ON state and theUPM inverter102A is in the ON state. Thesecond switch116 is closed such that there is electrical communication between the IOM and the grid. However, no power is provided from fuel cell segment(s)106A through theIOM inverter104A to thegrid114 due to the load spike. Thecontrol logic switch110A is in the second position to provide power from the fuel cell segment(s)106A in thepower module106 and from thegrid114 through the DC bus passing throughIOM104 and through theinverter102A of theUPM102 and then through thecontrol logic module110 to theload108. In this mode, the power to the load is provided from both the fuel cell segment(s) and the grid. As shown, 200 kW from the segment(s)106A is provided through theDC bus112,diode102B,inverter102A and switch110A to theload108, while 25 kW is provided from thegrid114 through therectifier102B,inverter102A and switch110A to theload108 to achieve a total 225 kW of power required by the load. Preferably, the power from the fuel cell segment(s) does not pass through theIOM inverter104A and/or thegrid114 to reach theload108.
• FIG. 1H illustrates operation of the system during a return to normal or steady state operation after thesudden load108 spike. The fuel cell segment(s)106A is in the ON state to power theload108. As shown in this figure, theenergy storage device106C is in the ON state to act as an emergency backup power source. TheIOM104bi-directional inverter104A is in the ON state and theUPM inverter102A is in the ON state. Thesecond switch116 is closed such that there is electrical communication between the IOM and the grid. Thecontrol logic switch110A is in the second position to provide power from the fuel cell segment(s)106A in thepower module106 through the DC bus passing throughIOM104 and through theinverter102A of theUPM102 and then through thecontrol logic module110 to theload108. In this mode, the fuel cell segment(s) continue to output steady state or maximum power (e.g., 200 kW) which is split between the load and the grid. As shown, 200 kW from the segment(s)106A is provided to theIOM104.IOM104 provides 100 kW of power from fuel cell segment(s)106A through theIOM inverter104A to thegrid114. TheDC bus112 provides the remaining 100 kW of power fromIOM104 throughdiode102B,inverter102A and switch110A to theload108. Preferably, the power does not pass through theIOM inverter104A and/or thegrid114 to reach theload108.
• FIG. 1I illustrates operation of the system during loss of power from the grid114 (e.g., during a black out). The fuel cell segment(s)106A is in the ON state to power theload108. As shown in this figure, theenergy storage device106C is in the ON state to absorb power from the fuel cell segment(s)106A and to the soften the “step” that occurs during the loss of the grid power. TheIOM104bi-directional inverter104A is in the ON state and theUPM inverter102A is in the ON state. Thesecond switch116 is opened such that there is no electrical communication between the IOM and the grid. A sensor can sense the loss of grid power and a controller can open theswitch116 in response to the sensed grid outage. Thecontrol logic switch110A is in the second position to provide power from the fuel cell segment(s)106A in thepower module106 through the DC bus passing throughIOM104 and through theinverter102A of the UPM and then through thecontrol logic module110 to theload108. In this mode, out of the 200 kW total power output from the segment(s)106A, 100 kW is provided to theDC bus112 and 100 kW is provided to theenergy storage device106C to soften the step. TheDC bus112 provides the 100 kW of power fromIOM104 throughdiode102B,inverter102A and switch110A to theload108. The power output of the segment(s)106A is then gradually reduced to 100 kW to meet the requirements of theload108.
• FIG. 1J illustrates operation of the system during loss of power from the grid114 (e.g., during a black out) and in case of a load transient (e.g., increased demand for power from load108) while the fuel cell segment(s) output a reduced amount of power (e.g., 100 kW) which meets the steady state requirements of the load. The fuel cell segment(s)106A is in the ON state to power theload108. As shown in this figure, theenergy storage device106C is in the ON state to provide additional power to theload108. TheIOM104bi-directional inverter104A is in the ON state and theUPM inverter102A is in the ON state. Thesecond switch116 is opened such that there is no electrical communication between the IOM and the grid. Thecontrol logic switch110A is in the second position to provide power from the fuel cell segment(s)106A and theenergy storage device106C in thepower module106 through the DC bus passing throughIOM104 and through theinverter102A of theUPM102 and then through thecontrol logic module110 to theload108. In this mode, 100 kW from the segment(s)106A and 50 kW from the energy storage device is provided to theDC bus112. Thus, theDC bus112 provides the 150 kW of power fromIOM104 throughdiode102B,inverter102A and switch110A to theload108. Preferably, the power does not pass through theIOM inverter104A and/or thegrid114 to reach theload108.
• FIG. 1K illustrates operation of the system during loss of power from the grid114 (e.g., during a black out) and in case of a continuing load transient (e.g., continued increased demand for power from load108). The operation is the same as that shown inFIG. 1J, except that the power output of theenergy storage device106C is ramped down to zero over time and the power output of the fuel cell segment(s) is ramped up to the power needed by the load (e.g., 150 kW) over the same time. Thus, over time, the load receives more and more power from the fuel cell segment(s)106A and less and less power from theenergy storage device106C until all of the required power is supplied to theload108 by the fuel cell segment(s). Thus, the energy storage device acts as a bridging power source during the initial load transient and is then phased out during the continuing load transient.
• Referring toFIGS. 2 and 3, the output of theDC sources 1 to N are paralleled at the DC-output point, and a DC bus is created. EachDC source 1 to N may comprise one or more power module(s) (i.e., power generator(s))106 and an associatedIOM104. The 1 to N sources feed the customer load via a single UPM. Thus, the plurality of power module/IOM pairs share a common UPM. For example, the DC bus may form a DC micro grid connecting any number of DC sources (e.g., SOFC and power conditioning systems, solar panels, wind turbines, etc.) or AC sources converted to DC outputs (e.g., diesel generator paired with a power converter, small generator attached to a ticket turnstile at a concert venue, etc.) together at one UPM. In this manner, any DC source or AC source, regardless of its power characteristics may be used to provide power to theUPM202. TheUPM202 may be a large assembly of individual UPM's102 shown inFIG. 1A capable of output of many multiples of the output of the source systems themselves. As illustrated, inFIG. 2, theUPM202 comprises “N” UPMs102 (i.e., one UPM for each DC source), with a separate DC bus connecting each DC power source to adedicated UPM102. The N UPM's102 may be arranged in close proximity (e.g., side by side) in one housing or in separate housings to form theUPM assembly202.
• In an alternative embodiment shown inFIG. 3, theassembly202 of smaller dedicated UPM's102 may be replaced by onelarge UPM302. In this embodiment, theUPM302 may include an electrical storage device (e.g., bank of batteries or ultracapcitors) and/or a synchronous motor. In general, UPM inverters may include rotating machinery (e.g., a motor, flywheel, etc.) to enhance stored energy content and/or increase reliability and inertia of output.
• In summary, the DC sources may comprise fuel cell power modules and an IOM. The inverter within each UPM may be a modular assembly of smaller inverters controlled as one large inverter acting with inputs and/or outputs in parallel. An inverter within the main IOM may be a modular assembly of smaller inverters which are controlled as one large inverter acting with inputs and/or outputs in parallel.
• In an embodiment, rectification is provided in the UPM to allow feed from the grid when the stacks are off-line, thus providing the load a protected bus. A boost converter may be used to maintain a good power factor to the grid.
• In another embodiment, power from stored energy within an SOFC system or the UPM is used to create a “UPS” unit which has three energy inputs: grid energy; SOFC segment energy; and stored energy (e.g., ultracapacitors, flywheels, or batteries).
• In yet another embodiment, a DC micro-grid is connected to other distributed generators such as solar power hardware or wind power hardware. In an embodiment in which fuel cells, such as SOFC systems, and other distributed generators such as solar power hardware and/or wind power hardware are connected to the DC micro-grid, when an oversupply of energy compared to the load requirements is produced by the solar power hardware and/or wind power hardware, power generation from the fuel cells may not be required. The oversupply of energy generated by the other distributed generators may be sent to the fuel cells, and the fuel cells may be operated in pump mode (i.e., electrolysis mode). In this manner, spent fuel (e.g., water or CO₂) may be run backwards through the fuel cells to produce useable fuel (e.g., H₂or hydrocarbon fuel), which is stored for future use by fuel cells in fuel cell mode, as described in U.S. patent application Ser. No. 10/653,240, filed Sep. 3, 2003 and entitled “Combined Energy Storage and Fuel Generation with Reversible Fuel Cells, which is incorporated herein by reference in its entirety.
• In an embodiment, the DC micro-grid is connected to DC loads such as the loads of DC data centers or DC vehicle chargers.
• In yet another embodiment, when an IOM and UPM are composed of a cluster of inverters acting in parallel, some or all these inverters may be de-energized depending upon customer load conditions. For example, in a 200 kW generation capacity scenario where the customer load is 150 kW, the IOM inverters may be de-energized such that they only support 50 kW instead of a full 200 kW of grid-tied output. Further, in this scenario, it may be that only a portion of the possible inverters in the IOM assembly may be installed into the IOM, thus providing cost savings in terms of equipment required to support the specific customer load scenario.
• Referring toFIG. 4, in an embodiment, anIOM404 comprisesinverters412 that are configured for “bi-directional” operation. Such an inverter may have four-quadrant operation. If the grid-tied inverter has “bi-directional” operation, then the rectified feed does not need to be supplied to theUPM402. Grid power during start-up may come through the grid tiedinverter412 instead of via a rectified input to theUPM402. This embodiment also provides power from power module(s)406 for protection of the customer load.
• Referring toFIG. 5, in an embodiment, a UPM is not utilized. In this embodiment, anIOM504 comprises aninverter512 that is configured for dual mode functionality. Thedual mode inverter512 is configured to operate with a grid reference and also in a stand-alone mode, supporting a customer load without a grid reference. In this embodiment an output power interruption would be required in order to switch between power generation in one mode and another mode.
• FIGS. 6A-6D illustrate various modes of operation of the system shown inFIG. 1A. in which an electric vehicle (EV) charging module (ECM) is used instead of or in addition to theUPM102. In some modes of operation the ECM may perform the functions of the UPM.
• The systems ofFIGS. 6A-6D offer several advantages when used in EV charging application. In particular, these systems remove the need for the grid to supply large peaks of power during quick charging of a large number of EVs. The systems can also be used for EV charging in areas where it would be too expensive to provide grid power, and where it would be more cost effective to lay a natural gas pipeline.
• Referring toFIG. 6A, an EV charging station comprises one ormore power modules106, anIOM104 and anECM602. ECM contains a DC/DC converter602A instead of theinverter102A ofUPM102. In this embodiment, the EV charging station (e.g., ECM602) has access to grid power. The EV charging station may feed power simultaneously to the grid and the EV battery. A quick (e.g., 10-20 minute) charge may be provided fromECM602 to theEV battery604 using power from theFCM106. Whenever anEV battery604 is connected to the charging station (e.g., ECM602) for a charge, theFCM106 power is automatically diverted from feeding the grid into the charging station. The diversion of power from the grid to theEV battery604 may be accomplished by the control logic as illustrated inFIG. 1A and as discussed previously. The grid power may serve as a backup power for the charging station when thepower modules106 are unavailable.
• Referring toFIG. 6B, an EV charging station comprises one ormore power modules106, anIOM104, aUPM102,control logic unit110 and anECM602. In this embodiment, theEV charging station602 may also be used to supply acustomer load108 while feeding grid power and charging anEV battery604. In this configuration, the EV charging station feeds the grid and also provides uninterrupted power to the customer load108 (such as an office building). TheIOM104 feeds power to the grid, while theUPM102 supplies power to thecustomer load108. TheECM602 acts as the EV charging station and draws power from the400V DC bus112. Thus, theUPM102 andECM602 are connected in parallel to theDC bus112. While thecustomer load108 is supplied without interruption, anytime a vehicle drives in to get charged by theECM602, a portion of the power being fed to the grid is diverted to theECM602 for the time it takes to charge theEV battery604. Again, this configuration overcomes the challenge of drawing high peak power from the grid, which is a major issue today especially during day time, when the grid is already supplying full capacity.
• A typical application of this configuration would be to supply power to an office building. Theload108 from the building (including data centers, lighting etc) can be supplied clean uninterrupted power from theUPM102, while power is being fed to the grid. Charging stations can be installed at the car park of this building for the employees and visitors of the company.EV batteries604 can be charged, and then parked at the car park. Options for both quick charging (1 C) and trickle charging (0.1 C) can be provided at the charging stations, based on the time constraints of the car owner.
• Referring toFIG. 6C an EV charging station comprises one ormore power modules106, aUPM102, anECM602 and aDG set608. This configuration is suitable for use in remote areas where grid power is not available. In this configuration, theUPM102 draws power from the DC bus connected to thepower modules106, and feeds thecustomer load108. Thiscustomer load108 also acts like a base load to thepower modules106, which allows the system to operate at a certain minimum efficiency (in the configurations illustrated inFIGS. 6A and 6B above, the grid provides the minimum base load for efficient performance). In an embodiment, thepower modules106 and theUPM102 are rated such that the maximum customer load is always supplied while theECM602 is operational. The DG set608 is used to start up thepower modules106.
• Referring toFIG. 6D, an EV charging station comprises one ormore power modules106 and anECM602. This configuration of EV charging stations is suitable for use where there is no grid power and no customer load is to be supplied. The EV charging station is needed only to act as a power source for charging theEV battery604. In this configuration, abattery bank610 acts as the base load to the EV charging station. Thisbattery bank610 may be charged using normal charging (0.1 C). An operator of an EV in need of charging theEV battery604 may obtain a charge from theECM602. Alternatively, the operator may exchange a dischargedEV battery604 for one of the batteries in thebattery bank610. TheDG608 set is used to start up thepower modules106.
• In an embodiment, the EV charging station is configured to take advantage of time-of-day pricing and to utilize the storage capacity of the EV batteries. For example, the cost of weekday electricity from 11 AM to 9 PM may be several times (e.g., 5 times) higher than the cost of electricity from 9 PM to 11 AM. In this embodiment, DC power is returned from the EV batteries to the fuel cell system to provide power during peak pricing periods and/or to support shortfalls in the power output from thepower modules106 due to aninternal power module106 fault.
• Referring toFIG. 6E, the fuel cell system comprises one ormore power modules106, anIOM104, aUPM102, a firstcontrol logic unit110 described above, aswitching module702 containing aswitch702A and secondcontrol logic unit702B, and anECM602. If desired, theseparate logic units110 and702B may be physically combined into a single unit which performs the functions of theunit110 described above and functions ofunit702B described below. In this embodiment, thepower modules106,IOM104 andUPM102 may be used to supply power to a customer load108 (e.g., a building, such as an office building) while also being able to provide power to the grid, while theECM602 may be used for charging anEV battery604 by drawing power from the400V DC bus112.Control logic unit110 performs the functions as previously described.Control logic unit702B performs the functions described below. Thus, theUPM102 andECM602 are connected in parallel to theDC bus112.
• In an embodiment, the UPM102 (e.g., theinverter102A of UMP102) is rated higher than would be required to provide power to load108 from thepower modules106 alone. The additional power handling capabilities are used to utilize additional DC power from EV batteries that are connected to the EV charging station (i.e., to ECM602). Thecontrol logic unit702B switches theswitch702A to connect theEV batteries604 to theECM602 receive power fromECM602, or toDC bus112 to provide power to theDC bus112.
• By way of illustration and not by way of limitation, the fuel cell system contains power module(s)106 which are capable of delivering a first value of maximum power (e.g., 200 kW). TheUMP102 is rated to convert DC to AC to provide a second value of maximum power (e.g., 400 kW AC) which is greater than the first value. In other words, theinverter102A is designed to convert more DC to AC power than the power module(s) are capable of providing. TheUMP102 uses the additional conversion capacity to convert DC power (e.g., up to 200 kW DC) from theEV batteries604 to AC power to provide to theload108 or to thegrid114.
• Thus, DC power from anelectric vehicle battery604 is received at an electric vehicle charging module (ECM)602 during a period of higher electricity price from the grid, the received power is provided to the at least oneinverter102A which converts the received DC power to AC power, and provides the AC power to a load (e.g.,108 or grid load114).
• In one embodiment, DC power is provided from the at least one fuelcell power module106 to theECM602, and then provided from the ECM to theelectric vehicle battery604 when the cost of electricity is lower, prior to the step of receiving DC power.
• The combination EV charging station and fuel cell system may be located at a business having employees that drive electric cars. Using the time of day pricing set forth above, these employees would generally park their EVs at the business recharging docks and connect theEV batteries604 to theECM602 for 8 to 10 hours during the work day. Typically, all theEV batteries604 are fully charged (with theswitch702A connecting batteries604 to ECM602) before the price of power from the grid increases (e.g., by 11 AM) using the power provided from theECM602. Then, after the price of the grid power increases (e.g., after 11 AM),logic702B switches theswitch702A position to connect theEV batteries604 to theDC bus112. Thebatteries604 are then used to provide a portion (e.g., 10-75%, for example 50%) of their stored charge to theDC bus112. For example, the EV batteries may receive more charge each day (or each week etc.) than they provide back to the DC bus. If desired, the owners of the EVs may not be charged for the net charge they received or be charged a reduced rate compared to the rate for charging EV batteries from the grid. The charging station could then deliver up to 400 kW AC to load108 in a peak-shaving load-following manner. All parties would financially benefit because of the increased price of the mid-day electricity.
• In another embodiment, the electric vehicle battery is charged at a location other than theECM602 during a lower cost electricity price period prior to the step of receiving DC power from theECM602 during the higher cost of electricity price period. For example, EVs are charged at a remote location (e.g., from the grid at home overnight) using lower cost, night time electricity. These EVs may then be connected to theECM602 in the morning. After the price of electricity increases mid-day (e.g., after 11 AM) theEV batteries604 deliver a predetermined portion of their stored charge to theDC bus112. Thus bus can then deliver up to 400 kW AC to load108 in a peak-shaving load-following manner. The EV owners may be reimbursed for the cost of provided power (i.e., for the power they stored at their home and delivered to the bus112). Here again all parties financially benefit because of the higher price of mid-day electricity.
• Of course, the times used in the foregoing examples are for illustrative purposes only. The charging station may be configured to utilize power from the EV batteries to address the time-of-day pricing for the region in which the charging station is located.
• The above described methods and systems can be readily used with multiple generators in parallel with a large load, while allowing tight control of frequency and voltage.
• An exemplary modular system which includes a modular enclosure which combination of housings containing severalpower module housings106 with the fuel cell containing hot boxes, theIOM104 housing containing theinverter104A and other electronics, and an optional housing containing a fuel processing module (which includes, e.g., a desulfurizer, etc.) is described in U.S. Provisional Patent Application Ser. No. 61/386,257, filed Sep. 24, 2010 and entitled “Fuel Cell Mechanical Components”, which is incorporated herein by reference in its entirety.
• FIG. 7 illustrates an embodiment direct current (DC)micro-grid700. The DC micro-grid700 may includeloads726a,726b,730a,730b,734a,734b,power generators704a,704b,706a,706b,710a,710b, andenergy storage devices714a,714b,718a,718b,722a,722bcoupled to acommon DC bus738.
• Power generators704aand704bmay be any type alternating current (AC) generators, such as micro turbines, wind turbines, distributed diesel generators, etc. and/or connections to an AC utility power grid.Power generators706a,706b,710a, and710b, may be any type DC generators, such as fuel cell systems (e.g., SOFC fuel cell systems), modular energy generation system, solar cells, etc. In an embodiment,power generators704a,704b,706a,706b,710a,710bmay be of different voltages and/or waveforms, such as 380 volt DC power generators, 480 volt AC power generators, and/or −48 volt DC power generators, and may be grouped by voltage and/or waveform, such as 480 voltAC power generators704aand704bgrouped together, 380 voltDC power generators706aand706bgrouped together, and −48 voltDC power generators710aand710bgrouped together.
• In an embodiment, different power generation buses for each voltage and/or waveform grouping may be created to deliver and/or draw power from each power generation group. GroupedAC power generators704aand704bmay be coupled topower generation bus705, groupedDC power generators706aand706bmay be coupled topower generation bus708, and groupedDC power generators710aand710bmay be coupled topower generation bus712.
• In an embodiment, thepower generation buses705,708, and712 may be coupled to thecommon DC bus738. In an embodiment, thepower generation buses705,708, and712 may be coupled to thecommon DC bus738 viapower electronics devices740,742, and744, respectively.Power electronics devices740,742, and744 may be power conversion devices, such as AC/DC converters (e.g., inverters), DC/DC converters, and/or DC/AC converters (e.g., inverters), coupled to thepower generation buses705,708, and712 and coupled to thecommon DC bus738.Power electronics devices740,742, and744 may transfer power from/to thepower generation buses705,708, and712 to/from thecommon DC bus738.Power electronics devices740,742, and744 may be configured to filter (e.g., isolate) injected signals in thecommon DC bus738 such that the injected signals do not pass along to thepower generation buses705,708, and712. For example,power electronics devices742 and744 may be isolated DC/DC converters.Power electronics devices740,742, and744 may contain hardware to enablepower generation buses705,708, and712 to be disconnected, individually or as a group, from thecommon DC bus738, such as in response to a trigger signal.Power electronics devices740,742, and744 may be fully isolated devices, providing galvanic isolation between thecommon DC bus738 and thepower generation buses705,708,712, such as full bridge DC/DC converters, half bridge DC/DC converters, and/or resonant DC/DC converters. In an embodiment, all thepower electronics devices740,742, and744 may provide isolation. In another embodiment, only a portion, or none, of thepower electronics devices740,742, and744 may provide isolation as long as isolation between theloads726a,726b,730a,730b,734a,734bof the DC micro-grid700 and thepower generators704a,704b,706a,706b,710a,710bandenergy storage devices714a,714b,718a,718b,722a,722bof the DC micro-grid700 is provided at least at one point in theDC micro-grid700.
• In an embodiment,power electronics device740 may be an AC/DC converter coupling thepower generation bus705 to thecommon DC bus738. In operation,power electronics device740 may convert AC received from thepower generation bus705 to DC provided to the common DC bus, or vice versa. Additionally, thepower electronics device740 may increase or decrease the voltage and/or current of the energy received from and/or sent to thepower generation bus705 and/or thecommon DC bus738. In an embodiment, thepower electronics device740 may be a high efficiency isolation transformer, such as a hexaformer, which may provide isolation between the ACpower generation bus705 and thecommon DC bus738. In an embodiment,power electronics device742 may be a DC/DC converter coupling thepower generation bus708 to thecommon DC bus738. In operation, thepower electronics device742 may increase or decrease the voltage and/or current of the energy received from and/or sent to thepower generation bus708 and/or thecommon DC bus738. In an embodiment,power electronics device744 may be a DC/DC converter coupling thepower generation bus712 to thecommon DC bus738. In operation, thepower electronics device744 may increase or decrease the voltage and/or current of the energy received from and/or sent to thepower generation bus712 and/or thecommon DC bus738. In other words,power electronics devices742 and744 may be buck or boost converters.
• Energy storage devices714a,714b,718a,718b,722a, and722b, may be any type energy storage devices, such as batteries, ultracapcitors, etc. In an embodiment,energy storage devices714a,714b,718a,718b,722a, and722bmay be of different voltages, such as 480 volts, 380 volts and/or −48 volts, and may be grouped by voltage, such as 480 voltenergy storage devices714aand714bgrouped together, 380 voltenergy storage devices718aand718bgrouped together, and −48 voltenergy storage devices722aand722bgrouped together.
• In an embodiment, different energy storage buses for each voltage and/or waveform grouping may be created to deliver and/or draw power from each energy storage device grouping. Groupedenergy storage devices714aand714bmay be coupled toenergy storage bus716, groupedenergy storage devices718aand718bmay be coupled toenergy storage bus720, and groupedenergy storage devices722aand722bmay be coupled toenergy storage bus724. In a further alternative embodiment, loads (e.g., loads726a,726b,730a,730b,734a,734band/or other loads) with voltage and waveform requirements that exactly match the voltage and waveform ofpower generation buses705,708, and/or712 and/orenergy storage buses716,720, and/or724 may be directly connected to thepower generation buses705,708, and/or712 and/orenergy storage buses716,720, and/or724, rather than applied to thecommon DC bus738. In such an embodiment, control schemes as discussed herein applied to thecommon DC bus738 may also be applied to thepower generation buses705,708, and/or712 and/orenergy storage buses716,720, and/or724. Additionally, in such an embodiment, thepower electronics devices740,742,744,746,748, and/or750 may be bidirectional devices configured to provide power to and/or draw power from thepower generation buses705,708, and/or712 and/orenergy storage buses716,720, and/or724.
• In an embodiment, theenergy storage buses716,720, and724 may be coupled to thecommon DC bus738. In an embodiment, theenergy storage buses716,720, and724 may be coupled to thecommon DC bus738, viapower electronics devices746,748, and750, respectively.Power electronics devices746,748, and750 may be power conversion devices, such as AC/DC converters, DC/DC converters, and/or DC/AC converters, coupled to theenergy storage buses716,720, and724 and coupled to thecommon DC bus738.Power electronics devices746,748, and750 may transfer power from/to theenergy storage buses716,748, and712 from/to thecommon DC bus738.Power electronics devices746,748, and750 may be configured to filter injected signals in thecommon DC bus738 such that the injected signals do not pass along to theenergy storage buses716,720, and724.Power electronics devices746,748, and750 may contain hardware to enableenergy storage buses716,720, and724 to be disconnected, individually or as a group, from thecommon DC bus738, such as in response to a trigger signal.Power electronics devices746,748, and750 may be fully isolated devices, providing galvanic isolation between thecommon DC bus738 and theenergy storage buses716,720,724, such as full bridge DC/DC converters, half bridge DC/DC converters, and/or resonant DC/DC converters. In an embodiment, all thepower electronics devices746,748, and750 may provide isolation. In another embodiment, only a portion, or none, of thepower electronics devices746,748, and750 may provide isolation as long as isolation between theloads726a,726b,730a,730b,734a,734bof the DC micro-grid700 and thepower generators704a,704b,706a,706b,710a,710bandenergy storage devices714a,714b,718a,718b,722a,722bof the DC micro-grid700 is provided at least at one point in theDC micro-grid700.
• In an embodiment,power electronics device746 may be a DC/DC converter coupling theenergy storage bus716 to thecommon DC bus738. In operation,power electronics device746 may increase or decrease the voltage and/or current of the energy received from and/or sent to theenergy storage bus716 and/or thecommon DC bus738. In an embodiment,power electronics device746 may control the charging and/or discharge of theenergy storage devices714aand/or714b. In an embodiment,power electronics device748 may be a DC/DC converter coupling theenergy storage bus720 to thecommon DC bus738. In operation, thepower electronics device748 may increase or decrease the voltage and/or current of the energy received from and/or sent to theenergy storage bus720 and/or thecommon DC bus738. In an embodiment,power electronics device748 may control the charging and/or discharge of theenergy storage devices718aand/or718b. In an embodiment,power electronics device750 may be a DC/DC converter coupling theenergy storage bus724 to thecommon DC bus738. In operation, thepower electronics device750 may increase or decrease the voltage and/or current of the energy received from and/or sent to theenergy storage bus724 and/or thecommon DC bus738. In an embodiment,power electronics device750 may control the charging and/or discharge of theenergy storage devices722aand/or722b.
• Loads726aand726bmay be any type alternating current (AC) loads, such as information technology (IT) loads (i.e., a device and/or devices operating in an IT system, such as a data center), electric vehicle loads, medical device loads, AC motors, etc.Loads730a,730b,734a, and734b, may be any type DC loads, such as information technology (IT) loads, electric vehicle loads, medical device loads, DC motors, etc. IT loads, (i.e., devices operating in an IT system) may include one or more of computer(s), server(s), router(s), rack(s), power supply connections, and other components found in a data center environment. In an embodiment, loads726a,726b,730a,730b,734a,734bmay be of different voltages and/or waveforms, such as 380 volt DC loads, 480 volt AC loads, and/or −48 volt DC loads, and may be grouped by voltage and/or waveform, such as 480 volt AC loads726aand726bgrouped together, 380 volt DC loads730aand730bgrouped together, and −48 volt DC loads734aand734bgrouped together.
• In an embodiment, different load buses for each voltage and/or waveform grouping may be created to deliver and/or draw power from each load group. Grouped AC loads726aand726bmay be coupled to loadbus728, grouped DC loads730aand730bmay be coupled to loadbus732, and grouped DC loads734aand734bmay be coupled to loadbus736.
• In an embodiment, theload buses728,732, and736 may be coupled to thecommon DC bus738. In an embodiment, theload buses728,732, and736 may be coupled to thecommon DC bus738 viapower electronics devices752,754, and756, respectively.Power electronics devices752,754, and756 may be power conversion devices, such as AC/DC converters, DC/DC converters, and/or DC/AC converters, coupled to theload buses728,732, and736 and coupled to thecommon DC bus738.Power electronics devices752,754, and756 may transfer power from/to theload buses728,732, and736 to/from thecommon DC bus738.Power electronics devices752,754, and756 may be configured to filter injected signals in thecommon DC bus738 such that the injected signals do not pass along to theload buses728,732, and736.Power electronics devices752,754, and756 may contain hardware to enableload buses728,732, and736 to be disconnected, individually or as a group, from thecommon DC bus738, such as in response to a trigger signal.Power electronics devices752,754, and756 may be fully isolated devices, providing galvanic isolation between thecommon DC bus738 and theload buses728,732, and736, such as full bridge DC/DC converters, half bridge DC/DC converters, resonant DC/DC converters, DC/AC converters, and/or hexaformers. In an embodiment, all thepower electronics devices752,754, and756 may provide isolation. In another embodiment, only a portion, or none, of thepower electronics devices752,754, and756 may provide isolation as long as isolation between theloads726a,726b,730a,730b,734a,734bof the DC micro-grid700 and thepower generators704a,704b,706a,706b,710a,710bandenergy storage devices714a,714b,718a,718b,722a,722bof the DC micro-grid700 is provided at least at one point in theDC micro-grid700.
• In an embodiment,power electronics device752 may be a DC/AC converter coupling theload bus728 to thecommon DC bus738. In operation,power electronics device752 may convert DC received from the common DC bus to AC. Additionally, thepower electronics device752 may increase or decrease the voltage and/or current of the energy received from thecommon DC bus738 before sending it to theload bus728. In an embodiment, thepower electronics device752 may be a high efficiency isolation transformer, such as a hexaformer, which may provide isolation between theAC load bus728 and thecommon DC bus738. In an embodiment,power electronics device754 may be a DC/DC converter coupling theload bus732 to thecommon DC bus738. In operation, thepower electronics device754 may increase or decrease the voltage and/or current of the energy received from thecommon DC bus738 before sending it to theload bus732. In an embodiment,power electronics device756 may be a DC/DC converter coupling theload bus736 to thecommon DC bus738. In operation, thepower electronics device756 may increase or decrease the voltage and/or current of the energy received from thecommon DC bus738 before sending it to theload bus736.
• In an embodiment, thecommon DC bus738 may be a bus which ties thepower generator buses705,708, and712, theenergy storage buses716,720, and724, and theload buses728,732, and736 together. Thecommon DC bus738 may be controlled such that the power requirement for theloads726a,726b,730a,730b,734a, and734bis maintained such that:
• i. P(to storages)=P(generators)−P(loads), if P(generators)>P(loads); or
• ii. P(from storages)=P(loads)−P(generators), if P(generators)<P(loads),
• where P is Power.
• In an embodiment, thecommon DC bus738 may be controlled to optimize for absolute value, such that the value of the P(generators)−P(loads) is equal to zero. In an embodiment, thecommon DC bus738 may be optimized by holding the power output of thepower generators704a,704b,706a,706b,710a,710bconstant and using theenergy storage devices714a,714b,718a,718b,722a,722bto buffer diurnal load transients, while the power output of thepower generators704a,704b,706a,706b,710a,710bmay only be increased and/or decreased when the load pattern diverges from its typical diurnal cycle. In another embodiment, thecommon DC bus738 may be optimized by constantly driving the power output of thepower generators704a,704b,706a,706b,710a,710bupward and/or downward to match the power requirements of theloads726a,726b,730a,730b,734a, and734bas best as possible based on rate of change limitations of thepower generators704a,704b,706a,706b,710a,710b. In an embodiment, the voltage of thecommon DC bus738 may be set to the highest voltage of thegenerator buses705,708, and712, theenergy storage buses716,720, and724, and/or theload buses728,732, and736. The voltage of any AC buses may be determined as the DC equivalent voltage for that respective bus. The setting of thecommon DC bus738 voltage to the highest voltage of thebuses705,708,712,716,720,724,728,732, or736 may optimize the operation of the DC micro-grid700 and minimize conductor costs in theDC micro-grid700. In an embodiment, the voltage of thecommon DC bus738 may be set to the most common of the voltages (i.e., the mode, rather than the mean or median voltage) of thegenerator buses705,708, and712, theenergy storage buses716,720, and724, and/or theload buses728,732, and736. The voltage of any AC buses may be determined as the DC equivalent voltage for that respective bus. The setting of thecommon DC bus738 voltage to the most common voltage of thebuses705,708,712,716,720,724,728,732, or736 may optimize the operation of the DC micro-grid700 and minimize conversion losses in theDC micro-grid700. When thecommon DC bus738 andload buses728,732, and/or736 are selected to be less than 380 volts DC, such as −48 volts DC, small DC/DC converters may be provided within thepower generators704a,704b,706a,706b,710a,710bto provide higher voltages for auxiliary devices (e.g., balance of plant pumps, blowers, etc.) with thepower generators704a,704b,706a,706b,710a,710b. In an embodiment, a controller and/or scheduler may control the voltage of thecommon DC bus738. In an embodiment, the operation of the powerelectronic devices740,742,744,746,748,750,752,754, and/or756 may control the voltage of thecommon DC bus738. In another embodiment, a separate bus controller device may control the voltage of thecommon DC bus738, as will be discussed below with respect toFIG. 9.
• FIG. 8 illustrates an embodiment direct current (DC)micro-grid800. The DC micro-grid800 is similar to the DC micro-grid700 illustrated inFIG. 7 and contains a number of components in common. Those components which are common to bothDC micro-grids700 and800 are numbered with the same numbers inFIGS. 7 and 8 and will not be described further.
• One difference between the DC micro-girds800 and700 is that DC micro-grid800 may include acommon DC bus802 in a split bus configuration. Thecommon DC bus802 may have more than one conductor, for example threeconductors804,806, and808. In an embodiment, the threeconductors804,806, and808 may be set to different voltages. For example, theconductor804 may be at +380 volts DC, theconductor806 may be neutral and theconductor808 may be at −380 volts DC.Power electronics devices810,812,814,816,818,820,822,824, and826 may be similar topower electronics devices740,742,744,746,748,750,752,754, and756 discussed above with reference toFIG. 7, except thatpower electronics devices810,812,814,816,818,820,822,824, and826 may include more than one conductor for sending/receiving power to/from thecommon DC bus802. As an example, each of thepower electronics devices810,812,814,816,818,820,822,824, and826 may include three connections to thecommon DC bus802, such as a first connection to theconductor804, a second connection to theconductor806, and a third connection to theconductor808. In an embodiment, thepower electronics devices810,812,814,816,818,820,822,824, and may be configured to output different voltages on each connection to thecommon DC bus802, for example +380 volts DC may be output on the first connection, the second connection may be neutral, and −380 volts DC may be output on the third connection. While illustrated as a three conductor split bus,common DC bus802 may have more or less than three conductors and thepower electronics devices810,812,814,816,818,820,822,824, and826 may have more or less than three connections to thecommon DC bus802.
• FIG. 9 illustrates an embodiment direct current (DC)micro-grid900. The DC micro-grid900 is similar to the DC micro-grid700 illustrated inFIG. 7 and contains a number of components in common. Those components which are common to bothDC micro-grids700 and900 are numbered with the same numbers inFIGS. 7 and 9 and will not be described further.
• One difference between the DC micro-girds900 and700 is that DC micro-grid900 may include acontroller902 for communicating with the various devices in the DC micro-grid900 and for controlling/scheduling the operation the various devices in theDC micro-grid900. In an embodiment, thecontroller902 may include aconnection904 to a communication network (e.g., a cellular, Wi-Fi, Ethernet, or other connection to the Internet) for sending/receiving information with devices/systems/entities, such as public utilities, fuel dispatchers, DC micro-grid900 operators, DC micro-grid900 devices (e.g., the various power generators, energy storage devices, loads, and/or power electronics devices, etc. comprising the DC micro-grid900), emergency response personnel, etc. In this manner, information may be exchanged between the devices/systems/entities and thecontroller902. In an embodiment, the various power generators, energy storage devices, loads, and/or power electronics devices, etc. comprising the DC micro-grid900 may include wired and/or wireless modems and logic to enable communication between thecontroller902 and various DC micro-grid900 devices and various logic and controls (e.g., switches, transistors, relays, etc.) to enable the various DC micro-grid900 devices to perform operations (such as power output changes, start-ups, shut downs, disconnects, discharges, etc.) in response to signals received from thecontroller902. In this manner, the controller DC m may control the operations of the various DC micro-grid900 devices via wired or wireless communication. In an optional embodiment, thecontroller902 may be connected to the devices in the DC micro-grid900 by a series ofwires906, such as electrical and/or fiber optic transmission lines, placed in parallel to the wiring of the inputs/outputs to/from thecommon DC bus738. The series ofwires906 may connect thecontroller902 to theloads726a,726b,730a,730b,734a,734b,power generators704a,704b,706a,706b,710a,710b,energy storage devices714a,714b,718a,718b,722a,722b, and/orpower electronics devices740,742,744,746,748,750,752,754, and756. In this manner, cascaded signals may be passed from thecontroller902 to the various devices in the DC micro-grid900 via the series ofwires906 to control the operations of theloads726a,726b,730a,730b,734a,734b,power generators704a,704b,706a,706b,710a,710b,energy storage devices714a,714b,718a,718b,722a,722b, and/orpower electronics devices740,742,744,746,748,750,752,754, and756, individually or as groups. As examples, communications signals from thecontroller902 received via the series ofwires906 may indicate to afuel cell generator706bto go off line, may switchstorage devices722aand722bfrom charge to discharge mode, and/or may directpower electronics device756 to disconnectload bus736 from thecommon DC bus738.
• In an embodiment, signals (e.g., DC pulses) may be injected by thecontroller902 into thecommon DC bus738. The signals injected into thecommon DC bus738 may have specific waveforms. In an embodiment, the signals injected into thecommon DC bus738 may serve as triggers to indicate to theloads726a,726b,730a,730b,734a,734b, thepower generators704a,704b,706a,706b,710a,710b, and/or theenergy storage devices714a,714b,718a,718b,722a,722bto shutdown and/or disconnect from thecommon DC bus738. Theloads726a,726b,730a,730b,734a,734b, thepower generators704a,704b,706a,706b,710a,710b, and/or theenergy storage devices714a,714b,718a,718b,722a,722bmay include communication devices (e.g., modems), logic, and controls (e.g., switches, transistors, relays, etc.) to enable shutdown and/or disconnect from thecommon DC bus738 in response to signals injected into thecommon DC bus738. In an embodiment, different waveforms may trigger different devices to disconnect from thecommon DC bus738. In an embodiment, the injected signals may pass through the variouspower electronics devices740,742,744,746,748,750,752,754, and756 to therespective loads726a,726b,730a,730b,734a,734b,power generators704a,704b,706a,706b,710a,710b, and/orenergy storage devices714a,714b,718a,718b,722a,722b. In an alternative embodiment, the injected signals may be filtered by thepower electronics devices740,742,744,746,748,750,752,754, and756 such that the injected signals do not pass through and affect the power quality of the variousdownstream buses705,708,712,716,720,724,728,732, and736. The injected signals on thecommon DC bus738 may provide individual and/or synchronized commands to control the operations of theloads726a,726b,730a,730b,734a,734b,power generators704a,704b,706a,706b,710a,710b,energy storage devices714a,714b,718a,718b,722a,722b, and/orpower electronics devices740,742,744,746,748,750,752,754, and756, individually or as groups. As an example, the injected signals on thecommon DC bus738 may be watchdog signals (e.g., standard repeated timing signals, the absence of which may indicate a fault), and if synchronization to the watchdog signals is lost, then theloads726a,726b,730a,730b,734a,734b,power generators704a,704b,706a,706b,710a,710b,energy storage devices714a,714b,718a,718b,722a,722b, and/orpower electronics devices740,742,744,746,748,750,752,754, and756 may be configured to disconnect from thecommon DC bus738.
• In an embodiment, the variouspower electronics devices740,742,744,746,748,750,752,754, and756 may be DC/DC, AC/DC, and/or DC/AC converters containing hardware to enable them to disconnect individually from thecommon DC bus738 in response to communication signals (e.g., communication signals received from thecontroller902 viawires906, wireless form thecontroller902 via awireless connection904, and/or signals injected into the common DC bus738). The variouspower electronics devices740,742,744,746,748,750,752,754, and756 may include communication devices (e.g., modems), logic, and controls (e.g., switches, transistors, relays, etc.) to enable shutdown and/or disconnect from thecommon DC bus738 in response to communication signals. The disconnect of individualpower electronics devices740,742,744,746,748,750,752,754, or756 may enable the DC micro-grid900 to continue operations with one or more power generators, storage devices, and/or loads removed.
• In an embodiment, theloads726a,726b,730a,730b,734a,734b,power generators704a,704b,706a,706b,710a,710b,energy storage devices714a,714b,718a,718b,722a,722b, and/orpower electronics devices740,742,744,746,748,750,752,754, and756 may be configured to communicate with each other and/or thecontroller902 over thecommon DC bus738 via signals, such as load commands, operation feedback, etc., injected onto thecommon DC bus738, overwires906 via signals sent overwires906, and/or wirelessly via wireless links, such as cellular network links. In this manner, communication over thecommon DC bus738,wires906, or wirelessly may balance power generation, storage, and/or use in theDC micro-grid900. In an embodiment in which the power requirements of theloads726a,726b,730a,730b,734a, and734bmay be time dependent, communication signals may be used to optimize the configuration of the DC micro-grid900 based on likely load events which may create transient power requirements. As an example, at a certain time of day, such as during factory load start-up, larger power requirements may be needed and communication signals may cause the power output of the DC micro-grid900 to be increased. As another example, in an embodiment in which the DC micro-grid900 provides power to IT loads, a significant press release may drive large search engine demands and the communication signals may cause the power output of the DC micro-grid900 to be increased. In an embodiment, communication signals may be utilized to communicate device alarms. As an example, thecontroller902 may store the geographic location of each device in the DC micro-grid900, and if a fire occurs in one device, forexample power generator710b, thecontroller900 may signal other devices in close physical proximity to shut down, such aspower generator710aandpower electronics device744. Other devices physically separated from the device on fire may remain in operation. In an embodiment, communication signals may be sent from one load, such asload726ato another load, such as734b, via thecommon DC bus738,wires906, and/or wirelessly to coordinate functions within a region or site. In an embodiment, communication signals may be encrypted and/or may include authentication keys. In this manner, unauthorized use of the DC micro-grid900 may not occur.
• In an embodiment, a digital addressing scheme may be used in the signals injected onto thecommon DC bus738. As an example, the signals may include address bits, data bits, and check sum bits. In an embodiment, frequency and/or amplitude modulation may be used for addressing.
• In an embodiment, thecontroller902 may be function as a scheduler in communication with theloads726a,726b,730a,730b,734a,734b,power generators704a,704b,706a,706b,710a,710b,energy storage devices714a,714b,718a,718b,722a,722b, andpower electronics devices740,742,744,746,748,750,752,754, and756 and configured to optimize the operation of theloads726a,726b,730a,730b,734a,734b,power generators704a,704b,706a,706b,710a,710b,energy storage devices714a,714b,718a,718b,722a,722b, andpower electronics devices740,742,744,746,748,750,752,754, and756. As a scheduler thecontroller902 may communicate with thepower generators704a,704b,706a,706b,710a,710bto coordinate load steps, coordinate warm up times, optimize efficiency (e.g., peaking with the most efficient peaking device), coordinate fuel supplies (e.g., ramping down usage of a generator which has a failing or limited fuel supply), and manage the cost of power generation (e.g., selecting the least expensive combination of generators to operate). As a scheduler thecontroller902 may communicate with theenergy storage devices714a,714b,718a,718b,722a,722bto manage the state of the charge, manage the cost of generator or grid power in an arbitrage format, and manage round trip efficiency of different storage devices by scheduling optimization. As a scheduler thecontroller902 may communicate with theloads726a,726b,730a,730b,734a,734bto manage load criticality (e.g., balancing the criticality of loads versus available energy such that the least critical loads are switched off first if energy availability is limited), manage load start up (e.g., ramping generators and/or storage outputs to match load requirement increases), and manage load shut downs (e.g., ramping generators and/or storage outputs to match load requirement decreases). In an embodiment, thecontroller902 may dispatch fuel storage to various power generators (e.g., usingconnection904 to a communication network) if generator performance crashes, signals from the generator indicate a failing supply of one fuel source (e.g., a failing pipeline pressure or failing tank level), and/or in response to signals from the utility (e.g., messages indicating that pipeline supply may be impacted by a natural gas grid infrastructure issue). In this manner, additional fuel may be supplied to the various power generators from fuel storage sources (e.g., on-site truck delivery, on-site reserve tank storage, etc) to avoid power generation interruptions.
• In an embodiment, thecontroller902 may be a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but, in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. Alternatively, some steps or methods may be performed by circuitry that is specific to a given function.
• FIG. 10 illustrates an embodiment direct current (DC)micro-grid portion1000. In an embodiment, the DCmicro-grid portion1000 may be a portion ofDC micro-grids700,800, and/or900 discussed above. The DCmicro-grid portion1000 may includeDC generators1002,1004,1006,1008,1010,1012, anenergy storage device1014, and acommon DC bus1024. In an embodiment, the output of theDC generators1002,1004,10061008,1010, and1012 may be + or −380 volts DC output to thecommon DC bus1024. In an embodiment, theenergy storage device1014 may include an AC/DC converter1016 for converting an AC input, such as an AC grid input, to DC, a charge module1018 (e.g., a DC/DC converter, such as a boost or buck converter), one ormore storage devices1020, and a discharge module1022 (e.g., a DC/DC converter, such as a boost or buck converter). In an embodiment, the AC/DC converter1016,charge module1018, and/ordischarge module1022 may be in communication with acontroller1015. Thecontroller1015 may be part of theenergy storage device1014 or may be a separate device, such as an overall controller of theDC micro-grid1000 similar tocontroller902 discussed above with reference toFIG. 9. Thecontroller1015 may control the operation of the AC/DC converter1016,charge module1018, and/ordischarge module1022 via signals sent to controls (e.g., switches, transistors, relays, etc.) within the AC/DC converter1016,charge module1018, and/ordischarge module1022. The output of the AC/DC converter1016 may be coupled to thecommon DC bus1024 and coupled to thecharge module1018. Thecharge module1018 may be coupled to thestorage device1020 which may be coupled to thedischarge module1022. The output of thedischarge module1022 may be coupled to the output of the AC/DC converter1016 and thereby, coupled to thecommon DC bus1024. The output of theenergy storage device1014 may be + or −380 volts DC output to thecommon DC bus1024. In operation theenergy storage module1014 may receive an AC input. The AC/DC converter1016 may convert the AC input to DC. The AC/DC converter1016 may output DC, such as + or −380 volt DC to thecharge module1018 and/orcommon DC grid1024. In this manner, the AC/DC converter1016 may rectify the AC input to provide power to thecommon DC bus1024, such as during surges in demand on thecommon DC bus1024. Thecharge module1018 may receive the DC output from the AC/DC converter1016 and may provide DC to thestorage device1020 to charge thestorage device1020. In this manner, thestorage device1020 may store energy. Thestorage device1020 may output energy to thecommon DC bus1024 via thedischarge module1022, which may be configured to provide DC from thestorage device1020 to thecommon DC bus1024.
• FIG. 11 illustrates an embodiment high reliability direct current (DC)module1102. In an embodiment, a highreliability DC module1102 may be part of a DC micro-grid, such asDC micro-grids700,800, and/or900 discussed above. In an embodiment, highreliability DC module1102 may receive inputs from various sources, including DC inputs from a fuel cell (e.g., power module having plural fuel cell stacks or segments)1104, solar cell (e.g., one or more photovoltaic modules)1106, and/orother DC sources1108, and AC inputs from apublic utility grid1110. The highreliability DC module1102 may includeDC inputs1112,1114, and1116 which may receive DC from thefuel cell1104,solar cell1106, and/orother DC sources1108, respectively.DC inputs1112,1114, and1116 may be coupled to a DC/DC converter1122. The highreliability DC module1102 may include anAC input1118 which may receive AC from thepublic utility grid1110. TheAC input1118 may be coupled to an AC/DC converter1124. The outputs of the DC/DC converter1122 and the AC/DC converter1124 may be couple to astorage module1120 and aDC output1126. Thestorage module1120 may be one or more storage device, such as a battery or ultracapacitor. Thestorage module1120 may receive DC input from the DC/DC converter1122 and the AC/DC converter1124 to store energy and may output to DC to theDC output1126. In an embodiment theDC output1126 of the highreliability DC module1102 may be coupled to acommon DC bus1130 which may be similar tocommon DC buses738,802, and/or1024 discussed above. In this manner, the highreliability DC module1102 may be high reliability because multiple energy sources are always available to output DC from theDC output1126.
• FIG. 12 illustrates an embodiment direct current (DC)micro-grid1200. TheDC micro-grid1200 is similar to the DC micro-grid700 illustrated inFIG. 7 and contains a number of components in common. Those components which are common to bothDC micro-grids700 and1200 are numbered with the same numbers inFIGS. 7 and 12 and will not be described further.
• One difference between the DC micro-girds1200 and700 is that in DC micro-grid1200 theload buses728,732, and736 may be fed by two independentcommon DC buses738 and1242. While discussed in terms of two independentcommon DC buses738 and1242, more than two independent DC buses may feedload buses728,732, and736. Independentcommon DC buses738 and1242 may be coupled toseparate power generators704a,704b,706a,706b,1210a,1210b,1212a, and1212band/or separateenergy storage devices714a,714b,1214a, and1214b. In a manner similar to that discussed above with reference topower generators704aand704b,AC power generators1210aand1210bmay be coupled topower generation bus1222 andpower electronics device1234. In a manner similar to that discussed above with reference topower generators706aand706b,DC power generators1212aand1212bmay be coupled topower generation bus1224 andpower electronics device1236. In a manner similar to that discussed above with reference toenergy storage devices714aand714b,energy storage devices1214aand1214bmay be coupled tostorage bus1226 andpower electronics device1238.Power electronics devices1234,1236, and1238 may be similar topower electronics devices740,742, and744 discussed above.Power electronics devices1234,1236, and1238 may be coupled tocommon DC bus1242.Power electronics devices1246,1250, and1254 may be similar topower electronics devices752,754, and756 discussed above, and may couple thecommon DC bus1242 to loadbuses728,732, and736, respectively. The second set ofpower electronics devices1246,1250, and1254 may be added in parallel to loadbuses728,732, and736 respectively. In this manner, a second set ofpower electronics devices1246,1250, and1254 may be coupled to a second common DC bus1248 which may be coupled to a second set ofpower generators1210a,1210b,1212a,1212band a second set ofenergy storage devices1214a,1214b. The presence of independentcommon DC buses738 and1242 may improve the reliability of power provided to theloads726a,726b,730a,730b,734a, and734b. In this manner, if necessary power for theload buses728,754, and756 cannot be provided by one common DC bus the other common DC bus may be able to meet the power demands. In an embodiment,common DC buses738 and1242 may be split buses, similar tocommon DC bus802 described above with reference toFIG. 8.
• The foregoing method descriptions and the process flow diagrams are provided merely as illustrative examples and are not intended to require or imply that the steps of the various embodiments must be performed in the order presented. As will be appreciated by one of skill in the art the order of steps in the foregoing embodiments may be performed in any order. Further, words such as “thereafter,” “then,” “next,” etc. are not intended to limit the order of the steps; these words are simply used to guide the reader through the description of the methods.
• One or more block/flow diagrams have been used to describe exemplary embodiments. The use of block/flow diagrams is not meant to be limiting with respect to the order of operations performed. The foregoing description of exemplary embodiments has been presented for purposes of illustration and of description. It is not intended to be exhaustive or limiting with respect to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the disclosed embodiments. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.
• Control elements may be implemented using computing devices (such as computer) comprising processors, memory and other components that have been programmed with instructions to perform specific functions or may be implemented in processors designed to perform the specified functions. A processor may be any programmable microprocessor, microcomputer or multiple processor chip or chips that can be configured by software instructions (applications) to perform a variety of functions, including the functions of the various embodiments described herein. In some computing devices, multiple processors may be provided. Typically, software applications may be stored in the internal memory before they are accessed and loaded into the processor. In some computing devices, the processor may include internal memory sufficient to store the application software instructions.
• The various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
• The hardware used to implement the various illustrative logics, logical blocks, modules, and circuits described in connection with the aspects disclosed herein may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but, in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. Alternatively, some blocks or methods may be performed by circuitry that is specific to a given function.
• The preceding description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the described embodiment. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the scope of the disclosure. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the following claims and the principles and novel features disclosed herein.

Claims (53)

What is claimed is:

1. A Direct Current (DC) micro-grid, comprising:

at least one power generator coupled to at least one power generation bus;

at least one energy storage device coupled to at least one energy storage bus;

at least one load coupled to at least one load bus;

a common DC bus;

a first power electronics device configured to provide power transfer coupling the at least one power generation bus to the common DC bus;

a second power electronics device configured to provide power transfer coupling the at least one energy storage bus to the common DC bus; and

a third power electronics device configured to provide power transfer coupling the at least one load bus to the common DC bus.

2. The DC micro-grid ofclaim 1, wherein:

the at least one power generator is a plurality of power generators;

the at least one energy storage device is a plurality of energy storage devices;

the at least one load is a plurality of loads; and

the plurality of power generators, plurality of energy storage devices, and plurality of loads are grouped by voltage and waveform.

3. The DC micro-grid ofclaim 2, wherein the groupings of voltage and waveform are one or more of 380 volts DC, 480 volts alternating current (AC), 48 volts DC, and −48 volts DC.

4. The DC micro-grid ofclaim 1, further comprising:

a controller coupled to the common DC bus and configured to control operation of the DC micro-grid such that a power requirement of the at least one load is maintained according to the following:

i. P(to storages)=P(generators)−P(loads), if P(generators)>P(loads); or

ii. P(from storages)=P(loads)−P(generators), if P(generators)<P(loads),

where P is Power.

5. The DC micro-grid ofclaim 4, wherein the controller is further configured to control the operation of the DC micro-grid such that the voltage of the common DC bus is equal to a highest voltage selected from the at least one power generation bus, at least one energy storage bus, and at least one load bus.

6. The DC micro-grid ofclaim 4, wherein the controller is further configured to control the operation of the DC micro-grid such that the voltage of the common DC bus is equal to a most common of the voltages among the at least one power generation bus, at least one energy storage bus, and at least one load bus.

7. The DC micro-grid ofclaim 4, wherein the controller is further configured to control the operation of the DC micro-grid such that the voltage of the common DC bus is equal to −48 volts DC.

8. The DC micro-grid ofclaim 4, wherein the controller is further configured to control the operation of the DC micro-grid such that the voltage of the common DC bus is less than 380 volts DC, the DC micro-grid further comprising:

a DC/DC converter within the at least one power generator, wherein the DC/DC converter is configured to provide voltage above the voltage of the common DC bus to auxiliary devices within the at least one power generator.

9. The DC micro-grid ofclaim 4, wherein the controller acts as a scheduler for the DC micro-grid and is further configured to coordinate the operation of the at least one power generator, at least one energy storage device, and the at least one load.

10. The DC micro-grid ofclaim 4, wherein the at least one power generator is a fuel cell generator.

11. The DC micro-grid ofclaim 1, wherein the common DC bus is split bus.

12. The DC micro-grid ofclaim 11, wherein the split bus has a first conductor of +380 volts DC, a second conductor that is neutral, and a third conductor of −380 volts DC.

13. The DC micro-grid ofclaim 1, wherein the at least one power generator is one or more of a fuel cell, modular energy generation system, solar cell, microturbine, wind turbine, utility power grid, and distributed diesel generator.

14. The DC micro-grid ofclaim 1, wherein the at least one load is one or more of an information technology (IT) load, a medical device load, and electric vehicle load.

15. The DC micro-grid ofclaim 1, wherein the at least on energy storage device is one or more of batteries, ultracapacitors, and flywheels.

16. The DC micro-grid ofclaim 1, wherein one or more of the first power electronics device, second power electronics device, and third power electronics device comprise isolated devices.

17. The DC micro-grid ofclaim 16, wherein the one or more of the first power electronics device, second power electronics device, and third power electronics device are selected from one of a full bridge DC/DC converter, half bridge DC/DC converter, resonant DC/DC converter, or hexaformer inverter.

18. The DC micro-grid ofclaim 16, wherein:

isolation is provided at least at one point between the at least one power generator and at least one energy storage device and the at least one load; and

the at least one load is an information technology (IT) load.

19. The DC micro-grid ofclaim 1, wherein:

the at least one power generation bus is an alternating current (AC) bus; and

the first power electronics device is a high efficiency isolation transformer.

20. The DC micro-grid ofclaim 19, wherein the high efficiency isolation transformer is a hexaformer.

21. The DC micro-grid ofclaim 1, wherein the first power electronics device, the second power electronics device, and the third power electronics device are configured to connect or disconnect from the common DC bus in response to communication signals received via wired communication links or the common DC bus.

22. The DC micro-grid ofclaim 21, wherein the communication signals are synchronization signals.

23. The DC micro-gird ofclaim 21, wherein the communication signals are alarm signals.

24. The DC micro-grid ofclaim 21, wherein the communication signals are encrypted and include an authentication key.

25. A method for operating a direct current (DC) micro-grid, comprising:

providing at least one power generator to a power generation bus;

providing at least one energy storage device to an energy storage bus;

providing at least one load to a load bus;

providing the power generation bus, the energy storage bus, and the load bus to a common DC bus, wherein each of the power generation bus, the energy storage bus, and the load bus, respectively, are coupled to the common DC bus via a respective power electronics device; and

operating the DC micro-grid such that a power requirement of the at least one load is maintained according to a following:

i. P(to storages)=P(generators)−P(loads), if P(generators)>P(loads); or

ii. P(from storages)=P(loads)−P(generators), if P(generators)<P(loads),

where P is Power.

26. The method ofclaim 25, further comprising:

controlling the voltage of the common DC bus to match a highest voltage of the power generation bus, energy storage bus, or load bus.

27. The method ofclaim 25, further comprising:

controlling the voltage of the common DC bus to match a most common of the voltages among the power generation bus, energy storage bus, and load bus.

28. The method ofclaim 25, wherein the common DC bus is a split bus.

29. The method ofclaim 28, wherein the split bus comprises a +380 volt DC conductor, a −380 volt DC conductor, and a neutral conductor.

30. The method ofclaim 25, wherein the at least one power generator is selected from one or more of a fuel cell, modular energy generation system, solar cell, microturbine, wind turbine, utility power grid, or distributed diesel generator.

31. The method ofclaim 25, wherein the power electronics devices are fully isolated devices.

32. The method ofclaim 31, wherein the power electronics devices individually comprise one or more of a full bridge DC/DC converter, half bridge DC/DC converter, resonant DC/DC converter, or AC/DC hexaformer inverter.

33. The method ofclaim 25, wherein isolation is provided by the power electronics devices at least at one point between the at least one power generator and the at least one energy storage device and the at least one load.

34. The method ofclaim 25, further comprising:

controlling the voltage of the common DC bus to be less than 380 volts DC; and

providing higher voltage than 380 volts DC for auxiliary devices with the at least one power generator using DC/DC converters located within the at least one power generator.

35. The method ofclaim 25, wherein an input or output to the common DC bus is an alternating current (AC) bus, and the method further comprising:

coupling an isolation transformer between the DC bus and the AC bus to provide isolation.

36. The method ofclaim 35, wherein the isolation transformer is a hexaformer.

37. The method ofclaim 25, further comprising:

communicating between the at least one power generator, the at least one energy storage device, and the at least one load.

38. The method ofclaim 37, wherein the communicating is performed using wires run in parallel to the inputs and outputs from the common DC bus.

39. The method ofclaim 38, wherein the wires are electrical wires or fiber optic transmission lines.

40. The method ofclaim 37, wherein the communication is performed by injecting signals into the common DC bus.

41. The method ofclaim 40, wherein the power electronics devices are configured to filter the injected signals such that the injected signals do not affect a power quality of their respective power generation bus, energy storage bus, and load bus.

42. The method ofclaim 40, wherein the power electronics devices are configured to disconnect from the common bus in response to a trigger.

43. The method ofclaim 42, wherein the trigger is a loss of synchronization with the signal.

44. The method ofclaim 42, wherein the trigger is an alarm event.

45. The method ofclaim 40, further comprising:

optimizing a power output of the at least one power generator or the at least one energy storage device based on communication signals sent in response to predicted transients in power requirements of the at least one load.

46. The method ofclaim 40, wherein communicating between the at least one power generator, the at least one energy storage device, and the at least one load includes using encryption and authentication keys.

47. The method ofclaim 40, further comprising a scheduler in communication with the at least one power generator, the at least one energy storage device, the at least one load, the common DC bus, and the power electronics devices, wherein the scheduler controls the operation of the at least one power generator, the at least one energy storage device, the at least one load, the common DC bus, and the power electronics devices.

48. The method ofclaim 47, wherein the scheduler controls the operation of the at least one power generator to coordinate load steps, coordinate warm up times, optimize efficiency, coordinate fuel supplies, or manage a cost of power generation.

49. The method ofclaim 47, wherein the scheduler controls the operation of the at least one energy storage device to manage a state of charge, manage a cost of power generation, or manage round trip efficiency.

50. The method ofclaim 47, wherein the scheduler controls the operation of the at least one load to manage at least one of load start up, load shut down, and load criticality.

51. The method ofclaim 47, wherein the scheduler dispatches fuel to storage in response to performance outages in the at least one power generator or dispatches fuel from storage in response to low fuel supply indications from the at least one power generator.

52. The method ofclaim 25, wherein:

the at least one power generator is a plurality of power generators;

the at least one energy storage device is a plurality of energy storage devices; and

the at least one load is a plurality of loads;

the method further comprising:

grouping the plurality of power generators, the plurality of energy storage devices, and the plurality of loads by voltage and waveform.

53. The method ofclaim 52, wherein the groupings voltage and waveform are one or more of 380 volts DC, 480 volts alternating current (AC), +48 volts DC, or −48 volts DC.

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