US20090000654A1 - Distributed inverter and intelligent gateway - Google Patents

Abstract

A system and method for converting DC from one or more sources to AC power utilizing a novel partitioning scheme are disclosed. This partitioning scheme is particularly well suited for photovoltaic (PV) microinverter applications. The primary goals are to make installation, operation and maintenance of the system safe and simple. Secondary goals are to improve reliability and lifetime of the converter in a cost effective manner. In one embodiment, the microinverters are placed in one-to-one proximity with the photovoltaic modules, each proximate microinverter incorporating a reduced number of functions and components. Remaining common functions and controls are implemented separately.

Description

• The present application relates to and claims the benefit of priority to U.S. Provisional Patent Application No. 60/938,663 filed May 17, 2007, which is hereby incorporated by reference in its entirety for all purposes as if fully set forth herein. The present application is further related to co-pending U.S. patent application Ser. No. LAR004 entitled, “Photovoltaic AC Inverter Mount and Interconnect” and U.S. patent application Ser. No. LAR003 entitled “Photovoltaic Module-Mounted AC Inverter”, both of which are hereby incorporated by this reference in their entirety.
BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• The invention relates to power conversion including direct current (DC) to alternating current (AC) and, more particularly, to photovoltaic module output power conversion to AC.
• 2. Discussion of the Related Art
• In coming years, distributed generation of electricity is likely to become a larger and larger part of the energy sourced to utility grids. Distributed sources of electrical energy such as solar photovoltaic modules, batteries, fuel cells and others generate direct current (DC) power, which must be converted to alternating current (AC) power for transmission and usage in residential and commercial settings.
• Also, as distributed generation increases, the utility grid, commonly known as the “grid,” will be transformed to a still to be defined smart-grid that will support increased coordination between multiple generators and multiple loads. “Grid tied” photovoltaic systems are the most common form of solar electric systems today and they use a form of coordination called net-metering.
• The larger number of photovoltaic installations are residential having an average capacity of about 2-3 kW. The bulk of new generating capacity is being installed in commercial buildings and utility scale installations. Residential systems commonly utilize single phase AC, while commercial systems most often use three phase AC.
• Residential rooftops present a special challenge for the placement and interconnection of photovoltaic modules, due to the presence of gables, multiple roof angles, and other such obstructions. Such rooftops often do not expose a sufficiently large, commonly directed surface to the sun for photovoltaic modules to be positioned to harvest maximum power. Currently, conventional inverter-based interconnections are optimized to minimize IR (current times resistance) loss. This is referred to as string design. The inverters perform a function called maximum power point tracking (MPPT) on strings of PV modules. The MPPT process evaluates the PV module string output current-voltage curve on a continuous or sampled basis to determine the correct load voltage thus maximizing the string output power calculated as the string output voltage times current. Due to the nature of residential rooftops, the string design results in MPPT performance at the levels of the least power producing modules in the photovoltaic (PV) array. This degrades the AC power harvest from the entire array.
• The use of microinverters in a one-to-one configuration with the PV modules removes the string design challenge, thereby enabling each PV module to produce current at its full capacity and truly permits MPPT at a per PV module level. The one-to-one arrangement of microinverters and PV modules is also referred to as AC PV modules in related art.
• Commercial buildings and larger installations present slightly different challenges. In commercial buildings, large, commonly directed surfaces are generally available, but even then, obstructions, such as HVAC components must be dealt with as the components may block solar radiation. String design and MPPT also continue to be of concern. Additionally, since such installations often consist of thousands of PV modules, monitoring, operation and maintenance can be time consuming and expensive.
• The use of AC PV modules for commercial installations simplifies string design, improves AC power harvest and provides the ability to remotely monitor the entire PV array on a module by module basis. A multiphase microinverter has the additional advantage of delivering substantially balanced multiphase AC power.
• The benefits of microinverters have been documented in related art dating back almost three decades. Yet, the use of microinverters continues to be negligible due to their inferior reliability and efficiency as well as their high cost as compared to conventional inverters.
• Typically, PV modules are placed in hostile outdoor environments in order to gain maximum exposure to solar radiation. Microinverters must be placed in proximity to the PV modules to realize their full benefits. Conventional inverters are typically placed in more benign environments, often indoors, e.g., on a protected wall or in a utility closet.
• When microinverters are placed in proximity to PV modules, the hostile outdoor environment exacerbates the design challenge for achieving high reliability, high efficiency and low cost. Similarly, servicing and replacing microinverters on a rooftop is potentially more challenging and labor intensive than servicing and replacing centralized inverters.
• The related art design approach for microinverters has been to implement them as miniaturized versions of conventional inverters, incorporating all the functions and components that were used in conventional inverters. Early versions of related art for microinverters utilized electrolytic capacitors, having a lifespan susceptible to degradation at high temperatures. Other versions of related art microinverters eliminate the electrolytic capacitor, thereby improving the lifespan.
• FIG. 1 shows a simplified diagram of a related art grid tied photovoltaic system utilizing a conventional inverter. Referring toFIG. 1,PV modules102 are mounted outdoors110 for direct access to solar radiation and connected to aconventional inverter105 usingDC wiring104. Bothinverter105 andDC wiring104 are located in a weather protectedregion111 such as the interior of a structure. Theinverter105 output feedslocal AC loads106 throughAC wiring103. The inverter's output is also tied for bi-directional flow of energy for net-metering to theutility grid101 throughexterior AC wiring107.
• FIG. 2 shows a simplified diagram of a related art grid tied photovoltaic system including microinverters. Referring toFIG. 2,PV modules202 are mounted outdoors210 for direct access to solar radiation.Microinverters203 are electrically coupled in one-to-one proximity to the PV modules202 (typically under them) and convert individual PV module DC outputs to AC power which is then fed toAC wiring204. The AC wiring204 feedslocal loads206 and the utility grid201.
• A problem with the related art microinverters is that they either collocate all inverter functions including safety and code compliance within the microinverter or they do not address how these functions are to be implemented, thereby making the design for high reliability and long life difficult and expensive. The collocation may also require redevelopment and replacement of the microinverter when code compliance requirements change.
SUMMARY OF THE INVENTION
• Accordingly, the invention is directed to a distributed inverter and intelligent gateway that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
• An advantage of the invention is to provide a system and method of installation, operation, and maintenance of the a power conversion system that is simple and safe.
• Another advantage of the invention is to provide a high degree of reliability and a long lifetime to the microinverter.
• Yet another advantage of the invention is to provide upgradeability of the system during the lifetime of the system.
• Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The features of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
• To achieve these and other advantages and in accordance with the purpose of the invention, an embodiment of the invention is directed towards a system for transforming energy. The system for transforming energy includes a plurality of photovoltaic modules. The plurality of microinverters are electrically coupled to the photovoltaic modules in a one-to-one relationship. The system also includes a gateway electrically coupled to the plurality of microinverters and features of the gateway are capable of being upgraded with at least one of hardware, software, and firmware.
• In another aspect of the invention, an embodiment of the invention includes a gateway for use in a system for use in an energy generating system. The gateway includes an interface unit for interfacing with a plurality of microinverters and a utility grid. The gateway also includes a control unit electrically coupled to the interface unit for controlling at least one of safety functionality, synchronization functionality to synchronize the plurality of microinverters to the utility grid, and monitoring functionality to monitor the plurality of microinverters and the utility grid. The control unit is capable of being electrically coupled to an external monitor. In yet another aspect of the invention, an embodiment of the invention includes a photovoltaic system for transforming radiant energy into alternating current. The photovoltaic system includes a plurality of photovoltaic modules and a plurality of microinverters coupled to the photovoltaic modules in a one-to-one relationship. Each of the plurality of microinverters includes an inversion unit, a MPPT unit, a communications unit, a safety unit, an interface unit and a control unit. The inversion unit converts DC into AC and the MPPT unit optimizes power from the plurality photovoltaic modules. The communications unit provides communications to the gateway. The safety unit provides safety functions. In addition, a gateway is coupled to the plurality of microinverters. The gateway includes an interface unit and a control unit. The interface unit interfaces with a plurality of microinverters and a utility grid. The control unit is coupled to the interface unit for controlling at least one of safety functionality, synchronization to synchronize the plurality of microinverters to the utility grid and monitoring where the control unit is capable of being coupled to an external monitor.
• It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
• The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
• In the drawings:
• FIG. 1 is a diagram of a related art grid tied photovoltaic system using a conventional centralized inverter;
• FIG. 2 is a diagram of a related art grid tied photovoltaic system using conventional microinverters;
• FIG. 3 is a diagram of a grid tied photovoltaic system using distributed converters including microinverters and a gateway according to an embodiment of the invention;
• FIG. 4 is a block diagram of a distributed converter utilizing microinverters according to another embodiment of the invention;
• FIG. 5 is a block diagram of a distributed converter utilizing string inverters according to another embodiment of the invention;
• FIG. 6 is a block diagram of a distributed converter utilizing centralized inverters according to another embodiment of the invention;
• FIG. 7 is a block diagram of a PV system utilizing microinverters according to another embodiment of the invention;
• FIG. 8 is a block diagram of a PV system utilizing multiple string inverters according to another embodiment of the invention; and
• FIG. 9 is a block diagram of a PV system utilizing centralized inverters according to another embodiment of the invention.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
• Embodiments of the invention include a novel approach whereby only those functions and components that are necessary to achieve the advantages of microinverters are placed in assemblies in proximity to the PV modules and other functions including, for example, system control, are located elsewhere. This separation of functions and components is termed portioning. The control and coordination of the system is performed without additional wiring. Communications may occur via powerline, wired and/or wireless channels. Disabling the communications channel provides a way for turning the microinverters off thereby facilitating inverter or PV module replacement, maintenance or other desired tasks. Moreover, the partitioning provides for enhanced safety as compared to the related art. In the related art, in the presence of solar radiation, the PV module outputs are always enabled and are thus capable of electrocuting the installer. Accordingly, embodiments of the invention provide for safer and simpler installation and maintenance procedures.
• In addition, the partitioning reduces the number and type of components placed in the PV module proximate assemblies that are subject to the hostile outdoors environment, such as temperature. Fewer components and simplified assembly also result in improved reliability and increased system lifetime. Cost is reduced by eliminating common system functions from the microinverter. In embodiments of the invention where these functions are realized with cheaper or less robust components located in a less hostile environment, the cost may also be further reduced.
• In some embodiments, the partitioning may include physically locating programmable functions in an area distinct from the PV module assemblies, such as, in a gateway. Accordingly, the features located in the gateway are decoupled or portioned from the PV module assemblies. The functions and components in the gateway may be upgraded over the lifetime of the system. Therefore, the development cycle of the gateway is decoupled from the development cycle of the microinverter assemblies coupled to the PV module assemblies, and thus several generations of gateways having different value added functions can be developed for use with the same microinverter assemblies. This leads to an upgradeable system at a significantly reduced cost as compared to the related art.
• Reference will now be made in detail to embodiments of the invention, examples of which are illustrated in the accompanying drawings.
• FIG. 3 is a diagram of a grid tied photovoltaic system using distributed converters including microinverters and a gateway according to an embodiment of the invention. The grid tied photovoltaic system includes a plurality ofPV modules302 mounted outdoors310 each coupled electrically and mechanically tomicroinverter assemblies303. In this embodiment, thegateway305 is located in a weather protectedenvironment311, e.g., indoors, for accessibility and protection from the elements. However, thegateway305 could be located in an outdoor environment or other location. Thegateway305 receives AC current from the plurality ofmicroinverters303 via afirst AC wiring304. Thegateway305 is connected to thegrid301 and tolocal loads306 via asecond AC wiring307. Theloads306 are thereby always connected to thegrid301. Thegateway305 provides a point of measurement of the AC performance of the PV system and also the electrical behavior of thegrid301. Thegateway305 also provides control and monitoring of themicroinverters303.
• FIG. 4 is a block diagram of a distributed converter according to another embodiment of the invention. Referring toFIG. 4, a system for transforming energy includes a firstphotovoltaic module401 and a secondphotovoltaic module411 coupled to a distributedinverter410 with DC wiring402,412. The distributedinverter410 is functionally partitioned into agateway406 and afirst microinverter404 and asecond microinverter414. Thefirst PV module401 connects to thefirst microinverter404 via first DC wiring402 and thesecond PV module411 connects to thesecond microinverter414 via second DC wiring412. Additional PV modules can be connected via independent DC wires to associated additional microinverters.
• The AC output of all microinverters is connected in parallel viaAC wiring405 to thegateway406. Thegateway406 includes aninterface unit407 and acontrol unit408. Theinterface unit407 is connect to thecontrol unit408 viainterface wiring409. The interface unit connects to the utility grid viaAC power wiring420. The control unit connects to an external monitor via data communications wiring421 or via a wireless data communications channel.
• The first andsecond microinverters404,414 include a power inversion unit, a maximum power point tracking (MPPT) unit, a communications unit and a safety unit. The power inversion unit converts DC power from the associated PV module to AC power. The AC power may be generated in single-phase or multi-phase form. The MPPT unit detects the output power of the associated PV module and adjusts the load voltage presented to the PV module in such a way as to maximize the power available from the PV module. The MPPT unit and functionality are described by Hussein K. H., Mutta I., Hoshino T. and Osakada M., in “Maximum photovoltaic power tracking: An algorithm for rapidly changing atmospheric conditions”, IEE Proceedings, Generation, Transmission and Distribution, Vol. 142, No. 1, January 1995, which is hereby incorporated by reference as if fully set forth herein. The communications unit provides bi-directional data communications between themicroinverter404,414 and thegateway406. Data communications from thegateway406 to themicroinverter404,414 includes, for example, power conversion control, status requests, fail-safe shutdown operation and other relevant data operations. Data communications from themicroinverter404,414 to thegateway406 includes PV module DC output voltage and current data, microinverter AC output voltage and current data, microinverter operational status and other relevant data.
• The safety unit establishes conditions to enable or disable current flow from thePV module401,411 to themicroinverter404,414 and from themicroinverter404,414 to thegateway406. One safety function of the safety unit is to establish that the utility grid voltage available at theAC wiring405 is within specifications to allow the inverter to safely drive the grid. If the appropriate grid voltage specifications are met, then the safety unit enables both input and output current through themicroinverter404,414. This first function is also performed by thegateway407 and the function is secondary within themicroinverter404,414 as a backup fail-safe system in case of failure of the primary safety function ofgateway406.
• Another safety function of the safety unit is to test for a communications signal from thegateway406 indicating that the grid is safe to drive with AC output current. If the gateway were disabled by any means, the communications signal emitted by thegateway406 would be disabled. The safety unit detects this condition and immediately disables all current flow into and out of themicroinverter404,414. The communications signal from thegateway406 is termed a “heartbeat” and provides a primary fail-safe mechanism for disabling PV system AC and DC power flow in the event of a grid failure, fire or other safety hazard.
• Yet another safety function of the safety unit is to support removal and re-attachment of a themicroinverter404,414 while the entire PV system is enabled. This is termed a hot-swap and requires that themicroinverter404,414 shut down upon detection of the removal or reattachment of the microinverter to suppress any arcs or high voltages that may develop at themicroinverter DC wiring402,412 orAC wiring405 terminals. High voltages at the microinverter terminals are suppressed as a means to insure that maintenance personnel are not able to contact the exposed terminals while they are energized. Themicroinverter404,414 shuts down if either the AC output voltage atAC wiring405 does not meet prescribed conditions, such as a disconnect or grid failure, or if the PV module DC input voltage at DC wiring402,412 appears to be disconnected.
• Thegateway406 acts as master controller in the distributedinverter410 by performing functions such as providing the above described heartbeat to the microinverters, monitoring their output, monitoring the grid and other related functions. Thegateway407 can turn off the heartbeat when, for example, the gateway detects a fault or unsafe conditions in the environment, maintenance is to be performed, an AC power failure occurs and/or other related operating conditions. Similarly, if thegateway406 is physically absent, the heartbeat is thereby also absent, resulting in the disabling of the microinverters.
• The communication between thegateway406 and themicroinverters404,414 may be performed over theAC wiring405, wirelessly, or by other suitable means such as independent wiring. Both communication over AC wiring and wireless communication have the advantage that no additional wiring is required beyond that to support the transfer of AC power in the system. In the case of communication over the AC wiring405 a wireline modulator/demodulator sub-function included within both thegateway406 and themicroinverters404,414 to perform the communication functions utilizing theAC wiring405.
• In this embodiment, thegateway406 functions are split into aninterface unit407 and acontrol unit408. Theinterface unit407 includes a sensor unit, a communications unit and an isolation unit. The sensor unit provides a way to dynamically monitor grid conditions, for example to dynamically measure grid AC voltage, current, frequency, phase and other related grid signal characteristics. In addition, thecommunications unit408 provides means to send and receive data fromconnected microinverters404,414. Theisolation unit407 substantially prevents data communications between themicroinverters404,414 and thegateway406 from appearing at thegrid wiring420 or onto the grid. Similarly, noise and other signals, with the exception of the desired grid AC power voltage and current, are substantially prevented from appearing at theAC wiring405 between themicroinverters404,414 and thegateway406.
• Thecontrol unit408 provides monitoring and control functions to monitor themicroinverters404,414. Some of the control includes controlling at least safety functionality and synchronization functionality to synchronize themicroinverters404,414 to the grid and monitoring functionality to monitor themicroinverters404,414 and the utility grid. In addition, thecontrol unit408 provides grid synchronization, communications protocols, grid connection performance compliance and system monitoring. The control unit can be implemented with a computer or microcontroller.
• In this embodiment, software and firmware run on thecontrol unit408 to implement functions such as generating the heartbeat, monitoring the microinverters, monitoring the grid and monitoring any AC loads. Using the previously described communications system thecontrol unit408 can address each microinverter404,414 individually, in subsets, or as an entire ensemble.
• For example in one embodiment, thecontrol unit408 provides synchronization signals for matching the frequency and phase of themicroinverter404,414 AC output to the grid AC power. The heartbeat fail-safe is also implemented in thecontrol unit408. Other functions may include monitoring the health and productivity of each microinverter and each PV module.
• Thecontrol unit408 also performs grid related protocols such as detection of grid failure, anti-islanding detection, adjustment of parameters utilized in the anti-islanding detection and related functions. New grid related protocols will be defined to implement a future smart-grid in which the grid operator may enable, disable or modify the control system of a grid-connected PV system. Thecontrol unit408 is constructed with flexible hardware, software and firmware to adapt to future grid-defined control and communications protocols, without requiring changes to themicroinverters404,414.
• Thegateway406 as a whole can also be upgraded to support future system requirements by changing the hardware, software or firmware while utilizing thesame microinverters404,414. For thegrid connection420 of thegateway406, thecontrol unit408 can perform load management functions, as directed through the grid protocol or other external sources. Related art monitoring and display functions can also be implemented in thecontrol unit408.
• Thewiring409 carries all data between theinterface unit407 and thecontrol unit408. External communications to thegateway406 from an external monitor occurs viacommunications wiring421, or other communications means such as wireless communications. This is used to externally monitor and control operation of thegateway406 and allows for system remote control via internet connection or other remote communications means.
• By reducing the functions performed within themicroinverter404,414 a reduction in the required microinverter complexity is achieved, thereby leading to simpler implementation of the microinverter and increased reliability, increased lifetime, and reduced cost as compared to the related art. In particular, the elimination from the microinverter of precision grid signal measurement requirements to support anti-islanding functionality for grid connection specification compliance as defined, for example, by IEEE standard IEEE-1547, eliminates considerable complexity, expense and lifetime limiting components from the microinverter.
• IEEE standard IEEE-1547, and related standards used throughout the world, defined a narrow set of circumstances upon which the grid is driven by the inverter. If a break in the grid wiring occurs, an inverter could continue driving power into the un-connected branch of the grid. This region in which the primary grid generators no longer apply power is termed an island. The inverter is required by the IEEE-1547 standard to disable its output power under such conditions so as not to drive the island in the grid for both safety and technical reasons. This is known as anti-islanding. Thegateway406 assumes the primary role in detecting the defined islanding condition and communicates the associated inverter shut-down command to themicroinverters401,411 to implement the anti-islanding function. Example grid conditions for an anti-islanding shutdown are a very high grid voltage, a low grid voltage, a high grid frequency, a low grid frequency or a significant variation in grid impedance. The grid is usually of low impedance, therefore the usual grid impedance variation is an increase when the island occurs.
• The system ofFIG. 4 can also be used to convert power for primary or secondary power sources other thanPV modules401,411 such as wind turbines, fuel cells, batteries, and other power sources.
• FIG. 5 is a block diagram of a PV system according to another embodiment of the invention. A firstPV module string501 includes afirst PV module502, asecond PV module503 and athird PV module504 that are connected in series. A firstoutput DC wire505 and a secondDC output wire506 from thePV module string501 are connected to afirst string inverter521. A secondPV module string511 includes afourth PV module512, afifth PV module513 and asixth PV module514 that are connected in series. A thirdoutput DC wire515 and a fourthDC output wire516 from thePV module string511 are connected to asecond string inverter522. The AC outputs of thefirst string inverter521 andsecond string inverter522 are connected in parallel viaAC wiring523 to thegateway524. The PV module strings501,511 may include any number of PV modules that are series connected. Any number of PV module strings may be used in conjunction with associated string inverters in this system.
• PV module strings501,511 are not required to include equal numbers ofPV modules502,503,504,512,513,514 as is the case in related art. This provides the benefit of a simple string design in which the string DC output voltages are not required to be matched betweenstrings501,511. Moreover, MPPT may be performed on a per string basis, so one string does not degrade the performance of another, as is the case with related art where equal length strings are connected in parallel. This arrangement has the potential to provide greater AC power harvest than conventional inverters, but less AC power harvest than microinverters.
• A distributedinverter520 is functionally portioned into agateway524 andstring inverters521,522. The functions of thegateway524 in this embodiment are the same as the functions of thegateway406 as described herein. Thegateway524 includes aninterface unit525 and acontrol unit526, both of which are the same as described with reference toFIG. 4 herein. Accordingly, the benefits of partitioning thegateway524 from the multiple-string inverters521,522 inFIG. 5 are substantially similar to the benefits of partitioning thegateway406 from themicroinverters404,414 inFIG. 4. For example, the benefits include using a heartbeat for safety and independent upgradeability of the gateway from that of the string inverters. In this embodiment, the multiple-string inverters521,522 are placed close to the gateway and away from the hostile outdoors environment. The AC output of allstring inverters521,522 are connected to the gateway in parallel viaAC power wiring523. Thegateway524 is connected to the grid viawiring530. External communications to thegateway524 from an external monitor occurs viacommunications wiring531, or other communications means such as wireless communications. This is used to externally monitor and control operation of thegateway524 and allows for system remote control via internet connection or other remote communications means.
• FIG. 6 is a block diagram of a PV system according to another embodiment of the invention. A firstPV module string601 includes afirst PV module602, asecond PV module603 and athird PV module604 that are connected in series. A firstoutput DC wire605 and a secondDC output wire606 from thePV module string601 are connected to theDC combiner621. A secondPV module string611 includes afourth PV module612, afifth PV module613 and asixth PV module614 that are connected in series. A thirdoutput DC wire615 and a fourthDC output wire616 from thePV module string611 are connected to theDC combiner621.
• Afirst DC output622 and asecond DC output623 from the DC combiner connects to the DC inputs of aninverter624. The AC outputs of theinverter624 are connected in parallel to other inverters viaAC wiring625 to thegateway626. The PV module strings601,611 can include any number of PV modules that are connected in series. Any number of PV module strings can be used in conjunction with associated DC combiners. A plurality ofinverters624 may be used with outputs connected in parallel in the system.
• In this embodiment, the PV module strings601,611 must be of equal length when connected to acommon DC combiner621. This scheme is consistent with connection of conventional inverters as known to one of ordinary skill in the art. The AC output of theinverter624 is connected to thegateway626 in parallel viaAC power wiring625.
• In addition, theinverter624 is similar to conventional inverters as known to one of ordinary skill in the art except that control functions are implemented in agateway626 rather than within the inverters. The functions of thegateway626 in this embodiment are substantially similar to its functions in the embodiment shown inFIG. 4. Thegateway626 includes aninterface unit627 and acontrol unit628, both of which are the same as discussed with reference toFIG. 4 herein. Accordingly, the development cycles of the inverters and controllers can be decoupled with improved system performance and the ability to upgrade without changing the inverters. Thegateway626 is connected to the grid viawiring630. External communications to thegateway626 from an external monitor occurs viacommunications wiring631, or other communications means such as wireless communications. This is used to externally monitor and control operation of thegateway626 and allows for system remote control via internet connection or other remote communications means.
• FIG. 7 is a block diagram showing a PV system according to another embodiment of the invention. Referring toFIG. 7, a distributed inverter including agateway712 based on the concepts embodied inFIG. 4. Thegateway712 includes an interface unit727 and a control unit728, both of which are the same as discussed with reference toFIG. 4 herein.
• PV modules701 are individually coupled to microinverters702 on afirst chain703, andPV modules707 are individually coupled to microinverters706 on asecond chain708. The outputs of themicroinverters702 are connected in parallel to each other and, throughAC wire704, to anAC circuit breaker705, and on toAC wiring711. The outputs of themicroinverters706 are connected in parallel to each other and, throughAC wire709, to an AC circuit breaker710 and on toAC wiring711.
• TheAC wiring711 is connected to thegateway712,AC cutoff713, and to the grid throughAC wiring714. Note that components andwiring704, wiring711, wiring710,AC cutoff713 andwiring714 are conventional AC electrical components and their selection and installation is consistent with the understanding of one of ordinary skill in the art.
• FIG. 7 illustrates the scalability of installation using distributed inverters. The concept of hierarchical or replicated gateways suggests itself for much larger capacity systems, as does the concept of additional chains to thesame gateway712. Without loss of generality, the output of the microinverters can be single-phase AC, split-phase AC or multi-phase AC.
• FIG. 8 is a block diagram showing a PV system according to another embodiment of the invention. Referring, toFIG. 8, a distributed inverter, includes a gateway and a multiple-string inverter, based on the concepts embodied inFIG. 5. Thegateway816 is the same as the gateway as described inFIG. 5. Accordingly, the upgradeability, safety features, and enhanced performance benefits may also be similar. A plurality ofPV modules801 are connected in a first series string and coupled tofirst string inverter803 viaDC wiring802. A plurality ofPV modules805 are connected in a second series string and coupled tosecond string inverter807 viaDC wiring806. A plurality ofPV modules809 are connected in a third series string and coupled tothird string inverter811 viaDC wiring810.
• The AC output of thefirst string inverter803 is coupled through anAC circuit breaker804 intoAC wiring814. The AC output of thesecond string inverter807 is coupled through anAC circuit breaker808 intoAC wiring814. The AC output of thethird string inverter811 is coupled through an AC circuit breaker812 intoAC wiring814.
• TheAC wiring814 is connected to thegateway816,AC cutoff815, and to the grid through AC wiring818. Optionally, theinverters803,807,811 and theAC circuit breakers804,808,812 may be placed in acommon enclosure813 to simplify installation and protect the inverters and circuit breakers from environmental effects. The system may be expanded by increasing the number of PV modules in a string, strings, string inverters and AC circuit breakers.
• FIG. 9 is a block diagram showing a PV system according to another embodiment of the invention. Referring toFIG. 9, a distributed converter including a gateway and a multiple inverter, based on the concepts embodied inFIG. 6. Thegateway917 is the same as the gateway as described inFIG. 5. Accordingly, the upgradeability, safety features, and enhanced performance benefits may also be similar. A plurality ofPV modules901 are connected in a first series string and coupled to afirst DC combiner903 viaDC wiring902. A plurality ofPV modules906 are connected in a second series string and coupled to afirst DC combiner903 viaDC wiring907. A plurality ofPV modules908 are connected in a third series string and coupled to asecond DC combiner910 viaDC wiring909. A plurality ofPV modules913 are connected in a fourth series string and coupled to asecond DC combiner910 viaDC wiring914.
• The DC output of thefirst DC combiner903 is connected to the DC input of afirst inverter904. The AC output of thefirst inverter904 is coupled through anAC circuit breaker905 intoAC wiring915. The DC output of thesecond DC combiner910 is connected to the DC input of asecond inverter911. The AC output of thesecond inverter911 is coupled through anAC circuit breaker912 intoAC wiring915.
• TheAC wiring915 is connected to thegateway917,AC cutoff916, and to the grid throughAC wiring918. TheAC circuit breakers905,912,AC wiring915,AC cutoff916 andgrid wiring918. Optionally, theinverters904,911, theDC combiners903,910, and theAC circuit breakers905,912 may be placed in a common enclosure (not shown) to simplify installation and to protect them from environmental effects.
• It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Claims (20)

1. A system for transforming energy, comprising:

a plurality of photovoltaic modules;

a plurality of microinverters electrically coupled to the photovoltaic modules in a one-to-one relationship; and

a gateway electrically coupled to the plurality of microinverters, wherein features of the gateway are capable of being upgraded with at least one of hardware, software, and firmware.

2. The system ofclaim 1, wherein the gateway comprises an interface unit and control unit.

3. The system ofclaim 1, wherein the interface unit, comprises:

a plurality of sensors to detect dynamic utility grid conditions;

a communication unit to communicate with the plurality of microinverters and the gateway; and

an isolation unit to substantially prevent communication signals from the microinverters from appearing on the utility grid.

4. The system ofclaim 1, wherein the control unit provides a monitoring functions to monitor the plurality of microinverters.

5. The system ofclaim 1, wherein each of the plurality of microinverters, comprise:

an inversion unit to convert DC into AC;

a maximum power point tracking (MPPT) unit to optimize power output from the plurality photovoltaic modules;

a communications unit to provide communications to the gateway; and

a safety unit to provide safety functions.

6. The system ofclaim 1, wherein the communications unit permits communication in at least one of wireless communication, wired communication, and powerline communication.

7. The system ofclaim 5, wherein the safety unit is capable of disabling the microinverter upon detection of the microinverter being electrically decoupled from either the gateway or the PV module.

8. The system ofclaim 5, wherein the safety unit is capable of disabling the microinverter in response to a communication signal from the communication unit of the gateway.

9. The system ofclaim 5, wherein the safety unit is capable of disabling the microinverter upon detection of predetermined grid conditions.

10. The system ofclaim 9, wherein the predetermined grid conditions include at least one of a low grid voltage, a high grid voltage, a low grid frequency, a high grid frequency and a predetermined change in grid impedance.

11. A gateway for use in a system for use in an energy generating system, comprising:

an interface unit for interfacing with a plurality of microinverters and a utility grid;

a control unit electrically coupled to the interface unit for controlling at least one of safety functionality, synchronization functionality to synchronize the plurality of microinverters to the utility grid, and monitoring functionality to monitor the plurality of microinverters and the utility grid, wherein the control unit is capable of being electrically coupled to an external monitor.

12. The gateway ofclaim 11, wherein the interface unit, comprises:

a plurality of sensors to detect dynamic utility grid conditions;

a communication unit to communicate with the plurality of microinverters and the control unit; and

an isolation unit to substantially prevent communication signals from the plurality of microinverters from appearing on the utility grid.

13. The system ofclaim 12, wherein the communications unit is capable of communication in at least one of wireless communication, wired communication, and powerline communication.

14. The system ofclaim 12, wherein each of the plurality of microinverters includes a safety unit capable of disabling the microinverter upon detection of the microinverter being electrically decoupled from either the gateway or a power module.

15. The system ofclaim 12, wherein the power module is a wind turbine.

16. The system ofclaim 12, wherein each of the plurality of microinverters includes a safety unit capable of disabling the microinverter upon detection of predetermined utility grid conditions.

17. A photovoltaic system for transforming radiant energy into alternating current, comprising:

a plurality of photovoltaic modules;

a plurality of microinverters coupled to the photovoltaic modules in a one-to-one relationship, wherein each of the plurality of microinverters comprise:

an inversion unit to convert DC into AC;

a MPPT unit to optimize power from the plurality photovoltaic modules;

a communications unit to provide communications to the gateway; and

a safety unit to provide safety functions;

a gateway coupled to the plurality of microinverters, wherein the gateway comprises:

an interface unit for interfacing with a plurality of microinverters and a utility grid; and

a control unit coupled to the interface unit for controlling at least one of safety functionality, synchronization to synchronize the plurality of microinverters to the utility grid, and monitoring, wherein the control unit is capable of being coupled to an external monitor.

18. The system ofclaim 17, wherein the interface unit comprises a communications unit permitting communication in at least one of wireless communication, wired communication, and powerline communication.

19. The system ofclaim 17, wherein the safety unit is capable of disabling the microinverter upon detection of the microinverter being electrically decoupled from either the gateway or a photovoltaic module.

20. The system ofclaim 17, wherein each of the safety unit is capable of disabling the microinverter upon detection of predetermined utility grid conditions.

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