The invention relates to a charging station for charging electric energy storages of electric vehicles, such as cars, motorbikes, buses, trucks, trains, or boats to name a few. The invention also relates to a method for charging electric energy storages of charging electric vehicles.
Technical Background
Electric vehicles use one or more electric motors for propulsion. In case an electric vehicle comprises a battery for storing electrical energy and to power the electric motors, this battery has to be charged from time to time. Most electric vehicles are equipped with an internal charger, which has to be connected to an external power source for charging the battery. Such an external power source is for example the power socket connected to the public power grid, for example at home in the garage. There are also electric vehicles which change their battery at a battery changing station. However the discharged batteries still have to be re-charged in the same way. The invention therefore also relates to charging stations not only for on board batteries of electric vehicles but also where batteries of electric vehicles are separated from the electric vehicle to be re-charged.
Despite the environmental issues with combustion engines, electric vehicles are not widely accepted yet as the users of electric vehicles are used to the relatively short time it takes to re-fuel their vehicle with a combustion engine. It is therefore crucial to provide a network of charging stations which allow re-charging of an electric vehicle in a very short time. Although internal chargers for the electric vehicle for charging the battery from a charging station have been developed which allow relatively fast recharging of the battery, the power that a charging station can request from the electrical grid limits the power a charging station can deliver to the electric vehicle. At the time, quick chargers are available that can charge an electric vehicle with 50kW but a 3phase power socket of the public power grid would only provide 22kW. In order to overcome this problem, charging stations exists which are equipped with a buffer, for example a lithium battery, which provides the extra current requested by the electric vehicle. The buffer is recharged at times when no electric vehicle is connected to the charging station.
Object of the invention
Charging stations with such energy buffers have to manage issues that come with high currents such as high heat losses and dissipating heat. A further object of the invention is to allow a flexible adaption of the charging station to various applications and configurations
Summary of the invention
In order to solve these problems the invention proposes a charging station for charging electric energy storages of electric powered vehicles comprising an input circuit for connecting the charging station to an electrical power source and providing a first intermediate DC voltage DCi at a first DC output at a first DC voltage level; at least one DC/DC converter which receives the first intermediate DC voltage DCi and which provides at a DC/DC converter output a second DC voltage DC2 at a second DC voltage level; an electrical DC charging buffer connected to the DC/DC converter output; an output circuit for converting the second intermediate DC voltage DC2 to the DC current or AC current requested by for example an on board battery of an electric vehicle.
The invention proposes to convert an input voltage of any power source, whether a AC power source or a DC power source, to a first intermediate DC voltage and further to convert the first DC intermediate voltage into a second intermediate DC voltage. Basically the DC output part of the input circuit acts as a first intermediate circuit, wherein the first intermediate DC voltage is buffered, for example with buffer capacitors. The first intermediate DC voltage is then distributed via the DC/DC converters to the DC charging buffers. The DC charging buffer which may be seen as a part of a second intermediate DC circuit, which distributes the second intermediate DC voltage to the output circuit. The term intermediate circuit shall denote in this application circuitry with buffer capabilities, whether the buffers are capacitors, coils, batteries, or whatever elements that can for a short time or a long time keep electrical charges at a nearly constant level.
Two intermediate DC voltages, respectively two intermediate circuits, increase the stability of the charging station and allow for a higher degree of flexibility, especially when a not predetermined number of charging points/charging interfaces are combined in a single charging station, i.e. in a single housing. In this application the term charging module shall denote the logical combination of a DC/DC converter, a second intermediate circuit, and an output circuit for generating the charging current from the second intermediate DC voltage of the second intermediate circuit.
Another advantage is that the invention allows for an easier heat dissipation management, but also adds greater flexibility when higher currents I higher voltages should be introduced in a later stage for charging the electrical storages of electrical vehicles. In such an event, the charging stations have to be equipped only with modified output circuits and very likely the input circuits and DC/DC converters can be continued to be in use without substantial changes. Ideally for the modification of the output circuit it should suffice to apply a software upgrade for changing the control signals for the control of switching elements. Physically only the interfaces, e.g. plugs or sockets might need a mechanical exchange or add-on. This provides a perfect upgrade path for future standards or quasi standards.
The distribution of the electrical functions over at least a first intermediate circuit and at least one charging module also allows for easy provision of multiple charging modules without the risk that any of the input circuits is electrically overloaded. Several input circuits can be connected in parallel with their DC outputs, i.e. the outputs of the first intermediate circuits at the first DC voltage level on the common first intermediate power rail in case the power source to which the several input circuits are connected to provides more power than a standard power supply. Additionally or alternatively several charging modules, can be connected with their DC input to the common first intermediate DC power rail of the first intermediate circuit/circuits. Thanks to the individual energy buffer of each second intermediate circuit the number of charging modules that can be connected to the common first intermediate DC power rail is not limited to a specific number, although the increased charging time for each additional energy buffer of a charging module imposes a practical limit at which a charging station with too many output circuits in respect to the available input power of the energy source renders the charging station impracticable to use and not economic with view on the costs.
In another aspect of the invention a control circuit of the charging station is configured to measure an output current provided by the at least one DC/DC converter, to determine on basis of the measured output current the power consumed by the input circuit, and to control the current provided by the at least one DC/DC converter such that the power consumed by the input circuit does not exceed a predetermined level.
In case there are several charging modules arranged in one charging station the control circuit measures the sum of all output currents of the individual DC/DC converters of each charging module, it can determine approximatively the power consumed from the input circuit as the sum of all DC/DC converters output currents. This information is used by the control circuit for example to control the input circuit such that it reduces the power consumed from the external power source. This is especially beneficial when the charging station is powered up and empty energy buffers draw a lot of power. The power consumption of the input circuit could for example be controlled by a controllable rectifier build of thyristor instead of diodes for example. The thyristors can be pulse width modulated. A long control pulse would let pass the full period of a half sinus wave, whereas if the pulses with respect to the zero crossing of the half sinus wave start later, only part of the half sinus wave would be rectified and thus reduces the power that is available after the thyristor bridge.
Additionally or alternatively, the control circuit may control the individual DC/DC converters to reduce their output current so that the power consumed by the input circuits is controlled individually for each DC/DC converter. This seems to be the preferred solution for a smooth control of the input circuit once the charging station has transitioned from start-up phase into steady state operation.
In another aspect of the invention the first intermediate voltage DCi is higher than the second intermediate voltage DC2.
Ideally the output voltage of the first intermediate DC/DC converter is sufficiently lower than the voltage of the power source, so that even when the power source experiences severe voltage drops the voltage of the power source still stays higher than the output voltage of the first intermediate DC/DC voltage. With this prerequisite the first intermediate DC/DC converter can be implemented as a simple voltage-down converter. Having a very stable first intermediate DC voltage the second intermediate circuits are provided with a perfect input voltage for either up-converting or down-converting the second intermediate voltage.
In another aspect of the invention the electrical power source is a public power grid with an AC voltage. This invention is especially beneficial for power sources with limited power supply, such as power sockets in a domestic environment, or power supplied to lamp posts. Usually a fuse would interrupt the power supply if a predetermined power limit is exceeded.
In another aspect of the invention wherein the second intermediate voltage is in a range of 100 Volts to 500 Volts, preferably in the range between 400 to 450 Volts.
In continental Europe with a line voltage of nominal 230 Volts for single phase current power and 400 Volts for three phase power supply systems a first intermediate DC voltage of almost 325 Volts can be achieved for input circuits connected to single phase current power systems and a first intermediate DC voltage of approximately 565 Volts can be achieved for input circuits connected to three phase power supply systems with rectifiers and smoothing capacitors. In order to achieve a stable second intermediate DC voltage a good compromise is to down-convert the first intermediate DC voltage of 565 Volts of a input circuit connected to a three-phase AC power grid to about 420 Volts. However, due to a stable intermediate DC voltage the up-converter would even run reasonably stable and efficient with an input voltage as far down as 100 Volts. But even a second intermediate voltage up to 500 Volts in normal circumstances, e.g. not too big power fluctuations of the power source should still achieve sufficient results.
In another aspect of the invention the number of DC/DC converter connected to an input circuit is two or more.
Although some of the beneficial aspects of the invention are available in a charging station with a single DC/DC converter, i.e. consequently a single charging module, the full benefit of the invention becomes apparent when more than one DC/DC converter, respectively charging modules are connected to the power rail with the second intermediate DC voltage. Apart from a wall charging point that charges only a single car, charging stations with more than one charging points can share the input circuit and the housing and thus are more cost efficient.
In another aspect of the invention the input circuit comprises a bridge rectifier which as a function of a control input signal is configured to limit the current provided at the first DC output to a predefined level.
In another aspect of the invention the control circuit compares current levels signalled to the control circuit with a predetermined current level and generates a control signal to control the bridge rectifier to limit the current provided at the first DC output.
In another aspect of the invention the input circuit comprises a bridge rectifier which as a function of a control input signal is configured to cut off the electric power source.
This aspect of the invention protects the charging station in the event of over voltages occur.
In another aspect of the invention the control circuit is powered by the energy buffer module.
This allows in case the input circuit is disconnected from the power source to continue to operate the charging function of the charging station.
In another aspect of the invention at least a second input circuit is connected with its output to the output of the input circuit.
This aspect of the invention makes the charging station easily adaptable to different input power offerings. Instead of having to provide different sizes, respectively types of input circuits, only one size/one type of input circuit needs to be produced. In case a power source with a higher power rating is available, only a respective number of input circuits of identical build can be connected with their output DC rail. Thus renders the charging station very scalable.
In another aspect of the invention a process for charging electric powered vehicles comprises receiving input power from an electrical power source and providing a first intermediate DC voltage DCi at a first DC voltage level; receiving the first intermediate DC voltage DCi and providing a second intermediate DC voltage DC2 at a second DC voltage level; buffering electrical energy at the second DC voltage level; converting the second intermediate DC voltage (DC2) to a DC current or AC current requested by the electric vehicles.
These steps may be controlled by one or more microcontrollers controlling an input circuit, at least a DC/DC converter circuit and at least an output circuit of a charging station for energy storages of electric vehicles.
In order to solve these problems, the invention further proposes to distribute the components of a charging station into separate modules.
Brief Description of the Drawings
Aspects of the present invention will now be described in detail, by way of example only with reference to the following drawings in which:Figure 1 shows a schematic block diagram of a charging station for an electric vehicle according to the invention;
Figure 2 shows a schematic diagram of a first intermediate DC/DC circuit for an electric charger according to the invention
Figure 3 shows an electric diagram of a second intermediate circuit and an output circuit for an electric charger according to the invention.
Detailed Description
In the accompanying figures, like numerals refer to like elements throughout the description.
Figure 1 shows a schematic overview of a charging station 1 which is electrically connected by an AC input module 3 to a public electrical grid 2, and by a transformer 8 via at least one socket/plug 9b to an electric vehicle 9. The AC input module 3 basically comprises a three-phase-bridge which converts the 400 volts of a 3-phase AC to a DC voltage of about 565 volts. The DC output voltage of the AC input module 3 forms a first intermediate DC voltage DCi. Preferably the three-phase bridge is a full bridge, as this reduces the ripples of the first intermediate DC voltage DCi. For example if costs are an issue, a person skilled in the art also may consider to use a three-phase half bridge for rectification of the input AC power.
In this embodiment the three-phase full bridge comprises as rectifying elements thyristors (not shown) which can be controlled by an input module control circuit (not shown). The input module control circuit may comprise an overvoltage detector (not shown) which blocks the thyristors in the event the voltage of the input AC voltage exceeds a predetermined overvoltage threshold. In a variant of the embodiment the overvoltage detector may also detect under voltage situations. Similarly the input module control circuit may comprise current sensing means (not shown) to measure the current drawn by the input module 1 and may limit the input current to a predetermined input current level. Alternatively or additionally the information about the power consumed in the various modules of the charging station may be communicated by the other modules of the charging station to the input module control circuit and the input module control circuit may control the input AC current accordingly. Optionally the input module 3 may also include a power-factor correction circuit (PFC) (not shown) for improving the total harmonic distortion (THD) and electromagnetic interference (EMI) with the connected grid 2.
Alternatively or in combination with an AC input module 3 a DC input module (not shown) may provide the first intermediate DC voltage from a DC power source such as fuel cell or solar panels. Similarly, to a public grid the power provided by a DC power source may be limited, or even worse may vary for example in case of solar panels with the solar radiation. The person skilled in the art readily appreciates that the advantages of the invention are beneficial to all kinds of electrical power sources where the provided power is somewhat limited.
The first intermediate DC voltage DC-1 is distributed by a first intermediate DC rail 30 to three first intermediate DC/DC modules 4. In the abstract schematic drawing of Fig. 1 the DC power rail 30 is depicted as a single line. The person skilled in the art readily appreciates that in reality the DC rail 30 comprises a first positive DC power rail DCi+ and a negative DC power rail DCi- as explicitly shown later in Figure 2. Each first intermediate DC/DC module 4 provides at its respective first intermediate output DC2 a second intermediate voltage Vdc2. Each first intermediate output DC2 supplies the second intermediate voltage Vdc2 to a second intermediate DC/DC module 5.
Each first intermediate DC/DC module 4 may comprise a control circuit 41 for measuring the current that is provided by each DC/DC converter 4. For this purpose the control circuit 41 is connected to first current sensors 42. Additionally or alternatively the control circuit 41 measures by means of voltage sensors (not shown in Figure 1) the second intermediate voltage Vdc2 each DC/DC converter 4 delivers at its first intermediate output DC2. In this embodiment the DC/DC converters 4 are designed as voltage-down converters which convert the first intermediate voltage of nominal 565 volts down to the second intermediate DC voltage Vdc2, which in this embodiment has been chosen to 420 volts. A second intermediate voltage Vdc2 which is substantially lower than the voltage at the input of the input circuit 2, respectively the first intermediate DC voltage Vdci simplifies the mitigation of voltage drops of the power source 1. As long as the second intermediate voltage Vdc2 is that much lower than the voltage drops of the external power source 1 expected in a worst case scenario, the DC/DC converter 4 can be designed as a simple voltage down converter. The grid voltage needs only to be down-converted to the second intermediate DC voltage Vdc2 and no up-conversion is needed by the DC/DC converters 4.
In this embodiment the central control logic 41 is adapted to limit the current that is provided to each DC/DC converter 4 such that the sum of the current multiplied with the input voltage of the input circuit 2 does not exceed the nominal power, respectively allowed short term peak power taken in by the input module 3. This ensures that the maximum power input provided by the external power source 2 is not exceeded and avoids that overcurrent protection devices of the external power source 2 are triggered.
A second intermediate circuit 5 with an energy buffer module 6 is connected with its input to the output of a DC/DC converter 4. The second intermediate circuit 5 supplies an output switching circuit 7 with the buffered second intermediate voltage Vdc2. The output switching circuit 7 supplies a transformer 8 with currents for primary windings of the transformer 8. Secondary windings of the transformer 8 eventually generate the currents to charge the battery of an electric vehicle 9. The DC/DC converter 4, the second intermediate circuit 5 with an energy buffer module 6, the output switching circuit 7, and the transformer 8 logically form an output circuit, which according to its function is termed within this application as a charging module. The idea of the invention is that one or more charging modules, with its DC/DC converter 4 as an input circuit, can be connected to the first intermediate power rail 30.
For reason of conciseness Figure 1 shows only one of the three charging modules. All three charging modules are identical. Figure 2 shows the second intermediary circuit 5 of a charging module in more detail. Each second intermediate DC/DC circuit 5 is provided with a buffer capacitor 52 which smooths the ripples on the output current provided on a second intermediate DC rail 50 by the DC/DC converter 4. This buffer capacitor 52 may be chosen to have a capacity of 1500 micro Farad.
An energy buffer module 6 is also electrically connected with the second intermediate DC voltage rail 50 and provides additional energy if the current consumed by the output switching circuit 7 is higher than the current that is supplied by the respective DC/DC converter 4. The energy buffer module 6 may comprise as an energy buffer 60 a lithium-ion battery or a lithium-ion supercapacitor battery. The person skilled in the art readily appreciates that any kind of electrical storage element, that is able to provide sufficient capacity and current could be chosen as an energy buffer 60, as for example a redox flow battery. With the general set-up of this embodiment the energy buffer 60 should provide a discharge current peak of greater than 50 Amperes and should allow a charge current peak of greater than 10 Amperes. The capacity of the electric buffer 60 depends on the energy that the charging station 1 shall provide to the electric vehicle. With the power that were usual at the time of the application a capacity between 10 and 100 kWh is a reasonable choice. With higher charging powers of course the person skilled in the art would choose an electric buffer 60 with an adequate capacity. Due to its size the energy buffer 60 is arranged in an external buffer module 6. In a specific aspect of the invention a discharging resistor R of approximately 10 to 20 Ohms is arranged in close proximity to the energy buffer 60 inside the buffer module 6. By means of a discharging switch So the discharging resistor R can be switched in parallel to the energy buffer 60. In contrast to the discharging resistor R the discharging switch So is arranged in the second intermediate DC/DC module 5 and controlled by second intermediate circuit control logic 51.
The second intermediate circuit control logic 51 measures by means of a current sensor 53 the current that flows into the corresponding output module 7, i.e. the sum of the current provided by the respective second intermediate DC/DC module 4 and the current provided by the energy buffer 60. A voltage sensor 54 measures the voltage at the output 55 of the second intermediate DC circuit 5. A energy buffer current sensor 54 measures the current that flows from the second DC power rail 50 into the energy buffer 6, i.e. the charging current for the energy buffer 60, or in case the current flows from the energy buffer 60 to second DC rail 50 this energy buffer current sensor 54 measures the current that the energy buffer 60 supplies as a buffer current to the output 55 of the second intermediate DC circuit 5. By closing the discharging switch So the energy buffer 60 discharges over the discharging resistor R. The person skilled in the art appreciates that during this test the first intermediate DC/DC module 4 has to be switched off. By measuring the discharging current with the discharging current sensor 54 the second intermediate circuit control logic 51 is able to evaluate the health of the energy buffer 60, i.e. how much capacity the energy buffer has lost due to aging effects. In this embodiment the energy buffer current sensor 54 is arranged in the second intermediate DC/DC module 4. However it is evident that alternatively it may be also arrange in the energy buffer module 6.
Optionally the discharging resistor R is arranged in close proximity to the energy buffer 60 for enabling heat transfer from the discharging resistor R to the energy buffer 60. In this application the second intermediate circuit control logic 51 measures the temperature of the energy buffer 60 and compares the measured temperature with a minimum operation temperature of the energy buffer 60. In the event the measured temperature is lower than the operation temperature of the energy buffer 60 the second intermediate circuit control logic 51 connects the discharging resistor R with the discharging switch So to the DC rail 50 and uses the discharging resistor R to heat the energy buffer 60 until the energy buffer 60 has reached its operation temperature. This heating is effectively powered by the power grid 2 via the first intermediate DC/DC module 4 with a power of approximately 250 W. The heating power may even be pulse modulated to adapt an adequate power as a function of the temperature of the energy buffer 60.
Optionally a heat sensor 61 communicates the temperature of the energy buffer to the second intermediate circuit control logic 51. In case no electric vehicle 9 is connected to the respective output module 7, all current provided by the respective first intermediate DC/DC module 4 flows into the energy buffer and re-charges the energy buffer 6. In this embodiment, a lithium battery has been chosen as an energy buffer 6 as at the time the lithium battery is able to provide a high discharge current at relatively low cost. Optionally the lithium battery may be equipped with a battery management system that ensures that all cells of the lithium -ion battery are on an equal voltage level. However, the person skilled in the art would choose the most appropriate energy buffer 6 for a special application. It is therefore also conceivable to choose a bank of super capacitors for the energy buffer 6, if costs are a less concern.
It was mentioned above that the second intermediate DC voltage Vdc2 in this embodiment has been chosen to 420 volts to be sufficiently lower than expected voltage drops on the power grid 2. The second intermediate DC voltage Vdc2 however also depends on the energy buffer 60 that has been chosen for the energy buffer modules 6. The concept of the first intermediate DC/DC module 4 and the second intermediate modules 5 allows a large range within the second intermediate DC voltage Vdc2 can be set. It is for example possible to choose the second intermediate DC voltage Vdc2 inbetween 100 Volts and 430 Volts in order to accommodate different types of energy buffers 6.
Advantageously the central control logic 41 may also be adapted to limit the current provided to second DC/DC modules 5 and thus to limit the charging current of the energy buffer modules 60 for different types of energy buffers 60. The central logic 41 may provide a constant charging current to all second intermediate circuit 5 until the energy buffers have reached for example 90 percent of their capacity and then switch to so-called trickle charge for improving the life and capacity of the energy buffer 60. The central logic 41 may alternatively limit the current provided to each second intermediate circuit 5 individually according to an internal charging strategy, for example by predominantly re-charging the energy buffer that has the highest charging level among all energy buffers 6 of a charging station. This strategy achieves the object to offer at least one reasonably full buffer 6 at all times. Other strategies are possible, for example always re-filling the buffer 6 with the lowest charge level among all buffers 6 of a charging station 1, which would ensure that all buffers are on a similar charging level.
The output switching circuit 7 converts the available energy into the electrical power that is requested by the electric vehicle 9. At the moment, several power options and socket varieties for recharging an electric vehicle have to be served. In order of increasing power most common sockets/plugs options are:
a) domestic socket, single phase 230V AC / 10 A / 2.3 kW
b) so-called blue caravan socket, single phase 230 V AC / 16 A / 3.6 kW
c) socket type CEE 16 A, three phase 400 V AC / 16 A / 11 KW
d) socket type CEE 32 A, three phase 400 V AC / 32 A / 22 KW
e) socket type CEE 63 A, three phase 400 V AC / 63 A / 43 KW
f) charging station type 1, 240 V AC / 16 A / 3.8 kW or 240 V AC / 24 A / 5.8 kW or 240 V AC / 30 A / 7.2 kW
g) charging station type 2, 400 V AC three phase, typically 2.6 kW / 11 kW / 22 kW I 43 kW
h) charging station CCS combo 2, DC 50 kW
i) charging station CHAdeMO, DC, typically 22 kW / 50 kW
j) charging station Tesla super charger, DC typically 135 kW
The length of time an electric vehicles batteries take to recharge is limited by the minimum rate between how many kilowatts (kW) the charging station can provide and how many the batteries of the car can accept. It seems that at the time of the application the term slow charging is used for charging a vehicles battery from empty to full in around eight hours at an approximate rate of 3kW, for example with a wall charger at home; the term fast charging is used for fully replenishing a vehicles batteries in approximately three to four hours at a rate of 5kW to 22kW; and the term rapid charging is used for a charging rate of 43kW to lOOkW, which will replenish a vehicles battery to 80% in as little as 30 minutes. The flexible concept of the invention allows to arrange its modules and circuits to meet any of the requirements of the listed charging modes. As will be described further down below the flexible architecture of the invention allows to serve most, if not all of these modes and probably most modes that may still emerge.
The domestic options usually are passive chargers, e.g. the charging station does not exchange any information with the internal charger of the electric vehicle. For the more powerful charging modes usually the internal charger communicates with the charging station 1, for example over a dedicated signal wire using for example the socalled CAN bus protocol to control the power provided by the charging station 1.
In this embodiment, the input module 3 and three first intermediate DC/DC modules 4 are arranged in one module and each second intermediate DC/DC module and the respective output module 7 are paired in one module. The charging station 1 in this example therefore comes with one housing for the input module 3 and three first intermediate DC/DC modules 4 in the same housing and three housings each containing a second intermediate DC/DC module 5 and an output module 7. Each lithium battery 6 is connected to its second intermediate DC/DC module 5 and each transformer 8 is separately connected to its respective output module 7.
Turning to Figure 3 the output module 7 and its interaction with the galvanic isolating transformer 8 is described in more detail. The transformer 8 comprises three primary windings LT, LT, LT and three secondary windings L'T, L'T, L'T . The output switching circuit 7 comprises six switching elements for controlling the current flow from the second positive intermediate DC rail 50 through the primary windings LT, LT, LT back to the negative DC rail DC-. In this embodiment, the switching elements are insulated - gate bipolar transistors (IGBT) Τι, T2, T3, T4, T5, and Te. IGBTs combine high efficiency and fast switching at high switching currents. Generally all power semiconductor switching elements with low switching losses, such as integrated gatecommutated thyristor (IGCT) are suitable as switching elements.
Each transistor Τι, T2, T3, T4, T5, Te is protected by a free wheeler diode Di, D2, D3, D4, Ds, De connected with their anode to the emitter of their respective transistor and with their cathode connected to the collector of their respective transistor. A pulse width modulation control circuit 71 generates six control signals Bi, B2, B3, B4, B5, Be for controlling individually the base of each transistor Τι, T2, T3, T4, Ts, Te. As a function of the current flow created through the primary windings L'i, L'2, L'3 the first secondary winding Li, produces a first output voltage V, the second secondary winding L2 produces a second output voltage V, and the third secondary winding L3 produces a third output voltage W. It should be noted that as a function of the control signals the first output voltage U, the second output voltage V, and the third output voltage W may be generated with a 120 degree phase offset to form a three-phase AC current, or only two voltages, for example at the second output V and the third output W might be generated leaving the first output basically zero potential. Optionally filter capacitors (not shown) may be connected either in a Y-formation or a Delta formation to the three secondary windings Li, L2, L3. The filter capacitors usually would have a capacitance of 1 micro Farad.
An AC/DC mode selector 72 detects which charging voltage/current system is required by an electric vehicle 9 which is connected to the output module 7 and communicates to the pulse width modulation circuit 71 which control signals Bi, B2, B3, B4, B5, Be to produce. Primary current sensors 71 are provide in each conductor leading to a primary winding L'i, L'2, L'3 for measuring the current provided to each primary winding L'i, L'2, L'3. The sensor signals of the primary current sensors 71 are forwarded to the pulse width modulation circuit 71 in order to be able to control the current consumed by each primary winding L'i, L'2, L'3. Alternatively or additionally secondary current sensors 75 are provided for each secondary conductors U, V, W, N in order to measure the current in each of the secondary conductors U, V, W, N and to provide the information to the pulse with modulation control 71. With this information the pulse with modulation control circuit 71 by adjusting the switch on/switch off time of the control signals Bi, B2, B3, B4, B5, Be can control the voltage/current to be generated by each secondary windings Li, L2, L3.
The detected AC/DC mode also controls a first switch Si, a second switch S2, a third switch S3 and a fourth switch S4 to connect or disconnect the first output voltage U, the second output voltage V, and the third output voltage W to respectively from the pins of the sockets, respectively plugs of the charging station 1.
In case a one phase AC current is required, the AC/DC mode selector connects with the second switch S2 the first output voltage U to a line conductor pin P of a AC single phase socket/plug. The neutral conductor N is permanently connected to a neutral conductor pin N of a single phase socket/plug. In this mode the first switch and the third switch are in off position. The plugs served by single phase AC are for example a AC plug according to IEC 62196 Type 2 or a combined AC/DC plug CCS according to IEC 62196. It is evident that also domestic socket outlet or a blue caravan type socket outlet could be served by the charging station of the invention. The electric buffer would allow for slow charging several electric vehicles at the same time at a low power outlet, for example from a lamp post.
In case a three-phase AC current is required, the AC/DC mode selector 72 connects all three secondary transformer windings Li, L2, L3 to the respective pins Li, l_2, L3 of the respective charging plug. In this embodiment the second switch S2 and the third switch S3 are in connected position and the first switch Si is in a non-connected position.
In case the AC/DC mode selector 72 detects that the connected electric vehicle requires a DC current, the AC/DC mode selector 72 disconnects with the second switch S2 the first secondary winding Li from the output conductor U, and disconnects with the third switch S3 the second secondary winding L2 from the second output conductor V. By means of the first switch Si a fly back filter 73, 74 is connected to the first secondary winding Li. In this embodiment the fly back filter 73, 74 comprises a fly back diode 73 and a fly back capacitor 74. The fly back diode 73 is connected with its anode to the first secondary winding and Li and with its cathode to the DC output of the vehicle interface 80. The fly back capacitor 74 is connected with one of its terminal to the DC charging terminal DCout+ of respective plugs of the charging plugs and with its other terminal to the second secondary winding L2, which at the same time forms the negative charging DC charging terminal DCout-. In this embodiment the winding direction of the first secondary winding L'T is opposite to the winding direction of the second secondary winding l_2, which is indicated in Fig. 2 by the dots close to the winding symbols. With the opposite windings it is possible to invert the voltage vector of the second secondary winding L2 which allows almost to double the voltage that is available between the terminal of the first secondary winding L1 and the terminal of the second secondary winding L2. As rapid DC charging systems need voltages up to 800 Volts this allows to achieve this voltage with a transformer that usually would produce 400 Volts three phase voltages. However, to produce 400 Volts three phase voltages the phase of the control signals switching the switching elements has to be reversed to compensate for the different winding directions. Alternatively all secondary windings could be in the same winding direction and the phase of the control signals for the switching elements is adapted accordingly when the charging station is in DC charging mode, in another embodiment an auxiliary switch (not shown) may be used to connect the terminal of the second secondary winding L”2 with the terminal of the third secondary winding L”3 in case an even higher DC output voltage has to be achieved.
The pulse with modulation control 71 also receives a mode signal from the AC/DC mode selector 72 and controls the transistors Τι, T2, T3, T4, T5, Te, such that either a one phase AC current, a three phase AC current or a DC current at the interface conductors U, V, W, N. The control signals generated by the pulse with modulation control 71 in case of a three-phase AC mode control the transistors Τι, T2, T3, T4, T5, Te are phase-shifted by 120°, the current through the primary windings LT, L'2, L'3 are pulse with modulated in order to control the charging current on the secondary windings of the transformer. The primary windings LT, LT, L'3 of the transformer Tr are connected in a triangle and the secondary windings L'T, L'T, L'T of the transformer Tr are connected in a start configuration, whereby the common connection of all three winding ends forms the interface conductor N. The transformer Tr thus achieves a galvanic isolation of the charging current provided at the charging interface from the electric grid 1. It also reduces EMI because the secondary windings L'T, L'T, L'T of the transformer Tr is prohibited from introducing high frequency earth currents.
In this embodiment, there are three DC/DC converter 4, each of which powers a charging module. The number of DC/DC converter 4 and charging modules may vary, there may be embodiments where the number of DC/DC converter 4 and charging modules is less than three, i.e. one or two. Alternatively in other embodiments the number of DC/DC converter and charging modules could be chosen to be higher than the number of three. There is no logical limit to the number of DC/DC converter 4 and charging modules that can be supplied by the input circuit 3 as long as any limitation of the power source does not prevent the energy buffers from being re-charged in a reasonable time. For example assuming a company with regular working hours and closed at night has deployed on their business car park charging stations 1 according to the invention. In a worst case scenario all charging buffers are empty at the end of a business day when all employees have left with their cars the company's parking site. In such a scenario the charging stations 1 should be able to re-charge all energy-buffers before the first car from an employee or a client arrives the next morning.
It should be noted that the term charging station is used throughout this description to refer to any charger that is suitable for charging at least one electric vehicle. Sometimes the term charging point is used to indicate that only one electric vehicle can be re-charged at a time, for example in a domestic garage from a charger fixed to the wall of the garage, and the term charging station seems to be used when 10 more than one electric vehicles can be charged simultaneously at one site. It is evident that the term charging station as used in this description should be not restricted to the number of electric vehicles to be charged. Therefore in this description the term charging stations should be interpreted to embrace charging points.
The embodiment has been described with a public power grid as a power source.
The person skilled in the art will appreciated that the invention is not limited to public power grids, but is also applicable for singular power sources and/or non-public power, such as solar panels, water turbines or wind turbines.
Table of reference numerals charging station power source input module first intermediate DC rail
DC/DC converter control circuit first current sensors second intermediate circuit second intermediate DC rail energy buffer module energy buffer output switching circuit pulse width modulation control circuit primary current sensors mode selector flyback diode flyback capacitor secondary current sensors transformer charging interface electric vehicle
LT, LT, LT primary windings
L'T, L'T, L'T secondary windings