Method and system for vehicle-to-vehicle charging of electric vehicles

Abstract

A method for vehicle-to-vehicle charging of electric vehicles, controlling a three-phase bidirectional on-board charger (32) of a first electric vehicle to provide direct current from an energy storage system (31) of the first electric vehicle at a first terminal L1 (40) and a second terminal L1 (41) of the three-phase bidirectional on-board charger (32) of the first electric vehicle; transmitting the direct current from the first terminal L1 (40) of the first electric vehicle to an energy storage system (34) of a second electric vehicle and from the second terminal L2 (41) of the first electric vehicle to an energy storage system (35) of a third electric vehicle.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a method for vehicle-to-vehicle charging of an electric vehicle, an electric vehicle configured to perform such a method, an application of a multiport unit in such an electric vehicle, and a system for such vehicle-to-vehicle charging. BACKGROUND

[0002] In the prior art, it is well known that an electric vehicle comprises an electric driveline for driving the electric vehicle. This electric driveline is provided with energy by an electrical energy storage system. Sometimes, this energy storage system has to be charged with electrical energy, which can be done at home or in a charging station, where the electric car can be connected to the electrical grid via a charging cable for alternating current charging, which is for example a type 2 / type 1 charging cable. For this purpose, the electric car usually comprises an alternating current-direct current (AC-DC) on-board charger to allow charging of the energy storage system, for example a lithium-ion battery. For this purpose, alternating current is provided from the electrical grid to the on-board charger, which converts the alternating current into direct current, which can be used to charge the energy storage system of the electric car.

[0003] However, one of the main problems of this technology is still the limited range of the electric vehicle, wherein one particular problem is considered to be the risk that an electric car can run out of charge in a remote location where no charging station is accessible. One possible solution to reduce this problem is to provide vehicle-to-vehicle charging. Such a possibility allows one electric car to charge another car, usually via its on-board charger. For this purpose, the possible source vehicle, i.e. the electric vehicle acting as an energy source, has to be equipped with a bidirectional on-board charger, which allows current to flow into and out of the electric vehicle. Such an electric vehicle equipped with a bidirectional on-board charger is able to provide alternating current to the input / interface of the electric vehicle and can power a load electric vehicle, an electric vehicle with an empty battery, via a charging cable. The on-board charger of the load electric car can be a bidirectional or a unidirectional on-board charger. SUMMARY

[0004] In view of this, it was found that there is a further need to improve vehicle-to-vehicle charging. In particular, there is a further need to improve the charging efficiency when charging from vehicle-to-vehicle.

[0005] In view of the above, it is an object of the present invention to provide a method and a system allowing for improved vehicle-to-vehicle charging. In particular, it is an object of the present invention to provide an improved charging efficiency when charging from vehicle-to-vehicle.

[0006] These and other objects, which will become apparent during the following description, are solved by the subject matter of the present invention.

[0007] According to a first aspect, there can be provided a method for vehicle-to-vehicle charging of electric vehicles, comprising the steps of: controlling a bidirectional on-board charger of a first electric vehicle to provide direct current from an energy storage system of the first electric vehicle at an electric vehicle input of the first electric vehicle; transferring the direct current to an electric vehicle input of a second electric vehicle; transferring the direct current from the electric vehicle input of the second electric vehicle directly to an energy storage system of the second electric vehicle.

[0008] The present disclosure is based on the finding that in known vehicle-to-vehicle charging scenarios, the efficiency of such charging is relatively low due to losses in directing the electric charge in the intended way through the on-board chargers of the two electric vehicles, i.e. converting direct current from an energy storage system of a source electric vehicle to alternating current, providing it to an alternating current input of a source electric input, and converting the alternating current transferred in the load electric vehicle to direct current to charge an energy storage system of the load electric vehicle. A schematic of such a known vehicle-to-vehicle charging scenario is shown in Fig. 1. For example, if a source electric vehicle 1 comprises an 11 kW bidirectional on-board charger 2 connected to an energy storage system 3, e.g. a high voltage battery 3, and a load electric vehicle 4 comprises an 11 kW unidirectional on-board charger 5 connected to an energy storage system 6, e.g. a high voltage battery 6. The source electric vehicle 1 provides alternating current at its alternating current input 7, which is transferred via a charging cable 9 to the alternating current input 8 of the load electric vehicle 4. Thereby, the load electric vehicle 4 can charge its energy storage system 6, similar to the load electric vehicle 4 being connected to a power grid via a charging station. In practice, the typical efficiency of known unidirectional on-board chargers and known bidirectional on-board chargers is about 94%. Thus, in such an example, the total efficiency during the charging would be 0.94 x 0.94 = 0.883, i.e. 88.3%, wherein cable losses are negligible compared to the losses of the on-board chargers. As a result, in such a system, about 12% of losses can occur, i.e. 6% of losses per on-board charger.

[0009] In comparison to the known vehicle-to-vehicle charging, the disclosure proposes to provide the first electric vehicle's AC input with DC power and to bypass the second electric vehicle's on-board charger, such that the first electric vehicle's on-board charger's isolated DC-DC converter's DC power can be provided directly to the second electric vehicle's energy storage system. In one example, the DC power can be provided to the first electric vehicle's AC input by controlling the first electric vehicle's bidirectional on-board charger to provide at least DC+ and DC- lines at the first electric vehicle's AC input by switching the first electric vehicle's bidirectional on-board charger's power factor correction unit's switches. Thus, the provided DC power bypasses the second electric vehicle's on-board charger and it is possible that the DC power provided by the first / source electric vehicle can charge the second electric vehicle's high voltage battery. Thereby, a higher overall charging system efficiency can be provided. For example, in the above example, the efficiency can be kept at 94%, i.e. 6% higher than the efficiency of the conventional charging method.

[0010] In one implementation, the step of controlling the first electric vehicle's bidirectional on-board charger to provide DC power at the electric vehicle input from the first electric vehicle's energy storage system can comprise controlling the charging current by the first electric vehicle's bidirectional on-board charger. In one example, the data / control communication can be provided by means of power line communication (PLC) or CAN communication. The first vehicle's on-board charger can control the charging current to the second / load electric vehicle by regulating the primary side of its isolated DC-DC converter, wherein a power line communication protocol can be used to facilitate the charging between the electric vehicles.

[0011] In one implementation, the charging current can be controlled by controlling the first electric vehicle's bidirectional on-board charger's isolated DC-DC converter. In the known vehicle-to-vehicle charging, the source electric vehicle's on-board charger can generate AC power that is fed to the load electric vehicle. However, in this implementation, the source vehicle can use the same topology to generate DC power. The generated DC power can then be fed directly to the load electric vehicle's high voltage battery, instead of having to go through its on-board charger. The source electric vehicle's on-board charger can control the charging current to the first electric vehicle by regulating the primary side of its isolated DC-DC converter.

[0012] In one implementation, the second electric vehicle can comprise a DC input, preferably selected from the group consisting of: a CCS interface, a CHAdeMO interface and / or a GB / T interface. These interfaces comprise a DC input that allows to bypass the second electric vehicle's on-board charger and to provide DC power directly to the second electric vehicle's energy storage system.

[0013] In one implementation, the bidirectional on-board charger can comprise at least one power factor correction unit and at least one isolated DC-DC converter.

[0014] According to a second aspect, an electric vehicle configured to perform the above-mentioned method can be provided, the electric vehicle comprising: at least one bidirectional on-board charger comprising at least one power factor correction unit and at least one isolated DC-DC converter; the power factor correction unit comprising a switch configured to be switched such that at least DC+ and DC- lines are provided from the isolated DC-DC converter to the electric vehicle input.

[0015] According to a third aspect, an application of an on-board charger in the above-mentioned electric vehicle is suggested, wherein the on-board charger comprises at least one power factor correction unit and at least one isolated DC-DC converter. Yet another aspect relates to an application of a charging cable for connecting two electric vehicles in the above-mentioned method.

[0016] Yet another aspect relates to a control unit for controlling a bidirectional on-board charger of an electric vehicle to provide direct current from an energy storage system of the electric vehicle at an electric vehicle input of the electric vehicle, the control unit being configured to switch a switch of a power factor correction unit of the bidirectional on-board charger to provide at least DC+ and DC- lines at the electric vehicle input of the electric vehicle. Another aspect relates to a computer program element which, when being executed by a processor, is configured to perform the above-mentioned method.

[0017] Furthermore, another aspect relates to a system for vehicle-to-vehicle charging configured to perform the above-mentioned vehicle-to-vehicle charging method, the system comprising: a bidirectional on-board charger of a first electric vehicle; an energy storage system of the first electric vehicle; an energy storage system of a second electric vehicle; a control unit configured to control the bidirectional on-board charger of the first electric vehicle to provide direct current from the energy storage system of the first electric vehicle at an electric vehicle input of the first electric vehicle; a charging cable configured to transmit the direct current to an electric vehicle input of the second electric vehicle; an on-board charger of the second electric vehicle configured to transmit the direct current directly from the electric vehicle input of the second electric vehicle to an energy storage system of the second electric vehicle. In one implementation of the system, the control unit can be configured to control charging of the energy storage system of the second electric vehicle.

[0018] A further aspect relates to a method for vehicle-to-vehicle charging of electric vehicles, controlling a three-phase bidirectional on-board charger of a first electric vehicle to provide direct current from an energy storage system of the first electric vehicle at a first terminal LI and a second terminal L2 of the three-phase bidirectional on-board charger of the first electric vehicle; transferring the direct current from the first terminal LI of the first electric vehicle to an energy storage system of a second electric vehicle and from the second terminal L2 of the first electric vehicle to an energy storage system of a third electric vehicle. This can be advantageous because two electric vehicles, i.e. the second electric vehicle and the third electric vehicle, can be charged in parallel by one electric vehicle, i.e. the first vehicle. In this respect, all explanations above regarding the electric vehicles, the details of the bidirectional on-board charger of the first electric vehicle also apply here. In the following, only the details related to this aspect, i.e. the method for charging more than one vehicle by means of a first vehicle, are explained in more detail.

[0019] In an implementation form, the second electric vehicle and the third electric vehicle are charged simultaneously.

[0020] In an implementation form, the voltage range of the energy storage system of the second electric vehicle and the voltage range of the energy storage system of the third electric vehicle are smaller than the voltage range of the energy storage system of the first electric vehicle.

[0021] In an implementation form, the voltage range of the energy storage system of the second electric vehicle is different from the voltage range of the energy storage system of the third electric vehicle.

[0022] In an implementation form, the first electric vehicle is connected to the second electric vehicle and the third electric vehicle by means of one multi-port unit, wherein the multi-port unit comprises a common neutral conductor and wherein the multi-port unit is configured to provide communication between the first electric vehicle and the second electric vehicle and the third electric vehicle. As used herein, the term “communication” means exchange of data, e.g. control signals, and electrical energy.

[0023] In an implementation form, the energy storage system of a fourth electric vehicle is charged by the first electric vehicle, the first electric vehicle charging the second electric vehicle and the third electric vehicle simultaneously.

[0024] Yet another aspect relates to a system for vehicle-to-vehicle charging of electric vehicles, configured to perform the method for vehicle-to-vehicle charging of electric vehicles as described above, the system comprising: a three-phase bidirectional on-board charger of a first electric vehicle; an energy storage system of the first electric vehicle; an energy storage system of a second electric vehicle; an energy storage system of a third electric vehicle; a multi-port unit configured to connect the three-phase bidirectional on-board charger of the first electric vehicle and the energy storage system of the second electric vehicle and the energy storage system of the third electric vehicle; a control unit configured to control the three-phase bidirectional on-board charger of the first electric vehicle to provide direct current from the energy storage system of the first electric vehicle at a first terminal LI and a second terminal L2 of the three-phase bidirectional on-board charger of the first electric vehicle.

[0025] Yet another aspect relates to the use of a multi-port unit in the method as described above or in the system as described above.

[0026] In another implementation, a method for vehicle-to-vehicle charging of electric vehicles is provided, comprising: controlling a three-phase bidirectional on-board charger of a first electric vehicle to provide direct current from an energy storage system of the first electric vehicle at a first terminal LI (40) of the three-phase bidirectional on-board charger; transferring the direct current from the first terminal LI (40) of the first electric vehicle to an energy storage system (34) of a second electric vehicle. For example, the first electric vehicle has an 800V energy storage system, while the second electric vehicle has a 400V energy storage system. Switching the switches of the three-phase bidirectional on-board charger such that L2 and L3 are connected to LI. The DC-DC converter of the three-phase bidirectional on-board charger can work as a regulated 800V-400V DC-DC converter and can charge the energy storage system of the second vehicle. The LI phase terminal and the neutral terminal can be connected to the DC+ and DC- terminals of the energy storage system of the second vehicle in order to charge the 400V energy storage system. In other words, the three-phase bidirectional on-board charger is used here as a step-down converter.

[0027] In the following, a non-exhaustive list of non-limiting examples is provided. Any one or more features of these examples can be combined with any one or more features of another example, embodiment or aspect described herein.

[0028] A. A method for vehicle-to-vehicle charging of electric vehicles (1, 4):

[0029] controlling a bidirectional on-board charger (10) of a first electric vehicle (1) to provide direct current from an energy storage system (3) of the first electric vehicle (1) at an electric vehicle input (7) of the first electric vehicle (1);

[0030] transferring the direct current to an electric vehicle input (8) of a second electric vehicle (4);

[0031] transmitting the direct current from an electric vehicle input (8) of the second electric vehicle (4) to an energy storage system (6) of the second electric vehicle (4).

[0032] B. The method according to claim A, controlling a bidirectional onboard charger (10) of the first electric vehicle (1) to provide direct current from an energy storage system (3) of the first electric vehicle (1) at an electric vehicle input (7), comprising:

[0033] switching a switch of a power factor correction unit (11) of the bidirectional onboard charger (10) of the first electric vehicle (1) such that at least a DC+ and a DC- line is provided at the electric vehicle input (7) of the first electric vehicle (1).

[0034] C. The method according to claim A or B, controlling a bidirectional onboard charger (10) of the first electric vehicle (1) to provide direct current from an energy storage system (3) of the first electric vehicle (1) at an electric vehicle input (7), comprising:

[0035] controlling a charging current by the bidirectional onboard charger (10) of the first electric vehicle (1).

[0036] D. The method according to any of the preceding claims, controlling the charging current by controlling an isolated DC-DC converter (12) of the bidirectional onboard charger (10) of the first electric vehicle (1).

[0037] E. The method according to any of the preceding claims, providing data communication by means of power line communication (PLC) or CAN communication.

[0038] F. The method according to any of the preceding claims, the second electric vehicle (4) comprising a DC-input, preferably selected from the group consisting of: a CCS interface, a CHAdeMO interface and / or a GB / T interface.

[0039] G. The method according to any of the preceding claims, the direct current bypassing an onboard charger (5) of the second electric vehicle (4).

[0040] H. The method according to any of the preceding claims, the bidirectional onboard charger (10) of the first electric vehicle (1) comprising at least one power factor correction unit (11) and at least one isolated DC-DC converter (12).

[0041] I. Electric vehicle (1) configured to perform the method according to any of the preceding claims, the electric vehicle comprising:

[0042] at least one bidirectional on-board charger (10) comprising at least one power factor correction unit (11) and at least one isolated DC-DC converter (12);

[0043] The power factor correction unit (11) comprises switches (S1-S4) configured to be switched such that at least DC+ and DC- lines are provided from the isolated DC-DC converter (12) to an electric vehicle input (7) of the electric vehicle.

[0044] J. Use of an on-board charger comprising at least one power factor correction unit (11) and at least one isolated DC-DC converter (12) in an electric vehicle (1) according to claim I.

[0045] K. Use of a charging cable for connecting two electric vehicles (1, 4) in a method according to any one of claims A to H.

[0046] L. Control unit for controlling a bidirectional on-board charger (10) of an electric vehicle (1) to provide direct current from an energy storage system (3) of the electric vehicle (1) at an electric vehicle input (7) of the electric vehicle (1), the control unit being configured to switch switches (S1-S4) of a power factor correction unit (11) of the bidirectional on-board charger (10) to provide at least DC+ and DC- lines at the electric vehicle input (7) of the electric vehicle (1).

[0047] M. A computer program element, which, when being executed by a processor, is configured to carry out the method according to any one of claims A to H.

[0048] N. A system for vehicle-to-vehicle charging configured to carry out the method for vehicle-to-vehicle charging according to any one of claims A to H, the system comprising:

[0049] a bidirectional on-board charger (10) of a first electric vehicle (1);

[0050] an energy storage system (3) of the first electric vehicle (1);

[0051] an energy storage system (6) of a second electric vehicle (4);

[0052] a control unit configured to control a bidirectional on-board charger (10) of the first electric vehicle (1) to provide direct current from an energy storage system (3) of the first electric vehicle (1) at an electric vehicle input (7) of the first electric vehicle (1);

[0053] a charging cable (9) configured to transmit the direct current to an electric vehicle input (8) of the second electric vehicle (4);

[0054] an on-board charger (20) of the second electric vehicle (4) configured to transmit the direct current from the electric vehicle input (8) of the second electric vehicle (4) directly to an energy storage system (6) of the second electric vehicle (4).

[0055] O. The system according to claim N, the control unit being configured to control charging of the energy storage system (6) of the second electric vehicle (4). BRIEF DESCRIPTION OF DRAWINGS

[0056] In the following, the present disclosure will be exemplified with reference to the accompanying drawings, in which

[0057] Fig. 1 is a schematic illustration of a known vehicle-to-vehicle charging by a source electric vehicle and an on-board charger of a load electric vehicle;

[0058] Fig. 2 is a schematic illustration of a known bidirectional on-board charger comprising a power factor correction unit and an isolated DC-DC converter;

[0059] Fig. 3 is a schematic illustration of a topology of a single-phase bidirectional on-board charger;

[0060] Figure 4 is a schematic illustration of an on-board charger of a source electric vehicle used in one embodiment of the present disclosure;

[0061] Figure 5 is a schematic illustration of an on-board charger of a load electric vehicle used in one embodiment of the present disclosure;

[0062] Figure 6 is a schematic illustration of a system used in one embodiment of the present disclosure;

[0063] Figure 7 is a schematic illustration of a three-phase on-board charger of a first electric vehicle for charging a second electric vehicle; and

[0064] Figure 8 is another schematic illustration of a three-phase on-board charger of a first vehicle for charging a second electric vehicle.

[0065] It is noted that the drawings are merely schematic and are non-limiting illustrations of embodiments of the present disclosure. Identical or equivalent elements are generally provided with the same reference signs. DETAILED DESCRIPTION

[0066] Fig. 2 is a schematic diagram of a known bidirectional on-board charger 10 comprising a power factor correction (PFC) unit 11 and an isolated DC-DC converter 12, which can be used for both a first / source electric vehicle and a second / load electric vehicle. The known on-board charger has two stages of power conversion. The first stage can be connected to an AC grid and is responsible for keeping the power factor close to unity while charging, also known as the power factor correction (PFC) unit 11. The second stage is an isolated DC-DC converter 12, which can regulate the current and voltage in order to charge an energy storage system 3, such as a high voltage (HV) battery 3, as shown in Fig. 1. In addition to controlling the charging operation, the second stage also provides isolation from the AC input, typically implemented as a full bridge LLC resonator or a phase shifted full bridge circuit.

[0067] Fig. 3 is a schematic topology of a single-phase bidirectional on-board charger 10. The power stages for both unidirectional and bidirectional are in principle the same, but in bidirectional operation the power factor correction unit 11 can generate a three-phase or single-phase AC voltage. In order to achieve bidirectionality from the same power stage, the bidirectional on-board charger 10 can be equipped with active switches S1-S4 instead of diodes, which are typically used in unidirectional on-board chargers.

[0068] In known vehicle-to-vehicle charging, the on-board charger 10 inside the first / source electric vehicle generates an AC voltage, which is fed to the second / load electric vehicle. However, in the shown embodiment, it is proposed that the source vehicle uses the same topology to generate a DC voltage by permanently closing the power factor correction unit 11 MOSFET S1 and S4, or S2 and S3. Thereby, the power factor correction unit 11 MOSFET can be used as two lines connected to the primary side of the isolated DC-DC converter 12. The equivalent circuit after closing MOSFET S1 and S4 is shown in Fig. 4. At this point, the switching lines of switches S1 and S4 can act as DC+ and DC-, respectively. Similarly, by closing MOSFET S2 and S3 and opening S1 and S4, the on-board charger 10 can generate a DC voltage, but with opposite polarity. Either of these combinations can be used. Figure 4

[0069] The generated DC voltage can then be directly fed to the high voltage battery of the second electric vehicle, instead of having to go through its on-board charger. The on-board charger of the first vehicle can be used to regulate the voltage and current, as well as to provide isolation from the AC input. Figure 4 ​The primary side of its isolated DC-DC converter is shown to control the charging current to the first electric vehicle. In this regard, Powerline Communication or CAN communication can be used for direct current charging and can be used to facilitate charging between electric vehicles. In this way, the power from the first vehicle will only pass through one onboard charger and thus the power loss can be reduced by half. Such an implementation is compatible with both single phase and three phase configurations. If there is three phase, the AC side of the onboard charger can be reconfigured to single phase by using AC relays to deliver full power. No additional components or modules are required in the shown implementation.

[0070] In one implementation, the second electric vehicle can comprise a DC input, preferably selected from the group consisting of: a CCS interface, a CHAdeMO interface and / or a GB / T interface. These interfaces comprise a DC input that allows to also bypass the onboard charger of the second electric vehicle and provide direct current to the energy storage system of the second electric vehicle. In this regard, preferably, the connector between the two electric vehicles comprises a type 2 / type 1 interface for the source electric vehicle and a CCS DC / CHAdeMO / GBT DC interface for the load electric vehicle.

[0071] However, the parties can also use a conventional type 2 / type 1 charging cable, which is typically the standard configuration for most electric vehicles. In this case, the direct current from the source electric vehicle can pass through Figure 5 The onboard charger 20 of the load electric vehicle is shown to deliver power. The load electric vehicle can still have a unidirectional or bidirectional onboard charger. If the load electric vehicle uses a known unidirectional diode rectifier 21, diodes D1 and D4 or D2 and D3 will conduct depending on the polarity of the voltage once direct current is applied. When the voltage at the input of the load electric vehicle is already high enough to charge the energy storage system, e.g. a high voltage battery 23, the power factor correction unit 22 MOSFET can be turned off and when the voltage at the input of the load electric vehicle is not high enough to charge the energy storage system, the power factor correction unit 22 MOSFET can be turned on. In this way, the power factor correction unit 22 MOSFET can be fully regulated by the onboard charger of the source electric vehicle. Figure 4 The power factor correction unit 22 MOSFET can be fully regulated by the onboard charger of the source electric vehicle when used as shown. After the power factor correction unit 22 capacitor, the power can flow through the isolated DC-DC converter 24 of the load electric vehicle to charge the high voltage battery 23 of the load electric vehicle. In this way, the onboard charger 20 of the load electric vehicle can also act as a DC-DC converter 24, but the overall charging efficiency is practically slightly below 90%.

[0072] Figure 6is a schematic diagram of a system 30 used in embodiments of the present disclosure. The system is used for vehicle-to-vehicle charging configured to perform the method as described above. The system 30 comprises a three-phase bidirectional on-board charger 32 of a first electric vehicle; an energy storage system 31 of the first electric vehicle; an energy storage system 34 of a second electric vehicle; an energy storage system 35 of a third electric vehicle; a multi-port unit 33 configured to connect the three-phase bidirectional on-board charger 32 of the first electric vehicle and the energy storage system 34 of the second electric vehicle and the energy storage system 35 of the third electric vehicle; a control unit 51 configured to control the three-phase bidirectional on-board charger 32 of the first electric vehicle to provide direct current from the energy storage system 31 of the first electric vehicle at a first terminal LI 40 and a second terminal L2 41 of the three-phase bidirectional on-board charger 32 of the first electric vehicle. The three-phase bidirectional on-board charger 32 further comprises a third terminal L3 42 and a neutral conductive terminal 43. The first terminal LI 40, the second terminal L2 41, the third terminal L3 42 are associated with one of the phases LI, L2, L3 of the three-phase on-board charger 32, respectively. The first terminal LI 40, the second terminal L2 41, the third terminal L3 42 are connected to the multi-port unit 33, respectively. The multi-port unit 33 comprises a common neutral conductor 44 connected to the neutral conductive terminal 43. The multi-port unit 33 is configured to provide communication between the first electric vehicle, the second electric vehicle, the third electric vehicle and a fourth electric vehicle. For charging the second energy storage system 34, the third energy storage system 35 and the fourth energy storage system 36, the following switching procedure is performed in the three-phase on-board charger 32. Switches SI, S4 and inductor LA working as step-down converters are connected to LI. Similarly, other two step-down DC-DC converters are formed by using S2, S5 and LB connected to L2 and switches S3, S6 and LC connected to L3. These three step-down DC-DC converters are capable of charging three electric vehicles independently with a common return path through the neutral terminal. Relays Rl and R2 are switched so that phases L2 and L3 are independent of LI. Relay R3 is connected to the common source point of switches S4, S5 and S6. Terminals LI, L2, L3 and the neutral terminal are connected to the multi-port unit 33 from which three output ports are formed with a common neutral point for return current. The multi-port unit is connected to DC+ 45 and DC- 46 of the second electric vehicle, to DC+ 47 and DC- 48 of the third electric vehicle and to DC+ 49 and DC- 50 of the fourth electric vehicle in order to charge the energy storage system 34 of the second electric vehicle, the energy storage system 35 of the third electric vehicle, the energy storage system 36 of the fourth electric vehicle. This multi-port unit 33 is used to connect three different electric vehicles simultaneously to the first electric vehicle.The first electric vehicle is able to charge three electric vehicles, which can have different voltages depending on the state of charge of each electric vehicle. The communication between the first vehicle and the other vehicles can also be taken care of by the multiport unit 33.

[0073] Figure 7 is a schematic of a three-phase on-board charger 62 of a first electric vehicle for charging the energy storage system 63 of a second electric vehicle. The energy storage system 61 of the first electric vehicle has 800 V. The energy storage system 63 of the second electric vehicle has 400 V. The three-phase full-bridge semiconductor switches S1, S2 and S3 are on and the relays R1 and R2 are switched such that the phases L2 and L3 are connected to L1. The relay R3 is connected to the midpoint of the two capacitors. Each capacitor has a voltage rating of at least 500 V. In this case, the DC-DC converter of the three-phase on-board charger inside the first electric vehicle works as a regulated 800 V - 400 V DC-DC converter and charges the second electric vehicle with the 400 V battery. The L1 and neutral terminal of the first vehicle are connected to the DC+ 64 and DC- 65 of the second electric vehicle in order to charge the 400 V energy storage system 63. The main contactors 2 and 3, the DC charging contactors 4 and 5 inside the second vehicle are on in order to charge the 400 V energy storage system 63.

[0074] Figure 8 is another schematic of a three-phase on-board charger 72 of a first vehicle for charging a second electric vehicle. Compared to the depiction shown in Figure 7 This three-phase on-board charger does not support the full voltage range of the energy storage system of the second electric vehicle. For this operation, the relays R1 and R2 are switched to be connected to L1 and the relay R3 is switched to be connected to the common source point of S4, S5 and S6. The switches S1, S4 and the inductor L A together work as a first step-down DC-DC converter. The switches S2, S5 and the inductor L B together work as a second step-down DC-DC converter and S3, S6 and the inductor L Coperates as a third step-up DC-DC converter. The three step-up DC-DC converters have a 120 degree phase shift to reduce the total current ripple. A operates as a first step-up DC-DC converter. The switch S2, S5 and the inductor L B operates as a second step-up DC-DC converter, similarly, the switch S3, S6 and the inductor L C operates as a third step-up DC-DC converter. The three step-up DC-DC converters have a 120 degree phase shift to reduce the total current ripple.

[0075] As a result, the present disclosure provides vehicle-to-vehicle charging with loss reduction, resulting in higher efficiency and shorter charging time, without the need to provide additional components. This is because it is possible, for example, by means of switching / control of the switch of the power factor correction unit of the on-board charger of the first / source electric vehicle, to provide the direct current of the isolated DC-DC converter to the alternating current input of the first electric vehicle, which is then passed to the alternating current input of the second / load electric vehicle, from which the energy storage system of the second electric vehicle can be directly supplied.

[0076] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed subject matter, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude a plurality or a plurality of. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope of the claims.

[0077] List of reference signs:

[0078] 1 source electric vehicle

[0079] 2 bidirectional on-board charger of the source electric vehicle

[0080] 3 Energy storage system / high voltage battery

[0081] 4 Load electric vehicle

[0082] 5 Unidirectional or bidirectional on-board charger for load electric vehicle

[0083] 6 Energy storage system / high voltage battery

[0084] 7 AC input for source electric vehicle

[0085] 8 AC input for load electric vehicle

[0086] 9 Charging cable

[0087] 10 Bidirectional on-board charger for source electric vehicle

[0088] 11 Power factor correction (PFC) unit

[0089] 12 Isolated DC-DC converter

[0090] 20 Unidirectional or bidirectional on-board charger for load electric vehicle

[0091] 21 Unidirectional diode rectifier

[0092] 22 Power factor correction (PFC) unit

[0093] 23 Energy storage system / high voltage battery

[0094] 24 Isolated DC-DC converter

[0095] 30 System

[0096] 31 Energy storage system for first electric vehicle

[0097] 32, 62, 72 Three-phase bidirectional on-board charger for first electric vehicle

[0098] 33 Multi-port unit

[0099] 34, 63, 73 Energy storage system for second electric vehicle

[0100] 35 Energy storage system for third electric vehicle

[0101] 36 Energy storage system for fourth electric vehicle

[0102] 40, 41, 42 L1, L2, L3 terminals

[0103] 43 Neutral conductive terminal

[0104] 44 Common neutral conductor

[0105] 45 to 50 DC terminals

[0106] 51 control unit

[0107] 64, 65, 74, 75 DC terminals

Claims

1. A method for vehicle-to-vehicle charging of electric vehicles, comprising the following steps: providing a three-phase bidirectional on-board charger of a first electric vehicle (1), the three-phase bidirectional on-board charger comprising at least one power factor correction unit (11) and at least one isolated DC-DC converter (12), wherein the power factor correction unit (11) comprises switches (S1-S4), providing a multi-port unit (33), switching the switches (S1-S4) of the power factor correction unit (11) of the three-phase bidirectional on-board charger of the first electric vehicle (1) such that direct current is provided from an energy storage system (31) of the first electric vehicle at a first terminal LI (40) and a second terminal L2 (41) of the three-phase bidirectional on-board charger of the first electric vehicle; transmitting the direct current from the first terminal LI (40) of the first electric vehicle to an energy storage system (34) of a second electric vehicle and from the second terminal L2 (41) of the first electric vehicle to an energy storage system (35) of a third electric vehicle, wherein the first electric vehicle (1) is connectable to the second electric vehicle (4) and the third electric vehicle by means of the multi-port unit (33), wherein the multi-port unit (33) comprises a common neutral conductor (44), and wherein the multi-port unit (33) is configured to provide communication between the first electric vehicle (1) and the second electric vehicle (4) and the third electric vehicle.

2. The method of claim 1, wherein, The second electric vehicle and the third electric vehicle are charged simultaneously.

3. The method of claim 1 or 2, wherein, A voltage range of the energy storage system (34) of the second electric vehicle and a voltage range of the energy storage system (35) of the third electric vehicle are smaller than a voltage range of the energy storage system (31) of the first electric vehicle.

4. The method of claim 1 or 2, wherein, A voltage range of the energy storage system (34) of the second electric vehicle and a voltage range of the energy storage system (35) of the third electric vehicle are different.

5. The method according to claim 1 or 2, controlling the charging current by controlling the isolated DC-DC converter of the three-phase bidirectional on-board charger of the first electric vehicle.

6. The method according to claim 1 or 2, providing data communication by means of power line communication (PLC) or CAN communication.

7. The method according to claim 1 or 2, the second electric vehicle and / or third electric vehicle comprising a direct current input selected from the following: a CCS interface, a CHAdeMO interface and / or a GB / T interface.

8. The method according to claim 1 or 2, the direct current bypassing an on-board charger of the second electric vehicle.

9. The method according to claim 1 or 2, wherein an energy storage system (36) of a fourth electric vehicle is charged by the first electric vehicle, the first electric vehicle charging the second electric vehicle and the third electric vehicle simultaneously.

10. A computer program element, which, when being executed by a processor, is configured to carry out the method according to any one of claims 1 to 9.

11. An electric vehicle (1) configured to perform the method according to any one of claims 1 to 9.

12. A system for vehicle-to-vehicle charging, the system being configured to perform the method for vehicle-to-vehicle charging according to any one of claims 1 to 9 and comprising: - an electric vehicle according to claim 11 as a first electric vehicle; - an energy storage system (34) of a second electric vehicle; - an energy storage system (35) of a third electric vehicle; - a control unit (51) configured to switch switches (S1-S4) of a power factor correction unit (11) of a three-phase bidirectional onboard charger of the first electric vehicle.

13. A multiport unit for use in the method according to any one of claims 1 to 9 or the system according to claim 12.

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