Electric drive system with battery protection by dissipating more thermal energy

Abstract

The invention relates to an electric drive system (1) for a vehicle, said electric drive system comprising: an electric machine (2) coupled via an energy storage unit (3) to a BoP unit (4) designed to supply oxygen and / or hydrogen to an FCS system (5); and a cooling unit (6) fluidly connected to the FCS system (5) and to the electric machine (2), the cooling unit (6) being designed in such a way that, in at least one recovery state in which the electric machine (2) generates electrical energy, the cooling unit releases thermal energy, which can be provided by the electric machine (2) and / or by the FCS system (5), to the surroundings. The invention also relates to a method for operating an electric drive system (1).

Description

TECHNICAL FIELD

[0001] The invention relates to an electric drive system for a vehicle, having an electric machine which is coupled via an energy storage unit to a BoP (boiler plant auxiliary) unit which is designed to supply oxygen and / or hydrogen to a FCS (fuel cell stack) system, and having a cooling unit which is fluidically connected to the FCS system and to the electric machine. The invention also relates to a method for operating an electric drive system.

[0002] The invention relates to an electric drive system for a vehicle, preferably for a road vehicle such as a car, truck or bus, or a rail vehicle. BACKGROUND

[0003] General electric drive systems are already known and are implemented as xEV systems, including battery electric vehicles (BEV), hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV) and fuel cell electric vehicles (FCEV). However, these systems often have the problem that additional electrical energy obtained by recuperation cannot be supplied to the battery as soon as the battery is fully charged or defective, when the electric machine is in a recuperation state. In certain cases, this can even lead to safety-relevant problems. For example, the entire system can fail, or the recuperation can suddenly switch on or off. This is uncomfortable for the driver.

[0004] On this basis, systems are also known from the prior art in which a brake chopper is used, which converts the excess electrical energy into heat via a heating element and heats a water circuit. The water is then pumped through a heat exchanger. This is in turn cooled by a fan, and the generated thermal energy is released into the environment. It is apparent that there is a safety system for releasing excess electrical energy which has a relatively high level of complexity. SUMMARY

[0005] It is therefore an object of the invention to provide an electric drive system which on the one hand allows safe operation of the vehicle in any recuperation state and on the other hand remains as simple as possible in its construction, using few components.

[0006] According to the invention, this is achieved by the subject matter of claim 1.

[0007] According to the invention, this is achieved in that the cooling unit is designed in such a way that in at least one recuperation state in which the electric machine generates electrical energy, the cooling unit releases thermal energy which can be provided by the electric machine and / or by the FCS system to the environment.

[0008] In other words, the present application relates to the use of the electrical energy generated by recuperation to drive a BoP (balance of plant) unit, which already exists in the case of a fuel cell vehicle. The BoP unit is an air compressor to supply oxygen to the cell stack of a fuel cell stack system (FCS), as well as a water pump for the cooling of the cell stack, possibly also a hydrogen pump, and even a DC-DC converter to bring the voltage of the cell stack to the required voltage (for example, a low voltage for various units or components, or a high voltage to supply a battery or drive a motor).

[0009] Due to this design of the electrical drive system, in the case of a fully charged battery or a defective battery, the electrical energy available to the electric machine in the recuperation state is dissipated as directly as possible, thus avoiding damage to the electric machine or the connected battery system. The structure is also kept as simple as possible, since only components already present in the vehicle need to be used or controlled in a different way in the operating mode of the vehicle.

[0010] Advantageous embodiments are claimed in the dependent claims and explained in more detail below.

[0011] It is advantageous if the BoP unit is prepared to be supplied by means of the electrical energy provided by the energy storage unit.

[0012] It is advantageous if the BoP unit comprises an air compressor for supplying oxygen to the FCS system, at least one pump for supplying water and / or hydrogen to the FCS system, and a DC-DC converter for regulating the voltage of the FCS system.

[0013] Preferably, the FCS system is electrically connected to the energy storage unit and is designed to supply electrical energy to the energy storage unit.

[0014] Preferably, the cooling unit is designed as a water-air heat exchanger and is configured to release thermal energy generated by the electric machine and the FCS system as waste heat to the environment, which thermal energy is absorbed by a coolant of the cooling circuit and is converted from water heat to air heat in the water-air heat exchanger. The coolant can be a fluid with a high thermal conductivity.

[0015] Furthermore, the present application relates to a method for operating an electrical drive system according to one of the embodiments explained above, wherein in a recuperation state in which the electric machine generates electrical energy, thermal energy generated by the electric machine and / or by the FCS system is released to the environment via a cooling unit.

[0016] Preferably, in the recuperation state, the electric machine is controlled such that the electrical energy provided by the electric machine is converted into thermal energy and released to the environment via the cooling unit.

[0017] Preferably, in the recuperation state, the FCS system is operated in an operating state with less oxygen supplied from the BoP unit to reduce the efficiency in order to convert the electrical energy provided by the FCS system into thermal energy. Via the cooling circuit and thus via the cooling unit, the thermal energy is released into the environment.

[0018] In other words, the solution according to the present application is to reduce the recuperation energy by generating more thermal energy. This can be done directly via the FCS system. In order to increase the recuperation, the FCS system is operated at a "diluted" operating point. This means that less oxygen is supplied to the cell stack in order to artificially reduce the efficiency. This means that more waste heat is generated than electrical energy. This enables the FCS system to return less energy from the battery, which is particularly beneficial when the battery is almost fully charged. This means that more energy can be recuperated via the electric drive machine for a longer period of time. It is even conceivable to limit the dilution range such that 100% of the electrical energy generated by the cell stack is used to supply the BoP unit, thus preventing the SOC of the battery from rising further.

[0019] In order to further reduce the electrical recuperation energy, it is also possible to generate more waste heat by the electric drive machine. By adjusting the control of the electric drive machine, it can generate more thermal energy than electrical energy in the case of a recuperation phase or if the electric machine is operated as a generator. By using a direct-cooled electric machine, for example with oil cooling directly on the stator winding, the maximum amount of waste heat from the electric machine can be transferred into the cooling circuit.

[0020] By these two processing options, a greater proportion of the recuperation energy can be converted into thermal energy and returned to the environment in the form of waste heat via the cooling system. BRIEF DESCRIPTION OF DRAWINGS

[0021] The application is explained in more detail below with the aid of the drawings.

[0022] In the drawings: Figure 1 A schematic representation of an electric drive system according to the application is shown according to an exemplary embodiment.

[0023] The drawings are purely schematic and serve only for understanding the application. Identical elements are provided with the same reference signs. DETAILED DESCRIPTION

[0024] Figure 1 A schematic representation of an electric drive system 1 according to the application is shown according to an exemplary embodiment.

[0025] The electric drive system 1 according to the present application is realized as an xEV system and accordingly has electrical units which generate electrical energy / power during operation. Thus, the drive system 1 is preferably used to drive the wheels of a vehicle by means of electrical energy. The vehicle is a road vehicle or a rail vehicle. Thus, the drive system 1 according to the present application can be designed as a battery electric vehicle (BEV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (HEV) or a fuel cell electric vehicle (FCEV) system.

[0026] In Figure 1 In the first exemplary embodiment, it can first be seen with reference to the first exemplary embodiment that the electric machine 2 is connected to the energy storage unit 3 in the usual manner. Thus, the electric machine 2 serves as a drive machine for mechanical propulsion of the vehicle in at least one driving state, consuming electrical energy previously stored in the energy storage unit 3. In a recuperation state, the electric machine 2 also serves as a generator to convert the mechanical kinetic energy of the wheels / vehicle back into electrical energy and to supply this electrical energy to the energy storage unit 3. For the sake of clarity, the more detailed mechanical coupling of the electric machine 2 to the wheels of the vehicle is not shown here.

[0027] Furthermore, the electric machine 2 is indirectly coupled to a BoP (boiler plant auxiliary) unit 4 by means of an electrical connection 8. The BoP unit 4 is designed to supply oxygen and hydrogen to a FCS (fuel cell stack) system 5. The BoP unit 4 comprises an air compressor for supplying oxygen to the FCS system 5, at least one pump for supplying water and / or hydrogen to the FCS system 5, and a DC-DC converter for regulating the voltage of the FCS system 5. The air compressor, the at least one pump and the DC-DC converter are not shown separately in the figure, but are contained in the block of the BoP unit 4. The FCS system 5 is electrically connected to the energy storage unit 3 and is designed to supply electrical energy to the energy storage unit 3. Furthermore, the drive system 1 comprises a cooling unit 6, which is fluidically connected to the electric machine 2 and the FCS system 5 by means of a fluid connection 9. This results in a coolant circuit which transports a fluid which absorbs the heat generated by the electric machine 2 and the thermal energy generated by the FCS system 5 and transports it to the cooling unit 6. The cooling unit 6 is designed as a water-air heat exchanger and is designed to release the thermal energy transported by the coolant as waste heat 11 to the environment 7 by means of air.

[0028] With the electric drive system 1, it is thus provided that in the recuperation state in which the electric machine 2 is operated as a generator, the heat energy generated by the electric machine 2 and by the FCS system 5 is released into the environment 7 via the cooling unit 6. The electric machine 2 is controlled in such a way that the electrical energy provided by the electric machine 2 is converted into heat energy and the heat energy is transferred via the coolant to the cooling unit 6 by means of the cooling circuit and then from the cooling unit in the form of waste heat 11 to the environment 7. In addition, the electrical energy provided by the FCS system 5 is also converted into heat energy and the heat energy is transferred via the coolant to the cooling unit 6 via the cooling circuit. In the cooling unit, the heat energy of the FCS system 5 is also released as waste heat 11 into the environment 7.

[0029] In other words, the solution according to the invention is to reduce the recuperation energy by generating more heat energy. This can be done directly via the FCS system 5. In order to increase the recuperation, the FCS system 5 is operated at a "lean" operating point. This means that less oxygen is supplied to the FCS system 5 in order to artificially reduce the efficiency. As a result, more waste heat 11 is produced than electrical energy. This enables the FCS system 5 to return less energy to the energy storage unit 3, which is particularly advantageous when the energy storage unit 3 is about to be fully charged. This means that energy can be recuperated via the electric drive machine for a longer period of time. It is even conceivable to limit the lean range so that 100% of the electrical energy generated by the FCS system 5 is used to supply the BoP unit 4, thus preventing the SOC of the energy storage unit from rising further.

[0030] As a result of the further reduction in electrical recuperation energy, it is also possible to generate more waste heat 11 in the electric drive machine, i.e. the electric machine 2. By means of appropriate control of the electric machine 2, it can generate more heat energy than electrical energy in the recuperation phase or in the case of operation of the electric machine 2 as a generator. By using a direct-cooled electric machine, for example oil cooling directly on the stator winding, it is possible to transfer the maximum amount of waste heat 11 from the electric machine 2 into the cooling circuit.

[0031] By means of these two processing options, a greater proportion of the recuperation energy can be converted into heat energy and returned to the environment 7 in the form of waste heat 11 via the cooling system.

[0032] The invention is not limited to the embodiments shown in the drawings. The above description is therefore not to be regarded as limiting, but rather as illustrative. The following claims are to be understood as meaning that the stated features are present in at least one embodiment of the invention. This does not exclude the presence of further features. Where the claims and the above description define a "first" feature and a "second" feature, this nomenclature is used to distinguish between two features of the same type, for example, without limiting the order of precedence.

[0033] List of reference signs 1 Drive system 2 Electric machine 3 Energy storage unit 4 BoP unit 5 FCS system 6 Cooling unit 7 Environment 8 Electrical connection 9 Fluid connection 10 Water compound and / or oxygen compound 11 Waste heat

Claims

1. An electric drive system (1) for a vehicle, the electric drive system having an electric motor (2) coupled to a BoP unit (4) via an energy storage unit (3), the BoP unit being designed to supply oxygen and / or hydrogen to an FCS system (5), and the electric drive system having a cooling unit (6) fluidly connected to the FCS system (5) and the electric motor (2), the cooling unit (6) being designed such that, in at least one recovery state in which the electric motor (2) generates electrical energy, the cooling unit is able to release the heat energy provided by the electric motor (2) and / or the FCS system (5) to the surrounding environment.

2. The drive system (1) according to claim 1, characterized in that, The BoP unit (4) is prepared to be supplied with electrical energy provided by the energy storage unit (3).

3. The drive system (1) according to claim 1 or 2, characterized in that, The BoP unit (4) includes an air compressor for supplying oxygen to the FCS system (5).

4. The drive system (1) according to any one of claims 1 to 3, characterized in that, The BoP unit (4) has at least one pump for supplying water and / or hydrogen to the FCS system (5).

5. The drive system (1) according to any one of claims 1 to 4, characterized in that, The BoP unit (4) has a DC-DC converter for voltage regulation of the FCS system (5).

6. The drive system (1) according to any one of claims 1 to 5, characterized in that, The FCS system (5) is electrically connected to the energy storage unit (3) and is designed to supply electrical energy to the energy storage unit (3).

7. The drive system (1) according to any one of claims 1 to 6, characterized in that, The cooling unit (6) is designed as a water-air heat exchanger.

8. A method for operating an electric drive system (1) according to any one of claims 1 to 7, wherein, In the state of recovering electrical energy generated by the motor (2), the heat generated by the motor (2) and / or by the FCS system (5) is released to the environment via the cooling unit (6).

9. The method according to claim 8, characterized in that, In the recycling state, the motor (2) is controlled so that the electrical energy provided by the motor (2) is converted into heat energy, which is then released into the environment via the cooling unit (6).

10. The method according to claim 8, characterized in that, In the recovery state, the FCS system (5) is operated in an operating state where less oxygen is supplied from the BoP unit (4) to reduce efficiency, so as to convert the electrical energy provided by the FCS system into thermal energy, which is released to the environment via the cooling unit (6).

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