Electric drive system and charging method

Abstract

The invention relates to an electric drive system for a vehicle, comprising an electric machine (2) with three stator windings (L1 to L3) for driving the vehicle, a high-voltage battery (3) and an inverter (1), wherein the inverter (1) has three half-bridges (HB1 to HB3), each with two semiconductor switches (S1 to S6), to whose center taps one of the stator windings (L1 to L3) is connected, wherein furthermore a charging socket (5) is arranged for charging the high-voltage battery (3) by means of a direct voltage and / or for charging the high-voltage battery (3) by means of an alternating voltage, wherein - a diode (D1) or a semiconductor switch (D1) with diode function is arranged between the center tap of one of the half-bridges (HB1 to HB3) and a contact of the charging socket (5) polarized in the reverse direction, - a diode (D2) or a semiconductor switch with diode function is arranged between the center tap of another of the half-bridges (HB1 to HB3) and another contact of the charging socket (5) with reverse polarity, - one diode (D3, D4) or one semiconductor switch with diode function is arranged from a negative high-voltage potential (HV_N) of the inverter (1) to each of the two contacts of the charging socket (5) with forward polarity, - an isolating DC / DC converter (8) is connected between the DC terminals of the inverter (1) and the DC terminals of the high-voltage battery (3) and can be bridged by means of two main contactors (S_Main_P, S_Main_N).

Description

The invention relates to an electric drive system for a vehicle according to the preamble of claim 1 and to a method for charging a high-voltage battery of the electric drive system according to the preamble of claim 6, 7 or 8.In charging stations according to the NACS system (North American Charging System), only two terminals are available, via which either AC or DC is charged. With the opening of the Tesla ®- Superchargers for non-corporate customers, a large DC-400 V charging network can be used, which, however, requires additional measures within the vehicle for 800 V vehicles in order to be able to carry out a DC charging process. Such measures may be:internal boost converters: A disadvantage here is that additional large and expensive components, contactors are required for the DC charging operation with and without boost converters (bypass),Switching batteries: The disadvantage here is that additional switching contactors are required and that the usable installation space for battery cells is reduced. Furthermore, the ancillary units must be configured from the 800 V voltage range to operation in the 400 V voltage range (i.e. to approximately 200 V when the battery is empty).Boost function using the inverter and the leakage inductance of the E-machine: Disadvantageous in this case is that the star point on the E-machine must be made accessible, that only the leakage inductance of the E-machine is effective, and that a bypass contactor is required for charging at 800 V (and higher current than at 400 V).Boost function using the inverter in DC-400 V feed between a phase terminal of the electric machine and the switching module output of the inverter: Disadvantageous in this case is that the charging current is limited to the design of an inverter half bridge, and that a bypass contactor is required for charging at 800 V with higher current.In the AC network, only single-phase charging is possible in the USA. The input voltage may be 120 Vrms or 240 Vrms. As the target value for the current, up to 80 arms are usual.DE 10 2021 003 883 A1 describes an electric drive system for a vehicle, having a shifting device which has:a first switching state in which a charging connection is directly connected to an electrical energy store of the vehicle, such that the electrical energy store can be charged with an input voltage which is present at the charging connection,a second and third switching state, in which the charging connection is connected to the electrical energy store via an inverter, so that the electrical energy store can be charged as a function of the inverter.DE 10 2021 003 852 A1 describes an electric drive system for a vehicle, withan electric three-phase machine for driving the vehicle,an electrical energy store for electrically supplying the electrical three-phase machine during a driving operation of the vehicle,an inverter of the electric three-phase machine, which is electrically coupled to the electric energy store, anda vehicle-side charging connection for electrically coupling the electrical energy store to a vehicle-external charging unit, whereina charging voltage of the vehicle-side charging connection can be converted into a supply voltage for charging the electrical energy store as a function of the inverter.From DE 10 2010 048 673 A1, a vehicle is known, comprising an electric motor for driving the vehicle, an electrical energy store for supplying the electric motor with electrical energy, and a charging connection for charging the electrical energy store by feeding electrical current into the electrical energy store, wherein the vehicle additionally comprises a residual current protection device which is arranged between the charging connection and the electrical energy store, such that the electrical current is conducted during charging from the charging connection via the residual current protection device to the electrical energy store and the residual current protection device interrupts an electrical connection between the charging connection and the electrical energy store when a residual current is detected.The object of the invention is to specify a novel electric drive system for a vehicle and a novel method for charging a high-voltage battery of the electric drive system.The object is achieved according to the invention by an electric drive system for a vehicle having the features of claim 1 and a method for charging a high-voltage battery of the electric drive system having the features of claim 6, 7 or 8.Advantageous embodiments of the invention are the subject matter of the dependent claims. An electric drive system for a vehicle is proposed, having an electric machine having three stator windings for driving the vehicle, a high-voltage battery and an inverter for converting a DC voltage of the high-voltage battery into an AC voltage for supplying the electric machine, wherein the inverter has a B6 bridge composed of three half bridges which are formed from in each case two semiconductor switches, to the center taps of which in each case one of the stator windings is connected, wherein a charging box for charging the high-voltage battery by means of a DC voltage and / or for charging the high-voltage battery in one phase by means of an AC voltage is furthermore arranged. Furthermore, an insulating DC / DC converter is connected between the DC terminals of the inverter and the DC terminals of the high-voltage battery and can be bridged by means of two main contactors.According to the invention, a diode or a semiconductor switch with diode function is arranged between the center tap of one of the half bridges and a contact of the charging socket in reverse polarity. Furthermore, a diode or a semiconductor switch with diode function is arranged between the center tap of another of the half bridges and another contact of the charging socket in reverse polarity. Furthermore, a diode or a semiconductor switch with diode function is arranged in each case in a biased manner from a negative high-voltage potential of the inverter to each of the two contacts of the charging socket in the forward direction.In one embodiment, at least one of the semiconductor switches of the half bridge and / or at least one of the semiconductor switches with diode function is designed as a MOSFET or IGBT with free-wheeling diode.In one embodiment, the inverter includes a DC link capacitor.In one embodiment, the inverter has current measurement devices for alternating current measurement between the center taps of the half bridges and the stator windings.In one embodiment, for the voltage-free connection of two conductors of the charging socket, two relay contacts are arranged between the respective conductor and the diodes or semiconductor switches with diode function connected thereto.According to one aspect of the present invention, a method for charging the high-voltage battery of the above-described electric drive system at a DC charging station having a boost function is proposed, wherein the DC charging station is connected to the charging box. According to the invention, a semiconductor switch arranged as a low-side switch of one of the half bridges, which is connected to the charging socket via one of the diodes or semiconductor switches with diode function, is driven in a clocked manner, wherein the insulating DC / DC converter is operated in a clocked manner for the transmission of power from the DC link capacitor to the high-voltage battery or is bypassed by means of the main contactors.According to a further aspect of the present invention, a method for charging the high-voltage battery of the above-described electric drive system at an AC charging station is proposed, wherein the AC charging station is connected to the charging socket. According to the invention, during a positive half wave of an alternating voltage fed in from the AC charging station, a semiconductor switch, arranged as a low-side switch, of one of the half bridges, which is connected to the charging socket via one of the diodes or semiconductor switches with diode function, is activated in a clocked manner. During a negative half wave of the alternating voltage fed in from the AC charging station, a semiconductor switch, arranged as a low-side switch, of another of the half bridges, which is connected to the charging socket via one of the diodes or semiconductor switches with diode function, is activated in a clocked manner. A power transmission from the DC link capacitor to the high-voltage battery takes place via the insulating DC / DC converter.According to a further aspect of the present invention, a method for charging the high-voltage battery of the above-described electric drive system at a DC charging station without a boost function is proposed, wherein the DC charging station is connected to the charging box. According to the invention, a current for charging is conducted via the body diodes or freewheeling diodes of the semiconductor switches arranged as high-side switches, wherein the insulating DC / DC converter is operated in a clocked manner for the transmission of power from the DC link capacitor to the high-voltage battery or is bypassed by means of the main contactors.In one embodiment, at least one of the semiconductor switches and diode-functional semiconductor switches is closed as soon as a current flows via its body diode or free-wheeling diode.According to a further aspect of the present invention, a method for emergency operation of the above-described electric drive system is proposed, wherein the insulating DC / DC converter is operated in a clocked manner in the event of a problem in the activation and / or in the event of an insulation fault in the high-voltage battery or in a subsystem on the side of the main contactors facing the high-voltage battery or in the event of a triggered main fuse for transmitting power from the high-voltage battery to the inverter.In one embodiment, a setpoint current is regulated by the timing of the semiconductor switches.According to the present invention, the inverter is extended by two semiconductors with diode function for two half bridges each. This allows a single-phase PFC function to be represented using the inverter and the motor inductance. In addition, an insulated DC / DC converter is used to establish galvanic isolation in AC charging or (if necessary) in DC charging. The boost function can likewise be realized by the inverter and the motor inductance.The PFC function in AC charging is represented by the inverter and the low overhead E-machine (two diodes, two semiconductor switches). This makes it possible to dispense with the PFC of the onboard charger. The main inductance of the electric machine acts as a PFC reactor. During the charging process, no rotation of the electric machine takes place. Furthermore, the bulk capacitor of a typical on-board charger (OBC) can be omitted, since the DC link capacitor is used for this purpose. The electric machine and the inverter are used as boost DC / DC converters from 400 V to 800 V, so that an alternative charging solution such as boost converter or changeover battery etc. can be dispensed with. Emergency charging possibilities exist via the inverter and the insulating DC / DC converter (e.g. if a limit of the C1 characteristic curve could be exceeded). An emergency driving function is when the battery main contactors are opened due to a failure (e.g., an insulation failure at the start of the vehicle). During DC charging at 400 V and insulation fault in the vehicle occurring (varistor triggering in EVSE due to insulation overload), a battery short circuit is avoided. The connections outside the critical commutation cell between MOSFET and DC link capacitor have no influence on the inverter switching function (efficiency / voltage utilization). The solution according to the invention enables the representation of a NACS charging system for DC 800 V, DC 400 V and AC (single-phase) without additional switching elements in the charging path.Exemplary embodiments of the invention are explained in more detail below with reference to drawings.The following are shown: FIG. 1 is a schematic view of an inverter for operating an electric machine with a circuit including a charging socket, FIG. 2 shows a schematic view of the inverter during charging with a boost function at a DC charging station, FIG. 3 shows a schematic view of the inverter during charging without a boost function at the DC charging station, FIG. 4 shows a schematic view of the inverter when an emergency charging function with a boost function is carried out at the DC charging station, FIG. 5 shows a schematic view of the inverter when an emergency charging function without a boost function is carried out at the DC charging station, FIG. 6 shows a schematic view of the inverter when performing an AC charging function at an AC charging station during a positive voltage half-wave, FIG. 7 shows a schematic view of the inverter when performing an AC charging function at an AC charging station during a negative voltage half wave, FIG. 8 is a schematic view of the inverter when an emergency driving function is performed with reduced power, FIG. 9 shows a schematic diagram with signals of a simulation of the inverter during charging at a DC charging station with boost function, FIG. 10 is a schematic diagram showing signals of the simulation of the inverter when insulation faults occur, FIG. 11 shows a schematic diagram with further signals of the simulation of the inverter for illustrating a potential distribution, FIG. 12 shows a schematic diagram with signals of a simulation of the inverter during charging at the AC charging station, FIG. 13 is a schematic diagram showing signals of the simulation of the inverter in AC charging at the beginning of the positive half wave; and FIG. 14 is a schematic diagram showing signals of the simulation of the inverter in AC charging at the beginning of the negative half wave.Corresponding parts are provided with the same reference numerals in all figures.FIG. 1 is a schematic view of an inverter 1 for operating an electric machine 2, for example a drive machine of an electrically driven vehicle, in particular a passenger car, a commercial vehicle or a bus. The inverter 1 has a B6 bridge composed of three half bridges HB1, HB2, HB3connected between a positive high-voltage potential HV_P and a negative high-voltage potential HV_N, which are formed from in each case two semiconductor switches S1 to S6, in particular MOSFET or IGBT with a freewheeling diode. Furthermore, the inverter 1 has an intermediate circuit capacitor C and current measurement devices A, in particular for alternating current measurement, at the center taps of the half bridges HB 1 to HB 3. The electric machine 2 has three stator windings L 1 to L 3, which are connected to the center taps of the half bridges HB 1 to HB 3.The inverter 1 is configured by appropriate circuitry to be used when charging a high-voltage battery 3 of the vehicle by means of DC voltage or by means of a single-phase AC voltage via a charging box 5, in particular a NACS charging box.Two charging relays S_Charge_ 1, S_Charge_ 2 are provided for de-energizing the charging socket 5.Furthermore, a diode D 1 for the center tap of a first half bridge HB 1 of the inverter 1 is arranged as coupling element D 1 in reverse polarity with respect to a first terminal of the first charging relay (e.g. S_Charge_ 1). As an alternative to the diode D 1, it is also possible, as shown in FIG. 1, to use another semiconductor component D 1, for example a MOSFET with body diode in the direction of the diode D 1 shown, an IGBT with a corresponding free-wheeling diode, etc.Furthermore, a diode D 2 for the center tap of a second half bridge HB 2 of the inverter 1 is arranged as coupling element D 2 in reverse polarity with respect to a second terminal of the second charging relay (e.g. S_Charge_ 2). Alternatively to the diode D 2, it is also possible to use another semiconductor component D 2, for example a MOSFET with body diode in the direction of the diode D 2 shown, an IGBT with a corresponding free-wheeling diode, etc.Furthermore, a diode D 3 is connected as coupling element D 3 in the forward direction from the negative high-voltage potential HV_N to the first charging relay S_Charge_ 1, and a diode D 4 is connected as coupling element D 4 in the forward direction from the negative high-voltage potential HV_N to the second charging relay S_Charge_ 2. Alternatively to the diodes D 3, D 4, in each case it is also possible to use a different semiconductor component D 3, D 4, for example a MOSFET with body diode in the direction of the diode D 3, D 4 shown, an IGBT with a corresponding free-wheeling diode, etc.In order to enable a floating AC charging function, an insulating DC / DC converter 8 is connected between the DC terminals of the inverter 1, that is to say between the positive high-voltage potential HV_P and the negative high-voltage potential HV_N, and the DC terminals of the HV battery 3 (an insulating DC / DC converter 8 is shown in LLC topology by way of example in FIG. 1. Alternatively, other insulating DC / DC converter topologies are possible, for example dual-active bridge, phase shift full bridge, etc.).The insulating DC / DC converter 8 can be directly connected to the DC terminals or HV potentials of the HV battery 3 or have separate connection elements (not shown).If a bidirectional charging function (V2x) or an emergency driving function are desired, the insulating DC / DC converter 8 is to be designed bidirectionally. In the charging functions, only the charging mode is shown. The feeding in of the bidirectional charging function (V2x) is usually effected with the current direction reversed and is not shown.The DC terminals of the HV battery 3 are connected via main contactors S_Mai_P, S_Mai_N to the positive high-voltage potential HV_P and the negative high-voltage potential HV_N and thus also to the DC terminals of the inverter 1. Other components of the HV system, not shown, may be: LV DC / DC converters, heaters, refrigerant compressors, etc.The coupling elements D 1 to D 4 can be selected in particular such that the DC charging current (boost function or 800 V charging) flows via components which are optimized with respect to their forward losses and the current carrying capacity, such as IGBTs, for example, while low-cost diodes which are designed for the AC currents can be selected for the AC function. In general, a diode D1 to D4 or a semiconductor switch D1 to D4 with a blocking effect for one current direction can be selected as desired for both components.For charging a high-voltage battery 3 of a battery-electric vehicle at a DC charging station 6, which provides a maximum output voltage (for example 500 V) that is lower than a rated voltage (for example 800 V) of the high-voltage battery 3, various solutions are known in the prior art, for example a changeover battery, a separate boost DC / DC converter, boosting via the inverter 1 with or without splitting the neutral point, etc.The present invention proposes a solution in which, during DC charging, a DC charging station 6 is connected to the inverter 1 and the electric machine 2 via the charging box 5, the charging relays S_Charge_ 1 and S_Charge_ 2 and at least one of the coupling elements D 1 to D 4 (in particular coupling elements D 1, D 4 designed as IGBTs) in such a way that the function of a galvanically coupled DC / DC converter 8 can be represented only by means of a specific actuation of the semiconductor switches S 1 to S 6. Since the current flow through the stator windings L 1 to L 3 represents a realistic operating point of the electric machine 2, the complete stator inductance can be used here. The electric machine 2 nevertheless does not move.In the event of an insulation fault in the vehicle, an overload of the insulation in the opposite HV_N potential of the DC charging station 6 can occur as a direct consequence. Protective varistors in the DC charging station 6 result in a short circuit of the high-voltage battery 3. When a semiconductor switch D 4 is used as the coupling element D 4, the short circuit can be quickly detected and the semiconductor switch D 4 can be opened. An early detection can be determined by the shift of the HV potentials with respect to the protective conductor PE and / or potential compensation PA, so that the semiconductor switch D 4 can be opened before the varistor triggers in the DC charging station 6 and thus also before a short-circuit current is in the process of building up. In addition, it is important that the clocked semiconductor switch S 1 to S 6 in the inverter 1 is no longer activated (switched on) in the event of this double insulation fault. However, a short circuit of the DC charging station 6 can remain.FIG. 2 is a schematic view of the inverter 1 when charging at the boost-type DC charging station 6. It is evident that only two of the four semiconductor switches D 1 to D 4, namely the semiconductor switches D 1 and D 4, are necessary for the boost function. They can also be replaced by MOSFETs or IGBTs for optimization at higher currents.For DC charging by means of boost operation, the charging relays S_Charge_ 1, S_Charge_ 2 and the main contactors S_Mai_P, S_Mai_N are closed. In this case, the semiconductor switch S 4, that is to say the low-side switch S 4, of one of the half bridges HB 1 to HB 3, in particular of the half bridge HB 2, is driven in a clocked manner. When the semiconductor switch S 4 is closed, a current I 1 flows from the DC charging station 6 via the charging relay S_Charge_ 1, the coupling element D 1, the stator winding L 1, the neutral point of the electric machine 2, the stator winding L 2, the semiconductor switch S 4, the coupling element D 4 and the charging relay S_Charge_ 2 back to the DC charging station 6. When the semiconductor switch S 4 is open, a current I 2 flows from the DC charging station 6 via the charging relay S_Charge_ 1, the coupling element D 1, the stator winding L 1, the neutral point of the electric machine 2, the stator winding L 2, the body diode of the semiconductor switch S 3, the high-voltage battery 3, the coupling element D 4 and the charging relay S_Charge_ 2 back to the DC charging station 6.As soon as the activated semiconductor switch S 4 is closed, the voltage of the DC charging station 6 is applied to the two stator windings L 1 and L 2. The current I1 through the two stator windings L1 and L2 increases. In this phase, no charge of the high-voltage battery 3 takes place. If the controlled semiconductor switch S 4 is opened, the only possible free-wheeling path for the current I 2 impressed in the stator windings L 1 and L 2 is via the body diode of the high-side switch located in the same half bridge, in this case the semiconductor switch S 3. For loss optimization, this semiconductor switch S 3 can be closed as soon as the current I 2 flows. The current path that results leads via the high-voltage battery 3, so that the latter is charged.FIG. 3 is a schematic view of the inverter 1 when charging without boosting at the DC charging station 6 at, for example, 800 V.In order to charge the vehicle on an 800 V charging column (output voltage of approximately 920 V-950 V, for example), no clocking operation of the inverter 1 is necessary. Nevertheless, the entire DC charging current is conducted via the inverter 1. Alternatively, an additional contactor pair for charging at an 800V station may be provided between the charging terminals and the battery terminals. In order to minimize the losses in the inverter 1 and to divide the charging current (approximately) into three paths, the three high-side switches S 1, S 3, S 5 of the half bridges HB 1 to HB 3 are switched on for this purpose. In addition, the coupling elements D 1, D 4 embodied as IGBTs are switched through close to the charging relays S_CHARGE_ 1, S_CHARGE_ 2. A current I 1 thus flows from the DC charging station 6 via the charging relay S_charge_ 1, the coupling element D 1 and three parallel current paths through the inverter 1, the high-voltage battery 3, the coupling element D 4 and the charging relay S_charge_ 2 back to the DC charging station 6. The maximum charging current to be commanded on the part of the high-voltage battery 3 must be matched to the maximum current of the charging path shown. If a semiconductor switch S 1, S 3, S 5 of the inverter 1 or the electric machine 2 should reach a critical temperature value, the maximum current on the side of the DC charging station 6 can be commanded to a lower value.FIG. 4 is a schematic view of the inverter 1 when performing an emergency charging function with a boost function at the DC charging station 6 at, for example, 400 V, wherein isolated charging is performed.If a galvanic connection of the complete vehicle to a DC charging station 6 is not desired or allowed, then there is nevertheless the possibility of charging the vehicle with reduced power. By opening the main contactors S_Mai_P, S_Mai_N, the high-voltage battery 3 is galvanically isolated from the DC charging station 6. The inverter 1 with the coupling elements D 1 to D 4 functions as in the boost function described above when charging on a 400 V charging column, for example with the low-side switch S 4 operated in a clocked manner. As a result, the DC link capacitor C or intermediate circuit capacitor C is charged. At the same time, the insulating DC / DC converter 8 is in clocked operation and transfers power from the DC link capacitor C from its side connected to the DC link capacitor C to its side connected to the high-voltage battery 3, wherein the two sides are galvanically separated from one another by the main contactors S_Mai_P, S_Mai_N. The transmittable power is limited by the insulating DC / DC_ converter 8.FIG. 5 is a schematic view of the inverter 1 when performing an emergency charging function without a boost function at the DC charging station 6 at, for example, 800 V, wherein isolated charging is performed.If a galvanic connection of the complete vehicle to a DC charging station 6 is not desired or allowed, there is nevertheless the possibility of charging the vehicle with reduced power. By opening the main contactors S_Mai_P, S_Mai_N, the high-voltage battery 3 is galvanically isolated from the DC charging station 6. The inverter 1 now assumes the state as in the case of DC charging at an 800 V charging station without a boost function. Due to the lower transmission power, it is also possible to switch on only one or two of the high-side switches S 1, S 3, S 5 instead of the three switched-on high-side switches S 1, S 3, S 5. The DC link capacitor C is now charged by the charging station 6. At the same time, the insulating DC / DC converter 8 is in clocked operation and transfers power from the DC link capacitor C from its side connected to the DC link capacitor C to its side connected to the high-voltage battery 3. The transmittable power is limited by the insulating DC / DC converter 8.FIG. 6 is a schematic view of the inverter 1 when performing an AC charging function at an AC charging station 7 during a positive voltage half wave.The AC charging function for the positive voltage half-wave, in which the potential at the charging relay S_Charge_ 1 is higher than at the charging relay S_Charge_ 2, is identical or similar to the function during boosting with respect to the current characteristics in the inverter 1 (PFC function). In AC charging, galvanic isolation is provided. Therefore, the main contactors S_Mai_P and S_Mai_N are open and the power transmission from the DC link capacitor C of the inverter 1 to the high-voltage battery 3 takes place via the galvanically insulating DC / DC converter 8, which is activated in a clocked manner for this purpose. The DC link capacitor C of the inverter 1 replaces the function of the bulk capacitor and reduces the current ripple on the high-voltage battery 3 side.In a first state, the low-side switch S 4 is closed. As soon as the low-side switch S 4 is closed, a current I 1 builds up via the stator windings L 1 and L 2. The two stator windings L 1 and L 2 are therefore supplied with the voltage of the AC charging station 7. At this time, the current I1 through the stator windings L1 and L2 increases. No charge of the high-voltage battery 3 takes place in this phase.In a second state, the low-side switch S 4 is open. In this case, a free-wheeling current I 2 flows from the stator windings L 1 and L 2 via the body diode of the high-side switch S 3 to the DC link capacitor C, from which the power transmission to the high-voltage battery 3 takes place via the galvanically insulating DC / DC converter 8, which is put into operation in a clocked manner for this purpose. When the low-side switch S 4 is opened, the only possible free-wheeling path for the current I 1 impressed in the stator windings L 1 and L 2 runs via the body diode of the high-side switch S 3. For loss optimization, this high-side switch S 3 can be closed as soon as the current flow begins. The current path that results leads via the DC link capacitor C, from which the power transmission to the high-voltage battery 3 takes place via the galvanically insulating DC / DC converter 8, so that the high-voltage battery 3 is now charged. The current path leads from the negative high-voltage potential HV_N back to the AC charging station 7 via the coupling element D 4.FIG. 7 is a schematic view of the inverter 1 when performing an AC charging function at an AC charging station 7 during a negative voltage half wave.In the AC charging function for the negative voltage half-wave, in which the potential at the charging relay S_Charge_ 1 is lower than at the charging relay S_Charge_ 2, the low-side switch S 2 of another half-bridge HB 1 of the inverter 1 is operated in a clocked manner in comparison with charging with the positive voltage half-wave. The current flow via the coupling elements D 1 to D 4 is also now effected via the semiconductors represented as diodes D 2, D 3. The coupling elements D 1, D 4, which are situated parallel thereto and are illustrated as IGBTs, must be open. To ensure the galvanic isolation, as in the case of charging with the positive half wave, the main contactors S_Mai_P, S_Mai_N are opened and the power transmission from the DC link capacitor C to the high-voltage battery 3 takes place via the insulating DC / DC converter 8.In a first state, the low-side switch S 2 is closed. As soon as the low-side switch S 2 is closed, a current I 1 builds up via the stator windings L 2 and L 1. As soon as the low-side switch S 2 is closed, the voltage of the AC charging station 7 is applied to the two stator windings L 1 and L 2. The current I1 through the stator windings L1 and L2 increases. No charge of the high-voltage battery 3 takes place in this phase.In a second state, the low-side switch S 2 is open. In this case, a free-wheeling current I 2 flows from the stator windings L 1 and L 2 via the body diode of the high-side switch S 1 to the DC link capacitor C, from which the power transmission to the high-voltage battery 3 takes place via the galvanically insulating DC / DC converter 8, which is put into operation in a clocked manner for this purpose. For loss optimization, this high-side switch S 1 can be closed as soon as the current flow begins. The current path that results leads via the DC link capacitor C, from which the power transmission to the high-voltage battery 3 takes place via the galvanically insulating DC / DC converter 8, so that the high-voltage battery 3 is now charged. The current path leads from the negative high-voltage potential HV_N back to the AC charging station 7 via the coupling element D 3.FIG. 8 is a schematic view of the inverter 1 when performing an emergency running function with reduced power. If, for example, the main contactors S_Mai_P, S_Mai_N have opened or are held on account of a fault, emergency driving operation is possible via the insulating DC / DC converter 8. In this state, the charging relays S_Charge_ 1, S_Charge_ 2 are also open. The insulating DC / DC converter 8 transfers power from the high-voltage battery 3 to the inverter 1.Triggers for such an opening of the main contactors S_Mai_P, S_Mai_N can be a problem in the actuation, an insulation fault in the high-voltage battery 3 or in the subsystem on the side of the main contactors S_Mai_P, S_Mai_N facing the high-voltage battery 3 or a triggered main fuse (not shown).In the solution shown, the PFC function (power factor correction) is represented with little additional outlay during AC charging by the inverter 1 and the electric machine 2 (two diodes D 2, D 3, two semiconductor switches D 1, D 4). As a result, power factor correction (PFC) of an on-board charger can be omitted. The main inductances of the stator windings L 1 to L 3 of the electric machine 2 are effective as PFC chokes. During the charging process, no rotation of the electric machine 2 takes place. The electric machine 2 and the inverter 1 are used as boost DC / DC converters from 400 V to 800 V, so that an alternative charging solution such as boost converter or changeover battery etc. can be dispensed with. Emergency charging possibilities exist via the inverter 1 and the insulating DC / DC converter 8 (e.g. if a limit of the C1 characteristic curve could be exceeded). An emergency driving function exists when the main contactors S_Mai_P, S_Mai_N open due to a fault (e.g., an isolation fault at vehicle start). During the DC charging at 400 V and insulation fault in the vehicle occurring (varistor triggering in the DC charging station 6 due to insulation overload), a battery short circuit is avoided. The connections outside the critical commutation cell between MOSFET and DC link capacitor C have no influence on the inverter switching function (efficiency / voltage utilization). The solution according to the invention enables the representation of a NACS charging system for DC 800 V, DC 400 V and AC (single-phase) without additional switching elements in the charging path.FIG. 9 is a schematic diagram with signals of a simulation of the inverter 1 (shown in FIG. 1 ) with the circuit arrangement, wherein the boost function at a DC charging station 6 (shown in FIG. 1 ) has been shown at 400 V. A target current has been set within the limits of 120 A to 125 A. The following two diagrams show the currents of the stator windings L 1 to L 3 (illustrated in FIG. 1 ) and a control signal Gate_S 4 for driving the semiconductor switch S 4 (illustrated in FIG. 1 ). At a time t=0.5 s, an insulation fault occurs in the vehicle from the positive high-voltage potential HV+ to the potential compensation PA. At a time t=0.6 s, the clock operation of the semiconductor switch S 4 is stopped and the semiconductor switch S 4 remains open. At a time t=0.7 s, a second insulation fault takes place in the DC charging station 6 from the negative high-voltage potential HV_N (illustrated in FIG. 1 ) to the potential compensation PA.The parameters used for the simulation were:Insulation resistances: 1 MohmInductance of the stator windings L 1 to L 3: 1000 μFInternal resistance Ri_Ba of the high-voltage battery 3 (illustrated in FIG. 1 ) and of the DC charging station 6: 0.1 OhmFIG. 9 shows a source voltage U_Q of the DC charging station 6, the control signal Gate_S4 for driving the semiconductor switch S4, a current I_DC+ in the positive high-voltage potential HV+, a current I_DC- in the negative high-voltage potential HV-, a current I_Q from the DC charging station 6 and a charging current I_L flowing into the high-voltage battery 3.When the semiconductor switch S 4 is closed, the current in the two stator windings L 1 and L 2 increases. It can be seen that the current I_Q of the DC charging station 6 is identical to the amount of current in the stator windings L 1 and L 2. During this time, no charge of the high-voltage battery 3 takes place (charging current I_L=0). The current I_Q rises in this phase until it has reached the setpoint value of 125 A. Normally, however, this would still be the case by the large intermediate circuit capacitor C (illustrated in FIG. 1 ) of the inverter 1. However, it has been omitted here in order to be able to better illustrate the function. As soon as the semiconductor switch S 4 is opened when 125 A is reached, the current I_Q of the DC charging station 6 flows both through the two stator windings L 1 and L 2 and through the high-voltage battery 3. From the falling below the value of 120 A, the semiconductor switch S 4 is closed again.FIG. 10 is a schematic diagram showing signals of the simulation of the inverter 1 (shown in FIG. 1 ) including the circuitry when insulation failures occur:Over the entire time window of the simulation, an insulation fault initially occurs in the vehicle from the positive high-voltage potential HV+ to the potential compensation PA (insulation value is an ideal short circuit, that is to say 0 ohm, time t=0.5 s). In this state, the circuit still functions without errors, i.e. the inverter 1 operating as a booster can set the setpoint current and thus charges the high-voltage battery 3 (illustrated in FIG. 1 ). There are no short-circuit currents of the high-voltage battery 3 or of the DC charging station 6 (illustrated in FIG. 1 ). Starting from the time t=0.6 s, the timing of the semiconductor switch S 4 (illustrated in FIG. 1 ) is adjusted. As soon as the timing of the semiconductor switch S 4 is adjusted, the charging current I_L from the DC charging station 6 to the high-voltage battery 3 ends.From the time t=0.7 s, the second insulation fault from the negative high-voltage potential HV_N to the potential compensation PA takes place in the DC charging station 6. No short-circuit current of the DC charging station 6 is formed, but a current which is very high here, however, due to the value of 0.1 mOhm assumed to be quite low. In reality, this would mean that the DC charging station 6 is set to the maximum current of the command by the vehicle or the current corresponds to the maximum current of its power electronics (for example possible value for command by the vehicle 150 A or for maximum current of the DC charging station 6,500 A).FIG. 11 is a schematic diagram with further signals of the simulation of the inverter 1 (shown in FIG. 1 ) with the circuit for illustrating the potential distribution.In the simulation, the high-voltage potentials HV_P, HV_N of the DC charging station 6 (illustrated in FIG. 1 ) in the vehicle were recorded. This is of interest especially when considering insulation faults. In the time before t=0.5 s, the insulation is still intact. A uniform distribution of the insulation resistances is assumed (1 MOh each). This leads to an approximately symmetrical high-voltage distribution in the vehicle (500 V HV+ to PA and 300 V HV- to PA). The high-voltage distribution of HV- to PA of the vehicle is transferred to the side of the DC charging station 6, since the booster function is a galvanically coupled booster with a common negative high-voltage potential HV-, HV_N. The positive high-voltage potential HV_P is lowered by the value of the booster at the DC charging station 6, i.e. starting from a voltage of HV+ to PA of 500 V in the vehicle and a voltage increase by the booster of 400 V, a voltage between HV_P and PA on the side of the DC charging station 6 of 100 V results.From the occurrence of the first insulation fault in the vehicle at t=0.5 s, the potentials both in the vehicle and in the DC charging station 6 shift downward by 500 V. Once the pulsing of the semiconductor switch S 4 (shown in FIG. 1 ) is stopped, the voltage difference between the high-voltage battery 3 (shown in FIG. 1 ) (800 V) and the DC charging station 6 (400 V) across the diode D 4 (shown in FIG. 1 ) drops. Since the positive high-voltage potential HV_P is identical to the potential compensation PA, the negative high-voltage potential HV_N is now below the potential compensation PA (-400 V) by the amount of the voltage of the DC charging station 6.Starting from t=0.7 s, a second insulation fault in the DC charging station 6 is now assumed from the negative high-voltage potential HV_N for potential compensation PA. This insulation fault is also assumed to be an ideal short circuit of 0 ohm. This results in a potential distribution of 0 V from HV_P for potential compensation PA and simultaneously from 0 ohm from HV_N for potential compensation PA on the side of the DC charging station 6.FIG. 12 is a schematic diagram with signals of a simulation of the inverter 1 (shown in FIG. 1 ) with the circuit, wherein the AC charging function has been shown at an AC charging station 7 (shown in FIG. 1 ). By means of a voltage measurement, the instantaneous value of the alternating voltage U_Q fed in from the AC charging station 7 is determined. Subsequently, depending on the sign, the correct semiconductor switch S 2, S 4 is controlled in such a way that the correct current is established for each half wave. The setpoint current is, for example, 16 A, which is to be set in the peak value of the voltage half wave.The diagram shows the source voltage U_Q of the AC charging station 7, the control signals Gate_S2, Gate_S4 of the semiconductor switches S2, S4 (shown in FIG. 1 ), the current I_L1 in the stator winding L1 (shown in FIG. 1 ), the current I_L2 in the stator winding L2 (shown in FIG. 1 ), the current I_Q flowing from the AC charging station 7 and the charging current I_L of the high-voltage battery 3 (shown in FIG. 1 ). The task of the PFC function of inverter 1 is to set a current for both half-waves, which is proportional to the voltage curve and whose peak value is 16 A. The set current is set by a comparison with a proportionally reduced value of the voltage measurement. Here, a tolerance of + / - 1 A, for example, is specified as the maximum deviation from the setpoint current, that is to say as soon as the current 1 A is below the setpoint specification in the positive half-wave, the corresponding semiconductor switch S 4 is switched on in order to increase the current I_L 1, I_L 2 through the stator windings L 1, L 2. If the current current value is above the setpoint value by 1 A, the semiconductor switch S 4 is opened again. In this case, the free-wheeling of the current I_L 1, I_L 2 through the stator windings L 1, L 2 takes place via the high-voltage battery 3, so that the latter is charged.In the negative half-wave, the switch is switched with the opposite sign, that is to say as soon as the current lies below the (negative) setpoint current by 1 A, the semiconductor switch S 2 is opened. As soon as the current is above the setpoint current by 1 A, the semiconductor switch S 2 is closed again.FIG. 13 is a schematic diagram showing signals of the simulation of the inverter 1 (shown in FIG. 1 ) including the circuitry in AC charging at the beginning of the positive half wave. FIG. 14 is a schematic diagram showing signals of the simulation of the inverter 1 (shown in FIG. 1 ) including the circuitry in AC charging at the beginning of the negative half wave.If the voltage between the negative high-voltage potential HV- (illustrated in FIG. 1 ) and the potential compensation PA is considered in the simulation, it arises that the negative high-voltage potential HV- is identical to the phase of the source voltage U_Q during the negative half-wave. In other words: in the negative half-wave, the HV potentials HV+, HV- (illustrated in FIG. 1 ) of the vehicle are shifted according to a sinusoidal half-wave with respect to the potential compensation PA=N=PE (protective conductor). This is also a typical behavior of a PFC. In the case of large Y capacitances between HV+ or HV- and PA, this would lead to a leakage current which could cause an FI switch of a domestic installation to be triggered (compensation current flows on protective conductors PE).This can be remedied by remedying1. Furthermore, small Y capacitances can be arranged in the region of the PFC and subsequently a galvanic isolation can be carried out via an insulating DC / DC converter 8, or 2. a compensating current can be fed in on the protective conductor PE.Note that for 800 V vehicles, the Y capacities of the vehicle must be kept lower than for 400 V vehicles because of the C1 characteristic. Breaking down to the Y capacitance of the inverter 1 (shown in FIG. 1 ) including the electric machine 2 (shown in FIG. 1 ) means:In a 400 V inverter, a Y capacitance of approximately 500 nF per high voltage potential HV+, HVshould be reduced.In an 800 V inverter, a Y capacitance of approximately 50 nF to 80 nF per high voltage potential HV+, HV- should be provided.It is clear that in 800 V vehicles the leakage current is significantly lower.List of reference characters1 Inverter 2 Electric machine 3 High-voltage battery 5 Charging box 6 DC charging station 7 AC charging station 8 Insulating DC / DC converter A Current measuring device C Intermediate circuit capacitor, DC link capacitor D1, D2, D3, D4 Coupling element, diode, semiconductor component, semiconductor switch Gate_S2, Gate_S4 Control signal HB1, HB2, HB3 Half bridge HV+, HV_N, HV-, HV_P High-voltage potential I1, I2, I_HV+, I_HV-, I_Q, I_L1, I_L2 Current, free-wheeling current I_L Charging current L1, L2, L3 Stator winding S1, S3, S 5 high-side switches, semiconductor switches S 2, S 4, S 6 low-side switches, semiconductor switches S_Charge_ 1, S_Charge_ 2 charging relays, charging contactor, relay contact S_Mai_P, S_Mai_N main contactor, main contactor contact U_Q source voltage

Claims

An electric drive system for a vehicle, having an electric machine (2) with three stator windings (L1 to L3) for driving the vehicle, a high-voltage battery (3) and an inverter (1) for converting a DC voltage of the high-voltage battery (3) into an AC voltage for supplying the electric machine (2), wherein the inverter (1) has a B6 bridge composed of three half bridges (HB1 to HB3) which are formed from in each case two semiconductor switches (S1 to S6), to the centre taps of which in each case one of the stator windings (L1 to L3) is connected, wherein a charging box (5) for charging the high-voltage battery (3) by means of a DC voltage and / or for charging the high-voltage battery (3) in one phase by means of an AC voltage is arranged, and wherein an insulating DC / DC converter (8) is connected between the DC terminals of the inverter (1) and the DC terminals of the high-voltage battery (3) and can be bridged by means of two main contactors (S_Mai_P, S_Mai_N), characterized in that - a diode (D1) or a semiconductor switch (D1) with a diode function is arranged in reverse polarity between the center tap of one of the half bridges (HB1 to HB3) and a contact of the charging box (5), a diode (D2) or a semiconductor switch (D2) with diode function is arranged between the center tap of another of the half bridges (HB1 to HB3) and another contact of the charging socket (5) in reverse biased manner, a diode (D3, D4) or a semiconductor switch (D3, D4) with diode function is arranged in forward biased manner from a negative high voltage potential (HV_N) of the inverter (1) to each of the two contacts of the charging socket (5).Electric drive system according to Claim 1, characterized in that the semiconductor switches (S1 to S6) and / or the semiconductor switches (D1 to D4) with diode function are designed as MOSFETs or IGBTs with free-wheeling diodes.Electric drive system according to Claim 1 or 2, characterized in that the inverter (1) has a DC link capacitor (C).Electric drive system according to Claim 1 or 2, characterized in that the inverter (1) has current measurement devices (A) for alternating current measurement between the centre taps of the half bridges (HB1 to HB3) and the stator windings (L1 to L3).Electric drive system according to one of the preceding claims, characterized in that, for the voltage-free connection of two conductors of the charging socket (5), two relay contacts (S_Charge_1, S_Charge_2) are arranged between the respective conductor and the diodes (D1 to D4) connected thereto or semiconductor switches (D1 to D4) with diode function.Method for charging the high-voltage battery (3) of the electric drive system according to one of the preceding claims at a DC charging station (6) with boost function, wherein the DC charging station (6) is connected to the charging box (5), characterized in that a semiconductor switch (S2, S4, S6), which is arranged as a low-side switch, of one of the half bridges (HB1 to HB3) and is connected to the charging box (5) via one of the diodes (D1, D2) or semiconductor switches (D1 to D4) with diode function, is activated in a clocked manner, wherein the insulating DC / DC converter (8) is operated in a clocked manner for the transmission of power from the DC link capacitor (C) to the high-voltage battery (3) or is bypassed by means of the main contactors (S_Mai_P, S_Mai_N).Method for charging the high-voltage battery (3) of the electric drive system according to one of Claims 1 to 5 at an AC charging station (7), wherein the AC charging station (7) is connected to the charging box (5), characterized in that during a positive half wave of an alternating voltage fed in from the AC charging station (7), a semiconductor switch (S2, S4, S6), arranged as a low-side switch, of one of the half bridges (HB1 to HB3), which is connected to the charging box (5) via one of the diodes (D1, D2) or semiconductor switches (D1 to D4) with diode function, is actuated in a clocked manner, wherein during a negative half wave of the alternating voltage fed in from the AC charging station (7), a semiconductor switch (S2, S4, S6), arranged as a low-side switch, of another of the half bridges (HB1 to HB3) which is connected to the charging can (5) via one of the diodes (D1, D2) or semiconductor switches with diode function is clocked, wherein a power transmission from the DC link capacitor (C) to the high-voltage battery (3) takes place via the insulating DC / DC converter (8).Method for charging the high-voltage battery (3) of the electric drive system according to one of Claims 1 to 5 at a DC charging station (6) without a boost function, wherein the DC charging station (6) is connected to the charging box (5), characterized in that a current (I1) for charging is conducted via the body diodes or freewheeling diodes of the semiconductor switches (S1, S3, S5) arranged as high-side switches, wherein the insulating DC / DC converter (8) is operated in a clocked manner for transmitting power from the DC link capacitor (C) to the high-voltage battery (3) or is bypassed by means of the main contactors (S_Mai_P, S_Mai_N).Method according to one of Claims 6 to 8, characterized in that semiconductor switches (S1 to S6) and semiconductor switches with diode function are closed as soon as a current flows via their body diode or freewheeling diode.Method for emergency operation of an electric drive system according to one of Claims 1 to 5, characterized in that the insulating DC / DC converter (8) is operated in a clocked manner in the event of a problem in the activation and / or in the event of an insulation fault in the high-voltage battery (3) or in a subsystem on the side of the main contactors (S_Mai_P, S_Mai_N) facing the high-voltage battery (3) or in the event of a triggered main fuse for transmitting power from the high-voltage battery (3) to the inverter (1).

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