Electric drive system and method for charging

Abstract

This invention relates to an electric drive system for a vehicle, comprising an electric motor (2) having three stator windings (L1, L2, L3), a high-voltage battery (3), and an inverter (1) for supplying power to the electric motor (2), wherein the inverter (1) has three half-bridges (HB1, HB2, HB3), each half-bridge being composed of two semiconductor switches (S1 to S6), and each stator winding (L1, L2, L3) being connected to the midpoint of these half-bridges, wherein a DC junction box (4) for charging the high-voltage battery (3) by means of a DC voltage and / or an AC junction box (5) for charging the high-voltage battery (3) by means of an AC voltage in at least a single phase, wherein in these half-bridges (HB1 to HB3) A diode (D1) or a semiconductor with diode function is arranged between the midpoint of one half-bridge of the inverter (1) and the contact of the AC junction box (5) and / or the DC junction box (4) in a manner polarized toward the reverse cutoff direction. A diode (D2) or a semiconductor with diode function is arranged between the midpoint of the other half-bridge of these half-bridges (HB1 to HB3) and the other contact of the AC junction box (5) and / or the DC junction box (4) in a manner polarized toward the reverse cutoff direction. A diode (D3, D4) or a semiconductor with diode function is arranged from the negative high voltage potential (HV-) of the inverter (1) to each of the two contacts of the AC junction box (5) and / or the DC junction box (4) in a manner polarized toward the forward conduction direction.

Description

[0001] The present invention relates to an electric drive system for a vehicle according to the preamble of claim 1, and a method for charging a high-voltage battery of the electric drive system according to the preamble of claim 7 or 8.

[0002] DE 10 2021 003 883 A1 describes an electric drive system for a vehicle, the electric drive system having - A switching device having: - First switching state, in which the charging interface is directly connected to the vehicle's energy storage device, thereby enabling the energy storage device to be charged using the input voltage applied to the charging interface. - Second and third switching states, in which the charging interface is connected to the energy storage device via the inverter, thereby enabling the energy storage device to be charged by relying on the inverter.

[0003] DE 10 2021 003 852 A1 describes an electric drive system for a vehicle, the electric drive system having - An electric three-camera system for driving vehicles. - An electrical energy storage device used to supply power to the electric three-phase detector during vehicle operation. - A converter for an electric three-phase machine, which is electrically coupled to an energy storage device, and - A vehicle-side charging interface for electrically coupling the energy storage device to an external charging unit, wherein... - The charging voltage of the vehicle-side charging interface can be converted by the converter into a supply voltage for charging the energy storage device.

[0004] An integrated structure comprising a converter, a charger, and motor windings is known from CN 215793 231 U, wherein the converter switches between a high-voltage battery and a motor with motor windings for motor operation. An AC voltage supply is connected to the output phase of the converter via a rectifier bridge through an interface, and to the high-voltage DC voltage phase of the converter via another interface, thereby connecting to the high-voltage battery.

[0005] The purpose of this invention is to provide a novel electric drive system for vehicles and a novel method for charging the high-voltage battery of the electric drive system.

[0006] According to the present invention, this objective is achieved 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 7 or 8.

[0007] Advantageous designs of the present invention are the subject of the dependent claims.

[0008] An electric drive system for a vehicle is proposed, comprising an electric motor with three stator windings for driving the vehicle, a high-voltage battery, and an inverter for converting the DC voltage of the high-voltage battery into an AC voltage for supplying power to the electric motor. The inverter has a B6 bridge consisting of three half-bridges, each composed of two semiconductor switches, with each stator winding connected to the midpoint of one of the half-bridges. A DC junction box for charging the high-voltage battery using DC voltage and / or an AC junction box for charging the high-voltage battery using AC voltage (at least in a single phase) are also provided. According to the invention, - A diode or a semiconductor with diode function is arranged between the midpoint of one of these half-bridges and the contacts of the AC junction box and / or DC junction box in a manner polarized toward the reverse cutoff direction. - A diode or a semiconductor with diode function is arranged between the midpoint of the other half of these half-bridges and another contact of the AC junction box and / or DC junction box in a manner polarized toward the reverse cutoff direction. - Each of the two contacts from the negative high voltage potential of the inverter to the AC junction box and / or DC junction box is respectively arranged with a diode or a semiconductor with diode function in a manner polarized in the forward conduction direction.

[0009] In one implementation, the semiconductor switch and / or the semiconductor with diode function is designed as a MOSFET or an IGBT with a freewheeling diode.

[0010] In one implementation, the inverter has an intermediate circuit capacitor.

[0011] In one embodiment, the inverter has a current measuring device for measuring alternating current between the midpoint of the half-bridge and the stator winding.

[0012] In one embodiment, to interrupt the voltage of two conductors (including a phase conductor and a neutral conductor) in an AC junction box, two relay contacts are arranged between the respective conductor and a diode connected to the respective conductor. Alternatively or additionally, to interrupt the voltage of two conductors (including a positive potential conductor and a negative potential conductor) in a DC junction box, two relay contacts are arranged between the respective conductor and a diode connected to the respective conductor.

[0013] In one embodiment, the relay contacts corresponding to the DC junction box and the relay contacts corresponding to the AC junction box are connected to each other in a pair, facing the inverter direction.

[0014] According to one aspect of the invention, a method is provided for charging the high-voltage battery of the described electric drive system at a DC charging station with boost capability, wherein the DC charging station is connected to a DC junction box. According to the invention, one of the half-bridges is arranged as a low-side switch with semiconductor switches pulse-controlled, and the half-bridge is connected to the DC junction box via one of the diodes.

[0015] According to another aspect of the invention, a method is provided for charging a high-voltage battery of the described electric drive system at an AC charging station, wherein the AC charging station is connected to an AC junction box. According to the invention, during the positive half-wave of the AC voltage fed from the AC charging station, a semiconductor switch of one half-bridge arranged as a low-side switch is pulse-controlled, the half-bridge being connected to the DC junction box via one of the diodes; wherein during the negative half-wave of the AC voltage fed from the AC charging station, a semiconductor switch of the other half-bridge arranged as a low-side switch is pulse-controlled, the other half-bridge being connected to the DC junction box via one of the diodes.

[0016] In one implementation, when the low-side switch is open, the semiconductor switch arranged as the high-side switch in the same half-bridge can be closed once current flows through its body diode or freewheeling diode.

[0017] In one implementation, the target current is adjusted by pulse control of a semiconductor switch.

[0018] The solution according to the invention eliminates the need for contactors to separate the star points of the electric motor. The boost function utilizes the main inductance of the stator windings of the electric motor. The electric motor and inverter can be used as a single-phase PFC. Furthermore, the electric motor and inverter can be used as a boost DC / DC converter, for example, from 400V to 800V. The solution according to the invention avoids battery short circuits (Chademo problem) that occur in the event of insulation failure in the vehicle and when the varistor is triggered in the charging station.

[0019] Embodiments of the present invention will now be explained in more detail with reference to the accompanying drawings.

[0020] in: Figure 1 A schematic view shows an inverter and wiring for operating electric motors, including DC and AC junction boxes. Figure 2 A schematic view showing the simplified wiring of the inverter is provided. Figure 3 A schematic view showing further simplified wiring of the inverter is provided. Figure 4 Showing according to Figure 2A schematic view of the simplified wiring of an inverter during charging at a DC charging station with boost capability. Figure 5 A schematic graph showing the simulated signals of the inverter charging at a DC charging station with boost capability is presented. Figure 6 A schematic graph showing the simulated signals of the inverter when an insulation fault occurs. Figure 7 Schematic graphs of other simulation signals for the inverter used to illustrate the potential distribution are shown. Figure 8 This diagram shows a schematic view of the inverter wiring during charging at an AC charging station in the positive half-wave. Figure 9 This diagram shows a schematic view of the inverter wiring during charging at an AC charging station in the negative half-wave. Figure 10 A schematic graph showing the simulated signals of the inverter charging at an AC charging station is displayed. Figure 11 A schematic graph showing the simulated signal of the inverter at the beginning of the positive half-wave during AC charging is presented, and Figure 12 A schematic graph showing the simulated signal of the inverter at the beginning of the negative half-wave during AC charging is presented.

[0021] Corresponding parts in all the accompanying figures are labeled with the same reference numerals.

[0022] Figure 1 This is a schematic view of an inverter 1 used to operate an electric motor 2, such as a drive unit for an electric vehicle, particularly a passenger car, commercial vehicle, or bus. The inverter 1 has a B6 bridge consisting of three half-bridges HB1, HB2, and HB3, each half-bridge consisting of two semiconductor switches S1 to S6, particularly MOSFETs or IGBTs with freewheeling diodes. Furthermore, the inverter 1 has an intermediate circuit capacitor C and a current measuring device A, specifically for measuring alternating current at the midpoint of the half-bridges HB1 to HB3. The electric motor 2 has three stator windings L1 to L3 connected to the midpoint of the half-bridges HB1 to HB3.

[0023] Inverter 1 is configured via corresponding wiring to charge the vehicle's high-voltage battery 3 using DC voltage via DC junction box 4 and single-phase AC voltage via AC junction box 5.

[0024] The wiring includes two relays or relay contacts L and N for interrupting the voltage of the two conductors in the AC junction box 5, specifically the phase conductor and the neutral conductor. Additionally, two relays or relay contacts EVSE_P and EVSE_N are arranged for interrupting the voltage of the two conductors in the DC junction box, specifically the positive potential conductor and the negative potential conductor. Facing the inverter 1, relay contacts L and N and relay contacts EVSE_P and EVSE_N are connected to each other in pairs; for example, relay contact L is connected to relay contact EVSE_P on one side, and relay contact N is connected to relay contact EVSE_N on the other side.

[0025] In addition, a diode D1 is arranged between the midpoint of one of the half-bridges HB1 to HB3 (e.g., the midpoint of half-bridge HB1) and a pair of interconnected relay contacts L, EVSE_P in a manner polarized toward the reverse cutoff direction.

[0026] In addition, a diode D2 is arranged between the midpoint of another half-bridge (e.g., the midpoint of half-bridge HB2) and another pair of interconnected relay contacts N, EVSE_N in a manner polarized toward the reverse cutoff direction.

[0027] In addition, diodes D3 and D4 are arranged in the positive conduction direction from the negative high voltage potential HV- of inverter 1 to each pair of interconnected relay contacts L, EVSE_P and N, EVSE_N.

[0028] Instead of diodes D1 to D4, alternative semiconductor components with diode functions can be used, such as MOSFETs with body diodes facing the corresponding diode direction, IGBTs with corresponding freewheeling diodes, etc.

[0029] In order to charge the high-voltage battery 3 of the pure electric vehicle at the DC charging station 6, the DC charging station provides a maximum output voltage (e.g., 500V), which is lower than the rated voltage of the high-voltage battery 3 (e.g., 800V). Various solutions are known in the prior art, such as battery switching, separate boost DC / DC converters, etc.

[0030] This invention proposes a solution in which, during DC charging, the DC charging station 6 is connected to the inverter 1 and the electric motor 2 via the DC junction box 4, relay contacts EVSE_P and EVSE_N, and at least one or more of diodes D1, D2, D3, and D4, such that the function of a current-coupled DC / DC converter can be represented by special control of at least one or more semiconductor switches S1 to S6. Since the current flowing through the stator windings L1 to L3 represents the actual operating point of the electric motor 2, the full stator inductance can be used in this case. Nevertheless, the electric motor 2 does not move.

[0031] In the event of an insulation failure in the vehicle, the direct consequence is an insulation overload at the opposite HV_N potential of the DC charging station 6. Here, a short circuit to the high-voltage battery 3 is generated via the protective varistor in the DC charging station 6. In the proposed architecture, the problem of a battery short circuit (thousands of amperes) is avoided by diode D4. Furthermore, it is important that in the event of such a double insulation failure, the semiconductor switches S1 to S6 in the inverter 1, each performing pulse-controlled operation, are no longer activated (closed). However, a short circuit to the DC charging station 6 may still occur.

[0032] Figure 2 This is a schematic view of the simplified wiring of inverter 1, without AC junction box 5. Figure 1 (as shown) and relay contacts L, N ( Figure 1 As shown in the diagram). Diode D4 is used to prevent insulation failure due to the positive high voltage potential HV+ in the vehicle to the potential balance PA, and thus due to the negative high voltage potential HV_N in the DC charging station 6. Figure 7 The high-voltage battery 3 is short-circuited due to an insulation failure to the potential balance PA (as shown in the diagram). The arrangement shown demonstrates the boost function during charging at the DC charging station 6.

[0033] Figure 3 This is a schematic view of the simplified wiring of inverter 1, without AC junction box 5. Figure 1 (as shown), relay contacts L, N ( Figure 1 (as shown) and diodes D1 to D3 ( Figure 1 (As shown in the diagram). Instead of connecting via diode D1, the relay contact EVSE_P is directly connected to the midpoint of half-bridge HB1. The arrangement shown is the minimum configuration for representing the boost function when charging at DC charging station 6.

[0034] Figure 4 It is based on Figure 2A simplified wiring diagram of inverter 1 during charging at DC charging station 6 with boost function. Here, semiconductor switch S4 is pulse-controlled, specifically the low-side switch of one of the half-bridges HB1 to HB3, particularly half-bridge HB2. When semiconductor switch S4 is closed, current I1 flows from DC charging station 6 through relay contact EVSE_P, diode D1, stator winding L1, and the star point of motor 2 (…). Figure 1 As shown), stator winding L2, semiconductor switch S4, diode D4 (as shown), stator winding L2, semiconductor switch S4, diode D4 Figure 1 As shown in the diagram, current I2 flows from the DC charging station 6 through the relay contact EVSE_P, diode D1, stator winding L1, the star point of the motor 2, stator winding L2, the body diode of the semiconductor switch S3, the high-voltage battery 3, diode D4, and relay contact EVSE_N back to the DC charging station 6.

[0035] from Figure 4 As can be seen, for the boost function, only two of the four diodes D1 to D4 are needed, namely diodes D1 and D4. For optimization at higher currents, they can also be replaced with MOSFETs. Compared to existing technologies, they offer the advantage of avoiding battery short circuits in the event of an insulation failure (Chademo problem).

[0036] Once the controlled semiconductor switch S4 is closed, the voltage of the DC charging station 6 is applied to the two stator windings L1 and L2. The current I1 flowing through the two stator windings L1 and L2 increases. During this stage, the high-voltage battery 3 is not charged. If the controlled semiconductor switch S4 is opened, the only possible freewheeling path for the current I2 already established in the stator windings L1 and L2 is through the body diode of the high-side switch located in the same half-bridge, in this case, the body diode of semiconductor switch S3. For loss optimization, semiconductor switch S3 can be closed once the current I2 flows. The resulting current path is through the high-voltage battery 3, thereby charging the high-voltage battery.

[0037] Figure 5 Inverter 1 with this wiring ( Figure 1 A schematic diagram of the simulation signal shown in the figure, wherein at a 400V DC charging station 6 ( Figure 1 The step-up function is indicated at (shown in the diagram). The target current is limited to 120A to 125A. The stator windings L1, L2, and L3 are shown in the following two diagrams. Figure 1 The current shown) and the current used to control the semiconductor switch S4 (as shown) Figure 1The control signal Gate_S4 (shown in the diagram) is activated. At time t=0.5s, an insulation fault occurs in the vehicle from the positive high voltage potential HV+ to the potential equilibrium PA. At time t=0.6s, the pulse operation of semiconductor switch S4 stops, and semiconductor switch S4 remains open. At time t=0.7s, an insulation fault occurs in the DC charging station 6 from the negative high voltage potential HV_N- (shown in the diagram). Figure 1 As shown in the diagram, a second insulation fault occurs when the potential balance PA is reached.

[0038] The parameters used for simulation are: Insulation resistance: 1 MOhm Inductance of stator windings L1, L2, and L3: 1000µF High-voltage battery 3 ( Figure 1 (as shown) and the internal resistor Ri_Batt of the DC charging station 6 Figure 1 (As shown): 0.1 Ohm Figure 5 The diagram shows the source voltage U_Q of the DC charging station 6, the control signal Gate_S4 used to control the semiconductor switch S4, and the positive high voltage potential HV+. Figure 1 The current I_HV+ and the negative high voltage potential HV- shown in the figure are: Figure 1 The current I_HV- (shown in the diagram), the current I_Q originating from the DC charging station 6, and the charging current I_L flowing into the high-voltage battery 6.

[0039] When semiconductor switch S4 is closed, the current in the two stator windings L1 and L2 increases. It can be seen that the current I_Q of the DC charging station 6 is numerically the same as the current in the stator windings L1 and L2. During this period, the high-voltage battery 3 is not charged (current I_L = 0). In this stage, the current rises until it reaches the target value of 125A. However, under normal circumstances, this still occurs through the large intermediate circuit capacitor C of inverter 1 (…). Figure 1 (As shown in the diagram). However, this capacitor is omitted here to better represent the function. Once the semiconductor switch S4 opens at 125A, the current I_Q of the DC charging station 6 flows through both the two stator windings L1 and L2, as well as the high-voltage battery 3. Here, the current I_Q decreases. Starting from a value below 120A, the semiconductor switch S4 closes again.

[0040] Figure 6 Inverter 1 with this wiring ( Figure 1 (As shown in the image) A schematic diagram of the simulated signal when an insulation fault occurs: Throughout the simulation's entire time window, the voltage is first increased from the positive high voltage potential HV+ in the vehicle. Figure 1As shown in the diagram, an insulation fault occurs at PA when the potential balance is reached (the insulation value is an ideal short circuit, i.e., 0 Ohm, at time t=0.5s). In this state, the circuit still functions fault-free; that is, inverter 1, operating as a boost converter, can set the target current, and thereby supply power to high-voltage battery 3 (…). Figure 1 (As shown) charging. There is no high-voltage battery 3 or DC charging station 6 (as shown). Figure 1 The short-circuit current of semiconductor switch S4 (as shown in the diagram) is set. Starting from time point t=0.6s, the short-circuit current of semiconductor switch S4 (as shown in the diagram) is set. Figure 1 The pulse control (shown in the diagram) is used. Once the pulse control of semiconductor switch S4 is set, the charging current I_L from DC charging station 6 to high-voltage battery 3 ends. There is still no short circuit.

[0041] Starting from time point t=0.7s, in DC charging station 6, from the negative high voltage potential HV_N ( Figure 7 (As shown) a second insulation fault occurs at the potential balance PA. No short-circuit current is formed at DC charging station 6, but a current is formed, albeit a very high one, due to the assumed value of 0.1 mOhm. In reality, this means that DC charging station 6 is set to the maximum current commanded by the vehicle, or that current corresponds to the maximum current of the charging station's power electronics (e.g., a possible value commanded by the vehicle is 150 A, or the maximum current of DC charging station 6 is 500 A).

[0042] Figure 7 Inverter 1 with this wiring ( Figure 1 (See the diagram) Schematic charts of other simulated signals used to illustrate the potential distribution.

[0043] In the simulation, data from 6 DC charging stations in the vehicle were collected. Figure 1 The high-voltage potentials HV_P and HV_N are shown in the diagram. This is particularly significant when considering insulation faults. The insulation remains intact until t=0.5s. It is assumed that the insulation resistance is uniformly distributed (1 MOhm each). This results in an approximately symmetrical high-voltage distribution within the vehicle: HV+ is 500V relative to PA, and HV- is 300V relative to PA. Since the boost function uses a current-coupled booster with common negative high-voltage potentials HV- and HV_N, the high-voltage distribution of HV- relative to PA in the vehicle is transmitted to the DC charging station 6 side. When using DC charging station 6, the negative high-voltage potential HV_P is reduced accordingly based on the booster value; that is, based on the 500V voltage of HV+ relative to PA in the vehicle and the 400V voltage boost through the booster, the voltage between HV_P and PA on the DC charging station 6 side is 100V.

[0044] Starting from the first insulation fault occurring in the vehicle at t=0.5s, the overall potential in the vehicle and DC charging station 6 drops by 500V. Once semiconductor switch S4 ( Figure 1 The pulse control shown in the diagram stops the high-voltage battery 3. Figure 1 The voltage difference between the DC charging station 6 (400V) and the DC charging station 8 (800V) shown in the diagram is determined by diode D4 (800V). Figure 1 As shown in the diagram, HV_N is now lower than the voltage of DC charging station 6 (-400V) relative to PA because HV_P is the same as PA.

[0045] Starting at t=0.7s, we now assume a second insulation fault occurs in DC charging station 6 from HV_N to PA. This insulation fault is also assumed to be an ideal short circuit of 0 Ohm. Therefore, on the DC charging station 6 side, we obtain a potential distribution of 0V for HV_P relative to PA, and simultaneously 0Ohm for HV_N relative to PA. However, this is only considered a theoretical distribution, because it can be assumed that although the insulation fault has a low ohmic value, it will never reach 0Ohm.

[0046] Figure 8 This is a schematic view of the wiring of inverter 1 when charging at AC charging station 7. For single-phase AC charging, a pair of diodes D1 and D3 are connected to the relay contact L for phase, and a second pair of diodes D2 and D4 are connected to the relay contact N for neutral. In the illustrated embodiment, the pair of diodes D1 and D3 corresponding to the first half-bridge HB1 are selected for the relay contact L for phase, and the pair of diodes D2 and D4 corresponding to the second half-bridge HB2 are selected for the relay contact N for neutral. In other embodiments, other variations may be chosen for the connection of relay contacts N and L with the diode pairs.

[0047] In the positive half-wave of the AC voltage fed by AC charging station 7, the circuit functions the same as the boost converter shown above. The target current is regulated via pulse control of semiconductor switch S4. This target current depends on the instantaneous value of the currently applied AC voltage. This regulation method corresponds to existing technology for regulating AC current for power factor correction (PFC). When semiconductor switch S4 is closed, current I1 flows from AC charging station 7 through relay contact L, diode D1, stator winding L1, and the star point of motor 2 (…). Figure 1As shown in the diagram, current I2 flows from the AC charging station 7 through the stator winding L2, semiconductor switch S4, diode D4, and relay contact N back to the AC charging station 7. When semiconductor switch S4 is open, current I2 flows from the AC charging station 7 through the relay contact L, diode D1, stator winding L1, the star point of motor 2, stator winding L2, the body diode of semiconductor switch S3, high-voltage battery 3, diode D4, and relay contact N back to the AC charging station 7.

[0048] Figure 9 This is a schematic view of the wiring of inverter 1 during charging at AC charging station 7, during the negative half-wave of the AC voltage fed in through AC charging station 7. In the negative half-wave of the AC voltage, the current flow is opposite to that in the positive half-wave. Correspondingly, the low-side switch of the other half-bridge HB1 of module B6 must also be pulsed, for example, semiconductor switch S2, to regulate the current to the target value. The freewheeling current of the inductor is achieved via the body diode of the high-side switch (e.g., semiconductor switch S1) arranged above this half-bridge HB1. When semiconductor switch S2 is closed, current I1 flows from AC charging station 7 through relay contact N, diode D2, stator winding L2, and the star point of motor 2 (…). Figure 1 As shown in the diagram, current I2 flows from the AC charging station 7 through the stator winding L1, semiconductor switch S2, diode D3, and relay contact L. When semiconductor switch S2 is open, current I2 flows from the AC charging station 7 through relay contact N, diode D2, stator winding L2, the star point of motor 2, stator winding L1, the body diode of semiconductor switch S1, high-voltage battery 3, diode D3, and relay contact L back to the AC charging station 7.

[0049] Figure 10 Inverter 1 with this wiring ( Figure 1 A schematic diagram of the simulation signal shown in the figure, wherein at AC charging station 7 ( Figure 1 (As shown in the diagram) indicates the AC charging function. The instantaneous value of the AC voltage U_Q fed from the AC charging station 7 is determined via voltage measurement. Subsequently, according to the symbols, the correct semiconductor switches S2 and S4 are controlled such that the correct current is set for each half-wave. The target current is, for example, 16A, and this target current should be set at the peak of the voltage half-wave.

[0050] The diagram shows the source voltage U_Q of AC charging station 7, and the semiconductor switches S2 and S4 ( Figure 1 The control signals Gate_S2, Gate_S4, and stator winding L1 (as shown in the diagram) Figure 1 The current I_L1 in the stator winding L2 (as shown) Figure 1 The current I_L2 in the diagram, the current I_Q flowing out of the AC charging station 7, and the current from the high-voltage battery 3 (shown in the diagram) Figure 1The charging current I_L (shown in the diagram). The task of the PFC function of inverter 1 is to set a current proportional to the voltage curve and with a peak value of 16A for each of the two half-waves. The target current is set by comparing it with a proportionally reduced voltage measurement. In this case, a tolerance of + / - 1A is specified for the maximum deviation from the target current. That is, once the current is lower than the target value of 1A in the positive half-wave, the corresponding semiconductor switch S4 is turned on to increase the current I_L1, I_L2 through the stator windings L1, L2. If the current value is higher than the target value of 1A, the semiconductor switch S4 is turned off again. In this case, the current I_L1, I_L2 through the stator windings L1, L2 is freewheeled through the high-voltage battery 3, thereby charging the high-voltage battery.

[0051] During the negative half-wave, the switching occurs with the opposite sign: once the current falls below the (negative) target current of 1A, semiconductor switch S2 opens. Once the current rises above the target current of 1A, semiconductor switch S2 closes again.

[0052] Figure 11 Inverter 1 with this wiring ( Figure 1 (See diagram) A schematic graph of the simulated signal at the start of the positive half-wave during AC charging.

[0053] Figure 12 Inverter 1 with this wiring ( Figure 1 (See diagram) A schematic graph of the simulated signal at the start of the negative half-wave during AC charging.

[0054] If the negative high voltage potential HV- is observed during simulation ( Figure 1 As shown in the diagram, the voltage between the high-voltage potential HV- and the potential balance PA is such that the negative high-voltage potential HV- is in phase with the source voltage U_Q during the negative half-wave. In other words, during the negative half-wave, the vehicle's high-voltage potentials HV+ and HV- (shown in the diagram) are in phase. Figure 1 As shown in the diagram, PA=N=PE (ground wire) moves in a sinusoidal half-wave relative to the potential balance. This is also a typical behavior of PFC. In the case of a large Y capacitance between HV+ or HV- and PA, this will result in leakage current, which may trigger the FI switch of the home electrical system (compensation current flows through the ground wire PE).

[0055] To remedy this, one can 1. Place a small Y capacitor in the PFC region, and then provide current isolation via an isolated DC / DC converter, or 2. Feed compensation current into the ground wire PE.

[0056] Regarding point 1: In 800V vehicles, constrained by the C1 characteristic curve, the Y capacitor in the vehicle must be kept lower than in 400V vehicles. This is converted to inverter 1 (including motor 2) Figure 1 The Y (capacitor) shown in the figure Figure 1 As shown in the image, this means: For a 400V inverter, approximately 500nF of Y capacitors should be installed at each high-voltage potential HV+ and HV-.

[0057] For an 800V inverter, approximately 50nF to 80nF of Y capacitors should be installed at each high-voltage potential HV+ and HV-.

[0058] It is clear that the leakage current is significantly lower in 800V vehicles.

[0059] List of reference numerals 1 Inverter 2 Electric machines 3. High-voltage battery 4 DC junction box 5 AC junction box 6 DC charging stations 7 AC charging stations A current measuring device C. Intermediate circuit capacitor Diodes D1 to D4 EVSE_N Relay Contact EVSE_P Relay Contacts Gate_S2 and Gate_S4 control signals HB1 to HB3 half-bridge HV+, HV_P high voltage potential, positive high voltage potential HV-, HV_N high voltage potential, negative high voltage potential I1, I2, I_HV+, I_HV-, I_Q, I_L1, I_L2 current I_L charging current L Relay Contacts L1 to L3 stator windings N Relay Contact S1 to S6 semiconductor switches Ri_Batt internal resistance U_Q source voltage

Claims

1. An electric drive system for a vehicle, the electric drive system comprising an electric motor (2) for driving the vehicle and having three stator windings (L1, L2, L3), a high-voltage battery (3), and an inverter (1) for converting the DC voltage of the high-voltage battery (3) into an AC voltage for supplying power to the electric motor (2), wherein, The inverter (1) has a B6 bridge consisting of three half-bridges (HB1, HB2, HB3), each of which is composed of two semiconductor switches (S1 to S6). Each stator winding in the stator windings (L1, L2, L3) is connected to the midpoint of the half-bridge. A DC junction box (4) for charging the high-voltage battery (3) with DC voltage and / or an AC junction box (5) for charging the high-voltage battery (3) with AC voltage in at least a single phase are also provided. Its features are, - A diode (D1) or a semiconductor having diode function is arranged between the midpoint of one of the half-bridges (HB1 to HB3) and the contact of the AC junction box (5) and / or the DC junction box (4) in a manner polarized toward the reverse cutoff direction. - A diode (D2) or a semiconductor having diode function is arranged between the midpoint of the other half of the half-bridge (HB1 to HB3) and another contact of the AC junction box (5) and / or the DC junction box (4) in a manner polarized toward the reverse cutoff direction. - From the negative high voltage potential (HV-) of the inverter (1) to each of the two contacts of the AC junction box (5) and / or the DC junction box (4), diodes (D3, D4) or semiconductors with diode functions are respectively arranged in a manner polarized in the forward conduction direction.

2. The electric drive system according to claim 1, characterized in that, The semiconductor switches (S1 to S6) and / or the semiconductors with diode functions are designed as MOSFETs or IGBTs with freewheeling diodes.

3. The electric drive system according to claim 1 or 2, characterized in that, The inverter (1) has an intermediate circuit capacitor (C).

4. The electric drive system according to claim 1 or 2, characterized in that, The inverter (1) has a current measuring device (A) for measuring alternating current between the midpoint of the half-bridge (HB1 to HB3) and the stator windings (L1, L2, L3).

5. The electric drive system according to any one of the preceding claims, characterized in that, In order to cut off the voltage of the two wires including the phase wire and the neutral wire of the AC junction box (5), two relay contacts (L, N) are arranged between the corresponding wire and the diode (D1 to D4) connected to the corresponding wire, and / or in order to cut off the voltage of the two wires including the positive potential wire and the negative potential wire of the DC junction box (4), two relay contacts (EVSE_P, EVSE_N) are arranged between the corresponding wire and the diode (D1 to D4) connected to the corresponding wire.

6. The electric drive system according to claim 5, characterized in that, The relay contacts (L, N) corresponding to the DC junction box (4) and the relay contacts (EVSE_P, EVSE_N) corresponding to the AC junction box (5) are connected to each other in a pair towards the inverter (1).

7. A method for charging the high-voltage battery (3) of an electric drive system according to any one of the preceding claims at a DC charging station (6) having a boost function, wherein the DC charging station (6) is connected to the DC junction box (4), characterized in that, One of the half-bridges (HB1, HB2, HB3) is arranged as a low-side switching semiconductor switch (S2, S4, S6) that is pulse-controlled, and the half-bridge is connected to the DC junction box (4) via one of the diodes (D1, D2).

8. A method for charging the high-voltage battery (3) of an electric drive system according to any one of claims 1 to 6 at an AC charging station (7), wherein the AC charging station (7) is connected to the AC junction box (5), characterized in that, During the positive half-wave of the AC voltage fed by the AC charging station (7), a semiconductor switch (S2, S4, S6) of one half-bridge (HB1, HB2, HB3) arranged as a low-side switch is pulse-controlled, and the half-bridge is connected to the DC junction box (4) via one of the diodes (D1, D2). During the negative half-wave of the AC voltage fed by the AC charging station (7), a semiconductor switch (S2, S4, S6) of the other half-bridge (HB1, HB2, HB3) arranged as a low-side switch is pulse-controlled, and the other half-bridge is connected to the DC junction box (4) via one of the diodes (D1, D2).

9. The method according to claim 7 or 8, characterized in that, When the low-side switch is open, the semiconductor switches (S1, S3, S5) arranged as high-side switches in the same half-bridge (HB1, HB2, HB3) close once current flows through their body diodes or freewheeling diodes.

10. The method according to any one of claims 7 to 9, characterized in that, The target current is adjusted by pulse control of the semiconductor switches (S1 to S6).

Images