Electric drive system and charging method
Patent Information
- Application Number
- EP2025703077
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2024-02-01
- Filing Date
- 2025-01-30
- Publication Date
- 2025-12-03
AI Technical Summary
Existing electric drive systems for vehicles face challenges in efficiently charging high-voltage batteries without the need for contactors to isolate the star point of the electric machine, and are prone to battery short circuits due to insulation faults and varistor trips during charging.
An electric drive system with an inverter comprising a B6 bridge of half-bridges, diodes, and semiconductor switches, which utilizes the stator windings' inductance for boost function and current regulation, eliminating the need for contactors and preventing battery short circuits through controlled semiconductor switch operation.
The system enables efficient charging with single-phase power factor correction and boost DC/DC conversion, preventing battery short circuits and insulation faults, and optimizing energy transfer during both DC and AC charging.
Smart Images
Figure EP2025052438_07082025_PF_FP_ABST
Abstract
Description
[0001] Electric drive system and charging method
[0002] 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 7 or 8.
[0003] DE 10 2021 003 883 A1 describes an electric drive system for a vehicle, with
[0004] - a switching device which comprises:
[0005] - a first switching state in which a charging connection is directly connected to an electrical energy storage device of the vehicle, so that the electrical energy storage device can be charged with an input voltage applied to the charging connection,
[0006] - a second and third switching state in which the charging connection is connected to the electrical energy storage device via an inverter, so that the electrical energy storage device can be charged depending on the inverter.
[0007] DE 102021 003 852 A1 describes an electric drive system for a vehicle, with
[0008] - an electric three-phase machine to drive the vehicle,
[0009] - an electrical energy storage device for supplying the three-phase electric machine during ferry operation of the vehicle,
[0010] - an inverter of the three-phase electric machine, which is electrically coupled to the electrical energy storage device, and
[0011] - a vehicle-side charging connection for electrically coupling the electrical energy storage device with a vehicle-external charging unit, wherein
[0012] - depending on the inverter, a charging voltage of the vehicle-side charging connection can be converted into a supply voltage for charging the electrical energy storage device.
[0013] CN 215793231 U discloses an integrated structure comprising an inverter, a charger, and a motor winding. The inverter is connected between a high-voltage battery and a motor with the motor winding for its operation. An AC power supply is connected via a rectifier bridge through one terminal to an output phase of the inverter and through another terminal to an HV DC voltage phase of the inverter and thus to the HV battery.
[0014] The invention is based on the object of providing a novel electric drive system for a vehicle and a novel method for charging a high-voltage battery of the electric drive system.
[0015] 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 7 or 8.
[0016] Advantageous embodiments of the invention are the subject of the subclaims.
[0017] An electric drive system for a vehicle is proposed, comprising an electric machine with three stator windings for driving the vehicle, a high-voltage battery, and an inverter for converting a direct voltage of the high-voltage battery into an alternating voltage for supplying the electric machine. The inverter comprises a B6 bridge consisting of three half-bridges, each formed from two semiconductor switches, to whose center taps one of the stator windings is connected. Furthermore, a DC connection box for charging the high-voltage battery using a direct voltage and / or an AC connection box for at least single-phase charging of the high-voltage battery using an alternating voltage is provided. According to the invention,
[0018] - a diode or a semiconductor with diode function is arranged between the center tap of one of the half-bridges and a contact of the AC junction box and / or the DC junction box, polarized in the reverse direction,
[0019] - a diode or a semiconductor with diode function is arranged between the center tap of another of the half-bridges and another contact of the AC junction box and / or the DC junction box, polarized in the reverse direction,
[0020] - One diode or one semiconductor with diode function is arranged, forward-biased, from a negative high-voltage potential of the inverter to each of the two contacts of the AC junction box and / or the DC junction box. In one embodiment, the semiconductor switches and / or the semiconductors with diode function are designed as MOSFETs or IGBTs with a freewheeling diode.
[0021] In one embodiment, the inverter has an intermediate circuit capacitor.
[0022] In one embodiment, the inverter has current measuring devices for measuring the alternating current between the center taps of the half-bridges and the stator windings.
[0023] In one embodiment, two relay contacts are arranged between the respective conductor and the connected diodes to de-energize two conductors, including a phase conductor and a neutral conductor, of the AC junction box. Alternatively or additionally, two relay contacts are arranged between the respective conductor and the connected diodes to de-energize two conductors, including a positive potential conductor and a negative potential conductor, of the DC junction box.
[0024] In one embodiment, in the direction of the inverter, one relay contact assigned to the DC connection box and one relay contact assigned to the AC connection box are connected to each other to form a pair.
[0025] According to one aspect of the present invention, a method for charging the high-voltage battery of the described electric drive system at a DC charging station with a boost function is proposed, wherein the DC charging station is connected to the DC junction 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 DC junction box via one of the diodes, is controlled in a clocked manner.
[0026] According to a further aspect of the present invention, a method for charging the high-voltage battery of the described electric drive system at an AC charging station is proposed, wherein the AC charging station is connected to the AC junction box. According to the invention, during a positive half-wave of an alternating voltage fed in by the AC charging station, a semiconductor switch arranged as a low-side switch of one of the half-bridges, which is connected to the DC junction box via one of the diodes, is controlled in a clocking manner, wherein during a negative half-wave of the alternating voltage fed in by the AC charging station, a semiconductor switch arranged as a low-side switch of another of the half-bridges, which is connected to the DC junction box via one of the diodes, is controlled in a clocking manner.In one embodiment, when the low-side switch is open, the semiconductor switch of the same half-bridge arranged as a high-side switch can be closed as soon as a current flows through its body diode or freewheeling diode.
[0027] In one embodiment, a target current is regulated by timing the semiconductor switches.
[0028] The inventive solution eliminates the need for contactors to isolate the star point of the electric machine. The boost function utilizes the main inductances of the electric machine's stator windings. The electric machine and inverter can be used as a single-phase power factor correction (PFC). Furthermore, the electric machine and inverter can be used as a boost DC / DC converter, for example, from 400 V to 800 V. The inventive solution prevents battery short circuits in the event of an insulation fault in the vehicle and in the event of a varistor trip in the charging station (Chademo problem).
[0029] Embodiments of the invention are explained in more detail below with reference to drawings.
[0030] Showing:
[0031] Fig. 1 is a schematic view of an inverter for operating an electrical machine with a circuit including a DC connection box and an AC connection box,
[0032] Fig. 2 is a schematic view of a simplified circuit of the inverter,
[0033] Fig. 3 is a schematic view of a further simplified circuit of the
[0034] Inverters,
[0035] Fig. 4 is a schematic view of the simplified circuitry of the inverter according to Figure 2 when charging at a DC charging station with boost function,
[0036] Fig. 5 is a schematic diagram with signals from a simulation of the inverter when charging at a DC charging station with boost function, Fig. 6 is a schematic diagram with signals from the simulation of the inverter when insulation faults occur,
[0037] Fig. 7 is a schematic diagram with further signals of the simulation of the inverter to illustrate a potential distribution,
[0038] Fig. 8 is a schematic view of the inverter circuitry when charging at an AC charging station during a positive half-wave,
[0039] Fig. 9 is a schematic view of the inverter circuitry when charging at the AC charging station during a negative half-wave,
[0040] Fig. 10 is a schematic diagram showing signals from a simulation of the inverter during charging at the AC charging station,
[0041] Fig. 11 is a schematic diagram showing signals from the simulation of the inverter during AC charging at the beginning of the positive half-wave, and
[0042] Fig. 12 is a schematic diagram showing signals from the simulation of the inverter during AC charging at the beginning of the negative half-wave.
[0043] Corresponding parts are provided with the same reference numerals in all figures.
[0044] Figure 1 is a schematic view of an inverter 1 for operating an electrical machine 2, for example a drive motor of an electrically powered vehicle, in particular a passenger car, a commercial vehicle or a bus. The inverter 1 has a B6 bridge consisting of three half-bridges HB1, HB2, HB3, each formed from two semiconductor switches S1 to S6, in particular MOSFET or IGBT with a freewheeling diode. The inverter 1 also has an intermediate circuit capacitor C and current measuring devices A, in particular for measuring alternating current, at the center taps of the half-bridges HB1 to HB3. The electrical machine 2 has three stator windings L1 to L3, which are connected to the center taps of the half-bridges HB1 to HB3.
[0045] The inverter 1 is configured by means of appropriate wiring to be used when charging a high-voltage battery 3 of the vehicle by means of direct voltage via a DC connection box 4 and by means of a single-phase alternating voltage via an AC connection box 5.
[0046] The circuit comprises two relays or relay contacts L, N for the voltage isolation of two conductors, in particular a phase conductor and a neutral conductor, of the AC connection box 5. Furthermore, two relays or
[0047] Relay contacts EVSE_P, EVSE_N are arranged to de-energize two conductors, specifically a positive potential conductor and a negative potential conductor, of the DC junction box. Toward inverter 1, one relay contact L, one relay contact N and one relay contact EVSE_P, one relay contact EVSE_N are connected to each other in a pair, for example, relay contact L is connected to relay contact EVSE_P, and relay contact N is connected to relay contact EVSE_N.
[0048] Furthermore, a diode D1 is arranged between the center tap of one of the half-bridges HB1 to HB3, for example the half-bridge HB1, and a pair of the interconnected relay contacts L, EVSE_P polarized in the reverse direction.
[0049] Furthermore, a diode D2 is arranged between the center tap of another of the half-bridges HB1 to HB3, for example the half-bridge HB2, and the other pair of interconnected relay contacts N, EVSE_N, polarized in the reverse direction.
[0050] Furthermore, a diode D3, D4 is arranged in the forward direction from a negative high-voltage potential HV- of the inverter 1 to each pair of the interconnected relay contacts L, EVSE_P and N, EVSE_N.
[0051] Instead of the diodes D1 to D4, an alternative semiconductor component with diode function can also be used, for example a MOSFET with a body diode in the direction of the respective diode, an IGBT with a corresponding freewheeling diode, etc.
[0052] 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 nominal voltage (for example 800 V) of the high-voltage battery 3, various solutions are known in the prior art, for example a switching battery, a separate boost DC / DC converter, etc.
[0053] 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 DC junction box 4, the relay contacts EVSE_P, EVSE_N and at least one or more of the diodes D1, D2, D3, D4 in such a way that the function of a galvanically coupled DC / DC converter can be represented only by means of a special control of at least one or more of the semiconductor switches S1 to S6. Since the current flow through the stator windings L1 to L3 represents a realistic operating point of the electric machine 2, the entire stator inductance can be used here. The electric machine 2 nevertheless does not move.
[0054] In the event of an insulation fault in the vehicle, this can directly result in an insulation overload in the opposite HV_N potential of the DC charging station 6. Protective varistors in the DC charging station 6 cause a short circuit in the high-voltage battery 3. The problem of battery short circuits (several thousand amperes) is avoided in the proposed architecture by the diode D4. Furthermore, it is important that the respective clocked
[0055] Semiconductor switches S1 to S6 in inverter 1 are no longer activated (switched on) in the event of this double insulation fault. However, a short circuit in DC charging station 6 may remain.
[0056] Figure 2 is a schematic view of a simplified circuit of inverter 1 without the AC junction box 5 (shown in Figure 1) and the relay contacts L, N (shown in Figure 1). Diode D4 serves to prevent a short circuit of the high-voltage battery 3 as a result of an insulation fault between the positive high-voltage potential HV+ and a potential equalization PA in the vehicle and, as a result, an insulation fault between a negative high-voltage potential HV_N (shown in Figure 7) and the potential equalization PA in the DC charging station 6. With the arrangement shown, the boost function can be implemented when charging at a DC charging station 6.
[0057] Figure 3 is a schematic view of a simplified circuit of inverter 1 without the AC junction box 5 (shown in Figure 1), the relay contacts L, N (shown in Figure 1), and the diodes D1 to D3 (shown in Figure 1). Instead of via diode D1, the relay contact EVSE_P is connected directly to the center tap of the half-bridge HB1. The arrangement shown is the minimum configuration for implementing the boost function when charging at a DC charging station 6.
[0058] Figure 4 is a schematic view of the simplified circuitry of inverter 1 according to Figure 2 during charging at DC charging station 6 with boost function. The semiconductor switch S4, i.e., the low-side switch of one of the half-bridges HB1 to HB3, in particular the half-bridge HB2, is controlled in a clocked manner. When semiconductor switch S4 is closed, a current I1 flows from DC charging station 6 via relay contact EVSE_P, diode D1, stator winding L1, the star point of electric machine 2 (shown in Figure 1), stator winding L2, semiconductor switch S4, diode D4 (shown in Figure 1), and relay contact EVSE_N back to DC charging station 6.When the semiconductor switch S4 is open, a current I2 flows from the DC charging station 6 via the relay contact EVSE_P, the diode D1, the stator winding L1, the star point of the electric machine 2, the stator winding L2, the body diode of the semiconductor switch S3, the high-voltage battery 3, the diode D4 and the relay contact EVSE_N back to the DC charging station 6.
[0059] Figure 4 shows that only two of the four diodes D1 to D4, namely D1 and D4, are required for the boost function. They can also be replaced by MOSFETs for optimization at higher currents. Unlike the state of the art, they offer the advantage of preventing a battery short circuit in the event of an insulation fault (Chademo problem).
[0060] As soon as the controlled semiconductor switch S4 is closed, the two stator windings L1 and L2 are supplied with the voltage of the DC charging station 6. The current I1 through the two stator windings L1 and L2 increases. During this phase, 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 impressed in the stator windings L1 and L2 is via the body diode of the high-side switch located in the same half-bridge, in this case the semiconductor switch S3. To optimize losses, this semiconductor switch S3 can be closed as soon as the current I2 flows. The resulting current path leads via the high-voltage battery 3, so that it is charged.
[0061] Figure 5 is a schematic diagram with signals from a simulation of inverter 1 (shown in Figure 1) with the circuitry, whereby the boost function was represented at a DC charging station 6 (shown in Figure 1) with 400 V. A target current was specified within the limits of 120 A to 125 A. The following two diagrams show the currents of the stator windings L1, L2, L3 (shown in Figure 1) and a control signal Gate_S4 for controlling the semiconductor switch S4 (shown in Figure 1). At a time t = 0.5 s, an insulation fault occurs in the vehicle from the positive high-voltage potential HV+ to the equipotential bonding PA. At a time t = 0.6 s, the clock operation of the semiconductor switch S4 is stopped and the semiconductor switch S4 remains open. At a time t = 0.7 s, a second insulation fault occurs in the DC charging station 6 from the negative high-voltage potential HV_N- (shown in Figure 1) to the potential equalization PA.
[0062] The following parameters were used for the simulation: Insulation resistance: 1 MOhm Inductance of the stator windings L1, L2, L3: 1000 pF Internal resistance Ri_Batt (shown in Figure 1) of the high-voltage battery 3 (shown in Figure 1) and the DC charging station 6: 0.1 Ohm
[0063] Figure 5 shows a source voltage U_Q of the DC charging station 6, the control signal Gate_S4 for controlling the semiconductor switch S4, a current l_HV+ in the positive high-voltage potential HV+ (shown in Figure 1), a current l_HV- (shown in Figure 1) in the negative high-voltage potential HV-, a current l_Q from the DC charging station 6 and a charging current l_L flowing into the high-voltage battery 6.
[0064] When the semiconductor switch S4 is closed, the current in the two stator windings L1, L2 increases. It can be seen that the current l_Q of the DC charging station 6 is identical to the current in the stator windings L1, L2. During this time, the high-voltage battery 3 is not charged (current l_L = 0). The current increases during this phase until it reaches the setpoint of 125 A. Normally, however, this would still be ensured by the large intermediate circuit capacitor C (shown in Figure 1) of the inverter 1. However, it has been omitted here to better illustrate the function. As soon as the semiconductor switch S4 is opened when 125 A is reached, the current l_Q of the DC charging station 6 flows through both stator windings L1, L2 and through the high-voltage battery 3. The current l_Q weakens in the process. When the value falls below 120 A, the semiconductor switch S4 is closed again.
[0065] Figure 6 is a schematic diagram with signals from the simulation of inverter 1 (shown in Figure 1) with the circuitry when insulation faults occur: Over the entire time window of the simulation, an insulation fault initially occurs in the vehicle from the positive high-voltage potential HV+ (shown in Figure 1) to the equipotential bonding PA (insulation value is an ideal short circuit, i.e. 0 ohms, time t = 0.5 s). In this state, the circuit still functions correctly, i.e., inverter 1, which operates as a booster, can set the target current and thus charge the high-voltage battery 3 (shown in Figure 1). There are no short-circuit currents in the high-voltage battery 3 or the DC charging station 6 (shown in Figure 1). From time t = 0.6 s, the timing of the semiconductor switch S4 (shown in Figure 1) is stopped. As soon as the timing of the semiconductor switch S4 is stopped, the charging current l_L from the DC charging station 6 to the high-voltage battery 3 ends.There are still no short circuits.
[0066] Starting at time t = 0.7 s, the second insulation fault occurs, from the negative high-voltage potential HV_N (shown in Figure 7) to the equipotential bonding PA in DC charging station 6. No short-circuit current is generated in DC charging station 6, but a current is generated, which is very high here due to the relatively low assumed value of 0.1 mOhm. In reality, this would mean that DC charging station 6 is set to the maximum current commanded by the vehicle, or that the current corresponds to the maximum current of its power electronics (for example, a possible value when commanded by the vehicle is 150 A, or 500 A at the maximum current of DC charging station 6).
[0067] Figure 7 is a schematic diagram with further signals of the simulation of inverter 1 (shown in Figure 1) with the circuitry to illustrate the potential distribution.
[0068] In the simulation, the high-voltage potentials HV_P, HV_N of DC charging station 6 (shown in Figure 1) were recorded in the vehicle. This is particularly interesting when considering insulation faults. Before t = 0.5 s, the insulation is still intact. A uniform distribution of the insulation resistances is assumed (1 MOhm each). This leads to an almost symmetrical high-voltage distribution in the vehicle (500 V HV+ to PA and 300 V HV- to PA). The high-voltage distribution from HV- to PA of the vehicle is transferred to the DC charging station 6 side, since the booster function is a galvanically coupled booster with a shared negative high-voltage potential HV-, HV_N.The negative high-voltage potential HV_P is reduced by the value of the booster at DC charging station 6, i.e., starting from a voltage from HV+ to PA of 500 V in the vehicle and a voltage increase of 400 V by the booster, the voltage between HV_P and PA on the DC charging station 6 side is 100 V.
[0069] From the occurrence of the first insulation fault in the vehicle at t=0.5 s, the potentials in both the vehicle and the DC charging station 6 shift downward by 500 V. As soon as the switching of semiconductor switch S4 (shown in Figure 1) is stopped, the voltage difference between the high-voltage battery 3 (shown in Figure 1) (800 V) and the DC charging station 6 (400 V) drops across diode D4 (shown in Figure 1). Since HV_P is identical to PA, HV_N is now below PA (-400 V) by the amount of the voltage of the DC charging station 6.
[0070] Starting at t=0.7s, a second insulation fault is assumed in DC charging station 6, from HV_N to PA. This insulation fault is also assumed to be an ideal short circuit with 0 ohms. This results in a potential distribution of 0 V from HV_P to PA and, at the same time, 0 ohms from HV_N to PA on the DC charging station 6 side. However, this should only be considered a theoretical distribution, since it can be assumed that an insulation fault, although low-resistance, will never reach 0 ohms.
[0071] Figure 8 is a schematic view of the wiring of inverter 1 when charging at an AC charging station 7. In order to enable single-phase AC charging, a pair of diodes D1, D3 is to be connected to relay contact L for the phase conductor and the second pair of diodes D2, D4 is to be connected to relay contact N for the neutral conductor. In the embodiment shown, the pair of diodes D1, D3 assigned to the first half-bridge HB1 was selected for relay contact L for the phase conductor and the pair of diodes D2, D4 assigned to the second half-bridge HB2 was selected for relay contact N for the neutral conductor. In other embodiments, other variants for connecting relay contacts N and L to the diode pairs can also be selected.
[0072] In the positive half-wave of the alternating voltage supplied by the AC charging station 7, the circuit functions identically to the booster function shown above. The timing of the semiconductor switch S4 regulates the current to a target current. This target current depends on the current instantaneous value of the alternating voltage. Such control methods correspond to the state of the art for regulating alternating currents using power factor correction (PFC). When the semiconductor switch S4 is closed, a current I1 flows from the AC charging station 7 via the relay contact L, the diode D1, the stator winding L1, the star point of the electric machine 2 (shown in Figure 1), the stator winding L2, the semiconductor switch S4, the diode D4, and the relay contact N back to the AC charging station 7.When the semiconductor switch S4 is open, a current I2 flows from the AC charging station 7 via the relay contact L, the diode D1, the stator winding L1, the star point of the electric machine 2, the stator winding L2, the body diode of the semiconductor switch S3, the high-voltage battery 3, the diode D4 and the relay contact N back to the AC charging station 7.
[0073] Figure 9 is a schematic view of the circuitry of inverter 1 when charging at an AC charging station 7 during the negative half-wave of the AC voltage supplied by the AC charging station 7. In the negative half-wave of the AC voltage, the current flow is reversed compared to the positive half-wave. Accordingly, a low-side switch, for example, semiconductor switch S2 of another half-bridge HB1 of the B6 module, must also be operated in a pulsed manner to regulate the current to the setpoint. The inductor current is freewheeled via the body diode of the high-side switch arranged above it, for example, semiconductor switch S1, of this half-bridge HB1.When the semiconductor switch S2 is closed, a current I1 flows from the AC charging station 7 via the relay contact N, the diode D2, the stator winding L2, the star point of the electrical machine 2 (shown in Figure 1), the stator winding L1, the semiconductor switch S2, the diode D3 and the relay contact L back to the AC charging station 7. When the semiconductor switch S2 is open, a current I2 flows from the AC charging station 7 via the relay contact N, the diode D2, the stator winding L2, the star point of the electrical machine 2, the stator winding L1, the body diode of the semiconductor switch S1, the high-voltage battery 3, the diode D3 and the relay contact L back to the AC charging station 7.
[0074] Figure 10 is a schematic diagram with signals from a simulation of inverter 1 (shown in Figure 1) with the circuitry, where the AC charging function was represented at an AC charging station 7 (shown in Figure 1). The instantaneous value of the alternating voltage U_Q fed in by the AC charging station 7 is determined via a voltage measurement. Depending on the sign, the appropriate semiconductor switch S2, S4 is then controlled so that the correct current is set for each half-wave. The target current, for example, is 16 A, which should be set at the peak value of the voltage half-wave.
[0075] 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 Figure 1), the current l_L1 in the stator winding L1 (shown in Figure 1), the current l_L2 in the stator winding L2 (shown in Figure 1), the current l_Q flowing from the AC charging station 7, and the charging current l_L of the high-voltage battery 3 (shown in Figure 1). The task of the PFC function of inverter 1 is to set a current for both half-waves that is proportional to the voltage curve and whose peak value is 16 A. The target current is set by comparison with a proportionally reduced value of the voltage measurement.A tolerance of, for example, + / - 1 A is specified as the maximum deviation from the target current. This means that as soon as the current in the positive half-wave falls below the target by 1 A, the corresponding semiconductor switch S4 is switched on to increase the current l_L1, l_L2 through the stator windings L1, L2. If the current value is 1 A above the target value, the semiconductor switch S4 is opened again. In this case, the current l_L1, l_L2 freewheels through the stator windings L1, L2 via the high-voltage battery 3, thus charging it.
[0076] In the negative half-wave, switching occurs with the opposite sign, meaning that as soon as the current is 1 A below the (negative) target current, semiconductor switch S2 opens. As soon as the current is 1 A above the target current, semiconductor switch S2 closes again.
[0077] Figure 11 is a schematic diagram with signals from the simulation of inverter 1 (shown in Figure 1) with the circuitry during AC charging at the beginning of the positive half-cycle.
[0078] Figure 12 is a schematic diagram with signals from the simulation of inverter 1 (shown in Figure 1) with the circuitry during AC charging at the beginning of the negative half-cycle.
[0079] If the voltage between the negative high-voltage potential HV- (shown in Figure 1) and the equipotential bonding PA is considered during the simulation, it is noticeable 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- (shown in Figure 1) of the vehicle are shifted according to a sine half-wave with respect to the equipotential bonding PA = N = PE (protective conductor). This is also typical behavior of a PFC. With large Y-capacitances between HV+ or HV- and PA, this would lead to a leakage current that could trigger an earth leakage circuit breaker in a domestic installation (equalizing current flows to the protective conductor PE).
[0080] To remedy this,
[0081] 1. small Y-capacitors are arranged in the PFC area and then galvanically isolated via an isolating DC / DC converter, or
[0082] 2. a compensating current is fed into the protective conductor PE.
[0083] Note 1: For 800V vehicles, the Y capacitances of the vehicle must be kept lower than for 400V vehicles due to the C1 characteristic curve. Broken down to the Y capacitance of inverter 1 (shown in Figure 1) including electric motor 2 (shown in Figure 1), this means: For a 400V inverter, a Y capacitance of approximately 500 nF per high-voltage potential HV+, HV- should be provided.
[0084] For an 800V inverter, a Y capacitance of approximately 50 nF to 80 nF per high-voltage potential HV+, HV- should be provided.
[0085] It is clear that the leakage current is much lower in 800V vehicles.
[0086] List of reference symbols
[0087] 1 inverter
[0088] 2 electric machine
[0089] 3 high-voltage battery
[0090] 4 DC junction box
[0091] 5 AC junction box
[0092] 6 DC charging station
[0093] 7 AC charging station
[0094] A ammeter
[0095] C DC link capacitor
[0096] D1 to D4 diode
[0097] EVSE_N relay contact
[0098] EVSE_P relay contact
[0099] Gate_S2, Gate_S4 control signal HB1 to HB3 half bridge
[0100] HV+, HV_P high-voltage potential, positive high-voltage potential
[0101] HV-, HV_N high-voltage potential, negative high-voltage potential
[0102] 11, I2, l_HV+, l_HV-, I— Q, LL1 , l_L2 current l_L charging current
[0103] L Relay contact
[0104] L1 to L3 stator winding
[0105] N Relay contact
[0106] S1 to S6 semiconductor switches
[0107] Ri_Batt internal resistance
[0108] U_Q source voltage
Claims
Patent claims 1. Electric drive system for a vehicle, comprising an electric machine (2) with three stator windings (L1, L2, L3) for driving the vehicle, a high-voltage battery (3) and an inverter (1) for converting a direct voltage of the high-voltage battery (3) into an alternating voltage for supplying the electric machine (2), wherein the inverter (1) comprises a B6 bridge of three Half-bridges (HB1, HB2, HB3) which are each formed from two semiconductor switches (S1 to S6), to whose center taps one of the stator windings (L1, L2, L3) is connected, wherein furthermore a DC connection box (4) for charging the high-voltage battery (3) by means of a direct voltage and / or an AC connection box (5) for at least single-phase charging of the high-voltage battery (3) by means of an alternating voltage is arranged, characterized in that - a diode (D1) or a semiconductor with diode function is arranged between the center tap of one of the half-bridges (HB1 to HB3) and a contact of the AC connection box (5) and / or the DC connection box (4) polarized in the reverse direction, - a diode (D2) or a semiconductor with diode function is arranged between the center tap of another of the half-bridges (HB1 to HB3) and another contact of the AC connection box (5) and / or the DC connection box (4) with reverse polarity, - one diode (D3, D4) or one semiconductor with diode function is arranged from a negative high-voltage potential (HV-) of the inverter (1) to each of the two contacts of the AC connection box (5) and / or the DC connection box (4) with forward polarity.
2. Electric drive system according to claim 1, characterized in that the semiconductor switches (S1 to S6) and / or the Semiconductors with diode function are designed as MOSFET or IGBT with freewheeling diode.
3. Electric drive system according to claim 1 or 2, characterized in that the inverter (1) has an intermediate circuit capacitor (C).
4. Electric drive system according to claim 1 or 2, characterized in that the inverter (1) has current measuring devices (A) for measuring alternating current between the center taps of the half-bridges (HB1 to HB3) and the stator windings (L1, L2, L3).
5. Electric drive system according to one of the preceding claims, characterized in that for the voltage isolation of two conductors, including a phase conductor and a neutral conductor, of the AC junction box (5) two relay contacts (L, N) are arranged between the respective conductor and the diodes (D1 to D4) connected thereto and / or that for the voltage isolation of two conductors, including a positive potential conductor and a negative potential conductor, of the DC junction box (4) two relay contacts (EVSE_P, EVSE_N) are arranged between the respective conductor and the diodes (D1 to D4) connected thereto.
6. Electric drive system according to claim 5, characterized in that in the direction of the inverter (1) a relay contact (L, N) assigned to the DC connection box (4) and a relay contact (EVSE_P, EVSE_N) assigned to the AC connection box (5) are connected to one another to form a pair.
7. 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 DC connection box (4), characterized in that a semiconductor switch (S2, S4, S6) arranged as a low-side switch of one of the half-bridges (HB1, HB2, HB3), which is connected to the DC connection box (4) via one of the diodes (D1, D2), is controlled in a clocked manner.
8. A method for charging the high-voltage battery (3) of the electric drive system according to one of claims 1 to 6 at an AC charging station (7), wherein the AC charging station (7) is connected to the AC connection box (5), characterized in that during a positive half-wave of an alternating voltage fed in by the AC charging station (7), a semiconductor switch (S2, S4, S6) arranged as a low-side switch of one of the half-bridges (HB1, HB2, HB3), which is connected to the DC connection box (4) via one of the diodes (D1, D2), is controlled in a clocked manner, wherein during a negative half-wave of the alternating voltage fed in by the AC charging station (7), a semiconductor switch (S2, S4, S6) arranged as a low-side switch of another of the half-bridges (HB1, HB2, HB3), which is connected to the DC connection box (4) via one of the diodes (D1, D2), is controlled in a clocked manner.
9. Method according to claim 7 or 8, characterized in that when the low-side switch is open, the semiconductor switch (S1, S3, S5) arranged as a high-side switch of the same half-bridge (HB1, HB2, HB3) is closed as soon as a current flows through its body diode or freewheeling diode.
10. Method according to one of claims 7 to 9, characterized in that a target current is regulated by the timing of the semiconductor switches (S1 to S6).