Charging circuit for an electrically drivable motor vehicle

Abstract

A charging circuit (125) for a motor vehicle (105) having an electrical energy store (120) comprises a half-bridge (205) having an upper and a lower current valve (S1, S2) connected in series between terminals of a DC link (203), thus producing a first connection point (215) between the current valves (S1, S2); an upper (C1) and a lower (C2) capacitor connected in series between terminals of the DC link (203), thus producing a second connection point (220) between the capacitors; an inductance (L1-L3) connected to the first connection point (215); a switching device (230) located between the first (215) and the second (220) connection point; and an upper (S13) and a lower (S14) switch connected in series via the lower capacitor (C2). A control device (205) can actuate the circuit (125) in a boost mode or in a power factor correction mode in order to charge the energy store (120).

Description

[0001] Charging circuit for an electrically powered motor vehicle

[0002] The present invention relates to a charging circuit for an electrically powered motor vehicle. In particular, the invention relates to a current converter for charging an electrical energy storage device of the motor vehicle.

[0003] A motor vehicle comprises an electric drive motor that can be operated with energy from an electrical energy storage device. An inverter is provided to convert a direct current from the energy storage device into one or more phase-shifted alternating currents for the drive motor. The energy storage device can have a nominal voltage of approximately 800 V, for example.

[0004] The energy storage device can be charged with energy from an external voltage source, such as a charging station. If an alternating voltage is used, it can be converted and rectified to a suitable voltage for the energy storage device. If a suitable direct voltage is provided, it can be used directly to charge the energy storage device. If a direct voltage is provided that is significantly lower than the nominal voltage of the energy storage device, it must be boosted accordingly.

[0005] A dedicated boost converter can be complex and expensive. It has been proposed to extend an existing on-board vehicle circuit with additional components to enable it to also function as a boost converter. However, known circuits extended in this way can be unbalanced when used as boost converters, which can place significant stress on individual components.

[0006] One object underlying the present invention is to provide an improved charging circuit that can be used both for power factor correction and as a boost converter for charging an electrical energy storage device. The invention solves this problem by means of the subject matter of the independent claims. Subclaims specify preferred embodiments.A charging circuit for a motor vehicle with an electrical energy storage device comprises a half-bridge with an upper and a lower current valve, which are connected in series between terminals of an intermediate circuit, so that a first connection point is formed between the current valves; an upper and a lower capacitor, which are connected in series between terminals of the intermediate circuit, so that a second connection point is formed between the capacitors; an inductance connected to the first connection point; a switching device, which is located between the first and the second connection point; an upper and a lower switch, which are connected in series across the lower capacitor, so that a third connection point is formed between the switches; and a control device.The control device is configured to periodically open and close the switching device in a boost mode; and, in parallel, to alternately open and close the two switches; so that an input voltage applied between the inductance and the third connection point can be converted into a higher output or intermediate circuit voltage for charging the electrical energy storage device.

[0007] The charging circuit can be based on a power factor correction (PFC) circuit and requires only a few additional components. A choke required for the PFC can also be advantageously used for the charging circuit. In one embodiment, essentially only the two switches and the control device need to be added. The control device can also be used to control the power factor correction, whereby an existing control device can be adapted or expanded to control the switches and enable boost operation.

[0008] The charging circuit can, for example, double the input voltage to the output voltage. For example, the charging circuit can be used to charge an electrical energy storage device with a nominal voltage of approximately 800 V using a DC voltage of approximately 400 V applied externally to the vehicle. Other factors are also possible, as long as the output voltage is greater than the input voltage. An additional or dedicated voltage converter is not required. This allows for increased charging power, reducing charging times compared to charging with lower-power AC current. The combined charging circuit can be used as a bridging technology until charging stations that provide sufficiently high DC voltages are widely available.

[0009] The switching frequency of the switching device can be higher than the switching frequency of the switches, preferably several times higher. For example, the switching device can be operated at approximately 40 times the switching frequency of the switches. For example, the switching frequency of the switching device can be approximately 200 kHz, while the switching frequency of the switches can be approximately 5 kHz. The switching frequency of the switching device can control the conversion of the input voltage into the output voltage, while the switching frequency of the switches can activate different branches of the circuit.

[0010] In boost mode, the inductor and switching device with the upper capacitor and the upper current valve can operate as the first boost converter when the upper switch is closed and the lower switch is open. Furthermore, the inductor and switching device with the lower capacitor and the lower current valve can operate as a second boost converter when the lower switch is closed and the upper switch is open. The two boost converters can operate alternately to charge the capacitors alternately. The capacitors can essentially only absorb the residual ripple of the output voltage; they are practically unaffected by the charging current from the energy storage device.

[0011] The current valves can be implemented as freewheeling diodes. The freewheeling diode has a cathode oriented toward a high potential of the intermediate circuit. Alternatively, a current valve can be controllable and include a freewheeling diode, so that current flow in the direction of the diode is possible even when the current valve is not closed. In this case, the circuit can be operated unidirectionally only as a boost converter. If a current valve is designed to be controllable, the circuit can also be operated as a buck converter to convert a DC voltage from the energy storage device to a lower DC voltage. A controllable current valve can be implemented, for example, as a MOSFET, particularly using SiC technology. The switching device can comprise two anti-serially connected semiconductors, which can be implemented, for example, as a GaN HEMT or SiC MOSFET.The switches can also be designed as semiconductors, for example as FETs, in particular MOSFETs.

[0012] It is particularly preferred that several half-bridges with associated inductors and switching devices are provided, which are operated in multi-phase mode in boost mode to convert the input voltage into a higher output voltage at the intermediate circuit. In multi-phase operation, a higher DC charging power can be provided for the energy storage device. Three half-bridges and three inductors can be provided, which can be used as 3-level DC / DC converters. Compared to a conventional 3-level T-type power correction circuit, essentially only the two switches are required as additional components. A different number of half-bridges with associated additional components is also possible.

[0013] The multi-phase, and especially three-phase, operation of the charging circuit allows inductors required in the PFC to be used in the boost converters. In multi-phase operation, a reduced current can flow through each inductor, and residual ripple at each inductor can be reduced. The inductors dimensioned for power factor correction can be advantageously used in boost mode to suit the boost converters. The circuit can operate in a balanced manner, and individual components cannot be overloaded. Furthermore, excessive heating of the switches can be avoided. Noise emanating from the circuit can be reduced.

[0014] The multiple phases can already be present for operation of the charging circuit as a power factor correction circuit for charging the energy storage device from a multi-phase AC voltage. Three-phase AC voltages are common, so the charging circuit preferably has three phases. It is particularly preferred for the phases to be operated with a phase shift relative to one another in multi-phase boost operation, which can also be referred to as interleaved. A residual ripple of a current can also be called ripple or current rib. The residual ripples at the inductors can be phase shifted relative to one another. When the phase-shifted residual ripples are superimposed in the various boost converters, a partial cancellation of the AC components in the total current can occur, so that the overall residual ripple in the mains current can be significantly reduced. A reduced total current ripple can result in the input current and / or the output current.This can reduce the emission of interference at the HV input, resulting in improved electromagnetic compatibility (EMC). Furthermore, the DC link capacitor can be smaller due to the reduced residual ripple. It should be noted that the charging circuit can also be designed with fewer or more than three phases.

[0015] A known 3-level T-type PFC circuit operated as a 2-level boost converter can exhibit significantly increased residual ripple in a choke because the inductance of the choke dimensioned for the PFC is far too low for the 2-level boost converter. If such operation is possible at all, it is often only with reduced power. It is therefore proposed to expand a 3-level T-type PFC to a 3-level boost converter. Both the PFC and the boost converter can operate as 3-level converters. Current ripple in chokes can be similar in PFC operation and in boost converter operation. The boost converter can therefore be operated at higher power.

[0016] It is further preferred that the charging circuit can also be used for power factor correction as an alternative to boost operation. The current valves can be opened and closed alternately to provide a predetermined voltage at the first connection point; and in parallel, the switching device can be controlled to correct a power factor of electrical power drawn from an AC voltage network. The power factor is controlled so that it approaches 1 as closely as possible, so that the reactive power approaches 0 as closely as possible. Power factor correction can be used so that the sinusoidal current drawn from the external network is as precisely in phase with the grid voltage as possible. This makes it possible to achieve a corrected power factor of 1 and minimize reactive power. The electrical energy storage device can thus also be charged alternatively from an AC voltage.The charging circuit can be implemented as a T-type PFC and expanded to a 3-level T-type boost converter or DC / DC converter using the two switches.

[0017] The AC voltage can have multiple phases, and each phase can be assigned a half-bridge in the charging circuit. In power factor correction mode, phase-shifted AC voltages can be present across the phases. The individual phases of the mains voltage are typically connected to the half-bridges via inductors, which can be designed as chokes. The charging circuit can comprise a 3-level T-type PFC and a 3-level T-type DC / DC converter in one. Control of the switches, current valves, and switching device can determine whether the charging circuit is operated for power factor correction or as a boost converter.

[0018] The charging circuit may further comprise a relay to connect the inductors to an AC voltage in power factor correction mode and to a DC input voltage in boost mode. A low potential of the DC input voltage may be connected to the third connection point between the switches. A high potential of the DC input voltage may be isolated from all inductors in power factor correction mode. The low potential may also be referred to as the negative pole and the high potential as the positive pole. A high-performance relay may also be called a contactor. In one embodiment, a relay with multiple contacts may be used to switch between power factor correction mode and boost mode. Preferably, multiple relays are used that can be controlled independently of one another to control the different operating modes.This also allows a third or additional operating mode to be controlled, for example, disconnecting the circuit from the charging socket. The control device is preferably configured to control the relay depending on the operation to be controlled. Multiple relays can also be used and controlled to configure the charging circuit for boost operation or power factor correction operation.

[0019] The control device is preferably configured to charge the energy storage device from an alternating voltage by means of power factor correction in a first operating mode, and to charge it from a direct voltage by means of boost converters in a second operating mode. Conceptually, the invention can convert a known power factor correction into a boost converter by adding a few components. The added components include the switches mentioned, which can be inexpensively available as standard components without special requirements, for example with regard to switching speed. A control device provided for the power factor correction can be configured or programmed with little effort to alternatively control the boost position. It is particularly preferred that the power factor correction and the boost converter each operate in three levels.

[0020] An electric drive axle comprises an electric drive motor and a charging circuit as described herein. Furthermore, the drive axle may comprise a transmission. Optionally, the drive axle may further comprise an inverter. Optionally, a further drive motor is provided on board the motor vehicle, which may be coupled to the transmission.

[0021] According to a further aspect of the present invention, a motor vehicle comprises an electric drive axle as described herein. The motor vehicle can be designed, in particular, as a passenger car, but alternatively, for example, as a motorcycle, a truck, or a bus.

[0022] The invention will now be described in more detail with reference to the accompanying figures, in which: Figure 1 shows a motor vehicle with an electric drive system and a charging circuit;

[0023] Figure 2 shows a charging circuit in a single-phase embodiment;

[0024] Figure 3 shows a charging circuit in a three-phase embodiment; and Figure 4 shows exemplary signal waveforms on a charging circuit.

[0025] Figure 1 shows an electric drive system 100 on board a motor vehicle 105. The drive system 100 comprises an electric drive motor 110, a charging socket 115, an electrical energy storage device 120, a charging circuit 125, and an inverter 130. The drive system 100 is configured to drive the motor vehicle 105. Optionally, a further drive motor, in particular an internal combustion engine, is provided. The drive system 100 may include an electric drive axle.

[0026] The electrical energy storage device 120 is preferably electrochemical. The drive motor 120 can be designed, for example, as a permanent magnet synchronous machine (PMM), but other designs are also possible.

[0027] The charging socket 115 is configured to be connected to an alternating voltage (AG) or a direct voltage (DO) in order to receive energy for charging the energy storage device 120, for example, from a charging station. For this purpose, the charging socket 115 can comprise an AC part and a DC part. The charging circuit 125 can further preferably be operated in two different operating modes. In a boost mode, the charging circuit can convert a lower direct voltage applied to the charging socket 115 into a higher direct voltage for charging the energy storage device 120. In a power factor correction mode, a single- or multi-phase alternating voltage can be converted into a direct voltage for charging the energy storage device 120. An output voltage provided by the charging circuit 125 is usually not fed directly to the energy storage device 120; instead, a DC / DC converter, which is not shown here, is interposed.The DC / DC converter can realize a galvanic isolation of the charging circuit 125 from the energy storage device 120.

[0028] Figure 2 shows an exemplary charging circuit 125 in a first, single-phase embodiment. A control device 205 is configured to appropriately control active elements of the charging circuit 125. The charging circuit 125 can be connected to the charging socket 115 and provides a voltage to an intermediate circuit 203 that can be used to charge the electrical energy storage device 120. In a single-stage charging circuit 125 with PFC, the intermediate circuit 203 can be connected directly to the electrical energy storage device 120; in a two-stage charging circuit 125 with PFC, a DC / DC converter is additionally provided, which converts the voltage of the intermediate circuit 203 into another DC voltage, which is applied to the electrical energy storage device 120.

[0029] A half-bridge 210 comprises an upper current valve S1 and a lower current valve S2, which are connected in series between potentials of the intermediate circuit 203, so that a first connection point 215 is formed between them. The current valves S1, S2 each comprise a diode, each of which has its cathode oriented toward the high potential of the intermediate circuit 203. The diodes can be implemented, for example, as MOSFETs, depending on the design of the current valves S1, S2. Diodes could also be used instead of the switches S1 and S2 for purely unidirectional operation of the charger 125.

[0030] An upper capacitor C1 and a lower capacitor C2 are also connected in series between the potentials of the intermediate circuit 203, forming a second connection point 220 between them. The capacitors C1 and C2 are designed as intermediate circuit capacitors and can have capacitances of approximately 1 mF. Two switches S13 and S14 are connected in series via the lower capacitor C2, forming a third connection point 225 between them.

[0031] Between the connection points 215 and 220, a (first) switching device 230 is provided, which can comprise two series-connected semiconductors S3, S4, which are preferably oriented opposite to one another, i.e., anti-serially. Between the first connection point and a high potential L1 / +HV_L of an input DC voltage provided by the charging socket 115 for operation as a boost converter, an inductor L1 is provided, which is preferably designed as a choke. The input voltage is DC voltage, which is connected to the DC part of the charging socket 115 and is provided, for example, by a DC charging station. The low potential -HV_L is connected to the third connection point 225 between the switches S13, S14.

[0032] In boost mode, charging circuit 125 can be operated as a boost converter. If upper switch S13 is closed and lower switch S14 is open, a first boost converter can be formed from inductance L1, switching device 230, upper current valve S1, and upper capacitor O1. If upper switch S13 is open and lower switch S14 is closed, a second boost converter can be formed from inductance L1, switching device 230, lower current valve S2, and lower capacitor O2. Switches S13, S14 are opened and closed alternately, so that the boost converters operate alternately and capacitors O1, O2 can be charged alternately. An output voltage corresponding to at least twice the input voltage can be provided at the potentials of intermediate circuit 203.

[0033] Figure 3 shows a charging circuit 125 in a second, three-phase embodiment, which builds on the embodiment of Figure 2. The illustrated charging circuit 125 is based on a 3-level T-type PFC, which is expanded into a 3-level boost converter. In addition to the half-bridge 210, two further half-bridges 305, 310 are provided, which comprise current valves S5 and S6, and S9 and S10, respectively. Switching devices 315 and 320, which comprise anti-serially connected semiconductors S7 and S8, and S11 and S12, respectively, are assigned to the half-bridges 305, 310.

[0034] The illustrated charging circuit 125 comprises three phases, with each phase assigned a half-bridge 210, 305, 310. In boost converter operation, control signals to the switching devices 230, 315, 320 and to the half-bridges 210, 305, 310 are typically phase-shifted by T / n, where n indicates the number of phases and T the period of the clock frequency. In the three-phase case of Figure 3, this means a phase shift of T / 3 = 120°. Each phase can operate in boost converter mode similar to the embodiment of Figure 2 to convert an input voltage into a higher output voltage and provide it to the intermediate circuit 203.

[0035] It is preferred that the phases are controlled in an interleaved manner during boost converter operation, so that current ripples in the chokes L1-L3 overlap. A current ripple in the L1 / +HV_L terminal can thus be significantly smaller than the current ripples in the chokes L1-L3. The electromagnetic compatibility (EMC) of the charging circuit 125 can thereby be significantly improved. The inputs of the T-type boost converters are controlled in a phase-shifted manner via the chokes L1-L3, so that the current ripples are shifted relative to one another by the chokes L1-L3. In this case, for example, the leg with L1 / S1 / S2 / S3 / S4 can be controlled in a phase-shifted manner relative to the leg with L2 / S5 / S6 / S7 / S8.

[0036] At the charging socket 115, a single-phase alternating voltage can be provided via terminals L1 and N, a three-phase alternating voltage via terminals L1-L3 and N, or a direct voltage via terminals L1 / +HV_L and -HV_L. The alternating voltage is supplied via an AC part of the charging socket 115, and the direct voltage via a DC part. These two parts are separated from each other in the charging socket 115.

[0037] In addition to the described boost operation with boost converters, the charging circuit 125 can also be used in power factor correction mode to charge the energy storage device 120 from an alternating voltage. To select an operating mode, one or more relays can be provided, whose contacts K1 to K8 can be controlled as shown in the following table. A 1 represents a closed contact and a 0 represents an open contact.

[0038] Contact AC charging AC charging DC charging 3 phase 1 phase HV_L -> HV_H

[0039] K3 1 0 0

[0040] K4 1 0 0

[0041] K5 0 1 0

[0042] K6 0 0 1

[0043] K7 0 0 1

[0044] K8 0 0 1

[0045] K9 0 0 1

[0046] If a higher power is to be switched, a contactor can be used for switching. Like a relay, a contactor comprises an electromagnetically operated switch, but is usually designed for a higher switching voltage and / or current. In one embodiment, K1-5 are relays, and K6-9 are contactors. For the purposes of this document, the term "relay" also includes a contactor.

[0047] Figure 4 shows exemplary signal waveforms on a charging circuit 125 in the single-phase embodiment of Figure 2. Voltages or currents are plotted in a vertical direction and time is plotted in a horizontal direction.

[0048] A first curve 405 shows a current through the choke L1 .

[0049] A second curve 410 shows a voltage at the intermediate circuit 203 of the charging circuit 125.

[0050] A third curve 415 shows a voltage at the upper capacitor C1 .

[0051] A fourth curve 420 shows a voltage at the lower capacitor C2.

[0052] A fifth curve 425 shows an output current at the intermediate circuit 203. The current shown can, for example, flow through the terminal +HV_H.

[0053] A sixth curve 430 shows a control signal for the switching device S1. A seventh curve 435 shows a control signal for the switching devices S3 and S4, shown here as a common control signal.

[0054] An eighth curve 440 shows a control signal from S2.

[0055] A ninth curve 445 shows a control signal for switch S13. A high level represents a closed switch S13, a low level represents an open switch S13.

[0056] A tenth curve 450 shows a control signal for switch S14. A high level represents a closed switch S14, a low level represents an open switch S14.

[0057] Reference symbol

[0058] 100 drive system

[0059] 105 Motor vehicle

[0060] 110 electric drive motor

[0061] 115 Charging socket

[0062] 120 electrical energy storage units

[0063] 125 charging circuit

[0064] 130 inverters

[0065] 203 intermediate circuit

[0066] 205 Control device

[0067] 210 (first) half bridge

[0068] 215 first connection point

[0069] 220 second connection point

[0070] 225 third connection point

[0071] 230 (first) switching device

[0072] 305 (second) half bridge

[0073] 310 (third) half bridge

[0074] 315 second switching device

[0075] 320 third switching device

[0076] S1, S5, S9 upper flow valve

[0077] S2, S6, S10 lower flow control valve

[0078] S3, S4 semiconductors of the first switching device

[0079] S7, S8 semiconductors of the second switching device

[0080] S11 , S12 semiconductors of the third switching device

[0081] 513 upper switch

[0082] 514 lower switch

[0083] C1 , C2 capacitor

[0084] L1, L2, L3 inductance

[0085] K1-K9 Contact

[0086] 405 - 450 signal curves

Claims

Patent claims 1 . Charging circuit (125) for a motor vehicle (105) with an electrical energy storage device (120); wherein the charging circuit (125) has the following elements: a half-bridge (205, 305, 310) with an upper and a lower current valve (S1, S2, S5, S6, S9, S10), which are connected in series between terminals of an intermediate circuit (203), so that a first connection point (215) results between the current valves (S1, S2, S5, S6, S9, S10); an upper (C1) and a lower (C2) capacitor, which are connected in series between terminals of the intermediate circuit (203), so that a second connection point (220) results between the capacitors; an inductance (L1 - L3) connected to the first connection point (215); a switching device (230, 315, 320) located between the first (215) and the second (220) connection point;an upper (S13) and a lower (S14) switch, which are connected in series across the lower capacitor (C2), so that a third connection point (225) is formed between the switches (S13, S14); and a control device (205) which is configured to periodically open and close the switching device (230, 315, 320) in a boost mode; and, in parallel therewith, to alternately open and close the two switches (S13, S14); so that an input voltage applied between the inductance (L1-L3) and the third connection point (225) is converted into a higher output voltage at the intermediate circuit (203), which can be used to charge the electrical energy storage device (120).

2. Charging circuit (125) according to claim 1, wherein a switching frequency of the switching device (230, 315, 320) is several times higher than a switching frequency of the switches (S13, 14).

3. Charging circuit (125) according to claim 1 or 2, wherein in boost mode the inductance (L1 -L3) and the switching device (230, 315, 320) operate with the upper capacitor (C1) and the upper current valve (S1, S2, S5, S6, S9, S10) as a first boost converter when the upper switch (S13) is closed and the lower one (S14) is open; and with the lower capacitor (C2) and the lower current valve (S1, S2, S5, S6, S9, S10) as a second boost converter when the lower switch (S14) is closed and the upper switch (S13) is open.

4. Charging circuit (125) according to one of the preceding claims, wherein the current valves (S1, S2, S5, S6, S9, S10) are implemented as freewheeling diodes.

5. Charging circuit (125) according to one of the preceding claims, wherein a plurality of half-bridges (205, 305, 310) with associated inductances (L1 -L3) and switching devices (210, 305, 310) are provided, which are operated in multi-phase mode in step-up mode in order to convert the input voltage into a higher intermediate circuit voltage at the intermediate circuit (203).

6. Charging circuit (125) according to claim 5, wherein the phases are operated out of phase with each other.

7. Charging circuit (125) according to one of the preceding claims, wherein the control device (205) is configured to alternately open and close the current valves (S1, S2, S5, S6, S9, S10) in a power factor correction mode to provide a predetermined voltage at the first connection point (215); and, in parallel therewith, to control the switching device (210, 305, 310) to correct a power factor of a consumed electrical power.

8. Charging circuit (125) according to one of the preceding claims, further comprising a relay (K1 -K9) for connecting the inductors (L1 -L3) to an AC voltage in power factor correction mode and to a DC voltage in boost mode.

9. Charging circuit (125) according to claim 8, wherein the control device (205) is configured to control the relay (K1 -K9) in dependence on an operation to be controlled.

10. Charging circuit (125) according to one of the preceding claims, wherein the control device (205) is configured to charge the energy storage device (120) from an alternating voltage by means of power factor correction in a first operating mode; and to charge it from a direct voltage by means of boosting points in a second operating mode. 1 1. Charging circuit (125) according to claim 10, wherein a 3-level power factor correction and a 3-level boost converter are implemented.

12. Electric drive axle, comprising an electric drive machine (110) and the charging circuit (125).

13. Motor vehicle (105) comprising an electric drive axle according to claim 12.

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