Battery charger with reduced leakage current

Abstract

The invention relates to a battery charger (1), in particular for use as an on-board battery charger, for providing a battery charging voltage (VHV) on a high-voltage on-board electrical system (2) from a multi-phase supply system voltage of an AC supply system (3), comprising: - an AC / DC converter (6) designed to provide a DC link voltage (VZW) on the basis of the single-phase or multi-phase supply system voltage, - a DC / DC converter (8) designed to generate the battery charging voltage (VHV) on the basis of the DC link voltage (VZW); - a protective conductor (PE) which is capacitively coupled to at least the high-voltage on-board electrical system (3); - a compensation unit (12) for injecting a compensation current (Icomp) into the protective conductor (PE), which compensation current compensates for a leakage current in the protective conductor (PE), the compensation unit (12) having a control unit (121) in order to provide the compensation current (Icomp) depending on a common-mode voltage in the high-voltage on-board electrical system (3).

Description

[0001] Description

[0002] title

[0003] Battery charger with reduced leakage current

[0004] Technical field

[0005] The invention relates to battery chargers, in particular onboard chargers for electric vehicles, with which the electric vehicle can be charged via an AC power supply connection. The invention further relates to measures for reducing leakage current through the protective conductor in order to prevent a residual current device (RCD) from tripping during normal operation.

[0006] Technical background

[0007] Onboard battery chargers in electric vehicles serve as an interface between an AC mains connection and the vehicle's high-voltage DC electrical system. These chargers recharge the vehicle's high-voltage battery using electrical energy supplied via the mains connection. In the future, these onboard battery chargers will also be able to feed electrical energy from the high-voltage battery into the AC mains.

[0008] At the heart of such a battery charger is an AC / DC converter that provides an intermediate circuit voltage, which is then transformed to the voltage level of the high-voltage battery by a DC / DC converter. This DC / DC converter can be galvanically isolated, separating the mains-side input circuitry from the vehicle's high-voltage electrical system. This results in a lower risk of electric shock and greater robustness of the charging process, as the lower leakage current reduces the likelihood of a residual current device (RCD) tripping.

[0009] The parasitic capacitances between the two galvanically isolated circuit sections limit the propagation of common-mode currents, especially at low frequencies from the AC mains, and thus also avoid the problem of leakage current via the protective conductor.

[0010] As an alternative to DC / DC converters with galvanic isolation, the use of simple coupled DC / DC converter stages is advantageous because these reduce the weight and volume of the battery charger and offer higher efficiency. However, there is a higher risk of personal injury from electric shock, which must be compensated for by additional safety measures in the system design.

[0011] Because a non-galvanically isolated DC / DC converter creates direct coupling between the input and output, a low-frequency common-mode voltage, which lies outside the attenuation range of an EMC filter, can be present on components in the electric vehicle's high-voltage electrical system. Due to the high capacitance between the conductors in the vehicle's high-voltage network and the vehicle ground potential, particularly due to the EMC filter capacitors, the resulting leakage current can exceed permissible limits under certain operating conditions and trip a residual current device (RCD) in the electric vehicle or the AC power supply network. The resulting interruptions in the charging process are problematic and limit the use of battery chargers with non-galvanically isolated DC / DC converters.

[0012] One of the fundamental approaches to keeping the leakage current via the protective conductor within permissible limits and using non-galvanically isolated DC / DC converters is to provide AC / DC stages with a split DC-link structure with two capacitors, to whose center node the neutral conductor is connected, as proposed, for example, in B. Strothmann et al., Single-Phase Operation of Common-Mode-Free Bidirectional Three-Phase PFC-Rectifier for Non-Isolated EV Charger with Minimized DC-Link, PCIM Europe digital days 2021 and B. Strothmann et al., Common-Mode-Free Bidirectional Three-Phase PFC-Rectifier for Non-Isolated EV Charger, 2021 IEEE Applied Power Electronics Conference and Exposition (APEC), Phoenix, AZ, USA, 2021, pp. 2783-2790.

[0013] With such a structure, the common-mode voltage exhibits a leakage current with a low-frequency AC component that is proportional to the transmitted power and the DC link capacitances. While such an approach may be sufficient to limit the leakage current, in single-phase operation the AC ripple across the DC link capacitors can be significantly higher than in three-phase operation, potentially leading to a leakage current that trips the residual current device (RCD).

[0014] Document US 2022 / 224250 A1 discloses a bidirectional power converter with a first half-bridge consisting of two controlled power converter switches; an intermediate circuit; with a three-phase AC input and a three-phase AC output; with a first converter stage and with a second converter stage, wherein the first converter stage comprises a controlled bridge circuit with half-bridges, including chokes between the inputs and the bridge centers of the half-bridges, wherein the intermediate circuit includes a capacitor half-bridge comprising a first capacitor and a second capacitor, the first capacitor being connected to the first half-bridge at a first terminal.

[0015] The AC terminal of one phase branch of the AC-DC stage is connected to the neutral conductor via the power inductor. This phase branch is used to inject a mains current, phase-shifted by 180°, into the midpoint between the two DC link capacitors, thus compensating for the fundamental frequency in the common-mode voltage at the DC link. The output of the other phase branch of the AC-DC stage is connected to an additional energy storage capacitor. The resulting so-called "ripple port" serves as an active power buffer for the remaining low-frequency AC components in the DC link voltage.

[0016] While such an approach effectively eliminates the low-frequency common-mode voltage from the vehicle's high-voltage electrical system during single-phase operation, it requires a high capacitance for the ripple port capacitor. Furthermore, the efficiency in single-phase operation is lower compared to three-phase operation because three phases of the AC-DC stage are active, but only one transmits power to the output.

[0017] Patent application US 2022 / 2227242 A1 discloses a device for charging an electric vehicle with direct current, comprising a rectifier connected to a multi-phase power grid, an intermediate circuit arranged on the charging side of the rectifier and coupled to the rectifier, which has a number of capacitors and a center point, and a DC / DC converter arranged on the charging side of the intermediate circuit and coupled to the intermediate circuit for adapting an intermediate circuit voltage to a charging voltage of a battery of the battery vehicle, wherein the center point of the intermediate circuit is connected to a neutral conductor of the multi-phase power grid. A non-isolated DC / DC step-down converter is connected across each intermediate circuit capacitor to control its output voltage to a constant value with respect to the center point of the intermediate circuit capacitors.In this way, the AC component of the common-mode voltage of the high-voltage network is eliminated, and the leakage current is kept within permissible limits. The disadvantages of this approach are that, under all operating modes, lower efficiency is achieved due to the doubled number of components in the current path within the DC-DC stage, and it is not applicable in the US split-phase network due to a limited output voltage range.

[0018] Document US 10,809,755 B1 discloses a power converter and a leakage current suppression circuit in a metal enclosure, forming a charging module, wherein the leakage current suppression circuit includes a leakage current suppression current generator, wherein a common-mode current is present at a grounding node during operation of the power converter, wherein the leakage current suppression circuit receives a signal from an input or output of the power converter or from the grounding node, and the leakage current suppression current generator produces a leakage current suppression current without directly sensing the common-mode current.

[0019] The patent application US 11,186,179 B1 discloses a compensation device for compensating leakage currents on conductors containing live conductors, the compensation device comprising: a differential current measuring device, a power supply unit, a first signal generation device, an output stage, and a supply unit. The differential current measuring device is designed to detect a first signal as a differential current on the live conductors and supply it to the first signal generation device, the first signal generation device further being designed to generate a second signal to compensate for the differential current from the first signal and supply it to the output stage. The output stage injects a compensation current into at least one of the live conductors via the supply unit, depending on the second signal.The power supply device is designed to supply a first active conductor to which a phase can be connected. Based on the second signal, the output stage releases a compensation current for each phase angle of the phase in a first direction or in a second direction opposite to the first direction.

[0020] The last two publications describe active filtering by injecting an opposing leakage current. This compensation method is based on the implementation of an active filter that detects either the common-mode voltage or the leakage current and injects an opposing current at various points to achieve leakage current compensation.

[0021] It is an object of the present invention to provide an improved leakage current compensation for an onboard battery charger of an electric vehicle, which avoids the disadvantages of the prior art and in particular has high robustness against a false tripping of a residual current protection device.

[0022] Disclosure of the invention

[0023] This problem is solved by an onboard battery charger with compensation of a leakage current according to claim 1.

[0024] Further embodiments are specified in the dependent claims. According to a first aspect, a battery charger, particularly for use as an onboard battery charger, is provided for supplying a battery charging voltage on a high-voltage electrical system from a single- or multi-phase supply network voltage, comprising: an AC / DC converter configured to provide an intermediate circuit voltage based on the single- or multi-phase supply network voltage; a DC / DC converter configured to generate the battery charging voltage based on the intermediate circuit voltage; and a protective conductor capacitively coupled to the multi-phase supply network voltage, the intermediate circuit voltage, and the high-voltage electrical system.A compensation unit for injecting a compensation current into the protective conductor, which compensates for a leakage current in the protective conductor, wherein the compensation unit has a control unit to provide the compensation current depending on a common-mode voltage in the high-voltage on-board network and depending on a specification of the leakage current through the protective conductor.

[0025] The state of the art discussed at the outset has the disadvantage that a false tripping of a residual current device (RCD) due to an excessively high leakage current through the protective conductor cannot be ruled out in all operating modes. In particular, existing concepts rely on measuring a single quantity that indicates the leakage current and use this measurement to implement a control system to compensate for the leakage current. Due to a range of possible operating modes (single-phase or multi-phase), different system configurations, and variations in system parameters, the design space for the compensation control is very limited.

[0026] Furthermore, the potential oscillations of the compensation current, which is intended to compensate for the leakage current and is generated via switchable output stages, can also impair the robustness against nuisance tripping of the residual current device. These oscillations occur at the resonant frequency of the output stage's RLC circuit due to its low impedance, which can generate higher-order harmonics. The presence of such oscillations within the leakage current's frequency band leads to a reduced compensation effect and potentially to an unwanted tripping of the residual current protection circuit.

[0027] The battery charger described above refers to chargers that convert a mains supply voltage into an intermediate circuit voltage via an AC / DC converter. This intermediate circuit voltage is then converted into a high voltage for the electric vehicle's high-voltage electrical system by a downstream DC / DC converter. The DC / DC converter may or may not have galvanic isolation. If galvanic isolation is not provided, high leakage currents may occur due to capacitance between the high-voltage electrical system conductors and the neutral or protective earth conductor of the AC power supply.

[0028] The above onboard battery charging device for electric vehicles features a compensation unit that enables high charging stability in electric vehicles. The device refers to battery chargers with a non-isolated DC / DC converter that transforms the intermediate circuit voltage to the high-voltage network of the electric vehicle.

[0029] The control unit of the compensation unit can have a forward control to provide a control variable for generating the compensation current depending on the common-mode voltage in the high-voltage on-board network, and a feedback control to correct the control variable of the forward control depending on the information about the remaining leakage current in the protective conductor.

[0030] In particular, the control unit can be designed to correct the manipulated variable of the forward control by additive or multiplicative application.

[0031] The compensation unit uses the common-mode voltage of the electric vehicle's high-voltage electrical system and a measurement of the leakage current via the protective conductor to provide the compensation current. The common-mode voltage of the battery charging voltage in the high-voltage electrical system, detected by a corresponding voltage sensor, represents the main source of the leakage current in the system, as it directly affects the capacitances between the high-voltage electrical system conductors and the protective conductor or earth potential. The common-mode voltage of the high-voltage electrical system is used to implement a forward control circuit that generates a compensation current capable of almost completely eliminating the leakage current in a system with nominal parameters. The measurement of the leakage current serves as the input for a feedback control circuit, which provides information about the effectiveness of the leakage current compensation and is therefore used to implement feedback control.

[0032] The battery charger may be provided with the following for determining the leakage current: a differential current sensor configured to detect a differential current as an indication of the leakage current through the protective conductor, wherein the differential current indicates a difference in phase currents through phase terminals and through a neutral conductor of the supply network voltage; or a current sensor configured to directly measure the leakage current through the protective conductor; or a capacitance network with a star point capacitively connected to the phase terminals and the neutral conductor of the supply network voltage and providing a common-mode voltage of the supply network voltage as an indication of the leakage current through the protective conductor.

[0033] The information on the leakage current via the protective conductor can, for example, correspond to or be determined from a differential current between the phase terminals of the AC power supply network and the neutral conductor, a common-mode voltage of the phase terminals of the AC power supply network and the neutral conductor, or from a direct measurement of the leakage current on the protective conductor.

[0034] Residual current monitoring (RCM) devices, which can be installed at the phase terminals of vehicles, contain such residual current sensors. These can be used to measure and provide the residual current.

[0035] The compensation unit may be provided with an output stage to generate the compensation current, with the output stage being powered by the intermediate circuit voltage.

[0036] The compensation unit can be built with a small number of components and easily integrated into the battery charger. To ensure its compact size, the compensation unit draws the power for its output stage from the battery charger's DC link. This DC link voltage is regulated to a constant value by the AC / DC converter in a known manner, so that only a small capacitance is required for coupling the compensation current. Because the output stage of the compensation unit is powered via the DC link, a rectifier circuit and power buffering within the compensation unit can be avoided.

[0037] Alternatively, the output stage can be supplied by means of a rectifier designed to rectify the input supply voltage and provide a DC voltage to supply the output stage, in particular its power driver.

[0038] The rectifier can be designed as a bridge rectifier, wherein the input terminal of the bridge rectifier that is connected to the neutral conductor is connected via a switch to a center node of a series circuit of two capacitors, to which the output voltage of the bridge rectifier is applied.

[0039] Determining whether the neutral or phase conductor is connected to the live wire of the AC power supply can be done by measuring the common-mode voltage at no-load (i.e., before the battery charger starts transferring current). The measured common-mode voltage will have an AC component of nearly zero when the neutral conductor is connected to the center point, but a very high AC component when a live wire is connected to the center point (i.e., the reverse polarity case). A live wire connected to the neutral conductor can also be detected using another voltage sensor that directly measures the voltage between the protective earth conductor and the neutral conductor. In the case of reverse polarity (live wire connected to neutral), a significant voltage will be present here. The switch's standard state connects the neutral conductor to the center point K of the internal DC link.If a "polarity reversal" is detected, it is switched so that the phase connection is connected to the center point K of the internal DC intermediate circuit.

[0040] An analogous implementation of the logic for controlling the SRP is possible within the compensation unit 12: Comparator on Vcm,sens signal or output of the additional sensor 2) » Control signal for SRP (a latch is also required to hold the value during operation);

[0041] A digital implementation of the logic for controlling the SRP is also possible. This is particularly suitable for acquisition method 2). The signal acquired by the sensor is then processed in the central MCU / FPGA to generate the driver signal for the SRP.

[0042] Since system parameters can vary, a differential current sensor connected to the phase terminals of the AC power supply network and the neutral conductor enables precise measurement of the leakage current. The differential current sensor signal contains information about the effectiveness of the leakage current compensation and is therefore used for implementing feedback control. The approaches described above for measuring the leakage current via the protective conductor, such as measuring the common-mode voltage of the phase terminals of the AC power supply network and the neutral conductor, or directly measuring the leakage current on the protective conductor, are equivalent.

[0043] The purpose of the additional feedback control is to correct the mismatch between the forward control and the actual system parameters in order to ensure operation with a near-zero leakage current under all operating modes. The forward control enables improvements in transient response, leakage current compensation, and stability across the entire range of system parameter variation.

[0044] Furthermore, the output stage of the compensation unit can have an impedance network that is electrically connected to the protective conductor, in particular via a compensation capacitor, wherein the output stage of the compensation unit is in particular designed with a half-bridge, in particular in the form of a T-type driver or a multi-level flying capacitor driver, and the impedance network is designed to reduce the switching noise in the compensation current and to dampen the resonance between the capacitance of the output stage and the filter inductance.

[0045] According to another embodiment, a filter inductor can be provided on the output side of the output stage of the compensation unit, which can be implemented by the impedance network. This reduces the switching noise from the compensation current, i.e., the oscillations of the compensation current within the frequency band of the compensation unit, and thereby minimizes the influence of the compensation unit on the electromagnetic interference spectrum. The impedance network can further be configured with a series connection of a filter inductor and a damping resistor, or a parallel connection of a filter inductor and a series connection of a damping resistor and a damping inductor, or a filter inductor with several parallel and / or series damping stages.

[0046] Brief description of the drawings

[0047] The embodiments are explained in more detail below with reference to the accompanying drawings. These show:

[0048] Figure 1 shows a schematic representation of an onboard battery charger for a high-voltage battery of an electric vehicle;

[0049] Figures 2a and 2b show embodiments of a DC / DC converter for converting an intermediate circuit voltage into a high-voltage voltage of the high-voltage network;

[0050] Figure 3 shows a compensation unit according to a first embodiment;

[0051] Figure 4 shows a schematic representation of an onboard battery charger for a high-voltage battery of an electric vehicle according to a further embodiment; and

[0052] Figure 5 shows a schematic representation of an onboard battery charger for a high-voltage battery of an electric vehicle according to a further embodiment;

[0053] Figure 6 shows a circuit diagram of an exemplary impedance network; and

[0054] Figure 7 shows a compensation unit according to a further embodiment;

[0055] Figure 8 shows a schematic representation of an onboard battery charger for a high-voltage battery of an electric vehicle according to a further embodiment;

[0056] Figure 9 shows an exemplary circuit of a bridge rectifier for

[0057] Supply of an output driver;

[0058] Figure 10 shows exemplary designs of the bridge rectifier switch.

[0059] Description of embodiments

[0060] Figure 1 shows a schematic representation of a battery charger 1 for providing a high voltage VHV of e.g. approx. 200-900 volts on a high voltage on-board network 2 of an electric vehicle.

[0061] The battery charger 1 receives as input phase voltages L1, L2, L3 of a multi-phase supply network voltage of an AC power supply network 3, which are filtered in an EMC filter 4 to suppress the propagation of electromagnetic interference from the battery charger 1 into the AC power supply network 3.

[0062] Furthermore, a switching matrix 5 can be provided to enable operation as a reconfiguration battery charger in a manner known per se to support different phase usage, such as three-phase, single-phase, split operation and the like.

[0063] A DC link voltage VDC (with DC link potentials DC+, DC-) can be provided in a DC link 7 using a downstream AC / DC converter 6. The AC / DC converter 6 can also control the power factor on the AC side.

[0064] The intermediate circuit 7 is buffered by two series-connected capacitors Czw, whose center node M is connected to the neutral conductor. The intermediate circuit voltage VDC is converted by a downstream DC / DC converter 8 to provide the high-voltage voltage HV (voltage potentials HV+, HV-) for the high-voltage electrical system 2.

[0065] An EMC filter 9 can be provided on the output side of the DC / DC converter 8 to suppress the propagation of electromagnetic interference into the high-voltage electrical system 2 of the electric vehicle.

[0066] The high-voltage electrical system 2 is primarily connected to a high-voltage battery 9 and other high-voltage loads 10.

[0067] The parasitic capacitances of the high-voltage loads 10 (e.g., traction motor) and the y-capacitances CY,HV+, CY,HV-, CY.HVobc in their EMC filters can lead to significant capacitances between the lines of the high-voltage on-board network 2 to the vehicle chassis, which is connected to the protective conductor PE of the AC power supply network 3 during a charging process.

[0068] Figures 2a and 2b show exemplary embodiments of DC / DC converters 6. Figure 2a shows a DC / DC converter 6' with galvanic isolation, while Figure 2b shows a non-isolated DC / DC converter 6" as a simple buck converter circuit. In the DC / DC converter 6' of Figure 2a, which provides galvanic isolation, the propagation of common-mode currents, especially at low frequencies, is limited, and leakage currents generally occur only to a small extent.

[0069] Unlike a galvanically isolated DC / DC converter 6', the input and output of a non-galvanically isolated DC / DC converter 6" are electrically coupled, resulting in a low-frequency common-mode voltage being applied to the high-voltage loads 10 of the vehicle's high-voltage electrical system 2. Due to the high capacitance to the protective earth conductor (PE), the resulting leakage current can, under certain operating conditions, exceed the permissible limits and trip a residual current device (RCD) in the vehicle or the AC power supply.

[0070] A compensation unit 12 is provided to compensate for the leakage current through the protective conductor PE, which provides a compensation current l C om PThe compensation unit 12 is generated based on the common-mode voltage VCM, the high-voltage on-board network 2, and a leakage current value on the AC power supply network 3. The compensation unit 12 is connected to the protective earth conductor PE via a compensation capacitor Cy.comp.

[0071] The compensation unit 12 comprises a control unit 121 and an output stage 122. As shown in Figure 3, the control unit 121 includes a combination of a forward control 1211 and a feedback control 1212 to compensate for a leakage current. The output stage 122 of the compensation unit 12 can include a power driver 1222 and an impedance network 1221. The power driver 1222 can be configured as a switched-mode amplifier. Alternatively, the power driver 1222 can be configured as a linear amplifier, in which case the impedance network can be omitted.

[0072] The power driver 1222 of the output stage 122 can be supplied via the DC voltage of the intermediate circuit voltage DC+,DC-.

[0073] The forward control 1211 uses the common-mode voltage VCM, sens of the high-voltage electrical system 2 relative to the voltage or voltage potential of the protective conductor PE. A measuring amplifier 1213 ensures that the measured signal VCM, sens of the common-mode voltage does not contain a DC component of the common-mode voltage and that any AC harmonic content is limited to the frequency band relevant for compensating the leakage current. In particular, low-pass filtering can be provided in the measuring amplifier 1213. Subsequently, the measured signal is inverted in an inverter 1214, and its magnitude is adjusted by a forward gain 1215 of the forward control 1211 according to a predefined model of the system to be controlled.

[0074] A feedback control 1212 may be provided, designed to additively correct the forward control error resulting from deviations of the actual system parameters from ideal system parameters. These deviations can result from the influence of component parameter tolerances, different electric vehicle systems, system configurations, environmental influences on parasitic capacitances, and the like. Furthermore, deviations may also arise from a possible phase shift of the compensation current caused by the impedance network on the output side of the output stage 122.

[0075] The feedback control 1212 serves to correct a mismatch between the forward control 1211 and the real system parameters, and uses as a control stage a controller 1216, which is designed as a simple P, PI, PID controller or with other controller structure and whose output signal goes into a summing element 1217 for additive input.

[0076] The feedback control 1212 uses a measurement of the actual leakage current, which can be detected in various ways, as an indicator of the deviation of the actual system parameters. For example, a differential current sensor 14 can be provided that detects a differential current IRES, sens between the phase terminals L1, L2, L3 and the neutral conductor N and provides it as a measurement signal to the feedback control 1212.

[0077] Alternatively, as shown in Figure 4, the leakage current in the protective conductor PE can be measured directly with another current sensor 15 and a corresponding measurement signal can be provided as an indication of the deviation of the actual system parameters.

[0078] Alternatively, as shown in Figure 5, a common-mode voltage on the phase terminals L1, L2, L3 and the neutral conductor N can be detected, for example, via capacitors, and a corresponding measurement signal VACCM^S can be used as an indication of the deviation of the actual system parameters.

[0079] The forward and feedback control circuits 1211 and 1212 are designed so that rapid changes in the controlled variable caused by potential system errors are not compensated, thus ensuring the usual fast response of a residual current protection circuit. The output signals of the forward and reverse control circuits 1211 and 1212 are added in the summing element 1217 and fed to the input of a modulator 1218.

[0080] The modulator 1218 converts a resulting value for a compensation current Icomp into a suitable duty cycle for controlling the output stage 122, which provides the compensation current l C om P The output stage 122 features high-voltage transistors in the form of MOSFETs, IGBTs and the like, arranged in a half-bridge structure with associated gate drivers, which are controlled accordingly by the modulator 1218.

[0081] The impedance network 1221 is connected to the output side of the power driver 1222 of the output stage (122). This network filters the output signal of the power driver 1222 and couples it into the protective earth conductor (PE) via a compensation capacitor CY.com. The impedance network 1221 is shown in Figure 6 as an example configuration only and serves to eliminate the switching noise from the generation of the compensation current, to dampen the resonance between a capacitor and the filter inductance, and thus to minimize the effects of the compensation unit 12 on the electromagnetic interference spectrum.

[0082] The output stage 122 is preferably supplied by the DC link voltage VDC, which is regulated to a constant value in all operating modes via the AC / DC converter 6. This allows for a minimal size of the compensation capacitor CY.comp between the output of the output stage and the protective earth (PE) for given compensation currents. Furthermore, a rectifier circuit and power buffering within the compensation unit can be avoided.

[0083] Figure 7 shows another representation of the compensation unit 12. Here, the feedback control 1212 is applied to the gain of the gain unit of the forward control 1211 to provide a combined control signal for the modulator 1218, which takes into account both the output of the forward control and the feedback control 1212. The leakage current measurement signal is converted into a gain factor that determines the gain of the amplifier unit 1215 of the forward control 1211.

[0084] In general, the feedback control 1212 and the forward control 1211 can generate control signal components that are applied multiplicatively or additively to provide the control signal for the modulator 1218.

[0085] In this embodiment, an adjustable gain (forward gain) is provided, such that the role of the feedback is solely to tune the forward gain. Once this is done, the forward feedback can operate independently. The magnitude error of the compensation current l C om PThe error in the forward control 1211 is due to the mismatch between the actual system parameters and their nominal or predefined values. Since this error does not change significantly in the model during operation, it is possible to limit the activity of the feedback control 1212 to specific operating phases, such as start-up or mode changes. Once the feedback loop has adjusted the forward gain 1211 to ensure effective leakage current suppression, the feedback control 1212 can be deactivated, and the system resumes normal operation via forward control. The advantage of such a control strategy is increased system stability and reduced computational effort for the regular execution of the control algorithm.

[0086] The forward control 1211 is always active, and the forward gain has an initial value. This initial value is pre-calculated based on theoretical parameters (various capacitances). The forward gain can be adjusted accordingly. This adjustment is made by multiplying the forward gain by the output of the feedback control 1212, effectively adjusting the gain of the forward control 1211. The output of the feedback control 1212 is generated based on a measurement signal representative of the leakage current, as described above. Once the product of the output of the feedback control 1212 and the forward gain (i.e., the updated / adjusted forward gain) reaches a value sufficient for adequate compensation, the feedback control 1212 is deactivated, and the newly adjusted forward gain is stored until the end of the specific operating cycle.

[0087] Figure 8 shows an embodiment similar to that of Figure 1, in which the power driver 1222 is supplied by means of a rectifier 123, which rectifies the input AC voltage and provides a DC voltage to supply the power driver 1222. This alternative embodiment offers advantages in cases where the phase and neutral conductors are reversed when charging from a single-phase household socket. Connecting the phase conductor of the AC mains to the neutral conductor results in a significantly increased common-mode voltage of the high-voltage electrical system. The rectifier 123 can convert the input AC voltage into a DC voltage with a nearly constant common-mode voltage, independent of the phase and neutral connections of the AC mains supply.By supplying the output stage 122 of the compensation unit 12 with such a DC voltage from the rectifier 123, the supply to the output stage 122 becomes independent of the common-mode voltage of the high-voltage electrical system. This achieves effective compensation of the leakage current when the line and neutral conductors are reversed, without requiring a significant increase in the compensation capacitor between the impedance network 1221 and the protective conductor potential. Furthermore, the proposed embodiment also reduces the required compensation capacitance CY.comp in the case of split-phase inputs.

[0088] The rectifier 123 is preferably configured as a bridge rectifier with diodes D for supplying the output driver, as shown in Figure 9. This makes it possible to generate the same maximum compensation current regardless of the orientation of the LN connection and to achieve fully effective compensation in the event of LN reversal, without having to increase the size and capacitance of the compensation capacitor CY.comp. The switch SRP serves to reconfigure the rectifier so that the neutral conductor N is always connected to the center point K of the internal DC link of the rectifier 123 (regardless of the orientation of the LN connection at the input of the charger).

[0089] Figure 10 shows various implementations of the SRP switch. These can be designed as a combination of two TRIACs, as shown in Figure 10a.

[0090] Figure 10b shows an SRP switch constructed from two pairs of cascaded unidirectional transistors. These can be Si / SiC MOSFETs, IGBTs, GaN, HEMTs, or the like.

[0091] Figure 10c shows an SRP switch constructed from two bidirectional transistors. These could be monolithic bidirectional GaNs, monolithic Si-BJTs, or the like.

Claims

Claims 1. Battery charger (1), in particular for use as an onboard battery charger, for providing a battery charging voltage (HV) on a high-voltage electrical system (2) from a multi-phase supply voltage of an AC power supply network (3), comprising: an AC / DC converter (6) configured to provide an intermediate circuit voltage (Vzw) based on the single- or multi-phase supply voltage; a DC / DC converter (8) configured to generate the battery charging voltage (VHV) ZU based on the intermediate circuit voltage (Vzw); a protective conductor (PE) capacitively coupled at least to the high-voltage electrical system (2);a compensation unit (12) configured to inject a compensation current (Icomp) into the protective conductor (PE) which compensates for a leakage current in the protective conductor (PE), wherein the compensation unit (12) has a control unit (121) to provide the compensation current (Icomp) depending on a common-mode voltage in the high-voltage on-board network (2).

2. Battery charger (1) according to claim 1, wherein the control unit (121) of the compensation unit (12) is configured to control the compensation current (l C om P ) depending on a common-mode voltage (VcM.sens) in the high-voltage on-board network and depending on a specification of the leakage current through the protective conductor (PE).

3. Battery charger (1) according to claim 2, wherein the control unit (121) of the compensation unit has a forward control (1211) to generate a control variable for generating the compensation current (l C om P) depending on the common-mode voltage (VcM.sens) in the high-voltage on-board network (2), and has a feedback control (1212) to adjust depending on the Information about the remaining leakage current (IRES, sens) in the protective conductor (PE) is used to correct the control variable of the forward control (1211).

4. Battery charger (1) according to claim 3, wherein the feedback control (1212) is configured to correct the manipulated variable of the forward control (1211) by additive or multiplicative application.

5. Battery charger (1) according to claim 3 or 4, wherein the feedback control is configured to activate or deactivate itself depending on the measured leakage current (IRES, sens), in particular depending on a threshold comparison.

6. Battery charger (1) according to one of claims 1 to 5, wherein the compensation unit has an output stage (122) to generate the compensation current (Icomp), wherein the output stage (122) is supplied by the intermediate circuit voltage (Vzw).

7. Battery charger (1) according to one of claims 1 to 5, wherein the compensation unit has an output stage (122) to generate the compensation current (Icomp), wherein the output stage (122) is supplied by means of a rectifier (123) configured to rectify the input supply mains voltage and provide a DC voltage to supply the output stage.

8. Battery charger (1) according to claim 7, wherein the rectifier is designed as a bridge rectifier, wherein the input terminal of the bridge rectifier which is connected to the neutral conductor is connected via a switch to a center node of a series circuit of two capacitors to which the output voltage of the bridge rectifier is applied.

9. Battery charger (1) according to one of claims 6 to 8, wherein the output stage (122) of the compensation unit (12) comprises an impedance network (1221) which is electrically connected to the protective conductor (PE), in particular via a compensation capacitor (CY.com), wherein the output stage (122) of the compensation unit (12) is in particular connected to a half-bridge, in particular in the form of a T-type driver or a multi-level flying Capacitor driver, is designed and the impedance network (1221) is designed to reduce the switching noise in the compensation current (lC om P ) to reduce and dampen resonances.

10. Battery charger according to any one of claims 1 to 9, comprising for determining the leakage current: a differential current sensor (12) configured to determine a differential current (IRES, sens) as an indication of the leakage current through the protective conductor (PE), wherein the differential current (IRES, sens) indicates a difference of phase currents through phase terminals (L1, L2, L3) and through a neutral conductor (N) of the supply network voltage; or a current sensor (15) configured to directly measure the leakage current through the protective conductor (PE); or a capacitance network (16) with a star point capacitively connected to phase terminals (L1, L2, L3) and a neutral conductor (N) of the supply network voltage and providing a common-mode voltage of the supply network voltage as an indication of the leakage current through the protective conductor (PE).

11. Battery charger (1) according to any one of claims 1 to 10, wherein the DC / DC converter (8) is a galvanically isolated or a non-galvanically isolated converter and in particular comprises a dual active bridge, a phase-shift full bridge, an isolated resonant converter, a buck converter, a boost converter or a buck-boost converter.

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