Drive system with inverter for impedance spectroscopy of the traction battery of the drive system

Abstract

The invention relates to a drive system (1) for an electrified motor vehicle, comprising - a traction battery (2) with several interconnected battery modules (3), each battery module (3) having at least one battery cell, and - an inverter (8) connected to the traction battery (2) via a power line for converting a high-voltage direct current voltage provided by the traction battery (2) into a multi-phase alternating voltage, which is designed to monitor the battery modules (3) by means of electrochemical impedance spectroscopy by imprinting an excitation signal in the form of an alternating current signal with alternating currents of different frequencies on the battery modules (3), and - a measuring device (4) designed to detect voltage signals of the battery modules (3) as battery module-specific, frequency-dependent response signals to the excitation signal and to determine battery module-specific impedance spectra depending on the respective response signals, where - a signal line (6) is connected to each battery module (3), - at least one component (10, 9) of the inverter (8) is electrically connected to the signal lines (6) at least when performing impedance spectroscopy and is designed to generate the excitation signal at least indirectly and supply it to each battery module (3) via the associated signal line (6).

Description

[0001] The invention relates to a drive system for an electrified motor vehicle. The drive system comprises a traction battery with several interconnected battery modules, each battery module having at least one battery cell, and an inverter connected to the traction battery via a power line for converting a high-voltage direct current supplied by the traction battery into a multiphase alternating current. The inverter is designed to monitor the battery modules using electrochemical impedance spectroscopy by imprinting an excitation signal in the form of an alternating current signal with alternating currents of different frequencies onto the battery modules.Furthermore, the drive system comprises a measuring device designed to detect voltage signals from the battery modules as battery module-specific, frequency-dependent response signals to the excitation signal and to determine battery module-specific impedance spectra of the battery modules based on the respective response signals. The invention also relates to a motor vehicle and a method for monitoring battery modules of a traction battery of a motor vehicle.

[0002] The present study focuses on traction batteries for electrically powered vehicles. These traction batteries, designed as high-voltage energy storage devices, typically consist of several interconnected battery modules, each containing at least one battery cell. The battery modules are to be monitored during operation. For example, it is known to monitor cell voltage and temperature using voltage and temperature sensors on the battery cells. However, it is also desirable to monitor the dynamic behavior of the battery modules, such as the aging of the battery cells.It is known from the prior art to monitor battery cells using impedance spectroscopy by applying a current signal with currents of different frequencies as an excitation signal to the battery cells and recording the frequency-dependent cell voltage signal of the battery cells as the response signal. The impedance spectrum of the battery cells is determined from the relationship between the current signal and the cell voltage signal.

[0003] For impedance spectroscopy, corresponding, module-specific excitation circuits can be provided for each battery module, which can generate an excitation signal for each module. However, this is very complex and involves high costs as well as a large installation space requirement. Alternatively, the excitation signal can be generated using an external excitation circuit. Such an external excitation circuit can, for example, be an inverter, as described in DE 10 2022 205 892 A1, which is connected between the traction battery and an electric drive motor of the vehicle. To generate the excitation signal, switching elements of the inverter can be controlled accordingly and supplied to the traction battery via a power line electrically connected to the traction battery and the inverter.However, the inverter typically has an intermediate circuit capacitor for ripple damping, which is connected between the switching elements and the traction battery and which would smooth the generated AC signal in an undesirable way before it is impressed into the battery modules.

[0004] The object of the present invention is to provide a solution for how impedance spectroscopy for monitoring battery modules of a traction battery of a motor vehicle can be carried out in a simple, cost-effective and reliable manner.

[0005] This problem is solved according to the invention by a drive system, a motor vehicle, and a method with the features according to the respective independent claims. Advantageous embodiments of the invention are the subject of the dependent claims, the description, and the figures.

[0006] A drive system according to the invention for an electrified motor vehicle comprises a traction battery with several interconnected battery modules, each battery module having at least one battery cell. The drive system also includes an inverter, switchably connected to the traction battery via a power line, for converting a high-voltage direct current supplied by the traction battery into a multiphase alternating current. This inverter is designed to monitor the battery modules using electrochemical impedance spectroscopy by imprinting an excitation signal in the form of an alternating current signal with alternating currents of different frequencies onto the battery modules.Furthermore, the drive system includes a measuring device designed to acquire voltage signals from the battery modules as battery module-specific, frequency-dependent response signals to the excitation signal and to determine battery module-specific impedance spectra of the battery modules based on these response signals. A signal line is connected to each battery module, and at least one component of the inverter is electrically connected to the signal lines, at least during the impedance spectroscopy, and is designed to generate the excitation signal, at least indirectly, and supply it to each battery module via its corresponding signal line.

[0007] The invention also includes a method for monitoring battery modules of a motor vehicle traction battery using impedance spectroscopy. In this method, an excitation signal in the form of an alternating current signal with alternating currents of different frequencies is generated by an inverter of the motor vehicle and supplied to the battery modules. Furthermore, voltage signals of the battery modules are recorded as battery module-specific, frequency-dependent response signals to the excitation signal, and battery module-specific impedance spectra of the battery modules are determined as a function of the respective response signals. Signal lines of the battery modules are connected to at least one component of the inverter, and the excitation signal is generated at least indirectly by this component and supplied to the battery modules via the respective signal line.

[0008] An electrified motor vehicle according to the invention comprises a drive system according to the invention. The drive system includes at least one electric machine, which functions as a drive machine for the electrified motor vehicle and which is electrically connected to the traction battery via the inverter. The inverter is designed to convert the high-voltage direct current supplied by the traction battery into the multiphase alternating current for the electric machine. For this purpose, the inverter has a DC link with at least one DC link capacitor, which is connected in parallel to the traction battery. A switching unit, which may, for example, have three switching bridges, is also connected in parallel to the DC link, each switching bridge having two series-connected switching elements in the form of a high-side switch and a low-side switch.In the case of an n-level inverter with n ≥ 3, additional switches, such as midpoint switches, can be provided so that at least three voltage levels can be generated per phase. The switching elements can be designed as semiconductor switches, for example, IGBTs or power MOSFETs. The control terminals or gate terminals of the semiconductor switches are controlled by a driver circuit of the inverter, which can have a gate driver for each semiconductor switch that can be controlled by a microcontroller of the driver circuit, thereby switching the switch into a conducting or a blocking state.

[0009] The traction battery comprises battery modules, which can be connected in series and / or parallel. Each battery module contains at least one battery cell. The battery cells can be designed, for example, as prismatic or cylindrical cells. The battery cells can be electrically connected via cell connectors. The traction battery is connected to the inverter via a power line, i.e., a high-voltage electrical line, which can be switched. For this purpose, a high-voltage switching device, such as a contactor, can be installed in the power line. This device can provide power transmission via the power line when closed and interrupt it when open.

[0010] The inverter is also used to monitor the battery modules using impedance spectroscopy. Impedance spectroscopy allows for the detection and identification of physicochemical effects in the battery cells, which describe the dynamic behavior of the battery modules and are therefore particularly important for battery dynamics. For this purpose, each battery cell in the module is subjected to an alternating current signal with varying frequencies, ranging from several kilohertz down to the millihertz range. These currents can, for example, have a sinusoidal waveform. This current signal acts as an excitation signal for the respective battery module, to which the cell chemistry of at least one cell in the module reacts.This reaction of at least one battery cell to the current supplied to it can be detected by means of the frequency-dependent voltage signal, which is determined for each battery module as a response signal to the applied excitation signal.

[0011] In particular, the measuring device has a voltage sensor for each battery module to detect the corresponding voltage signal. Alternatively, the number of voltage sensors can be reduced by using only one voltage sensor for the entire traction battery or for a specific number of battery modules, which is then connected to the specific battery module being tested. From the relationship between the frequency-dependent current signal and the frequency-dependent voltage signal of a battery cell, an evaluation unit of the measuring device can then determine the impedance spectrum for that battery module. This evaluation unit can, for example, be a battery management unit (BMU).The measuring device is specifically designed to determine an accurate battery module-specific state of aging (SOH) from the impedance spectra of the battery modules.

[0012] The excitation signal is not supplied to the battery modules by the inverter via the power line, and therefore not via the DC link capacitor, but rather via signal lines connected to the battery modules. These signal lines can be existing communication lines through which communication signals can be exchanged between the battery modules and the battery control unit. Such communication signals can be, for example, measurement signals acquired by sensors in the battery modules or control signals, such as those used for cell balancing. These signal lines are connected, at least temporarily, to at least one component of the inverter. For example, this component can be connected, at least temporarily, to the battery control unit, so that the excitation signal is supplied to the battery modules via the battery control unit.The component can be, for example, the driver circuit or at least one of the inverter's switching elements. This component generates the excitation signal, at least indirectly, and supplies it to the battery modules as the excitation signal. At least indirect generation of the excitation signal means that the component generates the excitation signal itself, and thus directly, or that the component generates the excitation signal indirectly by providing a signal that is fed to a signal generator connected to the component. This signal generator modifies the signal's waveform, thereby producing the excitation signal with the desired waveform, for example, a sinusoidal waveform. For indirect generation of the excitation signal, the inverter can, for example, be equipped with a signal generator.

[0013] By performing impedance spectroscopy using the signal lines, an undesirable smoothing of the excitation signal via the inverter's intermediate circuit can be advantageously prevented, so that impedance spectra of the battery modules can be reliably determined.

[0014] The measuring device can be designed to compare the battery module-specific impedance spectra with a corresponding battery module-specific reference impedance spectrum. These reference impedance spectra are battery module-specific initial impedance spectra determined during an end-of-line (EOL) test of the traction battery. This test is performed based on an excitation signal applied to the battery module and a corresponding initial response signal. The EOL test is then stored in a memory unit of the drive system. The EOL test is carried out before the start of operation, for example, at the factory after the traction battery has been manufactured. During this test, the respective initial impedance spectrum of the battery modules is recorded and stored as the corresponding reference impedance spectrum.This reference spectrum, characterizing a healthy, unaged battery module, can be used by the evaluation unit of the measuring device, which is equipped with appropriate software, to compare it with the measured impedance spectra for assessing the aging of the battery module. If necessary, a warning can be sent to the driver to activate measures for gentler operation of the aged part of the battery, thus extending the overall battery lifespan.

[0015] It is advantageous if the drive system includes a power supply unit designed to provide electrical energy to at least one component of the inverter for performing impedance spectroscopy. The electrical supply energy is, in particular, a low-voltage direct current (DC) voltage. For example, the power supply unit can include at least one low-voltage energy storage device, in particular at least one capacitor or at least one low-voltage battery, and / or a DC-DC converter connected to the traction battery for converting a high-voltage DC voltage provided by the traction battery into a low-voltage DC voltage. The DC-DC converter can, for example, be a flyback converter already present in the drive system for stepping down the high-voltage DC voltage provided by the traction battery into the low-voltage DC voltage for a low-voltage electrical system of the vehicle.The at least one capacitor or the at least one low-voltage battery can also be existing components of the motor vehicle, which are used to carry out impedance spectroscopy.

[0016] In a further development of the invention, the drive system can include a disconnecting device designed to disconnect at least one component of the inverter from a traction battery-side section of the power line during impedance spectroscopy. The disconnecting device can be formed by the high-voltage switching device, which interrupts the power line during impedance spectroscopy, thereby disconnecting the inverter from the traction battery and thus at least one component of the inverter from a high-voltage side of the drive system.The isolation device can also be a low-voltage switching device, which is arranged, for example, between the inverter's driver circuit and the inverter's switching units, so that the driver circuit is isolated from the inverter's switching units, which are connected to the traction battery via the power line, and thus also from the high-voltage side of the drive system, when the excitation signal is provided.

[0017] The embodiments and advantages presented with reference to the drive system according to the invention apply accordingly to the motor vehicle according to the invention and to the method according to the invention.

[0018] Further features of the invention will become apparent from the claims, the figure, and the figure description. The features and combinations of features mentioned above in the description, as well as the features and combinations of features mentioned below in the figure description and / or shown in the figure alone, are not only usable in the combinations specified, but also in other combinations or individually.

[0019] The invention will now be explained in more detail with reference to a preferred embodiment and the drawing. The drawing shows the single figure. Fig. 1 A block diagram of a drive system 1 for an electrically powered motor vehicle.

[0020] The drive system 1 includes a traction battery 2 with several interconnected battery modules 3. Each battery module 3 has at least one battery cell. The drive system 1 includes a measuring device 4, which in this case has a voltage sensor 5 for each battery module 3 to detect the voltage drop across the battery module 3. The battery modules 3 are electrically connected to a battery control unit 7 via signal lines 6. These signal lines 6 allow, for example, the exchange of low-voltage electrical signals between the battery modules 3 and the battery control unit 7. The battery control unit 7 also serves as an evaluation unit for the measuring device 4.

[0021] The drive system 1 also includes an inverter 8, which comprises a switching unit 9 with several interconnected switching elements, such as semiconductor switches, and a driver circuit 10 for controlling the semiconductor switches. The driver circuit 10 can include a gate driver circuit 11 and a microcontroller 12 for controlling the gate driver circuit 11. A isolating device 13 in the form of a low-voltage switching device is connected between the gate driver circuit 11 and the switching unit 9, and this is controlled by the microcontroller 12. When the isolating device 13 is open, the electrical connection between the gate driver circuit 11 and the switching unit 9 is interrupted.

[0022] Inverter 8 is connected to traction battery 2 via a power line (not shown), through which electrical energy is transmitted at high voltage. Inverter 8 converts the high-voltage direct current supplied to it from traction battery 2 via the power line into high-voltage multiphase alternating current for powering the stator phases of an electric drive motor of the vehicle. Inverter 8 is also used to monitor the battery modules 3 of traction battery 2. For this purpose, inverter 8 can provide an excitation signal, which is supplied to the battery modules 3 to perform impedance spectroscopy. The excitation signal is an alternating current signal with currents of different frequencies, which is generated here by the gate driver circuit 11 and a signal generator 14 connected to the gate driver circuit 11.When the excitation signal is generated, the isolating device 13 is open, so that the gate driver circuit 11 is galvanically isolated from the high-voltage direct current (HV DC) line of the traction battery 2. The excitation signal is then fed to the battery control unit 7, which forwards the excitation signal to the battery modules 3 via the signal lines 6, either simultaneously or with a time delay. For time-delayed forwarding, corresponding switches (not shown here) can be arranged in the signal lines 6, which are only switched to a conducting state when the excitation signal is to be supplied to the corresponding battery module.

[0023] The gate driver circuit 11 is powered by a power supply unit 15, which may, for example, include a DC-DC converter 16 and at least one low-voltage capacitor 17. The voltage sensors 5 of the battery modules 3 measure the module voltages as response signals from the battery modules 3 to the excitation signal. In the case of a battery module 3 with only one battery cell, the module voltage corresponds to the cell voltage. Based on these frequency-dependent module voltages, the evaluation unit of the measuring device 4, for example, the battery control unit 7, can determine impedance spectra of the battery modules 3, which can then be used to determine, for example, the aging state of the respective battery module 3. This aging state can be compared with an initial aging state of the respective battery module 3, and based on this comparison, for example, the degradation of the respective battery module 3 can be determined.By measuring the degradation, the operating behavior or operating pattern of the battery could be changed to prevent further degradation and thus extend the lifespan of the entire battery. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2022 205 892 A1

[0003]

Claims

[1] Drive system (1) for an electrified motor vehicle, comprising - a traction battery (2) with several interconnected battery modules (3), each battery module (3) having at least one battery cell, and - an inverter (8) connected to the traction battery (2) via a power line for converting a high-voltage direct current voltage provided by the traction battery (2) into a multi-phase alternating voltage, which is designed to monitor the battery modules (3) by means of electrochemical impedance spectroscopy by imprinting an excitation signal in the form of an alternating current signal with alternating currents of different frequencies on the battery modules (3), and - a measuring device (4) designed to detect voltage signals of the battery modules (3) as battery module-specific, frequency-dependent response signals to the excitation signal and to determine battery module-specific impedance spectra depending on the respective response signals, characterized by , that - a signal line (6) is connected to each battery module (3), - at least one component (10, 9) of the inverter (8) is electrically connected to the signal lines (6) at least when performing impedance spectroscopy and is designed to generate the excitation signal at least indirectly and supply it to each battery module (3) via the associated signal line (6). [2] Drive system (1) according to claim 1, characterized by, that the measuring device (4) is designed to compare the respective battery module-specific impedance spectra with a respective battery module-specific reference impedance spectrum, wherein the reference impedance spectra are battery module-specific initial impedance spectra which are determined in an EOL test of the traction battery (2) as a function of an excitation signal supplied to the battery module (3) and an initial response signal dependent thereon and are stored in a storage device of the drive system (1). [3] Drive system (1) according to claim 1 or 2, characterized by , that the drive system (1) has a power supply device (15) which is designed to supply electrical energy to at least one component (9, 10) of the inverter (8) for carrying out impedance spectroscopy. [4] Drive system (1) according to claim 3, characterized by, that the power supply device (15) has at least a low-voltage energy storage device, in particular at least a capacitor (17) or at least a low-voltage battery, and / or a DC voltage converter (16) connected to the traction battery (2) for converting the high-voltage DC voltage provided by the traction battery (2) into a low-voltage DC voltage. [5] Drive system (1) according to any one of the preceding claims, characterized by , that the inverter (8) has a switching unit (9) with several switching elements and a driver circuit (10) for controlling the switching elements, wherein at least one component of the inverter (8) is the driver circuit (10) and / or at least one of the switching elements of the switching unit (9). [6] Drive system (1) according to any one of the preceding claims, characterized by, that the drive system (1) has a disconnecting device (13) which is designed to disconnect at least one component (9, 10) of the inverter (8) from a traction battery-side section of the power line when performing impedance spectroscopy. [7] Drive system (1) according to any one of the preceding claims, characterized by , that the measuring device (4) is designed to determine battery module-specific aging states from the impedance spectra of the battery modules (3). [8] Drive system (1) according to any one of the preceding claims, characterized by , that the measuring device (4) has a voltage sensor (5) for each battery module (3) to detect the respective voltage signal. [9] Motor vehicle with a drive system (1) according to any of the preceding claims. [10] Method for monitoring battery modules (3) of a traction battery (2) of a motor vehicle using impedance spectroscopy, wherein the method: - an excitation signal in the form of an alternating current signal with alternating currents of different frequencies is generated by an inverter (8) of the motor vehicle and supplied to the battery modules (3), - Voltage signals of the battery modules (3) are recorded as battery module-specific, frequency-dependent response signals to the excitation signal and - depending on the respective response signals, battery module-specific impedance spectra can be determined, characterized by , that - signal lines (6) connected to the battery modules (3) are connected to at least one component (9, 10) of the inverter (8) and the excitation signal is generated at least indirectly by the at least one component (9, 10) and supplied to the battery modules (3) via the respective signal line (6).

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