Method and data processing system for determining the state of at least one cell of a battery

Abstract

A method for determining the state of at least one cell (1, 2, 3) of a battery (4), wherein the battery (4) has a plurality of cells (1, 2, 3) connected in series with each other; wherein the method at least comprises the following steps: a) loading the plurality of cells (1, 2, 3) with an alternating current (5); b) measuring the resulting alternating voltages (6, 7) at at least one first cell (1) and a second cell (2); c) analyzing the phases (8, 9) of the measured alternating voltages (6, 7) of each cell (1, 2); wherein a difference between at least a first phase (7) of a first alternating voltage (6) measured at the first cell (1) and a second phase (9) of a second alternating voltage (7) measured at the second cell (2) gives an inference of a difference in the state of at least the first cell (1) and the second cell (2).

Description

Field of the Invention

[0001] The present invention relates to a method for determining the state of a cell, in particular a high-voltage cell, of a battery. In particular, the method aims to determine the state of a cell (taking into account the states of other cells of the same battery). Background Art

[0002] Such high-voltage cells are used in motor vehicles in particular for storing electrical energy for driving a traction drive unit. Here, a battery usually consists of a plurality of cells, where each cell has a terminal voltage of 1.5 to 4 volts. The cells are at least partially connected in series, so as to provide a traction voltage of 60 to 1500 volts DC voltage.

[0003] Due to current and future legislation, it is necessary to detect the state of the battery or the cells during the operation of a motor vehicle. In particular, by determining the state of a cell, early fault identification and early service identification can be carried out, so as to avoid faults of the cell or the battery during operation, and timely replacement of the cell or the battery can be carried out.

[0004] Damage to a high-voltage battery from below, for example, cannot be identified electronically. Thus, the user of the motor vehicle cannot be warned of a possible damage to the cell.

[0005] So-called thermal propagation is recognized very late. Currently, there is no early identification or direct temperature measurement of a defective cell (in which the internal temperature increases before the cell finally starts to burn). It is feasible that future legislation will require early warning of the user of the danger.

[0006] Currently, the internal temperature of a cell cannot be measured in a motor vehicle. Instead, the temperature of a cell module, i.e., the temperature of a plurality of cells, is measured indirectly. This indirect measurement of the temperature of a cell by measuring the temperature of the cell module is disadvantageous because changes in the internal temperature of the cell are sensed only with a very long time delay.

[0007] A method for determining the internal temperature of a cell is the so-called impedance spectroscopy (Impedanzspektroskopie). In impedance spectroscopy, the correlation between current and voltage is evaluated and thus the real or imaginary part of the cell resistance is determined. This is achieved by sweeping the frequency response of an applied (or external, i.e., ) current from a very low frequency (0.1 Hz) to a relatively high frequency (10 kHz). This method takes a lot of time and draws a lot of energy from the cell to apply the current. In addition, interference generated by the consumers (or loads, i.e., Verbraucher) of the motor vehicle strongly affects and distorts the measurement signal. The measurement results of voltage and current are evaluated by a complex algorithm. Here, then, the absolute value of, for example, the internal temperature of the cell can be inferred. This method is very sensitive to interference and is currently only used under laboratory conditions.

[0008] An evaluation circuit for determining complex impedance is known from DE 197 55 417 A1. This evaluation circuit is used to analyze the properties of liquids.

[0009] A lithium-air battery is known from DE 10 2014 222 950 A1.

[0010] A method for operating a battery device is known from DE 10 2014 202 927 A1. Here, the power state of each individual cell is determined. The weakest cell is identified and deactivated, thereby slowing down its aging due to use. Summary of the Invention

[0011] The object of the present invention is to at least partially solve the problems listed with reference to the prior art. In particular, a method for determining the state of a cell of a battery should be proposed. In particular, damaged cells should thus be identified early during the operation of a motor vehicle, and the danger to the user of the motor vehicle should be reduced or prevented.

[0012] The method according to the invention contributes to achieving these objects. Advantageous refinements are the subject of the present invention. The features listed separately in the present invention can be combined with one another in a technically meaningful way and can be supplemented by the explanatory facts from the description and / or the details from the drawings, wherein further exemplary embodiments of the present invention are illustrated.

[0013] A method for determining the state of at least one cell of a battery is proposed, wherein the battery has a plurality of cells connected in series with one another. The solution at least comprises the following steps:

[0014] a) Loading a plurality of cells with an alternating current;

[0015] b) Measuring the resulting alternating voltage at at least one first cell and a second cell;

[0016] c) Analyzing the phase of the measured alternating voltage of each cell; wherein a difference (or distinction, i.e., Unterschied) between a first phase of a first alternating voltage measured at least at the first cell and a second phase of a second alternating voltage measured at the second cell results in an inference of a difference in the state of at least the first cell and the second cell.

[0017] The above (non-exhaustive) division of the method steps into a) to c) should mainly only be used for differentiation and does not enforce an order and / or dependency. The frequency of each method step can also vary. It is also possible that the method steps at least partially overlap in time. Very particularly preferably, method steps b) and c) are carried out during step a). Step c) can be conditional and is only carried out if necessary when step b) indicates that the measured alternating voltage does not have a phase shift. In particular, steps a) to c) are carried out in the listed order.

[0018] In particular, in the method described here, also called "differential measurement impedance spectroscopy", only the difference of the imaginary parts of the monomer resistances relative to each other is determined. In particular, the correlation between current and voltage is not evaluated here, but only the phase or correlation of the measured alternating voltages at the monomers relative to each other. Possible interferences of the current signal act simultaneously and with the same magnitude on all monomers or series-connected monomers of the battery and are not measured here as a common-mode component. With this method, only the change of the imaginary parts of the monomer resistances relative to each other is measured and evaluated.

[0019] According to step a), an alternating current with a frequency of, for example, greater than 1 Hz [hertz], in particular between 1 Hz and 10 kHz, preferably between 10 Hz and 10 kHz, particularly preferably 100 Hz, is applied to the monomers of the battery.

[0020] According to step b), the alternating voltage thus generated is measured at each monomer of the battery, in particular at the selected monomer or all monomers of the battery.

[0021] According to step c), the correlation of the measured alternating voltages relative to each other is evaluated, for example electronically. In particular, the respective phase of each measured alternating voltage is detected and compared with the phases of the other alternating voltages. The difference in phases can be classified with the aid of (callable and / or preset) limit values, threshold values, acceptance ranges, empirical values, characteristic diagrams, etc., so as to enable the inference of the state of at least one of the tested monomers. The inference can include probability values for the necessity of a potential or impending failure for at least one monomer, the (existing or expected) damage to the monomer, the (additional) service necessity regarding at least one monomer, etc. The analysis or evaluation can be carried out purely computationally using a data processing device. Then these data processing devices can also output information about the inference.

[0022] In particular, within the scope of this method, only the alternating voltage applied at the monomer is measured.

[0023] In particular, the frequency can have any value between 1 Hz and 10 kHz. In particular, the alternating current can have a constant or variable frequency. In particular, the alternating current can also have only one cycle length.

[0024] In particular, the alternating voltage measured at the band-pass filter element is used, and the signal thus generated is changed by an amplifier with a comparator. The signals changed by the amplifier with a comparator are combined in a phase detector (or phase detector, i.e., Phasendetektor). The phase shift of the measured alternating voltage can be presented by a first output signal.

[0025] With the band-pass, it is possible to detect the alternating voltage associated with the applied alternating current and induced thereby at the element. Thus, the band-pass in particular enables the detection of an alternating voltage having the frequency of the alternating current. Thus in particular, the DC voltage components and alternating voltages of other frequencies are not detected or discarded.

[0026] In particular, the amplifier with a comparator provides a changed signal such that the measured and band-pass filtered alternating voltage is presented by a rectangular signal. If there is a phase shift relative to other alternating voltages, this becomes evident by a shift of the rectangular signal along the time axis.

[0027] In particular, the signal changed by the amplifier with a comparator is presented as a second output signal, so that it can be presented which alternating voltage or which alternating voltages have a phase shift relative to other alternating voltages.

[0028] Once the imaginary parts of the element resistances are different from each other and thus a phase shift of the alternating voltage measured at the element is generated, a rectangular signal is generated in particular by the first output signal. This allows the differences between the elements to be inferred, for example, the temperature increase at the start of heat propagation. The time length of the rectangular signal is in particular proportional to or equal to the intensity of the difference (i.e., for example, the temperature difference).

[0029] If, at the start of the journey of a motor vehicle (wherein in particular all element temperatures are the same), the rectangular signal of the first output signal is measured or determined, it can be assumed that at least one element is defective. The cause can be a damage event that occurred earlier in time, such as the pressing in of a battery from the underside of the motor vehicle through the terminal or a severely aged element.

[0030] If the absolute value of the temperature of a cell near the cell is measured, for example, using a temperature sensor, then the phase of each individual alternating voltage (which can be identified at the second output signal) can be used to infer the corresponding internal temperature of the cell. Using this additional information, the SOC (state-of-charge of the cell and optionally additionally of the battery, i.e., the charge state of the cell and optionally additionally of the battery) or SOH (state-of-health, i.e., the aging state of the cell) can be determined more precisely post hoc.

[0031] The output signal can be evaluated by an evaluation unit.

[0032] In particular, the alternating voltages of all cells relative to each other can be measured, or circuit units can be used separately for multiple (e.g., 6 or 12,...) cell stacks to determine the alternating voltage of the cell stack. This is particularly advantageous for constructing high-voltage batteries with cell modules or cell stacks, since the maximum voltage of a cell stack usually does not exceed 60 volts.

[0033] In particular, using the proposed method, the temperature difference between cells, mechanical damage to individual cells, or significant aging phenomena can be determined.

[0034] The circuit required to implement this method can be integrated into the control device of the battery or implemented separately, for example, as an application-specific integrated circuit - ASIC.

[0035] In particular, the alternating voltage measured at the cell is band-pass filtered respectively, and the signals thus generated are changed by an amplifier. The respectively changed signals are (respectively) supplied to a lock-in amplifier (or phase-locked amplifier, i.e., Lock-in- ) loaded with a reference voltage signal, where the (corresponding) lock-in amplifier outputs a direct current voltage for each measured alternating voltage, the corresponding level of which is at least proportional to the phase shift between the measured alternating voltage and the reference voltage signal.

[0036] In particular, the amplifier provides a changed signal such that the measured and band-pass filtered alternating voltage is presented by a rectangular signal.

[0037] In particular, the reference voltage signal is also a rectangular signal.

[0038] In particular, the reference voltage signal has the same frequency as the applied alternating current.

[0039] In particular, a lock-in amplifier is an amplifier for measuring weak electrical alternating signals, which are modulated by a reference signal known in terms of frequency and phase (or phase, i.e., Phase). The device is a narrowband band-pass filter and thus improves the signal-to-noise ratio (SNR).

[0040] (Corresponding) The two input signals of the lock-in amplifier (i.e., on the one hand the measured alternating voltage and on the other hand the reference voltage signal, the alternating voltage being filtered in the band-pass and converted into a changed signal by the amplifier) are multiplied with each other in a mixer or multiplier and then integrated in a low-pass. The low-pass serves to discard the high-frequency signals generated when the input signals are multiplied.

[0041] In particular, the lock-in amplifier calculates the cross-correlation (Kreuzkorrelation) between the changed signal and the reference voltage signal for a fixed phase shift between the changed signal of a single unit and the reference voltage signal. The cross-correlation of signals of different frequencies is zero. Thus, if the frequency of the changed signal is different from the frequency of the reference voltage signal, the lock-in amplifier does not provide an output signal. Only for the same frequency, the cross-correlation provides a value different from zero and thus a quantity in the output signal of the lock-in amplifier. Therefore, by selecting the appropriate frequency of the reference voltage signal, the phase shift between the changed signal of each single unit and the reference voltage signal for all single units can be determined.

[0042] The lock-in amplifier provides a DC voltage signal for each single unit, the value of which provides an indication of the phase of the measured alternating voltage relative to the reference voltage signal.

[0043] A DC voltage signal of a single unit that deviates from the other DC voltage signals of other single units means that there is a phase shift here and the single unit may be defective.

[0044] DC voltage signals that are not deviated from each other indicate that there is no phase shift and none of the single units is defective.

[0045] In particular, the DC voltage signals are respectively supplied to an analog-to-digital converter and converted into digital output signals there. The digital output signals can be supplied to an evaluation unit and evaluated therein.

[0046] In particular, the reference voltage signal has the frequency of the applied alternating current. But in particular, the phase of the reference voltage signal is not stable relative to the phase of the applied alternating current. Thus, the alternating voltage of the single units can change over time relative to the reference voltage signal but not relative to each other (i.e., relative to other single units).

[0047] Once the imaginary part of the monomer resistance of a monomer changes, for example due to a temperature increase at the start of heat propagation, the monomer has at any time a different alternating voltage or a different phase compared to other monomers.

[0048] In particular, the reference voltage signal corresponds in terms of frequency and phase to the band-pass filtered signal of a cell of the battery.

[0049] Therefore, the reference voltage signal can in particular have the same phase as the measured alternating voltage of a monomer, in particular a defect-free monomer.

[0050] In particular, the reference voltage signal is generated from the band-pass filtered signal of the measured alternating voltage of the monomer. This signal is converted by an amplifier into a changed signal and used as the reference voltage signal.

[0051] In particular, the band-pass filtered signal for the reference voltage signal of the monomer is shifted in terms of its phase, such that it forms the reference voltage signal of a lock-in amplifier as the phase-shifted signal of the monomer.

[0052] In particular, a phase shifter is provided, by means of which the reference voltage signal can be shifted in terms of phase. With the phase shifter, the phase of the reference voltage signal can be changed and thus only the imaginary part of the voltage (and thus the resistance) is amplified. Thereby, the voltage difference between the alternating voltages of the monomers can be adjusted better.

[0053] In particular, the measured alternating voltage at the monomer is band-pass filtered separately, and the signals thus generated separately are changed by an amplifier, wherein the separately changed signals of two monomers are supplied to a differential amplifier. Each monomer is connected to each other serially connected monomer via the differential amplifier respectively. The differential amplifier generates a measurement signal only when there is a phase shift between the changed signals of the two monomers.

[0054] In particular, monomers arranged successively in series are connected to the preceding monomer and the succeeding monomer via the differential amplifier respectively.

[0055] The measurement signal can be supplied to an analog-to-digital converter and converted into a digital output signal there. The digital output signal can be supplied to an evaluation unit and evaluated therein.

[0056] Furthermore, a data processing system is proposed, which is equipped, configured or programmed to carry out the described method, wherein the data processing system processes and mutually compares the phases of the measured alternating voltages at a plurality of monomers of the battery.

[0057] Furthermore, the method can also be implemented by a computer or by a processor using a control unit.

[0058] The method can in particular be implemented in a controller or a control unit, wherein the controller is at least provided for diagnosing the battery and, if necessary, also for operating the battery.

[0059] The battery can be used in a motor vehicle to store energy, wherein electrical energy is supplied to at least one traction drive of the motor vehicle via the battery.

[0060] In particular, a motor vehicle having a traction drive, the described battery, and a data processing system is proposed.

[0061] A computer-readable storage medium including instructions can be provided, which instructions, when executed by a computer / processor, cause the computer / processor to implement at least a part of the method or the steps of the proposed method.

[0062] In particular, the elaboration on the method can be transferred to the motor vehicle, the battery, and / or the computer-implemented method (i.e., the computer or processor, the data processing system, the computer-readable storage medium), and vice versa.

[0063] In particular, for the proposed method or data processing system, a synchronization circuit between current excitation and voltage measurement is not required because no phase with respect to the current is needed.

[0064] In particular, the circuit or data processing system suitable for performing the method is robust against interference.

[0065] In particular, no additional intelligence (μC) is required to evaluate the measured values determined using the method.

[0066] The time for performing the method or the time during which an alternating current is applied is very short, for example, at most one second, in particular less than two seconds. Thus, it can be ensured that only very little energy is extracted from at least one cell or battery.

[0067] To apply the alternating current, consumers already present in the motor vehicle can be used, such as an HV heater, a pulse inverter, or a heating pad control device. The varying current of the electric drive can also be used as a signal source.

[0068] The use of indefinite articles (“a”, “an”, “one”), especially in patent claims and the specification reflecting them, should be understood in itself and not as a numeral. The terms or components introduced accordingly should thus be understood as existing at least once and in particular but also can exist multiple times.

[0069] It should be noted for the sake of caution that the numerals used herein ("first", "second",...) are mainly (only) used to distinguish multiple similar objects, parameters or processes, i.e., in particular, there is no mandatory presupposition of the dependence and / or order of these objects, parameters or processes relative to each other. If dependence and / or order are required, this is explicitly stated herein or will be obvious to a person skilled in the art when studying the specifically described design. As long as a component can occur multiple times ("at least one"), the description of one of these components can equally apply to all or part of most of these components, but this is not mandatory. Description of the Drawings

[0070] The present invention and the technical environment will be explained in more detail below with the aid of the drawings. It should be noted that the present invention should not be limited to the listed embodiments. In particular, unless otherwise explicitly stated, partial aspects of the facts illustrated in the drawings can also be extracted and combined with other components and knowledge in this specification. In particular, it should be noted that the drawings and especially the presented dimensional ratios are only schematic. Wherein:

[0071] Figure 1 A diagram is shown;

[0072] Figure 2 A first circuit is shown;

[0073] Figure 3 A second circuit is shown;

[0074] Figure 4 A third circuit is shown; and

[0075] Figure 5 A fourth circuit is shown. Detailed Description of the Invention

[0076] Figure 1 A diagram is shown. The alternating current 5 and the alternating voltages 6, 7 are plotted on the vertical axis. The time 33 is plotted on the horizontal axis. The courses of the alternating current 5 and the first alternating voltage 6 are shown. The first alternating voltage 6 includes an imaginary part 31 and a real part 32. The imaginary part 31 has a phase shift 20 relative to the real part 32.

[0077] The method for directly measuring the internal temperature of a cell is the so-called impedance spectroscopy method. In the impedance spectroscopy method, the correlation between the current 5 and the voltage 6, 7 is evaluated, and thus the real part 32 or the imaginary part 31 of the cell resistance is determined. This is achieved by attaching the frequency response of the current 5 from a very low frequency (0.1 Hz) through to a relatively high frequency (10 kHz). This method takes a lot of time and extracts a lot of energy from the cells 1, 2, 3 to attach the current 5. In addition, the interference generated by the vehicle's consumers acts strongly and distorts the measurement signal. The measurement results of the voltage 6 and the current 5 are evaluated by a complex algorithm. Here, then, the absolute value of, for example, the internal temperature of the cell can be inferred. This method is very sensitive to interference and is currently only used under laboratory conditions.

[0078] In the method described here, also called "differential measurement impedance spectroscopy method", only the difference of the imaginary parts 31 of the cell resistances relative to each other is determined. In particular, here the correlation between the current 5 and the voltage 6 is not evaluated, but only the phase 8, 9 or the correlation of the measured alternating voltages 6, 7 at the cells 1, 2, 3 relative to each other. The possible interference of the current signal acts simultaneously and with the same magnitude on all cells 1, 2, 3 of the battery 4 or on the cells 1, 2, 3 connected in series, and is not measured here as a common-mode component. With this method, only the change of the imaginary part 31 of the cell resistance relative to each other is measured and evaluated.

[0079] Figures 2 to 5 The circuits 41, 42, 43, 44 shown in are data processing systems that are suitable for performing the implementation of this method. The corresponding reference is about Figure 1 the elaboration of.

[0080] Figure 2 The first circuit 41 is shown. The first circuit 41 enables the execution of a method for determining the state of at least one cell 1, 2, 3 of a battery 4, where the battery 4 has a plurality of cells 1, 2, 3,... up to n connected in series with each other. According to step a), a plurality of cells 1, 2, 3 are loaded with an alternating current 5. According to step b), the resulting alternating voltages 6, 7 are measured at at least a first cell 1 and a second cell 2 (and at additional cells, for example, the third cell 3 to cell n). According to step c), the analysis of the phase 8, 9 of the measured alternating voltages 6, 7 of each cell 1, 2, 3 is performed. The difference between at least the first phase 8 of the first alternating voltage 6 measured at the first cell 1 and the second phase 9 of the second alternating voltage 7 measured at the second cell 2 enables the inference of the difference in the state of at least the first cell 1 and the second cell 2.

[0081] According to step a), an alternating current 5 with a frequency of 10, for example, is applied to cells 1, 2, 3 of the battery 4. For this purpose, the circuit has a switch 35 and a consumer 34 operated by the applied alternating current 5.

[0082] The alternating voltages 6, 7 measured at cells 1, 2, 3 are respectively filtered by band - pass 11, and the signals 12, 13, 14 thus respectively generated are changed by an amplifier 15 with a comparator. The first signal 12 is the first alternating voltage 6 filtered by the band - pass, which has a first phase 8 and is measured at the first cell 1. The second signal 13 is the second alternating voltage 7 filtered by the band - pass, which has a second phase 9 and is measured at the second cell 2. The third signal 14 is the correspondingly filtered alternating voltage of the third cell 3. The signals 16, 17, 18 changed by the amplifier 15 with a comparator are respectively combined in a phase detector 19. The first changed signal 16 is based on the first signal 13, the second changed signal 17 is based on the second signal 13, and the third changed signal 18 is based on the third signal 14. The phase shift 20 of the measured alternating voltages 6, 7 can be presented by the first output signal 21.

[0083] The band - pass 11 can be used to detect the alternating voltages 6, 7 associated with the applied alternating current 5 and caused thereby at cells 1, 2, 3. Thus, the band - pass 11 enables the detection of alternating voltages 6, 7 with the frequency 10 of the alternating current 5.

[0084] The amplifier 15 with a comparator provides modified signals 16, 17, 18 such that the measured alternating voltages 6, 7 filtered by the band - pass 11 are presented by rectangular signals. If there is a phase shift 20 relative to the other alternating voltages 7, 6, this becomes clear through the shift of the rectangular signal along the time axis (see the illustration of the first output signal 21 in the diagram).

[0085] The signals 16, 17, 18 changed by the amplifier 15 with a comparator are presented as a second output signal 22, so that it can be presented which alternating voltage 6, 7 or which alternating voltages 6, 7 have a phase shift 20 relative to the other alternating voltages 7, 6.

[0086] Once the imaginary part 31 of the cell resistance is different and thus a phase shift 20 of the alternating voltages 6, 7 measured at cells 1, 2, 3 is generated, a rectangular signal is generated by the first output signal 21. This allows for an inference of the differences between cells 1, 2, 3, for example, an inference of the temperature increase at the start of heat propagation. The time length of the rectangular signal is in particular proportional to or equal to the intensity of the difference (i.e., for example, the temperature difference) (see the illustration of the first output signal 21 in the diagram, the upper diagram shows no recognizable first output signal 21, and the lower diagram shows the first output signal 21 of a rectangle indicating the presence of a phase shift 20).

[0087] The output signals 21, 22 are evaluated by an evaluation unit 36.

[0088] Figure 3 The second circuit 42 is shown. Refer to the description regarding Figure 2 Unlike the first circuit 41, the respectively modified signals 16, 17, 18 are supplied to a lock-in amplifier 23 loaded with a reference voltage signal 24, where the lock-in amplifier 23 outputs DC voltages 25, 26 for each measured AC voltage 6, 7, the respective levels of which are at least proportional to the phase shift 20 between the measured AC voltages 6, 7 and the reference voltage signal 24.

[0089] The amplifier 15 provides the modified signals 16, 17, 18 such that the measured AC voltages 6, 7 filtered by the bandpass 11 are presented by rectangular signals.

[0090] The reference voltage signal 23 is also a rectangular signal. The reference voltage signal 23 has the same frequency 10 as the applied AC current 5.

[0091] The lock-in amplifier 23 is an amplifier for measuring weak electrical alternating signals (here the modified signals 16, 17, 18), the alternating signals being modulated by a reference voltage signal 24 known in terms of frequency 10 and phase. The device is a narrowband bandpass filter, and thereby improves the signal-to-noise ratio (SNR).

[0092] The two input signals of the respective lock-in amplifier 23 (i.e., on the one hand the measured AC voltages 6, 7 and on the other hand the reference voltage signal 24, the AC voltages being filtered in the bandpass 11 and converted into modified signals 16, 17, 18 by the amplifier 15) are multiplied with each other in a mixer 37 or a multiplier, and are then integrated in a low-pass 38. The low-pass 38 serves to discard the signals of the higher frequency 10 generated when the input signals are multiplied.

[0093] The respective lock-in amplifier 23 calculates the cross-correlation between the modified signals 16, 17, 18 and the reference voltage signal 24 for the fixed phase shift 20 between the modified signals 16, 17, 18 and the reference voltage signal 24 for monomers 1, 2, 3. The lock-in amplifier 23 provides DC voltage signals 25, 26 for each monomer 1, 2, 3, here a first DC voltage signal 25 for the first monomer 1 and a second DC voltage signal 26 for the second monomer 2, the values of which provide an indication of the phase 8, 9 of the measured AC voltages 6, 7 relative to the reference voltage signal 24.

[0094] The DC voltage signals 25, 26 of monomers 1, 2, 3 that deviate from the other DC voltage signals 26, 25 of the other monomers 3, 2, 1 mean that there is a phase shift 20 present here and that monomers 1, 2, 3 may be defective.

[0095] DC voltage signals 25, 26 that are without deviation from each other indicate that there is no phase shift 20 present and that none of monomers 1, 2, 3 are defective.

[0096] The DC voltage signals 25, 26 are respectively supplied to an analog - digital converter 39 and are converted into digital output signals there. The digital output signals are supplied to an evaluation unit 36 and are evaluated therein.

[0097] Figure 4 The third circuit 43 is shown. Refer to the description regarding Figures 2 to 3 Unlike the second circuit 42, the reference voltage signal 24 corresponds in terms of frequency 10 and phase 8, 9 to the signal filtered by the band - pass 11 of the first monomer 1 of the battery 4. The reference voltage signal 24 can thus have a common first phase 8 with the measured first AC voltage 6 of the first monomer 1.

[0098] The reference voltage signal 24 is generated from the first signal 12 filtered by the band - pass of the measured first AC voltage 6 of the first monomer 1. The first signal 12 is converted into a changed signal by an amplifier 15 and is used as the reference voltage signal 24. The first signal 12 of the first monomer 1 for the reference voltage signal 24 and filtered by the band - pass 11 is shifted in terms of its phase 20 such that it forms the reference voltage signal 24 of the lock - in amplifier 23 as the phase - shifted signal 27 of the first monomer 1.

[0099] For this purpose, a phase shifter 40 is provided, by means of which the reference voltage signal 24 can be shifted in terms of phase 8, 9. By means of the phase shifter 40, the phase 8, 9 of the reference voltage signal 24 can be changed and thus only the imaginary part 31 of the voltage (and thus the resistance) is amplified.

[0100] Figure 5 The fourth circuit 44 is shown. Refer to the description regarding Figures 2 to 4 Unlike the second circuit 42, the respectively changed signals 16, 17, 18 of two monomers (here the first monomer 1 and the second monomer 2 and the second monomer 2 and the third monomer 3) are respectively supplied to a differential amplifier 28. Each monomer 1, 2, 3 is respectively connected to each other monomer 3, 2, 1 connected in series via the differential amplifier 28. Only when there is a phase shift 20 between the changed signals 16, 17, 18 of the two monomers 1, 2, 3 connected via the differential amplifier 28 respectively, then the corresponding differential amplifier 28 generates a measurement signal 29.

[0101] The measurement signal 29 is supplied to the analog-digital converter 39 and converted into a digital output signal there. These digital output signals are supplied to the evaluation unit 36 and evaluated therein.

[0102] List of reference signs

[0103] 1 First monomer

[0104] 2 Second monomer

[0105] 3 Third monomer

[0106] 4 Battery

[0107] 5 Alternating current

[0108] 6 First alternating voltage

[0109] 7 Second alternating voltage

[0110] 8 First phase

[0111] 9 Second phase

[0112] 10 Frequency

[0113] 11 Bandpass

[0114] 12 First signal

[0115] 13 Second signal

[0116] 14 Third signal

[0117] 15 Amplifier

[0118] 16 First modified signal

[0119] 17 Second modified signal

[0120] 18 Third modified signal

[0121] 19 Phase detector

[0122] 20 Phase shift

[0123] 21 First output signal

[0124] 22 Second output signal

[0125] 23 Lock-in amplifier

[0126] 24 Reference voltage signal

[0127] 25 First direct voltage

[0128] 26 Second direct voltage

[0129] 27 Phase-shifted signal

[0130] 28 Differential amplifier

[0131] 29 Measurement signal

[0132] 30 Data processing system

[0133] 31 Imaginary part

[0134] 32 Real part

[0135] 33 Time

[0136] 34 Consumer

[0137] 35 Switch

[0138] 36 Evaluation unit

[0139] 37 Mixer

[0140] 38 Low-pass

[0141] 39 Converter

[0142] 40 Phase shifter

[0143] 41 First circuit

[0144] 42 Second circuit

[0145] 43 Third circuit

[0146] 44 Fourth circuit.

Claims

1. A method for determining the state of at least one cell (1, 2, 3) of a battery (4), wherein, The battery (4) has a plurality of cells (1, 2, 3) connected in series with each other; wherein, the method at least comprises the following steps: a) Loading the plurality of cells (1, 2, 3) with an alternating current (5); b) Measuring the resulting alternating voltages (6, 7) at at least one first cell (1) and one second cell (2); c) Analyzing the phases (8, 9) of the measured alternating voltages (6, 7) of each cell (1, 2); wherein, a difference between at least a first phase (7) of a first alternating voltage (6) measured at the first cell (1) and a second phase (9) of a second alternating voltage (7) measured at the second cell (2) results in an inference of a difference in the states of at least the first cell (1) and the second cell (2), wherein only the phases (8, 9) of the alternating voltages (6, 7) measured at the cells (1, 2, 3) relative to each other are evaluated, and the correlation between the current and the voltage is not evaluated.

2. The method according to claim 1, wherein, Only the alternating voltages (6, 7) are measured.

3. The method according to any one of claims 1 to 2, wherein, The alternating current (5) has a constant frequency (10).

4. The method according to any one of claims 1 to 2, wherein The alternating current (5) has a varying frequency (10).

5. The method according to any one of claims 1 to 2, wherein, The alternating current (5) has a frequency (10) with only one period length.

6. The method according to any one of claims 1 to 2, wherein The alternating voltages (6, 7) measured at the cells (1, 2, 3) are respectively filtered by band-pass filters (11), and the signals (12, 13, 14) thus respectively generated are changed by an amplifier (15) having a comparator, wherein the respectively changed signals (16, 17, 18) are brought together in a phase detector (19), and the phase shift (20) of the measured alternating voltages (6, 7) can be presented by a first output signal (21).

7. The method according to claim 6, wherein, The changed signals (16, 17, 18) are presented as a second output signal (22), so that it can be presented which alternating voltages (6, 7) have a phase shift (20) relative to other alternating voltages (7, 6).

8. The method according to any one of claims 1 to 2, wherein The alternating voltages (6, 7) measured at the cells (1, 2, 3) are respectively filtered by band-pass filters (11), and the signals (12, 13, 14) thus respectively generated are changed by an amplifier (15), wherein the respectively changed signals (16, 17, 18) are supplied to a lock-in amplifier (23) loaded with a reference voltage signal (24), wherein the lock-in amplifier (23) outputs a direct current voltage (25, 26) for each measured alternating voltage (6, 7), the corresponding level of which is at least proportional to the phase shift (20) between the measured alternating voltage (6, 7) and the reference voltage signal (24).

9. The method according to claim 8, wherein The reference voltage signal (24) corresponds in terms of frequency (10) and phase (8) to the signals (12, 13, 14) filtered by the band-pass filter (11) of the cells (1, 2, 3).

10. The method according to claim 8, wherein Shift the signals (12, 13, 14) of the monomers (1, 2, 3) for the reference voltage signal (24) and filtered by the band-pass (11) in terms of their phase (8) such that the signals form the reference voltage signal (24) of the lock-in amplifier (23) as phase-shifted signals (27) of the monomers (1, 2, 3).

11. The method according to any one of claims 1 to 2, wherein, Filter the AC voltages (6, 7) measured at the monomers (1, 2, 3) respectively by the band-pass (11), and change the signals (12, 13, 14) thus generated respectively by the amplifier (15), wherein the respectively changed signals (16, 17, 18) of two monomers (1, 2, 3) are supplied to the differential amplifier (28); wherein each monomer (1, 2, 3) is connected to each other serially connected monomer (3, 2, 1) respectively via the differential amplifier (28); wherein the differential amplifier (28) generates the measurement signal (29) only when there is a phase shift (20) between the respectively changed signals (16, 17, 18) of the two monomers (1, 2, 3).

12. A data processing system (30) equipped, configured, or programmed to perform the method according to any one of claims 1 to 11, wherein, The data processing system (30) processes and mutually compares the phases (8, 9) of the AC voltages (6, 7) measured at a plurality of monomers (1, 2, 3) of the battery (4).

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