Impedance measurement device and impedance measurement method

Abstract

Provided is an impedance measurement device 100 for measuring the impedance of a battery cell. The device acquires a cell voltage signal between the positive and negative electrodes of a battery cell 20 while a measurement current wave is made to flow through the battery cell 20, modulates the cell voltage signal with a polarity inversion wave synchronized with the half wave of the measurement current wave, adds the modulated wave at the non-inverted and inverted half-cycles of the modulated wave, and adds the modulated wave a prescribed number of times at a cycle synchronized with the polarity inversion wave, thereby generating an AC voltage detection signal, and measures the impedance of the battery cell 20 from the amplitude ratio and the phase difference between the AC voltage detection signal and the measurement current wave.

Description

Impedance measuring device and impedance measuring method

[0001] The present invention relates to an impedance measuring device and an impedance measuring method.

[0002] Measurement circuits for measuring the internal impedance of a storage battery are known. The measurement circuit described in Patent Document 1 uses a single high-input common-mode voltage differential amplifier to expand the measurement range of the storage battery cell voltage, couples the impedance voltage contained in the DC component of the storage battery cell voltage using a capacitor, filters noise through a band-pass filter, converts this signal into a digital signal through an AD converter, and calculates the impedance value.

[0003] JP 2007-514148 A

[0004] The above measurement circuit uses a capacitor to remove the DC component, but the capacitance of the capacitor must be large to accommodate low frequency measurements, which causes a problem of reduced responsiveness in impedance measurement.

[0005] An object of the present invention is to provide an impedance measuring device and an impedance measuring method that can suppress a decrease in responsiveness in impedance measurement.

[0006] The present invention solves the above problem by acquiring a cell voltage signal between the positive and negative electrodes of a battery cell while a measurement current wave is flowing through the battery cell, modulating the cell voltage signal with a polarity-inverted wave synchronized with half of the measurement current wave, adding the modulated wave in the non-inverted half cycle and inverted half cycle of the modulated wave, and adding the modulated wave a predetermined number of times in a cycle synchronized with the polarity-inverted wave to generate an AC voltage detection signal, and measuring the impedance of the battery cell from the amplitude ratio and phase difference between the AC voltage detection signal and the measurement current wave.

[0007] According to the present invention, it is possible to suppress a decrease in responsiveness in impedance measurement.

[0008] FIG. 1 is a block diagram of a vehicle and a charger equipped with an impedance control device according to this embodiment. FIG. 2 is a block diagram of an impedance measurement device according to this embodiment. FIG. 3 is a graph showing the characteristics of a cell voltage signal (S1(ωt)), the polarity characteristics (characteristics of a polarity inversion wave signal) switched by a switching signal (Clk), and the characteristics of a modulated signal (S2(ωt)). FIG. 4 is a graph showing the characteristics of modulated waves (S2(ωt), S2(ωt+π)) and a sum signal (Sv(ωt)). FIG. 5 is a flowchart showing the control flow of an impedance measurement method. FIG. 6 is a circuit diagram of an input amplifier and a modulation circuit included in an impedance measurement device according to a first modification of this embodiment. FIG. 7 is a circuit diagram of an input amplifier, an analog switch, a polarity inverter, an adder, an AD converter (ADC), a measurement control microcomputer (MCU), a measurement current oscillator (SG), a current wave conversion circuit, and an integration circuit included in an impedance measurement device according to a second modification of this embodiment. Fig. 8 is a circuit diagram of an analog switch, a polarity inverter, an adder, an AD converter (ADC), a measurement current oscillator (SG), and an integrating circuit included in an impedance measuring device according to a second modification of this embodiment. Fig. 9 is a circuit diagram of an input amplifier, an analog switch, a polarity inverter, an adder, an integrating circuit, an AD converter (ADC), a measurement control microcomputer (MCU), a measurement current oscillator (SG), and a current wave conversion circuit included in an impedance measuring device according to a third modification of this embodiment. Fig. 10 is a block diagram of an AD converter 5 and a measurement control microcomputer 6 included in an impedance measuring device according to a fourth modification of this embodiment. Fig. 11 is a graph showing the characteristics of signals (S2, S4, S5).

[0009] An embodiment of an impedance measuring device and an impedance measuring method according to the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a vehicle and a charger equipped with an impedance control device. In this embodiment, the impedance control device is provided in the vehicle. Note that the impedance control device is not necessarily limited to the vehicle, and may be provided in a device other than the vehicle. The vehicle is a vehicle equipped with a secondary battery, such as an electric vehicle or a hybrid vehicle.

[0010] The vehicle 1000 includes an impedance measurement device (EIS) 100, a battery monitoring system (BMS) 200, a battery pack 300, an inverter (INV) 400, a motor 500, a charging port 600, and a charger 700. The inverter measurement device 100 measures the impedance of the battery cells included in the battery pack 300. The battery monitoring system 200 detects the deterioration state of the battery cells based on the impedance measured by the impedance measurement device 100. The battery monitoring system 200 also manages the SOC of the battery cells. The battery monitoring system 200 may transmit battery data of the battery cells to the outside of the vehicle via a communication unit and a wireless antenna.

[0011] The battery pack 300 includes a plurality of battery cells (battery groups) 20 connected in series or parallel and a current sensor 9. The battery pack 300 includes a plurality of battery modules each modularizing a plurality of battery cells 20. The battery cells 20 are, for example, lithium-ion secondary batteries. An example of a battery cell 20 is a flat-type laminate film lithium-ion secondary battery. The battery cell 20 includes a power generating element formed by stacking electrode layers (positive and negative electrode layers) and separators and filling them with an electrolyte, a positive electrode tab connected to the positive electrode layer, a negative electrode tab connected to the negative electrode layer, and an exterior member that houses and seals these components. While detailed descriptions of the materials contained in the lithium-ion secondary battery and its structure are omitted, well-known battery materials and structures can be applied to lithium-ion secondary batteries. The battery cells 20 are not limited to secondary batteries containing an electrolyte, and may be all-solid-state lithium-ion batteries. The battery pack 300 is connected to a motor 500 via an inverter 400 and supplies power to the motor 500. Furthermore, the battery cells 20 included in the battery pack 300 can be charged by regeneration of the motor 500. The battery pack 300 can be connected to an external charger 700 via a charging port 600 and charged by the charger 700. The vehicle 1000 is equipped with auxiliary devices, a vehicle control unit, etc. in addition to the impedance measurement device (EIS) 100 shown in FIG. 1 .

[0012] FIG. 2 is a block diagram of the impedance measuring device 100. The impedance measuring device 100 includes an input amplifier 1, an analog switch 2, a polarity inverter 3, an adder 4, an AD converter 5, a measurement control microcomputer (MCU) 6, a measurement current oscillator (SG) 7, a current wave conversion circuit 8, and a current sensor 9. The input side of the input amplifier 1 is connected to the positive and negative electrodes of a battery cell 20, and the output side is connected to the analog switch 2. The input amplifier 1 acquires a cell voltage signal between the positive and negative electrodes of the battery cell 20 while a measurement current wave is flowing through the battery cell 20, and amplifies and outputs the acquired cell voltage signal. The battery cell 20 has an internal resistance (Zc). The voltage between the negative input terminal of the battery cell 20 is the sum of the DC component Vdc and the voltage (AC component: Vac) applied to the internal resistance (Zc), and this voltage is input to the input amplifier 1.

[0013] The input amplifier 1 outputs the potential difference between the positive and negative input terminals of the battery cell 20 as a cell voltage signal to acquire the voltage between the electrodes of the battery cell being measured, regardless of the number of battery cells 20 connected in series within the battery module. Note that the input amplifier 1 may be provided with an anti-aliasing filter.

[0014] The analog switch 2 is a switch that switches the output of the cell voltage signal every half cycle, and is a switching element that switches and transmits the input cell voltage signal to two output terminals. A switching signal (Clk) is input to the analog switch 2, and the output terminal is switched based on the switching signal (Clk). The cycle for switching the output terminal of the analog switch 2 is synchronized with the half wave of the measurement current wave. For example, a mechanical, optical, or electromagnetically coupled relay or a semiconductor switch is used as the analog switch 2.

[0015] The polarity inverter 3 is a circuit element that inverts the polarity of the voltage of the cell voltage signal, and is connected between one of the pair of output terminals of the analog switch 2 and the adder 4. The polarity inverter 3 may be configured, for example, as an inverting amplifier of an operational amplifier. The analog switch 2 and the polarity inverter 3 invert the polarity of the voltage for half a cycle of the cell voltage signal. The adder 4 adds the non-inverted signal output from the other output terminal of the analog switch 2 and the inverted signal output from the polarity inverter 3 to convert them into a single signal. The adder 4 is configured, for example, as an adder circuit of an operational amplifier, or a current adder circuit using resistive elements.

[0016] The analog switch 2 and polarity inverter 3 invert the polarity of the voltage for half a cycle of the cell voltage signal, and the adder 4 adds the non-inverted signal of the cell voltage signal, whose polarity has not been inverted, to the inverted signal, whose polarity has been inverted. In other words, the analog switch 2, polarity inverter 3, and adder 4 perform a process of modulating (multiplying) the cell voltage signal with a polarity-inverted wave synchronized with the half-wave of the measurement current wave. The output signal of the adder 4 corresponds to the modulated wave modulated based on the cell voltage signal.

[0017] The AD converter 5 digitizes (quantifies) the level of the output signal (analog signal) from the adder 4. The measurement control microcomputer 6 receives the digitized signal and performs an addition process (conversion calculation process) to generate an AC voltage detection signal. The addition process performed by the measurement control microcomputer 6 will be described later. The measurement control microcomputer 6 also calculates the impedance of the battery cell 20 from the amplitude ratio and phase difference between the AC voltage detection signal and the measurement current wave. The measurement control microcomputer 6 may measure the AC impedance of the secondary battery 2 by changing the frequency of the measurement current wave over time using an AC impedance method. The measurement control microcomputer 6 may also be capable of simultaneously applying multiple measurement current waves with different frequencies to the battery cell 20. The method for measuring AC impedance using the AC impedance method is not particularly limited. The measurement control microcomputer 6 may have a function (noise removal function) to remove unnecessary signal components that may lead to measurement errors. The measurement control microcomputer 6 may also have a function (measurement current control function) of controlling the measurement current oscillator 11 so that it is started at a pre-programmed timing (timer) and applies a measurement current wave to the battery cell 20. The measurement control microcomputer 6 may also have a function (memory function) of storing the impedance measurement value in memory. The impedance measured by the measurement control microcomputer 6 is used to determine the deterioration state of the battery cell 20.

[0018] The measurement current oscillator 7 sets the frequency, amplitude, and phase in response to a control command from the measurement control microcomputer 6, generates a current control signal Sin(ωt+θ), and outputs it to the current wave conversion circuit 8. The control command from the measurement control microcomputer 6 sets the frequency, amplitude, and phase of the AC current to be passed through the battery cell 20. The measurement current oscillator 7 also outputs a switching signal (Clk). In other words, the measurement current oscillator 7 is a circuit that generates the current control signal Sin(ωt+θ) and the switching signal (Clk).

[0019] The current wave conversion circuit 8 converts the signal level from the measurement current oscillator 7 into a current value multiplied by a predetermined conversion coefficient (proportional constant), and applies the current value to the battery cell 20 to be measured. That is, the measurement current oscillator 7 and the current wave conversion circuit 8 pass a measurement current wave of a predetermined frequency through the battery cell 20 based on a control command from the measurement control microcomputer 6. The current wave conversion circuit 8 is configured, for example, by a Howland Current Pump type voltage-current conversion circuit.

[0020] The current sensor 9 detects the current flowing through the battery cell 20 and outputs a detection signal to the measurement control microcomputer 6. The detection signal corresponds to the detected value of the measurement current wave. The detection signal of the current sensor 9 is used as the measurement current wave when the measurement control microcomputer 6 calculates the impedance.

[0021] In the example of FIG. 2 , the impedance measuring device 100 is connected to a single battery cell 20, but multiple battery cells 20 may be connected between the input terminals of the input amplifier 1. The impedance measuring device 100 may also be configured such that the input amplifier 1, analog switch 2, polarity inverter 3, adder 4, and modulator having the same circuit configuration as the AD converter 5 are connected to the other battery cells 20, and the measurement control microcomputer 6 is shared. In this case, a signal (measured cell voltage) digitized by the AD converter 5 based on the cell voltage signal of the other battery cell 20 is input to the measurement control microcomputer 6. When measuring the cell voltage of the other battery cell 20, the measurement current oscillator 7 and current wave conversion circuit 8 may be shared, and the current sensor 9 may also be shared. This allows the impedance measuring device 100 to measure the cell voltage and impedance of each of the multiple battery cells 20.

[0022] Next, the modulation process and addition process in the impedance measuring device 100 will be described with reference to Figures 2 to 4. Figure 3 is a graph showing the characteristics of the cell voltage signal (S1(ωt)), the polarity characteristics (polarity inversion wave signal characteristics) switched by the switching signal (Clk), and the characteristics of the modulated signal (S2(ωt)). Note that ω corresponds to the angular frequency of the current control signal. The horizontal axis of each graph represents time.

[0023] The cell voltage signal (S1(ωt)) is the output signal of the input amplifier 1 and has sinusoidal characteristics with the DC component voltage (Vdc) of the battery cell 20 at its center and the AC component voltage (Vac) at its amplitude. The cell voltage signal (S1(ωt)) also contains noise components that oscillate with minute amplitude and are asynchronous (low-correlation) with the current control signal. The graph (Clk(ωt)) in Figure 3 corresponds to the polarity-inverted wave generated by the analog switch 2 and polarity inverter 3. The frequency of the polarity-inverted wave is the same as the current control signal and is synchronized with the switching signal (Clk). Therefore, the polarity-inverted wave inverts between 1 V and -1 V every half cycle of the cell voltage signal (S1(ωt)). The modulated wave (S2(ωt)) is the output signal of the adder 4 and has characteristics obtained by multiplying the cell voltage signal (S1(ωt)) by the polarity-inverted wave. As a result, a modulation circuit including an analog switch 2, a polarity inverter 3, and an adder 4 modulates the cell voltage signal with a polarity-inverted wave synchronized with a half-wave of the measurement current wave, and outputs a modulated signal (modulated wave).

[0024] The measurement control microcomputer 6 shifts the modulated wave (S2(ωt)) by half a period to add the non-inverted half period and the inverted half period of the modulated wave. S2(ωt+π) shown in FIG. 4 is the modulated wave after being shifted by half a period. The measurement control microcomputer 6 adds the modulated wave (S2(ωt)) and the modulated wave (S2(ωt+π)) shifted by half a period. In other words, the measurement control microcomputer 6 adds the non-inverted half period and the inverted half period of the modulated wave (hereinafter also referred to as the "first addition process"). The signal Sv(ωt) in FIG. 4 represents the signal after the non-inverted half period and the inverted half period of the modulated wave have been added. This addition process cancels out the DC component (Vdc) by adding the polarity inversions of each half period. Furthermore, the AC component (Vac) of the modulated wave (S2(ωt)) is polarity-inverted to become positive and is added to the non-inverted positive half wave, so the AC component (Vac) is doubled. In other words, Sv(ωt) = (Vdc + Vac(ωt)) - (Vdc - Vac(ωt)) = 2 × Vac(ωt).

[0025] The measurement control microcomputer 6 also adds the modulated wave a predetermined number of times in a cycle synchronized with the polarity-inverted wave (hereinafter also referred to as the "second addition process"). The signal obtained by adding the modulated wave over a non-inverted half cycle and an inverted half cycle is a signal in which a positive half wave repeats with the cycle of the modulated wave, as shown by Sv(ωt) in FIG. 4. The measurement control microcomputer 6 repeatedly adds the positive half wave in Sv(ωt) for the number of cycles of the modulated wave. The amplitude of the signal after the addition process is 2 × Vac × a predetermined number (number of additions). In other words, by repeating the second addition process, the amplitude of the AC component synchronized with the current control signal increases in proportion to the number of additions. Note that the predetermined number of times is preferably set so that the amplitude of the signal after the addition process is within the range of 10 mV to 1 V.

[0026] As shown in the S1(ωt) characteristic in Figure 3, the cell voltage signal (S1(ωt)) contains noise components that are asynchronous (low correlation) with the current control signal. By executing the first addition process and the second addition process, the measurement control microcomputer 6 can increase the probability (number of cancellations) of adding (cancelling) the positive and negative amplitudes of the noise components, thereby suppressing the noise components. This allows the amplitude of the signal component that is synchronized with the current control signal (measurement current wave) to be selectively amplified.

[0027] The measurement control microcomputer 6 generates an AC voltage detection signal based on the calculation result obtained by executing the first addition process and the second addition process on the modulated wave. For example, the measurement control microcomputer 6 may calculate the amplitude and phase of the AC voltage of the battery cell 20 from the calculation result obtained by executing the first addition process and the second addition process on the modulated wave, and generate the AC voltage detection signal from the amplitude and phase.

[0028] Next, an impedance measurement method using the impedance measuring device 100 will be described with reference to FIG. 5. FIG. 5 is a flowchart showing the control flow of the impedance measurement method. The impedance measuring device 100 has a memory for storing a program and a processor for executing the program. The processor is a control device such as a CPU or MPU. When the processor executes the program, it operates the circuit elements shown in FIG. 2 to execute the control flow described below.

[0029] In step S1, the measurement control microcomputer 6 outputs a control command to the measurement current oscillator 7 to set the frequency of the measurement current oscillator 7 (the frequency of the measurement current wave), etc., and starts outputting the current control signal and switching signal (Clk). In step S2, the measurement control microcomputer 6 clears the counter. Note that if data is stored in the buffer, the buffer may also be cleared. In step S3, the analog switch 2 switches the switch (SW = 1) so that the signal output is the non-inverted signal output side. In step S4, the AD converter 5 digitizes (quantifies) the level of the output signal (analog signal) of the adder 4. In step S5, the measurement control microcomputer 6 determines whether the AD converter 5 has performed the digitization conversion process for half a cycle of the measurement current wave. If the conversion process for half a cycle of the measurement current wave has not been performed (if the conversion process has not been completed for half a cycle of the measurement current wave), the impedance measuring device 100 returns to the control process of step S3 and executes the control flow. When the conversion process for half a cycle of the measurement current wave has been performed, in step S6, the measurement control microcomputer 6 performs an addition process on the non-inverted data and stores the data after the addition process in a buffer. The non-inverted data is data of the modulated wave with a non-inverted half cycle. By executing the control flow of step S6, the measurement control microcomputer 6 adds the modulated wave with a non-inverted half cycle a predetermined number of times. In other words, the measurement control microcomputer 6 performs a second addition process on the non-inverted data.

[0030] When the addition process of step S6 is performed, the analog switch 2 is switched so that the signal output is the non-inverted signal output side, and the value input to the adder 4 from the line on the SW=2 side is zero. Then, in the addition process of step S6, the "non-inverted signal" and "inverted signal (all data = 0)" of the AD converted time series data are matched for each time, and the AD converted values ​​are added together. This is part of the switch function that selects whether the signal to be guided to the AD converter is the "non-inverted signal" or the "inverted signal."

[0031] In step S7, the analog switch 2 switches the switch (SW = 2) so that the signal output is the inverted signal output side. In step S8, the AD converter 5 digitizes (quantifies) the level of the output signal (analog signal) of the adder 4. In step S9, the measurement control microcomputer 6 determines whether the digitization conversion process by the AD converter 5 has been performed for half a cycle of the measurement current wave. If the conversion process for half a cycle of the measurement current wave has not been performed (if the conversion process has not been completed for half a cycle of the measurement current wave), the impedance measuring device 100 returns to the control process of step S7 and executes the control flow. If the conversion process for half a cycle of the measurement current wave has been performed, in step S10, the measurement control microcomputer 6 executes an addition process on the inverted data and stores the data after the addition process in the buffer. The inverted data is data of the modulated wave for the inverted half cycle. By executing the control flow of step S10, the measurement control microcomputer 6 adds the modulated wave for the inverted half cycle a predetermined number of times. In other words, the measurement control microcomputer 6 executes a second addition process on the inverted data.

[0032] In step S11, the measurement control microcomputer 6 determines whether the digitization conversion process by the AD converter 5 has been performed for a predetermined number of cycles of the measurement current wave. The predetermined number of cycles is determined according to the number of additions. If the conversion process has not been performed for the predetermined number of cycles of the measurement current wave (if the conversion process has not been completed for the predetermined number of cycles of the measurement current wave), the impedance measuring device 100 returns to the control process of step S2 and executes the control flow.

[0033] When the conversion process for the predetermined period of the measurement current wave has been executed, the measurement control microcomputer 6 executes a process of adding the non-inverted data and the inverted data in step S12. By executing the control flow of step S12, the measurement control microcomputer 6 adds the modulated wave and the modulated wave of the non-inverted half period. In other words, the measurement control microcomputer 6 executes a first addition process on the non-inverted data and the inverted data.

[0034] In step S13, the measurement control microcomputer 6 performs impedance calculation. Specifically, the measurement control microcomputer 6 generates an AC voltage detection signal based on the calculation results obtained by performing a first addition process and a second addition process on the non-inverted data and the inverted data. The measurement control microcomputer 6 then measures the impedance of the battery cell 20 from the amplitude ratio and phase difference between the AC voltage detection signal and the measurement current wave. Note that the measurement control microcomputer 6 may also calculate the impedance by subtracting the amplitude of the measurement current wave from the amplitude of the AC voltage detection signal and using Ohm's law. Note that the amplitude of the AC voltage detection signal is obtained by adding the amplitude of a half cycle of the modulated wave, so the measurement control microcomputer 6 may calculate the impedance from the amplitude ratio between the AC voltage detection signal and the measurement current wave by matching the number of additions of the amplitude of the measurement current wave with the number of additions of the amplitude of a half cycle of the modulated wave.

[0035] In step S14, the measurement control microcomputer 6 determines whether the frequency of the measurement current wave has reached the final measurement frequency. The measurement control microcomputer 6 changes the frequency of the measurement current wave over time. If the frequency of the measurement current wave has not reached the final measurement frequency, the measurement control microcomputer 6 returns to the control flow of step S1, sets the frequency of the measurement current wave to a new frequency, and executes the control flow from step S1 onwards.

[0036] When the frequency of the measurement current wave reaches the final measurement frequency, the measurement control microcomputer 6 outputs the impedance measurement result to the battery monitoring system 200 (step S15). Then, the impedance measuring device 100 ends the control flow shown in FIG.

[0037] As described above, the impedance measuring device 100 and impedance measuring method according to this embodiment acquire a cell voltage signal between the positive and negative electrodes of the battery cell 20 while a measurement current wave is flowing through the battery cell 20. Based on the cell voltage signal, the device performs modulation, first summation, and second summation to generate an AC voltage detection signal. The impedance of the battery cell 20 is measured based on the amplitude ratio and phase difference between the AC voltage detection signal and the measurement current wave. The modulation process includes modulating the cell voltage signal with a polarity-inverted wave synchronized with a half-wave of the measurement current wave. The first summation process includes adding the modulated wave in the non-inverted half cycle and the inverted half cycle of the modulated wave modulated by the modulation process. The second summation process includes adding the modulated wave a predetermined number of times in a cycle synchronized with the polarity-inverted wave. This prevents a decrease in impedance measurement responsiveness. Furthermore, the impedance measuring device 100 modulates the cell voltage signal using the modulation process and then removes the DC component of the battery cell 20 using the first summation process. This allows for the removal of asynchronous noise. Incidentally, one method for amplifying the amplitude of an AC voltage detection signal is to use an amplifier and amplify the signal in proportion to the amplification factor (gain). However, this method also amplifies amplifier noise. On the other hand, in this embodiment, the amplitude is amplified after the number of additions is set by the second addition process, so amplification of noise components can also be suppressed. As a result, the impedance measurement accuracy can be improved.

[0038] As a first modification of this embodiment, the impedance measuring device 100 may include a double-pole double-throw switch 31 and a differential input AD converter 32 instead of the analog switch 2, polarity inverter 3, and adder 4. FIG. 6 is a circuit diagram of the input amplifier 1 and the modulation circuit 30. Note that FIG. 6 shows a portion of the circuit of the impedance measuring device 100. Although the circuit diagram of FIG. 6 only shows the input amplifier 1 and the modulation circuit 30, the impedance measuring device 100 also includes a measurement control microcomputer 6 and the like. The modulation circuit 30 is a circuit for performing modulation processing. Note that in the circuit shown in FIG. 2, the modulation circuit corresponds to a circuit including the analog switch 2, polarity inverter 3, and adder 4.

[0039] The double-pole double-throw switch 31 is a double-pole double-throw analog switch that has two pairs of contacts on the input side and one pair of settings on the output side. The input amplifier 1 is connected to the input side of the double-pole double-throw switch 31. The differential input AD converter 32 is a differential input AD converter that has a non-inverting polarity input terminal and an inverting polarity input terminal. The output terminal of the double-pole double-throw switch 31 is connected to the input terminal of the differential input AD converter 32. The output terminal of the differential input AD converter 32 is connected to the measurement control microcomputer 6.

[0040] Next, the circuit operation of the modulation circuit 30 will be described. When a non-inverting switching signal (Clk) is input to the double-pole double-throw switch 31, the double-pole double-throw switch 31 establishes electrical continuity between the upper terminal 1 and the high-potential output terminal, and between the lower terminal 1 and the low-potential output terminal. The cell voltage signal (S1(ωt)) flows from the upper terminal 1 through the closed switch and the high-potential output terminal to the + input terminal of the differential input AD converter 32. Meanwhile, the - input terminal of the differential input AD converter 32 is connected to circuit GND (reference potential) through the closed switch and the lower terminal 1. This allows the cell voltage signal to be input non-inverted to the differential input AD converter 32.

[0041] When an inverted switching signal (Clk) is input to the double-pole double-throw switch 31, the double-pole double-throw switch 31 establishes electrical continuity between the upper terminal 2 and the high-potential output terminal, and between the lower terminal 2 and the low-potential output terminal. The cell voltage signal (S1(ωt)) flows from the lower terminal 2 through the closed switch and the low-potential output terminal to the negative input terminal of the differential input AD converter 32. Meanwhile, the positive input terminal of the differential input AD converter 32 is connected to circuit GND (reference potential) through the closed switch and the upper terminal 2. This causes the cell voltage signal to be input in an inverted form to the differential input AD converter 32.

[0042] That is, the measurement control microcomputer 6 sends a control command to the measurement current oscillator 7, inputting a switching signal (Clk) to the double-pole, double-throw switch 31 to switch the polarity of the differential-input AD converter to which the cell voltage signal is output. The polarity switching is performed by switching the double-pole, double-throw switch 31 in synchronization with the half cycle of the measurement current wave. As a result, the signal input to the differential-input AD converter 32 becomes a modulated signal, and becomes a signal wave in which the cell voltage signal (S1(ωt)) alternates between positive and negative polarity every half cycle, as in the modulated wave (S2(ωt)) in Figure 3 . The differential-input AD converter 32 then digitizes (quantifies) the level of the output signal (analog signal) of the double-pole, double-throw switch 31.

[0043] As described above, the first modification of this embodiment includes a double-pole double-throw switch 31 and a differential input AD converter 32, and switches the double-pole double-throw switch 31 so that the polarity of the differential input AD converter 32, which is the output destination of the cell voltage signal, switches in synchronization with the half cycle of the measurement current wave. This eliminates the need for the polarity inverter 3 and adder 4, thereby enabling the circuit to be made smaller and less expensive.

[0044] Unlike Modification 1, the modulation circuit shown in FIG. 2 includes a polarity inverter 3 in the path of the polarity-inverted signal, which may result in amplifier noise being included in the polarity-inverted signal. This noise includes not only white noise but also a DC offset from the polarity inverter 3. The addition of a DC offset impairs the DC component cancellation effect achieved by the addition process. In other words, the DC offset component from the polarity inverter 3 is output as a residual error. Furthermore, high-power batteries, such as those installed in electric vehicles, have extremely low internal resistance (1 mΩ or less), making the residual error non-negligible. A typical operational amplifier has a DC offset of several mV. For example, when a measurement current wave (Iac = 1 A) is applied to a battery with an internal resistance of 1 mΩ, the resulting cell detection signal is 1 mV. Therefore, the operational amplifier's DC offset (several mV) results in a residual error that exceeds the voltage of the cell detection signal. On the other hand, Modification 1 eliminates the need for the polarity inverter 3, preventing amplifier noise and DC offset components from being included in the cell detection signal.

[0045] As another modification example 2 of this embodiment, the impedance measuring device 100 may include an integrating circuit 41. FIG. 7 is a circuit diagram of the input amplifier 1, analog switch 2, polarity inverter 3, adder 4, AD converter (ADC) 5, measurement control microcomputer (MCU) 6, measurement current oscillator (SG) 7, current wave conversion circuit 8, and integrating circuit 41. The integrating circuit 41 is connected between the adder 4 and the AD converter 5. The integrating circuit 41 removes DC components from the battery cell 20 and passes AC components. The output signal of the integrating circuit 41 is input to the AD converter 5. The integration period of the integrating circuit 41 is set so that the voltage of the output signal from the integrating circuit 41 falls within the input voltage range of the AD converter 5. The input voltage range of the AD converter 5 is a voltage range determined according to the circuit configuration included in the AD converter 5. The integration period of the integrating circuit 41 is set to one cycle of the current control signal or an integer multiple (e.g., 1000 times) of that cycle. The integration period is preferably set to 100 ms or more.

[0046] In response to a control command from the measurement control microcomputer 6, the measurement current oscillator 7 outputs a reset signal that resets the integration by the integrating circuit 41 and a trigger signal that starts AD conversion by the AD converter 5. Upon receiving the reset signal, the integrating circuit 41 terminates integration and resets the integration result during the reset period. The reset period is set in advance according to the discharge time of the capacitor included in the integrating circuit. After the reset period has elapsed, the integrating circuit 41 outputs the integration result (output signal) to the AD converter 5 and starts the next integration. Upon receiving the trigger signal, the AD converter 5 performs AD conversion and outputs the digitized signal to the measurement control microcomputer 6.

[0047] 8 is an example circuit diagram of the AD converter 5, measurement current oscillator (SG) 7, integrating circuit 41, and polarity switching circuit 42 of the impedance measuring device 100 according to Modification 2. In the example of FIG. 8, the polarity switching circuit 42 has the circuit functions of the analog switch 2, polarity inverter 3, and adder 4. The polarity switching circuit 42 utilizes the operating characteristics of the operational amplifier to switch polarity and add inverted and non-inverted signals. The integrating circuit 41 has a negative feedback path for the operational amplifier, an integrating capacitor, and a reset analog SW (411).

[0048] Next, the circuit operation of the integrating circuit 41 and the polarity switching circuit 42 will be described. When the analog SW 421 included in the polarity switching circuit 42 is closed, the input signal (S1) input from the input amplifier 1 is applied to the positive terminal of the operational amplifier. The operational amplifier becomes a non-inverting amplifier, and a signal of the same polarity as the signal (S1) flows to the integrating circuit 41. On the other hand, when the analog SW 421 is open, the input signal (S1) is applied to the negative terminal of the operational amplifier via resistor R1. The operational amplifier becomes an inverting amplifier, and a signal of the opposite polarity to the signal (S1) flows to the integrating circuit 41. Resistor R2 in the negative feedback path adjusts the amplification factor of the output signal, and is generally set to R1 = R2 (amplification factor 1).

[0049] When the analog switch 411 of the integrating circuit 41 is opened, integration is performed; when it is closed, the integration result is cleared. The output signal of the polarity switching circuit 42 is input to the negative terminal of the operational amplifier of the integrating circuit 41 via resistor R. The positive terminal of the operational amplifier is connected to a reference potential (typically GND). Due to the operation of the operational amplifier, a current of reversed polarity equal to the signal voltage (S2) divided by resistor R is charged into the integrating capacitor C, thereby integrating the signal (S2). The polarity of the integral output at this time is reversed, and the rate of change (time change) is determined by resistor R and capacitor C. It is necessary to set RC so that the operational amplifier output does not saturate during the integration period when the maximum voltage of the signal (S2) is input. The integration result by the integrating circuit 41 is then output to the AD converter 5 as signal (S3).

[0050] As described above, the second modification of this embodiment includes the integrating circuit 41 that performs the second addition process and the AD converter 5 that digitally converts the output signal of the integrating circuit 41. The integration period of the integrating circuit 41 is set so that the voltage of the output signal of the integrating circuit 41 falls within the input voltage range of the AD converter 5. This makes it possible to reduce the size and cost of the circuit.

[0051] Unlike the second modification, the AD converter 5 included in the impedance measuring device 100 shown in FIG. 2 converts signals containing DC components. Generally, an AD converter capable of AD conversion of AC and DC components requires high resolution. In the second modification, because the integrating circuit 41 removes the DC component, a low-resolution AD converter can be used for the AD converter 5. For example, if the input voltage range of the AD converter 5 is 4.2 V and the integrating circuit 41 integrates a 1 mV AC component for 1,000 cycles, the amplitude of the output signal from the integrating circuit 41 is 2 * 1 mV * 1,000 * 2 / π = 1.273 V. Therefore, for the AD converter 5 to digitize the input voltage at 1%, 1 / (1.273 * 0.01 / 4.2) ≒ 330, requiring only a 9-bit resolution. An AD converter (resolution: 10-12 bits) built into a typical general-purpose microcontroller can be used. Furthermore, since the output signal of the integrating circuit 41 is a DC signal, the AD conversion speed (digital value conversion time) can be slow, allowing the use of an inexpensive microcomputer (AD converter).Furthermore, the size and cost of the measurement control microcomputer 6 in the next stage can be reduced.

[0052] As another modification example 3 of this embodiment, the impedance measuring device 100 may include a circuit configuration that measures complex impedance based on the phase of the measurement current wave. FIG. 9 is a circuit diagram of the input amplifier 1, analog switches 51 and 52, polarity inverters 53 and 54, adders 55 and 56, integrator circuits 57 and 58, analog-to-digital converters (ADCs) 59 and 60, a measurement control microcomputer (MCU) 6, a measurement current oscillator (SG) 7, and a current wave conversion circuit 8. As shown in FIG. 9 , a two-system circuit configuration is formed from the analog switches 51 and 52 to the analog-to-digital converters (ADCs) 59 and 60, and the cell voltage signal is distributed to each system circuit. That is, the impedance measuring device 100 according to the modification example 3 includes two stages of the circuit configuration shown in the modification example 2. The impedance measuring device 100 measures the impedance of the battery cell 20 from the complex impedance (Nyquist diagram), and the absolute value of the impedance is separated into the real axis and the imaginary axis using the two-stage circuit configuration. In the following description, Modification 3 will be described using the circuit configuration shown in FIG. 9, in which the upper circuit is for real axis (Re) impedance and the lower circuit is for imaginary axis (Im) impedance.

[0053] The upper circuit generates a first AC voltage detection signal by modulating the cell voltage signal with a half cycle in phase with the measurement current wave. The lower circuit generates a second AC voltage signal by shifting the phase of the cell voltage signal by a quarter cycle of the cell voltage signal and modulating the cell voltage signal with a half cycle in phase with the measurement current wave. The first and second AC voltage signals are generated as follows. The measurement current oscillator 7 generates a polarity switching signal (Clk ｘ (sinωt)) and polarity switching signal for imaginary axis Im impedance (Clk ｙ (sinωt-90°)) to generate a polarity switching signal (Clk ｘ (sinωt)) is in phase with the measurement current wave. ｙ (sinωt-90°) lags behind the phase of the measurement current wave by 90° (1 / 4 cycle).

[0054] The analog switch 51 receives a polarity switching signal (Clk ｘThe switch is switched in accordance with the real part (sinωt) of the analog voltage signal. When the upper stage circuit including the analog switch 51 operates in the same manner as in the second modification, polarity inversion processing and integration processing by the integrator circuit 57 are performed. The integration result (signal (S3x)) by the integrator circuit 57 becomes a value proportional to the impedance of the real part (Re). The AD converter 59 performs AD conversion on the integration result (output signal) and outputs the digitized signal to the measurement control microcomputer 6. The signal digitized by the AD converter 59 corresponds to the first AC voltage detection signal.

[0055] The analog switch 52 receives a polarity switching signal (Clk ｙ The switch is switched in accordance with the signal (sinωt-90°). When the lower stage circuit including the analog switch 52 operates in the same manner as in Modification 2, polarity inversion processing and integration processing by the integrator circuit 58 are performed. The integration result (signal (S3y)) by the integrator circuit 58 becomes a value proportional to the impedance of the imaginary part (Im). The AD converter 5 performs AD conversion on the integration result (output signal) and outputs the digitized signal to the measurement control microcomputer 6. The signal digitized by the AD converter 5 corresponds to the second AC voltage detection signal.

[0056] The measurement control microcomputer 6 calculates the complex impedance value using the following equations: Z(Re) = G S3x / Iac and Z(Im) = G S3y / Iac. Note that G in these equations represents the reciprocal of the transmission gain from the input amplifier 1 to the AD converters 59 and 60, and Iac represents the current value of the measurement current wave.

[0057] As described above, in the third modification of this embodiment, a first AC voltage detection signal modulated with a half cycle in phase with the measurement current wave and a second AC voltage detection signal modulated with a half cycle and shifted in phase by a quarter cycle from the measurement current wave are generated, and a complex impedance value is calculated based on the first AC voltage detection signal and the second AC voltage detection signal. This allows the internal impedance of the cell to be separated into complex numbers, making it possible to diagnose the state of the positive and negative electrodes in addition to determining electrolyte degradation. As a result, the state of health (SoH) and state of charge (SoC) of the battery cell 20 can be estimated with high accuracy.

[0058] As another modification example 4 of this embodiment, the impedance measuring device 100 may remove the DC component from the cell voltage signal, alternately invert the polarity of the signal after the DC component removal at timing synchronized with half waves of the measurement current wave to generate a sine wave signal, and then filter the sine wave signal using a bandpass filter. Figure 10 is a block diagram of the AD converter 5 and the measurement control microcomputer 6. Note that although the block diagram of Figure 10 shows only the AD converter 5 and the AD converter 5, the impedance measuring device 100 also includes an input amplifier 1 and the like.

[0059] The measurement control microcomputer 6 has a buffer 61, a counter 62, a switch 63, an inverter 64, an adder 65, a band-pass filter 66, and an impedance calculation unit 67. The measurement control microcomputer 6 stores the value digitized by the AD converter 5 in the buffer 61. The measurement control microcomputer 6 executes a first addition process on the data of the output signal (S2) of the AD converter 5 recorded in the buffer 61. The output signal of the AD converter 5 contains a DC component of the battery cell 20, but the DC component can be removed by adding the non-inverted half cycle and the inverted half cycle of the signal.

[0060] The measurement current oscillator 7 divides the switching signal (Clk) in half to generate a switching signal (Clz = Clk / 2) and outputs it to the counter 62. The counter 62 increments the counter value in accordance with the switching signal (Clz = Clk). The switch 63 switches to the non-inverted output side for odd counter values ​​and to the inverted output side for even counter values. The adder 65 adds the non-inverted signal and the inverted signal to generate a signal (S4). Figures 11(a), (b), and (c) are graphs showing the characteristics of signals S2, S4, and S5. The output signal of the adder 65 is a sine wave as shown in Figure 11(b). That is, in the signal (S2), odd counter values ​​are output non-inverted and even counter values ​​are output inverted, resulting in a sine wave as shown in Figure 11(b). The band-pass filter 66 performs filtering on the output signal (sine wave signal) of the adder 65. The passband of the bandpass filter 66 is set according to the noise superimposed on the output signal. For example, the center frequency of the passband is set to the measurement frequency of the measurement current wave. The signal after passing through the bandpass filter 66 has the characteristics shown in FIG. 11(c), and noise components outside the measurement frequency are reduced. The measurement control microcomputer 6 then calculates the impedance of the battery cell 20 based on the signal after passing through the bandpass filter 66. This improves the signal-to-noise ratio of the cell voltage signal (detection signal) and also increases the accuracy of impedance measurement.

[0061] As described above, in the fourth modification of this embodiment, the DC component contained in the cell voltage signal is removed, and the polarity of the signal after the DC component removal is alternately inverted at timing synchronized with half waves of the measurement current wave to generate a sine wave signal, and the sine wave signal is then filtered using a band-pass filter. This improves the signal-to-noise ratio of the AC signal and enables high-resolution impedance measurement. Furthermore, the state of health (SoH) and state of charge (SoC) of the battery cell 20 can be estimated with high accuracy.

[0062] The measurement current oscillator 7 and the current wave conversion circuit 8 correspond to the "measurement current output means" of the present invention, and the input amplifier 1, the analog switches 2, 51, 52, the polarity inverters 3, 53, 54, the adders 4, 55, 56, the AD converters 5, 59, 60, the measurement control microcomputer 6, the integrating circuits 41, 57, 58, and the polarity switching circuit 42 correspond to the "impedance detection means" of the present invention.

[0063] Although the embodiments of the present invention have been described above, these embodiments are described to facilitate understanding of the present invention and are not described to limit the present invention. Therefore, each element disclosed in the above embodiments is intended to include all design modifications and equivalents that fall within the technical scope of the present invention.

[0064] REFERENCE SIGNS LIST 1 Input amplifier 2 Analog switch 3 Polarity inverter 4 Adder 5 AD converter (ADC) 6 Measurement control microcomputer (MCU) 7 Measurement current oscillator (SG) 8 Current wave conversion circuit 9 Current sensor 20 Battery cell 100 Impedance measurement device (EIS)

Claims

An impedance measuring device for measuring the impedance of a battery cell, a measurement current output means for causing a measurement current wave of a predetermined frequency to flow through the battery cell; an impedance measuring means for measuring the impedance of the battery cell based on an amplitude ratio and a phase difference between an AC voltage detection signal of the battery cell and the measurement current wave, The impedance measuring means includes: acquiring a cell voltage signal between the positive and negative electrodes of the battery cell while the measurement current wave is flowing through the battery cell; generating the AC voltage detection signal by executing a modulation process, a first addition process, and a second addition process; The modulation process includes a process of modulating the cell voltage signal with a polarity inversion wave synchronized with a half wave of the measurement current wave, the first addition process includes a process of adding the modulated wave in a non-inverted half cycle and an inverted half cycle of the modulated wave modulated by the modulation process, The second addition process includes a process of adding the modulated wave a predetermined number of times in a cycle synchronized with the polarity inversion wave. 　 The impedance measuring means a double-pole double-throw switch that receives the cell voltage signal as an input; and a differential input AD converter that is connected to an output side of the double-pole double-throw switch, 2. The impedance measuring device according to claim 1, wherein the double-pole double-throw switch is switched so that the polarity of the differential input AD converter to which the cell voltage signal is output is switched in synchronization with a half cycle of the measurement current wave. 　 The impedance measuring means includes: an integrating circuit for executing the second summation process; an AD converter that converts an output signal of the integrating circuit into a digital signal; 2. The impedance measuring device according to claim 1, wherein an integration period of said integrating circuit is set so that the voltage of said output signal falls within the input voltage range of said AD converter.

4. The impedance measuring device according to claim 3, wherein the integration period is set to 100 ms or more. 　 The impedance measuring means includes: a first AC voltage detection signal modulated with a half period in phase with the measurement current wave; generating a second AC voltage detection signal that is shifted in phase by a quarter cycle of the measurement current wave and modulated by a half cycle; 5. The impedance measuring device according to claim 1, wherein a complex impedance value is calculated based on the first AC voltage detection signal and the second AC voltage detection signal. 　 The impedance measuring means includes: removing a DC component contained in the cell voltage signal; generating a sine wave signal by alternately inverting the polarity of the signal from which the DC component has been removed at a timing synchronized with a half wave of the measurement current wave; 6. The impedance measuring device according to claim 1, further comprising a bandpass filter for filtering the sine wave signal. 　 An impedance measurement method for measuring an impedance of a battery cell, the method comprising: acquiring a cell voltage signal between the positive and negative electrodes of the battery cell while a measurement current wave having a predetermined frequency is applied to the battery cell; Executing a modulation process, a first summation process, and a second summation process based on the cell voltage signal to generate an AC voltage detection signal of the battery cell; measuring the impedance of the battery cell from an amplitude ratio and a phase difference between the AC voltage detection signal and the measurement current wave; The modulation process includes a process of modulating the cell voltage signal with a polarity inversion wave synchronized with a half wave of the measurement current wave, the first addition process includes a process of adding the modulated wave in a non-inverted half cycle and an inverted half cycle of the modulated wave modulated by the modulation process, The impedance measuring method, wherein the second adding process includes a process of adding the modulated wave a predetermined number of times in a cycle synchronized with the polarity inversion wave.

Images