Battery management system

Abstract

This invention provides a battery management system that accurately measures the complex impedance of secondary batteries using a simple circuit configuration. [Solution] The battery management system 200 includes a reference signal generation unit 109 that generates a quadrature reference signal, an AC signal superposition unit 104 that generates an excitation current and energizes multiple battery cells, a current measurement unit 112 that measures the excitation current, a voltage measurement unit (ADC of the measurement unit 122), a multiplexer of the measurement unit 122 that switches the connection between the multiple battery cells and the voltage measurement unit, and an integrated control unit 201 that measures the AC impedance of each of the multiple battery cells based on the measured excitation current and the measured voltage. The integrated control unit 201 uses the multiplexer to select one battery cell from the multiple battery cells and measures its AC impedance.

Description

Technical Field

[0001] The present disclosure relates to a battery management system for managing the state of a battery.

Background Art

[0002] The development of automobiles that run using a secondary battery as a power source, such as a HEV (Hybrid Electric Vehicle) or an EV (Electric Vehicle), is underway. In addition, techniques for estimating the remaining battery capacity and detecting abnormalities using a battery management system (BMS: Battery Management System) in order to safely use the secondary battery are known.

[0003] For example, Patent Document 1 discloses a battery state determination device that can measure the complex impedance of a battery and diagnose the capacity and deterioration amount of the battery.

[0004] Patent Document 2 discloses a capacity maintenance rate determination device that can determine the capacity maintenance rate without performing a full charge and discharge of the battery.

[0005] Patent Document 3 discloses a vehicle controller that programs the charge and discharge of a battery using parameters of an RC circuit model corresponding to the impedance of the battery.

[0006] Non-Patent Document 1 discloses a method for specifically measuring the complex impedance of a battery by applying an alternating current and measuring an alternating voltage, and measuring the complex impedance by an AC superposition method.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

[0008] [Non-Patent Document 1] “IC for online EIS in automotive batteries and hybrid architecture for high-current perturbation in low-impedance cells” Z. Gong, Z. Liu, Y. Wang et al. 2018 IEEE Applied Power Electronics Conference and Exposition (APEC) [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] However, conventional techniques have the problem that errors are easily introduced when measuring complex impedance.

[0010] This disclosure provides a battery management system that accurately measures the complex impedance of a secondary battery with a simple circuit configuration. [Means for solving the problem]

[0011] A battery management system according to one aspect of the present disclosure is a battery management system for managing the battery state of a plurality of battery cells, comprising: a reference signal generation unit that generates an AC quadrature reference signal consisting of a common-mode signal and a quadrature signal having a phase difference of 90 degrees with respect to the common-mode signal; an excitation signal generation unit that processes the common-mode signal of the quadrature reference signal to generate an excitation signal; a current generation unit that generates an excitation current based on the excitation signal and energizes the plurality of battery cells; a current measurement unit that measures the excitation current generated by the current generation unit by sampling using the quadrature reference signal; a voltage measurement unit that measures the voltage of the plurality of battery cells by sampling using the quadrature reference signal; a multiplexer that switches the connection between the plurality of battery cells and the voltage measurement unit; an impedance measurement unit that measures the AC impedance of each of the plurality of battery cells based on the excitation current measured by the current measurement unit and the voltage measured by the voltage measurement unit; and a control unit that controls the measurement of AC impedance by the impedance measurement unit, wherein the control unit selects one battery cell from the plurality of battery cells using the multiplexer and causes the impedance measurement unit to measure the AC impedance.

[0012] One aspect of the present disclosure is a battery management circuit for managing a secondary battery, comprising: a reference signal generation unit that generates a first reference frequency signal and a second reference frequency signal having a different phase from the first reference frequency signal; an AC superposition unit that superimposes an AC current having the frequency components of the first reference frequency signal onto the secondary battery; a voltage measurement unit that measures the voltage of the secondary battery by sampling at a frequency higher than the first reference frequency signal; a current measurement unit that measures the current of the secondary battery by sampling at a frequency higher than the first reference frequency signal; and a conversion unit that converts the measurement results from the voltage measurement unit and the current measurement unit into the real and imaginary components of a complex voltage and a complex current, respectively, by multiplying them by the first reference frequency signal and the second reference frequency signal.

[0013] Also, one aspect of the present disclosure is a battery management network, which includes the above battery management system and the server device, and the server device may generate battery information including a result of estimating the state of the secondary battery based on the measurement information.

Advantages of the Invention

[0014] According to the battery management system in one aspect of the present disclosure, the complex impedance of the secondary battery can be measured with high accuracy using a simple circuit configuration.

Brief Description of the Drawings

[0015] [Figure 1] FIG. 1 is a block diagram showing a configuration example of a battery management system and a battery management server according to an embodiment. [Figure 2] FIG. 2 is a diagram showing a configuration example of an integrated control unit according to an embodiment. [Figure 3] FIG. 3 is a flowchart showing a processing example of the integrated control unit according to an embodiment. [Figure 4] FIG. 4 is an explanatory diagram showing a structure example of a battery cell and an example of an equivalent circuit model according to an embodiment. [Figure 5A] FIG. 5A is a Cole-Cole plot showing an example of the complex impedance of a battery cell according to an embodiment. [Figure 5B] FIG. 5B is a Bode diagram showing an example of the complex impedance of a battery cell according to an embodiment. [Figure 6] FIG. 6 is a diagram showing an example of the temperature characteristics of the complex impedance of a battery cell according to an embodiment. [Figure 7] FIG. 7 is a block diagram showing a configuration example of a battery management network according to an embodiment. [Figure 8] FIG. 8 is a sequence diagram showing a processing example of a battery management network according to an embodiment. [Figure 9] FIG. 9 is a block diagram showing a configuration example of a battery management system and a battery management server according to a modified example.

BEST MODE FOR CARRYING OUT THE INVENTION

[0016] (Knowledge underlying the present disclosure) The present inventor has found that the following problems occur with respect to the device for managing a secondary battery described in the "Background Art" section.

[0017] When measuring the internal complex impedance (also referred to as AC impedance) of a secondary battery by the AC superposition method, generally, a method is used in which, based on the applied AC current, a complex voltage representing the phase lag of the voltage change generated by the internal complex impedance is measured as a complex number, and the measured complex voltage is divided by the applied current to calculate. The AC current to be applied is a current amplified based on a reference frequency signal and applied to the secondary battery.

[0018] In this method, due to the influence of the electrical wiring (e.g., wire harness) connecting the secondary battery and the device to be measured, or a drive amplifier that amplifies the reference frequency signal, etc., the phase of the AC current actually applied to the secondary battery often has a delay from the phase of the reference frequency signal.

[0019] On the other hand, voltage measurement is performed by an AD converter that samples with a sampling clock synchronized with the reference frequency signal. Therefore, the phase difference between the AC current actually applied to the secondary battery and the voltage measurement timing appears as a phase error of the complex impedance, so an error easily occurs in the complex impedance of the secondary battery.

[0020] To eliminate such a phase error, for example, it is necessary to perform feedback control of the AC current so that the frequency of the AC current actually applied to the secondary battery matches the original reference frequency signal.

[0021] However, even with this method, it is impossible to eliminate the influence of the phase error due to the frequency characteristics in the feedback loop and the phase error generated at the subsequent stage from the feedback point.

[0022] Furthermore, when implementing feedback control, the feedback loop must be designed to operate linearly. Since the complex impedance of actual secondary batteries is only a few tens of milliohms to a few milliohms, the applied AC current must be several amperes to several tens of amperes. Designing the frequency characteristics of the drive amplifier and other components so that they do not affect the feedback loop is extremely difficult, leading to another problem: increased current consumption.

[0023] Therefore, this disclosure provides a battery management circuit, a battery management system, and a battery management network that measure the complex impedance of a secondary battery with high accuracy using a simple circuit configuration without feedback control of the applied AC current.

[0024] To solve such problems, a battery management circuit according to one aspect of the present disclosure is a battery management circuit for managing a secondary battery, comprising: a reference signal generation unit that generates a first reference frequency signal and a second reference frequency signal having a different phase from the first reference frequency signal; an AC superposition unit that superimposes an AC current having the frequency components of the first reference frequency signal onto the secondary battery; a voltage measurement unit that measures the voltage of the secondary battery by sampling at a frequency higher than the first reference frequency signal; a current measurement unit that measures the current of the secondary battery by sampling at a frequency higher than the first reference frequency signal; and a conversion unit that converts the measurement results of the voltage measurement unit and the current measurement unit into the real and imaginary components of the complex voltage and complex current, respectively, by multiplying them by the first reference frequency signal and the second reference frequency signal.

[0025] According to this method, the complex impedance of a secondary battery can be measured with high accuracy using a simple circuit configuration, without errors in the orthogonality of the real and imaginary parts. In other words, by separating and measuring the real and imaginary parts of the complex voltage using a first and second reference signal generated to be orthogonal as a reference, and separating and measuring the real and imaginary parts of the complex current using the same first and second reference signals as the voltage measurement, and then dividing the measured complex voltage by the complex current, the orthogonality of the real and imaginary parts of the measured complex impedance depends only on the orthogonality of the first and second reference signals. This eliminates the phase error of the complex impedance caused by the phase error between the measured voltage and the superimposed current, enabling high-precision measurement.

[0026] Furthermore, since there is no need to use feedback control of the AC current to compensate for the phase lag of the superimposed current, the circuit configuration can be simplified.

[0027] The embodiments described below will be explained with reference to the drawings. The embodiments described below are all general or specific examples. The numerical values, shapes, materials, components, arrangement and connection configurations of components, steps, and the order of steps shown in the following embodiments are examples only and are not intended to limit the disclosure. Furthermore, the realization of this disclosure is not limited to the current independent claims and may also be expressed by other independent claims.

[0028] Please note that each figure is a schematic diagram and not necessarily a strictly accurate representation. Furthermore, in each figure, substantially identical components are denoted by the same reference numerals, and redundant explanations may be omitted or simplified.

[0029] (Embodiment 1) [composition] First, the configuration of the battery management system according to Embodiment 1 will be described.

[0030] Figure 1 is a block diagram showing an example configuration of the battery management system 200 and the battery management server 301 according to an embodiment.

[0031] The battery management system 200 in the figure comprises multiple battery packs 101, multiple battery management devices 100, and an integrated control unit 201. The integrated control unit 201 and the multiple battery management devices 100 are daisy-chained together by a communication line 132.

[0032] The battery pack 101 is a secondary battery and includes multiple battery cells B0 to B5 connected in series. Each battery cell is, for example, a lithium-ion battery, but may be other types of batteries such as nickel-metal hydride batteries. Alternatively, it may be a series-connected energy storage cell such as a lithium-ion capacitor. The battery pack 101 is connected to a load and a charging circuit. The load is, for example, the motor of an HEV or EV, but is not limited to this. Although Figure 1 shows an example of a battery pack 101 having six battery cells, the number of battery cells in the battery pack 101 is not limited to six.

[0033] The battery management device 100 is a device that manages the status of the battery pack 101, and is also called a cell management unit (CMU). The device 100 calculates the AC impedance of the battery pack 101, specifically the complex impedance (also called AC impedance) of each of the battery cells B0 to B5. For this purpose, the battery management device 100 is equipped with a battery management circuit 105 and a temperature sensor 107 (e.g., a thermistor).

[0034] The battery management circuit 105 may be configured as, for example, a single-chip integrated circuit (IC). Alternatively, the battery management device 100 may be configured as a printed circuit board (PCB) on which the IC chip of the battery management circuit 105 and the temperature sensor are mounted.

[0035] The battery management circuit 105 includes an AC superposition unit 104, a reference signal generation unit 109, a current measurement unit 112, a clock generation unit 113, a voltage measurement unit 115, a reference voltage generation unit 117, a conversion unit 118b, an integration unit 118c, a holding unit 118d, a temperature measurement unit 120, and a communication interface unit 131.

[0036] The AC superposition unit 104 superimposes an AC current having the frequency components of the first reference frequency signal generated by the reference signal generation unit 109 onto the secondary battery. The AC superposition unit 104 in Figure 1 has a differential buffer that applies the first reference frequency signal as a differential signal to the positive and negative electrodes of the battery pack 101.

[0037] The reference signal generator 109 generates a first reference frequency signal and a second reference frequency signal having a phase orthogonal to the first reference frequency signal. For example, the first reference frequency signal is a sine wave signal, and the second reference frequency signal is a cosine wave signal. It is desirable that the first and second reference frequency signals be orthogonal within an acceptable range of phase error, but they do not need to be exactly 90 degrees apart, and some error is acceptable. Furthermore, although the calculation becomes very complex due to distortion in the complex plane, it is possible to measure the first and second reference frequency signals with a phase other than 90 degrees, for example, 45 degrees apart, and then convert the measurement to a complex plane where the real and imaginary parts are orthogonal.

[0038] Furthermore, the reference signal generation unit 109 receives a specification of the frequency f of the first reference frequency signal from the integrated control unit 201 via the communication interface unit 131, and generates the first reference frequency signal according to the specification.

[0039] The current measurement unit 112 measures the AC current superimposed on the battery pack 101 by sampling the current of the battery pack 101 using a sampling clock signal from the clock generation unit 113. The current of the battery pack 101 is measured as the voltage drop across a current-sensing resistor element 106 inserted in the path through which the AC current applied by the AC superimposition unit 104 flows. This voltage drop is proportional to the AC current and therefore represents the AC current value. More specifically, the current measurement unit 112 includes an analog-to-digital converter for measuring the current of the battery pack 101, which is a secondary battery. This analog-to-digital converter uses a sampling clock signal from the clock generation unit 113 to sample the voltage drop across the current-sensing resistor element 106 and converts the sampled voltage drop into a digital signal.

[0040] The clock generation unit 113 generates a sampling clock signal that is higher in frequency than the first reference frequency signal and synchronized with the first reference frequency signal. The sampling clock signal is supplied to the current measurement unit 112 and the voltage measurement unit 115. For example, when measuring a complex impedance of about 5 kHz, the frequency of the first reference frequency signal will be about 5 kHz, and the sampling clock must be set to satisfy the required phase resolution. Therefore, if the measurement frequency is about 5 kHz and the phase resolution is about 1 degree, the sampling clock should be about 1.8 MHz, which is 360 times 5 kHz.

[0041] The voltage measurement unit 115 measures the voltage of the battery pack 101 by sampling the voltage of the battery pack 101 using a sampling clock signal from the clock generation unit 113. More specifically, the voltage measurement unit 115 is equipped with the same number of analog-to-digital converters (ADC0 to ADC5) corresponding to the battery cells B0 to B5 in the battery pack 101. Each analog-to-digital converter uses a sampling clock signal from the clock generation unit 113 to sample the voltage of the corresponding battery cell among the multiple battery cells B0 to B5, and converts the sampled voltage into a digital signal. Since the voltage measurement unit 115 uses the same sampling clock as the current measurement unit 112, it is possible to achieve highly accurate complex frequency measurement with minimal phase error between the measurement frequency and the sampling clock.

[0042] The reference voltage generation unit 117 supplies a common reference voltage to the multiple analog-to-digital converters (ADC0 to ADC5) of the voltage measurement unit 115, the analog-to-digital converter of the current measurement unit 112, and the analog-to-digital converter of the temperature measurement unit 120. Specifically, the reference voltage generation unit 117 is a BGR (BandGapReference) circuit that generates a stable and constant voltage value in response to fluctuations in temperature and power supply voltage, for example, by generating a voltage of about 1.25V due to the silicon bandgap. Since the multiple analog-to-digital converters of the voltage measurement unit 115 and the analog-to-digital converter of the current measurement unit 112 use the same reference voltage, the absolute error of the reference voltage is canceled out by division of the numerator and denominator during complex impedance calculation. This makes it possible to measure complex impedance with high accuracy.

[0043] The conversion unit 118b converts the measurement results of the voltage measurement unit 115 and the current measurement unit 112 into the real and imaginary components of complex voltage and complex current, respectively, by multiplying them by the first reference frequency signal and the second reference frequency signal. Therefore, the conversion unit 118b comprises the same number of multiplier pairs corresponding to the analog-to-digital converters (ADC0 to ADC5) of the voltage measurement unit 115, and the corresponding multiplier pairs for the analog-to-digital converters of the current measurement unit 112. Each multiplier pair corresponding to the voltage measurement unit 115 consists of a multiplier that multiplies the conversion result of the corresponding analog-to-digital converter (i.e., the sampled digital voltage value) by the first reference frequency signal, and a multiplier that multiplies the said conversion result by the second reference frequency signal. The result of the former multiplication shows the real component when the sampled voltage is expressed as a complex voltage. The result of the latter multiplication shows the real component when the sampled voltage is expressed as a complex voltage. The multiplier pair corresponding to the current measurement unit 112 consists of a multiplier that multiplies the conversion result of the corresponding analog-to-digital converter (i.e., the sampled digital current value) by a first reference frequency signal, and a multiplier that multiplies the said conversion result by a second reference frequency signal. The result of the former multiplication shows the real part component when the sampled current is expressed as a complex current. The result of the latter multiplication shows the real part component when the sampled current is expressed as a complex current.

[0044] Each of the analog-to-digital converters (ADC0 to ADC5) can be, for example, a delta-sigma type analog-to-digital converter. Furthermore, multiple analog-to-digital converters (ADC0 to ADC5) have the same analog-to-digital conversion characteristics. Analog-to-digital conversion characteristics refer to various parameters such as resolution (number of bits). Specifically, the same analog-to-digital converter is used for multiple analog-to-digital converters (ADC0 to ADC5). This reduces measurement errors caused by differences in conversion time (latency) between battery cells B0 to B5 due to differences in the type of analog-to-digital converter.

[0045] The integrating unit 118c averages the real and imaginary components of the complex voltage and complex current, which are repeatedly measured by the voltage measurement unit 115 and converted by the conversion unit 118b. This averaging also reduces the measurement error of the complex voltage and complex current, and oversampling improves the resolution (measurement accuracy). This averaging also improves the accuracy of the measurement. More specifically, the integrating unit 118c has the same number of averaging circuit pairs corresponding to the multiplier pairs of the conversion unit 118b. Each averaging circuit pair consists of an averaging circuit that averages the real component of the complex voltage or complex current, and an averaging circuit that averages the imaginary component of the complex voltage or complex current. If the battery cell is a lithium-ion battery, the internal complex impedance is, for example, several mΩ. Assuming a superimposed AC current of 1A, the change in output voltage is only a few mV. On the other hand, since the DC output voltage of a lithium-ion battery is approximately 3.4V, a dynamic range of about 4 to 5V is required to measure the voltage with an analog-to-digital converter connected to the battery cell. In this case, if a complex impedance measurement accuracy of about 8 bits is required, an analog-to-digital converter with about 18 to 20 effective bits is needed, but high-resolution AD converters consume more power and take up more space. On the other hand, the internal complex impedance measured for electrochemical impedance analysis of a lithium-ion battery is measured in a low-frequency range from approximately 0.01Hz to several tens of kHz near DC, so it is not possible to measure the complex voltage with an AC connection. In the configuration shown in Figure 1, by repeatedly applying an AC current to separate the complex voltage and complex current into real and imaginary parts and average them, it is possible to increase the resolution by integration through oversampling, making it possible to obtain complex impedance measurement results with 20 to 24 bits accuracy even with an analog-to-digital converter with a small number of bits (e.g., about 16 bits). This improves the accuracy of complex voltage measurement, making it possible to reduce the magnitude of the applied AC current and facilitating the measurement of secondary batteries with large capacities and low internal complex impedance.

[0046] The storage unit 118d stores the real and imaginary components of the complex voltage and complex current after averaging. Therefore, the storage unit 118d includes the same number of register pairs as the number of battery cells in the battery pack 101 for storing the complex voltage, and a register pair for storing the complex current. Each register pair for storing the complex voltage consists of a register (Re(Vi)) for storing the real component of the complex voltage of the corresponding battery cell and a register for storing the imaginary component (Im(Vi)). Here, i is an integer from 0 to 5. Similarly, the register pair for storing the complex current consists of a register (Re(I0)) for storing the real component of the complex current of the corresponding battery pack 101 and a register for storing the imaginary component (Im(I0)).

[0047] The temperature measurement unit 120 measures the temperature of the battery pack 101 using a temperature sensor 107 provided on the battery pack 101. The temperature sensor 107 may be, for example, a thermistor, but it may also be a temperature sensor using other elements such as a thermocouple. Specifically, the temperature measurement unit 120 comprises an analog-to-digital converter and a temperature calculation unit 121. The analog-to-digital converter samples the voltage from the temperature sensor 107 and converts the sampled voltage into a digital value. The temperature calculation unit 121 calculates the temperature corresponding to the digital voltage from the analog-to-digital converter.

[0048] The communication interface unit 131 is a communication circuit for the battery management circuit 105 to communicate with other battery management circuits 100 or the integrated control unit 201. The communication interface unit 131 is used, for example, to transmit the complex impedance calculated by the holding unit 118d to the integrated control unit 201. The communication conducted by the communication interface unit 131 may be wireless communication or wired communication. There are no particular limitations on the communication standard used for communication conducted by the communication interface unit 131.

[0049] The integrated control unit 201 specifies the frequency f of the first reference frequency signal to the battery management circuit 100, and collects the real and imaginary components held in the holding unit 118d from multiple battery management devices 100 via the communication line 132. From the collected real and imaginary components of the complex voltage and complex current, it calculates the complex impedance at the specified frequency. In calculating the impedance, the AC impedance is calculated by dividing each complex voltage held in the holding unit 118d by the complex current. Specifically, the integrated control unit 201 has a division function, and for example, as the AC impedance of battery cell B0, it is calculated by dividing the complex voltage represented by (Re(V0), Im(V0)) by the complex current represented by (Re(I0), Im(I0)).

[0050] The battery management device 100 is a lower-level CMU (Cell Management Unit) that measures and manages individual battery cells. The control unit 201 is the Battery Management Unit (BMU) of the higher-level system that manages the entire battery pack. Unit 1 is equipped with an MCU (Microcontroller) capable of performing calculations faster and with greater capacity than the battery management device 100, and it controls the battery. The configuration is as shown in Figure 1. In this system, the functions of the CMU (Chemical Mass Unit) battery management device 100 are limited to measuring complex voltage and complex current, while the higher-level integrated control unit 201, which has greater computing power, calculates the complex impedance. This eliminates the need to incorporate calculation circuits for complex impedance on multiple CMUs in complex impedance measurement, simplifying the CMU circuit and enabling low-cost complex impedance measurement. Furthermore, by having the integrated control unit 201 collect complex voltage and complex current, it becomes easier to perform calculations and corrections, such as temperature correction for fluctuations in complex impedance due to measurement temperature, and shortening measurement time by decimating and interpolating the measurement frequency interval.

[0051] Next, we will describe an example configuration of the integrated control unit 201.

[0052] Figure 2 shows an example of the configuration of the integrated control unit 201 according to the embodiment.

[0053] As shown in the figure, the integrated control unit 201 includes a CPU 31, memory 32, communication circuit 33, and wireless circuit 34.

[0054] The CPU 31 executes the program stored in memory 32.

[0055] The memory 32 stores various programs for managing multiple battery management devices 100, and various data such as battery status data including the AC impedance of the battery pack 101.

[0056] The communication circuit 33 communicates with multiple battery management devices 100 that are daisy-chained together via communication lines 132.

[0057] The wireless circuit 34 communicates wirelessly with the battery management server 301.

[0058] [Operation] Next, we will explain a specific example of processing performed by the integrated control unit 201.

[0059] Figure 3 is a flowchart showing an example of processing by the integrated control unit 201 according to the embodiment.

[0060] The figure shows an example of processing for one of the multiple battery management devices 100. The integrated control unit 201 then sequentially performs the same processing for the other battery management devices 100.

[0061] First, the integrated control unit 201 specifies the frequency f of the first reference frequency signal to the battery management device 100 (S11). The battery management device 100 then generates a first reference frequency signal at the specified frequency and measures the complex voltage, complex current, and temperature of the secondary battery pack 101. When these measurements are complete, the integrated control unit 201 obtains data from the battery management device 100 via the communication line 132, indicating the measured complex voltage, complex current, and temperature of the battery pack 101 (S12-S14). Alternatively, instead of obtaining the temperature of the battery pack 101, the calculated complex impedance can be used to estimate the temperature of the secondary battery at the time of measurement from previously converted complex impedance and secondary battery temperature information. This estimation is useful for battery management devices 100 that do not have a temperature sensor 107.

[0062] Next, the integrated control unit 201 calculates the complex impedance at a specified frequency from the real and imaginary components of the complex voltage and complex current, respectively, in the acquired data (S15). The integrated control unit 201 may specify the frequency f of the first reference frequency signal multiple times while changing it, and calculate the change in complex impedance corresponding to the change in the specified frequency.

[0063] Furthermore, the integrated control unit 201 generates plotting data showing a Cole-Cole plot, where the complex impedance is represented as a trajectory on the complex plane (S16). Alternatively, the integrated control unit 201 may generate plotting data showing a Bode plot obtained by converting the complex impedance into magnitude and phase, instead of plotting data showing a Cole-Cole plot.

[0064] Furthermore, the integrated control unit 201 normalizes the complex impedance based on the acquired (or estimated) temperature (S17). Specifically, the integrated control unit 201 converts the complex impedance according to the acquired temperature into a complex impedance corresponding to a predetermined temperature. Note that the order of steps S16 and S17 may be reversed. In other words, the integrated control unit 201 may generate the plotting data after the temperature normalization.

[0065] Next, the integrated control unit 201 calculates the element constants of circuit elements such as resistors R and capacitors C that constitute the equivalent circuit model representing the corresponding battery cell, based on the complex impedance corresponding to a predetermined temperature (i.e., corrected to a standard temperature different from the measured temperature) (S18).

[0066] Furthermore, the integrated control unit 201 generates measurement information including complex impedance and the element constants, adds identification information to the measurement information to identify the corresponding battery cell (S19), and further adds information indicating the current time and operating time (S20). The integrated control unit 201 transmits the measurement information, to which the identification information, current time, and operating time have been added, as battery status data to the battery management server 301 via the network (S21).

[0067] Next, we will describe an equivalent circuit model of a battery cell and an example of its component constants.

[0068] Figure 4 is an explanatory diagram showing an example of the structure of a battery cell according to an embodiment and an example of an equivalent circuit model. Figure 4(a) shows the symbol for battery cell B0. Figure 4(b) schematically shows an example of the structure when battery cell B0 is a lithium-ion battery. As a premise of the equivalent circuit model, battery cell B0 has a negative electrode, negative electrode material, electrolyte, separator, positive electrode material, and positive electrode. Figure 4(c) shows an example of the equivalent circuit model of battery cell B0. This equivalent circuit model has an inductive component L0, resistive components R0 to R2, capacitive components C1 and C2, and a lithium-ion diffusion resistance component Zw. The inductive component L0 represents the impedance component of the electrode wire. The resistive component R0 represents the impedance component of the electrolyte. The parallel circuit of resistive component R1 and capacitive component C1 represents the impedance component of the negative electrode. The circuit portion consisting of resistive component R2, lithium-ion diffusion resistance component Zw, and capacitive component C2 represents the impedance component of the positive electrode. The lithium-ion diffusion resistance Zw is known as the Warburg impedance.

[0069] By calculating the element constants of each circuit element that constitutes such an equivalent circuit model, the state of the battery cell B0 can be estimated. For example, the degradation state of the battery cell B0 can be estimated by the change in element constants over time.

[0070] Next, we will explain an example of the complex impedance characteristics of a battery cell.

[0071] Figure 5A is a Cole-Cole plot showing an example of the complex impedance of a battery cell according to the embodiment. The thick solid lines in Figures 5A(a) and (b) show examples of correct complex impedance without phase error. The thick dashed line in Figure 5A(a) shows an example of complex impedance when a fixed-angle phase error occurs. The thick dashed line in Figure 5A(b) shows an example of complex impedance when a fixed-delay-time phase error occurs.

[0072] The Cole-Cole plot is also called a complex plane diagram or Nyquist plot. The thick solid lines in Figure 5A(a) and (b) correspond to the equivalent circuit model in Figure 4(c). In the method of calculating the complex impedance of a battery cell by superimposing an AC current, it is generally known that in the case of charge transfer-limited operation, it is represented by an equivalent circuit in which resistance and capacitance are arranged in parallel, and in the complex plane it is semicircular. In addition, it is generally known that when Warburg impedance is included, a straight line rises from the middle of the semicircle (near the upper right) at a 45-degree angle, due to the slope originating from Warburg impedance.

[0073] In calculating complex impedance, phase errors in the voltage and current measurement systems manifest as phase errors in the complex impedance. Generally, phase errors in measurement systems often exhibit frequency characteristics, posing a challenge when measuring complex impedance at different frequencies. In particular, when plotting the complex impedance at various frequencies on a Cole-Cole plot while varying the frequency, the phase error at each frequency appears as orthogonal errors between the real axis (horizontal axis) and the imaginary axis (vertical axis) on the complex plane of the Cole-Cole plot. Therefore, it becomes difficult to draw an accurate Cole-Cole plot. However, in the configuration shown in Figure 1, by measuring the complex voltage and complex current before calculating the complex impedance, the phase error in the voltage and current measurement systems is made extremely small, enabling the drawing of an accurate Cole-Cole plot. As shown by the thick dashed line in Figure 5A(a), when the angle of the phase error is fixed, the Cole-Cole plot has the characteristic of rotating around the origin. Furthermore, as shown by the thick dashed line in Figure 5A(b), when the phase error delay time is fixed, the Cole-Cole plot rotates only on the high-frequency side and overlaps with the thick solid line on the low-frequency side. In other words, the phase error occurs only on the high-frequency side and not on the low-frequency side.

[0074] Figure 5B is a Bode plot showing an example of the complex impedance of a battery cell according to an embodiment. The thick solid lines in the upper part of Figure 5B(a) and the upper part of Figure 5B(b) show examples of the magnitude of the correct complex impedance with respect to frequency, without phase error. The thick solid lines in the lower part of Figure 5B(a) and the lower part of Figure 5B(b) show examples of the phase θ of the correct complex impedance with respect to frequency, without phase error.

[0075] The thick dashed line in the lower part of Figure 5B(a) shows an example of the phase θ of the complex impedance with respect to frequency when a fixed-angle phase error occurs. Similarly, the thick dashed line in the lower part of Figure 5B(b) shows an example of the phase θ of the complex impedance with respect to frequency when a fixed-delay-time phase error occurs. The thick solid lines in Figures 5B(a) and (b) correspond to the equivalent circuit model in Figure 4(c).

[0076] When plotting complex impedance as a Bode plot, representing magnitude and phase, while varying the frequency, phase errors in the voltage and current measurement systems will appear as phase errors in the Bode plot. Therefore, it becomes difficult to accurately plot complex impedance as a Bode plot. However, in the configuration shown in Figure 1, by measuring the complex voltage and complex current and then calculating the complex impedance, the phase error in the voltage and current measurement systems can be made extremely small, making it possible to plot an accurate Bode plot. As shown by the thick dashed line in the lower part of Figure 5B(a), when the angle of the phase error is fixed, the Bode plot showing the phase with respect to frequency has the characteristic of being shifted in parallel. Also, as shown by the thick dashed line in the lower part of Figure 5B(b), when the delay time of the phase error is fixed, the Bode plot showing the phase with respect to frequency is affected only on the high-frequency side and overlaps with the thick solid line on the low-frequency side. In other words, the phase error occurs only on the high-frequency side and not on the low-frequency side.

[0077] Furthermore, Figures 5A and 5B are useful for estimating the state of the battery cells. For example, the thick solid line in Figure 5A is thought to become larger and shift to the right as the battery cell deteriorates. The thick solid line in the upper part of Figure 5B is thought to become larger and shift upward as the battery cell deteriorates.

[0078] Next, we will explain the temperature characteristics of the battery cell.

[0079] Figure 6 shows an example of the temperature characteristics of the complex impedance of a battery cell according to an embodiment. The figure shows Cole-Cole plots for battery cell temperatures of 20°C, 25°C, and 30°C. As shown, the complex impedance of a battery cell has a temperature dependence, but the effect of this temperature dependence can be reduced by normalization, which converts the complex impedance to one corresponding to a predetermined temperature.

[0080] As described above, the battery management circuit 105 can accurately measure the complex impedance of each battery cell of the battery pack 101 with a simple circuit configuration.

[0081] As described above, the battery management circuit 105 according to Embodiment 1 is a battery management circuit for managing a secondary battery, and includes a reference signal generation unit 109 that generates a first reference frequency signal and a second reference frequency signal having a phase shift of 90 degrees from the first reference frequency signal, an AC superposition unit 104 that superimposes an AC current having the frequency components of the first reference frequency signal onto the secondary battery, a voltage measurement unit 115 that measures the voltage of the secondary battery by sampling at a frequency higher than the first reference frequency signal, a current measurement unit 112 that measures the current of the secondary battery by sampling at a frequency higher than the first reference frequency signal, and a conversion unit 118b that converts the measurement results of the voltage measurement unit 115 and the current measurement unit 112 into the real and imaginary components of the complex voltage and complex current, respectively, by multiplying them by the first reference frequency signal and the second reference frequency signal.

[0082] According to this method, the complex impedance of a secondary battery can be measured with high accuracy using a simple circuit configuration.

[0083] Here, the battery management circuit 105 includes a clock generation unit 113 that generates a synchronized sampling clock signal at a frequency higher than the first reference frequency signal, and the voltage measurement unit 115 and the current measurement unit 112 may use the sampling clock signal generated by the clock generation unit 113 for sampling.

[0084] The clock generation unit 113 may generate one or more sampling clock signals.

[0085] Furthermore, the multiple sampling clock signals may or may not be synchronized with the first reference frequency signal. Even if the sampling clock signals are not synchronized with the first reference frequency signal, the voltage measurement unit 115 and the current measurement unit 112 can accurately measure voltage and current as long as their frequencies are sufficiently higher than those of the first reference frequency signal.

[0086] The voltage measurement unit 115 and the current measurement unit 112 may use the same sampling clock signal or different sampling clock signals. In other words, the sampling signals for voltage measurement and current measurement may be the same sampling clock signal or different sampling clock signals. Even if different sampling clock signals are used, as long as the frequency is sufficiently higher than the first reference frequency signal, measurements equivalent to those when using the same sampling clock signal are possible.

[0087] Here, the voltage measurement unit 115 and the current measurement unit 112 repeatedly measure the voltage and current of the secondary battery, and the battery management circuit 105 may include an integral unit 118c that averages the real and imaginary components of the complex voltage and complex current, respectively, corresponding to the repeated measurements.

[0088] According to this method, the resolution of voltage and current measurements can be increased by averaging, thereby improving measurement accuracy. If the measurement accuracy of complex voltage can be improved, it becomes possible to reduce the magnitude of the applied AC current, making it easier to measure secondary batteries with large capacities and low internal complex impedance.

[0089] Here, the voltage measurement unit 115 may include one or more analog-to-digital converters for measuring the voltage of the secondary battery, the current measurement unit 112 may include an analog-to-digital converter for measuring the current of the secondary battery, and the battery management circuit 105 may include a reference voltage circuit 117 that supplies a common reference voltage to the one or more analog-to-digital converters of the voltage measurement unit 115 and the analog-to-digital converters of the current measurement unit 112.

[0090] For example, even with an analog-to-digital converter with a small number of bits (e.g., around 16 bits), it becomes possible to obtain complex impedance measurement results with 20-24 bit accuracy. Furthermore, since the same reference voltage is used for both voltage and current measurements, the absolute error of the reference voltage cancels out in the calculation of complex impedance, i.e., the division of the measured voltage by the measured current, appearing in both the numerator and denominator. This makes it possible to measure complex impedance with high accuracy.

[0091] Here, the battery pack 101, which is a secondary battery, has multiple battery cells connected in series, and the voltage measurement unit 115 may be equipped with one or more analog-to-digital converters, the same number as the battery cells, and measure the voltage of each of the multiple battery cells.

[0092] According to this method, the voltage and current of multiple battery cells can be measured simultaneously in parallel using the same number of analog-to-digital converters as the number of battery cells. Accurate measurements can be achieved even in the event of rapid temperature changes.

[0093] Here, the battery management circuit 105 may be a single semiconductor integrated circuit (BMIC).

[0094] According to this, the cost reduction will be made easier by using an IC for the battery management device 100.

[0095] Furthermore, the battery management system 200 according to Embodiment 1 includes the battery management circuit 105 and an integrated control unit 201 that specifies the frequency of the first reference frequency signal to the battery management circuit 100. The battery management circuit 100 transmits the real and imaginary components of the complex voltage and complex current, respectively, to the integrated control unit 201, and the integrated control unit 201 calculates the complex impedance of the specified frequency from the transmitted real and imaginary components of the complex voltage and complex current, respectively.

[0096] Here, the battery management system 200 includes at least one battery management circuit 105 and a communication line 132 that daisy-chains the integrated control unit 201 and the at least one battery management circuit 105, and the integrated control unit 201 may collect the real and imaginary parts from the at least one battery management circuit 105 via the communication line 132.

[0097] According to this, the integrated control unit 201 is a higher-level system that manages the entire battery pack, and it calculates the complex impedance using the complex voltage and complex current measured by the battery management circuit 105. This simplifies the circuit configuration of the battery management circuit 105 in complex impedance measurement, enabling low-cost implementation. Furthermore, by having the integrated control unit 201 collect complex voltage and complex current, it becomes easier to perform advanced corrections for measurement errors and measurement temperature variations.

[0098] Here, the integrated control unit 201 may specify the frequency of the first reference frequency signal multiple times while changing it, and calculate the change in complex impedance corresponding to the change in the specified frequency.

[0099] According to this, under the control of the integrated control unit 201, the change in complex impedance corresponding to the change in frequency can be calculated.

[0100] Here, the integrated control unit 201 may generate plotting data showing a Cole-Cole plot, where the complex impedance is represented as a trajectory on the complex plane.

[0101] Here, the integrated control unit 201 may generate plotting data showing the Bode plot obtained by converting the complex impedance into magnitude and phase.

[0102] According to this method, the Cole-Cole plot or Bode plot of a secondary battery facilitates the estimation of the state of the battery cells (such as their degradation state).

[0103] Here, the integrated control unit 201 may acquire the temperature of the secondary battery and convert the complex impedance to a complex impedance corresponding to a predetermined temperature according to the acquired temperature.

[0104] According to this, the influence can be reduced by the temperature dependence of the complex impedance of the secondary battery.

[0105] Here, the integrated control unit 201 may estimate the temperature of the secondary battery at the time of measurement by using the calculated complex impedance from information indicating the complex impedance converted in the past and the temperature of the secondary battery.

[0106] According to this, even a battery management device without a temperature sensor can estimate the temperature of a secondary battery during measurement.

[0107] Here, the integrated control unit 201 may calculate the element constants of the circuit elements constituting the equivalent circuit model representing the secondary battery based on the complex impedance corresponding to a predetermined temperature.

[0108] This makes it possible to estimate the state of a secondary battery using an equivalent circuit model.

[0109] Here, the integrated control unit 201 may add identification information to the measurement information, including the calculated complex impedance, to identify the secondary battery, and transmit the measurement information with the added identification information to the server device via the network.

[0110] According to this, the battery management system 200 can manage batteries in cooperation with a server device (battery management server 301).

[0111] Here, the integrated control unit 201 may receive battery information from the server device, including the result of estimating the state of the secondary battery based on the measurement information.

[0112] (Embodiment 2) Next, we will describe an example of a battery management network configuration when the battery management server 301 is a so-called cloud server device.

[0113] Figure 7 is a block diagram showing an example configuration of a battery management network according to an embodiment. The battery management network in the figure includes an automobile 400 and a cloud system 300.

[0114] The automobile 400 is equipped with a battery management system 200 and a motor 401.

[0115] The battery management system 200 has already been described in Embodiment 1. The integrated control unit 201 in Figure 7 communicates with the server device of the cloud system 300 via the wireless circuit 34. A relay device may be interposed between the wireless circuit 34 and the server device 301.

[0116] The cloud system 300 is a group of server devices on a network, including server device 301. The battery management server 301 is a server device located separately from the battery management system 200. Server device 301 is a so-called cloud server.

[0117] Figure 8 is a sequence diagram showing an example of processing in a battery management network according to an embodiment.

[0118] In Embodiment 1, the battery management system 200 of the automobile 400 adds identification information to the measurement information including the calculated complex impedance, and transmits the measurement information with the added identification information as battery status data to the server device 301 via the network (S21).

[0119] The battery management server 301 estimates the state of the secondary battery based on the battery state data (S22) and generates battery information including the estimated result. The state of the secondary battery includes, for example, the battery's charge state, degradation state, and operating history. Furthermore, the server device 301 transmits the battery information, which is the result of the state estimation, to the automobile 400 (S23).

[0120] Furthermore, the battery management system 200 issues a block, which includes measurement information or battery information, and transmits it to the server device 301 (S24).

[0121] The battery management server 301 performs a sharing process to share the issued block data with the cloud server group (S25). The sharing process may be, for example, a process called mining. The cloud server group shares the collection of block data as a blockchain and performs a process (i.e., mining) to connect the block data issued from the automobile 400 to the blockchain, and performs state estimation and degradation diagnosis.

[0122] After completing the process of linking to the blockchain, the battery management server 301 sends data indicating block approval to the automobile 400 (S26).

[0123] As described above, the server device 301 according to Embodiment 2 is included in a group of server devices that share battery information over a network.

[0124] According to this, cloud battery telematics can be implemented. Here, cloud battery telematics refers to battery management as part of an information service that makes various information available using a cloud server system and a network-connected battery management system 200 installed in a vehicle.

[0125] Here, the integrated control unit 201 may share the collection of block data with the server devices by transmitting block data containing measurement information or battery information to the server devices.

[0126] According to this, block data containing measurement information or battery information can be shared and managed by a group of server devices. For example, if the group of server devices manages block data using blockchain technology, battery information can be managed securely.

[0127] (modified version) Next, we will describe some variations of the battery management system 200 according to Embodiments 1 and 2.

[0128] Figure 9 is a block diagram showing an example configuration of a battery management system and a battery management server related to a modified example.

[0129] This figure differs from Figure 1 in that it includes a battery management circuit 105A (first semiconductor integrated circuit) and a battery management circuit 105B (second semiconductor integrated circuit) instead of the original battery management circuit 105. The following explanation will focus on these differences. The battery management circuit 105, which is a single-chip semiconductor integrated circuit, is now divided into two semiconductor integrated circuits. Furthermore, the circuit configurations of the current measurement unit 112 and the voltage measurement unit 115 have been simplified.

[0130] The battery management circuit 105A differs from the battery management device 100 mainly in that it has a voltage measuring unit 122, a first reference signal generating unit 109 which is a reference signal generating unit, and a first signal synchronization unit 119.

[0131] The battery management circuit 105B includes a current measurement unit 112, a first signal synchronization unit 119, a second reference signal generation unit equivalent to the reference signal generation unit 109, and a second synchronization unit 119.

[0132] The first signal synchronization unit controls the first reference signal generator to synchronize the phases of the first reference frequency signal inside the battery management circuit 105A and the first reference frequency signal inside the battery management circuit 105B.

[0133] The second signal synchronization unit controls the second reference signal generation unit to synchronize the phase of the first reference frequency signal inside the battery management circuit 105A with the first reference frequency signal inside the battery management circuit 105B.

[0134] The measurement unit 122 includes a multiplexer (MUX) that selects one battery cell from a plurality of battery cells, an analog-to-digital converter that measures the voltage of the battery cell selected by the multiplexer, and a demultiplexer that distributes the conversion results of the analog-to-digital converter. The measurement unit 122 sequentially selects one battery cell from the plurality of battery cells and measures its voltage. The measurement unit 122 also measures temperature.

[0135] As described above, the modified battery management system 200 has a secondary battery having a plurality of battery cells connected in series, the battery management circuit 105 includes a multiplexer that selects one battery cell from the plurality of battery cells, and one or more analog-to-digital converters of the voltage measurement unit 115 is a single analog-to-digital converter that measures the voltage of the battery cell selected by the multiplexer.

[0136] According to this, a single analog-to-digital converter can sequentially measure the voltage and current of multiple battery cells, simplifying the circuit configuration.

[0137] Here, the battery management circuit is composed of a first semiconductor integrated circuit (battery management circuit 105A) and a second semiconductor integrated circuit (battery management circuit 105B). The first semiconductor integrated circuit has a voltage measurement unit 115, a first reference signal generation unit which is a reference signal generation unit 109, and a first signal synchronization unit 119. The second semiconductor integrated circuit has a current measurement unit 112, a first signal synchronization unit 119, a second reference signal generation unit equivalent to the reference signal generation unit 109, and a second signal synchronization unit 119. The first signal synchronization unit controls the first reference signal generation unit to align the phase of a first reference frequency signal inside the first semiconductor integrated circuit with the first reference frequency signal inside the second semiconductor integrated circuit. The second signal synchronization unit controls the second reference signal generation unit to align the phase of a first reference frequency signal inside the first semiconductor integrated circuit with the first reference frequency signal inside the second semiconductor integrated circuit.

[0138] According to this, if the entire battery management system 200 is equipped with only one second semiconductor integrated circuit, the current can be measured in common for multiple battery packs 101 at a single location. In other words, since it is not necessary to measure the current individually for multiple battery packs 101, the circuit configuration can be made simpler. Moreover, the first and second signal synchronization units synchronize the phase of the first reference frequency signal in the first semiconductor integrated circuit with the first reference frequency signal in the second semiconductor integrated circuit, so that measurements can be taken with high precision.

[0139] (Other embodiments) Although embodiments have been described above, this disclosure is not limited to the embodiments described above.

[0140] For example, the above embodiment describes a battery management system that manages batteries used in automobiles such as EVs, but the battery management system may manage batteries for any purpose.

[0141] Furthermore, the circuit configuration described in the above embodiment is merely an example, and this disclosure is not limited to the above circuit configuration. In other words, circuits that can realize the characteristic functions of this disclosure in the same way as the above circuit configuration are also included in this disclosure. For example, circuits in which elements such as switching elements (transistors), resistors, or capacitive elements are connected in series or parallel to a certain element, to the extent that they can realize the same functions as the above circuit configuration, are also included in this disclosure.

[0142] Furthermore, in the above embodiment, the components included in the integrated circuit were realized by hardware. However, some of the components included in the integrated circuit may be realized by executing a software program suitable for that component. Some of the components included in the integrated circuit may be realized by a program execution unit such as a CPU (Central Processing Unit) or processor reading and executing a software program recorded on a recording medium such as a hard disk or semiconductor memory.

[0143] Furthermore, in the above embodiment, the processing performed by a specific processing unit may be performed by another processing unit. Also, in the operation described in the above embodiment, the order of multiple processing units may be changed, or multiple processing units may be performed in parallel.

[0144] Furthermore, this disclosure also includes forms obtained by applying various modifications to each embodiment that a person skilled in the art could conceive, or forms realized by arbitrarily combining the components and functions of each embodiment without departing from the spirit of this disclosure. [Industrial applicability]

[0145] This disclosure can be used in battery management circuits, battery management systems, and battery management networks for managing secondary batteries. [Explanation of Symbols]

[0146] 31 CPU 32 memory 33 Communication Circuit 34 Radio circuit 100, 100A, 100B battery management device 101 Battery Pack 104 AC superposition section 105, 105A, 105B battery management circuit 106 detection resistor 107 Temperature Sensor 109 Reference signal generation unit 110 Reference frequency generator 111 Phase shifter 112 Current Measurement Unit 113 Clock generation unit 115 Voltage Measurement Unit 117 Reference Voltage Generation Unit 118b Conversion section 118c Integral part 118d Holding part 119 Synchronization Unit 120 Temperature measurement unit 121 Temperature calculation section 122 Measurement Unit 131 Communication Interface Section 132 communication lines 200 Battery Management System 201 Integrated Control Unit 300 Cloud Systems 301 Battery Management Server 302 Communication Line 400 cars 401 Motor B0~B5 Battery Cells

Claims

1. A battery management system for managing the battery state of multiple battery cells, A reference signal generation unit that generates an AC quadrature reference signal consisting of an in-phase signal and a quadrature signal with a phase difference of 90 degrees relative to the in-phase signal, An excitation signal generation unit that processes the in-phase signal of the orthogonal reference signal to generate an excitation signal, A current generation unit that generates an excitation current based on the excitation signal and energizes the plurality of battery cells, A current measuring unit measures the excitation current generated by the current generating unit by sampling it using the quadrature reference signal. A voltage measurement unit measures the voltage of the plurality of battery cells by sampling them using the quadrature reference signal, A multiplexer that switches the connection between the plurality of battery cells and the voltage measuring unit, An impedance measuring unit measures the AC impedance of each of the plurality of battery cells based on the excitation current measured by the current measuring unit and the voltage measured by the voltage measuring unit. The system comprises a control unit that controls the measurement of AC impedance by the impedance measuring unit, The control unit is a battery management system that uses the multiplexer to select one battery cell from the plurality of battery cells and causes the impedance measurement unit to measure the AC impedance.

2. The battery management system according to claim 1, wherein the control unit switches the multiplexer to a different battery cell when the AC impedance of one of the plurality of battery cells is measured.

3. The battery management system according to claim 1, wherein the control unit performs switching of the multiplexer at each sampling period.

4. The battery management system according to claim 3, further comprising a synchronization unit that adjusts the voltage sampling rate in the voltage measuring unit and the current sampling rate in the current measuring unit to be equal.

5. The battery management system according to claim 3, further comprising a synchronization unit that aligns the phase of voltage sampling in the voltage measurement unit with the phase of current sampling in the current measurement unit.

6. The battery management system according to any one of claims 1 to 5, comprising a plurality of sets of the voltage measuring unit and the multiplexer.

Images