Battery monitoring device and battery monitoring method

Abstract

A battery monitoring device (1) is provided with: a motor drive current frequency information acquisition unit (25) that acquires frequency information of the drive current of a motor (28), which is the load of a battery assembly (6); a control unit (9) that determines a measurement frequency on the basis of the frequency information; an AC superimposition unit (11) that supplies an AC current at the measurement frequency to the battery assembly (6); a voltage measurement unit (13) that measures the voltage of each of a plurality of batteries (5) through which the AC current flows; an AC superimposed current measurement unit (21) that measures the current value of the AC current; and an impedance calculation unit (23a) that measures the AC impedance of each of the plurality of batteries (5) on the basis of the voltage of each of the plurality of batteries (5) and the current value of the AC current.

Description

Battery Monitoring Device and Battery Monitoring Method

[0001] The present disclosure relates to a battery monitoring device and a battery monitoring method for monitoring the states such as voltage, current, and temperature of a secondary battery such as a lithium-ion battery.

[0002] In Patent Document 1, an alternating current is supplied to a battery pack composed of a plurality of batteries, and the voltages and currents of the plurality of batteries to which the alternating current is supplied are multiplied and integrated by SIN waves and COS waves having a phase difference of 90 degrees from each other to be converted into complex numbers, and complex voltages and complex currents are measured, that is, a technique for measuring the AC impedance of a battery is disclosed.

[0003] International Publication No. 2020 / 003841

[0004] Thermistors are widely used for measuring and monitoring the temperature of secondary batteries such as lithium-ion batteries used in electric vehicles and the like. However, since the number of secondary batteries used in electric vehicles and the like is large, the same number of thermistors as the number of batteries is required to measure the temperature of all secondary batteries. Therefore, a large number of thermistors and harnesses for connecting the thermistors to the battery monitoring device are required, resulting in cost and space problems. Therefore, in many cases, the temperature of the entire battery module and battery pack is monitored with a limited number of thermistors. Secondary batteries such as lithium-ion batteries are vulnerable to heat, and the higher the temperature, the more likely they are to deteriorate, and the higher the temperature, the greater the risk of smoke and fire such as thermal runaway. In addition, rapid charging is becoming widespread, and the opportunity for temperature rise due to self-heating is also increasing. As the opportunity to use secondary batteries in electric vehicles and the like increases, thermal management for suppressing deterioration and the risk of smoke and fire has become important.

[0005] In this context, a technology is being considered that replaces thermistor-based temperature measurement by measuring the internal impedance of a battery with a battery monitoring device and estimating the temperature from that impedance. A typical example of this technology involves superimposing an AC current of an arbitrary frequency onto the battery, measuring the impedance from the changes in the battery's voltage and current, and estimating the battery's temperature using a pre-prepared relationship formula between impedance and battery temperature. By adopting this technology, the temperature of each battery in a battery pack can be determined without installing a thermistor or increasing the number of thermistors installed. Furthermore, when a thermistor is installed, its installation location is on the battery surface, which may cause a difference between the internal temperature generated by the battery's self-heating and the temperature measured by the thermistor. On the other hand, since the internal temperature of the battery can be estimated using impedance measurement, more precise thermal management of the battery becomes possible.

[0006] However, when the battery load is active, such as when an electric vehicle is running or charging, for example, when the load is a motor and the motor is being driven (rotating), the motor's drive current also flows through the battery. The motor's drive current is an alternating current (noise current) that includes ripple in its frequency components, which depends on the motor's rotation frequency. Depending on the motor's rotation speed, the frequency or harmonic frequency of the aforementioned ripple-containing alternating current may match, or be close to, the frequency of the AC superimposed current used to measure impedance.

[0007] In AC impedance measurement, as in the technology disclosed in Patent Document 1, the voltage and current values ​​measured by the voltage measurement unit and current measurement unit are multiplied and integrated by sine and cosine waves at measurement frequencies with a 90-degree phase difference from each other to convert them into complex numbers. The bandwidth exhibits the characteristics of a bandpass filter (BPF) centered on the impedance measurement frequency, as shown in Figure 3 below. Therefore, if there is noise from other frequency components caused by a motor or the like near the measurement frequency, it becomes a factor in impedance measurement errors, making accurate impedance measurement difficult. For example, when the load current flowing through the battery is zero, such as when an electric vehicle is parked, there is no problem measuring impedance. However, when a load current flows through the battery, such as when driving or charging, if the frequency of the AC component (ripple noise, etc.) of that load current, including harmonic components, is near the frequency at which the AC impedance is measured, the measured AC impedance will contain errors, resulting in errors in the estimation of the battery's internal temperature.

[0008] Therefore, this disclosure provides a battery monitoring device and the like that can suppress errors in the measurement results of AC impedance.

[0009] The battery monitoring device according to this disclosure is a battery monitoring device for monitoring a battery pack composed of a plurality of batteries connected in series, comprising: a motor drive current frequency information acquisition unit that acquires frequency information of the drive current of a motor which is the load of the battery pack; a control unit that determines a measurement frequency based on the frequency information; an AC superposition unit that supplies an AC current of the measurement frequency to the battery pack; a voltage measurement unit that measures the voltage of each of the plurality of batteries through which the AC current flows; an AC superposition current measurement unit that measures the current value of the AC current; and an impedance calculation unit that measures the AC impedance of each of the plurality of batteries based on the voltage of each of the plurality of batteries and the current value of the AC current.

[0010] The battery monitoring method according to this disclosure is a battery monitoring method performed by a battery monitoring device that monitors a battery pack consisting of a plurality of batteries connected in series, and includes: a motor drive current frequency information acquisition step of acquiring frequency information of the drive current of a motor which is the load of the battery pack; a control step of determining a measurement frequency based on the frequency information; an AC superposition step of supplying an AC current of the measurement frequency to the battery pack; a voltage measurement step of measuring the voltage of each of the plurality of batteries through which the AC current flows; an AC superposition current measurement step of measuring the current value of the AC current; and an impedance calculation step of measuring the AC impedance of each of the plurality of batteries based on the voltage of each of the plurality of batteries and the current value of the AC current.

[0011] These comprehensive or specific embodiments may be implemented as a system, method, integrated circuit, computer program, or recording medium such as a computer-readable CD-ROM, or as any combination of a system, method, integrated circuit, computer program, and recording medium.

[0012] According to one aspect of this disclosure, a battery monitoring device, etc., can suppress errors in the measurement results of AC impedance.

[0013] This is a diagram showing an example of a battery monitoring device according to an embodiment. This is a diagram showing an example of a superimposed signal generation unit and an impedance calculation unit according to an embodiment. This is a diagram showing an example of the frequency characteristics of the impedance calculation unit according to an embodiment. This is a diagram showing an example of a Nyquist plot. This is a diagram showing an example of a battery equivalent circuit. This is a diagram showing the relationship between AC impedance and equivalent circuit parameters. This is a diagram showing an example of the correlation between AC impedance and battery temperature. This is a diagram showing an example of the correlation formula between AC impedance and absolute temperature. This is a diagram showing an example of a correlation table between AC impedance and temperature for each SOH (State Of Health). This is a diagram showing the effects of the battery monitoring device according to an embodiment. This is a flowchart showing the first example of the operation of the battery monitoring device according to an embodiment. This is a flowchart showing the second example of the operation of the battery monitoring device according to an embodiment. This is a flowchart showing the third example of the operation of the battery monitoring device according to an embodiment. This is a flowchart showing the fourth example of the operation of the battery monitoring device according to an embodiment. This is a diagram for explaining the fourth example of the operation of the battery monitoring device according to an embodiment. This is a flowchart showing the fifth example of the operation of the battery monitoring device according to an embodiment. This is a flowchart showing the sixth example of the operation of the battery monitoring device according to an embodiment. This is a diagram for explaining the sixth example of the operation of the battery monitoring device according to an embodiment. This is a flowchart showing an example of a battery monitoring method according to another embodiment.

[0014] The embodiments will be described in detail below with reference to the drawings.

[0015] 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 this disclosure.

[0016] (Embodiment) The following describes a battery monitoring device according to an embodiment.

[0017] Figure 1 is a configuration diagram showing an example of a battery monitoring device 1 according to an embodiment. In addition to the battery monitoring device 1, Figure 1 also shows a higher-level control unit 2, a motor drive control device 3, a relay 4, a battery pack 6, a shunt resistor 14a, an external thermometer 16, a rotation position detection device 26, a current detection resistor 27, and a motor 28.

[0018] The battery pack 6 consists of multiple batteries 5 (for example, batteries C0 to C7) connected in series. The motor drive control device 3 and the motor 28 are loads on the battery pack 6. The motor drive control device 3 controls the drive (rotation) of the motor 28. For example, the motor 28 is equipped with a rotation position detection device 26 and a current detection resistor 27, and the motor drive control device 3 controls the drive of the motor 28 using the rotation position of the motor 28 detected by the rotation position detection device 26 and the drive current of the motor 28 detected by the current detection resistor 27. The rotation position detection device 26 is a Hall element or resolver. A relay 4 is provided between the battery pack 6 and the motor drive control device 3 to turn the connection between the battery pack 6 and the motor drive control device 3 ON / OFF. The motor 28 is driven according to the ON / OFF connection between the battery pack 6 and the motor drive control device 3 by the relay 4. For example, the battery pack 6, motor drive control device 3 and motor 28 are mounted in an electric vehicle.

[0019] The shunt resistor 14a is a shunt resistor for detecting the load current flowing to the motor drive control device 3 and the motor 28, among other loads. The external thermometer 16 is a thermistor for measuring the temperature of the battery pack 6. Note that the external thermometer 16 does not have to be permanently installed on the battery pack 6; it may be installed temporarily when calibration, which will be described later, is performed.

[0020] The battery monitoring device 1 is a device that monitors the voltage, current, and temperature of the battery pack 6. For example, the battery monitoring device 1 is installed in an electric vehicle. The battery pack 6 and the battery monitoring device 1 are connected by a plurality of voltage detection lines 12. The battery monitoring device 1 measures the AC impedance of each of the plurality of batteries 5 using EIS (Electrochemical Impedance Spectroscopy). As will be described in detail later, the battery monitoring device 1 has a function that can suppress errors in the AC impedance measurement results even when the motor 28 is active. The battery monitoring device 1 comprises a measurement unit 7, a battery state estimation unit 8, a control unit 9, a communication unit 10, and a motor drive current frequency information acquisition unit 25. The battery monitoring device 1 may also be a computer (for example, an MCU (Micro Control Unit)) having a processor and memory.

[0021] The measurement unit 7 includes an AC superposition unit 11, a voltage measurement unit 13, a current measurement unit 14, an external temperature measurement unit 15, a superposition signal generation unit 20, an AC superposition current measurement unit 21, and a timing generation unit 22.

[0022] The AC superposition unit 11 includes a load resistor 17, a transistor 18, and a shunt resistor 19 to supply AC current to the battery pack 6. The transistor 18 is a transistor that allows current to flow to the shunt resistor 19. The transistor 18 is, for example, an FET (Field Effect Transistor), but it may also be a bipolar transistor. The drain of the transistor 18 is connected to the load resistor 17, the source of the transistor 18 is connected to the shunt resistor 19, and the gate of the transistor 18 is connected to the superposition signal generation unit 20, which will be described later. The AC superposition unit 11 supplies the battery pack 6 with a square wave current (AC superposition current: also referred to as AC current) whose peak is determined by the current value determined by the voltage of the load resistor 17 and the battery pack 6, by controlling the gate of the transistor 18 with a square wave signal by the superposition signal generation unit 20. This alternating current generates an alternating voltage across each battery 5 of the battery pack 6 due to the internal resistance of each battery 5, and also generates an alternating voltage across the shunt resistor 19 installed in the system through which the alternating current flows.

[0023] The voltage measurement unit 13 measures the voltage of each battery 5 in the battery pack 6. Specifically, the voltage measurement unit 13 measures the voltage V0 of battery C0, the voltage V1 of battery C1, ..., and the voltage V7 of battery C7. For example, the voltage measurement unit 13 has an A / D converter and converts the measured voltage (analog value) into a digital value. The voltage measurement unit 13 outputs the measured voltages V0 to V7 (for example, digital values) to the battery state estimation unit 8. The voltage measurement unit 13 sets the measurement timing via the timing generation unit 22 in order to measure the voltages of the multiple batteries 5 constituting the battery pack 6 at the same time. The timing generation unit 22 is controlled by the control unit 9.

[0024] The superimposed signal generation unit 20 generates a sine wave signal of a predetermined frequency, a cosine wave signal of a predetermined frequency having a phase orthogonal to the sine wave signal, and a pulse signal of a predetermined frequency. The superimposed signal generation unit 20 applies the pulse signal of the predetermined frequency to the gate of the transistor 18. This allows an alternating current of a predetermined frequency to flow through the battery pack 6.

[0025] The AC superimposed current measurement unit 21 measures the AC current superimposed on the battery pack 6. Since an AC voltage corresponding to the AC current flowing through the battery pack 6 is generated in the shunt resistor 19, the AC superimposed current measurement unit 21 can measure the AC current flowing through the battery pack 6 by acquiring the AC voltage generated in the shunt resistor 19. For example, the AC superimposed current measurement unit 21 has an A / D converter and converts the measured current (analog value) into a digital value. The AC superimposed current measurement unit 21 outputs the measured AC current Iac (for example, a digital value) to the battery state estimation unit 8. The AC superimposed current measurement unit 21 sets the measurement timing via the timing generation unit 22 so that it measures the AC current flowing through the battery pack 6 at the same timing as the voltage measurement unit 13 measures the voltage of each battery 5.

[0026] The current measurement unit 14 measures the load current flowing through the battery pack 6 while the electric vehicle is running, that is, while the motor 28 is in operation. Since an AC voltage corresponding to the load current flowing through the battery pack 6 is generated across the shunt resistor 14a, the current measurement unit 14 can measure the load current flowing through the battery pack 6 by acquiring the voltage generated across the shunt resistor 14a. The current measurement unit 14 outputs the measured load current to the higher-level control unit 2.

[0027] The external temperature measurement unit 15 measures the temperature of the battery pack 6 measured by the external thermometer 16. The external temperature measurement unit 15 outputs the measured temperature T to the battery state estimation unit 8.

[0028] The battery state estimation unit 8 includes a calculation unit 23 and a storage unit 24.

[0029] The calculation unit 23 includes an impedance calculation unit 23a, an internal temperature estimation unit 23b, and an internal temperature correction unit 23c.

[0030] The impedance calculation unit 23a measures the AC impedance of each of the multiple batteries 5 based on the voltage of each battery 5 and the current value of the AC current (specifically, the AC voltage generated across the shunt resistor 14a).

[0031] The internal temperature estimation unit 23b estimates the internal temperature of each of the multiple batteries 5 based on the AC impedance of each of the multiple batteries 5 measured by the impedance calculation unit 23a.

[0032] The internal temperature correction unit 23c corrects (i.e., calibrates) the predetermined correlation between the AC impedance of the battery 5 and its internal temperature in response to the degradation of the battery 5. Specifically, it performs calibration of the predetermined correlation between the AC impedance of the battery 5 and its internal temperature based on the temperature of the battery pack 6 measured by the external temperature measurement unit 15.

[0033] The memory unit 24 stores the AC impedance measured by the impedance calculation unit 23a and the internal temperature estimated by the internal temperature estimation unit 23b. The memory unit 24 also stores a predetermined correlation between the AC impedance of the battery 5 and its internal temperature.

[0034] In order to drive the electric vehicle, a drive current is supplied to the motor 28 by the motor drive control device 3. The motor 28 operates with a drive current that includes frequency components corresponding to the rotational speed of the motor 28. At this time, since the drive current is supplied from the battery pack 6, a noise current containing ripple noise corresponding to the rotational speed of the motor 28, which is included in the drive current, flows through the battery pack 6. In response to this, the motor drive current frequency information acquisition unit 25 acquires the frequency information of the drive current of the motor 28, which is the load of the battery pack 6. The frequency information of the drive current of the motor 28 is information that indicates the frequency of the ripple noise current that flows through the battery pack 6, which is generated by the operation of the motor 28.

[0035] The motor drive current frequency information acquisition unit 25 may acquire the inverter frequency as frequency information from the motor drive control device 3, or the rotational speed information of the motor 28 as frequency information from the rotational position detection device 26, or it may acquire the voltage change occurring in the current detection resistor 27 that detects the drive current of the motor 28 as frequency information. By acquiring the inverter frequency, the rotational speed information of the motor 28, or the voltage change occurring in the current detection resistor 27 that detects the drive current of the motor 28, the frequency of the noise current caused by the drive current of the motor 28 can be easily determined.

[0036] The control unit 9 determines the measurement frequency based on the frequency information acquired by the motor drive current frequency information acquisition unit 25. The control unit 9 calculates the frequency of the noise current flowing through the battery pack 6, which includes ripple noise corresponding to the rotational speed of the motor 28, from the frequency information obtained from the motor drive current frequency information acquisition unit 25, and transmits information of measurement frequencies that do not match this frequency to the superimposed signal generation unit 20. The measurement frequency is a frequency different from the frequency of the motor 28 drive current, frequencies near that frequency, harmonic frequencies, and frequencies near harmonic frequencies. For example, if the current measurement frequency matches or is near the frequency of the motor 28 drive current or harmonic frequencies, the control unit 9 moves the measurement frequency away from the frequency of the motor 28 drive current or harmonic frequencies.

[0037] The AC superposition unit 11 supplies an AC current at a measurement frequency determined by the control unit 9 to the battery pack 6, the voltage measurement unit 13 measures the voltage of each of the multiple batteries 5 through which the AC current of the measurement frequency flows, and the AC superposition current measurement unit 21 measures the current value of the AC current at the measurement frequency. For example, if the frequency of the drive current of the motor 28 is 100 Hz, by setting the frequency of the AC current supplied from the AC superposition unit 11 to 150 Hz, which is the intermediate frequency between 100 Hz and the harmonic frequency of 200 Hz, or to an intermediate frequency between each harmonic frequency (such as 250 Hz, 350 Hz, or 450 Hz), the influence of the frequency of the drive current of the motor 28 can be avoided, and stable measurement of AC impedance becomes possible.

[0038] Furthermore, by sequentially detecting the frequency of the motor 28's drive current and controlling it to determine the optimal measurement frequency, the measurement frequency can be switched sequentially even if the rotational speed of the motor 28 changes over time in accordance with the electric vehicle's speed, enabling continuous and stable measurement of AC impedance. In addition, by using this AC impedance, it becomes possible to continuously and stably estimate the temperature inside the battery.

[0039] Furthermore, if there is an abnormality in the AC impedance or internal temperature of the battery 5, the control unit 9 notifies the higher-level control unit 2 of the abnormality via the communication unit 10. When the higher-level control unit 2 receives notification of an abnormality from the control unit 9, it controls the relay 4 to the OFF state. Also, the higher-level control unit 2 controls the relay 4 to the OFF state if the load current value indicates an abnormality.

[0040] Next, the details of the superimposed signal generation unit 20 and the impedance calculation unit 23a will be explained using Figure 2.

[0041] Figure 2 is a configuration diagram showing an example of a superimposed signal generation unit 20 and an impedance calculation unit 23a according to an embodiment.

[0042] The superimposed signal generation unit 20 includes a signal generation unit 201 and a π / 2 phase shift unit 202. The signal generation unit 201 generates a SIN wave signal of the measurement frequency, and the π / 2 phase shift unit 202 shifts the phase of the SIN wave signal by 90 degrees to generate a COS wave signal of the measurement frequency. FIG. 2 also shows examples of the time waveforms of the SIN wave signal and the COS wave signal.

[0043] The impedance calculation unit 23a measures the AC impedance of each of the batteries 5 of the battery pack 6 from each voltage (V0 to V7) measured by the voltage measurement unit 13 and the applied current (Iac) measured by the AC superimposed current measurement unit 21. The impedance calculation unit 23a includes a real part and imaginary part separation unit 231, an integration unit 232, and an impedance calculation unit 233.

[0044] The real part and imaginary part separation unit 231 has the same number of multiplier pairs corresponding to each measured voltage and current. Each multiplier pair multiplies the digital value from each A / D converter by the SIN wave signal and the COS wave signal. As a result, each digital value is separated into the real part component and the imaginary part component of each of the complex voltage and the complex current. The multiplication result of the digital value output from the A / D converter and the SIN wave signal indicates the real part component when the sampled voltage is expressed as a complex voltage, and also indicates the real part component when the sampled current is expressed as a complex current. The multiplication result of the digital value output from the A / D converter and the COS wave signal indicates the imaginary part component when the sampled voltage is expressed as a complex voltage, and also indicates the imaginary part component when the sampled current is expressed as a complex current.

[0045] The integration unit 232 has the same number of averaging circuit pairs corresponding to the multiplier pairs of the real and imaginary part separation unit 231, and averages the real and imaginary part components of the repeatedly measured complex voltage and complex current. By this averaging, the measurement errors of the complex voltage and complex current can be reduced, and the resolution (measurement accuracy) can be improved by oversampling. Therefore, even with an A / D converter having a small number of bits (for example, about 16 bits), it is possible to obtain measurement results of AC impedance with an accuracy of 20 to 24 bits. FIG. 2 shows the complex voltage (complex V0) of the battery C0, ..., the complex voltage (complex V7) of the battery C7, and the complex current (complex Iac) of the applied current.

[0046] The impedance calculation unit 233 calculates the AC impedance of each battery 5 by dividing the complex voltage of each battery 5 by the complex current. The impedance calculation unit 233 calculates the AC impedance of the battery C0 by calculating complex V0 / complex Iac, ..., and calculates the AC impedance of the battery C7 by calculating complex V7 / complex Iac.

[0047] FIG. 3 is a diagram showing an example of the frequency characteristics of the impedance calculation unit 23a.

[0048] As shown in FIG. 3, the impedance calculation unit 23a shows the characteristics of a band-pass filter (BPF) centered on the measurement frequency of the AC impedance (for example, 1 kHz). The control unit 9 calculates the frequency of the ripple noise current caused by the drive current of the motor 28 from the frequency information acquired by the motor drive current frequency information acquisition unit 25, and considers this frequency and the harmonic frequencies and the attenuation amount of the band-pass filter shown in FIG. 3, and determines a measurement frequency at which the ripple noise has no effect or a small effect. The impedance calculation unit 23a can avoid the influence of the ripple noise current and avoid the measurement error of the AC impedance by measuring the AC impedance at this measurement frequency.

[0049] The impedance calculation unit 23a measures AC impedance at various frequencies. By plotting the measured AC impedance on the complex plane, a Nyquist plot diagram like the one shown in Figure 4A can be obtained.

[0050] Figure 4A shows an example of a Nyquist plot. In Figure 4A, the horizontal axis shows the real part Re(Z) of the AC impedance (complex impedance), and the vertical axis shows the imaginary part Im(Z) of the AC impedance (complex impedance).

[0051] In a Nyquist plot diagram like the one shown in Figure 4A, the impedance components of a lithium-ion battery can be analyzed by dividing it into regions (i) to (iv), for example. Region (i) corresponds to the impedance of the terminals and wiring. Region (ii) corresponds to the impedance of the transfer resistance in the electrolyte of the lithium-ion battery. The semicircular portions of regions (iii) and (iv) correspond to the impedance of the charge transfer resistance of the lithium-ion battery, region (iii) corresponds to the impedance of the negative electrode, and region (iv) corresponds to the impedance of the positive electrode. From the Nyquist plot diagram created in this way, the equivalent circuit of the lithium-ion battery shown in Figure 4B can be estimated.

[0052] Figure 4B shows an example of a battery equivalent circuit.

[0053] Figure 4B shows an example of an equivalent circuit for the internal resistance of a lithium-ion battery. In this example, the resistor R0 corresponds to the transfer resistance in the electrolyte, the resistor R1 corresponds to the charge transfer resistance of the negative electrode, and the resistor R2 corresponds to the charge transfer resistance of the positive electrode. The wiring is defined by an inductor L. Inductor L1 corresponds to region (i) in the Nyquist plot shown in Figure 4A. The resistor R0 corresponds to region (ii) in the Nyquist plot shown in Figure 4A. The RC parallel circuit consisting of resistor R1 and capacitor C1 corresponds to region (iii) in the Nyquist plot shown in Figure 4A. The RC parallel circuit consisting of resistor R2 and capacitor C2 corresponds to region (iv) in the Nyquist plot shown in Figure 4A.

[0054] Figure 4C shows the relationship between AC impedance and equivalent circuit parameters.

[0055] The AC impedance of a lithium-ion battery can be expressed by the equation shown in Figure 4C, with the impedances corresponding to each of the regions (i) to (iv) shown.

[0056] The internal temperature estimation unit 23b estimates the temperature of the battery 5 from the AC impedance at the measurement frequency.

[0057] Figure 5A shows an example of the correlation between AC impedance and the temperature of battery 5.

[0058] Figure 5B shows an example of a correlation equation between AC impedance and absolute temperature.

[0059] Figure 5C shows an example of a correlation table between the AC impedance and temperature of each SOH.

[0060] As shown in Figure 5A, it can be seen that AC impedance has a negative correlation with temperature. Therefore, temperature estimation becomes possible by storing the temperature fluctuation characteristics of AC impedance for each frequency (a table or calculation formula showing the relationship between temperature and AC impedance for each frequency) in the memory unit 24 as a predetermined correlation between AC impedance and internal temperature, as shown in Figure 5B. Note that since the relationship between temperature and AC impedance also changes when the SOH changes, the correlation between the AC impedance and temperature of each battery 5 (for example, a table as shown in Figure 5C) may also be stored in the memory unit 24 for each SOH.

[0061] Due to aging or individual differences in the battery pack 6, the relationship between AC impedance and internal temperature may change, potentially increasing the estimation error of the internal temperature. Therefore, when the battery 5 deteriorates, the internal temperature correction unit 23c calibrates the correlation (table or calculation formula) stored in the memory unit 24. For example, when the charging and discharging of the battery 5 stops and a certain period of time has elapsed, such as when an electric vehicle is parked, the internal temperature of the battery 5 and the temperature measurement result using the external thermometer 16 installed on the battery pack 6 match. At this time, the internal temperature correction unit 23c corrects the table or calculation formula stored in the memory unit 24 using the temperature from the external thermometer 16.

[0062] In this way, by measuring the temperature of the battery pack 6 via an external thermometer 16 such as a thermistor using the external temperature measurement unit 15, and performing correlation calibration, estimation errors of the internal temperature can be suppressed. This suppresses errors due to aging degradation or individual differences in the battery pack 6, enabling stable estimation of the internal temperature by measuring AC impedance over a long period of time. For example, the relationship between AC impedance and internal temperature can be mathematically formulated using the Arrhenius method, errors due to aging degradation or individual differences in the battery pack 6 can be treated as offset errors, and calibration can be performed by using the measurement value from the external temperature measurement unit 15 to offset the offset error when the temperature of the battery 5 is in thermal equilibrium.

[0063] Next, the effects of the battery monitoring device 1 will be explained using Figure 6.

[0064] Figure 6 is a diagram showing the effects of the battery monitoring device 1 according to the embodiment. The upper part of Figure 6 shows the standard deviation of EIS measurement at each measurement frequency when the frequency of the motor 28 drive current is 250 Hz, and the lower part of Figure 6 shows the standard deviation of EIS measurement at each measurement frequency when the frequency of the motor 28 drive current is 500 Hz.

[0065] As shown in Figure 6, in both the case where the frequency of the motor 28's drive current (transient load) is 250 Hz and 500 Hz, the standard deviation worsens (i.e., the EIS measurement results vary) when the measurement frequency matches the frequency of the motor 28's drive current. The standard deviation also worsens when the measurement frequency matches the harmonic frequency of the motor 28's drive current. On the other hand, when the measurement frequency does not match the frequency and harmonic frequency of the motor 28's drive current, the standard deviation does not worsen (i.e., the EIS measurement results do not vary). Note that in Figure 6, experiments were not conducted when the measurement frequency was the third harmonic frequency (750 Hz in the upper part of Figure 6, and 1500 Hz in the lower part of Figure 6), so the experimental results for that case are not shown, but the standard deviation also worsens when the measurement frequency matches the third harmonic frequency of the motor 28's drive current frequency.

[0066] As explained above, if the frequency or harmonic frequency of noise current such as ripple flowing through the battery pack 6 due to the drive current of the motor 28 is close to the frequency of the AC current supplied to the battery pack 6 when measuring the AC impedance, the measurement error of the AC impedance will be large. Therefore, by supplying the battery pack 6 with an AC current at a measurement frequency different from the frequency and harmonic frequency of the drive current of the motor 28, which is determined based on the frequency information of the drive current of the motor 28, it is possible to suppress errors in the measurement results of the AC impedance. This makes it possible to measure the AC impedance of the battery 5 stably even when a load such as the motor 28 is being driven in an electric vehicle. For example, by switching the measurement frequency as needed, it becomes possible to measure the AC impedance stably and continuously, regardless of the rotational speed of the motor 28, which is proportional to the speed of the electric vehicle.

[0067] Furthermore, by utilizing the correlation between the AC impedance of the battery 5 and its internal temperature, it becomes possible to estimate the internal temperature of the battery 5. When measuring the internal temperature using a thermistor, space is required to install the thermistor and a harness is needed to connect it, which increases the size of the battery monitoring device 1. However, by estimating the internal temperature using the above correlation, the number of thermistors and harnesses can be reduced, making it possible to miniaturize the battery monitoring device 1. As a result, cost increases are suppressed, and it becomes possible to estimate the temperature of more batteries 5, leading to enhanced safety for the battery monitoring device 1 and equipment such as the battery pack 6 to which the battery monitoring device 1 is applied. In addition, since the temperature of the battery 5 can be estimated in more detail, detailed temperature management of the battery 5 can be performed, and it is expected that the lifespan of the battery 5 will be improved by optimizing temperature management.

[0068] The operation of the battery monitoring device 1 will be explained in detail below, with examples from the first to the sixth.

[0069] [First Example] First, the first example will be explained using Figure 7.

[0070] Figure 7 is a flowchart showing a first example of the operation of the battery monitoring device 1 according to the embodiment.

[0071] (i) For each of the multiple frequencies, the correlation between the AC impedance and the internal temperature of the battery 5 is stored in a database (step S101). In other words, the storage unit 24 stores the correlation for each of the multiple frequencies. For example, the multiple frequencies are all the frequencies for which the AC impedance is measured.

[0072] (ii) The motor drive current frequency information acquisition unit 25 acquires motor drive current frequency information (step S102).

[0073] (iii) The control unit 9 identifies the frequencies that affect the measurement of AC impedance (i.e., the frequency of the motor 28 drive current and its harmonic frequencies) from the motor drive current frequency information acquired in (ii) (step S103).

[0074] (iv) The control unit 9 determines a measurement frequency for an AC impedance that is different from the frequency identified in (iii) (step S104).

[0075] (v) The impedance calculation unit 23a measures the AC impedance at the measurement frequency determined in (iv) (step S105).

[0076] (vi) The internal temperature estimation unit 23b uses the AC impedance measured in (v) to estimate the internal temperature of the battery 5 from the correlation in (i) (step S106). In other words, the internal temperature estimation unit 23b uses the correlation at the measurement frequency among the multiple frequencies in (i) to estimate the internal temperature of each of the multiple batteries 5.

[0077] This allows the system to determine a measurement frequency that is different from the frequency of the motor 28's drive current and its harmonic frequencies among the multiple frequencies whose correlations are stored, thereby suppressing errors in the AC impedance measurement results. Furthermore, by utilizing the correlation at the determined measurement frequency, estimation errors in the internal temperature can be suppressed.

[0078] [Second Example] Next, we will explain the second example using Figure 8.

[0079] Figure 8 is a flowchart showing a second example of the operation of the battery monitoring device 1 according to the embodiment.

[0080] (i) For each of the multiple frequencies, the correlation between the AC impedance and the internal temperature of the battery 5 is recorded in a database (step S201). For example, the multiple frequencies are all the frequencies for which the AC impedance is measured.

[0081] (ii) The impedance calculation unit 23a measures the AC impedance for each of the multiple frequencies in (i) (step S202).

[0082] (iii) The motor drive current frequency information acquisition unit 25 acquires motor drive current frequency information (step S203).

[0083] (iv) The control unit 9 identifies the frequency that affects the measurement of AC impedance from the motor drive current frequency information acquired in (iii) (step S204).

[0084] (v) The control unit 9 determines a measurement frequency of AC impedance that is different from the frequency identified in (iv) among the frequencies measured in (ii) (step S205).

[0085] (vi) The impedance calculation unit 23a selects the AC impedance at the measurement frequency determined by (v) from among the multiple frequencies (step S206).

[0086] (vii) The internal temperature estimation unit 23b estimates the internal temperature of each of the multiple batteries 5 using the AC impedance selected in (vi) and the correlation in (i) (step S207).

[0087] Thus, after measuring the AC impedance for each of the multiple frequencies for which the correlation has been stored, the internal temperature may be estimated using the AC impedance at the measured frequency and the correlation at the measured frequency among the measured AC impedances of the multiple frequencies.

[0088] [Third Example] Next, the third example will be explained using Figure 9.

[0089] Figure 9 is a flowchart showing a third example of the operation of the battery monitoring device 1 according to the embodiment.

[0090] (i) For each of the multiple frequencies, the correlation between the AC impedance and the internal temperature of the battery 5 is recorded in a database (step S301). For example, the multiple frequencies are all the frequencies at which the AC impedance is measured.

[0091] (ii) The motor drive current frequency information acquisition unit 25 acquires motor drive current frequency information (step S302).

[0092] (iii) The control unit 9 identifies the frequency that affects the measurement of AC impedance from the motor drive current frequency information acquired in (ii) (step S303).

[0093] (iv) The control unit 9 determines a measurement frequency for an AC impedance that is different from the frequency identified in (iii) (step S304).

[0094] (v) The impedance calculation unit 23a measures the AC impedance multiple times at the measurement frequency determined in (iv) (step S305).

[0095] (vi) The control unit 9 calculates the variation (deviation) of the AC impedance measured multiple times (step S306).

[0096] (vii) The control unit 9 determines whether the variation exceeds a predetermined variation threshold (step S307). For example, the control unit 9 measures the AC impedance multiple times in succession and calculates the deviation when performing the averaging process.

[0097] If the variation in the AC impedance measured multiple times exceeds a predetermined variation threshold (Yes in step S307), the control unit 9 determines a new measurement frequency that is different from the current measurement frequency among the multiple frequencies, and (viiii) the impedance calculation unit 23a measures the AC impedance multiple times at a different frequency among the multiple frequencies in (i) (i.e., the new measurement frequency) (step S308). Then, the process from step S306 to step S308 is repeated until the variation in the AC impedance measured multiple times no longer exceeds the predetermined variation threshold.

[0098] If the variation in the AC impedance measured multiple times does not exceed a predetermined variation threshold (No in step S307), (ix) the internal temperature estimation unit 23b uses the AC impedance measured this time to estimate the internal temperature of the battery 5 from the correlation in (i) (step S309).

[0099] Noise may also be generated at frequencies different from the frequency of the noise current caused by the drive current of the motor 28, and the AC impedance measured multiple times at measurement frequencies different from the frequency of the noise current may vary. In such cases, switching the measurement frequency to yet another frequency can suppress errors in the AC impedance measurement results, and consequently, suppress errors in the estimation of the internal temperature.

[0100] [Fourth Example] Next, the fourth example will be explained using Figures 10 and 11.

[0101] Figure 10 is a flowchart showing a fourth example of the operation of the battery monitoring device 1 according to the embodiment.

[0102] (i) For each of the multiple frequencies, the correlation between the AC impedance and the internal temperature of the battery 5 is recorded in a database (step S401). For example, the multiple frequencies are all the frequencies for which the AC impedance is measured.

[0103] (ii) The motor drive current frequency information acquisition unit 25 acquires motor drive current frequency information (step S402).

[0104] (iii) The control unit 9 identifies the frequency that affects the measurement of AC impedance from the motor drive current frequency information acquired in (ii) (step S403).

[0105] (iv) The control unit 9 determines a measurement frequency for an AC impedance that is different from the frequency identified in (iii) (step S404).

[0106] (v) The impedance calculation unit 23a measures the AC impedance multiple times for each of the multiple frequencies in (i) (step S405).

[0107] (vi) The control unit 9 calculates the variation in AC impedance measured in (v) for each of the multiple frequencies (step S406), and determines whether the variation in AC impedance measured multiple times at the measurement frequency determined in (iv) among the multiple frequencies exceeds a predetermined variation threshold.

[0108] (vii) If the variation at the measurement frequency determined in (iv) exceeds a predetermined variation threshold, the control unit 9 determines the frequency with the smallest variation in the AC impedance measured multiple times among the multiple frequencies as the new measurement frequency (step S407).

[0109] (viiii) The internal temperature estimation unit 23b uses the AC impedance of the measurement frequency determined in (vii) to estimate the internal temperature of the battery 5 from the correlation in (i) (step S408).

[0110] Figure 11 is a diagram illustrating a fourth example of the operation of the battery monitoring device 1 according to the embodiment. As shown in Figure 11, if the deviation of the AC impedance measured multiple times at frequency 1 is large, frequency 2, which has the smallest deviation, is adopted.

[0111] Noise may also occur at frequencies different from the frequency of the noise current caused by the drive current of the motor 28, and the AC impedance measured multiple times at measurement frequencies different from the noise current frequency may vary. Therefore, the AC impedance is measured multiple times in advance for each of the multiple frequencies for which correlations are stored. Then, if the AC impedance measured multiple times at a measurement frequency varies, the measurement frequency is switched to the frequency with the least variation in AC impedance, thereby suppressing errors in the AC impedance measurement results and, consequently, suppressing errors in the estimation of the internal temperature.

[0112] [Fifth Example] Next, the fifth example will be explained using Figure 12.

[0113] Figure 12 is a flowchart showing a fifth example of the operation of the battery monitoring device 1 according to the embodiment.

[0114] (i) For each of the multiple frequencies, the correlation between the AC impedance and the internal temperature of the battery 5 is recorded in a database (step S501). For example, the multiple frequencies are all the frequencies at which the AC impedance is measured.

[0115] (ii) The motor drive current frequency information acquisition unit 25 acquires motor drive current frequency information (step S502).

[0116] (iii) The control unit 9 identifies the frequency that affects the measurement of AC impedance from the motor drive current frequency information acquired in (ii) (step S503).

[0117] (iv) The control unit 9 determines a measurement frequency for an AC impedance that is different from the frequency identified in (iii) (step S504).

[0118] (v) The voltage measuring unit 13 selects the measurement frequency determined in (iv) (step S505).

[0119] (vi) The voltage measurement unit 13 measures the voltage without supplying AC current at the selected frequency (step S506). Specifically, the voltage measurement unit 13 measures the voltage of each of the multiple batteries 5 at the measurement frequency while no AC current is supplied to the battery pack 6.

[0120] (vii) The AC superposition unit 11 determines whether the voltage (i.e., the amount of noise) measured in (vi) is below a threshold (step S507). If a voltage of a certain magnitude is measured when no AC current is supplied to the battery pack 6, it is considered that noise is being generated at the measurement frequency.

[0121] If the voltage measured in (vi) is below a threshold (Yes in step S507), the AC superposition unit 11 supplies an AC current at the measurement frequency to the battery pack 6, and (viiii) the impedance calculation unit 23a measures the AC impedance at the selected frequency (step S508).

[0122] If the voltage measured in (vi) is greater than the threshold (No in step S507), the voltage measuring unit 13 (ix) selects a different frequency from the multiple frequencies in (i) (step S509). Then, steps S506, S507, and S509 are repeated until the measured voltage is less than or equal to the threshold.

[0123] In some cases, noise different from the noise current caused by the drive current of the motor 28 may be generated. Therefore, by determining whether the voltage of each of the multiple batteries 5 at the measurement frequency is below a threshold when no AC current is supplied to the battery pack 6, the magnitude of the noise's influence at the measurement frequency can be confirmed in advance. After confirming that the noise's influence at the measurement frequency is small, supplying AC current at the measurement frequency to the battery pack 6 and measuring the AC impedance can suppress errors in the AC impedance measurement results, and consequently, suppress errors in the estimation of the internal temperature.

[0124] [Sixth Example] Next, the sixth example will be explained using Figure 13.

[0125] Figure 13 is a flowchart showing a sixth example of the operation of the battery monitoring device 1 according to the embodiment.

[0126] (i) For each of the multiple frequencies, the correlation between the AC impedance and the internal temperature of the battery 5 is recorded in a database (step S601). For example, the multiple frequencies are all the frequencies at which the AC impedance is measured.

[0127] (ii) The motor drive current frequency information acquisition unit 25 acquires motor drive current frequency information (step S602).

[0128] (iii) The control unit 9 identifies the frequency that affects the measurement of AC impedance from the motor drive current frequency information acquired in (ii) (step S603).

[0129] (iv) The control unit 9 determines a measurement frequency for an AC impedance that is different from the frequency identified in (iii) (step S604).

[0130] (v) The impedance calculation unit 23a measures the AC impedance multiple times at the measurement frequency determined in (iv) (step S605).

[0131] (vi) The impedance calculation unit 23a calculates the standard deviation of the AC impedance measured multiple times in (v) (step S606).

[0132] (vii) The impedance calculation unit 23a determines the variability threshold from the standard deviation calculated in (vi) (step S607).

[0133] (viiii) The impedance calculation unit 23a calculates the average value of the AC impedance that does not exceed the variation threshold determined in (vii) (step S608).

[0134] (ix) The internal temperature estimation unit 23b uses the average value of the AC impedance calculated in (viiii) and estimates the internal temperature of the battery 5 from the correlation in (i) (step S609).

[0135] Figure 14 is a diagram illustrating a sixth example of the operation of the battery monitoring device 1 according to the embodiment.

[0136] As shown in Figure 14, the AC impedance is measured multiple times consecutively at the measurement frequency, and the deviation is calculated during the averaging process. Measurement values ​​with a deviation greater than a certain level are excluded, and averaging is performed only on measurements within that deviation level, thus avoiding the effects of noise.

[0137] Furthermore, if the difference between the AC impedance measured this time and the AC impedance measured last time at the measurement frequency exceeds a certain level, the previous value may be used instead of the current value. Also, if the current value deviates significantly from the trend of multiple previous measurement values, the previous value may be used instead of the current value.

[0138] (Other Embodiments) Embodiments have been described above as examples of the technology relating to this disclosure. However, the technology relating to this disclosure is not limited thereto and can be applied to embodiments that are modified, replaced, added to, or omitted as appropriate. For example, the following modified examples are also included in one embodiment of this disclosure.

[0139] For example, the battery monitoring device 1 does not necessarily have to include a motor drive current frequency information acquisition unit 25.

[0140] A modified example of the third example described above will be explained in which the battery monitoring device 1 does not include a motor drive current frequency information acquisition unit 25.

[0141] The impedance calculation unit 23a measures the AC impedance multiple times at any measurement frequency among a plurality of frequencies for which a correlation exists. If the variation in the AC impedance measured multiple times exceeds a predetermined variation threshold, the control unit 9 may determine a new measurement frequency that is different from the current measurement frequency among the plurality of frequencies.

[0142] If the frequency or harmonic frequency of noise currents such as ripple in the drive current of the motor 28 flowing through the battery pack 6 is close to the frequency at which the AC impedance is measured, the variation in the AC impedance when repeatedly measured will increase due to interference from the noise current. Therefore, if the variation exceeds a predetermined variation threshold, the frequency is switched to a different frequency and the AC impedance is measured multiple times. If the variation is small, an AC impedance with less error at that frequency can be obtained, and consequently, the estimation error of the internal temperature can be suppressed. In this way, highly accurate temperature estimation can be performed without using frequency information of noise currents such as ripple in the drive current of the motor 28.

[0143] Next, a modified example of the fourth example described above will be explained in which the battery monitoring device 1 does not include a motor drive current frequency information acquisition unit 25.

[0144] The impedance calculation unit 23a measures the AC impedance multiple times for each of the multiple frequencies for which a correlation exists, and the control unit 9 calculates the variation in the measured AC impedance for each of the multiple frequencies and determines the frequency with the smallest variation in the AC impedance measured multiple times among the multiple frequencies as the measurement frequency.

[0145] If the frequency or harmonic frequency of noise currents such as ripple in the drive current of the motor 28 flowing through the battery pack 6 is close to the frequency at which the AC impedance is measured, the variation in AC impedance when repeatedly measured will increase due to interference from the noise current. Therefore, the AC impedance is measured multiple times at each of several frequencies in advance, and the AC impedance at the frequency with the least variation in the measured values ​​is selected. This makes it possible to estimate the temperature with a small error without using frequency information of noise currents such as ripple in the drive current of the motor 28. Since temperature changes are continuous, it is also possible to select a value that is continuous with past temperatures from among the two temperature estimations.

[0146] Next, a modified example of the fifth example described above will be explained in which the battery monitoring device 1 does not include a motor drive current frequency information acquisition unit 25.

[0147] The voltage measurement unit 13 measures the voltage of each of the multiple batteries 5 at any measurement frequency among multiple correlated frequencies, while no AC current is supplied to the battery pack 6. The AC superposition unit 11 supplies AC current at the measurement frequency to the battery pack 6 if the measured voltage is below a threshold.

[0148] If the frequency or harmonic frequency of noise currents such as ripple in the drive current of the motor 28 flowing through the battery pack 6 is close to the frequency at which the AC impedance is measured, the error in the measurement result will be large. Therefore, by measuring the complex voltage with no AC current flowing through the battery pack 6 before measuring the AC impedance, the degree of influence of noise currents such as ripple in the drive current of the motor 28 can be determined by the magnitude of the complex voltage. Then, by starting the measurement of the AC impedance after confirming that the influence of noise currents such as ripple in the drive current of the motor 28 is small, it becomes possible to estimate the temperature with a small error without using frequency information of noise currents such as ripple in the drive current of the motor 28.

[0149] For example, in the above embodiment, an example was described in which the battery monitoring device 1 is equipped with an internal temperature estimation unit 23b, but the battery monitoring device 1 does not have to be equipped with an internal temperature estimation unit 23b. In other words, the battery monitoring device 1 does not have to have a function to estimate the internal temperature of the battery 5. In this case, a predetermined correlation between the AC impedance of the battery 5 and the internal temperature does not have to be stored in the storage unit 24.

[0150] For example, in the above embodiment, an example was described in which the battery monitoring device 1 is equipped with an internal temperature correction unit 23c, but the battery monitoring device 1 does not necessarily have to be equipped with an internal temperature correction unit 23c.

[0151] For example, this disclosure can be implemented not only as a battery monitoring device 1, but also as a battery monitoring method that includes steps (processes) performed by the components constituting the battery monitoring device 1.

[0152] Figure 15 is a flowchart showing an example of a battery monitoring method according to another embodiment.

[0153] The battery monitoring method is a battery monitoring method performed by a battery monitoring device 1 that monitors a battery pack 6 composed of multiple batteries 5 connected in series, and as shown in Figure 15, includes: a motor drive current frequency information acquisition step (step S11) which acquires frequency information of the drive current of a motor 28 which is the load of the battery pack 6; a control step (step S12) which determines the measurement frequency based on the frequency information; an AC superposition step (step S13) which supplies an AC current of the measurement frequency to the battery pack 6; a voltage measurement step (step S14) which measures the voltage of each of the multiple batteries 5 through which the AC current flows; an AC superposition current measurement step (step S15) which measures the current value of the AC current; and an impedance calculation step (step S16) which measures the AC impedance of each of the multiple batteries 5 based on the voltage of each of the multiple batteries 5 and the current value of the AC current.

[0154] For example, this disclosure can be implemented as a program that causes a computer (processor) to execute the steps included in the battery monitoring method. Furthermore, this disclosure can be implemented as a non-temporary computer-readable recording medium, such as a CD-ROM, on which the program is recorded.

[0155] For example, if this disclosure is implemented in a program (software), each step is executed by the program using hardware resources such as the computer's CPU, memory, and input / output circuits. In other words, each step is executed by the CPU obtaining data from memory or input / output circuits, performing calculations, and outputting the calculation results to memory or input / output circuits.

[0156] In the above embodiment, each component included in the battery monitoring device 1 may be implemented by dedicated hardware or by executing a software program suitable for each component. Each component may also be implemented by a program execution unit such as a CPU or processor reading and executing a software program recorded on a recording medium such as a hard disk or semiconductor memory.

[0157] Some or all of the functions of the battery monitoring device 1 according to the above embodiment are typically implemented as an LSI, which is an integrated circuit. These may be individually integrated onto a single chip, or some or all of them may be integrated onto a single chip. Furthermore, the implementation is not limited to an LSI, but may also be implemented using a dedicated circuit or a general-purpose processor. An FPGA (Field Programmable Gate Array) that can be programmed after LSI manufacturing, or a reconfigurable processor that can reconfigure the connections and settings of circuit cells inside the LSI may also be used.

[0158] Furthermore, if advances in semiconductor technology or other derived technologies lead to the emergence of integrated circuit technology that can replace LSIs, then naturally, that technology may be used to integrate each component included in the battery monitoring device 1 into an integrated circuit.

[0159] Furthermore, this disclosure also includes forms obtained by applying various modifications to the embodiments that a person skilled in the art could conceive, and forms realized by arbitrarily combining the components and functions of each embodiment without departing from the spirit of this disclosure.

[0160] (Note) The above description of embodiments discloses the following technology.

[0161] (Technical 1) A battery monitoring device for monitoring a battery pack consisting of multiple batteries connected in series, comprising: a motor drive current frequency information acquisition unit that acquires frequency information of the drive current of a motor which is the load of the battery pack; a control unit that determines a measurement frequency based on the frequency information; an AC superposition unit that supplies an AC current of the measurement frequency to the battery pack; a voltage measurement unit that measures the voltage of each of the multiple batteries through which the AC current flows; an AC superposition current measurement unit that measures the current value of the AC current; and an impedance calculation unit that measures the AC impedance of each of the multiple batteries based on the voltage of each of the multiple batteries and the current value of the AC current.

[0162] When the frequency of noise currents such as ripple flowing through the battery pack due to the motor's drive current, or the harmonic frequencies, are close to the frequency of the AC current supplied to the battery pack during AC impedance measurement, the measurement error of the AC impedance becomes large. Therefore, by supplying the battery pack with an AC current at a measurement frequency different from the frequency and harmonic frequencies of the motor's drive current, which are determined based on the frequency information of the motor's drive current, it is possible to suppress errors in the AC impedance measurement results. This makes it possible to measure the AC impedance of the battery stably even when a load such as a motor is being driven in an electric vehicle. For example, by switching the measurement frequency as needed, it becomes possible to measure the AC impedance stably and continuously, regardless of the motor's rotational speed, which is proportional to the speed of the electric vehicle.

[0163] (Technology 2) The battery monitoring device according to Technology 1, wherein the motor drive current frequency information acquisition unit acquires the frequency of the inverter as frequency information from the motor drive control device that controls the drive of the motor.

[0164] According to this method, by obtaining the inverter frequency, the frequency of the noise current caused by the motor's drive current can be easily determined.

[0165] (Technology 3) The motor is equipped with a rotational position detection device, and the motor drive current frequency information acquisition unit acquires the rotational speed information of the motor as the frequency information from the rotational position detection device, the battery monitoring device according to Technology 1 or 2.

[0166] According to this method, by acquiring motor rotation speed information, the frequency of noise current caused by the motor's drive current can be easily determined.

[0167] (Technical 4) The battery monitoring device described in Technical 3, wherein the rotational position detection device is a Hall element.

[0168] Thus, the rotational speed of the motor may be detected using a Hall element.

[0169] (Technical 5) The battery monitoring device according to Technical 3, wherein the rotational position detection device is a resolver.

[0170] Thus, the motor's rotational speed may be detected using a resolver.

[0171] (Technical 6) The motor drive current frequency information acquisition unit acquires the voltage change occurring in a current detection resistor that detects the drive current of the motor as the frequency information, as described in any of Technical 1 to 5.

[0172] According to this method, by acquiring the voltage change occurring in the current sensing resistor that detects the motor's drive current, the frequency of the noise current caused by the motor's drive current can be easily determined.

[0173] (Technical 7) The battery monitoring device further comprises an internal temperature estimation unit that estimates the internal temperature of each of the plurality of batteries based on the AC impedance of each of the plurality of batteries, and a storage unit that stores a predetermined correlation between the AC impedance and the internal temperature of the batteries, wherein the internal temperature estimation unit estimates the internal temperature of each of the plurality of batteries using the correlation, the battery monitoring device according to any one of Technical 1 to 6.

[0174] According to this method, it becomes possible to estimate the internal temperature of a battery by utilizing the correlation between the battery's AC impedance and its internal temperature. When measuring the internal temperature using a thermistor, space is required to install the thermistor and a harness is needed to connect it, resulting in a larger battery monitoring device. However, by estimating the internal temperature using the above correlation, the number of thermistors and harnesses can be reduced, making it possible to miniaturize the battery monitoring device.

[0175] (Technical 8) The battery monitoring device according to Technical 7, wherein the storage unit stores the correlation for each of the multiple frequencies, and the internal temperature estimation unit estimates the internal temperature of each of the multiple batteries using the correlation at the measurement frequency among the multiple frequencies.

[0176] According to this method, a measurement frequency different from the motor drive current frequency and harmonic frequency among multiple frequencies with stored correlations can be determined, thereby suppressing errors in the AC impedance measurement results. Furthermore, by utilizing the correlation at the determined measurement frequency, estimation errors for the internal temperature can be suppressed.

[0177] (Technical 9) The battery monitoring device according to Technical 8, wherein the impedance calculation unit measures the AC impedance for each of the plurality of frequencies, selects the AC impedance at the measurement frequency among the plurality of frequencies, and the internal temperature estimation unit estimates the internal temperature of each of the plurality of batteries using the selected AC impedance and the correlation.

[0178] Thus, after measuring the AC impedance for each of the multiple frequencies for which the correlation has been stored, the internal temperature may be estimated using the AC impedance at the measured frequency and the correlation at the measured frequency among the measured AC impedances of the multiple frequencies.

[0179] (Technical 10) The battery monitoring device according to Technical 8, wherein the impedance calculation unit measures the AC impedance multiple times at the measurement frequency, and the control unit determines a frequency different from the current measurement frequency among the multiple frequencies as the new measurement frequency if the variation of the AC impedance measured multiple times exceeds a predetermined variation threshold.

[0180] Noise may also be generated at frequencies different from the noise current caused by the motor's drive current, and the AC impedance measured multiple times at different measurement frequencies may vary. In such cases, switching the measurement frequency to yet another frequency can suppress errors in the AC impedance measurement results, and consequently, suppress errors in the estimation of the internal temperature.

[0181] (Technical 11) The battery monitoring device according to Technical 8, wherein the impedance calculation unit measures the AC impedance multiple times for each of the multiple frequencies, and the control unit determines the frequency with the smallest variation in the AC impedance measured multiple times at the measurement frequency among the multiple frequencies as the new measurement frequency if the variation in the AC impedance measured multiple times at the measurement frequency among the multiple frequencies exceeds a predetermined variation threshold.

[0182] Noise may also occur at frequencies different from the noise current caused by the motor's drive current, and the AC impedance measured multiple times at different measurement frequencies may vary. Therefore, the AC impedance is measured multiple times in advance for each of several frequencies for which correlations are stored. Then, if the AC impedance measured multiple times at a given measurement frequency varies, the measurement frequency is switched to the frequency with the least variation in AC impedance. This suppresses errors in the AC impedance measurement results, and consequently, reduces errors in the estimation of the internal temperature.

[0183] (Technical 12) The battery monitoring device according to Technical 8, wherein the voltage measuring unit further measures the voltage of each of the plurality of batteries at the measurement frequency when the AC current is not supplied to the battery pack, and the AC superposition unit supplies the AC current at the measurement frequency to the battery pack when the measured voltage is below a threshold.

[0184] In some cases, noise different from the noise current caused by the motor's drive current may be generated. Therefore, by determining whether the voltage of each of the multiple batteries at the measurement frequency is below a threshold when no AC current is supplied to the battery pack, the magnitude of the noise's influence at the measurement frequency can be confirmed in advance. After confirming that the noise's influence at the measurement frequency is small, supplying AC current at the measurement frequency to the battery pack and measuring the AC impedance can suppress errors in the AC impedance measurement results, and consequently, suppress errors in the estimation of the internal temperature.

[0185] (Technical 13) The battery monitoring device according to any one of Technical 7 to 12, further comprising an internal temperature correction unit that performs calibration of the correlation relationship based on the temperature of the battery pack measured by an external temperature measuring unit.

[0186] Due to aging or individual variations in battery packs, the relationship between AC impedance and internal temperature can change, potentially increasing the estimation error of the internal temperature. In such cases, measuring the temperature of the battery pack using an external temperature measurement unit via a thermistor or similar device and calibrating the correlation can suppress the estimation error of the internal temperature. This suppresses errors caused by aging or individual variations in battery packs, enabling stable estimation of the internal temperature by measuring AC impedance over a long period. For example, the relationship between AC impedance and internal temperature can be mathematically formulated using the Arrhenius method, errors due to aging or individual variations in battery packs can be treated as offset errors, and calibration can be performed by offsetting these offset errors using measurements from the external temperature measurement unit when the battery temperature is in thermal equilibrium.

[0187] (Technical 14) A battery monitoring method performed by a battery monitoring device that monitors a battery pack consisting of a plurality of batteries connected in series, comprising: a motor drive current frequency information acquisition step of acquiring frequency information of the drive current of a motor which is the load of the battery pack; a control step of determining a measurement frequency based on the frequency information; an AC superposition step of supplying an AC current of the measurement frequency to the battery pack; a voltage measurement step of measuring the voltage of each of the plurality of batteries through which the AC current flows; an AC superposition current measurement step of measuring the current value of the AC current; and an impedance calculation step of measuring the AC impedance of each of the plurality of batteries based on the voltage of each of the plurality of batteries and the current value of the AC current.

[0188] This provides a battery monitoring method that can suppress errors in the measurement results of AC impedance.

[0189] This disclosure can be applied to devices that monitor battery packs installed in electric vehicles and the like.

[0190] 1 Battery monitoring device 2 Higher-level control unit 3 Motor drive control device 4 Relay 5 Battery 6 Battery pack 7 Measurement unit 8 Battery state estimation unit 9 Control unit 10 Communication unit 11 AC superposition unit 12 Voltage detection line 13 Voltage measurement unit 14 Current measurement unit 14a, 19 Shunt resistor 15 External temperature measurement unit 16 External thermometer 17 Load resistor 18 Transistor 20 Superposition signal generation unit 21 AC superposition current measurement unit 22 Timing generation unit 23 Calculation unit 23a Impedance calculation unit 23b Internal temperature estimation unit 23c Internal temperature correction unit 24 Memory unit 25 Motor drive current frequency information acquisition unit 26 Rotation position detection device 27 Current detection resistor 28 Motor 201 Signal generation unit 202 π / 2 phase shift unit 231 Real / imaginary separation unit 232 Integration section 233 Impedance calculation section

Claims

1. A battery monitoring device for monitoring a battery pack consisting of multiple batteries connected in series, comprising: a motor drive current frequency information acquisition unit that acquires frequency information of the drive current of a motor that is the load of the battery pack; a control unit that determines a measurement frequency based on the frequency information; an AC superposition unit that supplies an AC current of the measurement frequency to the battery pack; a voltage measurement unit that measures the voltage of each of the multiple batteries through which the AC current flows; an AC superposition current measurement unit that measures the current value of the AC current; and an impedance calculation unit that measures the AC impedance of each of the multiple batteries based on the voltage of each of the multiple batteries and the current value of the AC current.

2. The battery monitoring device according to claim 1, wherein the motor drive current frequency information acquisition unit acquires the frequency of the inverter as frequency information from a motor drive control device that controls the drive of the motor.

3. The motor is equipped with a rotational position detection device, and the motor drive current frequency information acquisition unit acquires the rotational speed information of the motor as the frequency information from the rotational position detection device, the battery monitoring device according to claim 1 or 2.

4. The battery monitoring device according to claim 3, wherein the rotational position detection device is a Hall element.

5. The battery monitoring device according to claim 3, wherein the rotational position detection device is a resolver.

6. The battery monitoring device according to any one of claims 1 to 5, wherein the motor drive current frequency information acquisition unit acquires, as the frequency information, a voltage change occurring in a current detection resistor that detects the drive current of the motor.

7. The battery monitoring device further comprises: an internal temperature estimation unit that estimates the internal temperature of each of the plurality of batteries based on the AC impedance of each of the plurality of batteries; and a storage unit that stores a predetermined correlation between the AC impedance and the internal temperature of the batteries, wherein the internal temperature estimation unit estimates the internal temperature of each of the plurality of batteries using the correlation.

8. The battery monitoring device according to claim 7, wherein the storage unit stores the correlation for each of the multiple frequencies, and the internal temperature estimation unit estimates the internal temperature of each of the multiple batteries using the correlation at the measurement frequency among the multiple frequencies.

9. The battery monitoring device according to claim 8, wherein the impedance calculation unit measures the AC impedance for each of the plurality of frequencies, selects the AC impedance at the measurement frequency among the plurality of frequencies, and the internal temperature estimation unit estimates the internal temperature of each of the plurality of batteries using the selected AC impedance and the correlation.

10. The battery monitoring device according to claim 8, wherein the impedance calculation unit measures the AC impedance multiple times at the measurement frequency, and the control unit determines a frequency different from the current measurement frequency among the multiple frequencies as the new measurement frequency if the variation of the AC impedance measured multiple times exceeds a predetermined variation threshold.

11. The battery monitoring device according to claim 8, wherein the impedance calculation unit measures the AC impedance multiple times for each of the multiple frequencies, and the control unit determines the frequency with the smallest variation in the AC impedance measured multiple times at the measurement frequency among the multiple frequencies as the new measurement frequency if the variation in the AC impedance measured multiple times at the measurement frequency among the multiple frequencies exceeds a predetermined variation threshold.

12. The battery monitoring device according to claim 8, wherein the voltage measuring unit further measures the voltage of each of the plurality of batteries at the measurement frequency when the AC current is not supplied to the battery pack, and the AC superposition unit supplies the AC current at the measurement frequency to the battery pack when the measured voltage is below a threshold.

13. The battery monitoring device according to any one of claims 7 to 12, further comprising an internal temperature correction unit that performs calibration of the correlation relationship based on the temperature of the battery pack measured by an external temperature measuring unit.

14. A battery monitoring method performed by a battery monitoring device that monitors a battery pack consisting of multiple batteries connected in series, comprising: a motor drive current frequency information acquisition step of acquiring frequency information of the drive current of a motor that is the load of the battery pack; a control step of determining a measurement frequency based on the frequency information; an AC superposition step of supplying an AC current of the measurement frequency to the battery pack; a voltage measurement step of measuring the voltage of each of the multiple batteries through which the AC current flows; an AC superposition current measurement step of measuring the current value of the AC current; and an impedance calculation step of measuring the AC impedance of each of the multiple batteries based on the voltage of each of the multiple batteries and the current value of the AC current.

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