Impedance measurement device

Abstract

An impedance measurement device (50) comprises: a plurality of electrical paths (81) respectively connected to both ends of each of battery cells (42) connected in series; an AC current generation unit (51, 84) that causes an AC current to flow to the battery cells; a voltage fluctuation measurement unit (52, 86) that measures a voltage fluctuation responsive to the AC current; a connection operation unit (54) that, when the impedance of a cell to be measured is measured, creates a state in which the AC current of the AC current generation unit is made to flow to a pair of electrical paths which serve as the positive electrode side and the negative electrode side and sandwich the cell to be measured, and that connects the voltage fluctuation measurement unit to a pair of electrical paths which serve as the positive electrode side and the negative electrode side and sandwich the cell to be measured but which are constituted by a combination different from the pair of electrical paths to which the AC current of the AC current generation unit flows; and a calculation unit (54) that calculates an impedance value of the cell to be measured on the basis of the amplitude of the AC current and the voltage fluctuation.

Description

Impedance Measuring Device CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Japanese Application No. 2023-139238, filed on August 29, 2023, the contents of which are incorporated herein by reference.

[0002] The present disclosure relates to an impedance measuring device.

[0003] Conventionally, in order to monitor the state of a storage battery, the impedance of the storage battery is measured (for example, see Patent Document 1). Specifically, in a battery monitoring device, an alternating current is passed through the storage battery, and a voltage fluctuation generated as a response signal is acquired, and the impedance value of the storage battery is calculated based on the amplitude of the alternating current and the voltage fluctuation.

[0004] Japanese Patent Application Laid-Open No. 2021-12065

[0005] When measuring impedance, it is conceivable to pass an AC current through an electrical path connected to both ends of a storage battery, and measure voltage fluctuations in the electrical path through which the AC current flows using a voltage measurement unit. In this case, there is a concern that measurement errors in voltage fluctuations may occur due to the fact that the path through which the AC current flows and the path through which the voltage is measured may result in a decrease in the accuracy of the impedance measurement. That is, a voltage drop occurs in the electrical path through which the AC current flows due to wiring resistance and the AC current itself. If the voltage drop causes a decrease in the accuracy of the voltage measurement, the accuracy of the impedance measurement may also decrease.

[0006] The present disclosure has been made in view of the above-mentioned problems, and has an object to provide an impedance measuring device that can improve the accuracy of impedance measurement.

[0007] In order to solve the above problems, the present disclosure provides an impedance measurement device that is applied to a battery module having a plurality of battery cells connected in series and that measures the impedance of the battery cells, comprising: a plurality of electrical paths connected to both ends of each of the battery cells, an AC current generation unit connected to the electrical paths and flowing an AC current through the battery cells, a voltage fluctuation measurement unit connected to the electrical paths and measuring voltage fluctuations responsive to the AC current from the AC current generation unit, and a connection operation unit that, when measuring the impedance of one of the plurality of battery cells as a measurement target cell, causes the AC current from the AC current generation unit to flow through a pair of electrical paths that are on the positive and negative sides of the measurement target cell in the series connection paths of the plurality of battery cells, and connects the voltage fluctuation measurement unit to a pair of electrical paths that are on the positive and negative sides of the measurement target cell, and that are a different combination from the pair of electrical paths through which the AC current from the AC current generation unit flows. and a calculation unit that calculates the impedance value of the cell to be measured based on the amplitude of the AC current flowing from the AC current generation unit and the voltage fluctuation measured by the voltage fluctuation measurement unit in a connected state by the connection operation unit.

[0008] In the above configuration, when measuring the impedance of a target cell, an AC current from the AC current generator is passed through a pair of electrical paths on the positive and negative sides of the target cell in a series-connected path of multiple battery cells, and a voltage fluctuation measurement unit is connected to a pair of electrical paths on the positive and negative sides of the target cell, which are different from the pair of electrical paths through which the AC current from the AC current generator flows. In this case, the electrical path through which the AC current flows is different from the electrical path through which voltage fluctuations are measured. Then, in this path connection state, the impedance value of the target cell is calculated based on the amplitude of the AC current passed by the AC current generator and the voltage fluctuation measured by the voltage fluctuation measurement unit. This prevents a voltage drop caused by wiring resistance and the AC current when the AC current flows, which can reduce the accuracy of voltage fluctuation measurement. As a result, the accuracy of impedance measurement can be improved.

[0009] The above and other objects, features, and advantages of the present disclosure will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which Fig. 1 is an electrical circuit diagram of a power supply system, Fig. 2 is a block diagram of a battery monitoring unit, Fig. 3 is a circuit diagram showing a specific circuit configuration of the battery monitoring unit, Fig. 4 is a diagram explaining a specific method of impedance measurement, Fig. 5 is a flowchart showing battery monitoring processing, Fig. 6 is a diagram explaining a specific method of impedance measurement, Fig. 7 is a diagram explaining a specific method of impedance measurement of a cell with the highest potential, Fig. 8 is a diagram explaining a specific method of impedance measurement of a cell with the lowest potential, Fig. 9 is a diagram explaining a specific method of impedance measurement in a second embodiment, Fig. 10 is a flowchart showing battery monitoring processing in the second embodiment, and Fig. 11 is a flowchart showing the battery monitoring processing in the second embodiment. FIG. 1 is a diagram for explaining a specific method for measuring the impedance of a cell with the highest potential, FIG. 12 is a diagram for explaining a specific method for measuring the impedance of a cell with the lowest potential, FIG. 13 is a plan view showing a cell stacking state of a battery module in a third embodiment, FIG. 14 is a diagram for explaining a specific method for measuring impedance, FIG. 15 is a schematic diagram showing a closed circuit region when measuring the impedance of a battery cell, FIG. 16 is a diagram for explaining a specific method for measuring impedance, FIG. 17 is a schematic diagram showing a closed circuit region when measuring the impedance of a battery cell, FIG. 18 is a perspective view showing another configuration of a battery module, and FIG. 19 is a time chart showing the on / off operation of each switch.

[0010] The power supply system of this embodiment will be described below with reference to the drawings. In this embodiment, a power supply system mounted on an electrically powered vehicle such as a hybrid vehicle or an electric vehicle will be described.

[0011] 1, a power supply system 10 includes a motor 20 as a rotating electric machine, an inverter 30 as a power converter that supplies three-phase current to the motor 20, a chargeable and dischargeable battery pack 40 (secondary battery), a battery monitoring unit 50 that monitors the state of the battery pack 40, a battery control ECU 60 that controls the battery pack 40, and another ECU 70 such as a motor ECU that controls the motor 20. The battery monitoring unit 50 is, for example, a battery monitoring board (CSC: Cell Supervision Circuit). The battery control ECU 60 is, for example, a BMU (Battery Management Unit).

[0012] The motor 20 (motor generator) is an on-board main engine capable of transmitting power to drive wheels (not shown). In this embodiment, a three-phase permanent magnet synchronous motor is used as the motor 20. The inverter 30 is configured with a full-bridge circuit having the same number of upper and lower arms as the number of phases of the phase windings. The current flowing through each phase winding is adjusted by turning on and off switches (semiconductor switching elements) provided in each arm. For example, an IGBT (Insulated Gate Bipolar Transistor) can be used as the switch.

[0013] The inverter 30 is provided with an inverter control device (not shown), which controls the energization by turning on and off each switch in the inverter 30 based on various detection information from the motor 20 and requests for power running and power generation. As a result, the inverter control device supplies power from the battery pack 40 to the motor 20 via the inverter 30, powering the motor 20. Furthermore, when the motor 20 generates power using power from the drive wheels, the inverter control device converts the generated power via the inverter 30 and supplies it to the battery pack 40, charging the battery pack 40.

[0014] The battery pack 40 is electrically connected to the motor 20 via the inverter 30. The battery pack 40 has a terminal voltage of, for example, 100 V or more and is configured by connecting multiple battery modules 41 in series. Each battery module 41 is configured by connecting multiple battery cells 42 in series. For example, a lithium iron phosphate battery (LFP battery), a lithium ion battery, or a nickel-metal hydride battery can be used as the battery cells 42. Each battery cell 42 is a battery having an electrolyte (a solution consisting of an electrolyte and a solvent) and multiple electrodes.

[0015] Although not shown because it is well known, each battery cell 42 has a positive terminal and a negative terminal, and the battery module 41 is configured such that the positive terminals and negative terminals of different battery cells 42 in the order of series connection are electrically connected by conductive members such as bus bars. Note that, in each battery cell 42, the positive terminal and the negative terminal may be arranged side by side on the same side surface of the battery cell 42, or may be arranged on two different sides of the battery cell 42 (for example, a side surface on one end side and a side surface on the other end side in the cell longitudinal direction).

[0016] 1 , a positive terminal of an electrical load such as an inverter 30 is connected to a positive power supply path L1 connected to a positive power supply terminal of the battery pack 40. Similarly, a negative terminal of an electrical load such as an inverter 30 is connected to a negative power supply path L2 connected to a negative power supply terminal of the battery pack 40. Note that a relay switch SMR (system main relay switch) is provided in each of the positive power supply path L1 and the negative power supply path L2, and the relay switch SMR is configured to be able to switch between energizing and deenergizing.

[0017] A battery monitoring unit 50 is provided for each battery module 41. The battery monitoring unit 50 is a device that monitors the state of charge (SOC) and state of health (SOH) of each battery cell 42. The battery monitoring unit 50 is capable of communicating with the battery control ECU 60, and measures and outputs the complex impedance (impedance) of each battery cell 42.

[0018] The other ECU 70 requests the inverter control device to perform power running and generate electricity based on various information, such as accelerator and brake operation information, vehicle speed, and the state of the battery pack 40. The other ECU 70 also receives input of measurement results of the state of each battery cell 42 from the battery control ECU 60.

[0019] Next, the battery monitoring unit 50 will be described in detail. As shown in Fig. 2, the battery monitoring unit 50 is configured to be able to measure the battery state of each battery cell 42. The battery monitoring unit 50 includes an AC current generating unit 51 connected to the battery cell 42 via an electrical path L11, and a voltage fluctuation measuring unit 52 connected to the battery cell 42 via an electrical path L12. The battery monitoring unit 50 also includes a modulation signal generator 53 connected to the AC current generating unit 51, an arithmetic processing unit 54 connected to the voltage fluctuation measuring unit 52 and the modulation signal generator 53, and a communication unit 55 connected to the arithmetic processing unit 54.

[0020] The AC current generation unit 51 outputs an AC current using the battery cell 42, which is the measurement target, as a power source. Specifically, the AC current generation unit 51 outputs an AC current from the battery cell 42 based on an instruction signal input from the modulation signal generator 53. When the AC current flows from the battery cell 42, a response signal (voltage fluctuation) reflecting information about the complex impedance is generated in the terminal voltage of the battery cell 42. The voltage fluctuation measurement unit 52 measures the response signal (voltage fluctuation) reflecting information about the complex impedance of the battery cell 42 between the terminals of the battery cell 42.

[0021] The voltage fluctuation can be calculated, for example, by subtracting the terminal-to-terminal voltage of the battery cell 42 under measurement measured during the input of AC current from the terminal-to-terminal voltage of the battery cell 42 under measurement measured before the input of AC current.

[0022] The modulation signal generator 53 includes an oscillator that generates an AC signal of an arbitrary waveform, and causes the oscillator to generate the AC signal in accordance with an instruction from the arithmetic processing unit 54.

[0023] In this embodiment, the AC signal is a sine wave signal, but the AC signal may be any signal, such as a square wave or a triangular wave. A DC bias is applied to the AC signal to prevent the AC current flowing from the battery cell 42 from becoming a negative current (a reverse current to the battery cell 42).

[0024] The modulation signal generator 53 then converts the AC signal into a digital signal to generate an instruction signal, and instructs (outputs) the AC current generating unit 51 to generate an AC current based on the instruction signal.

[0025] The calculation processing unit 54 includes a microcomputer including a CPU (calculation device) and a storage device (various memories), and realizes various functions by executing programs stored in the storage device. The various functions may be realized by electronic circuits, which are hardware, or may be realized by both hardware and software.

[0026] The arithmetic processing unit 54 has a function of calculating the complex impedance of the battery cell 42. Here, an overview of the method for calculating the complex impedance will be described. The arithmetic processing unit 54 instructs the modulation signal generator 53 on the measurement frequency of the complex impedance. Based on the instruction from the arithmetic processing unit 54, the modulation signal generator 53 generates an AC current from the battery cell 42 via the AC current generation unit 51. The voltage fluctuation measurement unit 52 measures the voltage between the terminals of the battery cell 42, measures a response signal (voltage fluctuation) responding to the AC current, and outputs the measured response signal to the arithmetic processing unit 54.

[0027] The calculation processing unit 54 calculates information about the complex impedance of the battery cell 42 based on the response signal. The calculation processing unit 54 repeats this series of processes until the complex impedance for a plurality of predetermined measurement frequencies within the measurement range is calculated. The calculation processing unit 54 also notifies the battery control ECU 60 of the calculation results. The battery control ECU 60 creates, for example, a complex impedance plane plot (Cole-Cole plot) based on the calculation results, and determines the characteristics of the electrodes, electrolyte, etc. The battery control ECU 60 also determines the state of charge (SOC) and state of health (SOH).

[0028] It is not necessary to create the entire Cole-Cole plot, and attention may be focused on a portion of it. For example, while driving, the complex impedance at a specific frequency may be measured at regular time intervals, and changes in the SOC, SOH, battery temperature, etc. during driving may be determined based on the time change in the complex impedance at the specific frequency. Alternatively, the complex impedance at a specific frequency may be measured at time intervals such as once a day, once a week, or once a year, and changes in the SOH, etc. may be determined based on the time change in the complex impedance at the specific frequency. Furthermore, the complex impedance plane plot is not limited to a Cole-Cole plot, and a Bode plot, etc., may also be used.

[0029] Fig. 3 is a circuit diagram showing a specific circuit configuration of the battery monitoring unit 50. Fig. 3 shows three battery cells 42 connected in series, and an electrical path 81 is connected to both ends of each battery cell 42. The electrical path 81 is made of electrical wiring. Each battery cell 42 has an impedance component Z, and each electrical path 81 has a wiring resistance component.

[0030] The battery monitoring unit 50 has connection paths 82 that connect electrical paths 81 extending from both ends of each battery cell 42 to each battery cell 42. A current sensor 83 and a switch 84 are provided on the connection paths 82 for each battery cell 42. The switch 84 is a semiconductor switching element such as a MOSFET. The switch 84 constitutes an equalization circuit that equalizes the charge levels of each battery cell 42. Turning on the switch 84 causes each battery cell 42 to discharge, thereby eliminating variations in the charge levels of each battery cell 42. It is preferable that at least one of the paths 81, 82 is provided with a resistor. This resistor serves to adjust the current during impedance measurement or during equalization.

[0031] The current sensor 83 may be disposed in the electrical path 81. In other words, the current sensor 83 may be disposed anywhere on the closed circuit formed by the battery cell 42, paths 81 and 82, and switch 84, excluding paths near the battery through which inverter current and the like flow. The current sensor 83 may be configured, for example, with a resistor (e.g., a shunt resistor) and a voltmeter. Although not shown, the shunt resistor may be disposed outside the battery monitoring unit 50, for example, in the electrical path 81, and the voltage across the shunt resistor may be measured by the battery monitoring unit 50. A resistor that serves to measure impedance and adjust current during equalization may also serve as the shunt resistor of the current sensor 83.

[0032] The switch 84 constitutes the AC current generating unit 51 shown in FIG. 2, and by turning the switch 84 on and off at a predetermined cycle, a predetermined AC signal (AC current) is output using the battery cell 42 as a power source.

[0033] A voltage measurement circuit 86 is connected to each electrical path 81 via a switch 85. The voltage measurement circuit 86 has a positive electrode path 86a, a negative electrode path 86b, and a voltage sensor 86c connected to each of the paths 86a and 86b. Each electrical path 81 can be selectively connected to the positive electrode path 86a and the negative electrode path 86b of the voltage measurement circuit 86 by the respective switches 85. That is, each switch 85 can be switched between a state in which the electrical path 81 is disconnected from the voltage measurement circuit 86 (the state shown in the figure), a state in which the electrical path 81 is connected to the positive electrode path 86a of the voltage measurement circuit 86, and a state in which the electrical path 81 is connected to the negative electrode path 86b of the voltage measurement circuit 86. By switching each switch 85, the battery cell 42 to be measured by the voltage measurement circuit 86 is selected. The voltage measurement circuit 86 measures the terminal voltage of each battery cell 42.

[0034] The voltage measurement circuit 86 constitutes the voltage fluctuation measurement unit 52 shown in FIG. 2 , and the voltage fluctuation measurement unit 52 calculates the voltage fluctuation responsive to the AC current of the AC current generation unit 51 from the inter-terminal voltage of the battery cell 42 measured by the voltage measurement circuit 86.

[0035] When measuring the impedance of a battery cell 42, one of the multiple battery cells 42 is selected as the cell to be measured, and the impedance of that cell is measured. In this case, an AC current flows through the cell to be measured by turning on and off a switch 84 on a path connecting both ends of the cell to be measured. In this state, a voltage fluctuation in response to the AC current is measured by a voltage measurement circuit 86. In addition, the voltage fluctuation measurement unit 52 shown in FIG. 2 calculates the voltage fluctuation using the voltage measured by the voltage measurement circuit 86, and the arithmetic processing unit 54 calculates the impedance value of the cell to be measured based on the amplitude of the AC current and the amount of voltage fluctuation.

[0036] During impedance measurement, an AC current is passed through the electrical path 81 connected to both ends of the cell under test, and voltage fluctuations are measured via the electrical path 81 also connected to both ends of the cell under test. In this case, there is a concern that errors in measuring the voltage fluctuations may occur due to the AC current flowing through a common path, which may result in a decrease in the accuracy of the impedance measurement. That is, a voltage drop occurs in the electrical path 81 through which the AC current flows due to the wiring resistance and the AC current itself. If the voltage drop causes a decrease in the accuracy of the voltage measurement, the accuracy of the impedance measurement will also decrease.

[0037] Therefore, during impedance measurement, the electrical path 81 through which the AC current is passed by the AC current generator 51 is different from the electrical path 81 through which voltage fluctuations are measured by the voltage fluctuation measurement circuit 52 (voltage measurement circuit 86), thereby suppressing a decrease in impedance measurement accuracy. That is, in this embodiment, the AC current from the AC current generator 51 is passed through a pair of electrical paths 81 that are on the positive and negative sides of the cell to be measured in the series-connected path of the plurality of battery cells 42, and the voltage fluctuation measurement unit 52 is connected to a pair of electrical paths 81 that are on the positive and negative sides of the cell to be measured, but that are a different pair from the pair of electrical paths 81 through which the AC current from the AC current generator 51 passes. A specific method of impedance measurement will be described below with reference to FIG. 4.

[0038] 4 shows three battery cells 42 connected in series as battery cells 42A-42C, with battery cell 42B being the cell under test for impedance measurement. In FIG. 4, the connection paths 82 and switches 84 provided for each of battery cells 42A-42C are designated as connection paths 82A-82C and switches 84A-84C, respectively. Furthermore, each electrical path 81 is designated as an electrical path 81A-81D, and the switches 85 connected to each electrical path 81A-81D are designated as switches 85A-85D. The wiring resistance of electrical path 81 is not shown. In FIG. 4, the path R1 through which AC current flows is indicated by a thick solid line, and the path R2 for voltage measurement is indicated by a thick dashed line.

[0039] When battery cell 42B is the cell to be measured, switch 84B on the path connecting both ends of battery cell 42B, among switches 84A to 84C, is turned on and off at a predetermined cycle, causing an AC current to flow through battery cell 42B. At this time, the AC current flows through path R1, which includes battery cell 42B, electrical paths 81B and 81C between both ends of battery cell 42B, and connection path 82B.

[0040] Furthermore, the voltage measurement circuit 86 measures the inter-terminal voltage of a battery cell group including the battery cell 42B and the battery cells 42A and 42C adjacent to it. Specifically, by switching the switch 85A, the positive electrode side electrical path 81A of the battery cell 42A is connected to the positive electrode side path 86a of the voltage measurement circuit 86, and by switching the switch 85D, the negative electrode side electrical path 81D of the battery cell 42C is connected to the negative electrode side path 86b of the voltage measurement circuit 86. As a result, voltage fluctuations are measured on path R2, which includes the battery cell group of the battery cells 42A to 42C, the electrical paths 81A and 81D at both ends of the battery cell group, and the voltage measurement circuit 86. Then, the impedance value of the battery cell 42B is calculated based on the voltage fluctuations measured by the voltage measurement circuit 86 and the amplitude of the AC current measured by the current sensor 83.

[0041] As described above, the AC current path and the voltage measurement path are appropriately switched by controlling the on / off of each switch 84, 85. The on / off control of each switch 84, 85 may be performed by the arithmetic processing unit 54, which corresponds to the "connection operation unit."

[0042] Although the voltage measurement circuit 86 is configured to measure the inter-terminal voltage of three battery cells 42, including the cell under measurement (battery cell 42B) and the two battery cells 42A and 42C adjacent to it, this configuration may be any configuration that measures the inter-terminal voltage of a battery cell group that includes at least the cell under measurement and the two battery cells 42 adjacent to it. In other words, the battery cell group that is the subject of voltage fluctuation measurement may include one or more battery cells 42 on both the positive and negative sides of the cell under measurement.

[0043] 5 is a flowchart showing the battery monitoring process. This process is initiated in response to a command from a host ECU, such as the battery control ECU 60, and is repeatedly executed at a predetermined interval by the calculation processing unit 54 of the battery monitoring unit 50. Here, as an example, the process of measuring impedance and the like will be described using the battery cell 42B shown in FIG. 4 as the cell to be measured.

[0044] 5, in step S11, a battery cell 42 to be measured is selected from the plurality of battery cells 42. Here, for example, the battery cell 42B in FIG. 4 is selected. Note that the measurement target cells may include not only the battery cells 42 whose impedances are to be measured, but also the battery cells 42 whose terminal voltages (e.g., open circuit voltages) are to be measured as the state of the battery cells 42.

[0045] Then, in step S12, it is determined whether or not impedance measurement is to be performed on the cell being measured. If the result in step S12 is negative, the process proceeds to step S13. In step S13, switches 85B and 85C are turned on. This causes the voltage measurement circuit 86 to measure the terminal voltage of battery cell 42B. In the following step S14, the terminal voltage of battery cell 42B measured by the voltage measurement circuit 86 is acquired. Then, in step S20, the terminal voltage of battery cell 42B is transmitted to a higher-level ECU.

[0046] If the result of step S12 is affirmative, the process proceeds to step S15. In step S15, switches 85A and 85D are turned on. This causes the voltage measurement circuit 86 to measure the terminal voltage of the battery cell group of battery cells 42A to 42C. In step S16, switch 84B is turned on and off to allow an AC current to flow through battery cell 42B. With the AC current flowing, the current sensor 83 measures the amplitude of the AC current (current amplitude). According to steps S15 and S16, after the voltage measurement circuit 86 is connected to the electrical path between both ends of the battery cell group by turning on switch 85, switch 84 is turned on and off to generate an AC current.

[0047] Then, in step S17, the inter-terminal voltage of the battery cell group measured by the voltage measurement circuit 86 is acquired, and in the following step S18, the current amplitude measured by the current sensor 83 is acquired. In step S19, the impedance value is calculated by dividing the voltage fluctuation, which is a response signal of the AC current, by the current amplitude. Note that the voltage fluctuation may be calculated as the voltage difference between the inter-terminal voltage measured before AC current is passed through the battery cell 42B and the inter-terminal voltage measured with AC current passing through it. The inter-terminal voltage acquired in step S14 may also be used as the inter-terminal voltage before AC current is passed through the battery cell 42B.

[0048] Thereafter, in step S20, the impedance value is transmitted to a higher-level ECU.

[0049] The battery monitoring unit 50 measures the impedance of all battery cells 42 in the battery module 41, but cannot perform voltage measurement in the manner shown in Fig. 4 for the battery cell 42 on the highest potential side and the battery cell 42 on the lowest potential side among the multiple battery cells 42 included in the battery module 41 (i.e., the battery cell 42 at the end of the series connection of the battery module 41). Below, a method for measuring the impedance of the battery cell 42 at the end of the series connection will be described using Figs. 6 to 8.

[0050] In FIG. 6 , of the plurality of battery cells 42 connected in series in a battery module 41, the first battery cell 42 on the highest potential side is designated as battery cell 42_1, and the second battery cell 42 is designated as battery cell 42_2. Battery cell 42_1 is the battery cell on the highest potential side in the battery module 41, i.e., the highest potential cell. In FIG. 6 , two branched electrical paths X1 and X2 are connected to the positive electrode side of battery cell 42_1 as an electrical path 81. A current sensor 83 and a switch 84 are connected in series to electrical path X1, and a positive electrode path 86a of a voltage measurement circuit 86 is connected to electrical path X2 via a switch 85. Note that electrical path X1 corresponds to the "first positive electrode side path," and electrical path X2 corresponds to the "second positive electrode side path."

[0051] 7 is a diagram showing a state in which impedance measurement is performed on battery cell 42_1 as the cell to be measured. In Fig. 7, a path R11 through which AC current flows is shown by a thick solid line, and a path R12 for voltage measurement is shown by a thick dashed line.

[0052] When the battery cell 42_1 on the highest potential side is the cell to be measured, an AC current flows through the battery cell 42_1 by turning on and off the switch 84 on the path connecting both ends of the battery cell 42_1 at a predetermined cycle. At this time, the AC current flows through a path R11 that includes the battery cell 42_1 and the electrical paths X1 and 81 on both ends of the battery cell 42_1.

[0053] Furthermore, the voltage measurement circuit 86 measures the terminal voltage of a battery cell group including the battery cell 42_1 and the adjacent battery cell 42_2 as the measurement target. Specifically, by switching the switch 85 on the positive side of the battery cell 42_1 and the switch 85 on the negative side of the battery cell 42_2, voltage fluctuations are measured on a path R12 that includes the battery cell group of the battery cells 42_1 and 42_2, the electrical paths X2 and X1 between both ends of the battery cell group, and the voltage measurement circuit 86. Then, based on the voltage fluctuations measured by the voltage measurement circuit 86 and the amplitude of the AC current measured by the current sensor 83, the impedance value of the battery cell 42_1 is calculated.

[0054] When measuring the impedance of the highest potential cell, the voltage measurement circuit 86 is configured to measure the voltage fluctuation of the battery cell group using the electrical path X2 on the positive electrode side of the battery cell 42_1 (highest potential cell) and the electrical path 81 on the negative electrode side of the battery cell group that includes at least the battery cell 42_1 and the adjacent battery cell 42_2 on the lower potential side. In other words, the battery cell group that is the subject of voltage fluctuation measurement is only required to include one or more battery cells 42 on the negative electrode side of the battery cell 42_1 (highest potential cell).

[0055] In FIG. 8 , among a plurality (n) of serially connected battery cells 42 in a battery module 41, the nth battery cell 42 on the lowest potential side is designated as battery cell 42_n, and the n-1th battery cell 42 is designated as battery cell 42_n-1. Impedance measurement is performed on battery cell 42_n as the cell to be measured. Battery cell 42_n is the battery cell on the lowest potential side in the battery module 41, i.e., the lowest potential cell. In FIG. 8 , two branched electrical paths Y1 and Y2 are connected to the negative electrode side of battery cell 42_n as an electrical path 81. A current sensor 83 and a switch 84 are connected in series to electrical path Y1, and a negative electrode path 86b of a voltage measurement circuit 86 is connected to electrical path Y2 via a switch 85. Electrical path Y1 corresponds to the "first negative electrode path," and electrical path Y2 corresponds to the "second negative electrode path." In FIG. 8, a path R21 through which an AC current flows is indicated by a thick solid line, and a path R22 for measuring a voltage is indicated by a thick dashed line.

[0056] When the battery cell 42_n with the lowest potential is the cell to be measured, an AC current flows through the battery cell 42_n by periodically turning on and off the switch 84 on the path connecting both ends of the battery cell 42_n. At this time, the AC current flows through a path R21 that includes the battery cell 42_n and the electrical paths Y1, 81 on both ends of the battery cell 42_n.

[0057] Furthermore, the voltage measurement circuit 86 measures the terminal voltage of a battery cell group including the battery cell 42_n and the adjacent battery cell 42_n-1 as the measurement target. Specifically, by switching between the switch 85 on the negative side of the battery cell 42_n and the switch 85 on the positive side of the battery cell 42_n-1, voltage fluctuations are measured on a path R22 that includes the battery cell group of the battery cells 42_n and 42_n-1, the electrical paths Y2 and Y1 between both ends of the battery cell group, and the voltage measurement circuit 86. Then, based on the voltage fluctuations measured by the voltage measurement circuit 86 and the amplitude of the AC current measured by the current sensor 83, the impedance value of the battery cell 42_n is calculated.

[0058] When measuring the impedance of the lowest potential cell, the voltage measurement circuit 86 should measure the voltage fluctuation of the battery cell group using the electrical path Y2 on the negative electrode side of the battery cell 42_n (lowest potential cell) and the electrical path 81 on the positive electrode side of the battery cell group that includes at least the battery cell 42_n and the adjacent battery cell 42_n-1 on the lower potential side. In other words, the battery cell group that is the subject of voltage fluctuation measurement should include one or more battery cells 42 on the positive electrode side of the battery cell 42_n (lowest potential cell).

[0059] 6 to 8 , the electrical path 81 on the positive electrode side of the highest potential cell (battery cell 42_1) and the electrical path 81 on the negative electrode side of the lowest potential cell (battery cell 42_n) may each not be branched into two paths. In this case, when measuring the impedance of the highest potential cell or the lowest potential cell as the measurement target cell, the electrical path through which the AC current flows and the electrical path through which the voltage fluctuation is measured are the same on either the positive or negative side of the measurement target cell, but if the electrical path through which the AC current flows and the electrical path through which the voltage fluctuation is measured are different on the other side, the measurement error will be relatively small.

[0060] According to the present embodiment described above in detail, the following excellent effects can be obtained.

[0061] When measuring the impedance of one of the plurality of battery cells 42 as a target cell, an AC current from the AC current generator 51 is caused to flow through the electrical path 81 at both ends of the target cell, and a voltage measurement circuit 86 is connected to the electrical path 81 at both ends of a battery cell group including at least the target cell and the battery cells 42 adjacent to it. In this case, the electrical path 81 through which the AC current flows is different from the electrical path 81 through which voltage fluctuations are measured. Then, in this path connection state, the impedance value of the target cell is calculated based on the amplitude of the AC current flowed by the AC current generator 51 and the voltage fluctuation measured by the voltage measurement circuit 86. This prevents a voltage drop caused by wiring resistance and the AC current when the AC current flows, which can reduce the accuracy of voltage fluctuation measurement. As a result, the accuracy of impedance measurement can be improved.

[0062] When measuring the impedance of a cell to be measured, first switch 85 (second switch) is turned on to connect voltage measurement circuit 86 to the electrical path between both ends of the battery cell group including the cell to be measured, and then switch 84 (first switch) on and off on the path connecting both ends of the cell to be measured is turned on and off to allow AC current to flow. In this case, power consumption can be reduced compared to the opposite case where AC current begins to flow by turning switch 84 on and off, and then switch 85 is turned on to enable voltage measurement by voltage measurement circuit 86.

[0063] When measuring the impedance of the highest potential cell (battery cell 42_1), the AC current from the AC current generator 51 is passed across the highest potential cell using electrical path X1, one of the electrical paths X1 and X2 connected to the positive electrode side of the highest potential cell, and an electrical path 81 on the negative electrode side of the highest potential cell. Furthermore, the voltage measurement circuit 86 measures voltage across the battery cell group using electrical path X2, one of the electrical paths X1 and X2 on the positive electrode side of the highest potential cell, and an electrical path 81 on the negative electrode side of the battery cell group that includes at least the highest potential cell and the adjacent battery cell 42 on the lower potential side. This allows the electrical path through which the AC current flows to differ from the electrical path through which voltage fluctuations are measured when measuring the impedance of the highest potential cell, improving the accuracy of the impedance measurement.

[0064] When measuring the impedance of the lowest potential cell (battery cell 42_n), the AC current from the AC current generator 51 is passed across the lowest potential cell using the electrical path Y1 of the electrical paths Y1, Y2 connected to the negative electrode side of the lowest potential cell and the electrical path 81 on the positive electrode side of the lowest potential cell. Furthermore, the voltage measurement circuit 86 measures voltage across the battery cell group using the electrical path Y2 of the electrical paths Y1, Y2 on the negative electrode side of the lowest potential cell and the electrical path 81 on the positive electrode side of the battery cell group that includes at least the lowest potential cell and the adjacent battery cell 42 on the high potential side. This allows the electrical path through which the AC current flows to differ from the electrical path through which voltage fluctuations are measured when measuring the impedance of the lowest potential cell, improving the accuracy of the impedance measurement.

[0065] In each battery module 41, the electrical paths 81 connected to both ends of each battery cell 42 that branch into two paths are limited to only the electrical path 81 on the positive electrode side of the highest potential cell and the electrical path 81 on the negative electrode side of the lowest potential cell. Therefore, the increase in cost due to the increase in the number of electrical paths 81 is kept to a minimum.

[0066] Second Embodiment In this embodiment, the impedance measurement method described with reference to FIG. 4 is modified, and the impedance measurement method in this embodiment will be described with reference to FIG.

[0067] 9, similarly to Fig. 4, three series-connected battery cells 42 are designated as battery cells 42A to 42C, and impedance measurement is performed on battery cell 42B as the cell to be measured. In Fig. 9, a path R31 through which AC current flows is indicated by a thick solid line, and a path R32 for voltage measurement is indicated by a thick dashed line.

[0068] When battery cell 42B is the cell to be measured, all of switches 84A to 84C are turned on and off simultaneously at a predetermined cycle, causing an AC current to flow through a battery cell group including battery cell 42B and its adjacent battery cells 42A and 42C. At this time, an AC current flows through path R31, which includes the battery cell group of battery cells 42A to 42C, electrical paths 81A and 81D at both ends of the battery cell group, and connection paths 82A to 82C.

[0069] The voltage measurement circuit 86 measures the terminal voltage of the battery cell 42B as the measurement target. Specifically, by switching the switch 85B, the positive electrode side electrical path 81B of the battery cell 42B is connected to the positive electrode side path 86a of the voltage measurement circuit 86, and by switching the switch 85C, the negative electrode side electrical path 81B of the battery cell 42B is connected to the negative electrode side path 86b of the voltage measurement circuit 86. As a result, voltage fluctuations are measured on a path R32 that includes the battery cell 42B, the electrical paths 81B and 81C at both ends of the battery cell 42B, and the voltage measurement circuit 86. Then, based on the voltage fluctuations measured by the voltage measurement circuit 86 and the amplitude of the AC current measured by the current sensor 83, the impedance value of the battery cell 42B is calculated.

[0070] Although the configuration is such that AC current flows through three battery cells 42 including the measurement target cell (battery cell 42B) and the battery cells 42A and 42C adjacent to it by turning on and off switches 84A to 84C, this configuration may be any configuration that flows AC current through electrical path 81 at both ends of a battery cell group that includes at least the measurement target cell and the battery cells 42 adjacent to it. In other words, the battery cell group through which AC current flows may be any group that includes one or more battery cells 42 on both the positive and negative sides of the measurement target cell.

[0071] 10 is a flowchart showing the battery monitoring process in this embodiment. This process is started in response to a command from a host ECU such as the battery control ECU 60, and is repeatedly executed at a predetermined interval by the calculation processing unit 54 of the battery monitoring unit 50. Here, as an example, the process of measuring impedance and the like will be described using the battery cell 42B shown in FIG. 9 as the cell to be measured.

[0072] The process in Fig. 10 is a partial modification of the process in Fig. 5, and the same steps as those in Fig. 5 are given the same step numbers. Here, the differences from Fig. 5 will be described.

[0073] 10, if a positive result is obtained in step S12, the process proceeds to step S31. In step S31, switches 85B and 85C are turned on. This causes the voltage measurement circuit 86 to measure the terminal voltage of battery cell 42B. In step S32, switches 84A to 84C are simultaneously turned on and off to cause an AC current to flow through the battery cell group of battery cells 42A to 42C. With the AC current flowing, the current sensor 83 measures the amplitude of the AC current (current amplitude). According to steps S31 and S32, after the voltage measurement circuit 86 is connected to the electrical path across battery cell 42B by turning on switch 85, switch 84 is turned on and off to generate an AC current.

[0074] Then, in step S33, the inter-terminal voltage of the battery cell 42B measured by the voltage measurement circuit 86 is obtained, and in the following step S34, the current amplitude measured by the current sensor 83 is obtained. In step S19, the impedance value is calculated by dividing the voltage fluctuation, which is the AC response signal, by the current amplitude. Then, in step S20, the impedance value is sent to the host ECU.

[0075] Next, a method for measuring the impedance of the highest potential cell and the lowest potential cell (i.e., the battery cell 42 at the end of the series connection) of the battery module 41 will be described with reference to Figures 11 and 12. The circuit configurations in Figures 11 and 12 are the same as those in Figures 6 to 8.

[0076] 11 is a diagram showing a state in which impedance measurement is performed on the highest potential cell (battery cell 42_1) as the cell to be measured. In Fig. 11, a path R41 through which AC current flows is shown by a thick solid line, and a path R42 for voltage measurement is shown by a thick dashed line.

[0077] When the battery cell 42_1 on the highest potential side is the cell to be measured, two switches 84 on a path connecting both ends of a battery cell group including the battery cell 42_1 and its adjacent battery cell 42_2 are simultaneously turned on and off at a predetermined cycle, causing an AC current to flow through a path R41 including the battery cell group of the battery cells 42_1 and 42_2 and the electrical paths X1 and 81 on both ends of the battery cell group.

[0078] Furthermore, the voltage measurement circuit 86 measures the terminal voltage of the battery cell 42_1 as the measurement target. Specifically, by switching between the switch 85 on the positive side of the battery cell 42_1 and the switch 85 on the negative side of the battery cell 42_1, voltage fluctuations are measured on a path R42 that includes the battery cell 42_1, the electrical paths X2 and X81 between both ends of the battery cell 42_1, and the voltage measurement circuit 86. Then, based on the voltage fluctuations measured by the voltage measurement circuit 86 and the amplitude of the AC current measured by the current sensor 83, the impedance value of the battery cell 42_1 is calculated.

[0079] When measuring the impedance of the highest potential cell (battery cell 42_1), the battery cell group through which AC current flows may include one or more battery cells 42 on the negative electrode side of the highest potential cell.

[0080] 12 is a diagram showing a state in which impedance measurement is performed on the lowest potential cell (battery cell 42_n) as the cell to be measured. In FIG. 12, a path R51 through which AC current flows is shown by a thick solid line, and a path R52 for voltage measurement is shown by a thick dashed line.

[0081] When the battery cell 42_n on the lowest potential side is the cell to be measured, two switches 84 on a path connecting both ends of a battery cell group including the battery cell 42_n and its adjacent battery cell 42_n-1 are simultaneously turned on and off at a predetermined cycle, causing an AC current to flow through a path R51 including the battery cell group of the battery cells 42_n and 42_n-1 and the electrical paths Y1 and 81 on both ends of the battery cell group.

[0082] The voltage measurement circuit 86 measures the terminal voltage of the battery cell 42_n as the measurement target. Specifically, by switching between the switch 85 on the negative side of the battery cell 42_n and the switch 85 on the positive side of the battery cell 42_n, voltage fluctuations are measured on a path R52 that includes the battery cell 42_n, the electrical paths Y2 and Y81 between both ends of the battery cell 42_n, and the voltage measurement circuit 86. Then, based on the voltage fluctuations measured by the voltage measurement circuit 86 and the amplitude of the AC current measured by the current sensor 83, the impedance value of the battery cell 42_n is calculated.

[0083] When measuring the impedance of the lowest potential cell (battery cell 42_n), the battery cell group through which AC current flows may include one or more battery cells 42 on the positive electrode side of the lowest potential cell.

[0084] 11 and 12 , the electrical path 81 on the positive electrode side of the highest potential cell (battery cell 42_1) and the electrical path 81 on the negative electrode side of the lowest potential cell (battery cell 42_n) may not each be branched into two paths. In this case, when measuring the impedance of the highest potential cell or the lowest potential cell as the measurement target cell, the electrical path through which the AC current flows and the electrical path through which the voltage fluctuation is measured are the same on either the positive or negative side of the measurement target cell, but if the electrical path through which the AC current flows and the electrical path through which the voltage fluctuation is measured are different on the other side, the measurement error will be relatively small.

[0085] According to the present embodiment, the following effects can be obtained.

[0086] When measuring the impedance of one of the plurality of battery cells 42 as a measurement target cell, an AC current is passed from the AC current generator 51 through an electrical path 81 between both ends of a battery cell group including at least the measurement target cell and the battery cells 42 adjacent to it, and a voltage measurement circuit 86 is connected to the electrical path 81 between both ends of the measurement target cell. In this case, the electrical path 81 through which the AC current flows is different from the electrical path 81 through which voltage fluctuations are measured. Then, in this path connection state, the impedance value of the measurement target cell is calculated based on the amplitude of the AC current passed by the AC current generator 51 and the voltage fluctuations measured by the voltage measurement circuit 86. This prevents a voltage drop caused by wiring resistance and the AC current when the AC current flows, which can reduce the accuracy of voltage fluctuation measurement. As a result, the accuracy of impedance measurement can be improved.

[0087] When measuring the impedance of a cell to be measured, first switch 85 (second switch) is turned on to connect voltage measurement circuit 86 to the electrical path between both ends of the cell to be measured, and then switch 84 (first switch) on the path connecting both ends of the battery cell group including the cell to be measured is turned on and off to allow AC current to flow. In this case, power consumption can be reduced compared to the opposite case where AC current begins to flow by turning switch 84 on and off, and then switch 85 is turned on to enable voltage measurement by voltage measurement circuit 86.

[0088] When measuring the impedance of the highest potential cell (battery cell 42_1), the AC current from the AC current generator 51 is passed across the battery cell group using electrical path X1, one of electrical paths X1 and X2 connected to the positive electrode side of the highest potential cell, and an electrical path 81 on the negative electrode side of a battery cell group including at least the highest potential cell and the adjacent battery cell 42 on the lower potential side. Furthermore, the voltage measurement circuit 86 measures voltage across the highest potential cell using electrical path X2, one of electrical paths X1 and X2 on the positive electrode side of the highest potential cell, and the electrical path 81 on the negative electrode side. This allows the electrical path through which the AC current flows to differ from the electrical path through which voltage fluctuations are measured when measuring the impedance of the highest potential cell, improving the accuracy of the impedance measurement.

[0089] When measuring the impedance of the lowest potential cell (battery cell 42_n), the AC current from the AC current generator 51 is passed across the battery cell group using the electrical path Y1 of the electrical paths Y1, Y2 connected to the negative electrode side of the lowest potential cell and the positive electrode side electrical path 81 of the battery cell group including at least the lowest potential cell and the adjacent battery cell 42 on the high potential side. Furthermore, the voltage measurement circuit 86 measures the voltage across the lowest potential cell using the electrical path Y2 of the negative electrode side electrical paths Y1, Y2 of the lowest potential cell and the positive electrode side electrical path 81. This allows the electrical path through which the AC current flows to differ from the electrical path through which voltage fluctuations are measured when measuring the impedance of the lowest potential cell, improving the accuracy of the impedance measurement.

[0090] Third Embodiment In this embodiment, a specific configuration example regarding the connection between each battery cell 42 of a battery module 41 and an AC current generating unit 51 (switch 84) and a voltage measuring circuit 86 will be described.

[0091] FIG. 13 is a plan view showing a state in which multiple battery cells 42 are stacked in a battery module 41. Here, six battery cells 42, battery cells 42A to 42F, are shown as the multiple battery cells 42. Each battery cell 42 is a so-called blade cell having a long plate shape (a flat rectangular parallelepiped shape), and is stacked with its plate surfaces facing each other in the thickness direction. Each battery cell 42 has a positive terminal 101 at one end in the cell longitudinal direction (left-right direction in the figure) and a negative terminal 102 at the other end, and is arranged side by side in a direction perpendicular to the cell longitudinal direction. In the battery module 41, each battery cell 42 is arranged in series connection order such that the positive terminals 101 and negative terminals 102 alternate in the cell longitudinal direction. In other words, each battery cell 42 is stacked with its positive and negative sides staggered.

[0092] In the battery module 41, the positive terminal 101 of one of the adjacent battery cells 42 in the stacking direction (i.e., the battery cells 42 that are consecutive in the order of series connection) is electrically connected to the negative terminal 102 of the other battery cell 42 by a bus bar 103, which is a conductive member. This allows the battery cells 42 to be connected in series.

[0093] In this embodiment, one end of the battery module 41 in the longitudinal direction of the cells (the right end in the figure) is designated as a first battery end E1, and the other end (the left end in the figure) is designated as a second battery end E2. In this case, at the first battery end E1, the positive and negative terminals of the battery cells 42B and 42C and the positive and negative terminals of the battery cells 42D and 42E are electrically connected by bus bars 103. At the second battery end E2, the positive and negative terminals of the battery cells 42A and 42B, the positive and negative terminals of the battery cells 42C and 42D, and the positive and negative terminals of the battery cells 42E and 42F are electrically connected by bus bars 103.

[0094] At the first battery end E1 and the second battery end E2, an electrical path 81 is connected to each bus bar 103. As a result, the electrical path 81 is connected to both ends of each battery cell 42 that is connected in series. Here, the electrical paths 81 are designated as electrical paths 81A, 81B, 81C, 81D, 81E, 81F, and 81G in accordance with the order of the series connection of the battery cells 42A to 42F. Furthermore, the electrical paths 81A, 81C, 81E, and 81G on the first battery end E1 side are designated as first electrical paths W1, and the electrical paths 81B, 81D, and 81F on the second battery end E2 side are designated as second electrical paths W2.

[0095] Fig. 14 is a circuit diagram showing a specific circuit configuration of the battery monitoring unit 50 for a battery module 41 having six battery cells 42A-42F connected in series. The battery monitoring unit 50 in Fig. 14 has a similar configuration to those in Figs. 3 and 4 described above, although the number of cells is different. Electrical paths 81A-81G are provided for each of the battery cells 42A-42F, and current sensors 83 and switches 84A-84F are provided on the connection paths 82A-82F corresponding to each of the battery cells 42A-42F. A voltage measurement circuit 86 is also connected to the electrical paths 81A-81G via switches 85A-85G.

[0096] 14 shows a state in which impedance measurement is performed on battery cells 42C and 42D among battery cells 42A to 42F as the measurement target cells. In Fig. 14, a path R61 through which AC current flows is shown by a thick solid line, and a path R62 for voltage measurement is shown by a thick dashed line.

[0097] When measuring the impedance of the battery cells 42C, 42D, the switches 84C, 84D on the path connecting both ends of the battery cells 42C, 42D are simultaneously turned on and off at a predetermined cycle, causing an AC current to flow through the path R61 that includes the battery cells 42C, 42D, the electrical paths 81C, 81E between both ends of the battery cells 42C, 42D, and the connection paths 82C, 82D.

[0098] Furthermore, the voltage measurement circuit 86 measures the inter-terminal voltage of a battery cell group including the battery cells 42C and 42D and the adjacent battery cells 42B and 42E. Specifically, by switching the switch 85B, the positive electrode side electrical path 81B of the battery cell 42B is connected to the positive electrode side path 86a of the voltage measurement circuit 86, and by switching the switch 85F, the negative electrode side electrical path 81F of the battery cell 42E is connected to the negative electrode side path 86b of the voltage measurement circuit 86. As a result, voltage fluctuations are measured on a path R62 that includes the battery cell group of the battery cells 42B to 42E, the electrical paths 81B and 81F at both ends of the battery cell group, and the voltage measurement circuit 86. Then, based on the voltage fluctuations measured by the voltage measurement circuit 86 and the amplitude of the AC current measured by the current sensor 83, the impedance values ​​of the battery cells 42C and 42D are calculated.

[0099] 13 , the AC current flowing through the battery cells 42C, 42D flows through the electrical paths 81C, 81E, which are the first electrical path W1 on the first battery end E1 side. In this case, the electrical path 81C extending from the positive electrode side of the battery cell 42C and the electrical path 81E extending from the negative electrode side of the battery cell 42D are electrical paths drawn out from the same end (the first battery end E1 side) of both ends in the cell longitudinal direction of the battery module 41. Therefore, when a closed circuit (path R61) is formed by the battery cells 42C, 42D, the electrical paths 81C, 81E, and the connection paths 82C, 82D, the area enclosed by the closed circuit is smaller, and the magnetic flux generated by the AC current is reduced.

[0100] Furthermore, the inter-terminal voltage of the battery cell group consisting of the battery cells 42B to 42E is measured via the electrical paths 81B and 81F, which are the second electrical path W2 on the second battery end E2 side. In this case, the electrical path 81B extending from the positive electrode side of the battery cell 42B and the electrical path 81F extending from the negative electrode side of the battery cell 42E are electrical paths drawn out from the same end side (the second battery end E2 side) of both ends in the cell longitudinal direction of the battery module 41. Therefore, when a closed circuit (path R62) is formed by the battery cells 42B and 42E, the electrical paths 81B and 81F, and the voltage measurement circuit 86, the area enclosed by the closed circuit is reduced, and the influence of induced electromotive force is reduced.

[0101] Fig. 15 is a schematic diagram showing closed circuit regions during impedance measurement of battery cells 42C, 42D in battery module 41. In Fig. 15, the closed circuit region formed by the AC current flow path is designated as region S1, and the closed circuit region formed by the path for measuring voltage response is designated as region S2, and these regions S1, S2 are indicated by hatching.

[0102] The electrical paths 81C and 81E that form the AC current path both extend from the first battery end E1 of the battery module 41, and the area surrounded by these electrical paths 81C and 81E is area S1. In this case, if the impedance measurement target were only the battery cell 42C and the AC current were to flow through the electrical paths 81C and 81D at both ends of the battery cell 42C, the closed circuit area formed by the electrical paths 81C and 81E (the AC current path) would be large because the electrical paths 81C and 81D are located at both ends of the cell in the longitudinal direction. This raises concerns about the increase in magnetic flux generated by the AC current. In contrast, if the AC current path is formed as shown in FIG. 14, the electrical paths 81C and 81E extending from both ends of the battery cells 42C and 42D are relatively close to each other, thereby reducing the magnetic flux generated by the AC current.

[0103] Furthermore, the electrical paths 81B and 81F connected to the voltage measurement circuit 86 both extend from the second battery end E2 side of the battery module 41, and the area surrounded by these electrical paths 81B and 81F is area S2. In this case, in the closed circuit for measuring the voltage response, the area through which the magnetic flux generated by the AC current passes can be made smaller than in a configuration in which two electrical paths spaced apart from each other in the cell longitudinal direction of the battery module 41 are connected to the voltage measurement circuit 86. This improves the accuracy of measuring weak voltage response signals.

[0104] The battery monitoring process of this embodiment, which is executed by the arithmetic processing unit 54 of the battery monitoring unit 50, will now be briefly described with reference to the flowchart of FIG.

[0105] 5 , when impedance measurement is performed on battery cells 42C and 42D as measurement target cells, switches 85B and 85F are turned on (step S15). This allows the voltage measurement circuit 86 to measure the terminal voltage of the battery cell group consisting of battery cells 42B to 42E. Furthermore, switches 84C and 84D are turned on and off to allow AC current to flow through battery cells 42C and 42D (step S16). After that, the terminal voltage of the battery cell group measured by the voltage measurement circuit 86 and the current amplitude measured by the current sensor 83 are acquired (steps S17 and S18). An impedance value is calculated by dividing the voltage fluctuation, which is a response signal of the AC current, by the current amplitude (step S19).

[0106] It is preferable to measure the impedance of each pair of battery cells 42A to 42F in the order of their series connection in the battery module 41. In this case, the impedance may be measured for pairs of battery cells 42 that do not overlap with each other, or the impedance of pairs of battery cells 42 that are shifted by one cell to form different combinations may be measured.

[0107] According to the present embodiment described above, the following effects can be obtained.

[0108] In a case where the battery cells 42 each have a positive terminal 101 and a negative terminal 102 at one end and the other end in the cell longitudinal direction, and the connection positions of the positive and negative terminals of the cells are staggered in the order of series connection, the electrical paths 81 connected to both ends of each battery cell 42 are provided at separate locations at one end and the other end in the cell longitudinal direction. This increases the area surrounded by the closed circuit through which AC current flows and the area surrounded by the closed circuit for measuring the voltage response, which may result in a decrease in the accuracy of the voltage response signal. In this regard, when measuring the impedance of a target cell, an AC current is passed by the AC current generator through a first electrical path W1 that is located on the positive and negative sides of the target cell in the series connection path of the multiple battery cells 42 and is located on the first battery end E1 side of the battery module 41. Additionally, a voltage measurement circuit 86 (voltage fluctuation measurement unit) is connected to the second electrical path W2, which is on the positive and negative sides of the measurement target cell and on the second battery end E2 side of the battery module 41. This makes it possible to narrow the area surrounded by the closed circuit through which AC current flows and the area surrounded by the closed circuit through which voltage response is measured, thereby suppressing a decrease in the accuracy of the voltage response signal.

[0109] In particular, in the case of a blade cell, in which the longitudinal length of the cell is long and the positive electrode terminal 101 and the negative electrode terminal 102 are far apart, the effect of reducing the influence of induced electromotive force can be significantly achieved by configuring the cell so that an AC current flows through a pair of electrical paths 81 (wiring) at one longitudinal end of the cell and the voltage response is measured through a pair of electrical paths 81 (wiring) at the other end.

[0110] (Modification of the Third Embodiment) In the circuit configuration shown in Fig. 14, the AC current flow path and the voltage response measurement path during impedance measurement may be changed as follows. Here, the impedance of battery cell 42D is measured as the measurement target cell, and the AC current flow path and the voltage response measurement path are shown in Fig. 16. In Fig. 16, a path R71 through which the AC current flows is indicated by a thick solid line, and a path R72 for voltage measurement is indicated by a thick dashed line.

[0111] 16, switches 84C and 84D on the path connecting both ends of battery cells 42C and 42D are simultaneously turned on and off at a predetermined cycle, causing an AC current to flow through path R71 that includes battery cells 42C and 42D, electrical paths 81C and 81E between both ends of battery cells 42C and 42D, and connection paths 82C and 82D.

[0112] Furthermore, the voltage measurement circuit 86 measures the inter-terminal voltage of a battery cell group that includes the battery cell 42D and is a combination different from the battery cells 42C and 42D through which AC current flows, i.e., the battery cells 42D and 42E. The electrical paths 81D and 81F that serve as the voltage measurement paths may be alternate paths with respect to the electrical paths 81C and 81E through which AC current flows. In this case, by switching the switches 85D and 85F, the positive-side electrical path 81D and the negative-side electrical path 81F of the battery cell group consisting of the battery cells 42D and 42E are connected to the voltage measurement circuit 86. As a result, voltage fluctuations are measured on the path R72 that includes the battery cell group of the battery cells 42D and 42E, the electrical paths 81D and 81F at both ends of the battery cell group, and the voltage measurement circuit 86. Then, for a battery cell 42 (here, battery cell 42D) included in both directions of the path R71 through which the AC current flows and the path R72 for voltage measurement, an impedance value is calculated based on the voltage fluctuation measured by the voltage measurement circuit 86 and the amplitude of the AC current measured by the current sensor 83.

[0113] 17 , the electrical paths 81C and 81E that form the AC current paths are both electrical paths drawn out from the first battery end E1 side of the battery module 41. Therefore, when a closed circuit (path R71) is formed by the battery cells 42C and 42D, the electrical paths 81C and 81E, and the connection paths 82C and 82D, the area enclosed by the closed circuit is relatively small, thereby reducing the magnetic flux generated by the AC current.

[0114] Furthermore, the electrical paths 81D and 81F connected to the voltage measurement circuit 86 are both electrical paths drawn from the second battery end E2 side of the battery module 41. This reduces the area through which magnetic flux generated by AC current passes in the closed circuit where the voltage response is measured, thereby improving the accuracy of measurement of weak voltage response signals.

[0115] In both Figures 14 and 16, an AC current is caused to flow through a first electrical path W1, which is on the positive and negative sides of the cell to be measured in the series connection path of multiple battery cells 42 and is on the side of the first battery terminal E1 of the battery module 41, by an AC current generation unit, and a voltage fluctuation measurement unit is connected to a second electrical path W2, which is on the positive and negative sides of the cell to be measured and is on the side of the second battery terminal E2 of the battery module 41.

[0116] In the battery module 41, cylindrical cells can be used as the battery cells 42 instead of the long, plate-like blade cells. Specifically, as shown in FIG. 18 , the cylindrical battery cells 42 are arranged in two rows in a staggered pattern. In this configuration, each battery cell 42 is provided with a positive terminal 101 and a negative terminal 102 at one end and the other end in the cell longitudinal direction, respectively. The positive terminals 101 and negative terminals of different battery cells 42 in the series connection order are electrically connected by bus bars 103. In FIG. 18 , the upper side is the first battery end E1 of the battery module 41, and the lower side is the second battery end E2 of the battery module 41. The bus bars 103 of these ends E1 and E2 are connected to the electrical paths 81, respectively.

[0117] (Other Embodiments) The above embodiment may be modified as follows, for example.

[0118] In the second embodiment, when measuring the impedance of the battery cell 42B, which is the cell under measurement, as shown in FIG. 9, the on / off control of the switches 84A to 84C may be controlled as follows. As shown in FIG. 19(a), when turning the switches 84A to 84C on and off, the on time of the switches 84A and 84C on either side may be set longer than the on time of the switch 84B corresponding to the battery cell 42B, which is the cell under measurement (i.e., the middle switch 84B of the three switches 84A to 84C connected in series), so that the adjacent switches 84A and 84C are not turned off (opened) while the switch 84B is on (closed). This ensures the accuracy of voltage measurement by the voltage measurement circuit 86 while the switch 84B is on.

[0119] 19(b), when the switches 84A to 84C are turned on and off, the on time of the switches 84A and 84C on either side of the switch 84B corresponding to the battery cell 42B, which is the cell to be measured, may be set to be shorter than the on time of the switch 84B, so that the switches 84A and 84C on either side are not turned on (closed) while the switch 84B is off (open). This prevents unnecessary power consumption in the battery cells 42A and 42C caused by the switches 84A and 84C being on while the switch 84B is off.

[0120] 9 of the second embodiment, when measuring the impedance of the battery cell 42B, all three switches 84A to 84C corresponding to the battery cell group including the battery cell 42B are simultaneously turned on and off to cause an AC current to flow through the battery cell 42B, but this configuration may be changed. For example, an AC current may be caused to flow through the battery cell 42B by turning on or off one of the three switches 84A to 84C corresponding to the battery cell group including the battery cell 42B, and leaving the remaining two switches 84 on.

[0121] Furthermore, when an AC current is passed through each battery cell 42, an equalization current may be passed to equalize the voltages of the battery cells 42. In this case, if there is a battery cell 42 that needs to be discharged for equalization, it is preferable to pass the AC current through a path that includes that battery cell 42. For example, if battery cell 42B is the cell to be measured and it is desired to perform equalization discharge of battery cell 42A or battery cell 42C when turning on and off the three switches 84A to 84C, it is preferable to make the on time (closed time) of battery cell 42A or battery cell 42C longer than the on time of battery cell 42B.

[0122] When measuring impedance as shown in Fig. 9, it is sufficient that a current sensor 83 is provided in one battery cell 42 of a battery cell group of three battery cells 42. For example, in Fig. 9, it is possible to eliminate any two of the current sensors 83 provided in the three battery cells 42A to 42C.

[0123] In the above embodiment, the battery pack 40 is configured using a plurality of battery modules 41. However, this configuration may be changed. For example, the battery pack 40 may be configured to use a single battery module 41, i.e., the battery pack 40 and the battery module 41 may be configured to be substantially identical.

[0124] The battery pack having a plurality of battery cells may be a fuel cell that generates electrical energy through a chemical reaction between hydrogen and oxygen.

[0125] The present disclosure may be applied to other moving objects such as aircraft and ships, in addition to electric vehicles. It may also be applied to stationary systems.

[0126] Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and equivalent modifications. In addition, various combinations and forms, including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure.

Claims

1. An impedance measuring device (50) applied to a battery module (41) having a plurality of battery cells (42) connected in series, for measuring the impedance of the battery cells, comprising: a plurality of electrical paths (81) connected to both ends of each of the battery cells, an AC current generating unit (51, 84) connected to the electrical paths and flowing an AC current through the battery cells, a voltage fluctuation measuring unit (52, 86) connected to the electrical paths and measuring voltage fluctuations responsive to the AC current of the AC current generating unit, and a connection operation unit (54) for, when measuring impedance of one of the plurality of battery cells as a measurement target cell, causing the AC current of the AC current generating unit to flow through a pair of the electrical paths that are on the positive and negative sides of the measurement target cell in the series connection paths of the plurality of battery cells, and connecting the voltage fluctuation measuring unit to a pair of the electrical paths that are on the positive and negative sides of the measurement target cell and that are a different combination from the pair of the electrical paths through which the AC current of the AC current generating unit flows, a calculation unit (54) that calculates an impedance value of the measurement target cell based on an amplitude of an AC current flowing by the AC current generating unit and the voltage fluctuation measured by the voltage fluctuation measuring unit in a connected state by the connection operation unit.

2. The impedance measuring device of claim 1, wherein, when measuring the impedance of the target cell, the connection operation unit causes the AC current of the AC current generating unit to flow through the electrical path at both ends of the target cell and connects the voltage fluctuation measuring unit to the electrical path at both ends of a battery cell group including at least the target cell and the battery cells on both sides of the target cell, and the calculation unit causes the AC current of the AC current generating unit to flow through the electrical path at both ends of the target cell and connects the voltage fluctuation measuring unit to the electrical path at both ends of the battery cell group, and calculates the impedance value of the target cell based on the amplitude of the AC current flowing by the AC current generating unit and the voltage fluctuation measured by the voltage fluctuation measuring unit.

3. An impedance measuring device as described in claim 2, comprising: a first switch (84) provided as the AC current generating unit, which flows an AC current through the battery cell by turning it on and off; and second switches (85) connected to each of the multiple electrical paths for switching the battery cell that is the subject of voltage measurement by the voltage fluctuation measuring unit, wherein when measuring the impedance of the cell to be measured, the connection operation unit turns on the second switch to connect the voltage fluctuation measuring unit to the electrical paths at both ends of the battery cell group, and then turns the first switch on and off to flow the AC current.

4. A first positive side path (X1) and a second positive side path (X2) are connected as the electrical paths to a positive electrode side of a highest potential cell which is a battery cell on the highest potential side among the plurality of battery cells, and a first negative side path (Y1) and a second negative side path (Y2) are connected as the electrical paths to a negative electrode side of a lowest potential cell which is a battery cell on the lowest potential side, and when measuring impedance with the highest potential cell as the measurement target cell, the connection operation unit causes the AC current of the AC current generating unit to flow between both ends of the highest potential cell using the first positive side path and the electrical path on the negative side of the highest potential cell, and causes the voltage fluctuation measurement unit to measure voltages at both ends of the battery cell group using the second positive side path and the electrical path on the negative side of a battery cell group including at least the highest potential cell and the battery cell adjacent to it on the low potential side, 4. The impedance measuring device according to claim 2, wherein, when measuring impedance of the lowest potential cell as the measurement target cell, an AC current from the AC current generating unit is passed between both ends of the lowest potential cell using the first negative electrode side path on the negative electrode side of the lowest potential cell and the electrical path on the positive electrode side, and voltage measurement is performed by the voltage fluctuation measuring unit at both ends of the battery cell group using the second negative electrode side path and the electrical path on the positive electrode side of a battery cell group including at least the lowest potential cell and the battery cell adjacent to it on a high potential side.

5. The impedance measuring device of claim 1, wherein, when measuring the impedance of the target cell, the connection operation unit causes an AC current from the AC current generating unit to flow through the electrical path at both ends of a battery cell group including at least the target cell and the battery cells on both sides of the target cell, and connects the voltage fluctuation measuring unit to the electrical path at both ends of the target cell, and the calculation unit causes an AC current from the AC current generating unit to flow through the electrical path at both ends of the battery cell group, and connects the voltage fluctuation measuring unit to the electrical path at both ends of the target cell, and calculates the impedance value of the target cell based on the amplitude of the AC current flowing by the AC current generating unit and the voltage fluctuation measured by the voltage fluctuation measuring unit.

6. An impedance measuring device as described in claim 5, comprising: a first switch (84) provided as the AC current generating unit, which flows an AC current through the battery cell by turning it on and off; and second switches (85) connected to each of the multiple electrical paths for switching the battery cell that is the subject of voltage measurement by the voltage fluctuation measuring unit, wherein when measuring the impedance of the cell to be measured, the connection operating unit turns on the second switch to connect the voltage fluctuation measuring unit to the electrical paths at both ends of the cell to be measured, and then turns the first switch on and off to flow the AC current.

7. A first positive side path (X1) and a second positive side path (X2) are connected as the electrical paths to a positive electrode side of a highest potential cell which is the battery cell having the highest potential among the plurality of battery cells, and a first negative side path (Y1) and a second negative side path (Y2) are connected as the electrical paths to a negative electrode side of a lowest potential cell which is the battery cell having the lowest potential, and when measuring impedance with the highest potential cell as the measurement target cell, the connection operation unit causes an AC current of the AC current generating unit to flow between both ends of the battery cell group using the first positive side path on the positive electrode side of the highest potential cell and the electrical path on the negative electrode side of a battery cell group including at least the highest potential cell and the battery cell adjacent to it on the low potential side, and causes the voltage fluctuation measurement unit to measure voltages at both ends of the highest potential cell using the second positive side path on the positive electrode side of the highest potential cell and the electrical path on the negative electrode side, 7. The impedance measuring device according to claim 5, wherein, when measuring impedance of the lowest potential cell as the measurement target cell, an AC current from the AC current generating unit is passed between both ends of the battery cell group using the first negative electrode side path on the negative electrode side of the lowest potential cell and the electrical path on the positive electrode side of a battery cell group including at least the lowest potential cell and an adjacent battery cell on a high potential side, and voltage measurement is performed by the voltage fluctuation measuring unit at both ends of the lowest potential cell using the second negative electrode side path on the negative electrode side of the lowest potential cell and the electrical path on the positive electrode side.

8. Each of the battery cells is long and arranged in a direction perpendicular to the longitudinal direction of the cell, with a positive terminal (101) provided at one end of the cell in the longitudinal direction and a negative terminal (102) provided at the other end alternately between adjacent battery cells; the battery module is configured by electrically connecting the positive terminal of one battery cell and the negative terminal of the other battery cell among the battery cells connected in series to each other by a conductive member (103); a first electrical path (W1) is connected as the electrical path to the conductive member of a first battery end (E1) which is one end of the cell in the longitudinal direction of the battery module, and a second electrical path (W2) is connected as the electrical path to the conductive member of a second battery end (E2) which is the other end; and the connection operation unit is 2. The impedance measuring device according to claim 1, wherein, when measuring the impedance of the cell to be measured, an AC current is caused to flow through the first electrical path, which is on the positive and negative sides of the cell to be measured in the series connection path of the multiple battery cells and is on the side of the first battery end of the battery module, by the AC current generating unit, and the voltage fluctuation measuring unit is connected to the second electrical path, which is on the positive and negative sides of the cell to be measured and is on the side of the second battery end of the battery module.

Images