Impedance measuring device

Abstract

To improve the accuracy of impedance measurement.SOLUTION: A switch 84 constituting an AC current generation unit and a voltage measurement circuit 86 for measuring a voltage change responding to the AC current are connected to a plurality of electric paths 81 extending from both ends of each battery cell 42. When measuring the impedance of a cell that is the object to be measured, a battery monitoring unit 50 creates a state in which an AC current is made to flow to electric paths 81 at both ends of the cell to be measured and connects the voltage measurement circuit 86 to electric paths 81 at both ends of a battery cell group including at least the cell to be measured and battery cells 42 adjacent to both sides thereof. Furthermore, the battery monitoring unit 50 creates a state in which an AC current is made to flow to electric paths 81 at both ends of the cell to be measured while the voltage measurement circuit 86 is connected to electric paths 81 at both ends of the battery cell group, calculates the impedance value of the cell to be measured on the basis of the amplitude of the AC current and the voltage change measured by the voltage measurement circuit 86.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to an impedance measuring device. [Background technology]

[0002] Conventionally, in order to monitor the state of a storage battery, the impedance of the storage battery is measured (for example, Patent Document 1). Specifically, in a battery monitoring device, an AC current is applied to the storage battery, and a voltage fluctuation occurring as a response signal is acquired, and an impedance value of the storage battery is calculated based on the amplitude of the AC current and the voltage fluctuation. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-12065 Summary of the Invention [Problem to be solved by the invention]

[0004] When measuring impedance, it is possible to pass an AC current through an electrical path connected to both ends of the storage battery, and measure voltage fluctuations in the electrical path through which the AC current passes by a voltage measuring unit. In this case, there is a concern that a measurement error in the voltage fluctuation occurs due to the fact that the path through which the AC current passes and the path for voltage measurement are common, resulting in a decrease in the measurement accuracy of the impedance. That is, since a voltage drop occurs in the electrical path through which the AC current passes due to the wiring resistance and the AC current, if the voltage drop causes a decrease in the voltage measurement accuracy, the measurement accuracy of the impedance will also decrease.

[0005] The present invention has been made in consideration of the above-mentioned problems, and an object of the present invention is to provide an impedance measuring device capable of improving the accuracy of impedance measurement. [Means for solving the problem]

[0006] In order to solve the above problems, the present invention provides: 1. An impedance measuring device that is applied to a battery module having a plurality of battery cells connected in series and measures the impedance of the battery cells, comprising: A plurality of electrical paths respectively connected to both ends of each of the battery cells; an alternating current generating unit connected to the electrical path and configured to supply an alternating current to the battery cell; a voltage fluctuation measuring unit connected to the electrical path and configured to measure a voltage fluctuation responsive to the AC current of the AC current generating unit; a connection operation unit which, when measuring impedance of one of the plurality of battery cells as a measurement target cell, causes an AC current from the AC current generating unit to flow through a pair of electrical paths which are on the positive and negative sides of the measurement target cell in the series connection path of the plurality of battery cells, and connects the voltage fluctuation measurement unit to a pair of electrical paths which are on the positive and negative sides of the measurement target cell, respectively, and which are a different combination from the pair of electrical paths through which the AC current from the AC current generating unit flows; a calculation unit that calculates an impedance value of the measurement target cell based on an amplitude of an AC current generated by 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; and Equipped with.

[0007] In the above configuration, when the impedance of the cell to be measured is measured, the AC current of the AC current generating unit is caused to flow through a pair of electrical paths that are the positive and negative sides of the cell to be measured in the series connection path of the multiple battery cells, and the voltage fluctuation measuring unit is connected to a pair of electrical paths that are the positive and negative sides of the cell to be measured and that are a different combination from the pair of electrical paths through which the AC current of the AC current generating unit flows. In this case, the electrical path through which the AC current flows is different from the electrical path through which the voltage fluctuation is measured. Then, in this path connection state, the impedance value of the cell to be measured is calculated 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. This makes it possible to suppress the inconvenience that, even if a voltage drop occurs due to the wiring resistance and the AC current when the AC current flows, the accuracy of measuring the voltage fluctuation decreases due to the voltage drop. As a result, the accuracy of measuring the impedance can be improved. [Brief description of the drawings]

[0008] [Figure 1] Electrical diagram of the power supply system. [Diagram 2] FIG. [Diagram 3] FIG. 4 is a circuit diagram showing a specific circuit configuration of a battery monitoring unit. [Figure 4] FIG. 4 is a diagram for explaining a specific method of measuring impedance. [Diagram 5] 4 is a flowchart showing a battery monitoring process. [Figure 6] FIG. 4 is a diagram for explaining a specific method of measuring impedance. [Figure 7] FIG. 4 is a diagram for explaining a specific method for measuring the impedance of the highest potential cell. [Figure 8] FIG. 13 is a diagram for explaining a specific method for measuring the impedance of the lowest potential cell. [Figure 9] FIG. 11 is a diagram for explaining a specific method of measuring impedance in the second embodiment. [Figure 10] 10 is a flowchart showing a battery monitoring process in a second embodiment. [Figure 11] FIG. 4 is a diagram for explaining a specific method for measuring the impedance of the highest potential cell. [Figure 12] FIG. 13 is a diagram for explaining a specific method for measuring the impedance of the lowest potential cell. [Figure 13] FIG. 11 is a plan view showing a stacked state of cells in a battery module according to a third embodiment. [Figure 14] FIG. 4 is a diagram for explaining a specific method of measuring impedance. [Figure 15] FIG. 4 is a schematic diagram showing a closed circuit region during impedance measurement of a battery cell. [Figure 16] FIG. 4 is a diagram for explaining a specific method of measuring impedance. [Figure 17] FIG. 4 is a schematic diagram showing a closed circuit region during impedance measurement of a battery cell. [Figure 18] FIG. 13 is a perspective view showing another configuration of the battery module. [Figure 19] 4 is a time chart showing the on / off operation of each switch. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, a power supply system according to the present embodiment will be described with reference to the drawings. In the present embodiment, a power supply system mounted on an electrically powered vehicle such as a hybrid vehicle or an electric vehicle will be described.

[0010] (First embodiment) 1, the power supply system 10 includes a motor 20 as a rotating electric machine, an inverter 30 as a power converter that supplies a 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 an other 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).

[0011] The motor 20 (motor generator) is an in-vehicle 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 upper and lower arms in the same number as the number of phases of the phase windings, and the current flowing in each phase winding is adjusted by turning on and off a switch (semiconductor switching element) provided in each arm. As the switch, for example, an IGBT (Insulated Gate Bipolar Transistor) can be used.

[0012] The inverter 30 is provided with an inverter control device (not shown), which controls current flow by turning on and off each switch in the inverter 30 based on various detection information of 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, and powers the motor 20. In addition, when the motor 20 generates power using power from the drive wheels, the inverter control device converts the generated power and supplies it to the battery pack 40 via the inverter 30, thereby charging the battery pack 40.

[0013] 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 a plurality of battery modules 41 in series. The battery module 41 is configured by connecting a plurality of 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 electrolytic solution (a solution consisting of an electrolyte and a solvent) and a plurality of electrodes.

[0014] Although not shown as 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 a conductive member such as a bus bar. 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).

[0015] 1, a positive terminal of an electric 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 electric 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 energization and deenergization.

[0016] 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.

[0017] 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 the results of measuring the state of each battery cell 42 from the battery control ECU 60.

[0018] Next, the battery monitoring unit 50 will be described in detail. As shown in Fig. 2, the battery monitoring unit 50 is provided so as 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.

[0019] The AC current generating unit 51 outputs an AC current using the battery cell 42, which is the measurement target, as a power source. Specifically, the AC current generating 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 on the complex impedance is generated in the terminal voltage of the battery cell 42. The voltage fluctuation measuring unit 52 measures the response signal (voltage fluctuation) reflecting information on the complex impedance of the battery cell 42 between the terminals of the battery cell 42.

[0020] The voltage fluctuation can be calculated, for example, by subtracting the terminal voltage of the battery cell 42 under measurement measured during the input of AC current from the terminal voltage of the battery cell 42 under measurement measured before the input of AC current.

[0021] The modulation signal generator 53 includes an oscillator that generates an AC signal of an arbitrary waveform. The modulation signal generator 53 causes the oscillator to generate an AC signal in accordance with an instruction from the arithmetic processing unit 54.

[0022] The AC signal in this embodiment is a sine wave signal, but may be any AC signal, such as a square wave or a triangular wave. A DC bias is applied to the AC signal so that the AC current flowing from the battery cell 42 does not become a negative current (a reverse current to the battery cell 42).

[0023] Then, the modulation signal generator 53 converts the AC signal into a digital signal to generate an instruction signal, and instructs (outputs) the AC current generating section 51 to generate an AC current based on the instruction signal.

[0024] The arithmetic processing unit 54 includes a microcomputer consisting of a CPU (arithmetic unit) 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.

[0025] The arithmetic processing unit 54 has a function of calculating the complex impedance of the battery cell 42. Here, an overview of a method for calculating the complex impedance will be described. The arithmetic processing unit 54 instructs the modulation signal generator 53 of a measurement frequency for 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) that responds to the AC current, and outputs the measured response signal to the arithmetic processing unit 54.

[0026] 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 complex impedances for a plurality of predetermined measurement frequencies within the measurement range are 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 grasps the characteristics of the electrodes, electrolyte, etc. Also, it grasps the state of charge (SOC) and state of health (SOH).

[0027] It is not necessary to create the entire Cole-Cole plot, and attention may be paid to a part of it. For example, the complex impedance of a specific frequency may be measured at regular time intervals while driving, and changes in SOC, SOH, battery temperature, etc. while driving may be understood based on the time change of the complex impedance of the specific frequency. Alternatively, the complex impedance of a specific frequency may be measured at time intervals such as once a day, once a week, or once a year, and changes in SOH, etc. may be understood based on the time change of the complex impedance of the specific frequency. Furthermore, the complex impedance plane plot is not limited to the Cole-Cole plot, and a Bode plot, etc. may also be adopted.

[0028] 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.

[0029] The battery monitoring unit 50 has a connection path 82 that connects the electric path 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 in the connection path 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 amount of each battery cell 42. By turning on the switch 84, each battery cell 42 is discharged, and the variation in the charge amount of each battery cell 42 is eliminated. It is preferable that at least one of the paths 81, 82 is provided with a resistor. This resistor plays a role of adjusting the current during impedance measurement or during equalization.

[0030] The current sensor 83 may be disposed in the electrical path 81. In short, the current sensor 83 may be disposed in any position on the closed circuit formed by the battery cell 42, the paths 81 and 82, and the switch 84, excluding the path near the battery through which the inverter current and the like flows. 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 adjust the current during impedance measurement and equalization may serve as the shunt resistor of the current sensor 83.

[0031] 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 outputted using the battery cell 42 as a power source.

[0032] Further, 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 side path 86a, a negative electrode side 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 side path 86a and the negative electrode side path 86b of the voltage measurement circuit 86 by each switch 85. That is, each switch 85 can be switched to any one of a state in which the electrical path 81 and the voltage measurement circuit 86 are not connected (a state shown in the figure), a state in which the electrical path 81 is connected to the positive electrode side path 86a of the voltage measurement circuit 86, and a state in which the electrical path 81 is connected to the negative electrode side path 86b of the voltage measurement circuit 86. By switching the switches 85, the battery cell 42 to be the target of voltage measurement in the voltage measurement circuit 86 is switched. The voltage measurement circuit 86 measures the terminal voltage of each battery cell 42.

[0033] The voltage measurement circuit 86 constitutes the voltage fluctuation measurement unit 52 shown in FIG. 2, and in the voltage fluctuation measurement unit 52, a voltage fluctuation responsive to the AC current of the AC current generation unit 51 is calculated based on the inter-terminal voltage of the battery cell 42 measured by the voltage measurement circuit 86.

[0034] When measuring the impedance of the battery cell 42, one of the multiple battery cells 42 is selected as a cell to be measured, and the impedance of the cell to be measured is measured. In this case, a switch 84 on a path connecting both ends of the cell to be measured is turned on and off, so that an AC current flows through the cell to be measured. In this state, a voltage fluctuation responsive to the AC current is measured by a voltage measurement circuit 86. In addition, in the voltage fluctuation measurement unit 52 shown in FIG. 2, the voltage fluctuation is calculated based on the voltage measured by the voltage measurement circuit 86, and in the calculation processing unit 54, the impedance value of the cell to be measured is calculated based on the amplitude of the AC current and the amount of voltage fluctuation.

[0035] Incidentally, when measuring impedance, it is considered that an AC current is passed through an electrical path 81 connected to both ends of a cell to be measured, and voltage fluctuations are measured through the electrical path 81 also connected to both ends of the cell to be measured. In this case, there is a concern that a measurement error in the voltage fluctuation occurs due to the fact that the path through which the AC current flows and the path through which the voltage is measured are common, resulting in a decrease in the measurement accuracy of the impedance. 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, and if the voltage measurement accuracy decreases due to the voltage drop, the measurement accuracy of the impedance also decreases.

[0036] Therefore, during impedance measurement, the electrical path 81 through which the AC current is passed by the AC current generating unit 51 is different from the electrical path 81 through which the voltage fluctuation is measured by the voltage fluctuation measuring unit 52 (voltage measurement circuit 86), thereby suppressing a decrease in the measurement accuracy of the impedance. That is, in this embodiment, the AC current of the AC current generating unit 51 is passed through a pair of electrical paths 81 that are the positive and negative sides of the measurement target cell in the series connection path of the multiple battery cells 42, and the voltage fluctuation measuring unit 52 is connected to a pair of electrical paths 81 that are the positive and negative sides of the measurement target cell and are a different combination from the pair of electrical paths 81 through which the AC current of the AC current generating unit 51 passes. A specific method of impedance measurement will be described below with reference to FIG. 4.

[0037] 4 shows a state in which three battery cells 42 connected in series are battery cells 42A to 42C, and among them, battery cell 42B is a cell to be measured, and impedance measurement is performed. In FIG. 4, the connection paths 82 and switches 84 provided for each of battery cells 42A to 42C are respectively referred to as connection paths 82A to 82C and switches 84A to 84C. Also, each electrical path 81 is referred to as electrical paths 81A to 81D, and switches 85 connected to each electrical path 81A to 81D are respectively referred to as switches 85A to 85D. Note that the wiring resistance of electrical path 81 is not shown. In FIG. 4, a path R1 through which an AC current flows is indicated by a thick solid line, and a path R2 for voltage measurement is indicated by a thick dashed line.

[0038] When the battery cell 42B is the measurement target cell, among the switches 84A to 84C, the switch 84B on the path connecting both ends of the battery cell 42B is turned on and off at a predetermined cycle, causing an AC current to flow through the battery cell 42B. At this time, an AC current flows through a path R1 that includes the battery cell 42B, the electrical paths 81B and 81C between both ends of the battery cell 42B, and the connection path 82B.

[0039] In addition, the voltage measurement circuit 86 measures the inter-terminal voltage of a battery cell group including the battery cell 42B and the adjacent battery cells 42A and 42C as the measurement target. Specifically, 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 by switching the switch 85A, and 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 by switching the switch 85D. This allows voltage fluctuations to be measured in the path R2 including 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, 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.

[0040] As described above, the AC current path and the voltage measurement path are appropriately switched by on / off control of each of the switches 84, 85. The on / off control of each of the switches 84, 85 may be performed by the arithmetic processing unit 54, which corresponds to the "connection operation unit."

[0041] Although the voltage measurement circuit 86 is configured to measure the inter-terminal voltage of three battery cells 42 including the measurement target cell (battery cell 42B) and the adjacent battery cells 42A, 42C on either side of the measurement target cell, this configuration may be any configuration in which the inter-terminal voltage is measured for a battery cell group including at least the measurement target cell and the adjacent battery cells 42 on either side of the measurement target cell. 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 measurement target cell.

[0042] Fig. 5 is a flowchart showing the battery monitoring process. This process is started in response to a command from a higher-level ECU such as the battery control ECU 60, and is repeatedly executed at a predetermined cycle by the calculation processing unit 54 of the battery monitoring unit 50. Note that, as an example, a process of measuring impedance and the like is described here with the battery cell 42B shown in Fig. 4 as the measurement target cell.

[0043] 5, in step S11, a battery cell 42 to be a measurement target cell is selected from the multiple 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 cell 42 whose impedance is to be measured, but also the battery cell 42 whose terminal voltage (e.g., open circuit voltage) is to be measured as the state of the battery cell 42.

[0044] Then, in step S12, it is determined whether or not to perform impedance measurement on the cell to be measured. If the result in step S12 is negative, the process proceeds to step S13. In step S13, the switches 85B and 85C are turned on. This causes the voltage measurement circuit 86 to measure the terminal voltage of the battery cell 42B. In the following step S14, the terminal voltage of the battery cell 42B measured by the voltage measurement circuit 86 is acquired. Then, in step S20, the terminal voltage of the battery cell 42B is transmitted to a higher-level ECU.

[0045] Also, if step S12 is positive, 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 addition, in step S16, switch 84B is turned on and off to cause an AC current to flow through battery cell 42B. With AC current flowing, the amplitude of the AC current (current amplitude) is measured by current sensor 83. 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.

[0046] 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. The voltage fluctuation may be calculated as the voltage difference between the inter-terminal voltage measured before the AC current is passed through the battery cell 42B and the terminal voltage measured with the AC current passing through it. It is also possible to use the inter-terminal voltage acquired in step S14 as the inter-terminal voltage before the AC current is passed through the battery cell 42B.

[0047] After that, in step S20, the impedance value is transmitted to a host ECU.

[0048] The battery monitoring unit 50 performs impedance measurement for 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 with reference to Figs. 6 to 8.

[0049] In FIG. 6, in a battery module 41, among a plurality of battery cells 42 connected in series, 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 battery module 41, i.e., the highest potential cell. In FIG. 6, electrical paths X1 and X2 branched into two paths are connected as an electrical path 81 to the positive electrode side of battery cell 42_1. A current sensor 83 and a switch 84 are connected in series to electrical path X1, and a positive electrode side 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."

[0050] Fig. 7 is a diagram showing a state in which impedance measurement is performed on the battery cell 42_1 as the measurement target cell. In Fig. 7, a path R11 through which an AC current flows is indicated by a thick solid line, and a path R12 for voltage measurement is indicated by a thick dashed line.

[0051] 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 a switch 84 on a path connecting both ends of the battery cell 42_1 at a predetermined cycle. At this time, an AC current flows through a path R11 that includes the battery cell 42_1 and the electrical paths X1, 81 between both ends of the battery cell 42_1.

[0052] Furthermore, the voltage measurement circuit 86 measures the inter-terminal voltage of a battery cell group including the battery cell 42_1 and the adjacent battery cell 42_2 as a measurement target. Specifically, by switching between the switch 85 on the positive electrode side of the battery cell 42_1 and the switch 85 on the negative electrode side of the battery cell 42_2, a voltage fluctuation is measured in a path R12 including the battery cell group of the battery cells 42_1 and 42_2, the electrical paths X2, 81 between both ends of the battery cell group, and the voltage measurement circuit 86. Then, 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, the impedance value of the battery cell 42_1 is calculated.

[0053] When measuring the impedance of the highest potential cell, the voltage measurement circuit 86 may 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 including at least the battery cell 42_1 and the adjacent battery cell 42_2 on the low potential side. In other words, the battery cell group to be the subject of voltage fluctuation measurement may include one or more battery cells 42 on the negative electrode side of the battery cell 42_1 (highest potential cell).

[0054] In FIG. 8, in a battery module 41, among a plurality (n pieces) of battery cells 42 connected in series, the n-th battery cell 42 on the lowest potential side is designated as a battery cell 42_n, and the n-1-th battery cell 42 is designated as a battery cell 42_n-1, and impedance measurement is performed on the battery cell 42_n as a measurement target cell. The battery cell 42_n is the battery cell on the lowest potential side in the battery module 41, that is, the lowest potential cell. In FIG. 8, two branched electrical paths Y1 and Y2 are connected as an electrical path 81 to the negative electrode side of the battery cell 42_n. A current sensor 83 and a switch 84 are connected in series to the electrical path Y1, and a negative electrode side path 86b of a voltage measurement circuit 86 is connected to the electrical path Y2 via a switch 85. The electrical path Y1 corresponds to a "first negative electrode side path", and the electrical path Y2 corresponds to a "second negative electrode side 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.

[0055] When the battery cell 42_n on the lowest potential side is the cell to be measured, an AC current flows through the battery cell 42_n by turning on and off a switch 84 on a path connecting both ends of the battery cell 42_n at a predetermined cycle. At this time, an AC current flows through a path R21 that includes the battery cell 42_n and the electrical paths Y1, 81 between both ends of the battery cell 42_n.

[0056] Furthermore, the voltage measurement circuit 86 measures the inter-terminal voltage of a battery cell group including the battery cell 42_n and the adjacent battery cell 42_n-1 as a measurement target. Specifically, by switching between the switch 85 on the negative electrode side of the battery cell 42_n and the switch 85 on the positive electrode side of the battery cell 42_n-1, a voltage fluctuation is measured in a path R22 including the battery cell group of the battery cells 42_n, 42_n-1, the electrical paths Y2, 81 between both ends of the battery cell group, and the voltage measurement circuit 86. Then, 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, the impedance value of the battery cell 42_n is calculated.

[0057] When measuring the impedance of the lowest potential cell, the voltage fluctuation of the battery cell group is measured in the voltage measurement circuit 86 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 including at least the battery cell 42_n and the adjacent battery cell 42_n-1 on the low potential side. In other words, the battery cell group to be the subject of voltage fluctuation measurement is only required to include one or more battery cells 42 on the positive electrode side of the battery cell 42_n (lowest potential cell).

[0058] 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 not be branched into two paths. In this case, when measuring the impedance of the highest potential cell and 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 common 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.

[0059] According to the present embodiment described above in detail, the following excellent effects can be obtained.

[0060] When one of the battery cells 42 is used as a measurement target cell and the impedance is measured, the AC current from the AC current generating unit 51 is caused to flow through the electrical path 81 at both ends of the measurement target cell, and the voltage measuring circuit 86 is connected to the electrical path 81 at both ends of the battery cell group including at least the measurement 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 the voltage fluctuation is measured. In this path connection state, the impedance value of the measurement target cell is calculated based on the amplitude of the AC current flowing from the AC current generating unit 51 and the voltage fluctuation measured by the voltage measuring circuit 86. This makes it possible to suppress the inconvenience of a voltage drop occurring due to the wiring resistance and the AC current when the AC current flows, which reduces the measurement accuracy of the voltage fluctuation. As a result, the measurement accuracy of the impedance can be improved.

[0061] 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 a battery cell group including the cell to be measured, and then switch 84 (first switch) on the path connecting both ends of the cell to be measured is turned on and off to allow an AC current to flow. In this case, power consumption can be reduced compared to the opposite case where switch 85 is turned on to enable voltage measurement by voltage measurement circuit 86 after AC current has started to flow by turning switch 84 on and off.

[0062] When measuring the impedance of the highest potential cell (battery cell 42_1), the AC current of the AC current generating unit 51 is caused to flow between both ends of the highest potential cell using the electrical path X1 of the electrical paths X1, X2 connected to the positive electrode side of the highest potential cell and the electrical path 81 on the negative electrode side of the highest potential cell. Also, the voltage measurement circuit 86 is caused to measure the voltage between both ends of the battery cell group using the electrical path X2 of the electrical paths X1, X2 on the positive electrode side of the highest potential cell and the electrical path 81 on the negative electrode side of the battery cell group including at least the highest potential cell and the adjacent battery cell 42 on the low potential side. As a result, when measuring the impedance of the highest potential cell, the electrical path through which the AC current flows and the electrical path through which the voltage fluctuation is measured are different, and the impedance measurement accuracy can be improved.

[0063] When measuring the impedance of the lowest potential cell (battery cell 42_n), the AC current of the AC current generating unit 51 is caused to flow between both ends of 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. In addition, the voltage measurement circuit 86 is caused to measure the voltage between both ends of 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 including at least the lowest potential cell and the adjacent battery cell 42 on the high potential side. As a result, when measuring the impedance of the lowest potential cell, the electrical path through which the AC current flows and the electrical path through which the voltage fluctuation is measured are different, and the impedance measurement accuracy can be improved.

[0064] In each battery module 41, the electrical paths 81 that are branched into two paths among the electrical paths 81 connected to both ends of each battery cell 42 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 electrical paths 81 is kept to a minimum.

[0065] 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.

[0066] In Fig. 9, similarly to Fig. 4, three battery cells 42 connected in series are designated as battery cells 42A to 42C, and among them, battery cell 42B is designated as the measurement target cell for impedance measurement. In Fig. 9, a path R31 through which an AC current flows is indicated by a thick solid line, and a path R32 for voltage measurement is indicated by a thick dashed line.

[0067] When battery cell 42B is the measurement target cell, all of switches 84A-84C are simultaneously turned on and off at a predetermined cycle, causing an AC current to flow through a battery cell group including battery cell 42B and adjacent battery cells 42A and 42C. At this time, an AC current flows through path R31 including the battery cell group of battery cells 42A-42C, electrical paths 81A and 81D at both ends of the battery cell group, and connection paths 82A-82C.

[0068] In addition, the voltage measurement circuit 86 measures the inter-terminal voltage of the battery cell 42B as a measurement target. Specifically, 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 by switching the switch 85B, and 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 by switching the switch 85C. This allows voltage fluctuations to be measured in the path R32 including 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.

[0069] Although an AC current is passed through three battery cells 42 including the measurement target cell (battery cell 42B) and the adjacent battery cells 42A, 42C on either side of it by turning on and off the switches 84A-84C, this configuration may be any configuration that passes an AC current through the electrical path 81 at both ends of a battery cell group that includes at least the measurement target cell and the adjacent battery cells 42 on either side of it. In other words, the battery cell group through which an AC current passes may include one or more battery cells 42 on both the positive and negative sides of the measurement target cell.

[0070] Fig. 10 is a flowchart showing the battery monitoring process in this embodiment. This process is started in response to a command from a higher-level ECU such as the battery control ECU 60, and is repeatedly executed at a predetermined cycle by the calculation processing unit 54 of the battery monitoring unit 50. Note that, as an example, a process of measuring impedance and the like is described here with the battery cell 42B shown in Fig. 9 as the measurement target cell.

[0071] 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.

[0072] In FIG. 10, if step S12 is judged to be positive, 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 addition, 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.

[0073] Then, in step S33, the 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 a response signal of the AC current, by the current amplitude. Then, in step S20, the impedance value is transmitted to a higher-level ECU.

[0074] Next, a method of measuring 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.

[0075] Fig. 11 is a diagram showing a state in which impedance measurement is performed on the highest potential cell (battery cell 42_1) as the measurement target cell. In Fig. 11, a path R41 through which an AC current flows is shown by a thick solid line, and a path R42 for voltage measurement is shown by a thick dashed line.

[0076] 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 period. This causes 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 between both ends of the battery cell group.

[0077] 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 electrode side of the battery cell 42_1 and the switch 85 on the negative electrode side of the battery cell 42_1, a voltage fluctuation is measured in a path R42 that includes the battery cell 42_1, electrical paths X2, 81 between both ends of the battery cell 42_1, and the voltage measurement circuit 86. Then, 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, an impedance value of the battery cell 42_1 is calculated.

[0078] 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.

[0079] Fig. 12 is a diagram showing a state in which impedance measurement is performed on the lowest potential cell (battery cell 42_n) as the measurement target cell. In Fig. 12, a path R51 through which an AC current flows is shown by a thick solid line, and a path R52 for voltage measurement is shown by a thick dashed line.

[0080] 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 the 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, 42_n-1 and the electrical paths Y1, 81 between both ends of the battery cell group.

[0081] Furthermore, 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 electrode side of the battery cell 42_n and the switch 85 on the positive electrode side of the battery cell 42_n, the voltage fluctuation is measured in the path R52 including the battery cell 42_n, the electrical paths Y2,81 between both ends of the battery cell 42_n, and the voltage measurement circuit 86. Then, 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, the impedance value of the battery cell 42_n is calculated.

[0082] 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.

[0083] 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 be branched into two paths. In this case, when measuring the impedance of the highest potential cell and the lowest potential cell as the measurement target cells, the electrical path through which the AC current flows and the electrical path through which the voltage fluctuation is measured are common 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.

[0084] According to the present embodiment, the following effects can be obtained.

[0085] When one of the battery cells 42 is used as a measurement target cell to measure the impedance, the AC current from the AC current generating unit 51 is caused to flow through the electrical path 81 at both ends of a battery cell group including at least the measurement target cell and the battery cells 42 adjacent thereto, and the voltage measuring circuit 86 is connected to the electrical path 81 at 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 the voltage fluctuation is measured. In this path connection state, the impedance value of the measurement target cell is calculated based on the amplitude of the AC current flowing from the AC current generating unit 51 and the voltage fluctuation measured by the voltage measuring circuit 86. This makes it possible to suppress the inconvenience of a voltage drop occurring due to the wiring resistance and the AC current when the AC current flows, resulting in a decrease in the measurement accuracy of the voltage fluctuation due to the voltage drop. As a result, the measurement accuracy of the impedance can be improved.

[0086] 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 an AC current to flow. In this case, power consumption can be reduced compared to the opposite case where switch 85 is turned on to enable voltage measurement by voltage measurement circuit 86 after AC current has started to flow by turning switch 84 on and off.

[0087] When measuring the impedance of the highest potential cell (battery cell 42_1), the AC current of the AC current generating unit 51 is caused to flow between both ends of the battery cell group using the electrical path X1 of the electrical paths X1, X2 connected to the positive electrode side of the highest potential cell and the negative electrode side electrical path 81 of the battery cell group including at least the highest potential cell and the adjacent battery cell 42 on the low potential side. Also, the voltage measurement circuit 86 is caused to measure the voltage between both ends of the highest potential cell using the electrical path X2 of the electrical paths X1, X2 on the positive electrode side of the highest potential cell and the negative electrode side electrical path 81. As a result, when measuring the impedance of the highest potential cell, the electrical path through which the AC current flows and the electrical path through which the voltage fluctuation is measured are different, and the impedance measurement accuracy can be improved.

[0088] When measuring the impedance of the lowest potential cell (battery cell 42_n), the AC current of the AC current generating unit 51 is caused to flow between both ends of 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. Also, the voltage measuring circuit 86 is caused to measure the voltage between both ends of 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. As a result, when measuring the impedance of the lowest potential cell, the electrical path through which the AC current flows and the electrical path through which the voltage fluctuation is measured are different, and the impedance measurement accuracy can be improved.

[0089] Third embodiment In this embodiment, a specific configuration example regarding the connection between each battery cell 42 of the battery module 41 and the AC current generating unit 51 (switch 84) and the voltage measuring circuit 86 will be described.

[0090] FIG. 13 is a plan view showing a state in which a plurality of battery cells 42 are stacked in a battery module 41. Here, six battery cells 42, battery cells 42A to 42F, are shown as the plurality of battery cells 42. Each battery cell 42 is a so-called blade cell having an elongated plate shape (flattened rectangular parallelepiped shape), and is stacked and arranged with the plate surfaces in the plate thickness direction facing each other. Each battery cell 42 has a positive terminal 101 at one end side in the cell longitudinal direction (left-right direction in the figure) and a negative terminal 102 at the other end side, 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 such that the positive terminals 101 and the negative terminals 102 are alternated in the cell longitudinal direction in the order of series connection. That is, each battery cell 42 is stacked in a direction in which the positive and negative sides are alternated.

[0091] In the battery module 41, among the adjacent battery cells 42 in the stacking direction (i.e., the battery cells 42 connected in series), the positive terminal 101 of one battery cell 42 and the negative terminal 102 of the other battery cell 42 are electrically connected by a bus bar 103 which is a conductive member. As a result, the battery cells 42 are connected in series.

[0092] In this embodiment, in the battery module 41, one end in the cell longitudinal direction (the right end in the figure) is the first battery end E1, and the other end (the left end in the figure) is the second battery end E2. In this case, at the first battery end E1, the positive and negative terminals of the battery cells 42B, 42C and the positive and negative terminals of the battery cells 42D, 42E are electrically connected by the bus bar 103. At the second battery end E2, the positive and negative terminals of the battery cells 42A, 42B, the positive and negative terminals of the battery cells 42C, 42D, and the positive and negative terminals of the battery cells 42E, 42F are electrically connected by the bus bar 103.

[0093] 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 paths 81 are connected to both ends of each battery cell 42 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. In addition, 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.

[0094] Fig. 14 is a circuit diagram showing a specific circuit configuration of a 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 that in Figs. 3 and 4 described above, although the number of cells is different, and electrical paths 81A-81G are provided for the battery cells 42A-42F, and current sensors 83 and switches 84A-84F are provided on the connection paths 82A-82F corresponding to the battery cells 42A-42F, respectively. A voltage measurement circuit 86 is connected to the electrical paths 81A-81G via switches 85A-85G.

[0095] Fig. 14 shows a state in which impedance measurement is performed on battery cells 42C and 42D among the battery cells 42A to 42F as measurement target cells. In Fig. 14, a path R61 through which an AC current flows is shown by a thick solid line, and a path R62 for voltage measurement is shown by a thick dashed line.

[0096] 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 including 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.

[0097] In addition, 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 as the measurement target. Specifically, the switch 85B is switched to connect the positive electrode side electrical path 81B of the battery cell 42B to the positive electrode side path 86a of the voltage measurement circuit 86, and the switch 85F is switched to connect the negative electrode side electrical path 81F of the battery cell 42E to the negative electrode side path 86b of the voltage measurement circuit 86. This allows voltage fluctuations to be measured in the path R62 including 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.

[0098] 13, the AC current flowing through the battery cells 42C, 42D flows through the electric paths 81C, 81E, which are the first electric path W1 on the first battery end E1 side. In this case, the electric path 81C extending from the positive electrode side of the battery cell 42C and the electric path 81E extending from the negative electrode side of the battery cell 42D are electric paths drawn out from the same end side (the first battery end E1 side) of both ends in the cell longitudinal direction in the battery module 41. Therefore, when a closed circuit (path R61) is formed by the battery cells 42C, 42D, the electric paths 81C, 81E, and the connection paths 82C, 82D, the area surrounded by the closed circuit becomes smaller, and the magnetic flux generated by the AC current is reduced.

[0099] 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, 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 in the battery module 41. Therefore, when a closed circuit (path R62) is formed by the battery cells 42B, 42E, the electrical paths 81B, 81F, and the voltage measurement circuit 86, the area surrounded by the closed circuit is reduced, and the influence of the induced electromotive force is reduced.

[0100] Fig. 15 is a schematic diagram showing closed circuit regions during impedance measurement of battery cells 42C, 42D in a battery module 41. In Fig. 15, the closed circuit region formed by the current path of AC current is designated as region S1, and the closed circuit region formed by the path for measuring the voltage response is designated as region S2, and these regions S1, S2 are indicated by hatching.

[0101] The electric paths 81C and 81E that form the AC current path both extend from the first battery end E1 side of the battery module 41, and the area surrounded by the electric paths 81C and 81E is the area S1. In this case, if the impedance measurement target is only the battery cell 42C and the AC current is passed through the electric paths 81C and 81D at both ends of the battery cell 42C, the closed circuit area formed by the electric paths 81C and 81E (AC current path) becomes wider because the electric paths 81C and 81D are disposed at both ends of the cell in the longitudinal direction. Therefore, there is a concern that the magnetic flux generated by the AC current will become larger. In contrast, when the AC current path is formed as shown in FIG. 14, the electric paths 81C and 81E that extend from both ends of the battery cells 42C and 42D are relatively close to each other, so that the magnetic flux generated by the AC current can be reduced.

[0102] Moreover, both of the electrical paths 81B and 81F connected to the voltage measurement circuit 86 extend from the second battery end E2 side of the battery module 41, and the area surrounded by the electrical paths 81B and 81F is area S2. In this case, in the closed circuit for measuring the voltage response, the passing area of ​​the magnetic flux generated by the AC current 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 measurement accuracy for weak voltage response signals.

[0103] The battery monitoring process of this embodiment executed by the arithmetic processing unit 54 of the battery monitoring unit 50 will be briefly described below with reference to the flowchart of FIG.

[0104] 5, when impedance measurement is performed on the battery cells 42C and 42D as the measurement target cells, for example, the 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 of the battery cells 42B to 42E. In addition, the switches 84C and 84D are turned on and off to allow AC current to flow through the 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 obtained (steps S17 and S18), and the impedance value is calculated by dividing the voltage fluctuation, which is a response signal of the AC current, by the current amplitude (step S19).

[0105] In the battery module 41, the impedance may be measured for each pair of battery cells 42A to 42F in the order of their series connection. In this case, the impedance may be measured for each pair of battery cells 42 that do not overlap, or the impedance may be measured for each pair of battery cells 42 that are shifted by one cell to create different combinations.

[0106] According to the present embodiment described above, the following effects can be obtained.

[0107] In the case where the battery cell 42 has 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 ends at one end and the other end in the cell longitudinal direction. Therefore, the area surrounded by the closed circuit through which the AC current flows and the area surrounded by the closed circuit for measuring the voltage response become large, which may lead to a decrease in accuracy of the voltage response signal. In this regard, when measuring the impedance of the measurement target cell, the AC current generating unit is configured to pass an AC current through the first electrical path W1, which is on the positive and negative sides of the measurement target cell in the series connection path of the multiple battery cells 42 and is on the first battery end E1 side of the battery module 41. Similarly, 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 is 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 the AC current flows and the area surrounded by the closed circuit for measuring the voltage response, thereby suppressing a decrease in accuracy of the voltage response signal.

[0108] 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 is remarkable by configuring the cell to pass an AC current through a pair of electrical paths 81 (wiring) at one longitudinal end and to measure the voltage response through a pair of electrical paths 81 (wiring) at the other end.

[0109] (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 is measured for battery cell 42D 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, path R71 through which the AC current flows is shown by a thick solid line, and path R72 for voltage measurement is shown by a thick dashed line.

[0110] 16, switches 84C, 84D on the path connecting both ends of battery cells 42C, 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, 42D, electrical paths 81C, 81E between both ends of the battery cells 42C, 42D, and connection paths 82C, 82D.

[0111] In addition, the voltage measurement circuit 86 measures the inter-terminal voltage of a battery cell group including the battery cell 42D and having a different combination from the battery cells 42C and 42D through which AC current flows, that is, the battery cells 42D and 42E. The electrical paths 81D and 81F that are the paths for voltage measurement may be alternate electrical paths with respect to the electrical paths 81C and 81E through which AC current flows. In this case, the electrical path 81D on the positive electrode side and the electrical path 81F on the negative electrode side of the battery cell group consisting of the battery cells 42D and 42E are connected to the voltage measurement circuit 86 by switching the switches 85D and 85F. As a result, the voltage fluctuation is measured in 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.

[0112] 17, the electrical paths 81C, 81E that form the current path of the AC current 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, 42D, the electrical paths 81C, 81E, and the connection paths 82C, 82D, the area surrounded by the closed circuit is relatively small. This reduces the magnetic flux generated by the AC current.

[0113] In addition, 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. Therefore, in the closed circuit for measuring the voltage response, the passing area of ​​the magnetic flux generated by the AC current can be made small, thereby improving the measurement accuracy for a weak voltage response signal.

[0114] In both Figures 14 and 16, an AC current is generated by an AC current generating unit and passed 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 located on the side of the first battery terminal E1 of the battery module 41, and a voltage fluctuation measuring 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 located on the side of the second battery terminal E2 of the battery module 41.

[0115] In the battery module 41, cylindrical cells may 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, and the positive terminals 101 and the negative terminals of the different battery cells 42 in the order of series connection are electrically connected by a bus bar 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, and the electrical paths 81 are connected to the bus bars 103 of these ends E1, E2, respectively.

[0116] (Other embodiments) The above embodiment may be modified, for example, as follows.

[0117] In the second embodiment, when measuring the impedance of the battery cell 42B, which is the cell to be measured, 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 on and off the switches 84A to 84C, the on time of the switches 84A and 84C adjacent to the switch 84B corresponding to the battery cell 42B, which is the cell to be measured (i.e., the middle switch 84B of the three switches 84A to 84C connected in series) may be set to be longer than the on time of the switch 84B, which corresponds to the battery cell 42B, which is the cell to be measured, so that the switches 84A and 84C adjacent to the switch 84B are not turned off (opened) while the switch 84B is on (closed). This ensures the accuracy of the voltage measurement by the voltage measurement circuit 86 while the switch 84B is on.

[0118] 19(b), when the switches 84A-84C are turned on and off, the on-time of the switches 84A, 84C adjacent to the battery cell 42B, which is the measurement target cell, may be set to be shorter than the on-time of the switch 84B corresponding to the battery cell 42B, so that the adjacent switches 84A, 84C are not turned on (closed) while the switch 84B is off (open). This makes it possible to prevent unnecessary power consumption in the battery cells 42A, 42C caused by the switches 84A, 84C being on while the switch 84B is off.

[0119] 9 in the second embodiment, when measuring the impedance of the battery cell 42B, all three switches 84A-84C corresponding to the battery cell group including the battery cell 42B are simultaneously turned on and off to pass an AC current through the battery cell 42B, but this configuration may be changed. For example, it may be configured such that one switch 84 of the three switches 84A-84C corresponding to the battery cell group including the battery cell 42B is turned on and off, and the remaining two switches 84 are left on to pass an AC current through the battery cell 42B.

[0120] Furthermore, when passing an AC current through each battery cell 42, an equalization current for voltage equalization of each battery cell 42 may be passed. In this case, if there is a battery cell 42 that needs to be discharged for equalization, it is preferable to pass an AC current through a path that includes that battery cell 42. For example, if battery cell 42B is the measurement target cell 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.

[0121] When performing impedance measurement as in Fig. 9, it is sufficient that a current sensor 83 is provided in one battery cell 42 among 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.

[0122] In the above embodiment, the battery pack 40 is configured by a plurality of battery modules 41, but this configuration may be changed. For example, the battery pack 40 may be configured to use one battery module 41, that is, the battery pack 40 and the battery module 41 may be configured to be substantially the same.

[0123] 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.

[0124] The present invention may be applied to other moving objects such as aircraft and ships other than electric vehicles. It may also be applied to stationary systems. [Explanation of symbols]

[0125] 41... battery module, 42... battery cell, 50... battery monitoring unit, 51... AC current generating unit, 52... voltage fluctuation measuring unit, 54... calculation processing unit, 81... electrical path, 84... switch, 86... voltage measuring circuit.

Claims

1. An impedance measuring device (50) that is applied to a battery module (41) having a plurality of battery cells (42) connected in series and measures the impedance of the battery cells, a plurality of electrical paths (81) respectively connected to both ends of each of the battery cells; an alternating current generating unit (51, 84) connected to the electrical path and supplying an alternating current to the battery cell; a voltage fluctuation measuring unit (52, 86) connected to the electrical path and configured to measure voltage fluctuations responsive to the AC current of the AC current generating unit; a connection operation unit (54) that, when measuring impedance of one of the plurality of battery cells as a measurement target cell, causes the AC current of the AC current generating 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 path 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 of the AC current generating unit flows; a calculation unit (54) that calculates an impedance value of the measurement target cell 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; Equipped with When measuring the impedance of the measurement target cell, the connection operation unit causes the AC current from the AC current generation unit to flow through the electrical path at both ends of the measurement target cell, and connects the voltage fluctuation measurement unit to the electrical path at both ends of a battery cell group including at least the measurement target cell and the battery cells on both sides of the measurement target cell; The calculation unit 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, with the AC current from the AC current generation unit flowing in the electrical path at both ends of the cell to be measured and the voltage fluctuation measurement unit connected to the electrical path at both ends of the battery cell group.

2. 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; a second switch (85) connected to each of the plurality of electrical paths for switching the battery cell that is the subject of voltage measurement by the voltage fluctuation measurement unit; 2. The impedance measuring device according to claim 1, wherein, when measuring the impedance of the measurement target cell, the connection operation unit turns on the second switch to connect the voltage fluctuation measurement unit to the electrical path at both ends of the battery cell group, and then turns on and off the first switch to allow the AC current to flow.

3. a first positive electrode side path (X1) and a second positive electrode 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 electrode side path (Y1) and a second negative electrode 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; The connection operation unit When measuring impedance using the highest potential cell as the measurement target cell, an AC current from the AC current generating unit is passed between both ends of the highest potential cell using the first positive electrode side path on the positive electrode side of the highest potential cell and the electrical path on the negative electrode side, and voltage is measured by the voltage fluctuation measuring unit between both ends of the battery cell group using the second positive electrode side path 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; 3. The impedance measurement device according to claim 1, wherein, when measuring impedance using the lowest potential cell as the measurement target cell, the AC current of the AC current generator 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 the voltage fluctuation measurement unit measures voltages 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.

4. An impedance measuring device (50) that is applied to a battery module (41) having a plurality of battery cells (42) connected in series and measures the impedance of the battery cells, a plurality of electrical paths (81) respectively connected to both ends of each of the battery cells; an alternating current generating unit (51, 84) connected to the electrical path and supplying an alternating current to the battery cell; a voltage fluctuation measuring unit (52, 86) connected to the electrical path and configured to measure voltage fluctuations responsive to the AC current of the AC current generating unit; a connection operation unit (54) that, when measuring impedance of one of the plurality of battery cells as a measurement target cell, causes the AC current of the AC current generating 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 path 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 of the AC current generating unit flows; a calculation unit (54) that calculates an impedance value of the measurement target cell 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; Equipped with Each of the battery cells is elongated, and is 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 of the cell alternately between adjacent battery cells; The battery module is configured by electrically connecting the positive electrode terminal of one battery cell and the negative electrode terminal of the other battery cell among battery cells connected in series by a conductive member (103), a first electrical path (W1) is connected as the electrical path to the conductive member at a first battery end (E1) which is one end side in the cell longitudinal direction of the battery module, and a second electrical path (W2) is connected as the electrical path to the conductive member at a second battery end (E2) which is the other end side, The connection operation unit When measuring the impedance of the cell under test, the impedance measurement device causes the AC current generation unit to flow through the first electrical path, which is on the positive and negative sides of the cell under test in the series connection path of the multiple battery cells and is on the side of the first battery end of the battery module, and connects the voltage fluctuation measurement unit to the second electrical path, which is on the positive and negative sides of the cell under test and is on the side of the second battery end of the battery module.

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