JP2014223003A - Power storage system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine whether or not a leakage current flows in a voltage detection circuit or discharge circuit connected in parallel with a power storage unit.SOLUTION: During a balancing process of equalizing voltage values of a plurality of power storage units (11) to a reference voltage value, if an amount of discharge of a power storage unit during the balancing process is equal to or greater than a predetermined amount, it is determined that a leakage current flows in a voltage detection circuit (40, D) or discharge circuit (SW1) corresponding to a power storage unit indicating the reference voltage value. The amount of discharge during the balancing process can be found to be equal to or greater than the predetermined amount when the duration of the balancing process is equal to or longer than a predetermined time.

Description

  The present invention relates to a power storage system that performs processing (equalization processing) for suppressing variations in voltage values among a plurality of power storage units connected in series.

  In Patent Document 1, a discharge circuit is connected in parallel to each of a plurality of batteries connected in series. When this discharge circuit is used, only a specific battery can be discharged, and voltage values in a plurality of batteries can be equalized. The discharge circuit includes a transistor connected in parallel with each battery. By turning on the transistor, the battery corresponding to the transistor can be discharged.

JP 2011-172433 A JP 2003-282155 A

  In the circuit configuration described in Patent Document 1, when the transistor is in an abnormal state, a leakage current may flow through the transistor. In this case, the battery may continue to be discharged due to the occurrence of a leakage current, and the battery may be in an overdischarged state. For this reason, it is necessary to detect the occurrence of leakage current, but this detection method is not disclosed in Patent Document 1.

  The power storage system of the present invention has a plurality of power storage units connected in series, and the plurality of power storage units are connected to a load for charging and discharging. The voltage detection circuit is connected to each power storage unit via a voltage detection line, and detects the voltage value of each power storage unit. Moreover, the discharge circuit is connected in parallel with each power storage unit, and discharges each power storage unit. Based on the detection result of the voltage detection circuit, the controller performs processing (referred to as equalization processing) for aligning the voltage values in the plurality of power storage units with the reference voltage value.

  In the equalization process, the voltage value in the plurality of power storage units is made equal to the reference voltage value by operating the discharge circuit to discharge the power storage unit. Here, the reference voltage value is specified from the detection result of the voltage detection circuit. For example, the lowest voltage value among the voltage values in the plurality of power storage units can be set as the reference voltage value. When a discharge amount of the power storage unit during the equalization process is equal to or greater than a predetermined amount, a leak current is flowing in the voltage detection circuit or the discharge circuit corresponding to the power storage unit indicating the reference voltage value. Determine.

  When a leak current flows in the voltage detection circuit or the discharge circuit, the power storage unit located on the current path through which the leak current flows is discharged. As the leakage current continues to flow, the voltage value of the power storage unit continues to decrease. Here, if the reference voltage value continues to decrease, the discharge circuit may continue to operate as the reference voltage value decreases. Thereby, the amount of discharge of the power storage unit during the equalization process tends to increase.

  Therefore, in the present invention, it is determined that a leakage current is flowing in the voltage detection circuit or the discharge circuit by confirming that the discharge amount during the equalization process is equal to or greater than a predetermined amount. Yes. By determining the occurrence of the leak current, it is possible to take measures to prevent the power storage unit from being overdischarged by leaving the occurrence of the leak current.

  In addition, when a leak current flows through the voltage detection circuit, the voltage value detected by the voltage detection circuit is likely to be lower than the actual voltage value of the power storage unit due to the occurrence of the leak current. In other words, the actual voltage value of the power storage unit tends to be higher than the voltage value detected by the voltage detection circuit. If charging control of the power storage unit is performed in such a state, the power storage unit may be overcharged. Therefore, according to the present invention, it is possible to take measures to prevent the power storage unit from being overcharged by determining the occurrence of leakage current.

  Here, when the duration during the equalization process is a predetermined time or more, it can be determined that the discharge amount during the equalization process is a predetermined amount or more. That is, instead of grasping the discharge amount, it is possible to determine whether or not the leak current is flowing by grasping the duration time during the equalization process. Specifically, when the duration time is equal to or longer than a predetermined time, it can be determined that a leak current is generated. Further, when the duration time is shorter than the predetermined time, it can be determined that no leakage current has occurred.

  The discharge circuit can be provided with a switch that switches between ON for discharging the power storage unit and OFF for not discharging the power storage unit. In this case, a leakage current may flow through the switch due to a switch abnormality. Therefore, when the discharge amount is equal to or greater than the predetermined amount, it can be determined that a leak current is generated in the discharge circuit (switch) corresponding to the power storage unit that indicates the reference voltage value.

  The voltage detection circuit can be provided with a Zener diode connected in parallel with each power storage unit via a voltage detection line. Here, the cathode of the Zener diode can be connected to the positive terminal of the power storage unit, and the anode of the Zener diode can be connected to the negative terminal of the power storage unit. When a current greater than the allowable value flows from the power storage unit to the voltage detection circuit, the Zener diode can be energized to prevent a current greater than the allowable value from flowing into the voltage detection circuit.

  In the configuration in which the Zener diode is provided, a leakage current may flow through the Zener diode due to an abnormality of the Zener diode. Therefore, when the discharge amount is equal to or greater than the predetermined amount, it can be determined that a leak current is generated in the voltage detection circuit (zener diode) corresponding to the power storage unit indicating the reference voltage value. Note that the discharge circuit can discharge the power storage unit using the voltage detection line. Thereby, the current paths in the discharge circuit and the voltage detection circuit can be shared, and the configuration of the discharge circuit and the voltage detection circuit can be simplified.

It is a figure which shows the structure of a battery system. It is a figure which shows the structure of an assembled battery and a monitoring unit in a battery system. It is a flowchart which shows equalization processing. It is explanatory drawing when a leak current flows into a switch in an assembled battery and a monitoring unit. It is a figure explaining the continuation of the equalization process accompanying a leak abnormality. It is a flowchart which shows the process which discriminate | determines leak abnormality.

  Examples of the present invention will be described below.

  The battery system in Example 1 of this invention is demonstrated using FIG. FIG. 1 is a schematic diagram showing the configuration of the battery system in the present embodiment.

  The battery system shown in FIG. 1 can be mounted on a vehicle. Such vehicles include electric vehicles and hybrid vehicles. An electric vehicle is a vehicle that includes only an assembled battery as a power source for the vehicle. A hybrid vehicle is a vehicle provided with a fuel cell, an engine, and the like as a power source for running the vehicle, in addition to an assembled battery described later. In a hybrid vehicle, the assembled battery can be charged using electric power from an external power source. The external power source is a power source (for example, commercial power source) installed outside the vehicle. Note that the present invention can be applied to any system that charges and discharges an assembled battery.

  A positive electrode line PL is connected to the positive electrode terminal of the assembled battery 10, and a system main relay SMR1 is provided in the positive electrode line PL. Moreover, the negative electrode line NL is connected to the negative electrode terminal of the assembled battery 10, and the system main relay SMR2 is provided in the negative electrode line NL. System main relays SMR1, SMR2 are switched between on and off in response to a control signal from controller 30. The controller 30 can connect the assembled battery 10 to a load (a booster circuit 22 described later) by switching the system main relays SMR1 and SMR2 from off to on.

  The current sensor 21 detects the current value Ib flowing through the assembled battery 10 and outputs the detection result to the controller 30. In the present embodiment, a positive value is used as the current value Ib when the assembled battery 10 is discharged, and a negative value is used as the current value Ib when the assembled battery 10 is charged. In the present embodiment, the current sensor 21 is provided on the negative electrode line NL, but is not limited thereto. The current sensor 21 only needs to detect the current value Ib flowing through the assembled battery 10. For example, the current sensor 21 can be provided in at least one of the positive electrode line PL and the negative electrode line NL. In addition, a plurality of current sensors 21 can be provided for one of the positive electrode line PL and the negative electrode line NL.

  The assembled battery 10 is connected to the booster circuit 22 via the positive electrode line PL and the negative electrode line NL. The booster circuit 22 boosts the output voltage of the assembled battery 10 and outputs the boosted power to the inverter 23. The inverter 23 converts the DC power output from the booster circuit 22 into AC power, and outputs the AC power to the motor / generator 24. The motor / generator 24 receives AC power from the inverter 23 to generate kinetic energy for running the vehicle. The vehicle can be driven by transmitting the kinetic energy generated by the motor / generator 24 to the wheels.

  When the vehicle is decelerated or the vehicle is stopped, the motor / generator 24 converts kinetic energy generated during braking of the vehicle into electric energy (AC power). Here, also when the vehicle travels downhill, the motor generator 24 converts kinetic energy into electrical energy in order to generate a braking force. The AC power generated by the motor / generator 24 is converted into DC power by the inverter 23. In addition, the booster circuit 22 steps down the output voltage of the inverter 23 and supplies the lowered power to the assembled battery 10. Thereby, regenerative electric power can be stored in the assembled battery 10.

  The controller 30 includes a memory 31, and the memory 31 stores information used when the controller 30 performs a specific process (particularly, a process described in the present embodiment). The controller 30 has a timer 32, and the timer 32 is used for time measurement. In this embodiment, the memory 31 and the timer 32 are built in the controller 30, but at least one of the memory 31 and the timer 32 may be provided outside the controller 30.

  Information about on / off of the ignition switch of the vehicle is input to the controller 30. When the ignition switch is switched from OFF to ON, the controller 30 connects the assembled battery 10 to the booster circuit 22 by switching the system main relays SMR1 and SMR2 from OFF to ON. Thereby, the battery system shown in FIG. 1 will be in a starting state (Ready-On).

  On the other hand, when the ignition switch is switched from on to off, the controller 30 cuts off the connection between the assembled battery 10 and the booster circuit 22 by switching the system main relays SMR1 and SMR2 from on to off. Thereby, the battery system shown in FIG. 1 will be in a halt condition (Ready-Off).

  The monitoring unit (corresponding to the voltage detection circuit of the present invention) 40 detects the voltage value Vb of the assembled battery 10 or the voltage value Vb of the single cell included in the assembled battery 10 and outputs the detection result. Output to the controller 30. FIG. 2 shows configurations of the assembled battery 10 and the monitoring unit 40.

  As shown in FIG. 2, the assembled battery 10 includes a plurality of unit cells 11 that are electrically connected in series. The number of unit cells 11 constituting the assembled battery 10 can be appropriately set based on the required output of the assembled battery 10 and the like. As the cell 11, a secondary battery such as a nickel metal hydride battery or a lithium ion battery can be used. An electric double layer capacitor can be used instead of the secondary battery.

  In the present embodiment, the monitoring unit 40 detects the voltage value Vb of the single cell (corresponding to the power storage unit of the present invention) 11, but is not limited to this. Specifically, the monitoring unit 40 can detect the voltage value of the battery block (corresponding to the power storage unit of the present invention). Each battery block is configured by a plurality of single cells 11 electrically connected in series, and the assembled battery 10 is configured by connecting the plurality of battery blocks electrically in series. Here, each battery block may include a plurality of single cells 11 electrically connected in parallel.

  The monitoring unit 40 is connected to each unit cell 11 via a plurality of voltage detection lines L1, L2. Here, although omitted in FIG. 2, switches can be provided on the voltage detection lines L <b> 1 and L <b> 2 located between the monitoring unit 40 and the unit cell 11. As this switch, for example, a photo MOS (Metal Oxide Semiconductor) relay can be used.

  The two voltage detection lines L1 are connected to the positive terminal and the negative terminal of the battery pack 10, respectively. The positive terminal of the assembled battery 10 corresponds to the positive terminal of the unit cell 11 positioned at one end of the assembled battery 10 in the circuit configuration of the assembled battery 10 shown in FIG. The negative terminal of the assembled battery 10 corresponds to the negative terminal of the unit cell 11 located at the other end of the assembled battery 10 in the circuit configuration of the assembled battery 10 shown in FIG. In the two unit cells 11 electrically connected in series, the voltage detection line L2 is connected to the negative terminal of one unit cell 11 and the positive terminal of the other unit cell 11.

  Each voltage detection line L1, L2 is provided with a resistance element R11. When a current larger than the allowable current value flows through the resistance element R11, the resistance element R11 is blown, whereby the electrical connection between the monitoring unit 40 and the assembled battery 10 can be cut off. Thereby, it can suppress that an excessive electric current flows into the monitoring unit 40 from the assembled battery 10 (unit cell 11).

  A Zener diode D is electrically connected in parallel to each unit cell 11 via voltage detection lines L1 and L2. The cathode of the Zener diode D is connected to the positive terminal of the unit cell 11, and a resistance element R11 is provided in the current path between the cathode and the positive terminal. The anode of the Zener diode D is connected to the negative terminal of the unit cell 11, and a resistance element R11 is provided in the current path between the anode and the negative terminal.

  The Zener diode D is used for suppressing application of an overvoltage from the assembled battery 10 to the monitoring unit 40. That is, when an overvoltage is applied from the assembled battery 10 to the monitoring unit 40, a current flows through the Zener diode D, thereby preventing the overvoltage from being applied to the monitoring unit 40. Here, the plurality of Zener diodes D are electrically connected in series.

  The voltage detection line L1 is provided with a resistance element R21, and the resistance element R21 is included in the monitoring unit 40. The resistance elements R11 and R21 are electrically connected in series, and the cathode of the Zener diode D is connected to the connection point of the resistance elements R11 and R21. The voltage detection line L2 is branched into two branch lines L21 and L22 inside the monitoring unit 40. The branch line L21 is provided with a resistance element R21, and the branch line L22 is provided with a resistance element R22.

  In the voltage detection line L2, the resistance elements R11 and R21 are electrically connected in series, and the anode of the Zener diode D is connected to the connection point of the resistance elements R11 and R21. In the voltage detection line L2, the resistance elements R11 and R22 are electrically connected in series, and the anode of the Zener diode D is connected to the connection point of the resistance elements R11 and R22. Here, the resistance values of the resistance elements R21 and R22 can be made higher than the resistance value of the resistance element R11.

  A capacitor (flying capacitor) C and a switch SW1 are connected to the voltage detection line L1 and the branch line L22. Specifically, the capacitor C and the switch SW1 are connected to a voltage detection line L1 located between the resistance element R21 and the sampling switch SW21, and a branch line L22 located between the resistance element R22 and the sampling switch SW22. Yes. The sampling switch SW21 is connected to the voltage detection line L1, and the sampling switch SW22 is connected to the branch line L22.

  In addition, regarding the two voltage detection lines L2 connected to the positive electrode terminal and the negative electrode terminal of each unit cell 11, a branch line L21 in one voltage detection line L2 and a branch line L22 in the other voltage detection line L2 include capacitors. C and switch SW1 are connected. Specifically, the capacitor C and the switch SW1 are connected to a branch line L21 located between the resistance element R21 and the sampling switch SW21, and a branch line L22 located between the resistance element R22 and the sampling switch SW22. . Here, the sampling switch SW21 is connected to the branch line L21, and the sampling switch SW22 is connected to the branch line L22.

  The switch SW1 is switched between on and off by receiving a control signal from the controller 30. The switch SW1 is used to equalize voltage values in all the unit cells 11 constituting the assembled battery 10.

  Specifically, when the voltage value of a specific unit cell 11 is higher than the voltage value of another unit cell 11, the switch SW1 electrically connected in parallel with the specific unit cell 11 is switched from OFF to ON. Thus, the specific unit cell 11 can be discharged. That is, when the switch SW1 is turned on, the discharge current of the specific unit cell 11 can flow through the resistance elements R21 and R22, and the voltage value of the specific unit cell 11 can be reduced.

  Thereby, the voltage value of the specific single battery 11 can be aligned with the voltage value of the other single battery 11. Here, the process of aligning the voltage value variation among the plurality of single cells 11 is referred to as an equalization process. The switch SW1 and the resistance elements R11, R21, R22 correspond to the discharge circuit in the present invention.

  Since the capacitor C is electrically connected to the unit cell 11 in parallel via the voltage detection lines L1, L2 or the voltage detection lines L2, L2, the charge stored in the unit cell 11 is stored in the capacitor C. Charged. Thereby, the voltage value of the capacitor C becomes equal to the voltage value of the unit cell 11.

  Sampling switches SW 21 and SW 22 connected to the positive terminal and the negative terminal of each unit cell 11 are connected to a comparator 41. Specifically, the sampling switch SW21 is connected to one input terminal of the comparator 41, and the sampling switch SW22 is connected to the other input terminal of the comparator 41. Here, each sampling switch SW21, SW22 is switched between ON and OFF in response to a control signal from the controller 30. The plurality of sampling switches SW21 and SW22 can be configured by a multiplexer.

  When only the sampling switches SW21 and SW22 corresponding to the specific cell 11 are turned on, the comparator 41 outputs the voltage value Vb of the specific cell 11 (the voltage value of the capacitor C corresponding to the specific cell 11). . Thus, by sequentially turning on the sampling switches SW21 and SW22 corresponding to each unit cell 11, the voltage value Vb of each unit cell 11 can be detected sequentially. The output signal of the comparator 41 is input to the controller 30 after AD conversion. Thereby, the controller 30 can detect the voltage value Vb of each unit cell 11.

  The present invention is not limited to the configuration shown in FIG. That is, the present invention is applied to any configuration that can detect the voltage value Vb of each unit cell 11 (or each battery block described above) and discharge each unit cell 11 (or each cell block). be able to. Specifically, it has a voltage sensor that detects the voltage value Vb of each cell 11 (or each battery block), and a discharge circuit is connected in parallel to each cell 11 (or each cell block). If so, the present invention can be applied. Here, the discharge circuit only needs to include a resistor and a switch. The switch is switched between ON for discharging and OFF for no discharging.

  Next, the equalization process will be described with reference to the flowchart shown in FIG. The process shown in FIG. 3 is executed by the controller 30. Moreover, the process (equalization process) shown in FIG. 3 can be performed, for example, while the ignition switch is OFF.

  In step S <b> 101, the controller 30 detects the voltage value Vb of each unit cell 11 based on the output of the monitoring unit 40. As a result, the controller 30 can detect the voltage values Vb of all the cells 11 constituting the assembled battery 10. Here, the voltage value Vb in the plurality of unit cells 11 may vary due to self-discharge of the unit cells 11 or variations in resistance values (internal resistance) in the plurality of unit cells 11.

  In step S102, the controller 30 specifies a voltage value (minimum value) Vb_min based on the voltage values Vb of the plurality of single cells 11 detected in the process of step S101. As described above, the voltage value (minimum value) Vb_min can be specified when there is a variation in the voltage value Vb in the plurality of single cells 11. Further, in step S102, the controller 30 calculates a voltage difference ΔV between the voltage value Vb and the voltage value (minimum value) Vb_min with respect to the other battery cells 11 excluding the cell 11 indicating the voltage value (minimum value) Vb_min.

  In step S103, the controller 30 determines whether or not the voltage difference ΔV calculated in the process of step S102 is greater than or equal to a threshold value ΔV_th. Here, the threshold value ΔV_th is a value for determining whether or not equalization processing is performed, and can be set as appropriate. For example, the threshold value ΔV_th can be set to a value larger than the voltage difference ΔV that can allow variation in the voltage value Vb (due to detection error). Information regarding the threshold value ΔV_th can be stored in the memory 31.

  When the voltage difference ΔV is equal to or greater than the threshold value ΔV_th, the controller 30 determines in step S104 that an equalization process needs to be performed. On the other hand, when the voltage difference ΔV is smaller than the threshold value ΔV_th, the controller 30 determines that it is not necessary to perform equalization processing, and ends the processing shown in FIG. Here, the determination as to whether or not the equalization processing is performed is performed for all the unit cells 11 other than the unit cell 11 indicating the voltage value (minimum value) Vb_min.

  In step S105, the controller 30 discharges the unit cell 11 by switching the switch SW1 included in the monitoring unit 40 from off to on. Here, the unit cell 11 to be discharged is the unit cell 11 determined to require the equalization process in the process of step S104. By discharging the cell 11, the voltage value Vb of the cell 11 decreases and approaches the voltage value (minimum value) Vb_min.

  In step S106, the controller 30 detects the voltage value Vb of each unit cell 11 based on the output of the monitoring unit 40, and determines whether or not the voltage value Vb is equal to or less than the voltage value (minimum value) Vb_min. Here, when the voltage value Vb is equal to or less than the voltage value (minimum value) Vb_min, the controller 30 stops the discharge of the unit cell 11. On the other hand, when the voltage value Vb is higher than the voltage value (minimum value) Vb_min, the controller 30 continues to discharge the single battery 11. With the process shown in FIG. 3, the voltage values Vb of all the cells 11 constituting the assembled battery 10 can be made equal to the voltage value (minimum value) Vb_min.

  In the configuration shown in FIG. 2, when a leak current flows through the switch SW1 due to a failure of the switch SW1, for example, a current flows through a path indicated by a dotted line in FIG. That is, although the switch SW1 is turned off, the cell 11 is discharged due to leakage current flowing through the switch SW1. In FIG. A leak current flows through the switch SW1 electrically connected in parallel with the k unit cells 11. In addition, No. 1 shown in FIG. k−1, k, k + 1 indicate the numbers of the unit cells 11 included in the assembled battery 10.

  No. When the voltage value Vb of the k unit cell 11 is detected, the voltage value output from the comparator 41 is lower than the actual voltage value of the unit cell 11 by the amount of leakage current flowing through the switch SW1. The voltage value Vd output from the comparator 41 is represented by the following formula (1).

  In the above formula (1), Vcell is the actual voltage value of the unit cell 11, and I_leak is the value of the leak current flowing through the switch SW1. R is a resistance value (combined resistance) of the resistance elements R11, R21, R22 included in the path through which the leak current flows. “I_leak × R” indicates the amount of voltage drop caused by leakage current flowing through the resistance elements R11, R21, and R22.

  As shown in the above equation (1), the voltage value Vd output from the comparator 41 is lower than the actual voltage value Vcell of the unit cell 11. For this reason, if charging / discharging of the cell 11 (assembled battery 10) is controlled based on the voltage value Vd, the cell 11 may be overcharged. Here, when the charging of the cell 11 is controlled, the charging of the cell 11 is controlled so that the voltage value Vd of the cell 11 does not become higher than the predetermined upper limit voltage value Vmax.

  When charging control of the cell 11 is performed based on the voltage value Vd, the cell 11 may be charged until the voltage value Vd reaches the upper limit voltage value Vmax. As described above, when the voltage value Vcell is higher than the voltage value Vd, the voltage value Vcell may exceed the upper limit voltage value Vmax when the voltage value Vd approaches the upper limit voltage value Vmax. May overcharge. On the other hand, if the state in which the leak current flows to the switch SW1 is left unattended, the voltage value Vb of the unit cell 11 continues to decrease, and the unit cell 11 enters an overdischarged state.

  Therefore, in this embodiment, in the circuit that detects the voltage value of the unit cell 11, an abnormality in which a leakage current flows (referred to as a leakage abnormality) is determined. In the example described with reference to FIG. 4, a leak current flows through the switch SW <b> 1, but there is also a possibility that a leak current flows through the Zener diode D. Even when a leakage current flows through the Zener diode D, it is necessary to determine the leakage abnormality.

  In the configuration shown in FIG. 2, the switch SW1 and the Zener diode D are connected to the two voltage detection lines L2, but this is not restrictive. That is, when an electrical element that may cause a leakage current is connected to the two voltage detection lines L2, it is necessary to determine the leakage abnormality as in the present embodiment.

  FIG. 5 shows the voltage behavior (one example) of the cell 11 in which a leakage abnormality has occurred and the voltage behavior (one example) of the cell 11 in which no leakage abnormality has occurred during the equalization process. ing. In FIG. 5, the vertical axis represents the voltage value Vb of the unit cell 11, and the horizontal axis represents time.

  As shown in FIG. 5, the voltage value Vb of the unit cell 11 that is the reference for the equalization process is the voltage value Vb_min, and the voltage value Vb of the unit cell 11 that is not the reference for the equalization process is the voltage value Vb_m. Here, when the equalization process is started, the voltage difference ΔV between the voltage value Vb_m and the voltage value Vb_min is equal to or greater than the threshold value ΔV_th. In addition, when the equalization process is started, only the unit cell 11 indicating the voltage value Vb_m is discharged. In other words, the unit cell 11 indicating the voltage value Vb_min is not discharged.

  When there is no leak abnormality in the unit cell 11 that is the reference for the equalization process, the voltage value Vb_min of the unit cell 11 does not change. That is, the cell 11 serving as the reference for the equalization process is not discharged, so the voltage value Vb_min does not change. In this case, the equalization process ends at time t_end when the voltage value Vb_m decreases to the voltage value Vb_min when the equalization process is started.

  On the other hand, if a leak abnormality has occurred in the unit cell 11 serving as a reference for the equalization process, as shown in FIG. 5, the unit cell 11 in which the leak abnormality has occurred even during the equalization process. Voltage value Vb_min continues to decrease. As a result, at time t_end, the voltage value Vb_min of the cell 11 that is the reference for the equalization process is lower than the voltage value Vb_min when the equalization process is started.

  When the voltage difference ΔV between the voltage value Vb_m and the voltage value Vb_min is equal to or greater than the threshold value ΔV_th at time t_end, the equalization process is continued. As described above, if a leak abnormality has not occurred, the equalization process ends at time t_end. However, if a leak abnormality has occurred, the equalization process continues after time t_end. For this reason, the discharge amount of the cells 11 during the equalization process is different between when the leak abnormality occurs and when the leak abnormality does not occur. That is, the discharge amount when the leak abnormality occurs is larger than the discharge amount when the leak abnormality does not occur.

  Therefore, in this embodiment, the occurrence of leak abnormality is determined by paying attention to the discharge amount of the unit cells 11 during the equalization process. Processing for determining the occurrence of a leak abnormality will be described with reference to the flowchart shown in FIG. The process shown in FIG. 6 is executed by the controller 30.

  In step S201, the controller 30 confirms that the voltage difference ΔV between the voltage value Vb and the voltage value (minimum value) Vb_min is equal to or greater than the threshold value ΔV_th, as described with reference to FIG. Start. In step S202, the controller 30 calculates the discharge amount Q [Ah] during the equalization process. The discharge amount Q can be calculated from the current value during discharge and the discharge time.

  Here, the discharge time is the time during the equalization process, and can be measured using the timer 32. Further, the current value at the time of discharging is calculated from the resistance value of the circuit (in particular, the resistance elements R11, R21, R22) that discharges the unit cell 11 during the equalization process and the voltage value Vb of the unit cell 11 to be discharged. be able to. When the resistance values of the resistance elements R11, R21, and R22 are sufficiently higher than the resistance value (internal resistance) of the unit cell 11, only the resistance values of the resistance elements R11, R21, and R22 can be considered.

  The resistance value of the circuit that discharges the unit cell 11 can be measured in advance. For example, when the occurrence of a leak abnormality is determined for the switch SW1, the resistance value in the current path indicated by the dotted line in FIG. 4 may be measured. The resistance value can be, for example, a combined resistance of the resistance elements R11, R21, and R22. In addition, regarding the Zener diode D, when determining the occurrence of leakage abnormality, the resistance value in the current path when the leak current flows through the Zener diode D may be measured. This resistance value can be a combined resistance of the two resistance elements R11.

  As a method for calculating the discharge amount Q, a known method can be used as appropriate. For example, the discharge amount Q can be calculated by detecting a current value during the equalization process using a current sensor and integrating the current values. On the other hand, when estimating the SOC (State of Charge) of the unit cell 11, the discharge amount Q can be calculated based on the change amount of the SOC accompanying the equalization process. The SOC is the ratio of the current charge capacity to the full charge capacity. As a method for estimating the SOC, a known method can be adopted as appropriate.

  In step S203, the controller 30 determines whether or not the discharge amount Q calculated in the process of step S202 is equal to or greater than a predetermined amount Q_th. The predetermined amount Q_th is a discharge amount from the start of the equalization process until the time t_end (see FIG. 5) is reached, and can be calculated in advance.

  Specifically, the predetermined amount Q_th can be calculated from the resistance value of the circuit that discharges the unit cells 11 during the equalization process and the threshold value ΔV_th. As described above, the resistance value of the circuit that discharges the unit cell 11 can be measured in advance, and the threshold value ΔV_th is also set in advance. For this reason, the predetermined amount Q_th can be calculated in advance. Information regarding the predetermined amount Q_th can be stored in the memory 31.

  When the discharge amount Q is equal to or greater than the predetermined amount Q_th, the controller 30 determines in step S204 that a leak abnormality has occurred with respect to the unit cell 11 serving as a reference for equalization processing. When the discharge amount Q is equal to or greater than the predetermined amount Q_th, as described with reference to FIG. 5, the equalization process is continued even after the time t_end has elapsed. For this reason, the controller 30 can determine the occurrence of a leak abnormality.

  Here, if identification information is allocated to each unit cell 11 constituting the assembled battery 10, the unit cell 11 serving as a reference for equalization processing can be specified. Thereby, the location where the leak abnormality has occurred can be specified. The identification information should just be the information which can distinguish all the cell 11 which comprises the assembled battery 10. FIG. For example, as the identification information, a number assigned to each unit cell 11 can be used.

  On the other hand, when the discharge amount Q is smaller than the predetermined amount Q_th, the controller 30 determines that no leak abnormality has occurred, and ends the processing shown in FIG. That is, when the discharge amount Q is smaller than the predetermined amount Q_th, the equalization process is completed by the time t_end as described with reference to FIG. Therefore, the controller 30 can determine that no leak abnormality has occurred.

  According to the present embodiment, as described above, it is possible to determine whether or not a leakage abnormality has occurred by grasping the discharge amount during the equalization process. If the occurrence of the leak abnormality is determined, it is possible to take measures for suppressing the unit cell 11 from being overdischarged by leaving the leak abnormality. For example, when the leak abnormality occurs, the unit cell 11 can be prevented from being charged / discharged. Specifically, in the configuration shown in FIG. 1, the system main relays SMR1, SMR2 can be prevented from being switched from off to on.

  Further, if the occurrence of a leak abnormality is determined, it is possible to take measures to prevent the unit cell 11 from being overcharged in the charging control of the unit cell 11. For example, when a leak abnormality occurs, the charging of the unit cell 11 can be restricted, or the unit cell 11 can be prevented from being charged.

  In the present embodiment, the discharge amount Q is calculated, and the discharge amount Q is compared with the predetermined amount Q_th to determine whether or not a leak abnormality has occurred, but this is not restrictive. For example, when performing the equalization process, the discharge amount and the discharge time are correlated, and therefore it is possible to determine whether or not a leak abnormality has occurred based on the discharge time.

  Specifically, first, a threshold value related to the discharge time is determined in advance. In FIG. 5, this threshold value (time) is the time from the start of the equalization process until the time t_end is reached. The time from when the equalization process is started is measured by the timer 32 or the like, and when the measurement time (that is, the discharge time) is equal to or greater than the threshold value (time), it can be determined that a leak abnormality has occurred. Here, the measurement time is a time during which the equalization process is continuously performed, and when the equalization process ends, the measurement of time is also ended.

  When the measurement time is equal to or greater than the threshold (time), as described with reference to FIG. 5, the equalization process is continued even after the time t_end has elapsed. For this reason, it can be determined that a leak abnormality has occurred. On the other hand, when the measurement time is shorter than the threshold value (time), the equalization process ends by the time t_end shown in FIG. Therefore, it can be determined that no leak abnormality has occurred.

  In this embodiment, as described with reference to FIG. 3, the voltage value (minimum value) Vb_min is used as the reference value for the equalization processing, but the present invention is not limited to this. A voltage value serving as a reference when performing the equalization process can be set as appropriate. If a leak abnormality occurs with respect to the unit cell 11 indicating the reference voltage value, the reference voltage value continues to decrease as in the case described with reference to FIG. Therefore, it is possible to determine whether or not a leak abnormality has occurred by the same method as in the present embodiment.

  Here, when the occurrence of a leak abnormality is determined, a user or the like can be warned that an abnormality has occurred in the circuit that detects the voltage of the unit cell 11. Accordingly, the user or the like can recognize that an abnormality has occurred, and can prevent the leakage abnormality from being left unattended after determining the occurrence of the leakage abnormality. Therefore, it is possible to prevent the unit cell 11 from being overdischarged due to leakage abnormality.

  As a warning means, a display or a speaker can be used. Specifically, information indicating that an abnormality has occurred can be displayed on the display, or information indicating that an abnormality has occurred can be output as a sound from a speaker. Here, the content displayed on the display and the content of the sound output from the speaker can be set as appropriate.

10: assembled battery, 11: single battery (storage unit), 21: current sensor, 22: booster circuit,
23: Inverter, 24: Motor generator, 30: Controller, 31: Memory,
40: monitoring unit (voltage detection circuit), 41: comparator,
R11, R21, R22: resistance elements, SW1, SW21, SW22: switches,
D: Zener diode, C: capacitor, PL: positive line, NL: negative line
L1, L2: Voltage detection line, L21, L22: Branch line

Claims (6)

A plurality of power storage units connected in series, connected to a load for charging and discharging;
A voltage detection circuit connected to each power storage unit via a voltage detection line and detecting a voltage value of each power storage unit;
A discharge circuit connected in parallel to each of the power storage units and discharging each of the power storage units;
A controller that specifies a reference voltage value from the detection result of the voltage detection circuit, performs an equalization process for operating the discharge circuit to align the voltage values of the plurality of power storage units with the reference voltage value, and
In the voltage detection circuit or the discharge circuit corresponding to the power storage unit indicating the reference voltage value when the discharge amount of the power storage unit during the equalization process is equal to or greater than a predetermined amount, A power storage system characterized by determining that a leak current is flowing.   The controller determines that a discharge amount during the equalization process is equal to or greater than the predetermined amount when a duration time during the equalization process is equal to or greater than a predetermined time. The power storage system according to claim 1. The discharge circuit includes a switch that switches between ON for discharging the power storage unit and OFF for not discharging the power storage unit;
3. The power storage system according to claim 1, wherein the controller determines that a leak current flows in the switch of the discharge circuit corresponding to the power storage unit indicating the reference voltage value. 4. The voltage detection circuit includes a Zener diode that is connected in parallel to each power storage unit via the voltage detection line, a cathode is connected to a positive terminal of the power storage unit, and an anode is connected to a negative terminal of the power storage unit. Including
4. The power storage system according to claim 1, wherein the controller determines that a leak current is flowing in the Zener diode corresponding to the power storage unit indicating the reference voltage value. 5. .   5. The power storage system according to claim 1, wherein the discharge circuit discharges the power storage unit using the voltage detection line. 6. The power storage system according to any one of claims 1 to 5, wherein the reference voltage value is a lowest voltage value specified from a detection result of the voltage detection circuit.