JP2023076984A - battery system - Google Patents

Abstract

To detect generation of leakage current even in a voltage detection circuit or a discharge circuit other than a voltage detection circuit or a discharge circuit corresponding to a block indicating a reference voltage of an equalization process.SOLUTION: A battery system 2 comprises: a battery pack 10; an equalization unit 30; and a battery ECU 50. The battery pack 10 includes a plurality of serially connected electric cells. The equalization unit 30 is configured to execute equalization control for equalizing voltages VB of the electric cells. The battery ECU 50 measures, when the equalization control is not executed, voltage drop amounts ΔVB of the electric cells, and determines generation of leakage current.SELECTED DRAWING: Figure 4

Description

TECHNICAL FIELD The present disclosure relates to a battery system, particularly a battery system including an assembled battery including a plurality of blocks connected in series.

In a battery system that includes a battery pack that includes multiple blocks connected in series, each block loses its strength after long-term use due to self-discharge of the single cells (battery cells) that make up each block and individual differences in internal resistance. variation occurs in the voltage of In the power storage system disclosed in Japanese Patent Application Laid-Open No. 2014-223003 (Patent Document 1), a voltage detection circuit that detects the voltage of the power storage unit (block) is provided, and a voltage difference of a predetermined value or more is detected between each power storage unit (block). If there is, a discharge circuit connected in parallel with each storage unit is used to perform discharge, thereby performing an equalization process to equalize the voltage values of the plurality of storage units.

When leakage current occurs in the voltage detection circuit or discharge circuit, the voltage value detected by the voltage detection circuit is lower than the actual value in the block (storage unit) where the leakage current occurs, and the block adjacent to the block where the leakage current occurs. will be higher than the actual value. Therefore, if charging/discharging is performed based on the voltage value detected by the voltage detection circuit, over-discharging or over-charging may occur.

In Patent Document 1, the amount of discharge during the equalization process is used to determine whether or not a leakage current is generated in a voltage detection circuit or a discharge circuit corresponding to a block indicating a reference voltage for the equalization process. ing.

Japanese Unexamined Patent Application Publication No. 2014-223003

In Patent Document 1, the leakage current of the voltage detection circuit or the discharge circuit corresponding to the block (storage unit) indicating the reference voltage for the equalization process is determined. Leakage current was not determined.

An object of the present disclosure is to make it possible to detect the occurrence of leakage current even in a voltage detection circuit or discharge circuit other than the voltage detection circuit or discharge circuit corresponding to the block indicating the reference voltage for equalization processing.

The battery system of the present disclosure includes a plurality of blocks connected in series, an assembled battery that is connected to a load and charges and discharges, a voltage detection circuit that detects the voltage of each of the plurality of blocks, and a plurality of blocks in parallel. When the connection between the connected discharge circuit, the equalization control unit that executes equalization control for equalizing the voltages of the plurality of blocks, and the load is cut off and the equalization control is not executed, and an abnormality determination unit that determines occurrence of leak current in the voltage detection circuit or the discharge circuit by measuring the amount of voltage drop in the block.

When a leakage current occurs in the voltage detection circuit or the discharge circuit, the voltage detection circuit or the discharge circuit in which the leakage current occurs when the connection with the load is cut off and the equalization control is not executed. The voltage of the block corresponding to drops due to discharge due to leakage current. By measuring the amount of voltage drop in a block whose occurrence of leak current is to be detected, it is possible to determine the occurrence of leak current in that block.

According to the present disclosure, it is possible to detect the occurrence of leakage current even in a voltage detection circuit or a discharge circuit other than the voltage detection circuit or discharge circuit corresponding to the block indicating the reference voltage for equalization processing.

1 is a diagram schematically showing the overall configuration of a vehicle 1 equipped with a battery system according to the present embodiment; FIG. 2 is a diagram illustrating the configuration of a battery system 2; FIG. FIG. 10 is a diagram showing a current flow when equalization control is executed to eliminate unevenness in voltage VB; 4 is a flowchart showing equalization control and leak current detection processing executed by a battery ECU 50. FIG. It is a figure which shows the voltage detection circuit 21M in a modification.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are denoted by the same reference numerals, and the description thereof will not be repeated.

A configuration in which the battery system according to the present embodiment is mounted on an electric vehicle will be described below as an example. However, the battery system according to the present embodiment can be applied not only to electric vehicles but also to general vehicles (hybrid vehicles, plug-in hybrid vehicles, fuel cell vehicles, etc.) equipped with an assembled battery for running. Furthermore, the application of the battery system according to the present embodiment is not limited to vehicle use, and may be stationary use, for example.

FIG. 1 is a diagram schematically showing the overall configuration of a vehicle equipped with a battery system according to the present embodiment. Referring to FIG. 1 , vehicle 1 is an electric vehicle and includes battery system 2 . The battery system 2 includes an assembled battery 10 , a monitoring unit 20 , an equalization unit 30 , a system main relay (SMR) 40 , and a battery ECU (Electronic Control Unit) 50 . The vehicle 1 further includes a power control unit (PCU: Power Control Unit) 60 , a motor generator 70 , driving wheels 80 and an integrated ECU 90 .

The assembled battery 10 includes a plurality of single cells (battery cells) 101 to 10M (see FIG. 2) connected in series. Battery pack 10 stores electric power for driving motor generator 70 and supplies electric power to motor generator 70 through PCU 60 . The assembled battery 10 is charged by receiving generated power through the PCU 60 when the motor generator 70 generates power. The assembled battery 10 can be externally charged using an external power supply (commercial power supply) via an inlet or the like (not shown).

Monitoring unit 20 includes a voltage detection circuit 21 , a current sensor 22 and a temperature sensor 23 . The voltage detection circuit 21 detects the voltage VB of the cells forming the assembled battery 10 . Current sensor 22 detects a current IB that is input to and output from assembled battery 10 . Temperature sensor 23 detects temperature TB of assembled battery 10 . These detection results are input to the battery ECU 50 .

The equalization unit 30 is provided to eliminate inequality in SOC (State Of Charge) among the plurality of single cells forming the assembled battery 10 . In the assembled battery 10, variations occur in the voltage VB of the plurality of cells over time due to variations in the self-discharge current, variations in the current consumption of the voltage detection circuit 21, individual differences in internal resistance, and the like. obtain. Variations in voltage among a plurality of single cells can also be caused by variations in charging efficiency. If the voltage VB of the cells varies, the SOCs of the cells become uneven. Equalization unit 30 discharges any one of the plurality of cells (one or more cells) in accordance with a control command from battery ECU 50 to eliminate unevenness in voltage VB of the cells. Detailed configurations of the assembled battery 10, the voltage detection circuit 21, and the equalization unit 30 will be described with reference to FIG.

SMR 40 is electrically connected to a power line connecting assembled battery 10 and PCU 60 . SMR 40 switches between power supply and cutoff between assembled battery 10 and PCU 60 in accordance with a control command from battery ECU 50 . The SMR 40 is closed (ON) when the vehicle 1 is in the IG-ON (ignition ON) state. Also, in the IG-OFF (ignition off) state, the SMR 40 is opened (OFF).

The battery ECU 50 includes a processor 51 such as a CPU (Central Processing Unit), a memory 52 such as a ROM (Read Only Memory) and a RAM (Random Access Memory), and input/output ports (not shown) for inputting and outputting various signals. ) and Battery ECU 50 manages assembled battery 10 based on signals received from monitoring unit 20 and programs and maps (described later) stored in memory 52 .

PCU 60 executes bidirectional power conversion between assembled battery 10 and motor generator 70 in accordance with a control command from integrated ECU 90 . PCU 60 includes, for example, a converter that boosts the DC power of battery pack 10 and an inverter (none of which is shown) that converts the DC power boosted by the converter into AC power and outputs the AC power to motor generator 70 . The PCU 60 corresponds to the "load" of the present disclosure.

Motor generator 70 is an AC rotating electrical machine, such as a three-phase AC synchronous motor in which permanent magnets are embedded in a rotor. Motor generator 70 is driven using power from assembled battery 10 . The driving force of motor generator 70 is transmitted to driving wheels 80 . On the other hand, the motor generator 70 performs regenerative power generation (regenerative braking) when braking the vehicle 1 or reducing the acceleration on a downward slope. Electric power generated by motor generator 70 is supplied to assembled battery 10 via PCU 60 .

Integrated ECU 90, like battery ECU 50, includes a processor, memory, and input/output ports (none of which are shown). Integrated ECU 90 controls the entire vehicle 1 in cooperation with battery ECU 50 based on signals received from various sensors and programs and maps stored in memory. The integrated ECU 90 may be configured separately for each function, or may be configured integrally with the battery ECU 50 .

FIG. 2 is a diagram illustrating the configuration of the battery system 2. As shown in FIG. In the assembled battery 10, a plurality of single cells (battery cells) 101 to 10M are connected in series. The cells 101 to 10M are chargeable/dischargeable secondary batteries, such as lithium ion batteries and nickel metal hydride batteries. Instead of the plurality of single cells 101 to 10M, the assembled battery 10 may be configured by connecting in series a module (stack) in which a plurality of single cells (battery cells) are connected in parallel. . In the present disclosure, each of the single cells 101 to 10M or each module in which a plurality of single cells are connected in parallel is also referred to as a "block."

The voltage detection circuit 21 detects voltages of the cells 101 to 10M via a plurality of voltage detection lines L1, branch lines L11, and branch lines L12. The voltage detection line L1 is connected to the positive terminal of the cell 101 and the negative terminal of the cell 10M. Further, the voltage detection line L1 is connected to the negative terminal of one cell and the negative terminal of the other cell between the cells 101 to 10M.

A fuse F and a chip bead Cb are provided on the voltage detection line L1. The fuse F melts when an overcurrent occurs to protect the circuit. The chip bead Cb reduces applied stress when a surge voltage is instantaneously applied.

A Zener diode D is connected in parallel to the cells 101 to 10M via a voltage detection line L1. The cathode of the Zener diode D is connected to the positive terminal side of the corresponding cell, and the anode is connected to the negative terminal side of the corresponding cell. When an overvoltage is applied from the assembled battery 10 (single cell) to the voltage detection circuit 21, a current flows through the Zener diode D, thereby protecting the voltage detection circuit 21 from the overvoltage.

The voltage detection line L1 branches into a branch line L11 and a branch line L12 on the monitor unit 20 side of the Zener diode D. FIG. The branch line L11 is connected to the comparator 21a through the switch So, and the branch line L12 is connected to the comparator 21a through the switch Sh. For the switch So and the switch Sh, for example, a photo MOS (Metal Oxide Semiconductor) relay can be used. A branch line L11 branched from the voltage detection line L1 connected to the positive terminal of the cell 101 arranged on the positive output terminal side of the assembled battery 10 is not connected to the comparator 21a. Also, the voltage detection line L1 connected to the negative terminal of the cell 10M arranged on the negative output terminal side of the assembled battery 10 does not include the branch line L12.

A resistor R1 is provided on the branch line L12. A capacitor (flying capacitor) C is provided between the branch line L12 connected to the positive terminal of each cell and the branch line L11 connected to the negative terminal. In branch line L12, capacitor C is connected between resistor R1 and switch Sh, and resistor R1 and capacitor C form an RC low-pass filter. The capacitor C is connected in parallel with the corresponding cell 101-10M, the charge of the corresponding cell 101-10M is charged in the capacitor C, and the voltage value of the capacitor C changes to the corresponding cell 101-10M. equal to the voltage value. By turning ON (closed) the switch Sh and the switch So corresponding to the specific cell 101-10M, the comparator 21a outputs the voltage VB of the specific cell 101-10M. As a result, the monitoring unit 20 can detect the voltage VB of each of the cells 101 to 10M using the voltage detection circuit 21 by sequentially turning on the switches Sh and So corresponding to the cells 101 to 10M. can.

The equalization unit 30 is composed of a discharge resistor Rd provided in the branch line L11 and a switch S1 that conducts (closes)/shuts off (opens) the adjacent branch lines L11. Switch S1 is switched between ON (closed) and OFF (open) by receiving a control signal from battery ECU 50 . FIG. 3 is a diagram showing the flow of current when equalization control is executed to eliminate unevenness in voltage VB. FIG. 3 shows a case where the voltage VB of the cell 102 is higher than the reference voltage (target voltage) Vh, the cell 102 is discharged, and equalization control is executed. When the voltage VB of the cell 102 is higher than the reference voltage Vh, the switch S1 corresponding to the cell 102 is turned ON (closed). When the switch S1 corresponding to the cell 102 is turned on (closed), the current discharged from the cell 102 is consumed by the discharge resistors Rd, Rd as indicated by the dashed-dotted arrow in FIG. The voltage VB of the single battery 102 is lowered, and the battery voltage is equalized. An electric circuit configured by the discharge resistor Rd and the switch S1 corresponds to the "discharge circuit" of the present disclosure.

In the battery system 2, due to deterioration or abnormality of the Zener diode D, capacitor C, switch S1, switch Sh, switch So, etc., a slight leak current may occur in the voltage detection circuit 21, the equalization unit 30 (discharge circuit), etc. have a nature. When a leak current occurs, the voltage VB detected by the voltage detection circuit 21 becomes lower than the actual value of the cell in which the leak current occurs, and becomes higher than the actual value of the cell adjacent to the cell in which the leak current occurs. Therefore, if charging/discharging is performed based on the voltage VB detected by the voltage detection circuit 21, over-discharging or over-charging may occur. Therefore, it is desirable to detect the occurrence of leakage current and avoid overdischarge and overcharge.

In this embodiment, when the equalization control is not executed, the occurrence of leakage current is detected by measuring the amount of drop in the voltage VB of the cells 101-10M.

FIG. 4 is a flow chart showing equalization control and leak current detection processing executed by battery ECU 50 . This flowchart is executed when the vehicle 1 is IG-OFF and the SMR 40 is OFF (open).

In step (hereinafter, step is abbreviated as "S") 10, it is determined whether equalization control of the assembled battery 10 is necessary. The voltage detection circuit 21 detects the voltage VB of each cell 101 to 10M, and sets the lowest voltage value among the detected voltages VB as the reference voltage Vh. Next, the voltage difference ΔVk between the voltage VB of each cell 101 to 10M and the reference voltage Vh is calculated. Then, it is determined whether or not the voltage difference ΔVk is equal to or greater than the threshold value Vs. The threshold value Vs is a value for determining whether or not equalization control is to be performed, and can be appropriately set through experiments or the like in consideration of the detection error of the voltage VB. If there is a unit cell whose voltage difference ΔVk is equal to or greater than the threshold value Vs, equalization control for that unit cell is necessary, so an affirmative determination is made and the process proceeds to S11. If there is no cell with the voltage difference ΔVk equal to or greater than the threshold value Vs, a negative determination is made and the process proceeds to S13.

In S11, it is determined whether or not a condition for interrupting the equalization control is satisfied. The conditions are, for example, a) that the frequency peak (battery temperature frequency peak) of the temperature TB of the assembled battery 10 in use up to the current IG-OFF of the vehicle 1 is equal to or less than the threshold value TBf, and b) the vehicle 1 this time. The SOC frequency peak of the assembled battery 10 in use until IG-OFF is equal to or less than the threshold value Sf, and c) the cell that is the target of equalization control (the cell whose voltage difference ΔVk is equal to or greater than the threshold value Vs) is equal to or greater than a predetermined value Tf. The battery temperature frequency peak is the value of the temperature TB that appears most frequently in the distribution of the temperature TB of the assembled battery 10 in use. The SOC frequency peak is the SOC value that appears most frequently in the SOC distribution in use. The equalization processing cumulative time is the cumulative (cumulative) time during which the equalization processing was executed in the unit cell.

In S11, for example, when all the conditions a to c are satisfied, it may be determined that the interruption condition is satisfied, and the process may proceed to S13. Alternatively, when a and b are established, a and c are established, or when b and c are established, it may be determined that the interruption condition is established, and the process proceeds to S13. If it is determined in S11 that the interruption condition is not satisfied, the process proceeds to S12.

In S12, the equalization process for the single cell, which is the target of the equalization control, is executed for a certain period of time. By turning ON (closed) the switch S1 corresponding to the cell whose voltage difference ΔVk is equal to or greater than the threshold value Vs, the current discharged from the cell is consumed by the discharge resistors Rd and Rd, as shown in FIG. As a result, the voltage VB of the single battery decreases, and the battery voltages are equalized. After the equalization process has been executed for a certain period of time, the switch S1 is turned OFF (opened) to terminate the equalization process and return to S10. Note that the execution time of the equalization process in S12 is added to the equalization process accumulated time.

If the equalization process of S12 is executed, or if the first process after IG-OFF is negatively determined in S10 or affirmatively determined in S11, the process proceeds to S13. In S13, the amount of drop ΔVB of the voltage VB of the cells 101 to 10M is measured over a predetermined period of time while the switch S1 is kept OFF (open). For example, after measuring the drop amount ΔVB of the voltage VB of the cells 101 to 10M over 6 to 12 hours, the process proceeds to S14.

In S14, it is determined whether or not the drop amount ΔVB of each of the cells 101 to 10M is equal to or greater than a predetermined value α. The predetermined value α is a judgment value for judging whether or not a leak current is generated, and can be appropriately set through experiments or the like in consideration of detection errors of the voltage VB. If there is a unit cell whose drop amount ΔVB is equal to or greater than the predetermined value α, a leak current is generated in the voltage detection circuit 21 or the discharge circuit (equalization unit 30) corresponding to the unit cell, so the affirmative determination is made. It is judged, and it progresses to S15. If there is no unit cell with the amount of descent ΔVB equal to or greater than the predetermined value α, a negative determination is made, and the current processing ends.

In S15, it is determined that a leakage current is generated in the voltage detection circuit 21 or the discharge circuit corresponding to the unit cell whose drop amount ΔVB is equal to or greater than a predetermined value α, and MIL (Malfunction Indication Lamp) is turned on, and after a diagnostic code indicating a leak failure is stored in the memory 52, the current process is terminated.

In the present embodiment, when the equalization control is not executed, in S13, the amount of drop in the voltage VB of the cells 101 to 10M is measured to detect the occurrence of leakage current. Therefore, it is possible to detect the occurrence of leak current in the voltage detection circuit 21 or the discharge circuit (equalization unit 30) other than the voltage detection circuit or discharge circuit corresponding to the cell indicating the reference voltage for the equalization process.

As in Patent Document 1, when detecting the occurrence of leakage current from the amount of discharge during the equalization process, it is necessary to accurately detect the voltage VB of the adjacent cells by the discharge due to the equalization process. may not be possible. In the present embodiment, when the equalization control is not executed, the occurrence of leakage current is determined by measuring the amount of drop in the voltage VB of the cells 101 to 10M. voltage VB can be detected, and the presence or absence of leakage current can be accurately determined.

In the present embodiment, even if it is determined in S10 that the equalization control is necessary, when it is determined in S11 that the equalization control interruption condition is satisfied, in S13 the unit cell By measuring the amount of drop in the voltage VB from 101 to 10M, occurrence of leakage current is detected. Therefore, even if there is some variation in voltage between the cells, the equalization control is interrupted and the occurrence of leakage current is determined. can.

In the present embodiment, the occurrence of leakage current is determined based on whether the amount of drop ΔVB of each of the cells 101 to 10M is equal to or greater than a predetermined value α. It may be determined that a leak current is generated when the quantity dVB/dt is equal to or greater than a predetermined value β. Also, the amount of descent ΔVB of each of the cells 101 to 10M is compared to calculate the difference between the amounts of descent ΔVB of the cells 101 to 10M. It may be determined that a leakage current is generated in the voltage detection circuit 21 or the like corresponding to .

(Modification)
FIG. 5 is a diagram showing a voltage detection circuit 21M in a modification. In the above-described embodiment, the capacitor C, which is provided between the branch line L12 and the branch line L11 and also functions as an RC low-pass filter, is used as a flying capacitor for detecting the voltage VB. The voltage detection circuit 21M of the modification includes a flying capacitor for voltage VB detection.

Referring to FIG. 5, switch So provided in branch line L11 (see FIG. 2) corresponding to each cell is connected to comparator 21a via switch Sw2 by voltage detection line L21. Also, the switch Sh provided in the branch line L12 (see FIG. 2) corresponding to each cell is connected to the comparator 21a via the switch Sw1 by the voltage detection line L22. PhotoMOS relays, for example, can be used for the switches Sw1 and Sw2.

A flying capacitor Cf is provided between the voltage detection line L21 and the voltage detection line L22 on the cell side of the switches Sw1 and Sw2. The monitoring unit 20 turns on (closes) the switches Sh and So corresponding to the selected (detecting the voltage VB) cells 101 to 10M while the switches Sw1 and Sw2 are turned off (opened). When the potential of the flying capacitor Cf becomes equal to the voltage of the selected cell, the monitoring unit 20 turns off (opens) the switch Sh and the switch So corresponding to the selected cell 101 to 10M, and switches Sw1 and The switch Sw2 is turned ON (closed). As a result, the comparator 21a outputs the voltage VB of the selected cell 101-10M. By sequentially turning on the switches Sh and So corresponding to the cells 101 to 10M, the monitoring unit 20 can detect the voltage VB of the selected cells 101 to 10M using the voltage detection circuit 21M.

According to this modification, the capacitor C can be used exclusively for the RC low-pass filter, making it easier to obtain an appropriate cutoff frequency.

Exemplifying embodiments in the present disclosure, the following aspects can be exemplified.
1) An assembled battery (10) including a plurality of blocks (101 to 10M) connected in series, connected to a load (60) for charging and discharging, and detecting the voltage of each of the plurality of blocks (101 to 10M). A voltage detection circuit (21), a plurality of discharge circuits (Rd, S1) connected in parallel to a plurality of blocks (101 to 10M), and an equalization control that equalizes the voltages of the plurality of blocks (101 to 10M). When the connection between the equalization control unit (50, S10 to S12) that executes An abnormality determination unit ( 50, S13-S15), and a battery system comprising:

2) In 1, the battery system is mounted on the vehicle (1), and the equalization control unit (50, S10-S12) controls each block (101-10M) when the ignition of the vehicle (1) is off. When the difference between the voltages (VB) of the two is equal to or greater than a predetermined value, the discharge circuit (Rd, S1) is used to discharge, thereby executing equalization control.

3) In 2, the equalization control unit (50, S10 to S12), when the equalization control interruption condition is established, even if the difference in voltage (VB) of each block (101 to 10M) is equal to or greater than a predetermined value, , the equalization control (S10) is stopped, and the abnormality determination unit (50, S13-S15) measures the amount of voltage drop in the blocks (101-10M) to determine whether the voltage detection circuit (21) or the discharge circuit Determine the occurrence of leakage current at (Rd, S1).

4) In 3, "the frequency peak of the temperature (TB) of the assembled battery (10) is equal to or less than the first threshold (TBf)", "the SOC frequency peak of the assembled battery (10) is equal to or less than the second threshold (Sf) or "the accumulated equalization processing time of blocks (101 to 10M) subject to equalization control is equal to or greater than a predetermined value (Tf)." It is determined that the control interruption condition is satisfied.

The embodiments disclosed this time should be considered as examples and not restrictive in all respects. The scope of the present disclosure is indicated by the scope of claims rather than the description of the above-described embodiments, and is intended to include all modifications within the scope and meaning equivalent to the scope of the claims.

1 vehicle, 2 battery system, 10 assembled battery, 101 to 10M cells, 20 monitoring unit, 21 voltage detection circuit, 21a comparator, 22 current sensor, 23 temperature sensor, 30 equalization unit, 40 SMR, 50 battery ECU, 51 Processor, 52 Memory, 60 PCU, 70 Motor Generator, 80 Drive Wheel, 90 Integrated ECU, C Capacitor, Cb Chip Bead, Cf Flying Capacitor, D Zener Diode, F Fuse, L1 Voltage Detection Line, L11 Branch Line, L12 Branch Line , L21 voltage detection line, L22 voltage detection line, R1 resistor, Rd discharge resistor, S1 switch, Sh switch, So switch, Sw1 switch, Sw2 switch.

Claims (1)

an assembled battery that includes a plurality of blocks connected in series and is connected to a load for charging and discharging;
a voltage detection circuit that detects the voltage of each of the plurality of blocks;
a plurality of discharge circuits connected in parallel to the plurality of blocks;
an equalization control unit that executes equalization control to equalize the voltages of the plurality of blocks;
When the connection between the assembled battery and the load is cut off and the equalization control is not executed, the voltage detection circuit measures the amount of voltage drop in each of the plurality of blocks, or and an abnormality determination unit that determines occurrence of leakage current in the plurality of discharge circuits.

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