JP6624012B2 - Control system for lithium ion secondary battery - Google Patents

Description

  The present invention relates to a control system for a lithium ion secondary battery.

  Japanese Patent Laying-Open No. 2010-66232 (Patent Document 1) discloses a deterioration determination device capable of determining the occurrence of precipitation deterioration in a lithium ion secondary battery. In this deterioration judging device, when the OCV (Open Circuit Voltage) of the lithium ion secondary battery is in a predetermined region, the SOC and OCV change characteristics are shifted from the characteristics at the time of new product by a specified amount. Sometimes, it is determined that precipitation deterioration has occurred in the lithium ion secondary battery (see Patent Document 1).

JP 2010-66232A JP 2011-222343 A JP 2012-195161 A

  The deterioration determination device described in Patent Literature 1 determines deterioration (occurrence of precipitation) of the lithium ion secondary battery from a change in the OCV of the lithium ion secondary battery. Data can be acquired only when there is no battery input / output, and the timing at which deterioration can be determined is limited. Further, in the above-described deterioration determination device, there is a possibility that the determination result may vary due to a difference in the temperature of the lithium ion secondary battery at the time of OCV calculation.

  Therefore, an object of the present invention is to provide a control system capable of judging the deterioration of a lithium ion secondary battery, making it possible to judge the deterioration during use of the battery, and having high accuracy in consideration of the temperature of the lithium ion secondary battery. This is to realize the deterioration determination.

  A control system for a lithium ion secondary battery according to the present disclosure includes a detection device that detects a temperature, a current, and a voltage of the lithium ion secondary battery, and a control device. The control device uses the previously determined relationship between the temperature of the lithium ion secondary battery and the capacity decrease rate indicating the deterioration rate of the lithium ion secondary battery, and calculates the lithium ion secondary battery from the temperature detected by the detection device. Estimate capacity. The control device calculates the capacity from the current and the voltage detected by the detection device. Then, when the calculation result of the capacity based on the current and the voltage is smaller than the estimation result of the capacity, the control device changes the use range of the lithium ion secondary battery from the first range to the lower SOC side than the first range. Change to the second range. The control device estimates the amount of lithium deposition from the amount of capacity recovery due to the use range being changed to the second range, using a relationship previously obtained between the amount of capacity recovery of the lithium ion secondary battery and the amount of lithium deposition. I do. When the estimated value of the lithium deposition amount is equal to or smaller than the predetermined value, the control device changes the use range from the second range to the first range, and the estimated value of the lithium deposition amount is larger than the predetermined value. In this case, the lithium ion secondary battery is not used.

  In this control system, the capacity of the lithium ion secondary battery is estimated in consideration of the temperature of the lithium ion secondary battery. Then, when the calculation result of the capacity based on the current and the voltage is smaller than the estimation result, it is determined that peculiar deterioration beyond expectation has occurred, and the following processing is executed. That is, the use range of the lithium ion secondary battery is changed to the low SOC side, and the amount of lithium deposition is estimated from the amount of capacity recovery due to the decrease in SOC. Then, continuation or non-use of the lithium ion secondary battery is determined based on the estimation result of the lithium deposition amount.

  According to this control system, it is possible to judge deterioration by estimating the amount of lithium deposition during use of the lithium ion secondary battery, and to perform highly accurate deterioration based on the capacity estimation value in consideration of the temperature of the lithium ion secondary battery. The determination can be realized.

FIG. 1 is a diagram schematically showing a configuration of a vehicle equipped with a control system for a lithium ion secondary battery according to an embodiment of the present invention. 4 is a flowchart illustrating a processing procedure of cell deterioration determination and Li deposition amount estimation performed by an ECU. FIG. 9 is a diagram illustrating an example of a relationship between a cell voltage change amount and a cell capacitance value when a constant current flows. 5 is a flowchart illustrating a procedure for calculating an estimated value of a capacity maintenance ratio. FIG. 4 is a diagram illustrating an example of a relationship between a cell temperature and a cell capacity deterioration rate. FIG. 4 is a diagram showing an example of a relationship between a cell capacity recovery amount and a Li deposition amount. FIG. 4 is a diagram illustrating an example of a relationship between a voltage change speed of a cell and a capacitance value of the cell when a constant current flows.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding portions have the same reference characters allotted, and description thereof will not be repeated.

  FIG. 1 is a diagram schematically showing a configuration of a vehicle 1 on which a control system for a lithium ion secondary battery according to an embodiment of the present invention is mounted. In the following, a case where vehicle 1 is a hybrid vehicle will be representatively described. However, the battery system according to the present invention is not limited to a vehicle mounted on a hybrid vehicle, and is generally applicable to vehicles equipped with a lithium ion secondary battery. The present invention is also applicable to uses other than vehicles.

  Referring to FIG. 1, a vehicle 1 includes an assembled battery 10, a monitoring unit 20, a power control unit (hereinafter, referred to as “PCU (Power Control Unit)”) 30, and a motor generator (hereinafter, “MG (Motor Generator)”). ) ".) 41, 42, the engine 50, the power split device 60, the drive shaft 70, the drive wheels 80, and an electronic control unit (hereinafter referred to as" ECU (Electronic Control Unit) ") 100. Is provided.

  The engine 50 is an internal combustion engine that outputs power by converting combustion energy generated when combusting a mixture of air and fuel into kinetic energy of a moving element such as a piston or a rotor. Power split device 60 includes, for example, a planetary gear mechanism having three rotation shafts of a sun gear, a carrier, and a ring gear. Power split device 60 splits the power output from engine 50 into power for driving MG 41 and power for driving drive wheels 80.

  MGs 41 and 42 are AC rotating electric machines, for example, three-phase AC synchronous motors in which permanent magnets are embedded in rotors. MG 41 is mainly used as a generator driven by engine 50 via power split device 60. The power generated by MG 41 is supplied to MG 42 or battery pack 10 via PCU 30.

  MG 42 mainly operates as a motor, and drives drive wheels 80. MG 42 is driven by receiving at least one of the electric power from battery pack 10 and the electric power generated by MG 41, and the driving force of MG 42 is transmitted to drive shaft 70. On the other hand, when braking the vehicle or reducing the acceleration on the downhill, the MG 42 operates as a generator to perform regenerative power generation. The power generated by MG 42 is supplied to battery pack 10 via PCU 30.

  The battery pack 10 includes a plurality of lithium ion secondary batteries (single cells) connected in series, and stores electric power for driving the MGs 41 and 42. That is, battery pack 10 can supply power to MGs 41 and 42 through PCU 30. Further, battery pack 10 is charged by receiving power generated through PCU 30 when MGs 41 and 42 generate power.

  The monitoring unit 20 includes a voltage sensor 21, a current sensor 22, and a temperature sensor 23. The voltage sensor 21 detects a voltage Vx for each cell of the battery pack 10. The current sensor 22 detects a charge / discharge current Ix of the battery pack 10. The temperature sensor 23 detects a temperature Tx of each cell of the battery pack 10. Then, each sensor outputs a signal indicating the detection result to ECU 100.

  The voltage sensor 21 and the temperature sensor 23 may detect the voltage and the temperature, respectively, using a plurality (for example, several) of cells as a monitoring unit. In this case, the voltage (average value) for each cell can be calculated by dividing the detection value for a plurality of cells by the number of cells.

  PCU 30 performs bidirectional power conversion between battery pack 10 and MGs 41 and 42 according to a control signal from ECU 100. PCU 30 is configured to be able to control the states of MGs 41 and 42 separately. For example, MGU 42 can be in a power running state while MG 41 is in a regenerative (power generation) state. PCU 30 is configured to include, for example, two inverters provided corresponding to MGs 41 and 42 and a converter for boosting the DC voltage supplied to each inverter to the output voltage of battery pack 10 or more.

  The ECU 100 includes a CPU (Central Processing Unit) 101, memories (ROM (Read Only Memory) and RAM (Random Access Memory)) 102, and input / output ports (not shown) for inputting and outputting various signals. It consists of. The ECU 100 controls charging and discharging of the battery pack 10 by controlling the PCU 30 and the engine 50 based on signals received from each sensor and various programs and maps stored in the memory 102.

  As a main control executed by the ECU 100, the ECU 100 determines whether the vehicle is stopped or running for a lithium ion secondary battery (hereinafter, also appropriately referred to as a "cell") constituting the battery pack 10. Regardless, it is determined whether unexpected deterioration (hereinafter, also referred to as “specific deterioration”) has occurred. If it is determined that the specific deterioration has occurred, the ECU 100 lowers the SOC by changing the use range of the cell to the low SOC side, and determines the lithium (Li) from the amount of cell capacity recovery due to the decrease in the SOC. Estimate the amount of precipitation. Then, the ECU 100 determines whether to continue using the cell or not to use the cell based on the estimation result of the Li deposition amount.

  Here, as a method of determining the deterioration of the cell, a method of determining the deterioration of the cell (the occurrence of Li precipitation) from the change in the OCV of the cell is known. Since data can be acquired only when there is no input / output, the timing at which deterioration can be determined is limited. In addition, there is a possibility that the determination result varies due to a difference in cell temperature during OCV calculation.

  Therefore, in vehicle 1 according to this embodiment, the cell capacity is estimated in consideration of cell temperature Tx. If the calculation result of the capacity based on the current Ix and the voltage Vx is smaller than the estimation result, it is determined that the specific deterioration has occurred, and the following processing is executed. That is, the use range of the cell is changed to the low SOC side, and the Li precipitation amount is estimated from the capacity recovery amount due to the SOC decrease. Then, based on the estimation result of the amount of Li deposited, continuation or non-use of the cell is determined. Thereby, regardless of whether the vehicle 1 is stopped or running, the amount of Li deposition can be estimated to determine the deterioration of the cell, and the highly accurate deterioration determination based on the capacity estimation in consideration of the temperature Tx can be performed. Can be realized.

  FIG. 2 is a flowchart illustrating a processing procedure of cell deterioration determination and Li precipitation amount estimation performed by ECU 100. The process shown in this flowchart is executed for each cell constituting the assembled battery 10, but is performed on some appropriately determined representative cells such as the substantially central portion and the end portion of the assembled battery 10. May be executed. Then, the process shown in this flowchart is executed for each of the degradation determination target cells when a substantially constant current Ix flows through the battery pack 10.

  Referring to FIG. 2, ECU 100 acquires a detection value of current Ix from current sensor 22. The ECU 100 also acquires from the voltage sensor 21 the detected value of the voltage Vx for the target cell for the deterioration determination, and calculates the voltage change amount ΔVx of the target cell due to the flow of the current Ix. Further, the ECU 100 obtains the time t during which the substantially constant current Ix flows (step S10). Then, the ECU 100 calculates the current capacity value Ccrnt of the target cell based on the obtained current Ix, voltage change amount ΔVx, and time t (step S20).

  FIG. 3 is a diagram showing an example of the relationship between the cell voltage change amount ΔVx and the cell capacitance value Ccrnt when a constant current Ix flows. FIG. 3 representatively shows the relationship between the voltage change amount ΔVx and the capacitance value Ccrnt when a constant current of Ix = I1 flows through the cell.

  Referring to FIG. 3, lines L1 to L4 indicate a relationship between a voltage change amount ΔVx and a capacitance value Ccrnt when a constant current of Ix = I1 flows for time t = t1 to t4 (t1 <t2 <t3 <t4), respectively. Show the relationship. For example, when the voltage change amount ΔVx of the target cell when the constant current of Ix = I1 flows for the time t = t3 is ΔV1, the current capacitance value Ccrnt of the target cell is C1 based on the line L3. Is required.

  The relationship as shown in FIG. 3 is obtained in advance for each current Ix by an experiment or the like, and is stored in the memory 102 of the ECU 100 as a map. Then, a map corresponding to the current Ix acquired in step S10 of FIG. 2 is selected, and using the map, the current value of the target cell is determined based on the voltage change amount ΔVx and the time t acquired in step S10 of FIG. Is obtained.

  Referring to FIG. 2 again, ECU 100 determines the target cell from an initial capacity Cini indicating a capacity value in an initial state (for example, before product shipment or immediately after shipment) and a capacity value Ccrnt calculated in step S20. The cell capacity maintenance ratio ΔCcrnt is calculated (step S30). The capacity retention rate ΔCcrnt is, for example, a value that represents the current capacity value Ccrnt with respect to the initial capacity Cini in percentage. Note that the initial capacity Cini is obtained in advance in the initial state and stored in the memory 102.

  Next, the ECU 100 acquires the estimated value ΔCx of the capacity maintenance ratio based on the temperature information of the target cell (step S40). The estimated value ΔCx of the capacity maintenance rate based on the temperature information is constantly calculated in another subroutine.

  FIG. 4 is a flowchart illustrating a procedure for calculating the estimated value ΔCx of the capacity maintenance ratio. The process shown in this flowchart is repeatedly executed at predetermined time intervals for each target cell for deterioration determination.

  Referring to FIG. 4, ECU 100 obtains, from temperature sensor 23, a detected value of temperature Tx for the target cell for deterioration determination (step S210). Next, the ECU 100 estimates the capacity deterioration rate β (capacity reduction rate) of the cell based on the acquired temperature Tx (step S220).

  FIG. 5 is a diagram showing an example of the relationship between the cell temperature Tx and the capacity deterioration rate β of the cell. In FIG. 5, the horizontal axis indicates the reciprocal of the temperature Tx, and the vertical axis indicates the natural logarithm of the capacity deterioration rate β. As shown in the figure, it is understood that the capacity deterioration rate β depends on the temperature according to the Arrhenius side.

  Such a relationship between the cell temperature Tx and the capacity deterioration rate β is obtained in advance by experiments or the like, and is stored in the memory 102 of the ECU 100 as a map. Then, based on the temperature Tx of the target cell detected by the temperature sensor 23, the capacity deterioration rate β of the target cell is estimated.

  Referring to FIG. 4 again, ECU 100 integrates the capacity deterioration rate β estimated in step S220, and calculates an estimated value ΔCx of the capacity maintenance rate of the target cell from the integrated value (step S230). As described above, since the capacity deterioration rate β is the capacity reduction rate, the integrated value of the capacity deterioration rate β indicates the amount of capacity reduction of the target cell. Therefore, by dividing the value obtained by subtracting the integrated value of the capacity deterioration rate β from the initial capacity Cini of the target cell by the initial capacity Cini, it is possible to calculate the estimated value ΔCx of the capacity maintenance rate. The estimated value ΔCx of the capacity retention ratio is a value calculated in consideration of the temperature information (temperature Tx) of the target cell.

  Referring again to FIG. 2, in step S30, a current capacity maintenance rate ΔCcrnt based on current Ix and voltage Vx (voltage change amount ΔVx) of the target cell is calculated, and in step S40, a capacity maintenance rate based on temperature information of the target cell. Is obtained, the ECU 100 determines whether or not the capacity maintenance ratio ΔCcrnt calculated in step S30 is smaller than the capacity maintenance ratio estimated value ΔCx obtained in step S40 (step S50). .

  If it is determined that the capacity maintenance ratio ΔCcrnt is equal to or larger than the capacity maintenance ratio estimated value ΔCx (NO in step S50), the deterioration state of the target cell is determined to be within the expected range (that is, it is determined that the specific deterioration has not occurred), ECU 100 ends the processing without executing the subsequent series of processing.

  If it is determined in step S50 that the capacity maintenance ratio ΔCcrnt is smaller than the capacity maintenance ratio estimated value ΔCx (YES in step S50), ECU 100 determines that peculiar deterioration has occurred, and performs the processes in and after step S60. Execute.

  That is, in order to lower the SOC of the target cell, the ECU 100 changes the use range of the target cell from the current first range to the second range lower in SOC than the first range (step S60). . As a result, when the SOC of the target cell decreases, the ECU 100 calculates the capacity recovery amount ΔCy of the target cell due to the SOC decrease due to the change of the use range of the target cell to the low SOC side (step S70). Specifically, the ECU 100 waits for the SOC decrease due to the change of the cell use range to the low SOC side, and calculates the capacity value Ccrnt of the target cell after the SOC decrease by the same calculation as in steps S10 to S30. Then, ECU 100 calculates a capacity recovery amount ΔCy due to the SOC decrease based on a comparison result between the capacity value Ccrnt of the target cell after the SOC decrease and the capacity value Ccrnt before the SOC decrease calculated in step S20.

  Next, the ECU 100 estimates the Li deposition amount ΔLx of the target cell from the magnitude of the calculated capacity recovery amount ΔCy (step S80).

  FIG. 6 is a diagram illustrating an example of the relationship between the cell capacity recovery amount ΔCy and the Li deposition amount ΔLx. Referring to FIG. 6, there is a correlation as shown between the capacity recovery amount ΔCy of the cell and the Li deposition amount ΔLx. Such a relationship between the capacity recovery amount ΔCy of the cell and the Li deposition amount ΔLx is obtained in advance by an experiment or the like, and is stored in the memory 102 of the ECU 100 as a map. Then, based on the capacity recovery amount ΔCy of the target cell calculated in step S70, the Li deposition amount ΔLx of the target cell is estimated.

  In FIG. 6, the threshold value ΔLth of the Li precipitation amount ΔLx is a value indicating an allowable range of Li deposition. If the Li deposition amount ΔLx is equal to or less than the threshold value ΔLth, the Li deposition is regarded as an allowable range. The use of the target cell is continued. On the other hand, when the Li deposition amount ΔLx exceeds the threshold value ΔLth, it is determined that the Li deposition exceeds the allowable range, and the use of the target cell is stopped.

  Therefore, for example, when the capacity recovery amount ΔCy of the target cell is ΔCy1, the Li deposition amount ΔLx is estimated to be ΔL1, and the Li deposition is determined to be in an allowable range, and the use of the target cell is continued. On the other hand, when the capacity recovery amount ΔCy of the cell is ΔCy2, the Li deposition amount ΔLx is estimated to be ΔL2, and it is determined that the Li deposition exceeds the allowable range, and the use of the target cell is stopped.

  Referring to FIG. 2 again, when the Li deposition amount ΔLx of the target cell is estimated based on the magnitude of the capacity recovery amount ΔCy of the target cell in step S80, ECU 100 determines that the Li deposition amount ΔLx is equal to threshold value ΔLth ( (FIG. 6) It is determined whether or not it is below (step S90). When it is determined that Li precipitation amount ΔLx is equal to or smaller than threshold value ΔLth (YES in step S90), ECU 100 changes the use range of the cell changed in step S60 from the second range to the first range. (Step S100). That is, in this case, it is determined that the Li deposition is within the allowable range, the use range of the target cell is returned, and the use of the target cell is continued.

  On the other hand, if it is determined in step S90 that Li deposition amount ΔLx is greater than threshold value ΔLth (NO in step S90), it is determined that Li deposition is outside the allowable range, and ECU 100 determines that the target cell is used. The operation stops (step S110).

  As described above, in the present embodiment, the capacity (capacity maintenance rate) of the lithium ion secondary battery is estimated in consideration of the temperature Tx of the lithium ion secondary battery (cell). Then, when the calculation result of the capacity (capacity maintenance rate) based on the current Ix and the voltage Vx is smaller than the estimation result, it is determined that peculiar deterioration beyond expectation has occurred, and the following processing is executed. You. That is, the usage range of the cell is changed to the low SOC side, and the Li deposition amount is estimated from the cell capacity recovery amount ΔCy due to the SOC decrease. Then, based on the estimation result of the amount of Li deposited, continuation or non-use of the cell is determined.

  As described above, according to this embodiment, regardless of whether the vehicle 1 is stopped or running, it is possible to estimate the amount of Li deposition during use of the battery and determine deterioration, and to determine the battery temperature Tx , It is possible to realize highly accurate deterioration determination based on capacity estimation in consideration of the above.

  In the above-described embodiment, as shown in FIG. 3, the current value of the target cell is determined using the relationship between the voltage change amount ΔVx of the cell when the constant current Ix flows and the capacitance value Ccrnt of the cell. Although the capacitance value Ccrnt is calculated, it is also possible to calculate the current capacitance value Ccrnt of the target cell from the speed of voltage change when the current Ix flows.

  FIG. 7 is a diagram illustrating an example of a relationship between the voltage change rate dVx of the cell and the capacitance Ccrnt of the cell when a constant current Ix flows. FIG. 7 representatively shows the relationship between the voltage change rate dVx and the capacitance Ccrnt when a constant current of Ix = I1 flows through the cell.

  Referring to FIG. 7, the relationship between the voltage change rate dVx when a constant current flows through the cell and the capacitance value Ccrnt is obtained in advance for each current Ix by an experiment or the like, and is stored in the memory 102 of the ECU 100 as a map. Then, when a constant current Ix flows through the target cell, a map corresponding to the current Ix is selected, and the speed of change of the voltage Vx is calculated, and the calculated voltage change speed is calculated using the selected map. Is used to determine the current capacitance value Ccrnt of the target cell.

  In the above description, monitoring unit 20 corresponds to one embodiment of the “detection device” of the present invention, and ECU 100 corresponds to one embodiment of the “control device” of the present invention. Then, the monitoring unit 20 and the ECU 100 constitute a “control system” in the present invention.

  The embodiments disclosed this time are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description of the embodiments, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  REFERENCE SIGNS LIST 1 vehicle, 2 battery system, 10 battery pack, 20 monitoring unit, 21 voltage sensor, 22 current sensor, 23 temperature sensor, 30 PCU, 41, 42 MG, 50 engine, 60 power split device, 70 drive shaft, 80 drive wheels , 100 ECU, 101 CPU, 102 memory.

Claims (1)

A control system for a lithium ion secondary battery,
A detecting device for detecting the temperature, current and voltage of the lithium ion secondary battery,
With a control device,
The control device includes:
Using a predetermined relationship between the temperature of the lithium ion secondary battery and the capacity reduction rate indicating the rate of deterioration of the lithium ion secondary battery, the temperature of the lithium ion secondary battery is calculated based on the temperature detected by the detection device. Estimate capacity,
Calculating the capacitance from the current and the voltage detected by the detection device,
When the calculation result of the capacity based on the current and the voltage is smaller than the estimation result of the capacity, the use range of the lithium ion secondary battery is changed from a first range to a low SOC side lower than the first range. Change to the range of 2,
Using a predetermined relationship between the capacity recovery amount of the lithium ion secondary battery and the lithium deposition amount, the lithium deposition amount is calculated from the capacity recovery amount due to the use range being changed to the second range. Presumed,
When the estimated value of the lithium deposition amount is equal to or less than a predetermined value, the use range is changed from the second range to the first range,
A control system for a lithium ion secondary battery, wherein the lithium ion secondary battery is not used when the estimated value is larger than the predetermined value.

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