Battery system
The battery system improves busbar temperature estimation through current-based evaluation functions, ensuring accurate power management to prevent overheating and maintain vehicle performance.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- TOYOTA JIDOSHA KK
- Filing Date
- 2024-12-23
- Publication Date
- 2026-07-03
AI Technical Summary
Existing methods for protecting bus bars in battery packs from overheating, such as using temperature detection units, increase costs and may lead to excessive power restrictions, affecting the performance of electric vehicles.
A battery system that includes a control device to estimate busbar temperature using current sensors, setting allowable power limits based on evaluation functions that account for heat generation and conduction, thereby reducing excessive power restrictions.
Accurate busbar temperature estimation allows for precise power control, preventing overheating while minimizing performance degradation.
Smart Images
Figure 2026111191000001_ABST
Abstract
Description
Technical Field
[0001] The present disclosure relates to a battery system.
Background Art
[0002] Japanese Patent Application Laid-Open No. 2016-122577 (Patent Document 1) describes an attachment structure for attaching a temperature detection unit to a bus bar that electrically connects electrode terminals of a plurality of power storage elements constituting a battery pack mounted on an electric vehicle.
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0004] As a protection measure against overheating of the bus bar, a method of limiting the power input to and output from the battery pack according to the temperature rise of the bus bar can be adopted without increasing the heat resistance specification level of the bus bar. According to Patent Document 1 above, the temperature of the bus bar can be directly detected using a temperature detection unit, but there is a concern that the cost for attaching the temperature detection unit to the bus bar increases.
[0005] In the above protection measure for the bus bar, by limiting the power input to and output from the battery pack with respect to the heat generation of the bus bar, there is a possibility that the electric vehicle may not be able to secure the desired output and the running performance of the electric vehicle may deteriorate. In order to suppress excessive limitation of the power input to and output from the battery pack, it is required to accurately estimate the temperature of the bus bar. <00000३३> The present disclosure has been made to solve such problems, and an object thereof is to improve the estimation accuracy of the temperature of the bus bar in the battery pack.
Means for Solving the Problems
[0007] A battery system according to this disclosure comprises a battery pack including a plurality of cells, each having electrode terminals; a busbar for electrically connecting the electrode terminals of the plurality of cells; a current sensor for detecting the current flowing through the battery pack; and a control device. The control device sets an allowable power for the power input to and output from the battery pack and controls the charging and discharging of the battery pack so that the power input to and output from the battery pack does not exceed the allowable power. The control device is configured to estimate the temperature of the busbar using an evaluation function that takes the detected value of the current sensor as input, and to reduce the allowable power if the output value of the evaluation function exceeds a predetermined limit starting value. The evaluation function includes a first function that represents the temperature change based on the heat generated by the busbar due to the current flowing through the battery pack, and a second function that represents the temperature change due to the heat conducted from the plurality of cells that have been heated by the current flowing through the battery pack. [Effects of the Invention]
[0008] According to this disclosure, by improving the accuracy of busbar temperature estimation, it is possible to suppress excessive restriction of the power input and output to the battery pack as a busbar protection measure. [Brief explanation of the drawing]
[0009] [Figure 1] This figure shows an example of the overall configuration of an electric vehicle to which the battery system according to this embodiment is applied. [Figure 2] This diagram provides a more detailed explanation of the configuration of the battery pack and monitoring unit. [Figure 3] This figure shows an example of the time-dependent change in the temperature of the busbars when current is passed through a battery pack. [Figure 4] This flowchart explains the calculation process for the charge / discharge power limit performed by the ECU. [Modes for carrying out the invention]
[0010] The embodiments of this disclosure will be described in detail below with reference to the drawings. In the drawings, identical or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated.
[0011] <Overall configuration of electric vehicles> Figure 1 shows an example of the overall configuration of an electric vehicle to which the battery system according to this embodiment is applied. The electric vehicle 1 according to this embodiment is, for example, an electric vehicle. The electric vehicle 1 may also be a hybrid vehicle, a plug-in hybrid vehicle, or the like.
[0012] The electric vehicle 1 comprises a motor generator (MG) 10, a power transmission gear 20, drive wheels 30, a power control unit (PCU) 40, a system main relay (SMR) 50, a battery pack 80, a monitoring unit 90, and an electronic control unit (ECU) 100.
[0013] The MG10 is an AC rotating electric machine, for example, a three-phase AC synchronous motor with permanent magnets embedded in the rotor. The MG10 is driven by power supplied from a battery pack 80 via a PCU 40. The driving force of the MG10 is transmitted to the drive wheels 30 via a power transmission gear 20 which includes a reduction gear and a differential gear.
[0014] When the electric vehicle 1 is braking or when acceleration is reduced on a downhill slope, the MG10 is driven by the drive wheels 30, and the MG10 acts as a generator to perform regenerative power generation. The electricity generated by the MG10 is stored in the battery pack 80 via the PCU 40.
[0015] The PCU40 is a power converter that converts power bidirectionally between the MG10 and the battery pack 80. The PCU40 includes, for example, an inverter and a converter that operate based on control signals from the ECU100.
[0016] The converter boosts the DC voltage supplied from the battery pack 80 during discharge of the battery pack 80 and supplies it to the inverter. The inverter converts the DC power supplied from the converter into AC power and drives the MG10.
[0017] During charging of the battery pack 80, the inverter converts the AC power generated by the MG10 into DC power and supplies it to the converter. The converter steps down the DC voltage supplied from the inverter to a voltage suitable for charging the battery pack 80 and supplies it to the battery pack 80.
[0018] The SMR50 is electrically connected to the power line 45 connecting the battery pack 80 and the PCU40. When the SMR50 is closed (ON) in response to a control signal from the ECU100, power can be exchanged between the battery pack 80 and the PCU40. On the other hand, when the SMR50 is opened (OFF) in response to a control signal from the ECU100, the electrical connection between the battery pack 80 and the PCU40 is interrupted.
[0019] The battery pack 80 stores power for driving the MG10. The battery pack 80 is a rechargeable DC power source (secondary battery) and includes a plurality of single cells. Each cell is, for example, a lithium-ion secondary battery. The electrode terminals of the plurality of cells are electrically connected by a bus bar.
[0020] The monitoring unit 90 is a device for monitoring the state of the battery pack 80 and includes a voltage sensor group 92, a current sensor 94, and a temperature sensor group 96. The voltage sensor group 92 includes a plurality of voltage sensors. Each of the plurality of voltage sensors detects the voltage V of the corresponding cell among the plurality of cells included in the battery pack 80. The current sensor 94 detects the current I input to and output from the battery pack 80. The temperature sensor group 96 includes at least one temperature sensor. Each of the at least one temperature sensors detects the temperature T of the corresponding cell among the plurality of cells included in the battery pack 8'. The monitoring unit 90 outputs the detection values by each sensor to the ECU100.
[0021] The electric vehicle 1 includes an inlet 60 and is configured to enable external charging of the assembled battery 80 using a charging facility (EVSE: Electric Vehicle Supply Equipment) 200. The inlet 60 is configured to be connectable to a connector 220 provided at the tip of a charging cable 210 of the EVSE 200. The inlet 60 is electrically connected to a power line 45 via a charging circuit 70. In the present embodiment, when the SMR 50 is closed, the inlet 60 and the assembled battery 80 are electrically connected and external charging becomes possible.
[0022] The ECU 100 includes a CPU (Central Processing Unit) 102, a memory 104 such as a ROM (Read Only Memory) and a RAM (Random Access Memory), and an input / output port (not shown) for inputting and outputting various signals. The ECU 100 executes control related to vehicle running and charging / discharging of the assembled battery 80 based on signals received from each sensor of the monitoring unit 90 and programs and maps stored in the memory 104.
[0023] Also, as a protection measure against heat generation of the bus bar through which the current input / output to the assembled battery 80 flows, the ECU 100 limits the current input / output to the assembled battery 80 based on the heat generation state of the bus bar.
[0024] The ECU 100 corresponds to an embodiment of the "control device". The ECU 100 may be divided into a plurality of ECUs for each function. Note that at least a part of the ECU 100 can also be constructed and processed by dedicated hardware (electronic circuit).
[0025] <Configuration of the assembled battery and the monitoring unit> FIG. 2 is a diagram for explaining the configuration of the assembled battery 80 and the monitoring unit 90 in more detail. As shown in FIG. 2, the assembled battery 80 includes M cells 801 to 80M connected in series. M may be an integer of 2 or more, and typically is a dozen to several dozen.
[0026] The voltage sensor group 92 is implemented, for example, by a voltage monitoring IC (Integrated Circuit) that integrates the processing circuits of numerous voltage sensors, and is configured as a single unit. The voltage sensor group 92 includes M voltage sensors 921 to 92M. Voltage sensor 921 detects the voltage V1 of cell 801. Voltage sensor 922 detects the voltage V2 of cell 802. The same applies to the other voltage sensors 923 to 92M.
[0027] The current sensor 94 detects the current I flowing through the battery pack 80 (i.e., the current I that flows in common through cells 801 to 80M).
[0028] The temperature sensor group 96 includes N temperature sensors 961 to 96N, where N is an integer between 1 and M. This means that not all cells are equipped with a temperature sensor. In the example in Figure 2, temperature sensor 961 detects the temperature T1 of cell 801. Temperature sensor 96N detects the temperature TN of cell 80N. However, the cells to which temperature sensors are installed are not limited to the end cells as in this example, but can be set as appropriate.
[0029] As shown on the right side of Figure 2, each cell is a rectangular cell with a rectangular prism shape. Each cell has a positive terminal 82 and a negative terminal 84 on the same plane. Two adjacent cells are arranged so that terminals of opposite poles are adjacent to each other. Specifically, cell 801 and its adjacent cell 802 are arranged so that terminals of opposite poles are adjacent to each other. Cell 802 and its adjacent cell 803 are arranged so that terminals of opposite poles are adjacent to each other. The same applies to cells 804 to 80M.
[0030] The busbar 86 connects the terminals of adjacent cells. The negative terminal 84 of cell 801 and the positive terminal 82 of cell 802 are connected using the busbar 86. The negative terminal 84 of cell 802 and the positive terminal 82 of cell 803 are connected using the busbar 86. The same applies to cells 804 to 80M.
[0031] <Protection measures for bus bars> In the electric vehicle 1 according to this embodiment, during charging and discharging of the battery pack 80, heat is generated in each of the M cells 801 to 80M, in proportion to approximately the square of the current flowing through the battery pack 80. The heat generated in each cell is conducted to the corresponding busbar 86 via the positive terminal 82 and the negative terminal 84.
[0032] Furthermore, in the busbar 86 that electrically connects the M cells 801 to 80M, heat is generated that is approximately proportional to the square of the current flowing through the battery pack 80. In other words, the temperature of the busbar 86 rises due to the heat conducted from the corresponding cells and its own heat generation. Therefore, protective measures against overheating of the busbar 86 are necessary.
[0033] In this embodiment, as a protection measure for the busbar 86, an evaluation function representing the temperature change of the busbar 86 is generated based on the current I flowing through the busbar 86 and the energizing time. Based on the output value of this evaluation function, the allowable power Win and Wout, which indicate the upper limit of the power input to and output from the battery pack 80, are limited. That is, the current flowing through the battery pack 80 is reduced in accordance with the temperature change of the busbar 86. The input allowable power Win is the upper limit of the power input to the battery pack 80, and the output allowable power Wout is the upper limit of the power output from the battery pack 80.
[0034] Here, the components in the current path of the current flowing through the battery pack 80 generate heat proportional to the square of the current flowing through the battery pack 80. Furthermore, the heat dissipation from the components can be approximated by a first-order lag system. This relationship can be expressed as an evaluation function F, for example, as shown in equation (1). F(n+1) = {(K(n)-1) × F(n) + I(n)} 2} / K(n)…(1) Here, n represents the number of control cycles since the start of control, i.e., the elapsed time. Also, I(n) represents the current value flowing through the battery pack 80 when the number of control cycles n is reached. K(n) is a coefficient for performing a first-order lag approximation, i.e., a coefficient equivalent to the time constant. The coefficient K(n) has a different value for each component.
[0035] As described above, the temperature of the busbar 86 changes depending on the amount of heat generated by the busbar 86 and the amount of heat conducted from each cell. These two amounts of heat change at different rates with respect to the square of the current value flowing through the battery pack 80. Therefore, in this embodiment, the evaluation function for the busbar 86 to be protected is constructed using two evaluation functions as shown in equation (2). F(n+1)=a×F1(n+1)+b×F2(n+1)…(2) Here, the evaluation function F1(n+1) in the first term on the right-hand side is an evaluation function that represents the temperature change of the busbar 86 due to the heat generated by the current flowing through the battery pack 80. The evaluation function F2(n+1) in the second term on the right-hand side is an evaluation function that represents the temperature change of the busbar 86 due to the heat conducted from the cells that have been heated by the current flowing through the battery pack 80. Note that the coefficient a multiplied by F1(n+1) and the coefficient b multiplied by F2(n+1) represent the weights of the output values of the corresponding evaluation functions.
[0036] The evaluation function F1(n+1) can be expressed as shown in equation (3), following equation (1). The evaluation function F2(n+1) can be expressed as shown in equation (4), following equation (1). F1(n+1)={(K1(n)-1)×F1(n)+I(n) 2} / K1(n)…(3) F2(n+1)={(K2(n)-1)×F2(n)+I(n) 2} / K2(n)…(4) Here, n represents the number of control cycles since the start of control, i.e., the elapsed time. Also, I(n) represents the current value flowing through the battery pack 80 when the number of control cycles n is reached. K1(n) and K2(n) are coefficients for performing a first-order lag approximation, i.e., coefficients corresponding to the time constant.
[0037] The coefficients K1 of the evaluation function F1 and K2 of the evaluation function F2 are determined in advance through experiments or other means. For example, consider the time change in the temperature of busbar 86 when current is passed through it. The temperature of busbar 86 rises in a curve that is approximately first order lag with respect to time after the start of current flow due to the heat generated by busbar 86. The coefficient K1 of the evaluation function F1 is determined to fit this curve.
[0038] Furthermore, the temporal change in the temperature of the busbar 86 when current is passed through the battery pack 80 is determined. The temperature of the busbar 86 rises in a curve that is approximately first order lag with respect to time after the start of current flow, due to the heat generated by the busbar 86 and the heat conducted from the cells. By subtracting the curve based on the heat generated by the busbar 86 as described above from this curve, a curve representing the temporal change in the temperature of the busbar 86 due to the heat conducted from the cells is obtained. Then, the coefficient K2 of the evaluation function F2 is determined to fit this curve.
[0039] For example, the output value of evaluation function F can be obtained by the simple average of the output values of evaluation function F1 and evaluation function F2. In this case, both coefficients a and b will be 1 / 2. Alternatively, the output value of evaluation function F can be obtained by the weighted average of the output values of evaluation function F1 and evaluation function F2. The values of coefficients a and b can be determined in advance through experiments or other means.
[0040] Figure 3 shows an example of the time change in the temperature of the busbar 86 when current is passed through the battery pack 80. The horizontal axis of Figure 3 represents the elapsed time since the start of current flow to the battery pack 80, and the vertical axis represents the temperature of the busbar 86. Temperature T0 represents the temperature of the busbar 86 at the start of current flow (initial temperature). Curve L4 in the figure shows the time change in the actual temperature of the busbar 86. After the start of current flow, the temperature of the busbar 86 rises from the initial temperature T0 in a curve that is approximately first order lag with respect to time.
[0041] Curves L1 and L2 in the figure show the time evolution of the estimated temperature of busbar 86 based on the output value of the evaluation function F shown in equation (1). The coefficient K values are different for curves L1 and L2. The coefficient K value for curve L1 is smaller than the coefficient K value for curve L2.
[0042] Curve L3 in the figure shows the time change of the estimated temperature of busbar 86 based on the output value of the evaluation function F shown in equation (2). Curve L3 almost overlaps with curve L4, indicating high estimation accuracy.
[0043] In this embodiment, the evaluation function F representing the temperature change of the busbar 86 is composed of an evaluation function F1 representing the temperature change of the busbar 86 due to heat generation by the busbar 86 and an evaluation function F2 representing the temperature change of the busbar 86 due to heat conducted from the cell, and the coefficients K1 and K2 of the evaluation functions F1 and F2 are determined based on experiments, etc. This makes it possible to estimate the temperature of the busbar 86 with high accuracy based on the current flowing through the battery pack 80 and the energizing time. By limiting the allowable power Win and Wout of the power input and output to the battery pack 80 using the output value of this evaluation function F, it becomes possible to appropriately suppress overheating of the busbar 86.
[0044] Figure 4 is a flowchart illustrating the calculation process for the charge / discharge power limit performed by the ECU 100. Each step in the flowchart in Figure 4 is implemented by being called from the main routine of a program pre-stored in the ECU 100 and executed at predetermined intervals. Alternatively, some steps can be implemented by constructing dedicated hardware (electronic circuits).
[0045] As shown in Figure 4, in step 01 (hereinafter, step 01 is abbreviated as S), the ECU 100 acquires the detected value of the current I that is input and output from the monitoring unit 90 to the battery pack 80.
[0046] In S02, ECU100 uses the detected current I to calculate the output value of the evaluation function F1 shown in equation (3).
[0047] In S03, ECU100 uses the detected current IB to calculate the output value of function F2 from the table shown in equation (4).
[0048] In S04, ECU100 calculates the output value of the evaluation function F of busbar 86 by substituting the output value of evaluation function F1 calculated in S02 and the output value of evaluation function F2 calculated in S03 into equation (2).
[0049] In S05, ECU100 calculates the input allowable power Win and output allowable power Wout of the battery pack 80 using the output value of the evaluation function F obtained in S04. In some cases, in S05, ECU100 compares the output value of the evaluation function F with a predetermined limit start value Ftag. The limit start value Ftag is the limit start value for initiating the limits on the input allowable power Win and output allowable power Wout.
[0050] If the output value of the evaluation function F is less than the control start value Ftag, the ECU 100 sets the input allowable power Win to the input allowable power SWin, which is determined based on the temperature and SOC of the battery pack 80. The ECU 100 also sets the output allowable power Wout to the output allowable power SWout, which is determined based on the temperature and SOC of the battery pack 80.
[0051] If the output value of the evaluation function F exceeds the limit start value Ftag, the ECU100 starts limiting the input power allowance Win and the output power allowance Wout. Limiting the input power allowance Win and the output power allowance Wout means reducing their magnitude (corresponding to their absolute value).
[0052] Specifically, the ECU100 calculates the input allowable power MWin and output allowable power MWout by performing control calculations to reduce the deviation F-Ftag of the output value of the evaluation function F relative to the limit start value Ftag. Then, the ECU100 corrects the input allowable power Win to input allowable power MWin and corrects the output allowable power Wout to output allowable power MWout.
[0053] The ECU 100 controls vehicle operation and charging / discharging of the battery pack 80 so that the power input and output to the battery pack 80 does not exceed the input allowable power Win and output allowable power Wout.
[0054] When the limits on the allowable power Win and Wout are applied, the magnitude of the input allowable power MWin becomes smaller than the magnitude of the input allowable power Swin, and the magnitude of the output allowable power MWout becomes smaller than the magnitude of the output allowable power SWout, according to the deviation F-Ftag of the output value of the evaluation function F relative to the limiting start value Ftag. By limiting the input allowable power Win and the output allowable power Wout in this way, the current flowing through the battery pack 80 is reduced, and the heat generated by the busbar 86 is suppressed. In addition, the heat conducted from each cell of the battery pack 80 to the busbar 86 is also suppressed. In this embodiment, since the temperature of the busbar 86 can be estimated with high accuracy from the output value of the evaluation function F, it is possible to suppress excessive restriction of the power input and output to the battery pack 80 as a protection measure for the busbar 86.
[0055] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than by the description of the embodiments described above, and is intended to include all modifications in the sense and scope equivalent to the claims. [Explanation of Symbols]
[0056] 1 Electric vehicle, 10 MG, 20 Power transmission gears, 30 Drive wheels, 45 Power lines, 50 SMR, 60 Inlet, 70 Charging circuit, 80 Battery pack, 801-80M cells, 82 Positive terminal, 84 Negative terminal, 86 Busbar, 90 Monitoring unit, 92 Voltage sensor group, 921-92M Voltage sensor, 94 Current sensor, 96 Temperature sensor group, 961-96N Temperature sensor, 100 ECU, 102 CPU, 104 Memory, 210 Charging cable, 220 Connector.
Claims
1. A battery pack comprising multiple cells, each having electrode terminals, A busbar for electrically connecting the electrode terminals of the plurality of cells, A current sensor for detecting the current flowing through the aforementioned battery pack, The system includes a control device that sets an allowable power for the power input and output to the battery pack, and controls the charging and discharging of the battery pack so that the power input and output to the battery pack does not exceed the allowable power, The control device is configured to estimate the temperature of the busbar using an evaluation function that takes the detected value of the current sensor as input, and to reduce the allowable power when the output value of the evaluation function exceeds a predetermined limit starting value. The aforementioned evaluation function is, A first function that represents the temperature change due to the heat generated by the busbar caused by the current flowing through the battery pack, A battery system comprising a second function that represents the temperature change due to the heat conducted from the plurality of cells, which are heated by the current flowing through the battery pack.
2. The battery system according to claim 1, wherein the control device calculates the output value of the evaluation function by averaging the output value of the first function and the output value of the second function.
3. The battery system according to claim 1, wherein the control device calculates the output value of the evaluation function by weighting the output value of the first function and the output value of the second function.