JP2019046638A - Battery system - Google Patents

Abstract

To highly accurately calculate current variations between a plurality of cells, in a battery system including a battery pack comprising the plurality of cells included therein, the cells being connected in parallel.SOLUTION: An ECU 100 calculates resistance of each of a plurality of cells from an initial state of current variations and states of the cells (temperature, SOC, etc.) and calculates the current variations between cells from resistance of each cell having been calculated. When changes of current variations having been calculated are greater than a convergence determination value, the ECU 100 re-calculates the resistance of each cell from current variations having been calculated and the states of the cells, and repeatedly performs calculations of the resistance of each cell and calculation of the current variations using the resistance of each cell having been calculated until changes of the current variations are equal to or less than a convergence determination value.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a battery system, and more particularly to a battery system including an assembled battery including a plurality of secondary batteries connected in parallel.

  A configuration including a plurality of secondary batteries connected in parallel (each secondary battery is also referred to as a "cell" or "unit cell", and each secondary battery may be hereinafter referred to as a "cell"). There is known a battery system provided with a battery pack. For example, a control device for a parallel secondary battery (cell assembly) in which a plurality of secondary batteries (cells) are connected in parallel is described in Japanese Patent Laid-Open No. 2013-230024 (Patent Document 1) (Patent Document 1) reference).

JP, 2013-230024, A JP, 2010-60406, A

  By accurately estimating the current variation among the plurality of cells connected in parallel, it is possible to appropriately protect the assembled battery including the plurality of cells. As a method of estimating the current variation between cells, it is conceivable to calculate the current variation between cells from the resistance of each cell (resistance variation between cells).

  However, since the cell resistance has current dependency, if the cell-to-cell variation in resistance occurs due to the cell-to-cell variation in resistance depending on the state of each cell (temperature, SOC, etc.), the cell-to-cell resistance Are affected. Therefore, on the premise that uniform current flows in a plurality of cells connected in parallel, current variation among cells based on resistance (resistance variation) of each cell according to the state (temperature, SOC, etc.) of each cell. Since the influence of the current variation on the resistance of each cell is not taken into account, the calculation accuracy of the current variation may decrease.

  The present disclosure has been made to solve such a problem, and an object of the present disclosure is to provide a battery system including a battery assembly including a plurality of cells connected in parallel, with current variations among the plurality of cells. It is to calculate accurately.

  The battery system of the present disclosure includes a battery assembly including a plurality of cells (secondary batteries) connected in parallel, and a variation (current variation) among the plurality of cells of the current flowing in a dispersed manner in the plurality of cells. And a controller configured to calculate The control device calculates the resistance of each cell from a predetermined initial state of current dispersion and the state (temperature, SOC, etc.) of a plurality of cells, and calculates the current dispersion among the cells from the calculated resistance of each cell Do. Then, when the change in the calculated current variation is larger than the predetermined amount, the control device recalculates the resistance of each cell from the calculated current variation and the states of the plurality of cells, and the change in the current variation is The calculation of the resistance of each cell and the calculation of the current variation using the calculated resistance of each cell are repeatedly performed until the above predetermined amount is reached.

  In the battery system of the present disclosure, the resistance of each cell is calculated from the calculated current variation among the cells and the states of the plurality of cells (such as temperature and SOC), and the change in the current variation becomes smaller than a predetermined amount. The calculation of the resistance of each cell in consideration of the calculated current variation between cells and the calculation of the current variation using the calculated resistance of each cell are repeatedly performed. Thereby, the current variation between cells is calculated in consideration of the current dependency of the cell resistance. Therefore, according to the battery system of the present disclosure, it is possible to accurately calculate the current variation among the plurality of cells.

FIG. 1 schematically shows a configuration of a vehicle equipped with a battery system according to a first embodiment of the present disclosure. It is the figure which showed an example of the detailed structure of the assembled battery shown in FIG. It is a figure which shows the 2 parallel model in which two cells were connected in parallel. It is the figure which showed the current-resistance characteristic map which shows the current dependency of the resistance value of the cell A and the cell B which are shown in FIG. It is a flowchart explaining the calculation procedure of the electric current variation between cells performed by ECU shown in FIG. FIG. 13 is a diagram showing an example of a current-resistance characteristic map used in the second embodiment. FIG. 16 is a flowchart illustrating a calculation procedure of current variation between cells performed by the ECU in the second embodiment. It is a figure showing an example of a current variation map.

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

First Embodiment
FIG. 1 schematically shows a configuration of a vehicle 1 equipped with a battery system according to an embodiment of the present disclosure. In addition, although the case where vehicle 1 is a hybrid vehicle is representatively described below, the battery system according to the present disclosure is not limited to the one mounted on a hybrid vehicle, but a whole vehicle mounted with a battery pack, and further Is applicable to applications other than vehicles.

  Referring to FIG. 1, the vehicle 1 is referred to as a battery system 2, a power control unit (hereinafter referred to as “PCU (Power Control Unit)) 30, and a motor generator (hereinafter referred to as“ MG (Motor Generator) ”). 41, 42, an engine 50, a power split device 60, a drive shaft 70, and a drive wheel 80. Battery system 2 includes a battery assembly 10, a monitoring unit 20, and an electronic control unit (hereinafter referred to as an "ECU (Electronic Control Unit)") 100.

  The engine 50 is an internal combustion engine that outputs motive power by converting combustion energy generated when the mixture of air and fuel is burned 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 axes 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 wheel 80.

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

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

  The battery assembly 10 is configured to include a plurality of cells (secondary batteries) connected in parallel (detailed configuration will be described later). The battery pack 10 stores power for driving the MGs 41 and 42. The assembled battery 10 can supply power to the MGs 41 and 42 through the PCU 30. Also, the battery pack 10 is charged by receiving the generated power through the PCU 30 when the 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 voltages (hereinafter also referred to as “cell voltages”) Vi of a plurality of cells connected in parallel in the assembled battery 10. The current sensor 22 detects the charge / discharge current I of the assembled battery 10. The temperature sensor 23 detects a temperature for each cell (hereinafter also referred to as “cell temperature”) Ti. The temperature sensor 23 may detect the temperature with a plurality of (for example, several) adjacent cells as a monitoring unit.

  PCU 30 executes bidirectional power conversion between battery assembly 10 and MGs 41 and 42 in accordance with a control signal from ECU 100. The PCU 30 is configured to be capable of separately controlling the states of the MGs 41 and 42. For example, the MGU can be brought into a power running state while the MG 41 is brought into a regeneration (power generation) state. PCU 30 includes, for example, two inverters provided corresponding to MGs 41 and 42, and a converter that boosts the DC voltage supplied to each inverter to an output voltage of assembled battery 10 or more.

  ECU 100 includes a central processing unit (CPU) 102, a memory (read only memory (ROM) and a random access memory (RAM)) 105, and an input / output port (not shown) for inputting / outputting various signals. It consists of ECU 100 controls charge / discharge of battery assembly 10 by controlling engine 50 and PCU 30 based on the signals received from the respective sensors and the program and map stored in memory 105.

  FIG. 2 is a view showing an example of a detailed configuration of the battery pack 10 shown in FIG. Referring to FIG. 2, in the battery assembly 10, a plurality of cells are connected in parallel to form a block (or module), and a plurality of blocks are connected in series to configure the battery assembly 10. Specifically, the battery assembly 10 includes blocks 10-1 to 10-M connected in series, and each of the blocks 10-1 to 10-M includes N cells connected in parallel.

  The voltage sensor 21-1 detects the voltage of the block 10-1. That is, the voltage sensor 21-1 detects the voltages V1 of the N cells constituting the block 10-1. The voltage sensor 21-2 detects voltages V2 of N cells constituting the block 10-2. The same applies to the voltage sensor 21-M. The current sensor 22 detects the current I flowing through each of the blocks 10-1 to 10-M. That is, the current sensor 22 detects the total current flowing in the N cells of each block.

  In the assembled battery 10 configured to include a plurality of cells connected in parallel, current variations occur among the N cells connected in parallel. Therefore, a current larger than the average current of N cells calculated from the detection value of the current sensor 22 may flow to a specific cell, and the current flowing to the cells may exceed a predetermined limit.

  Therefore, in the first embodiment, the current variation among the N cells connected in parallel is calculated. By calculating the current variation between cells, for example, the battery assembly 10 is subjected to current limitation with reference to the maximum current among the currents distributed and flowing in N cells connected in parallel. Can be properly protected.

  In the first embodiment, the current variation among the cells is calculated from the resistance of each of the N cells connected in parallel (resistance variation among the cells). Here, since the cell resistance has a current dependency, if the cell-to-cell variation in resistance occurs due to the cell-to-cell variation in resistance according to the state (eg, temperature) of each cell, the cell-to-cell resistance to be influenced. Therefore, for example, on the premise that uniform current flows in N cells connected in parallel, if current variation among cells is calculated based on the resistance (resistance variation) of each cell according to the temperature of each cell, Since the influence of the current variation on the resistance of each cell is not considered, the calculation accuracy of the current variation may be reduced.

  Therefore, in battery system 2 according to the first embodiment, an initial state (for example, a state in which there is no current variation) and a predetermined number of current variations are first set for N cells connected in parallel. The resistance of each cell is calculated from the state (temperature), and the current variation among the cells is calculated from the calculated resistance of each cell. Then, the resistance of each cell is recalculated from the calculated current variation and the state (temperature) of N cells, and the current variation between the cells is calculated again from the calculated resistance of each cell. Then, when the change from the previously calculated value of the calculated current variation is larger than the convergence determination value, the resistance of each cell is calculated again from the calculated current variation and the state (temperature) of N cells. The calculation of the resistance of each cell and the calculation of the current deviation using the calculated resistance of each cell are repeatedly performed until the change of the current deviation becomes equal to or less than the convergence determination value. According to this embodiment, since the current variation among the cells is calculated in consideration of the current dependency of the cell resistance, the current variation among the plurality of cells can be accurately calculated.

  Hereinafter, the method of calculating the current variation between cells in battery system 2 according to the first embodiment will be described in more detail using a simple configuration example in which two cells are connected in parallel.

  FIG. 3 is a view showing a configuration of a battery assembly in which two cells are connected in parallel. Referring to FIG. 3, in this example, two cells A and B are connected in parallel. The total current It flows dispersively in the cell A and the cell B, and the currents flowing in the cell A and the cell B are denoted by IA and IB, respectively. Also, let the resistances of the cell A and the cell B be RA and RB, respectively.

  FIG. 4 is a diagram showing the current dependency of the resistance of each cell shown in FIG. Referring to FIG. 4, the horizontal axis indicates the current (cell current) flowing through the cell, and the vertical axis indicates the cell resistance (cell resistance). The states of the cell A and the cell B are different, and a temperature difference occurs between the cell A and the cell B. In this example, the case where the temperature of the cell A is lower than the temperature of the cell B is shown. And, as illustrated, the lower the cell temperature (cell temperature), the higher the cell resistance. In the first embodiment, a current-resistance characteristic map showing such current dependency of cell resistance is prepared in advance for each cell temperature, and stored in memory 105 of ECU 100.

  In the first embodiment, the resistance value of each cell is calculated from the current variation between cells and the state of each cell (cell temperature), and the current variation between cells is calculated from the calculated resistance value of each cell. . In the calculation of the resistance values of the cell A and the cell B, first, it is illustrated that there is no current variation among the cells (initial state) and a uniform current value I0 (I0 = It / 2) flows in the cell A and the cell B. The resistance value RA1 of the cell A and the resistance value RB1 (RA1> RB1) of the cell B are calculated using the current-resistance characteristic map.

  In the cells connected in parallel, the current flows by dividing into the ratio of the reciprocal of the resistance value of each cell, so the current values flowing to the cell A and the cell B can be calculated from the calculated resistance values RA1 and RB1. The current value IA1 of the cell A and the current value IB1 of the cell B (IA1 <IB1) are calculated. However, as illustrated, since the cell resistance has current dependency, the resistance value of the cell A when the current of the IA1 flows in the cell A is estimated to be RA2 (RA2> RA1), and the cell B is IB1. The resistance value of the cell B when the current of (1) flows is estimated to be RB2 (RB2 <RB1). Therefore, when the currents flowing from the resistance values RA2 and RB2 to the cell A and the cell B are recalculated, the current value of the cell A is IA2 (IA2 <IA1), and the current value of the cell B is IB2 (IB2> IB1). Become.

  Thus, the current variation between cells (difference between current values IA2 and IB2) in the case where the current dependency of cell resistance is taken into consideration is higher than the current variation between cells in the case where the current dependency of cell resistance is not considered. It is understood that it becomes big.

  In battery system 2 according to the first embodiment, calculation calculation of current variation among cells is repeatedly executed in consideration of the current dependency of the cell resistance. Specifically, the resistance value of each cell is calculated again from the calculated current variation (for example, IA1, IB1 in FIG. 4) and the state of each cell (cell temperature) using the current-resistance characteristic map (for example, FIG. From RA2 and RB2 of 4) and the calculated resistance value of each cell, the current variation between the cells is calculated again (for example, IA2, IB2 in FIG. 4). The calculation of the current variation is repeated until the change in the current variation (variation in IA2, IB2 with respect to the variation in IA1, IB1) becomes equal to or less than the convergence determination value.

  FIG. 5 is a flow chart for explaining the calculation procedure of the current variation between cells which is executed by the ECU 100 shown in FIG. The process shown in this flowchart is called from the main routine and executed every predetermined time or when a predetermined condition is established, for each block constituting the battery assembly 10.

  Referring to FIG. 5, ECU 100 obtains temperatures Ti of the cells of the target block from temperature sensor 23 (step S10). Next, the ECU 100 sets an initial value for the current variation between cells (step S20). As an example, in the first embodiment, a current increase gain Igain indicating the current increment of the current maximum cell (cell in which the maximum current flows) to the average current of N cells connected in parallel is calculated, and this current increase gain Current gain is indicated by Igain. In the first embodiment, an initial value 1.0 is set to the current increase gain Igain in step S20. The fact that the current increase gain Igain is 1.0 corresponds to the assumption that a uniform current flows in each cell.

  The index indicating the current variation between cells is not limited to the current increase gain Igain, and other indexes such as the difference between the maximum current and the minimum current, the dispersion of the current of each cell, etc. Indicators can be adopted. Further, the initial value of the current variation is not limited to the value in the case where a uniform current flows in each cell, and may be appropriately set based on, for example, the arrangement of the cells (whether center or end).

  Next, the ECU 100 calculates the resistance of each cell from the current variation among the cells and the cell temperature acquired in step S10 (step S30). Specifically, the current-resistance characteristic map shown in FIG. 4 is prepared in advance for each cell temperature by experiment, numerical calculation, etc., and the resistance of each cell is calculated using this current-resistance characteristic map. . In the example shown in FIG. 4, the transition from step S20 to step S30 corresponds to the calculation of the resistance values RA1 and RB1 assuming that the uniform current I0 flows in the cell A and the cell B. In addition, at the time of transition from step S60 to step S30 described later, it is assumed that the cell current (for example, current values IA1 and IB1) based on the current variation calculated in step S40 flows in cell A and cell B. This corresponds to calculation of values (for example, resistance values RA2 and RB2 respectively corresponding to the current values IA1 and IB1).

  Next, the ECU 100 calculates the current variation among the cells from the resistance of each cell calculated in step S30 (step S40). Specifically, in N cells connected in parallel, the current flows by being divided to the inverse ratio of the resistance of each cell, so the current increase gain indicating the current flowing in each cell and the current variation between the cells Igain can be calculated.

  Furthermore, the ECU 100 calculates the amount of change in current variation (step S50). Specifically, the calculation of the current variation is repeatedly performed until it is determined that the calculated value converges as described later, and the change amount of the current variation is a change amount from the previous value of the current increase gain Igain. is there.

  Then, the ECU 100 determines whether the amount of change of the current variation (the amount of change of the current increase gain Igain from the previous value) is equal to or less than a predetermined convergence determination value (step S60). If it is determined that the amount of change in current variation is equal to or less than the convergence determination value (YES in step S60), ECU 100 takes the current variation calculated in the immediately preceding step S40 as the final calculated value and processes to the end. Transition.

  On the other hand, when it is determined in step S60 that the change amount of the current variation is larger than the convergence determination value (NO in step S60), the ECU 100 returns the process to step S30 and executes the process of step S30 again. That is, the ECU 100 recalculates the resistance of each cell with reference to the current-resistance characteristic map, using the current variation (the current value of each cell) calculated in step S40.

  As described above, the ECU 100 repeatedly executes the processing of steps S30 to S50 until it is determined in step S60 that the amount of change in current variation (current increase gain Igain) between cells is equal to or less than the convergence determination value.

  As described above, in the first embodiment, the resistance of each cell is calculated from the calculated current variation among cells and the state (temperature) of N cells, and the change in current variation is equal to or less than the convergence determination value. The calculation of the resistance of each cell in consideration of the calculated current variation among the cells and the calculation of the current variation using the calculated resistance of each cell are repeatedly performed until Thereby, the current variation among the cells is calculated in consideration of the influence of the current variation among the cells on the resistance of each cell (the current dependency of the cell resistance). Therefore, according to the first embodiment, it is possible to calculate current variations among a plurality of cells with high accuracy.

Second Embodiment
In the above-described first embodiment, the current-resistance characteristic map is prepared in advance for each cell temperature, and the cell temperature is considered as the state of the cell. However, in the second embodiment, the current-resistance characteristic map is The cell SOC is prepared in advance for each cell SOC, and the cell SOC is considered as the state of the cell.

  FIG. 6 is a diagram showing an example of a current-resistance characteristic map used in the second embodiment. 6 corresponds to FIG. 4 described in the first embodiment, and in FIG. 6 also, the current dependency of the resistance of cell A and cell B shown in FIG. 3 is shown. .

  Referring to FIG. 6, the states of cell A and cell B are different, and there is an SOC difference between cell A and cell B. In this example, the case where the SOC of cell A is lower than the SOC of cell B is shown. And, as illustrated, the lower the SOC, the higher the cell resistance. In the second embodiment, a current-resistance characteristic map showing the current dependency of the cell resistance is prepared in advance for each SOC of the cell, and stored in the memory 105 of the ECU 100.

  In the second embodiment, the resistance value of each cell is calculated from the current variation between cells and the state (SOC) of each cell, and the current variation between cells is calculated from the calculated resistance value of each cell. The specific description of the calculation of the resistance of each cell and the calculation of the current variation among the cells is the same as the description of FIG. 4, so the description will not be repeated here.

  In the battery system according to the second embodiment, the resistance value of each cell is calculated again using the current-resistance characteristic map from the calculated current variation (for example, IA1, IB1 in FIG. 6) and the state (SOC) of each cell. Then, the current variation among the cells is calculated again from the calculated resistance value of each cell (for example, IA2, IB2 in FIG. 6). Such calculation of the current variation is repeatedly performed until the change in the current variation (for example, the change amount of the current increase gain Igain) becomes equal to or less than the convergence determination value.

  FIG. 7 is a flow chart for explaining the calculation procedure of the current variation between cells performed by the ECU 100 in the second embodiment. The process shown in this flowchart is also called from the main routine and executed at predetermined time intervals or when a predetermined condition is satisfied, for each block constituting the battery assembly 10.

  Referring to FIG. 7, ECU 100 calculates the SOC of each cell of the target block (step S110). The SOC of each cell can be appropriately calculated using various known methods. Next, the ECU 100 sets an initial value for the current variation between cells (step S120). As one example, also in the second embodiment, the current increase gain Igain is calculated, and the current increase gain Igain indicates the current variation. Also in the second embodiment, the initial value 1.0 is set to the current increase gain Igain in step S120 (a uniform current flows in each cell).

  Next, the ECU 100 calculates the resistance of each cell from the current variation between the cells and the SOC calculated in step S110 (step S130). Specifically, the current-resistance characteristic map shown in FIG. 6 is prepared in advance for each SOC of the cell by experiment, numerical calculation, etc., and the resistance of each cell is calculated using this current-resistance characteristic map. Ru.

  The processes performed in subsequent steps S140 to S160 are the same as the processes performed in steps S40 to S60 shown in FIG. 5, respectively, and therefore the description of these processes will not be repeated. Then, ECU 100 repeatedly executes the processing of steps S130 to S150 until it is determined in step S160 that the amount of change in current variation is equal to or less than the convergence determination value.

As described above, according to the second embodiment, the same effect as that of the first embodiment can be obtained.
Although not particularly illustrated, as a combination of Embodiments 1 and 2, a current-resistance characteristic map is prepared in advance for each cell temperature and SOC, and both the cell temperature and SOC are considered as the cell state. You may

  In the above-described first and second embodiments, the convergence calculation is repeatedly performed until it is determined that the change amount of the current variation between the cells is equal to or less than the convergence determination value. The above convergence calculation may be performed in advance by (and / or SOC), and based on the result, a current variation map in consideration of the current dependency of the cell resistance may be calculated in advance.

  FIG. 8 is a diagram showing an example of the current variation map. Referring to FIG. 8, in this example, a maximum temperature difference ΔT between N cells connected in parallel, a lowest temperature TL indicating the temperature of the lowest temperature cell, and a cell as parameters of the current variation map, and a cell The maximum SOC difference ΔSOC between is used. By performing the convergence calculation as described in the first and second embodiments by appropriately changing each of the above parameters, the current variation (maximum current gain Igain) between the cells with respect to the above parameters is calculated and illustrated. Such current variation map can be created.

  By preparing such a current variation map in advance, the temperature difference ΔT, the minimum temperature TL, and the minimum temperature TL for N cells connected in parallel can be obtained without performing the convergence calculation as described in the first and second embodiments. From SOC difference ΔSOC, current variation between cells (maximum current gain Igain) can be calculated.

  It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

  Reference Signs List 1 vehicle, 2 battery system, 10 assembled batteries, 10-1 to 10-M block, 20 monitoring units, 21, 21-1 to 21-M 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, 102 CPU, 105 memory.

Claims (1)

An assembled battery including a plurality of secondary batteries connected in parallel;
A control device configured to calculate variations among the plurality of secondary batteries of the current flowing in a dispersed manner in the plurality of secondary batteries;
The controller is
The resistance of each secondary battery is calculated from the initial state of the variation of the current determined in advance and the states of the plurality of secondary batteries,
The variation of the current is calculated from the calculated resistance of each secondary battery,
If the calculated change in current variation is larger than a predetermined amount, the resistance of each secondary battery is calculated again from the calculated current variation and the states of the plurality of secondary batteries,
A battery system that repeatedly executes the calculation of the resistance of each secondary battery and the calculation of the current fluctuation using the calculated resistance of each secondary battery until the change in the current fluctuation is equal to or less than the predetermined amount.

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