JP6897362B2 - Rechargeable battery system - Google Patents

Description

The present disclosure relates to a secondary battery system, and more specifically to discharge control of an assembled battery including a plurality of battery blocks.

In recent years, hybrid vehicles and electric vehicles, which are vehicles equipped with a secondary battery system, have become widespread. In these secondary battery systems, an assembled battery including a plurality of battery blocks (each battery block is one or a plurality of cells) is used. Since the assembled battery deteriorates with repeated charging and discharging or with the passage of time, various techniques related to charging and discharging control in consideration of the deteriorated state of the assembled battery have been proposed.

For example, Japanese Patent Application Laid-Open No. 2013-106481 (Patent Document 1) discloses a control device for an assembled battery that controls charge / discharge of the assembled battery so that the SOC (State Of Charge) of the assembled battery becomes a target SOC. This control device sets a target SOC based on the data defining the relationship between the rate of decrease in the increased resistance of the assembled battery with the passage of time and the SOC. The target SOC is changed based on the change in the deterioration state with the decrease in the increased resistance.

Japanese Unexamined Patent Publication No. 2013-106481

It is known that the higher the temperature of the secondary battery, the more easily the deterioration of the secondary battery progresses. Inside the assembled battery mounted on a vehicle or the like, the temperature may be uneven (variable) between the battery blocks. If such temperature variations are state continues to occur, the parameter indicating the progress degree of deterioration (deterioration evaluation value described later) may become a different value for each battery block.

Generally, when the assembled battery is discharged, the voltage of all the battery blocks is controlled so as not to fall below a predetermined lower limit voltage in order to protect the assembled battery. More specifically, when the voltage of any of the battery blocks reaches the lower limit voltage, further discharge of the assembled battery is restricted (for example, stopped or prohibited).

In an assembled battery in which a plurality of battery blocks are connected in series, the currents flowing through all the battery blocks are equal. If the deterioration evaluation value varies between battery blocks, the magnitude of internal resistance will differ for each battery block, and as a result, the amount of voltage drop (= product of current and internal resistance) will differ for each battery block. It will be. Therefore, when the assembled battery is discharged, a situation may occur in which the voltage of some battery blocks reaches the lower limit voltage earlier than the voltage of other battery blocks.

Here, the present inventors have focused on the following points. That is, depending on the configuration and composition of the cell, the deterioration region defined by the deterioration evaluation value and the internal resistance of the battery block includes a region where the internal resistance decreases as the deterioration evaluation value increases (first region) and deterioration. There is a region (second region) in which the internal resistance increases as the evaluation value increases (see FIG. 5 described later for details).

It is also conceivable to uniformly control the discharge of the assembled battery without considering the variation in the deterioration evaluation value for each battery block (the variation in the voltage drop amount for each battery block) and the existence of the first and second regions. Be done. However, in that case, for example, when the discharge of the assembled battery is controlled based on the battery block in which the deterioration has progressed relatively, the discharge of the battery block in which the deterioration has not progressed so much is excessively limited, and the discharge performance of the assembled battery is performed. (Performance regarding the amount of power that can be taken out from the assembled battery) may decrease.

The present disclosure has been made to solve the above problems, and an object of the present disclosure is to provide a technique capable of exhibiting the required discharge performance in a secondary battery system including an assembled battery. ..

A secondary battery system according to a certain aspect of the present disclosure includes an assembled battery, a power conversion device, a switching device, and a control device. The assembled battery includes a plurality of battery blocks connected in series. The power converter is configured to discharge the assembled battery. The switching device is configured to be able to switch the electrical connection state between each of the plurality of battery blocks and the power conversion device when the assembled battery is discharged. The control device calculates a "deterioration evaluation value" for evaluating the deterioration state of each of the plurality of battery blocks from the temperature distribution in the assembled battery, and uses the calculated deterioration evaluation value to set the power conversion device and the switching device. Control. The deterioration region defined by the deterioration evaluation value and the internal resistance of each of the plurality of battery blocks includes the "first region", which is the region where the internal resistance decreases as the deterioration evaluation value increases, and the deterioration evaluation value. There is a "second region" in which the internal resistance increases as it increases.

In the control device, when the deterioration evaluation value of each of the plurality of battery blocks is within the first region, a part of the battery blocks of the plurality of battery blocks is connected to the power conversion device and a part of the control device is connected to the power conversion device. The switching device is controlled so that the battery block having a deterioration evaluation value lower than the deterioration evaluation value of the battery block is cut off from the power conversion device. On the other hand, in the control device, when the deterioration evaluation value of each of the plurality of battery blocks is within the second region, some other battery blocks of the plurality of battery blocks are connected to the power conversion device. The switching device is controlled so that the battery block having a deterioration evaluation value higher than the deterioration evaluation value of some other battery blocks is cut off from the power conversion device.

When the deterioration evaluation value is within the first region, the lower the deterioration evaluation value, the higher the internal resistance, and the voltage tends to reach the lower limit voltage. Therefore, according to the above configuration, a part of the battery blocks are connected to the power conversion device, and the battery block having a deterioration evaluation value lower than the deterioration evaluation value of the part of the battery blocks is cut off from the power conversion device. To. That is, a part of the battery blocks are discharged in a state where the discharge of the battery block having a relatively low deterioration evaluation value (= the battery block having a relatively high internal resistance) is restricted (stopped or prohibited). As a result, the dischargeable period of the assembled battery can be extended by the amount that some of the battery blocks are discharged, as compared with the case where all the battery blocks are discharged uniformly. Therefore, it is possible to exhibit the required discharge performance.

On the other hand, when the deterioration evaluation value is within the second region, the higher the deterioration evaluation value, the higher the internal resistance, and the voltage tends to reach the lower limit voltage. Therefore, according to the above configuration, a part of the battery blocks are connected to the power conversion device, and the battery block having a deterioration evaluation value higher than the deterioration evaluation value of the part of the battery blocks is cut off from the power conversion device. To. That is, some of the battery blocks are discharged in a state where the discharge of the battery block having a relatively high deterioration evaluation value (= the battery block having a relatively high internal resistance) is restricted. As a result, the dischargeable period of the assembled battery can be extended by the amount that some of the battery blocks are discharged, as compared with the case where all the battery blocks are discharged uniformly. Therefore, it is possible to exhibit the required discharge performance.

According to the present disclosure, a required discharge performance can be exhibited in a secondary battery system including an assembled battery.

It is a figure which shows schematic the whole structure of the vehicle which mounted the battery system which concerns on embodiment of this disclosure. It is a figure which shows the structure of the assembled battery and the switching device in more detail. It is a figure for demonstrating the switching of the electrical connection state between a block and a PCU by the control of a switching device. It is a figure for demonstrating the structure of each cell in more detail. It is a figure for demonstrating the deterioration area of an assembled battery. It is a flowchart explaining the calculation procedure of the deterioration evaluation value based on the temperature information. It is a figure which showed an example of the relationship between temperature and deterioration rate. It is a figure for demonstrating the discharge control of the assembled battery in the resistance reduction region. It is a time chart which shows an example of the discharge control of the assembled battery in the resistance reduction region. It is a figure for demonstrating the discharge control of the assembled battery in the resistance increase region. It is a time chart which shows an example of the discharge control of the assembled battery in the resistance increase region. It is a flowchart for demonstrating the discharge control of the assembled battery in this embodiment.

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 designated by the same reference numerals, and the description thereof will not be repeated.

In the following, a configuration in which the secondary battery system according to the present embodiment is mounted on the hybrid vehicle will be described as an example. However, the secondary battery system according to the present embodiment is not limited to the hybrid vehicle, but is a set for traveling. It can be applied to all vehicles equipped with batteries (for example, plug-in hybrid vehicles, electric vehicles, fuel cell vehicles). Further, the application of the secondary battery system according to the present embodiment is not limited to the vehicle, and may be, for example, stationary.

[Embodiment]
<Configuration of secondary battery system>
FIG. 1 is a diagram schematically showing an overall configuration of a vehicle equipped with a secondary battery system according to an embodiment of the present disclosure. With reference to FIG. 1, the vehicle 1 is a hybrid vehicle, which includes a secondary battery system 2, motor generators 210 and 220, an engine 230, a power splitting device 240, a drive shaft 250, and drive wheels 260. To be equipped. The secondary battery system 2 includes an assembled battery 10, a monitoring unit 20, a switching device 30, a power control unit (PCU: Power Control Unit) 40, and an electronic control unit (ECU: Electronic Control Unit) 100.

Each of the motor generators 210 and 220 is an AC rotating electric machine, for example, a three-phase AC synchronous motor in which a permanent magnet is embedded in a rotor. The motor generator 210 is mainly used as a generator driven by the engine 230 via the power splitting device 240. The electric power generated by the motor generator 210 is supplied to the motor generator 220 or the assembled battery 10 via the PCU 40.

The motor generator 220 mainly operates as an electric motor and drives the drive wheels 260. The motor generator 220 is driven by receiving at least one of the electric power from the assembled battery 10 and the electric power generated by the motor generator 210, and the driving force of the motor generator 220 is transmitted to the drive shaft 250. On the other hand, when the vehicle is braking or the acceleration is reduced on a downward slope, the motor generator 220 operates as a generator to generate regenerative power generation. The electric power generated by the motor generator 220 is supplied to the assembled battery 10 via the PCU 40.

The engine 230 is an internal combustion engine that outputs power by converting the combustion energy generated when the air-fuel mixture is burned into the kinetic energy of movers such as pistons and rotors.

The power splitting device 240 includes, for example, a planetary gear mechanism (not shown) having three rotating shafts of a sun gear, a carrier, and a ring gear. The power splitting device 240 divides the power output from the engine 230 into a power for driving the motor generator 210 and a power for driving the drive wheels 260.

The assembled battery 10 includes three blocks (battery blocks) 11 to 13 connected in series, as will be described later in FIG. Each block 11-13 is configured to include one or more cells 101. The assembled battery for a vehicle typically includes several tens to several hundreds of cells, but for convenience of explanation, in the present embodiment, the assembled battery 10 includes 12 cells 101 (each). A configuration in which blocks 11 to 13 include four cells 101) will be described as an example. However, it is confirmed that the number of blocks is not limited to 3 if there are a plurality of blocks, and the number of cells is not limited to 12.

The assembled battery 10 and the PCU 40 are electrically connected by power lines PL and NL. The assembled battery 10 stores electric power for driving the motor generators 210 and 220, and supplies electric power to the motor generators 210 and 220 through the PCU 40. Further, the assembled battery 10 is charged by receiving the generated power through the PCU 40 at the time of power generation of the motor generators 210 and 220.

The monitoring unit 20 includes a voltage sensor 21, a current sensor 22, and a temperature sensor 23. The voltage sensor 21 detects the voltage VB of each cell 101 included in the assembled battery 10. The current sensor 22 detects the current IB input / output to / from the assembled battery 10. The temperature sensor 23 detects the temperature TB for each cell 101. A plurality of temperature sensors 23 (a number smaller than the number of cells) may be provided for the assembled battery 10, and the temperature TB may be detected using a plurality of (for example, several) cells 101 adjacent to each other as monitoring units. In the following, the voltages of blocks 11 to 13 will be described as V1 to V3, respectively. Further, the temperatures of blocks 11 to 13 are described as TB1 to TB3, respectively.

The switching device 30 is configured to be able to switch the electrical connection state between each block 11 to 13 and the PCU 40 when the assembled battery 10 is discharged in response to a control signal from the ECU 100. The detailed configuration of the assembled battery 10 and the switching device 30 will be described with reference to FIG.

The PCU 40 executes bidirectional power conversion between the assembled battery 10 and the motor generators 210 and 220 according to the control signal from the ECU 100. The PCU 40 is configured so that the states of the motor generators 210 and 220 can be controlled separately. For example, the motor generator 220 can be put into a power running state while the motor generator 210 is in a regenerative state (power generation state). The PCU 40 includes, for example, two inverters provided corresponding to the motor generators 210 and 220, and a converter (neither shown) that boosts the DC voltage supplied to each inverter to a voltage higher than the output voltage of the assembled battery 10. Consists of including. The PCU 40 corresponds to the "power conversion device" according to the present disclosure.

The ECU 100 includes a CPU (Central Processing Unit) 100A, a memory (more specifically, a ROM (Read Only Memory) and a RAM (Random Access Memory)) 100B, and an input / output port for inputting / outputting various signals (shown in the figure). ) And is included. The ECU 100 controls the charging / discharging of the assembled battery 10 based on the signal received from each sensor and the program and the map stored in the memory 100B. More specifically, the ECU 100 controls the engine 230, the switching device 30, and the PCU 40 so that the voltage of each block 11 to 13 approaches the target voltage. Further, the ECU 100 calculates a parameter (hereinafter, also referred to as “deterioration evaluation value” D) for evaluating the deterioration state of the assembled battery 10 (more specifically, each block 11 to 13). Then, the ECU 100 controls the discharge of the assembled battery 10 based on the deterioration evaluation value D of each block 11 to 13. The discharge control of the assembled battery 10 will be described in detail later. The ECU 100 corresponds to the "control device" according to the present disclosure.

FIG. 2 is a diagram for explaining the configurations of the assembled battery 10 and the switching device 30 in more detail. With reference to FIG. 2, the assembled battery 10 includes a block 11 shown on the left side of the figure, a block 12 shown in the center, and a block 13 shown on the right side. Each block 11-13 contains four cells 101. In each block 11 to 13, the positive electrode terminal of a certain cell and the negative electrode terminal of a cell adjacent to the cell are fastened by a bus bar 102 and electrically connected. As a result, adjacent cells are connected in series inside each of the blocks 11 to 13.

The assembled battery 10 is provided with a switching device 30 for switching the connection state between the blocks 11 to 13. The switching device 30 includes terminals T1 to T4 and switching elements Q1 to Q3. The terminals T1 to T4 are configured to be appropriately connected to either the power line PL or NL connecting the assembled battery 10 and the PCU 40 by a relay circuit (not shown) that responds to a control signal from the ECU 100. Each of the switching elements Q1 to Q3 is a semiconductor element such as an IGBT (Insulated Gate Bipolar Transistor), and can be switched between on (conducting state) and off (non-conducting state) in response to a control signal from the ECU 100. .. However, the switching elements Q1 to Q3 may be other circuit components (for example, relays) that can be switched on and off.

FIG. 3 is a diagram for explaining switching of the electrical connection state between the blocks 11 to 13 and the PCU 40 under the control of the switching device 30. In FIG. 3A, the terminal T1 is electrically connected to the power line PL, the terminal T4 is electrically connected to the power line NL, and the switching elements Q1 to Q3 are controlled to be on, on, and off, respectively. The state is shown. As a result, all the blocks 11 to 13 can be connected in series to charge and discharge.

In FIG. 3B, the terminal T1 is electrically connected to the power line PL, the terminal T4 is electrically connected to the power line NL, and the switching elements Q1 to Q3 are controlled to be off, off, and on, respectively. The state is shown. As a result, the blocks 12 can be bypassed and the blocks 11 and 13 can be connected in series, and only the blocks 11 and 13 can be charged and discharged.

FIG. 3C shows a state in which the terminal T2 is electrically connected to the power line PL, the terminal T3 is electrically connected to the power line NL, and the switching elements Q1 to Q3 are all controlled to be off. Has been done. As a result, only the block 12 can be charged and discharged.

Note that, in FIGS. 2 and 3, a configuration including a plurality of cells 101 in which the assembled batteries 10 are connected in series has been described as an example, but the connection state of the cells 101 in the assembled batteries 10 is limited to this. is not it. For example, cells 101 connected in parallel to each other may be included in the assembled battery 10. Therefore, for example, when the number of cells 101 is 12, a configuration of 2 parallel × 6 series, a configuration of 3 parallel × 4 series, a configuration of 4 parallel × 3 series, a configuration of 6 parallel × 2 series, or the like is also possible.

FIG. 4 is a diagram for explaining the configuration of each cell 101 in more detail. The cell 101 in FIG. 4 is shown through the inside thereof. With reference to FIG. 4, in the present embodiment, the cell 101 is a lithium ion secondary battery.

The cell 101 has a square (substantially rectangular parallelepiped) battery case 111. The upper surface of the battery case 111 is sealed by the lid 112. One end of each of the positive electrode terminal 113 and the negative electrode terminal 114 projects outward from the lid 112. The other ends of the positive electrode terminal 113 and the negative electrode terminal 114 are connected to the internal positive electrode terminal and the internal negative electrode terminal (neither of them is shown) inside the battery case 111, respectively. The electrode body 115 is housed inside the battery case 111. The electrode body 115 is formed by laminating a positive electrode 116 and a negative electrode 117 via a separator 118 and winding the laminated body. The electrolytic solution is held in the positive electrode 116, the negative electrode 117, the separator 118, and the like.

For the positive electrode 116, the negative electrode 117, the separator 118, and the electrolytic solution, conventionally known configurations and materials as the positive electrode, the negative electrode, the separator, and the electrolytic solution of the lithium ion secondary battery can be used, respectively. As an example, a ternary material in which a part of lithium cobalt oxide is replaced with nickel and manganese can be used for the positive electrode. Graphite can be used for the negative electrode. Polyolefin (for example, polyethylene or polypropylene) can be used as the separator. The electrolytic solution is an organic solvent (for example, a mixed solvent of DMC (dimethyl carbonate), EMC (ethyl methyl carbonate) and EC (ethylene carbonate)), a lithium salt (for example, LiPF ₆ ), and an additive (for example, LiBOB (lithium bis)). (oxalate) borate) or Li [PF ₂ (C2O ₄ ) ₂ ]). However, the cell 101 is not limited to the lithium ion secondary battery, and may be, for example, a nickel hydrogen battery.

<Deterioration of assembled battery>
In the secondary battery system 2 configured as described above, deterioration (so-called material deterioration or aging) in which the internal resistance of each block 11 to 13 increases with the use of the assembled battery 10 (or with the passage of time). Deterioration) is known to occur. The present inventors have focused on the fact that deterioration may proceed as follows depending on the configuration and material of the assembled battery 10 (cell 101).

FIG. 5 is a diagram for explaining a deteriorated region of the assembled battery 10. In FIG. 5, the horizontal axis represents the deterioration evaluation value D of each block 11 to 13. The vertical axis shows the rate of increase (resistance increase rate) of the internal resistance R of each block 11 to 13 based on the initial state (for example, the state at the time of manufacturing the assembled battery 10).

The deterioration evaluation value D shown on the horizontal axis of FIG. 5 can be calculated based on the temperature information of the assembled battery 10 (or cell 101) as described below.

FIG. 6 is a flowchart illustrating a procedure for calculating the deterioration evaluation value D based on the temperature information. The flowchart shown in FIG. 6 and FIG. 12 to be described later is called from the main routine (not shown) every time a predetermined condition is satisfied or a predetermined calculation cycle elapses, and is executed by the ECU 100. Further, each step (hereinafter abbreviated as "S") included in this flowchart is basically realized by software processing by the ECU 100, but is realized by dedicated hardware (electric circuit) manufactured in the ECU 100. You may.

With reference to FIG. 6, in S1, the ECU 100 acquires the detected value of the temperature TB of the assembled battery 10 from the temperature sensor 23. Next, the ECU 100 estimates the deterioration rate β of the assembled battery 10 based on the temperature TB acquired in S1 (S2).

FIG. 7 is a diagram showing an example of the relationship between the temperature TB and the deterioration rate β. In FIG. 7, the horizontal axis represents the reciprocal of the temperature TB (1 / TB), and the vertical axis represents the natural logarithm (ln (β)) of the deterioration rate β. As shown in FIG. 7, the temperature dependence of the deterioration rate β according to the Arrhenius side is understood. The relationship between the temperature TB and the deterioration rate β is obtained in advance by an experiment or the like, and is stored in advance as a map in the memory 100B of the ECU 100. Therefore, the ECU 100 can estimate the deterioration rate β based on the temperature TB detected by the temperature sensor 23 by referring to the map. It is also possible to adopt the form of the relational expression (function) instead of the above map.

With reference to FIG. 6 again, in S3, the ECU 100 integrates the deterioration rate β estimated in S2, and calculates the deterioration evaluation value D from the integrated value.

<Deteriorated area>
When the deterioration evaluation value D calculated as described above is included in the region shown by K1 in FIG. 5, that is, the region between the initial value D0 and the reference value Dc where the resistance increase rate is the minimum, the internal resistance R is , It decreases as the deterioration evaluation value D increases. Therefore, this region is also referred to as a "resistance reduction region" K1. The decrease in internal resistance in the resistance reduction region K1 is due to the fact that the film initially formed on the electrodes (positive electrode 116 or negative electrode 117) of the cell 101 was removed (disappeared) as the assembled battery 10 was charged and discharged. It is considered to be.

After that, in K2 where the deterioration evaluation value D is in the region of the reference value Dc or more, the internal resistance increases as the deterioration evaluation value D increases. Hereinafter, this region is also referred to as a “resistance increase region” K2. The resistance decrease region K1 and the resistance increase region K2 correspond to the "first region" and the "second region" according to the present disclosure, respectively.

Inside the assembled battery 10 mounted on the vehicle 1, temperature variations may occur in each of the blocks 11 to 13. If the state in which such temperature variation occurs continues, the deterioration evaluation value D may be a different value for each block 11 to 13.

When the assembled battery 10 is discharged, in order to protect the assembled battery 10, the voltages of all the blocks 11 to 13 are controlled so as not to fall below a predetermined lower limit voltage LL. More specifically, when the voltage of any of the blocks 11 to 13 reaches the lower limit voltage LL, the discharge of the assembled battery 10 beyond that is stopped (prohibited). Since the currents IB flowing through all the blocks 11 to 13 are the same, if the deterioration evaluation value D varies between the blocks 11 to 13, the magnitude of the internal resistance R will be different for each block 11 to 13, and as a result. , The voltage drop amount (= IB × R) will be different for each block 11 to 13. Therefore, when the assembled battery 10 is discharged, the voltage of some blocks reaches the lower limit voltage LL earlier than the voltage of the other blocks, and a situation may occur in which the assembled battery 10 cannot be discharged any more.

Therefore, in the present embodiment, the deterioration evaluation values D (D1 to D3) of each of the blocks 11 to 13 are calculated according to the temperature distribution in the assembled battery 10. When the deterioration evaluation value D is in the resistance decrease region K1, the larger the deterioration evaluation value D is, the lower the target voltage Vtag is set, while when the deterioration evaluation value D is in the resistance increase region K2, the target voltage Vtag is set lower. The larger the deterioration evaluation value D, the higher the target voltage Vtag is set.

In the following, in order to avoid complicating the explanation of the discharge control of the assembled battery 10 in the present embodiment, it is assumed that the states (temperature, deterioration evaluation value, etc.) of the blocks 11 and 13 at both ends are substantially equal to each other. To do. Therefore, among the blocks 11 and 13, the block 11 will be described as a representative. First, the case where the deterioration evaluation value D1 of the block 11 and the deterioration evaluation value D2 of the block 12 are both within the resistance reduction region K1 will be described with reference to FIGS. 8 and 9. Subsequently, the case where the deterioration evaluation values D1 and D2 are both within the resistance increase region K2 will be described with reference to FIGS. 10 and 11.

<Discharge control in resistance reduction region>
FIG. 8 is a diagram for explaining the discharge control of the assembled battery 10 in the resistance reduction region K1. In FIG. 8 and FIG. 10 described later, the horizontal axis indicates the positions of blocks 11 to 13 in the assembled battery 10. The vertical axis shows the temperature TB of blocks 11 to 13, the deterioration evaluation value D, the internal resistance R, and the target voltage Vtag in order from the top.

With reference to FIG. 8, for example, when the temperature TB1 of the block 11 at the end is higher than the temperature TB2 of the block 12 at the center, the deterioration evaluation value D1 of the block 11 at the end is the deterioration evaluation of the block 12 at the center. Greater than the value D2. In the situation shown in FIG. 8, since the deterioration evaluation values D1 to D3 of the blocks 11 to 13 are all within the resistance reduction region K1, the internal resistance R2 of the block 12 is higher than the internal resistance R1 of the block 11.

In this case, it is conceivable to set the target voltage Vtag uniformly as in the comparative example. However, in the present embodiment, the target voltage Vtag1 of the block 11 at the end is set lower than the target voltage Vtag2 of the block 12 at the center. This is because the control as described below is realized.

FIG. 9 is a time chart showing an example of discharge control of the assembled battery 10 in the resistance reduction region K1. In FIG. 9 and FIG. 11 described later, the horizontal axis indicates the elapsed time. The vertical axis shows the voltage VB of blocks 11 to 13.

FIG. 9A shows a time chart for explaining the discharge control in the comparative example. As described with reference to FIG. 8, the internal resistance R2 of the block 12 is higher than the internal resistance R1 of the block 11. When all blocks 11 to 13 are connected in series (see FIG. 3A), the currents IB flowing through blocks 11 to 13 are equal. Therefore, when the assembled battery 10 is discharged, the voltage drop amount (= IB × R2) in the block 12 is larger than the voltage drop amount (= IB × R1) in the blocks 11 and 13. When the target voltage Vtag of blocks 11 to 13 is uniformly set, the voltage V2 of block 12 of blocks 11 to 13 reaches the lower limit voltage LL (see time t12), and the assembled battery 10 is discharged more than that. Is prohibited. That is, even though the voltage V1 of the block 11 has not reached the lower limit voltage LL, the discharge of the assembled battery 10 is limited.

On the other hand, FIG. 9B shows a time chart for explaining the discharge control in the present embodiment. According to this embodiment, the target voltage Vtag1 of the block 11 is set lower than the target voltage Vtag2 of the block 12. Therefore, first, from time t10 to time t11, as described in FIG. 3B, the switching device 30 is controlled so that the block 12 is bypassed and the discharge is performed only from the blocks 11 and 13. .. Then, when the voltage difference ΔV (= V2-V1) between the voltage V1 of the block 11 and the voltage V2 of the block 12 reaches ΔVc at time t11, all the blocks 11 to 13 are shown in FIG. 3 (A). The switching device 30 is controlled so that the discharge of the above is performed. As a result, the discharge of the assembled battery 10 can be continued until the time t13 after the time t12.

As described above, according to the present embodiment, the blocks 11 and 13 having relatively low internal resistance are preferentially discharged , and the block 12 is started to be discharged after the discharge of the blocks 11 and 13 is started. The timing at which the voltage V2 of 12 reaches the lower limit voltage LL can be delayed. Further, by setting the voltage difference ΔV to an appropriate value experimentally or by design, the timing at which the voltage V2 of the block 12 reaches the lower limit voltage LL and the timing at which the voltage V1 of the block 11 reaches the lower limit voltage LL. Can be set to be approximately equal. As a result, the assembled battery 10 can be continuously discharged until any one of the voltages V1 to V3 of the blocks 11 to 13 (V1 in the example shown in FIG. 9B) reaches the lower limit voltage LL. As a result, a larger amount of electric power can be taken out from the assembled battery 10 as compared with the comparative example. That is, the required discharge performance can be exhibited in the assembled battery 10.

<Discharge control in resistance increase region>
FIG. 10 is a diagram for explaining the discharge control of the assembled battery 10 in the resistance increasing region K2. FIG. 10 is contrasted with FIG. In FIG. 10, the difference between the deterioration evaluation value D and the internal resistance R shown in FIG. 8 is shown with diagonal lines.

With reference to FIG. 10, in the resistance increasing region K2 as well as the discharge control in the resistance decreasing region K1 (see FIGS. 8 and 9), the temperature TB1 of the block 11 at the end is higher than the temperature TB2 of the block 12 at the center. When it is high, the deterioration evaluation value D1 of the block 11 at the end becomes larger than the deterioration evaluation value D2 of the block 12 at the center. In FIG. 10, since the deterioration evaluation values D1 to D3 of the blocks 11 to 13 are all within the resistance increase region K2, the internal resistance R1 of the block 11 is higher than the internal resistance R2 of the block 12. In this case, in the present embodiment, the target voltage Vtag2 of the central block 12 is set lower than the target voltage Vtag1 of the end block 11.

FIG. 11 is a time chart showing an example of discharge control of the assembled battery 10 in the resistance increase region K2. FIG. 11 is contrasted with FIG.

With reference to FIG. 11, in the comparative example, all the blocks 11 to 13 are uniformly discharged, and the discharge of the assembled battery 10 is stopped at time t22 (see FIG. 11 (A)). On the other hand, in the present embodiment, as shown in FIG. 11B, first, the switching device 30 is controlled so that the discharge is performed only from the block 12 from the time t20 to the time t21. Then, when the voltage difference ΔV (= V1-V2) between the voltage V1 and the voltage V2 reaches ΔVc at time t21, all the blocks 11 to 13 are discharged as shown in FIG. 3 (A). The switching device 30 is controlled. After that, the assembled battery 10 is discharged from the time t21 to the time t23. As described above, according to the present embodiment, the discharge of the assembled battery 10 can be continued for a longer period from the time t22 to the time t23 as compared with the comparative example.

As described above, according to the present embodiment, by preferentially discharging the block 12 having a relatively low internal resistance R2, the timing at which the voltage V1 of the block 11 reaches the lower limit voltage LL can be delayed. As a result, similarly to the control in the resistance reduction region K1, the discharge of the assembled battery 10 can be continued until any one of the voltages V1 to V3 of the blocks 11 to 13 reaches the lower limit voltage LL, which is larger. The amount of electric power can be taken out from the assembled battery 10.

<Discharge control flow>
FIG. 12 is a flowchart for explaining the discharge control of the assembled battery 10 in the present embodiment. With reference to FIGS. 1 to 3 and 12, in S10, the ECU 100 acquires the temperatures TB1 to TB3 of the blocks 11 to 13 from the temperature sensors 23, respectively, and integrates them for a predetermined period.

In S20, the ECU 100 creates a temperature frequency distribution for each block 11-13. Then, the ECU 100 adopts the mode value of the temperature for each of the blocks 11 to 13 as the temperature of the block. However, for example, the average or median temperature may be adopted as the temperature of the block.

In S30, the ECU 100 calculates the deterioration evaluation values D1 to D3 of the blocks 11 to 13 based on the temperature frequency distribution created in S20, respectively. Since the calculation method of the deterioration evaluation values D1 to D3 has been described in detail with reference to FIGS. 6 and 7, the description will not be repeated here.

In S40, the ECU 100 determines whether or not the deterioration evaluation value D2 of the central block 12 has reached the reference value Dc (see FIG. 5). When the deterioration evaluation value D2 does not reach the reference value Dc, that is, when the deterioration evaluation value D2 is within the resistance reduction region K1 (NO in S40), the ECU 100 sets the target voltage Vtag of each block according to the deterioration evaluation value. And set (S50). More specifically, as described with reference to FIGS. 8 and 9, when the deterioration evaluation value D1 of the block 11 is larger than the deterioration evaluation value D2 of the block 12, the target voltage Vtag1 of the block 11 is the block 12. It is set lower than the target voltage Vtag2 (Vtag1 <Vtag2). After that, as described with reference to FIG. 9 (B), the block 11 is discharged while stopping the discharge of the block 12 (see the period from time t10 to time t11 in S60 and FIG. 9 (B)). .. Although not shown, on the contrary, when the deterioration evaluation value D2 is larger than the deterioration evaluation value D1, the target voltage Vtag2 is set lower than the target voltage Vtag1 (Vtag2 <Vtag1).

On the other hand, when the deterioration evaluation value D2 reaches the reference value Dc, that is, when the deterioration evaluation value D2 is within the resistance increase region K2 (YES in S40), the ECU 100 sets the target voltage Vtag of each block as the deterioration evaluation value. (S70). More specifically, as described with reference to FIGS. 10 and 11, when the deterioration evaluation value D2 is smaller than the deterioration evaluation value D1, the target voltage Vtag2 is set higher than the target voltage Vtag1 (Vtag2 <Vtag1). .. Then, as described in FIG. 11 (B), the block 12 is discharged while stopping the discharge of the blocks 11 and 13 (S80, the period from the time t20 to the time t21 in FIG. 11 (B)). reference). When the deterioration evaluation value D2 is larger than the deterioration evaluation value D1, the target voltage Vtag1 is set lower than the target voltage Vtag2 (Vtag1 <Vtag2).

In S90, the ECU 100 determines whether or not the voltage difference (absolute value) | ΔV | (= | V1-V2 |) between the voltage V1 of the block 11 and the voltage V2 of the block 12 has reached a predetermined value ΔVc. .. When the voltage difference ΔVc is less than the predetermined value ΔV (NO in S90), the ECU 100 returns the process to S60 or S80 and continues discharging only a part of the blocks. Then, when the voltage difference ΔV becomes a predetermined value ΔV or more (YES in S90), the ECU 100 controls the switching device 30 and the PCU 40 so that all the blocks 11 to 13 are discharged (S100).

After that, the assembled battery 10 is continuously discharged until the voltage of any of the blocks reaches the lower limit voltage LL (NO in S110). When the voltage of any block reaches the lower limit voltage LL (YES in S110), the ECU 100 controls the PCU 40 to stop the discharge of the assembled battery 10 (S120).

As described above, when the deterioration evaluation value D is within the resistance reduction region K1, the lower the deterioration evaluation value D, the higher the internal resistance R, and the voltage tends to reach the lower limit voltage LL. Therefore, in the example shown in FIGS. 8 and 9, only the blocks 11 and 13 are connected to the PCU 40, and the block 12 having a deterioration evaluation value D2 lower than the deterioration evaluation values D1 and D3 of the blocks 11 and 13 is Blocked from PCU40. That is, the blocks 11 and 13 are discharged while the discharge of the block 12 having a relatively low deterioration evaluation value D2 (in other words, the block 12 having a relatively high internal resistance R2) is stopped. As a result, as compared with the case where all the blocks 11 to 13 are uniformly discharged, the number of blocks 11 and 13 to be discharged (see the period between the time t10 and the time t11 in FIG. 9B) is set. The dischargeable period of the battery 10 can be extended. Therefore, the required discharge performance can be exhibited in the assembled battery 10. When the deterioration evaluation value D is within K2 in the resistance increase region, the relationship between the block to be discharged (block 12 in the example shown in FIG. 11B) and the block to stop the discharge (blocks 11 and 13) is reversed. However, the required discharge performance can be exhibited as in the case where the deterioration evaluation value D is within the resistance reduction region K1.

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

1 vehicle, 2 secondary battery system, 10 sets of batteries, 11, 12, 13 blocks, 20 monitoring units, 21 voltage sensor, 22 current sensor, 23 temperature sensor, 30 switching device, 100B memory, 101 cells, 102 bus bar, 111 Battery case, 112 lid, 113 positive electrode terminal, 114 negative electrode terminal, 115 electrode body, 116 positive electrode, 117 negative electrode, 118 separator, 210, 220 motor generator, 230 engine, 240 power divider, 250 drive shaft, 260 drive wheels, NL, PL power line, Q1 to Q3 switching elements.

Claims (2)

An assembled battery containing multiple battery blocks connected in series,
A power conversion device configured to discharge the assembled battery and
A switching device configured to be able to switch the electrical connection state between each of the plurality of battery blocks and the power conversion device when the assembled battery is discharged.
The deterioration evaluation value for evaluating the deterioration state of each of the plurality of battery blocks is calculated so that the higher the temperature of the assembled battery is, the faster the increase of the deterioration evaluation value is , and the calculated deterioration evaluation value is calculated. The power conversion device and the control device for controlling the switching device are provided by the device.
The deterioration region defined by the deterioration evaluation value and the internal resistance of each of the plurality of battery blocks is a first region which is a region in which the internal resistance decreases as the deterioration evaluation value increases with the passage of time. There is a second region in which the internal resistance increases as the deterioration evaluation value increases with the passage of time.
When the plurality of battery blocks include a first battery block and a second battery block having a lower deterioration evaluation value than the first battery block, the control device may be used.
When the deterioration evaluating value of each of the plurality of battery blocks is in said first region, said first cell block is connected to the power converter and the second battery block is the The switching device is controlled so as to be cut off from the power conversion device.
When the deterioration evaluating value of each of the plurality of battery blocks is in said second area, said second cell block is connected to the power converter, and said first cell block is the The switching device is controlled so as to be cut off from the power conversion device .
When the absolute value of the voltage difference between the voltage of the first battery block and the voltage of the second battery block exceeds a predetermined value, both the first and second battery blocks are connected to the power conversion device. A secondary battery system that controls the switching device so as to be performed. Further equipped with a temperature sensor for detecting the temperature of the assembled battery,
The control device is
By referring to the pre-determined relationship between the temperature and the deterioration rate, the deterioration rate of the plurality of battery blocks is estimated from the temperature detected by the temperature sensor.
The secondary battery system according to claim 1, wherein the deterioration evaluation value is calculated from the estimated integrated value of the deterioration rate.

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