JP2015109191A - Power storage system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power storage system which determines an abnormal state of a power storage element included in a power storage block to restrict input/output of a power storage device.SOLUTION: A power storage device (10) has a plurality of power storage blocks (11) which are connected in series. Each power storage block has a plurality of power storage elements (12) which are connected in parallel. A temperature sensor (23) detects temperature of the power storage block. A controller (40) presumes the temperature of the power storage block using an estimation formula in which a heat generating component in accordance with electric power which substantially uniformly flows to all power storage elements in the power storage block and radiation component in which heat is discharged from the power storage block are defined. When the detected temperature is higher than the estimated temperature and the difference between the detected temperature and the estimated temperature is a threshold value or more, the controller restricts input/output of the power storage device.

Description

  The present invention relates to a power storage system that determines an abnormal state of a power storage element in a power storage block in which a plurality of power storage elements are connected in parallel.

  In an assembled battery in which a plurality of single cells are connected in series, the internal resistance of each single battery can be calculated based on the voltage value of each single battery and the current value of the assembled battery (each single battery). An assembled battery may include a plurality of single cells connected in parallel. Specifically, a battery block is configured by connecting a plurality of single cells in parallel, and a battery pack is configured by connecting a plurality of battery blocks in series.

JP 2007-141558 A JP 2007-157348 A

  When only the internal resistance of some of the cells included in the battery block rises, the current easily flows to other cells except for this cell. Here, if the current value of each cell constituting the battery block is detected, it can be seen that the internal resistance of the cell is increased. However, in this case, a current sensor must be provided for each single cell, and the number of current sensors increases.

  The power storage system of the present invention includes a power storage device, a temperature sensor, and a controller. The power storage device has a plurality of power storage blocks connected in series. Each power storage block has a plurality of power storage elements connected in parallel. The temperature sensor detects the temperature of the power storage block. The controller calculates the temperature of the power storage block using an estimation formula that defines the heat generation component that accompanies current flow to all power storage elements in the power storage block substantially uniformly and the heat dissipation component that releases heat from the power storage block. presume. Here, when the detected temperature is higher than the estimated temperature and the difference between the detected and estimated temperatures is equal to or greater than a threshold value, the controller limits input / output of the power storage device.

  When the power storage element included in the power storage block is in an abnormal state, a current easily flows to another power storage element, and the temperature of the power storage block is likely to rise. Thereby, the temperature detected by the temperature sensor is likely to rise. Here, the abnormal state includes a state where the internal resistance of the power storage element is excessively increased and a state where the current path of the power storage element is interrupted.

  On the other hand, the temperature of the power storage block estimated from the estimation formula does not consider the abnormal state of the power storage element. Therefore, if it is determined that the difference between the detected and estimated temperatures is equal to or greater than the threshold value, it can be determined that the power storage element is in an abnormal state. In the present invention, it is possible to determine whether or not the storage element is in an abnormal state by comparing the temperatures (detected temperature and estimated temperature) of the storage block without detecting the current value of each storage element. If the power storage element is in an abnormal state, the power storage device can be protected by limiting the input / output of the power storage device.

It is a figure which shows the structure of a battery system. It is a figure which shows the structure of an assembled battery. It is a flowchart explaining the process which discriminate | determines the abnormal state of a battery block. It is a figure which shows the structure of a cell.

  Examples of the present invention will be described below.

  A battery system (corresponding to a power storage system) that is Embodiment 1 of the present invention will be described with reference to FIG. The battery system of this embodiment is mounted on a vehicle. Vehicles include hybrid cars and electric cars. The hybrid vehicle includes an engine or a fuel cell in addition to the assembled battery 10 as a power source for running the vehicle. The electric vehicle includes only the assembled battery 10 as a power source for running the vehicle.

  As will be described later, the monitoring unit 21 detects the voltage value Vb of each battery block included in the assembled battery 10 and outputs the detection result to the controller 40. The current sensor 22 detects the current value Ib of the assembled battery 10 and outputs the detection result to the controller 40. In this embodiment, the current value Ib when the assembled battery 10 is discharged is a positive value, and the current value Ib when the assembled battery 10 is charged is a negative value.

  The temperature sensor 23 detects a temperature Tb_d of a battery block, which will be described later, and outputs the detection result to the controller 40. The temperature sensor 24 detects the temperature Tf around the assembled battery 10 and outputs the detection result to the controller 40. For example, when the temperature of the assembled battery 10 is adjusted by driving the fan and supplying the air in the vehicle compartment to the assembled battery 10, the temperature sensor 24 detects the temperature Tf of the air supplied to the assembled battery 10. be able to.

  The controller 40 has a memory 41. The memory 41 stores information used when the controller 40 performs predetermined processing (particularly processing described in the present embodiment). Note that the memory 41 can also be provided outside the controller 40.

  A positive electrode line PL is connected to the positive electrode terminal of the assembled battery 10, and a negative electrode line NL is connected to the negative electrode terminal of the assembled battery 10. A system main relay SMR-B is provided in the positive electrode line PL, and a system main relay SMR-G is provided in the negative electrode line NL. System main relays SMR-B and SMR-G are switched between ON and OFF in response to a drive signal from controller 40.

  The assembled battery 10 is connected to the inverter 31 via the positive electrode line PL and the negative electrode line NL. Here, if the system main relays SMR-B and SMR-G are on, the assembled battery 10 is connected to the inverter 31, and the battery system shown in FIG. 1 is in a start-up state (Ready-On). On the other hand, if the system main relays SMR-B and SMR-G are off, the connection between the assembled battery 10 and the inverter 31 is cut off, and the battery system shown in FIG. 1 is in a stopped state (Ready-Off).

  The inverter 31 converts the DC power output from the assembled battery 10 into AC power, and outputs the AC power to the motor / generator 32. The motor / generator 32 receives AC power from the inverter 31 and generates kinetic energy (power) for running the vehicle. When the vehicle is decelerated or stopped, the motor / generator 32 converts kinetic energy generated during braking of the vehicle into electric energy (AC power). The inverter 31 converts the AC power generated by the motor / generator 32 into DC power and outputs the DC power to the assembled battery 10. Thereby, regenerative electric power can be stored in the assembled battery 10.

  A booster circuit can be provided in the current path between the assembled battery 10 and the inverter 31. The booster circuit can boost the output voltage of the assembled battery 10 and output the boosted power to the inverter 31. The booster circuit can step down the output voltage of the inverter 31 and output the stepped down power to the assembled battery 10.

  FIG. 2 shows the configuration of the assembled battery 10. The assembled battery (corresponding to the power storage device of the present invention) 10 has a plurality of battery blocks (corresponding to the power storage block of the present invention) 11 connected in series. The assembled battery 10 is configured by connecting a plurality of battery blocks 11 in series. The number of battery blocks 11 constituting the assembled battery 10 can be set as appropriate.

  Each battery block 11 has a plurality of single cells (corresponding to the storage element of the present invention) 12 connected in parallel. The number of the single cells 12 constituting the battery block 11 can be set as appropriate. As the unit cell 12, a secondary battery such as a nickel metal hydride battery or a lithium ion battery can be used. An electric double layer capacitor (capacitor) can be used instead of the secondary battery.

  In this embodiment, a temperature sensor 23 (see FIG. 1) is arranged for each battery block 11. Thereby, the temperature Tb_d of each battery block 11 can be detected using the temperature sensor 23. Note that the temperature sensor 23 may not be disposed in each battery block 11. The temperature of the battery block 11 in which the temperature sensor 23 is not arranged can be estimated using the detection result (temperature Tb_d) of the temperature sensor 23 arranged in another battery block 11.

  For example, the battery block 11 in which the temperature sensor 23 is not disposed may be disposed between the two battery blocks 11 in which the temperature sensor 23 is disposed. In this case, based on the two temperatures Tb_d detected by the two temperature sensors 23, the temperature of the battery block 11 where the temperature sensor 23 is not arranged can be estimated.

  Here, if the two temperatures Tb_d are substantially equal, it can be estimated that the temperature of the battery block 11 in which the temperature sensor 23 is not disposed is equal to the temperature Tb_d. Further, if the two temperatures Tb_d are different, the median value of these temperatures Tb_d can be estimated as the temperature of the battery block 11 in which the temperature sensor 23 is not disposed.

  Next, processing for determining an abnormal state of the unit cells 12 included in the battery block 11 will be described with reference to the flowchart shown in FIG. Here, the abnormal state is a state in which the actual internal resistance of the unit cell 12 is higher than the assumed internal resistance. The process shown in FIG. 3 is performed on each battery block 11 and executed by the controller 40.

  In step S <b> 101, the controller 40 detects the temperature Tb_d of the battery block 11 based on the output of the temperature sensor 23. As described above, the temperature of the battery block 11 can also be estimated based on the temperature Tb_d detected by the temperature sensor 23.

  In step S102, the controller 40 estimates the temperature Tb_m of the battery block 11. Specifically, the controller 40 calculates (estimates) the temperature Tb_m based on the following formula (1). Here, the temperature Tb_m when the current flows through all the unit cells 12 included in the battery block 11 substantially equally is calculated.

  In the above formula (1), Tb_m (n) and Tb_m (n−1) indicate the temperature Tb_m of the battery block 11. The temperature Tb_m (n) is the current temperature Tb_m, and the temperature Tb_m (n−1) is the previous temperature Tb_m. Every time the predetermined time (dt) elapses, the temperature Tb_m is calculated.

  Ib is a current value detected by the current sensor 22, and Ib / dt indicates a current value per unit time. Here, an absolute value is used as the current value Ib. R is the internal resistance of the battery block 11 (unit cell 12). The internal resistance R is a value determined in advance from the temperature and SOC of the battery block 11 (unit cell 12) in consideration of the assumed deterioration state of the battery block 11 (unit cell 12). For example, as the internal resistance of the battery block 11 (unit cell 12) increases with the passage of time, if the correspondence between the elapsed time and the internal resistance R is obtained in advance, the internal resistance R corresponding to the elapsed time is calculated. be able to.

  α is a heat generation coefficient and is set in advance. Tf is a temperature detected by the temperature sensor 24. β is a heat dissipation coefficient and is set in advance. κ is a cooling coefficient. In this embodiment, the assembled battery 10 is cooled by driving the fan and supplying air in the vehicle compartment to the assembled battery 10. For this reason, the cooling coefficient κ is set based on the air volume of the fan.

  As shown in the above formula (1), in consideration of a component that generates heat when the current flows through the battery block 11 (a heat generation term) and a component that releases heat from the battery block 11 (a heat dissipation term), A temperature Tb_m (n) is calculated. The method for estimating the temperature Tb_m is not limited to the above formula (1). That is, the temperature Tb_m may be estimated in consideration of a heat generation component that accompanies current flowing through the battery block 11 (unit cell 12) and a heat dissipation component that releases heat from the battery block 11 (unit cell 12). .

  In step S103, the controller 40 calculates the temperature difference ΔTb. The temperature difference ΔTb is a value obtained by subtracting the temperature Tb_m calculated in the process of step S102 from the temperature Tb_d detected in the process of step S101. When the temperature Tb_d is higher than the temperature Tb_m, the temperature difference ΔTb becomes a positive value. When the temperature Tb_d is lower than the temperature Tb_m, the temperature difference ΔTb becomes a negative value.

  In step S104, the controller 40 determines whether or not the temperature difference ΔTb is smaller than the first threshold value ΔTb_th1. The first threshold value ΔTb_th1 is a positive value, and information specifying the first threshold value ΔTb_th1 is stored in the memory 41. When the temperature difference ΔTb is smaller than the first threshold value ΔTb_th1, the controller 40 ends the process shown in FIG.

  When the temperature difference ΔTb is equal to or greater than the first threshold value ΔTb_th1, the controller 40 determines in step S105 whether the temperature difference ΔTb is equal to or greater than the second threshold value ΔTb_th2. The second threshold value ΔTb_th2 is a positive value larger than the first threshold value ΔTb_th1. Information for specifying the second threshold value ΔTb_th2 is stored in the memory 41.

  When the temperature difference ΔTb is smaller than the second threshold value ΔTb_th2, the controller 40 decreases the allowable input power Win and the allowable output power Wout in step S106. The allowable input power Win is an upper limit power value that allows charging (input) of the battery pack 10. The allowable output power Wout is an upper limit power value that allows discharge (output) of the battery pack 10. When charging / discharging the assembled battery 10, charging / discharging of the assembled battery 10 is controlled so that the electric power of the assembled battery 10 does not exceed the electric power Win, Wout.

  The allowable input power Win and the allowable output power Wout are set based on the temperature and SOC of the assembled battery 10. In the process of step S106, the electric power Win and Wout set based on the temperature and SOC of the assembled battery 10 are reduced. Here, the amount by which the powers Win and Wout are reduced can be set as appropriate. For example, as the temperature difference ΔTb increases, the amount of decrease in the electric power Win, Wout can be increased. Further, in a vehicle equipped with an engine, the allowable output power Wout can be reduced within a range that is greater than or equal to the electric power for starting the engine.

  In step S <b> 107, the controller 40 stops charging / discharging of the assembled battery 10. At this time, the above-described powers Win and Wout are set to 0 [kW]. In the process of step S107, the controller 40 switches the system main relays SMR-B and SMR-G from on to off.

  In the present embodiment, the temperature Tb_m of each battery block 11 can be estimated based on the above formula (1). That is, when it is assumed that the unit cell 12 included in the battery block 11 is not in an abnormal state, the temperature Tb_m of the battery block 11 can be estimated. Here, when the temperature Tb_d as the actually measured value deviates from the temperature Tb_m as the estimated value, it can be determined that the unit cell 12 included in the battery block 11 is in an abnormal state.

  If the internal resistance of the unit cell 12 included in the battery block 11 rises to an abnormal state, it becomes difficult for current to flow through the unit cell 12 and current easily flows through other unit cells 12. As a result, the other unit cells 12 are likely to generate heat, and the temperature Tb_d of the battery block 11 including the unit cells 12 in the heat generation state rises and deviates from the temperature Tb_m.

  In the present embodiment, as described in the processing of steps S106 and S107, charging / discharging of the assembled battery 10 is limited according to the deviation state of the temperature Tb_d from the temperature Tb_m. Thereby, it can suppress that an electric current flows into the unit cell 12 of a heat_generation | fever state, and can suppress the further heat_generation | fever of the unit cell 12. FIG.

  In the process shown in FIG. 3, when the temperature difference ΔTb is between the first threshold value ΔTb_th1 and the second threshold value ΔTb_th2, the electric power Win, Wout can be reduced stepwise. That is, as the temperature difference ΔTb approaches the second threshold value ΔTb_th2, the amount by which the electric power Win, Wout is reduced can be increased.

  On the other hand, as shown in FIG. 4, each cell 12 can be provided with a current breaker 12a. The unit cell 12 has a power generation element 12b connected to a current breaker 12a. The power generation element 12b is an element that performs charging and discharging. The power generation element 12b includes a positive electrode plate, a negative electrode plate, and a separator disposed between the positive electrode plate and the negative electrode plate. The power generation element 12 b is accommodated in a battery case that constitutes the exterior of the unit cell 12. The current breaker 12a may be accommodated in the battery case or may be disposed outside the battery case.

  The current breaker 12a is used to break the current path of the unit cell 12. For example, a fuse, a PTC (Positive Temperature Coefficient) element, or a current cutoff valve can be used as the current breaker 12a. The fuse is blown when an excessive current flows through the power generation element 12b. When the temperature of the PTC element rises, the resistance value of the PTC element rises, thereby suppressing an excessive current from flowing through the power generation element 12b. The current cutoff valve as the current breaker 12a is deformed in response to an increase in the internal pressure of the unit cell 12 (battery case), and breaks the mechanical connection with the power generation element 12b. Thereby, the electric current path in the inside of the cell 12 can be interrupted.

  When the current breaker 12a is activated, no current flows through the power generation element 12b (unit cell 12) connected to the activated current breaker 12a. Here, since the plurality of single cells 12 constituting the battery block 11 are connected in parallel, when no current flows through one single cell 12, current flows through the remaining single cells 12. As a result, the current value of the unit cell 12 increases, and the unit cell 12 easily generates heat. Therefore, the temperature Tb_d of the battery block 11 tends to be higher than the temperature Tb_m.

  According to the process shown in FIG. 3, it is determined whether or not the current breaker 12a is operating based on the temperature difference ΔTb, in other words, whether or not the unit cell 12 including the current breaker 12a is in an abnormal state. can do. Specifically, when the temperature difference ΔTb is equal to or greater than a predetermined threshold, it can be determined that the current breaker 12a is operating.

  In the battery block 11, as the number of the current breakers 12a in the activated state increases, the current easily flows through the single cells 12 in which the current breaker 12a is not activated. Therefore, the temperature Tb_d of the battery block 11 is likely to increase as the number of current breakers 12a in the operating state increases.

  Therefore, in each battery block 11, if the correspondence between the number of the current breakers 12a in the operating state and the temperature difference ΔTb is obtained in advance, the current circuit breaker in the operating state is calculated by calculating the temperature difference ΔTb. The number of 12a can be specified. Information for specifying the correspondence between the number of the current breakers 12a in the operating state and the temperature difference ΔTb can be stored in the memory 41.

10: assembled battery (power storage device), 11: battery block (power storage block),
12: single cell (storage element) 12a: current breaker, 12b: power generation element,
21: monitoring unit, 22: current sensor, 23, 24: temperature sensor,
31: Inverter, 32: Motor generator, 40: Controller,
41: Memory, PL: Positive line, NL: Negative line,
SMR-B, SMR-G: System main relay

Claims (1)

A power storage device in which a plurality of power storage blocks each having a plurality of power storage elements connected in parallel are connected in series;
A temperature sensor for detecting a temperature of the power storage block;
The temperature of the power storage block is determined using an estimation formula that defines a heat generation component that accompanies current flow to all the power storage elements in the power storage block substantially uniformly and a heat dissipation component that releases heat from the power storage block. A controller for estimating
The controller is configured to limit input / output of the power storage device when the detected temperature is higher than the estimated temperature and a difference between the detected and estimated temperatures is a threshold value or more.