JP2015061505A - Power storage system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that whether a current path is blocked or not is unknown, in a power storage element included in a power storage block, when a change amount in SOC of a power storage device does not become large.SOLUTION: A power storage device (10) has a plurality of power storage blocks (11) which are connected in series. Each of the power storage blocks has a plurality of power storage elements (12) which are connected in parallel. Whether the power storage element in which a current path is blocked is included or not is determined, in each power storage block, by comparing the change amount in SOC in the plurality of power storage blocks. When a predetermined time is elapsed while the change amount in SOC in the power storage device or each of the power storage blocks is smaller than a predetermined change amount, an upper limit power which permits input or output of the power storage device is lowered. When a predetermined time is elapsed, supposing the current path is blocked, it is suppressed that an excessive current flows to the power storage element in which the current path is not blocked, by lowering the upper limit power.

Description

  The present invention relates to a power storage system that controls input and output for a power storage block in which a plurality of power storage elements are connected in parallel.

  Some battery packs are configured by connecting a plurality of battery blocks in series. Here, each battery block has a plurality of single cells connected in parallel.

  In the assembled battery described above, there is a possibility that only the current path of a specific unit cell included in a specific battery block may be blocked. For example, in order to prevent an excessive current from flowing to each unit cell, a current circuit breaker (such as a fuse) may be provided to each unit cell. When the current circuit breaker is activated, this unit corresponds to this current circuit breaker. Only the current path of the unit cell is interrupted. Further, when an unintentional disconnection occurs in the wiring connecting each unit cell, only the current path of the unit cell is interrupted.

  In the battery block, a plurality of single cells are connected in parallel, so if no current flows through a single cell whose current path is interrupted, the current flowing through this single cell is transferred to the other single cells connected in parallel. Flowing. Thereby, the current value of the other unit cell becomes larger than the current value when the current path of the unit cell is not interrupted. Here, the higher the current value, the more likely the unit cell to increase in resistance due to the uneven salt concentration. In addition, when a lithium ion secondary battery is used as a single battery, lithium deposition is more likely to occur as the current value increases.

  Therefore, in order to suppress the increase in resistance and the occurrence of lithium deposition, it is necessary to determine whether or not the current path of the unit cell is interrupted.

  Here, the battery block including the single cells whose current paths are cut off (referred to as the first battery block) and the battery blocks where the current paths of all the single cells are not cut off (referred to as the second battery blocks) are described above. For the reason, the current value of the unit cell is different. Accordingly, the amount of change in SOC (State of Charge) in these battery blocks is different. For example, when the assembled battery is charged, the amount of increase in SOC in the first battery block is larger than the amount of increase in SOC in the second battery block.

  For this reason, if the change amount of SOC is grasped | ascertained in each battery block, it can be discriminate | determined whether the electric current path of the cell contained in a battery block is interrupted | blocked. That is, by comparing the amount of change in SOC between the two battery blocks, it can be determined whether or not the current path of the unit cell is interrupted.

JP 2011-135657 A JP 2009-216448 A JP 2013-160539 A

  As described above, when determining whether or not the current path of the unit cell is interrupted, in a state where the SOC of the assembled battery or the battery block is difficult to change, it is difficult to compare the amount of change in the SOC, It becomes difficult to determine whether or not the current path is interrupted.

  If it is not possible to determine whether the current path is interrupted, the battery pack is actually charged / discharged while ignoring that the current path is interrupted even though the current path is interrupted. There is. In this case, the current value of the cell increases, and as described above, there is a risk that resistance increases and lithium deposition occurs.

  The power storage system of the present invention includes a power storage device and a controller that controls charging / discharging of the power storage device. The power storage device has a plurality of power storage blocks connected in series, and each power storage block has a plurality of power storage elements connected in parallel. When the amount of change in SOC in the power storage device or each power storage block is equal to or greater than a predetermined amount of change, the controller compares the amount of change in SOC in the plurality of power storage blocks, thereby It is determined whether or not an element is included. In addition, the controller reduces the upper limit power that allows the input or output of the power storage device when a predetermined time has passed in a state where the SOC change amount in the power storage device or each power storage block is smaller than the predetermined change amount.

  According to the present invention, when a predetermined time has elapsed in a state where the SOC change amount is smaller than the predetermined change amount, the upper limit power is reduced by assuming that the current path of the power storage element is interrupted. Yes. Thereby, even when the current path is actually interrupted in a state where it cannot be determined whether or not the current path of the energy storage element is interrupted, it is possible to suppress an excessive current from flowing through the energy storage element.

It is a figure which shows the structure of a battery system. It is a flowchart which shows the process which restrict | limits charging electric power or discharging electric power.

  Examples of the present invention will be described below.

  A battery system (corresponding to the power storage system of the present invention) in this embodiment will be described with reference to FIG. FIG. 1 is a schematic diagram showing a configuration of a battery system. The battery system of the present embodiment can be mounted on a hybrid vehicle. The hybrid vehicle includes an engine or a fuel cell as a power source for running the vehicle in addition to the assembled battery described later.

  In the hybrid vehicle, an assembled battery described later can be charged using electric power from a power source (for example, commercial power source) installed outside the vehicle. Moreover, since the battery system mounted in a hybrid vehicle is well-known as described in patent documents 1-3, detailed description is abbreviate | omitted.

  The assembled battery 10 is connected to the load 20 via the positive electrode line PL and the negative electrode line NL. A motor / generator is used as the load 20. The motor generator receives the electric power output from the assembled battery 10 and generates kinetic energy for running the vehicle. The motor / generator converts kinetic energy generated during braking of the vehicle into electric power, and outputs the electric power to the assembled battery 10.

  The positive electrode line PL is connected to the positive electrode terminal of the assembled battery 10, and the negative electrode line NL is connected to the negative electrode terminal of the assembled battery 10. Each of positive line PL and negative line NL is provided with system main relays SMR-B and SMR-G. System main relays SMR-B and SMR-G receive control signals from controller 40, Switch between on and off.

  The current sensor 31 detects the current value of the assembled battery 10 and outputs the detection result to the controller 40. Here, a current value when the assembled battery 10 is discharged is a positive value, and a current value when the assembled battery 10 is charged is a negative value. The voltage sensor 32 detects the voltage value of the assembled battery 10 and outputs the detection result to the controller 40. The controller 40 has a memory 41, and predetermined information is stored in the memory 41. Further, the controller 40 has a timer 42 used for time measurement.

  The assembled battery 10 has a plurality of battery blocks (corresponding to the storage block of the present invention) 11 connected in series. Each battery block 11 has a plurality of single cells (corresponding to the storage element of the present invention) 12 connected in parallel. 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 can be used instead of the secondary battery. In addition, the number of the battery blocks 11 and the number of the single cells 12 in each battery block 11 can be set as appropriate.

  Each cell 12 can be provided with a current breaker. The current breaker is used to interrupt the current path of each unit cell 12 and can be provided inside or outside the unit cell 12. For example, a fuse or a current cutoff valve can be used as the current breaker.

  The current cutoff valve blocks the current path of the unit cell 12 by deformation according to the increase in the internal pressure of the unit cell 12. The inside of the unit cell 12 is in a hermetically sealed state, and when gas is generated from the inside of the unit cell 12, the internal pressure of the unit cell 12 increases as the gas is generated, and the unit cell 12 enters an abnormal state. When the internal pressure of the unit cell 12 rises, the current cutoff valve is deformed to block the current path of the unit cell 12, thereby preventing current from flowing through the unit cell 12 in an abnormal state. Note that the structure of the current cutoff valve is described in, for example, Japanese Patent Application Laid-Open No. 2013-145737.

  Next, in the battery system of the present embodiment, processing for limiting the input power and output power of the assembled battery 10 will be described with reference to the flowchart shown in FIG. The process shown in FIG. 2 is executed by the controller 40.

  In step S <b> 101, the controller 40 calculates the SOC change amount ΔSOC of the assembled battery 10. Specifically, the controller 40 calculates the SOC of the battery pack 10 at different timings, and calculates the difference between these SOCs as the change amount ΔSOC. The SOC of the battery pack 10 can be calculated (estimated) using the current sensor 31 and the voltage sensor 32. Since the calculation method of SOC is well-known, detailed description is abbreviate | omitted.

  In step S101, the controller 40 determines whether or not the change amount ΔSOC is smaller than the predetermined change amount ΔSOC_th. The predetermined change amount ΔSOC_th is a threshold value related to the change amount ΔSOC, and is set in advance based on a viewpoint capable of determining whether or not the current path of the single battery 12 included in the battery block 11 is interrupted.

  As described in the background art, the smaller the change amount ΔSOC, the harder it is to determine whether or not the current path of the unit cell 12 is interrupted. Here, the predetermined change amount ΔSOC_th is a lower limit value of the change amount ΔSOC that can determine whether the current path is interrupted. Information specifying the predetermined change amount ΔSOC_th can be stored in the memory 41.

  When the change amount ΔSOC of the battery pack 10 is equal to or greater than the predetermined change amount ΔSOC_th, the controller 40 determines that the current path of the unit cell 12 can be cut off, and ends the process shown in FIG. On the other hand, when the change amount ΔSOC of the battery pack 10 is smaller than the predetermined change amount ΔSOC_th, the controller 40 determines that the current path of the unit cell 12 cannot be cut off, and performs the processing from step S102 onward. In the present embodiment, the SOC change ΔSOC of the battery pack 10 is grasped, but the SOC change ΔSOC of the battery block 11 can also be grasped.

  If a voltage sensor for detecting the voltage value of each battery block 11 is provided, the SOC of each battery block 11 can be calculated (estimated). Then, based on the change in the SOC of the battery block 11, the change amount ΔSOC of the SOC can be calculated. When calculating the change amount ΔSOC of the battery block 11, it is only necessary to determine whether or not the change amount ΔSOC of the battery block 11 is smaller than the predetermined change amount ΔSOC_th, as in the process of step S101 described above.

  In step S102, the controller 40 uses the timer 42 to count up the time tm. In step S103, the controller 40 determines whether or not the time tm obtained in the process of step S102 is longer than the predetermined time t_th. The predetermined time t_th is a threshold value related to the time tm, and is set in advance in consideration of the time during which the probability that the interruption of the current path occurs in the unit cell 12 will be high. Information for specifying the predetermined time t_th can be stored in the memory 41.

  Specifically, by performing an experiment or the like in advance, the time until the current path is interrupted in a predetermined number (for example, one) of the unit cells 12 is measured, and this time is set as the predetermined time t_th. Can be set. In the present embodiment, when the time tm reaches the predetermined time t_th, it is assumed that the current path is interrupted in the predetermined number of unit cells 12.

  When the time tm is longer than the predetermined time t_th, the controller 40 determines that the current path of the unit cell 12 is interrupted, and performs the processes after step S104. On the other hand, when the time tm is equal to or shorter than the predetermined time t_th, the controller 40 determines that the current path of the unit cell 12 is not interrupted, and ends the process shown in FIG.

  In step S104, the controller 40 determines whether or not the current allowable input power Win of the assembled battery 10 is higher than the lower limit value Win_min. The allowable input power Win is an upper limit power that allows input (charging) of the battery pack 10. Here, charging of the assembled battery 10 is controlled so that the input power required for the assembled battery 10 does not exceed the allowable input power Win. The lower limit value Win_min is a lower limit value of the allowable input power Win, and can be appropriately set in consideration of the running performance of the vehicle. Information specifying the lower limit value Win_min can be stored in the memory 41.

  When the allowable input power Win is higher than the lower limit value Win_min, the controller 40 performs the process of step S105. When the allowable input power Win is less than or equal to the lower limit value Win_min, the controller 40 performs the process of step S106. In step S105, the controller 40 sets the power obtained by subtracting the predetermined power X from the currently set allowable input power Win as a new allowable input power Win.

  As described above, since the current value when charging the assembled battery 10 is a negative value, the allowable input power Win is also a negative value. Here, subtracting the predetermined power X is subtracting the predetermined power X from the allowable input power Win as an absolute value.

  The predetermined power X is set in consideration of suppressing an excessive charging current from flowing through the single cells 12 even when the current path is interrupted in the predetermined number of single cells 12. When the process proceeds from the process of step S103 to the process of step S104, it is assumed that the current path is interrupted in the predetermined number of unit cells 12. In the process of step S105, the allowable input power Win is reduced by the predetermined power X in order to suppress an excessive charging current from flowing through the single cell 12 under this assumption.

  Here, the predetermined power X may be set in advance in accordance with the number of cells 12 whose current path is interrupted (assumed number). Information for specifying the predetermined power X can be stored in the memory 41.

  According to the process of step S105, by reducing the allowable input power Win by the predetermined power X, the input power of the assembled battery 10 can be easily restricted, and the charging current flowing through the single battery 12 can be easily restricted. Thereby, in the battery block 11 including the unit cell 12 in which the current path is interrupted, the salt concentration of the unit cell 12 to be charged can be suppressed from being biased toward the charging side, and an increase in resistance due to the uneven salt concentration can be suppressed. . Moreover, when the single battery 12 is a lithium ion battery, it becomes easy to suppress the precipitation of lithium by limiting the charging current.

  In step S106, the controller 40 determines whether or not the current allowable output power Wout of the assembled battery 10 is higher than the lower limit value Wout_min. The allowable output power Wout is the upper limit power that allows the output (discharge) of the battery pack 10. Here, the discharge of the assembled battery 10 is controlled so that the output power of the assembled battery 10 does not exceed the allowable output power Wout. The lower limit value Wout_min can be appropriately set in consideration of the running performance of the vehicle. Information for specifying the lower limit value Wout_min can be stored in the memory 41.

  When the allowable output power Wout is higher than the lower limit value Wout_min, the controller 40 performs the process of step S107. When the allowable output power Wout is less than or equal to the lower limit value Wout_min, the controller 40 performs the process of step S108. In step S107, the controller 40 sets the power obtained by subtracting the predetermined power Y from the currently set allowable output power Wout as a new allowable output power Wout.

  The predetermined power Y is set in consideration of suppressing an excessive discharge current from flowing through the single cells 12 even when the current path is interrupted in the predetermined number of single cells 12. When the process proceeds from the process of step S103 to the process of step S104, it is assumed that the current path is interrupted in the predetermined number of unit cells 12. In the process of step S107, the allowable output power Wout is reduced by the predetermined power Y in order to suppress an excessive discharge current from flowing through the cell 12 under this assumption.

  Here, the predetermined power Y may be set in advance in accordance with the number of cells 12 (the expected number) in which the current path is interrupted. Information for specifying the predetermined power Y can be stored in the memory 41.

  According to the process of step S107, by reducing the allowable output power Wout by the predetermined power Y, the output power of the assembled battery 10 can be easily restricted, and the discharge current flowing through the single battery 12 can be easily restricted. Thereby, in the battery block 11 including the unit cell 12 in which the current path is cut off, it is possible to suppress the salt concentration of the discharged unit cell 12 from being biased toward the discharge side, and it is possible to suppress an increase in resistance due to the salt concentration bias. .

  In step S108, the controller 40 resets the time tm. According to the process shown in FIG. 2, the count up of the time tm is continued while the change amount ΔSOC of the battery pack 10 is smaller than the predetermined change amount ΔSOC_th. When the time tm becomes longer than the predetermined time t_th, the allowable input power Win decreases or the allowable output power Wout becomes lower than the lower limit value Wout_min on condition that the allowable input power Win is higher than the lower limit value Win_min. On the condition that it is high, the allowable output power Wout decreases.

  Further, when the change amount ΔSOC of the assembled battery 10 remains smaller than the predetermined change amount ΔSOC_th, every time the predetermined time t_th elapses, the predetermined power X is subtracted (processing in step S105) or the predetermined power Y is subtracted ( Step S107) is performed. That is, every time the predetermined time t_th elapses, the allowable input power Win and the allowable output power Wout continue to decrease. However, when the allowable input power Win is equal to or lower than the lower limit value Win_min, the allowable input power Win is maintained at the lower limit value Win_min. Further, when the allowable output power Wout is equal to or lower than the lower limit value Wout_min, the allowable output power Wout is maintained at the lower limit value Wout_min.

  According to the present embodiment, even if the change amount ΔSOC of the battery pack 10 is smaller than the predetermined change amount ΔSOC_th and it cannot be determined whether or not the current path of the unit cell 12 is interrupted, the elapse of the predetermined time t_th. Accordingly, it is assumed that the current path of the unit cell 12 is interrupted. Under this assumption, the input power and output power of the assembled battery 10 are limited. Thereby, it can suppress that the input electric power and output electric power of the assembled battery 10 are not restrict | limited, without interrupting | blocking of an electric current path | route.

  Moreover, since the predetermined time t_th is a time when the probability that the current path is interrupted is high, it is possible to suppress the input power and output power of the assembled battery 10 from being restricted more than necessary. Here, if the probability that the current path is interrupted is not considered, the input power and output power of the battery pack 10 are limited even though the probability that the current path is interrupted is low. As a result, the input power and output power of the battery pack 10 are unnecessarily limited. In the present embodiment, it is possible to limit the input power and output power of the assembled battery 10 while grasping with high probability that the current path is interrupted.

  In the present embodiment, when the change amount ΔSOC of the assembled battery 10 is equal to or greater than the predetermined change amount ΔSOC_th, the current paths are blocked in each battery block 11 by comparing the change amounts ΔSOC in the plurality of battery blocks 11. It can be determined whether or not the unit cell 12 is included. Here, for example, by using the technique described in Patent Document 3, it is possible to specify the number of unit cells 12 whose current paths are blocked.

  In this case, the allowable input power Win and the allowable output power Wout may be reduced according to the number of single cells 12 whose current paths are interrupted. Specifically, the amount by which the allowable input power Win and the allowable output power Wout are reduced can be increased as the number of the single cells 12 whose current paths are blocked increases.

  Further, when it is determined that the current path is not interrupted, the setting by the processes in steps S105 and S107 shown in FIG. 2 can be canceled. In this case, the allowable input power Win can be returned to the value before the predetermined power X is subtracted. Further, the allowable output power Wout can be returned to the value before the predetermined power Y is subtracted.

10: assembled battery (power storage device), 11: battery block (power storage block),
12: Cell (electric storage element), 20: Load, 31: Current sensor, 32: Voltage sensor,
40: Controller, 41: Memory, 42: Timer, PL: Positive line,
NL: Negative electrode line, SMR-B, SMR-G: System main relay

Claims (1)

A power storage device in which a plurality of power storage blocks each including a plurality of power storage elements connected in parallel are connected in series,
A controller for controlling charging and discharging of the power storage device,
The controller is
When the amount of change in SOC in the power storage device or each power storage block is greater than or equal to a predetermined change amount, the current path is blocked in each power storage block by comparing the amount of change in SOC in the plurality of power storage blocks Determining whether the power storage element is included;
When a predetermined time elapses with the SOC change amount in the power storage device or each power storage block being smaller than the predetermined change amount, the upper limit power that allows the input or output of the power storage device is reduced. A featured power storage system.

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