Power storage device, power storage system, and control method of power storage device
There is provided a power storage device including a plurality of modules each including secondary batteries, a charging switch that controls charging to the secondary batteries, a discharging switch that controls discharging of the secondary batteries, and a voltage measuring unit that measures a voltage of the module, and a switch control unit that controls one or both of the charging switch and the discharging switch. The modules are connected in parallel. The switch control unit maintains an on state of the discharging switch for at least one of the modules for a predetermined period, and controls the charging switch of the module in which a maximum module charging current estimated based on the voltage of the module is a predetermined value or less, to be in an on state.
1. A power storage device, comprising:
a plurality of modules, wherein the plurality of modules are connected in parallel, wherein each module of the plurality of modules includes a plurality of secondary batteries, a charging switch, a discharging switch, and a voltage measuring unit, wherein the charging switch is configured to control charge of the plurality of secondary batteries, the discharging switch is configured to control discharge of the plurality of secondary batteries, and the voltage measuring unit is configured to measure a voltage of a secondary battery of the plurality of secondary batteries; and
a switch control unit configured to:
control at least one of the charging switch or the discharging switch;
maintain a first state of the discharging switch for at least one module of the plurality of modules for a period; and
switch a first state of the charging switch to a second state of the charging switch for the at least one module of the plurality of modules based on a maximum module charging current, wherein the maximum module charging current is equal to or smaller than a first value, and wherein the maximum module charging current is estimated based on the voltage of the secondary battery.
2. The power storage device according to claim 1 ,
wherein the switch control unit is further configured to switch to the first state of the charging switch of the at least one module of the plurality of modules, based on a difference between a highest voltage among voltages of the plurality of secondary batteries and a lowest voltage among the voltages of the plurality of secondary batteries that is smaller than a second value.
3. The power storage device according to claim 2 , wherein the switch control unit is further configured to switch to the first state of the charging switch of the at least one module of the plurality of modules, based on a number of modules connected in parallel among the plurality of modules is equal to or larger than a first number.
4. The power storage device according to claim 3 , wherein the switch control unit is further configured to switch to the first state of the charging switch of the at least one module of the plurality of modules, based on a state of charge (SOC) of the plurality of modules that is larger than a third value.
5. The power storage device according to claim 3 , wherein the switch control unit is further configured to switch to the first state of the charging switch of the at least one module of the plurality of modules, based on a difference in a state of charge (SOC) of the plurality of modules that is smaller than a third value.
6. The power storage device according to claim 1 ,
wherein the switch control unit further configured to:
select a first module from the plurality of modules in which a voltage of the plurality of secondary batteries is highest,
count number of second modules of the plurality of modules in which a difference in the voltage of the plurality of secondary batteries from the first module is equal to or smaller than a second value,
divide a system charging current by the number of second modules to obtain an estimated module charging current, and
switch to the first state of the charging switch of the first module and the second modules, based on the estimated module charging current that is smaller than a maximum charging current.
7. The power storage device according to claim 1 ,
wherein the switch control unit is further configured to:
select a first module from the plurality of modules in which a voltage of the plurality of secondary batteries is highest,
select a third module from the plurality of modules having a state of charge (SOC) that is highest among the plurality of modules,
count number of fourth modules of the plurality of modules in which a first difference in the voltage of the plurality of secondary batteries from the first module is equal to or smaller than a second value, and a second difference in the state of charge (SOC) of the plurality of secondary batteries from the third module is equal to or smaller than a third value, among the plurality of modules,
divide a system charging current by the number of fourth modules to obtain an estimated module charging current, and
switch to the first state of the charging switch of the fourth modules, based on the estimated module charging current that is smaller than the maximum module charging current.
8. The power storage device according to claim 1 ,
wherein the switch control unit is further configured to switch to the first state of the charging switch in each module of the plurality of modules, based on
the plurality of modules are in a discharging state, and a difference between a highest current value of the plurality of modules and a lowest current value of the plurality of modules is smaller than a second value, or
the plurality of modules are in a charging state, and the difference is smaller than a third value.
9. The power storage device according to claim 1 ,
wherein the switch control unit is further configured to switch to the second state of the charging switch of each module, based on
at least one module of the plurality of modules has a charging current larger than a maximum charging current value, or
at least one module of the plurality of modules has a discharging current larger than a maximum discharging current value.
10. The power storage device according to claim 1 , wherein the switch control unit is further configured to switch to the second state of the charging switch of each module, based on a condition for switching to the first state of the charging switch becomes unsatisfied.
11. The power storage device according to claim 1 , wherein the switch control unit is further configured to switch to the second state of the charging switch of each module, based on a highest state of charge (SOC) value of the plurality of modules is equal to or larger than a second value.
12. The power storage device according to claim 10 , wherein based on the switching to the second state of the charging switch of each module, the switch control unit is further configured to start counting time, and maintain the second state of the charging switch of each module until a first time elapses.
13. The power storage device according to claim 1 , further comprising a pre-charging switch and a current limiting unit, wherein the pre-charging switch and the current limiting unit are connected in series between a positive side terminal of one of the plurality of secondary batteries and an external positive terminal or the pre-charging switch and the current limiting unit are between a negative side terminal of one of the plurality of secondary batteries and an external negative terminal, and wherein the switch control unit is further configured to maintain a first state of the pre-charging switch.
14. The power storage device according to claim 13 ,
wherein the switch control unit is further configured to:
switch to the second state of the charging switch and switch to a second state of the pre-charging switch, based on the voltage of the secondary battery that is equal to or larger than an overvoltage charging value, or based on a charging current of the plurality of secondary batteries that is equal to or larger than an overcurrent charging value, and
switch to a second state of the discharging switch, based on the voltage of the secondary battery that is equal to or smaller than an overvoltage discharging value, or based on a discharging current of the plurality of secondary batteries that is equal to or larger than an overcurrent discharging value.
15. A control method, comprising:
in a power storage device including a plurality of modules, wherein the plurality of modules are connected in parallel, each module of the plurality of modules includes a plurality of secondary batteries, a charging switch, a discharging switch, and a voltage measuring unit, wherein the charging switch is configured to control charge of the plurality of secondary batteries, the discharging switch is configured to control discharge of the plurality of secondary batteries, and the voltage measuring unit is configured to measure a voltage of a secondary battery of the plurality of secondary batteries:
controlling at least one of the charging switch or the discharging switch;
maintaining a first state of the discharging switch for at least one module of the plurality of modules for a period; and
controlling to switch a first state of the charging switch to a second state of the charging switch for the at least one module of the plurality of modules based on a maximum module charging current, wherein the maximum module charging current is equal to or smaller than a first value, wherein the maximum module charging current is estimated based on the voltage of the secondary battery.