Power storage system and secondary battery control method
A power storage system includes a plurality of secondary battery packs and an upper controller. When causing an additional discharge secondary battery pack that is not being discharged to start being discharged by connecting the additional discharge secondary battery pack in parallel with a discharging secondary battery pack that is being discharged, in a state in which some of the secondary battery packs are being discharged, the upper controller predicts discharge start timing at which inter-terminal voltages of the additional discharge secondary battery pack and the discharging secondary battery pack correspond to each other. Subsequently, the upper controller causes the additional discharge secondary battery pack to start being discharged at the discharge start timing.
1. A power storage system comprising:
a plurality of secondary battery packs; and
a controller that, when causing an additional discharge secondary battery pack that is not being discharged to be discharged by connecting the additional discharge secondary battery pack in parallel with a discharging secondary battery pack that is being discharged, predicts discharge start timing at which the inter-terminal voltage of the additional discharge secondary battery pack becomes equal to the inter-terminal voltage of the discharging secondary battery pack, and that causes the additional discharge secondary battery pack to start being discharged at the discharge start timing.
2. The power storage system according to claim 1 ,
wherein the secondary battery packs comprise
a battery detector that measures an inter-terminal voltage of the secondary battery packs, and
a current detector that measures a discharge current and a charge current of the secondary battery packs,
and wherein the controller predicts a change of an impedance of the discharging secondary battery pack based on a change of the inter-terminal voltage of the discharging secondary battery pack measured by the battery detector and a discharge current measured by the current detector, and sets a time when the impedance of the discharging secondary battery pack corresponds to an impedance of the additional discharge secondary battery pack that is measured in advance, as the discharge start timing.
3. The power storage system according to claim 2 ,
wherein the controller
retains in advance a value of an external impedance except for an internal impedance of a secondary battery included in the secondary battery pack, calculates an internal impedance of a secondary battery of the discharging secondary battery pack based on the inter-terminal voltage during discharge of the discharging secondary battery pack, and sets a sum of the external impedance and the internal impedance as the impedance of the secondary battery pack.
4. The power storage system according to claim 1 ,
wherein the controller
calculates a discharge waiting time period that is a time period until the discharge start timing, or an amount of power that is discharged by the discharge start timing, and when the discharge waiting time period elapses, or when the amount of power is discharged, determines that the discharge start timing has arrived.
5. The power storage system according to claim 1 ,
wherein the controller
calculates a discharge waiting time period that is a time period until the discharge start timing, and a discharge start voltage that is the inter-terminal voltage of the discharging secondary battery pack in the discharge start timing, determines whether or not the inter-terminal voltage of the discharging secondary battery pack has reached the discharge start voltage at a preset predetermined time before the discharge waiting time period, and causes the additional discharge secondary battery pack to start being discharged when the inter-terminal voltage of the discharging secondary battery pack has reached the discharge start voltage.
6. The power storage system according to claim 1 , the system further comprising:
a discharge switch that turns on and off discharge of the secondary battery pack; and
a charge switch that turns on and off charging the secondary battery pack,
wherein the controller turns on the discharge switch in a state in which the charge switch is turned off when starting discharge of the additional discharge secondary battery pack.
7. The power storage system according to claim 1 ,
wherein the controller,
when causing an additional charge secondary battery pack that is not being charged to start being charged by connecting the additional charge secondary battery pack in parallel with a charging secondary battery pack that is being charged, in a state in which some secondary battery packs from among the plurality of secondary battery packs are charged, predicts charge start timing at which inter-terminal voltages of the additional charge secondary battery pack and the charging secondary battery pack correspond to each other, and starts charging the additional charge secondary battery pack at the charge start timing.
8. The power storage system according to claim 7 ,
wherein the controller
predicts a change of an impedance of the charging secondary battery pack based on a change of the inter-terminal voltage of the charging secondary battery pack that is measured by the battery detector and a charge current that is measured by the current detector, and sets a time when the impedance of the charging secondary battery pack corresponds to an impedance of the additional charge secondary battery pack that is measured in advance, as the charge start timing.
9. The power storage system according to claim 7 , the system further comprising:
a discharge switch that turns on and off discharge of the secondary battery pack; and
a charge switch that turns on and off charging of the secondary battery pack,
wherein the controller
turns on the charge switch in a state in which the discharge switch is turned off when starting charging of the additional charge secondary battery pack.
10. A secondary battery pack control method for controlling a plurality of secondary battery packs,
wherein a computer,
when causing an additional discharge secondary battery pack that is not being discharged to be discharged by connecting the additional discharge secondary battery pack in parallel with a discharging secondary battery pack that is being discharged, predicts discharge start timing at which the inter-terminal voltage of the additional discharge secondary battery pack becomes equal to the inter-terminal voltage of the discharging secondary battery pack, and
causes the additional discharge secondary battery pack to start being discharged at the discharge start timing.
11. The power storage system according to claim 8 , the system further comprising:
a discharge switch that turns on and off discharge of the secondary battery pack; and
a charge switch that turns on and off charging of the secondary battery pack,
wherein the upper controller
turns on the charge switch in a state in which the discharge switch is turned off when starting charging of the additional charge secondary battery pack.