Power storage system, battery pack, and charging method

Abstract

A power storage system according to an embodiment of the present disclosure comprises: a plurality of battery packs each having a storage battery; a charging circuit capable of selectively performing a charging operation with respect to one of the plurality of battery packs; and a charging control circuit capable of acquiring data on a charging current in each of the plurality of battery packs, sequentially selecting the battery pack having the largest charging current as a charging target from among the plurality of battery packs, and controlling the operation of the charging circuit so as to perform the charging operation on the selected battery pack.

Description

Power storage system, battery pack, and charging method

[0001] The present disclosure relates to a power storage system including a storage battery, a battery pack, and a charging method used in such a power storage system and battery pack.

[0002] In recent years, storage batteries are provided in various electronic devices. For example, Patent Document 1 discloses a rotation charging device that charges a plurality of electronic devices in order.

[0003] Japanese Unexamined Patent Application Publication No. 2022 - 117081

[0004] By the way, a configuration in which one device includes a plurality of storage batteries is possible. Thereby, for example, the device can be operated for a long time. In such a device, when charging a plurality of storage batteries, it is desired that charging be performed efficiently even when the charging time is short.

[0005] It is desirable to provide a power storage system, a battery pack, and a charging method capable of performing efficient charging even when the charging time is short.

[0006] The power storage system according to an embodiment of the present disclosure includes a plurality of battery packs, a charging circuit, and a charging control circuit. Each of the plurality of battery packs has a storage battery. The charging circuit is capable of selectively performing a charging operation on one of the plurality of battery packs. The charging control circuit can acquire data on the charging current in each of the plurality of battery packs, can sequentially select, as a charging target, the battery pack having the largest charging current among the plurality of battery packs, and can control the operation of the charging circuit so as to perform a charging operation on the selected battery pack.

[0007] A battery pack in one embodiment of the present disclosure comprises a rechargeable battery and a charging control circuit. The charging control circuit is capable of controlling the operation of a charging circuit that can selectively perform a charging operation on one of a plurality of battery packs, including the pack itself. The charging control circuit is capable of acquiring data on the charging current of each of the plurality of battery packs, sequentially selecting the battery pack with the largest charging current among the plurality of battery packs as the target for charging, and controlling the operation of the charging circuit to perform a charging operation on the selected battery pack.

[0008] A charging method in one embodiment of the present disclosure includes acquiring data on the charging current in each of a plurality of battery packs, each having a storage battery; sequentially selecting the battery pack with the largest charging current from among the plurality of battery packs as the target for charging; and performing a charging operation on the selected battery pack.

[0009] According to one embodiment of the present disclosure, the energy storage system, battery pack, and charging method can be used to efficiently charge even when the charging time is short.

[0010] Figure 1 is a block diagram showing an example configuration of an energy storage system according to one embodiment of the present disclosure. Figure 2 is an explanatory diagram showing an example of a charging operation for the battery pack shown in Figure 1. Figure 3 is a flowchart showing an example of an operation of the energy storage system shown in Figure 1. Figure 4 is an explanatory diagram showing an example of a charging operation in the energy storage system shown in Figure 1. Figure 5 is another explanatory diagram showing an example of a charging operation in the energy storage system shown in Figure 1. Figure 6 is another explanatory diagram showing an example of a charging operation in the energy storage system shown in Figure 1. Figure 7 is a block diagram showing an example configuration of an energy storage system according to a modified example. Figure 8 is a block diagram showing an example configuration of an energy storage system according to another modified example. Figure 9 is a block diagram showing an example configuration of an energy storage system according to another modified example. Figure 10 is a block diagram showing an example configuration of an energy storage system according to another modified example.

[0011] The embodiments of this disclosure will be described in detail below with reference to the drawings.

[0012] <Embodiment> [Configuration Example] Figure 1 shows an example configuration of an energy storage system (energy storage system 1) according to one embodiment. The energy storage system 1 includes two battery packs 10 (battery packs 10A and 10B), a system control circuit 21, a switch 22, and a charger 30.

[0013] In this example, the energy storage system 1 is configured to charge the batteries of the two battery packs 10 based on power supplied from the grid power supply 90. The energy storage system 1 then supplies the stored power to a load device by disconnecting the connection between the switch 22 and the charging circuit 31 and connecting the switch 22 to a load device (not shown). This energy storage system 1 can be used, for example, in electric assist bicycles, power tools, etc. When the energy storage system 1 is used in an electric assist bicycle, the load device is a drive unit that controls the motor of the electric assist bicycle.

[0014] Each of the two battery packs 10 (battery packs 10A and 10B) is configured to store power and output the stored power. Each battery pack 10 includes a rechargeable battery 11 and a monitoring circuit 12.

[0015] The storage battery 11 is configured to store electricity. The storage battery 11 has a plurality of battery cells, for example, made using lithium-ion secondary batteries. The storage battery 11 is connected to the power terminal T1 of the battery pack 10. The storage battery 11 is configured to store electricity supplied through this power terminal T1, or to output electricity through this power terminal T1.

[0016] The monitoring circuit 12 is configured using a microcontroller and is set up to monitor the state of the battery 11. Specifically, the monitoring circuit 12 monitors, for example, the current of the battery 11, the voltage of the battery 11, the temperature of the battery 11, and the charge level of the battery 11. The monitoring circuit 12 also has a non-volatile memory and stores charging parameters that indicate the rated conditions for safely charging the battery 11 in this non-volatile memory. These charging parameters include data on the maximum current Imax and maximum voltage Vmax of the battery 11. The charging parameters stored in the monitoring circuit 12 of battery pack 10A and the charging parameters stored in the monitoring circuit 12 of battery pack 10B may be the same or different from each other. The monitoring circuit 12 is configured to supply this data on the state of the battery 11 and the charging parameters to the system control circuit 21 via the communication terminal T2.

[0017] The system control circuit 21 is configured using a microcontroller and communicates with the respective monitoring circuits 12 of the battery packs 10A and 10B, and controls the operation of the switch 22 and the charging circuit 31, thereby controlling the operation of the energy storage system 1.

[0018] When charging battery packs 10A and 10B, the system control circuit 21 communicates with the respective monitoring circuits 12 of battery packs 10A and 10B to obtain the charging parameters of each battery pack 10. When charging battery pack 10A, the system control circuit 21 controls the operation of switch 22 to connect battery pack 10A to the charging circuit 31. Then, based on the charging parameters supplied from battery pack 10A, the system control circuit 21 sets the operation of the charging circuit 31 so that the charging current does not exceed the maximum current Imax indicated by the charging parameters, and the battery voltage does not exceed the maximum voltage Vmax indicated by the charging parameters. Similarly, when charging battery pack 10B, the system control circuit 21 controls the operation of switch 22 to connect battery pack 10B to the charging circuit 31. Then, based on the charging parameters supplied from battery pack 10B, the system control circuit 21 sets the operation of the charging circuit 31 so that the maximum current Imax indicated by the charging parameters does not exceed, and the battery voltage does not exceed the maximum voltage Vmax indicated by the charging parameters. As will be described later, the system control circuit 21 is configured to select one of the battery packs 10A and 10B as the target for charging based on the respective charging currents of the battery packs 10A and 10B.

[0019] When discharging battery packs 10A and 10B, the system control circuit 21 communicates with the respective monitoring circuits 12 of battery packs 10A and 10B to acquire data on the state of the storage battery 11. Based on the state of the storage battery 11, the system control circuit 21 is configured to control the operation of the switch 22 so that one of the battery packs 10A or 10B is connected to the load device.

[0020] Based on instructions from the system control circuit 21, switch 22 is configured to connect one of the battery packs 10A and 10B, specifically the battery 11 of battery pack 10A and the battery 11 of battery pack 10B, to the charging circuit 31 during charging. Furthermore, based on instructions from the system control circuit 21, switch 22 is configured to connect one of the battery packs 10A and 10B, specifically the battery 11 of battery pack 10A and the battery 11 of battery pack 10B, to a load device (not shown) during discharge. Switch 22 is constructed, for example, using a transistor.

[0021] The charger 30 has a charging circuit 31. The charging circuit 31 is configured to perform a charging operation on the battery packs 10A and 10B based on the power supplied from the grid power supply 90. The charging circuit 31 is configured to charge the battery packs 10A and 10B based on the charging parameters supplied from the system control circuit 21, such that the charging current does not exceed the maximum current Imax indicated by the charging parameters, and the battery voltage does not exceed the maximum voltage Vmax indicated by the charging parameters.

[0022] Figure 2 shows an example of the charging operation for battery packs 10A and 10B, where (A) shows the charging operation for battery pack 10A and (B) shows the charging operation for battery pack 10B. Figure 2 shows the time variation of the charging current, the voltage of the storage battery 11 (storage battery voltage), and the charge rate for battery packs 10A and 10B.

[0023] When charging the battery pack 10A, the charging circuit 31 performs the charging operation such that the charging current does not exceed the maximum current Imax of the battery 11 of the battery pack 10A, and the battery voltage does not exceed the maximum voltage Vmax of the battery 11 of the battery pack 10A.

[0024] As shown in Figure 2(A), when the charging circuit 31 starts charging the battery pack 10A, constant current (CC) charging is performed in the battery pack 10A, where the charging current is constant. In this CC charging, the charging current is maintained at the maximum current Imax of the battery 11 of the battery pack 10A. As charging of the battery 11 progresses, the battery voltage increases. Then, at timing t1, when the battery voltage reaches the maximum voltage Vmax of the battery 11 of the battery pack 10A, constant voltage (CV) charging is performed in the battery pack 10A, where the charging voltage is constant. In this CV charging, the battery voltage is maintained at the maximum voltage Vmax of the battery 11 of the battery pack 10A. As charging of the battery 11 progresses, the charging current decreases.

[0025] Similarly, when charging battery pack 10B, the charging circuit 31 performs the charging operation such that the charging current does not exceed the maximum current Imax of the battery 11 of battery pack 10B, and the battery voltage does not exceed the maximum voltage Vmax of the battery 11 of battery pack 10B. As shown in Figure 2(B), when the charging circuit 31 starts charging battery pack 10B, CC charging is performed in battery pack 10B, similar to battery pack 10A. In this example, the maximum current Imax of the battery 11 of battery pack 10B is smaller than the maximum current Imax of the battery 11 of battery pack 10A. Then, at timing t2, when the battery voltage reaches the maximum voltage Vmax of the battery 11 of battery pack 10B, CV charging is performed in battery pack 10B. In this example, the maximum voltage Vmax of the battery 11 of battery pack 10B is smaller than the maximum voltage Vmax of the battery 11 of battery pack 10A.

[0026] Thus, in CC charging, the charging current is maintained at the maximum current Imax of the battery 11, while in CV charging, it decreases as charging of the battery 11 progresses. Therefore, the charge rate increases linearly in CC charging and gradually increases to approximately 100% in CV charging. The rate of change in the charge rate in CC charging is greater than the rate of change in the charge rate in CV charging. In other words, the charging efficiency in CC charging is higher than the charging efficiency in CV charging.

[0027] The charging circuit 31 is configured to charge the battery packs 10A and 10B by performing CC charging and CV charging in this manner.

[0028] Here, battery packs 10A and 10B correspond to one specific example of "multiple battery packs" in this disclosure. Storage battery 11 corresponds to one specific example of "storage battery" in this disclosure. Monitoring circuit 12 corresponds to one specific example of "monitoring circuit" in this disclosure. Charging circuit 31 corresponds to one specific example of "charging circuit" in this disclosure. System control circuit 21 corresponds to one specific example of "charging control circuit" in this disclosure. CC charging corresponds to one specific example of "first charging" in this disclosure. CV charging corresponds to one specific example of "second charging" in this disclosure.

[0029] [Operation and Function] Next, the operation and function of the energy storage system 1 of this embodiment will be described.

[0030] (Overall Operation Overview) First, the overall operation overview of the energy storage system 1 will be explained with reference to Figure 1. Each of the two battery packs 10A and 10B stores power and outputs the stored power. The system control circuit 21 controls the operation of the energy storage system 1 by controlling the operation of the switch 22 and the charging circuit 31. Based on instructions from the system control circuit 21, the switch 22 connects one of the battery packs 10A and 10B, either the battery 11 of battery pack 10A or the battery 11 of battery pack 10B, to the charging circuit 31 when charging the battery packs 10A and 10B. The charging circuit 31 charges the battery packs 10A and 10B based on the power supplied from the grid power supply 90.

[0031] (Detailed Operation) Figure 3 shows an example of the operation of the energy storage system 1 when charging battery packs 10A and 10B.

[0032] First, the system control circuit 21 of the energy storage system 1 acquires charging parameters from battery packs 10A and 10B respectively (step S101). Specifically, the system control circuit 21 acquires the charging parameters of battery pack 10A and battery pack 10B by communicating with the monitoring circuits 12 of battery packs 10A and 10B.

[0033] Next, the energy storage system 1 performs a preliminary charging operation on each of the battery packs 10A and 10B and acquires data on the charging current (step S102). Specifically, the system control circuit 21 first controls the operation of the switch 22 to connect battery pack 10A to the charging circuit 31, and sets the operation of the charging circuit 31 based on the charging parameters supplied from battery pack 10A. Then, the charging circuit 31 performs a preliminary charging operation on battery pack 10A. The monitoring circuit 12 of battery pack 10A monitors the state of the storage battery 11. The system control circuit 21 acquires data on the charging current of the storage battery 11 of battery pack 10A by communicating with the monitoring circuit 12 of battery pack 10A. In this way, the system control circuit 21 acquires data on the charging current of battery pack 10A at the start of charging. The same applies to battery pack 10B. Then, the system control circuit 21 stores the data on the charging current of each of the battery packs 10A and 10B.

[0034] Next, the energy storage system 1 starts charging the battery pack 10, which has a larger charging current, from among the battery packs 10A and 10B (step S103). Specifically, the system control circuit 21 selects the battery pack 10 with the larger charging current from among the battery packs 10A and 10B as the target for charging, based on the stored data on the charging current. The system control circuit 21 then controls the operation of the switch 22 to connect this battery pack 10 to the charging circuit 31, and sets the operation of the charging circuit 31 based on the charging parameters supplied from this battery pack 10. The charging circuit 31 then performs a charging operation on this battery pack 10 based on the instructions from the system control circuit 21.

[0035] Next, the energy storage system 1 checks whether the charging current of the battery pack 10 to be charged is the largest among the charging currents of the battery packs 10A and 10B (step S104). Specifically, the system control circuit 21 obtains data on the charging current of the battery 11 of the battery pack 10 by communicating with the monitoring circuit 12 of the battery pack 10 to be charged. Then, based on the charging current of this battery pack 10 and the stored data on the charging current of the other battery pack 10, the system control circuit 21 checks whether the charging current of the battery pack 10 to be charged is the largest among the charging currents of the battery packs 10A and 10B. If the charging current of the battery pack 10 to be charged is the largest ("Y" in step S105), the energy storage system 1 repeats the process in step S104 until the charging current of this battery pack 10 becomes smaller than the charging current of the other battery pack 10.

[0036] In other words, at the start of charging, the charging current of the battery pack 10 being charged is greater than the charging current of the other battery pack 10. However, as shown in Figure 2, the charging current decreases during CV charging, so the charging current of the battery pack 10 being charged may become smaller than the charging current of the other battery pack 10 as time passes. Therefore, the energy storage system 1 repeats the process in step S104 until the charging current of this battery pack 10 becomes smaller than the charging current of the other battery pack 10.

[0037] In step S104, if the charging current of the battery pack 10 to be charged is smaller than the charging current of the other battery pack 10 ("N" in step S104), the system control circuit 21 checks whether both battery packs 10A and 10B are fully charged (step S105). Specifically, the system control circuit 21 obtains data on the charge rate of the storage batteries 11 by communicating with the respective monitoring circuits 12 of battery packs 10A and 10B. Then, based on the data on the charge rate of the storage batteries 11 of battery packs 10A and 10B, the system control circuit 21 checks whether both battery packs 10A and 10B are fully charged.

[0038] In step S105, if at least one of the battery packs 10A and 10B is not fully charged ("N" in step S105), the system control circuit 21 checks whether the time of the current charging operation started in step S103 is shorter than a predetermined time (step S106). If the time of the current charging operation is longer than or equal to the predetermined time ("N" in step S106), the process proceeds to step S108.

[0039] In step S106, if the current charging operation time is shorter than a predetermined time (Y in step S106), the system control circuit 21 performs a wait process (step S107). Specifically, the system control circuit 21 waits, for example, until 5 minutes have elapsed.

[0040] The system control circuit 21 then stores data about the current charging current of the battery pack 10 that is to be charged (step S108). Specifically, the system control circuit 21 obtains data about the charging current of the battery 11 of the battery pack 10 by communicating with the monitoring circuit 12 of the battery pack 10 that is to be charged. The system control circuit 21 then stores this data about the charging current.

[0041] Then, based on instructions from the system control circuit 21, the charging circuit 31 stops the charging operation for the battery pack 10 that is to be charged (step S109). The process then returns to step S103. As a result, in step S103, one of the battery packs 10A and 10B, different from the battery pack 10 that was previously being charged, is selected as the target for charging, and the charging operation is started for this battery pack 10.

[0042] In step S105, if both battery packs 10A and 10B are fully charged (Y in step S105), the charging circuit 31 stops the charging operation for the battery pack 10 to be charged based on instructions from the system control circuit 21 (step S110).

[0043] With the above, this process ends. Thus, the power storage system 1 sequentially selects, as a charging target, the battery pack 10 with a large charging current among the battery packs 10A and 10B, and performs a charging operation on the selected battery pack 10.

[0044] Next, several specific examples will be given to explain the operation of the power storage system 1 in detail. First, the case (Case C1) where the charging rates of the battery packs 10A and 10B are zero before the start of charging will be described, and then, the case (Case C2) where the charging rate of the battery pack 10A is slightly high and the charging rate of the battery pack 10B is zero before the start of charging will be described.

[0045] (Case C1) Figure 4 shows an operation example of the power storage system 1 when the charging rates of the battery packs 10A and 10B are zero before the start of charging. (A) shows the charging operation for the battery pack 10A, and (B) shows the charging operation for the battery pack 10B. In this Figure 4, the time change of the charging current in the charging operation is shown.

[0046] First, the system control circuit 21 acquires charging parameters from each of the battery packs 10A and 10B (step S101 shown in FIG. 3). Then, the system control circuit 21 acquires data on the charging current (current I11) of the battery pack 10A and data on the charging current (current I21) of the battery pack 10B (step S102). In this example, since the charging rates of the battery packs 10A and 10B are zero, the current I11 corresponds to the maximum current Imax indicated by the charging parameters of the battery pack 10A, and the current I21 corresponds to the maximum current Imax indicated by the charging parameters of the battery pack 10B. As shown in FIG. 4, the current I11 is larger than the current I21. Therefore, the battery pack 10A related to this current I11 becomes the charging target, and the charging circuit 31 starts a charging operation on this battery pack 10A (step S103). As a result, as shown in FIG. 4, in the period P1, the charging circuit 31 performs a charging operation on the battery pack 10A.

[0047] In the battery pack 10A, first CC charging is performed, and then CV charging is started. In CV charging, the charging current decreases from the current I11. Then, the charging current of the battery pack 10A becomes smaller than the charging current (current I21) of the battery pack 10B ("N" in step S104).

[0048] Neither of the battery packs 10A and 10B is fully charged yet ("N" in step S105). In this example, during this period P1, since CC charging was performed on the battery pack 10A, the time of the current charging operation for the battery pack 10A (the time from the start of the period P1 to the present) is longer than the predetermined time ("N" in step S106). The system control circuit 21 acquires data on the charging current (current I12) of the battery pack 10A that is the charging target (step S108). Then, the charging circuit 31 stops the charging operation for the battery pack 10A (step S109). Thereby, the period P1 ends.

[0049] The current I21 is larger than the current I12. Therefore, the battery pack 10B related to this current I21 becomes the charging target, and the charging circuit 31 starts a charging operation on this battery pack 10B (step S103). Thereby, as shown in FIG. 4, in the period P2, the charging circuit 31 performs a charging operation on the battery pack 10B.

[0050] In the battery pack 10B, first CC charging is performed, and then CV charging is started. In CV charging, the charging current decreases from the current I21. Then, the charging current of the battery pack 10B becomes smaller than the charging current (current I12) of the battery pack 10A ("N" in step S104).

[0051] Neither battery pack 10A nor 10B is fully charged yet ("N" in step S105). In this example, CC charging was performed on battery pack 10B during this period P2, so the time of the current charging operation for battery pack 10B (time from the start of period P2 to the present) is longer than a predetermined time ("N" in step S106). The system control circuit 21 acquires data on the charging current (current I22) of battery pack 10B, which is the target of charging (step S108). Then, the charging circuit 31 stops the charging operation for battery pack 10B (step S109). This ends period P2.

[0052] Current I12 is greater than current I22. Therefore, the battery pack 10A related to this current I12 becomes the target for charging, and the charging circuit 31 starts charging this battery pack 10A (step S103). As a result, as shown in Figure 4, during period P3, the charging circuit 31 performs a charging operation on the battery pack 10A.

[0053] In battery pack 10A, CV charging continues, and the charging current decreases from current I12. The charging current of battery pack 10A becomes smaller than the charging current of battery pack 10B (current I22) ("N" in step S104).

[0054] Neither battery pack 10A nor 10B is fully charged yet ("N" in step S105). In this example, during this period P3, only CV charging is performed on battery pack 10A, so the time of the current charging operation for battery pack 10A (time from the start of period P3 to the present) is shorter than a predetermined time ("Y" in step S106). Therefore, the system control circuit 21 performs a wait process (step S107). The system control circuit 21 acquires data on the charging current (current I13) of battery pack 10A, which is the target of charging (step S108). Then, the charging circuit 31 stops the charging operation for battery pack 10A (step S109). This ends period P3.

[0055] Current I22 is greater than current I13. Therefore, the battery pack 10B related to this current I22 becomes the target for charging, and the charging circuit 31 starts charging this battery pack 10B (step S103). As a result, as shown in Figure 4, during period P4, the charging circuit 31 performs a charging operation on the battery pack 10B.

[0056] In battery pack 10B, CV charging continues, and the charging current decreases from current I22. The charging current of battery pack 10B becomes smaller than the charging current of battery pack 10A (current I13) ("N" in step S104).

[0057] Neither battery pack 10A nor 10B is fully charged yet ("N" in step S105). In this example, during this period P4, only CV charging is performed on battery pack 10B, so the time of the current charging operation for battery pack 10B (time from the start of period P4 to the present) is shorter than a predetermined time ("Y" in step S106). Therefore, the system control circuit 21 performs a wait process (step S107). The system control circuit 21 acquires data on the charging current (current I23) of battery pack 10B, which is the target of charging (step S108). Then, the charging circuit 31 stops the charging operation for battery pack 10B (step S109). This ends period P4.

[0058] The same applies to subsequent sections.

[0059] In this way, the energy storage system 1 sequentially selects the battery pack 10 with the larger charging current from among battery packs 10A and 10B as the target for charging, and performs a charging operation on the selected battery pack 10. As a result, the energy storage system 1 can efficiently charge even when the charging time is short, as will be explained below in comparison with the energy storage system 1R in the reference example.

[0060] (Reference Example) Next, the energy storage system 1 according to the embodiment will be described in comparison with the energy storage system 1R according to the reference example. The energy storage system 1R according to the reference example is configured to perform a charging operation on battery pack 10B after the charging operation on battery pack 10A is completed. That is, in this embodiment, the charging operation is performed alternately on battery pack 10A and battery pack 10B based on the charging current, but in the reference example, the charging operation on battery pack 10B is performed after the charging operation on battery pack 10A is completed. The other configurations are the same as in this embodiment.

[0061] Figure 5 shows an example of a charging operation, where (A) shows the operation of the energy storage system 1R and (B) shows the operation of the energy storage system 1. Figure 5 shows the time variation of the charging current and charge rate during the charging operation. In this example, for the sake of explanation, battery packs 10A and 10B have the same characteristics. In this example, the charging operation is performed during the period from timing t10 ​​to t11.

[0062] In the energy storage system 1R, as shown in Figure 5(A), CC charging is performed in the battery pack 10A, followed by CV charging. Then, at timing t11, which is part of the CV charging, charging is completed. The charge level when charging is completed is charge level A1.

[0063] In the energy storage system 1, as shown in Figure 5(B), CC charging is performed in battery pack 10A, and then CC charging is performed in battery pack 10B. Then, at timing t11, which is in the middle of CC charging in battery pack 10B, charging is completed. The charge level when charging is completed is charge level A2.

[0064] The rate of change in the charge rate during CC charging is greater than the rate of change in the charge rate during CV charging. In other words, the charging efficiency during CC charging is higher than that during CV charging. In energy storage system 1R, as shown in Figure 5(A), both CC charging, which has high charging efficiency, and CV charging, which has low charging efficiency, are performed. In energy storage system 1, as shown in Figure 5(B), CC charging, which has high charging efficiency, is performed, and CV charging, which has low charging efficiency, is not performed. Therefore, the charge rate A2 at the end of charging in energy storage system 1 is higher than the charge rate A1 at the end of charging in energy storage system 1R. As a result, energy storage system 1 can perform efficient charging even when the charging time is short.

[0065] (Case C2) Figure 6 shows an example of operation of the energy storage system 1 when, before charging begins, the charge level of battery pack 10A is slightly higher and the charge level of battery pack 10B is zero. (A) shows the charging operation for battery pack 10A, and (B) shows the charging operation for battery pack 10B. Figure 4 shows the time change of the charging current during the charging operation.

[0066] First, the system control circuit 21 acquires charging parameters from battery packs 10A and 10B respectively (step S101 shown in Figure 3). Then, the system control circuit 21 acquires data on the charging current (current I12) of battery pack 10A and data on the charging current (current I21) of battery pack 10B (step S102). In this example, battery pack 10A is partially charged, and CV charging is performed on battery pack 10A during the preliminary charging operation. As shown in Figure 6, current I21 is greater than current I12. Therefore, battery pack 10B, which corresponds to this current I21, becomes the target for charging, and the charging circuit 31 starts charging operation on battery pack 10B (step S103). As a result, as shown in Figure 6, during period P11, the charging circuit 31 performs a charging operation on battery pack 10B.

[0067] In battery pack 10B, CC charging is performed first, followed by CV charging. During CV charging, the charging current decreases from current I21. The charging current of battery pack 10B becomes smaller than the charging current of battery pack 10A (current I12) ("N" in step S104).

[0068] Neither battery pack 10A nor 10B is fully charged yet ("N" in step S105). In this example, CC charging was performed on battery pack 10B during this period P11, so the time of the current charging operation for battery pack 10B (time from the start of period P11 to the present) is longer than the predetermined time ("N" in step S106). The system control circuit 21 acquires data on the charging current (current I22) of battery pack 10B, which is the target of charging (step S108). Then, the charging circuit 31 stops the charging operation for battery pack 10B (step S109). This ends period P11.

[0069] Current I12 is greater than current I22. Therefore, the battery pack 10A related to this current I12 becomes the target for charging, and the charging circuit 31 starts charging this battery pack 10A (step S103). As a result, as shown in Figure 6, during period P12, the charging circuit 31 performs a charging operation on the battery pack 10A.

[0070] In battery pack 10A, CV charging continues, and the charging current decreases from current I12. The charging current of battery pack 10A becomes smaller than the charging current of battery pack 10B (current I22) ("N" in step S104).

[0071] Neither battery pack 10A nor 10B is fully charged yet ("N" in step S105). In this example, during this period P3, only CV charging is performed on battery pack 10A, so the time of the current charging operation for battery pack 10A (time from the start of period P12 to the present) is shorter than a predetermined time ("Y" in step S106). Therefore, the system control circuit 21 performs a wait process (step S107). The system control circuit 21 acquires data on the charging current (current I13) of battery pack 10A, which is the target of charging (step S108). Then, the charging circuit 31 stops the charging operation for battery pack 10A (step S109). This ends period P12.

[0072] Current I22 is greater than current I13. Therefore, the battery pack 10B related to this current I22 becomes the target for charging, and the charging circuit 31 starts charging this battery pack 10B (step S103). As a result, as shown in Figure 6, during period P13, the charging circuit 31 performs a charging operation on the battery pack 10B.

[0073] In battery pack 10B, CV charging continues, and the charging current decreases from current I22. The charging current of battery pack 10B becomes smaller than the charging current of battery pack 10A (current I13) ("N" in step S104).

[0074] Neither battery pack 10A nor 10B is fully charged yet ("N" in step S105). In this example, during this period P13, only CV charging is performed on battery pack 10B, so the time of the current charging operation for battery pack 10B (time from the start of period P13 to the present) is shorter than a predetermined time ("Y" in step S106). Therefore, the system control circuit 21 performs a wait process (step S107). The system control circuit 21 acquires data on the charging current (current I23) of battery pack 10B, which is the target of charging (step S108). Then, the charging circuit 31 stops the charging operation for battery pack 10B (step S109). This ends period P13.

[0075] The same applies to subsequent sections.

[0076] In this way, the energy storage system 1 sequentially selects the battery pack 10 with the larger charging current from among battery packs 10A and 10B as the target for charging, and performs the charging operation on the selected battery pack 10. As a result, the energy storage system 1 can efficiently charge even when the charging time is short.

[0077] In other words, in the energy storage system 1R according to the above-mentioned reference example, in case C2, the charging circuit 31 performs CV charging on battery pack 10A, and then CC charging on battery pack 10B. In this case, since CV charging, which has low charging efficiency, is performed first, it is difficult to increase the charge level. On the other hand, in energy storage system 1, as shown in Figure 6, the charging circuit 31 first performs CC charging on battery pack 10B. Therefore, since CC charging, which has high charging efficiency, is performed first, it is easy to increase the charge level. As a result, energy storage system 1 can perform efficient charging even when the charging time is short.

[0078] Thus, the energy storage system 1 includes a plurality of battery packs 10, each having a storage battery 11; a charging circuit 31 capable of selectively performing a charging operation on one of the plurality of battery packs 10; and a charging control circuit (system control circuit 21) capable of acquiring data on the charging current of each of the plurality of battery packs 10, sequentially selecting the battery pack 10 with the largest charging current among the plurality of battery packs 10 as the target for charging, and controlling the operation of the charging circuit 31 to perform a charging operation on the selected battery pack 10. As a result, in the energy storage system 1, the battery pack 10 with the largest charging current is sequentially selected as the target for charging among the plurality of battery packs 10. The battery pack 10 with the largest charging current can increase the amount of charge in a short time. As a result, the energy storage system 1 can perform charging efficiently even when the charging time is short.

[0079] Furthermore, in the energy storage system 1, the charging control circuit (system control circuit 21) can control the operation of the charging circuit 31 to perform a preliminary charging operation on each of the multiple battery packs 10 at the start of charging, and can acquire data on the charging current at the start of charging for each of the multiple battery packs 10. The operation of the charging circuit 31 can be controlled to start charging the first battery pack among the multiple battery packs 10 that has the largest charging current. As a result, in the energy storage system 1, at the start of charging, the battery pack 10 with the largest charging current can be selected as the target for charging. For example, in the case C1 described above (Figure 4), battery pack 10A can be selected as the target for charging. That is, in this case C1, since the charge rate of battery packs 10A and 10B is zero, battery pack 10A is selected as the target for charging first. Also, in the case C2 described above (Figure 6), battery pack 10B can be selected as the target for charging. In other words, in this case C2, the charge level of battery pack 10A is slightly higher and the charge level of battery pack 10B is zero, so battery pack 10B is selected as the target for charging first. With battery pack 10, which has a large charging current, the charge level can be increased in a short time. As a result, the energy storage system 1 can charge efficiently even when the charging time is short.

[0080] Furthermore, in the energy storage system 1, the charging control circuit (system control circuit 21) is able to continuously acquire data on the charging current of the first battery pack while the charging circuit 31 is performing a charging operation on the first battery pack. When the charging current of the first battery pack decreases and the charging current of the second battery pack becomes the largest among the charging currents of the multiple battery packs 10, the charging operation on the first battery pack is stopped and the charging operation on the second battery pack is started, thereby controlling the operation of the charging circuit 31. As a result, in the energy storage system 1, for example, in case C1 (Figure 4), when charging operation is being performed on battery pack 10A during period P1, if the charging current of battery pack 10A becomes smaller than the charging current of battery pack 10B, the charging target can be switched from battery pack 10A to battery pack 10B. As a result, the energy storage system 1 can more easily achieve a higher charge rate compared to the energy storage system 1R (Figure 5) according to the reference example.

[0081] Furthermore, in the energy storage system 1, the charging control circuit (system control circuit 21) is configured to control the operation of the charging circuit so that when the charging current of the second battery pack becomes the largest among the charging currents of the multiple battery packs, and the time for the charging operation of the first battery pack is shorter than a predetermined time, it performs a wait process, and then stops the charging operation of the first battery pack and starts the charging operation of the second battery pack. As a result, in the energy storage system 1, for example, when CV charging is performed on each of the battery packs 10A and 10B, as in period P3 and later in case C1 (Figure 4), the target of charging does not switch frequently between battery pack 10A and battery pack 10B in a short period of time. As a result, the energy storage system 1 can perform charging efficiently.

[0082] Furthermore, in the energy storage system 1, the charging circuit 31 is configured to perform a charging operation on the first battery pack using a first charging method (CC charging) in which the charging current of the first battery pack becomes constant, and then perform a charging operation on the first battery pack using a second charging method (CV charging) in which the charging voltage of the first battery pack becomes constant. The charging control circuit (system control circuit 21) is configured to control the operation of the charging circuit so as to stop the charging operation on the first battery pack using the second charging method (CV charging) and start the charging operation on the second battery pack. As a result, in the energy storage system 1, for example, as in the periods P1 and P2 of case C1 (Figure 4), CC charging is performed on battery pack 10A, and then CC charging is performed on battery pack 10B. In other words, the energy storage system 1 can perform charging operations on battery packs 10A and 10B using CC charging, which has high charging efficiency. As a result, the energy storage system 1 can perform efficient charging even when the charging time is short.

[0083] [Effects] As described above, this embodiment includes a plurality of battery packs, each having a rechargeable battery; a charging circuit capable of selectively performing a charging operation on one of the plurality of battery packs; and a charging control circuit capable of acquiring data on the charging current of each of the plurality of battery packs, sequentially selecting the battery pack with the largest charging current among the plurality of battery packs as the target for charging, and controlling the operation of the charging circuit to perform a charging operation on the selected battery pack. As a result, charging can be performed efficiently even when the charging time is short.

[0084] In this embodiment, the charging control circuit can control the operation of the charging circuit to perform a preliminary charging operation for each of the multiple battery packs at the start of charging, acquire data on the charging current at the start of charging for each of the multiple battery packs, and control the operation of the charging circuit to start charging for the first battery pack that has the largest charging current among the multiple battery packs. This enables efficient charging even when the charging time is short.

[0085] In this embodiment, the charging control circuit is capable of continuously acquiring data on the charging current of the first battery pack while the charging circuit is performing a charging operation on the first battery pack. When the charging current of the first battery pack decreases and the charging current of the second battery pack becomes the largest among the charging currents of the multiple battery packs, the charging operation on the first battery pack is stopped and the charging operation on the second battery pack is started. This allows for efficient charging even when the charging time is short.

[0086] In this embodiment, the charging control circuit is configured to control the operation of the charging circuit so that when the charging current of the second battery pack becomes the largest among the charging currents of the multiple battery packs, and the time required for the charging operation of the first battery pack is shorter than a predetermined time, it performs a wait process, then stops the charging operation of the first battery pack and starts the charging operation of the second battery pack. This enables efficient charging.

[0087] In this embodiment, the charging circuit is configured to perform a charging operation on the first battery pack by first charging, which maintains a constant charging current for the first battery pack, and then by second charging, which maintains a constant charging voltage for the first battery pack. The charging control circuit is configured to control the operation of the charging circuit so as to stop the second charging operation on the first battery pack and start the charging operation on the second battery pack. This allows for efficient charging even when the charging time is short.

[0088] [Modification 1] In the above embodiment, as shown in Figure 1, the system control circuit 21 and the charger 30 are provided separately, but the invention is not limited to this. Alternatively, for example, as shown in the energy storage system 2 in Figure 7, a charger 40 having a system control circuit 21 and a charging circuit 31 may be provided.

[0089] [Modification 2] In the above embodiment, as shown in Figure 1, the battery pack 10A and the system control circuit 21 are provided separately, but the embodiment is not limited to this. Alternatively, for example, as shown in the energy storage system 3 in Figure 8, the battery pack may have the system control circuit 21. This energy storage system 3 includes battery packs 50A and 10B and a charger 60.

[0090] The battery pack 50A includes a storage battery 11, a monitoring circuit 12, a switch 52, and a system control circuit 51.

[0091] Based on instructions from the system control circuit 51, switch 52 connects either the battery 11 of battery pack 50A or the battery 11 of battery pack 10B to the charging circuit 31 when charging battery packs 50A and 10B. Switch 52 is connected to the charging circuit 31 via power terminal T11 and to the battery 11 of battery pack 10B via power terminal T12.

[0092] The system control circuit 51 controls the operation of the energy storage system 4 by controlling the operation of the switch 52 and the charger 60. The system control circuit 51 communicates with the charger 60 via the communication terminal T13 and with the monitoring circuit 12 of the battery pack 10B via the communication terminal T14.

[0093] The charger 60 includes a charging circuit 31 and a control circuit 61. Based on the charging parameters supplied from the system control circuit 51 of the battery pack 50A, the control circuit 61 sets the operation of the charging circuit 31 so that the charging current does not exceed the maximum current Imax indicated by the charging parameters, and the battery voltage does not exceed the maximum voltage Vmax indicated by the charging parameters.

[0094] [Modification 3] In the above embodiment, the system control circuit 21 obtains data on the charging current of the batteries 11 of the battery packs 10A and 10B by communicating with the monitoring circuit 12 of the battery packs 10A and 10B, but it is not limited to this. Alternatively, for example, as shown in the energy storage system 4 in Figure 9, a current sensor may be provided in the charger, and the system control circuit may obtain data on the charging current of the batteries 11 of the battery packs 10A and 10B from this charger. This energy storage system 4 comprises battery packs 10A and 10B, a system control circuit 71, a switch 22, and a charger 80.

[0095] The charger 80 includes a charging circuit 31 and a current sensor 81. The current sensor 81 detects the charging current.

[0096] The system control circuit 71, similar to the system control circuit 21 in the above embodiment, communicates with the respective monitoring circuits 12 of the battery packs 10A and 10B, and controls the operation of the switch 22 and the charging circuit 31, thereby controlling the operation of the energy storage system 4. The system control circuit 71 also acquires data on the charging current from the charger 80.

[0097] The operation of the energy storage system 4 when charging the battery packs 10A and 10B is the same as in the above embodiment (Figure 3).

[0098] In step S102, the system control circuit 71 performs a preliminary charging operation on each of the battery packs 10A and 10B and acquires data on the charging current. Specifically, the system control circuit 71 first controls the operation of the switch 22 to connect battery pack 10A to the charger 80, and sets the operation of the charging circuit 31 based on the charging parameters supplied from battery pack 10A. Then, the charging circuit 31 performs a preliminary charging operation on battery pack 10A. The system control circuit 71 acquires data on the charging current from the charger 80. That is, since a preliminary charging operation is performed on battery pack 10A, the system control circuit 71 can acquire data on the charging current of the battery 11 of battery pack 10A from the charger 80. The same applies to battery pack 10B. Then, the system control circuit 71 stores the data on the charging current of each of the battery packs 10A and 10B.

[0099] Next, the energy storage system 4 starts charging the battery pack 10, which has a larger charging current than the battery packs 10A and 10B (step S103).

[0100] Next, the energy storage system 4 checks whether the charging current of the battery pack 10 to be charged is the largest among the charging currents of the battery packs 10A and 10B (step S104). Specifically, the system control circuit 71 obtains data from the charger 80 regarding the charging current of the battery 11 of the battery pack 10 to be charged. Then, based on this charging current of battery pack 10 and the stored charging current data for the other battery pack 10, the system control circuit 71 checks whether the charging current of the battery pack 10 to be charged is the largest among the charging currents of the battery packs 10A and 10B.

[0101] Although the present technology has been described above with reference to embodiments, the present technology is not limited to these embodiments and various modifications are possible.

[0102] In the above embodiment, as shown in Figure 1, two battery packs 10A and 10B are provided, but the embodiment is not limited to this. Instead, for example, three or more battery packs 10 may be provided, as in the energy storage system 5 shown in Figure 10. This energy storage system 5 comprises three battery packs 10 (battery packs 10A, 10B, and 10C), a system control circuit 91, a switch 92, and a charger 30. The system control circuit 91 communicates with the respective monitoring circuits 12 of the battery packs 10A to 10C and controls the operation of the switch 92 and the charging circuit 31, thereby controlling the operation of the energy storage system 4. Based on instructions from the system control circuit 71, the switch 92 connects one of the battery packs 10A to 10C to the charging circuit 31 when charging the battery packs 10A to 10C. The energy storage system 5 sequentially selects the battery pack 10 with the largest charging current among the battery packs 10A to 10C as the target for charging and performs a charging operation on the selected battery pack 10.

[0103] Furthermore, in the above embodiment, the energy storage system 1 is provided with multiple battery packs 10, but each of these multiple battery packs 10 may be configured to be detachable from the energy storage system 1. For example, when one battery pack 10 is installed in the energy storage system 1, the energy storage system 1 can continuously charge that battery pack 10. Also, when two battery packs 10 are installed in the energy storage system 1, the energy storage system 1 sequentially selects the battery pack 10 with the largest charging current from among the multiple battery packs 10 as the target for charging, and performs a charging operation on the selected battery pack 10. For example, if two battery packs 10 are initially installed in the energy storage system 1, and one of the battery packs 10 is removed during charging, the energy storage system 1 will continue to charge the installed battery pack 10 thereafter. Furthermore, for example, if one battery pack 10 is initially installed in the energy storage system 1, and a second battery pack 10 is installed during the charging process, the energy storage system 1 will subsequently select the battery pack 10 with the largest charging current as the target for charging and perform the charging operation on the selected battery pack 10.

[0104] The effects described herein are illustrative only, and the effects of this disclosure are not limited to those described herein. Therefore, other effects may be obtained with respect to this disclosure.

Claims

1. An energy storage system comprising: a plurality of battery packs, each having a rechargeable battery; a charging circuit capable of selectively performing a charging operation on one of the plurality of battery packs; and a charging control circuit capable of acquiring data on the charging current in each of the plurality of battery packs, sequentially selecting the battery pack with the largest charging current among the plurality of battery packs as the target for charging, and controlling the operation of the charging circuit to perform the charging operation on the selected battery pack.

2. The energy storage system according to claim 1, wherein the charging control circuit can control the operation of the charging circuit to perform a preliminary charging operation for each of the plurality of battery packs at the start of charging, can acquire data on the charging current at the start of charging for each of the plurality of battery packs, and can control the operation of the charging circuit to start charging for the first battery pack among the plurality of battery packs which has the largest charging current.

3. The energy storage system according to claim 2, wherein the charging control circuit is capable of continuously acquiring data on the charging current of the first battery pack during the period in which the charging circuit is performing the charging operation on the first battery pack, and when the charging current of the first battery pack decreases and the charging current of the second battery pack becomes the largest among the charging currents of the plurality of battery packs, the charging control circuit is capable of controlling the operation of the charging circuit to stop the charging operation on the first battery pack and start the charging operation on the second battery pack.

4. The energy storage system according to claim 3, wherein the charging control circuit is capable of controlling the operation of the charging circuit to perform a wait process when the charging current of the second battery pack becomes the largest among the charging currents of the plurality of battery packs, and the time for the charging operation of the first battery pack is shorter than a predetermined time, and thereafter stop the charging operation of the first battery pack and start the charging operation of the second battery pack.

5. The energy storage system according to claim 3 or 4, wherein the charging circuit, when performing the charging operation on the first battery pack, is capable of performing the charging operation by a first charge in which the charging current of the first battery pack becomes constant, and then performing the charging operation by a second charge in which the charging voltage of the first battery pack becomes constant, and the charging control circuit is capable of controlling the operation of the charging circuit to stop the charging operation by the second charge on the first battery pack and to start the charging operation on the second battery pack.

6. The energy storage system according to any one of claims 1 to 5, wherein the charging control circuit is provided in any one of the plurality of battery packs.

7. The energy storage system according to any one of claims 1 to 6, wherein each of the plurality of battery packs has a monitoring circuit capable of monitoring the state of the storage battery, and the charging control circuit is capable of acquiring data on the charging current in each of the plurality of battery packs from the monitoring circuit of each of the plurality of battery packs.

8. A battery pack comprising a rechargeable battery and a charging control circuit capable of controlling the operation of a charging circuit that can selectively perform a charging operation on one of a plurality of battery packs, including the battery pack itself, wherein the charging control circuit is capable of acquiring data on the charging current of each of the plurality of battery packs, sequentially selecting the battery pack with the largest charging current among the plurality of battery packs as the target for charging, and controlling the operation of the charging circuit to perform the charging operation on the selected battery pack.

9. A charging method comprising: acquiring data on the charging current in each of a plurality of battery packs, each having a storage battery; sequentially selecting the battery pack with the largest charging current from among the plurality of battery packs as the target for charging; and performing a charging operation on the selected battery pack.

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