Charging system

Abstract

The upper limit SOC makes it easy to suppress swelling of the battery.SOLUTION: A charging system includes a control device (a server 200 and a battery ECU232) for executing charging control of a battery so that an SOC estimation value of the battery does not exceed an upper limit SOC. The controller is configured to set the upper limit SOC to a first 1SOC value when the battery is not swollen, and set the upper limit SOC to a second 1SOC value lower than the first 2SOC value when the battery is swollen. The controller is configured to obtain a correction parameter for correcting the SOC estimation value by making the SOC of the battery higher than a first 2SOC value when it is determined that the battery swells and the SOC estimation value is large.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a charging system that controls charging of a battery. [Background technology]

[0002] Japanese Patent Application Laid-Open No. 2019-220260 (Patent Document 1) discloses a system that performs charging control so that the SOC (State Of Charge) of a battery does not exceed an upper limit SOC. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-220260 Summary of the Invention [Problem to be solved by the invention]

[0004] For example, gas generation inside a battery can cause the battery to swell. Battery swelling reduces battery performance. Battery overcharging accelerates battery swelling. Therefore, lowering the upper SOC limit can be considered to suppress battery swelling. However, lowering the upper SOC limit can reduce the accuracy of SOC estimation. If the accuracy of SOC estimation decreases, even if battery charging control is performed so that the estimated SOC value does not exceed the upper SOC limit, there is a possibility that the actual battery SOC will exceed the upper SOC limit due to estimation errors. Therefore, if the accuracy of SOC estimation decreases, it becomes difficult to sufficiently suppress battery swelling using the upper SOC limit.

[0005] The present disclosure has been made to solve the above-mentioned problems, and its purpose is to make it easier to suppress battery swelling by using an upper limit SOC. [Means for solving the problem]

[0006] A charging system according to one embodiment of the present disclosure includes a control device that controls charging of a battery so that an estimated SOC value of the battery does not exceed an upper limit SOC. The control device is configured to set the upper limit SOC to a first SOC value when the battery is not swollen, and to set the upper limit SOC to a second SOC value lower than the first SOC value when the battery is swollen. The control device is configured to increase the SOC of the battery above the second SOC value and calculate a correction parameter for correcting the SOC estimation error when the battery is swollen and the SOC estimation error is determined to be large. [Effects of the Invention]

[0007] According to the present disclosure, the upper limit SOC makes it easier to suppress battery swelling. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram illustrating a configuration of a charging system according to an embodiment of the present disclosure. [Figure 2] 2 is a diagram showing the internal configuration of the battery pack shown in FIG. 1. [Figure 3] 3 is a flowchart showing a method for estimating and correcting an SOC according to the present embodiment. [Figure 4] 4 is a flowchart showing details of the correction parameter update process shown in FIG. 3. [Figure 5] FIG. 2 is a diagram showing a modified example of the power storage system shown in FIG. [Figure 6] 3 is a flowchart showing a modified example of the processing flow shown in FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present disclosure will be described in detail with reference to the accompanying drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals and their description will not be repeated.

[0010] Fig. 1 is a diagram showing the configuration of a charging system according to an embodiment of the present disclosure. Referring to Fig. 1, the charging system according to this embodiment includes a power storage system 100, a server 200, and a PCS (Power Conditioning System) 300. This charging system can be installed in a building (e.g., a home, a factory, a public facility, or a commercial facility).

[0011] The server 200 executes charge control to store power supplied from a power system PG (external power supply) in the power storage system 100. The server 200 also executes discharge control to supply power discharged from the power storage system 100 to a power load. Examples of power loads include electrical machinery and appliances (such as lighting equipment and air conditioning equipment) used in a building. The PCS 300 includes a power path switching device and a power conversion circuit, and operates according to instructions from the server 200.

[0012] In this embodiment, a power grid PG supplies AC power. The power grid PG is a power network constructed by power transmission and distribution facilities. The power grid PG may include power generation facilities and / or transformer facilities. The server 200 may use the power storage system 100 to perform power adjustment (e.g., adjustment of the supply and demand balance) of the power grid PG.

[0013] The power storage system 100 includes a DC / AC conversion circuit 10, N relays 21-1 to 21-N (referred to as "relays 21" when not distinguished), N DC / DC conversion circuits 22-1 to 22-N (referred to as "DC / DC conversion circuits 22" when not distinguished), and N battery packs 23-1 to 23-N (referred to as "battery packs 23" when not distinguished). The power storage system 100 is controlled by a server 200. N is, for example, between 2 and 100, and may be around 30. However, N is arbitrary.

[0014] The battery packs 23-1 to 23-N are connected in parallel to one another. The battery packs 23-1 to 23-N are provided with relays 21-1 to 21-N and DC / DC conversion circuits 22-1 to 22-N, respectively. The relay 21 is provided on an electrical path connecting the DC / AC conversion circuit 10 and the DC / DC conversion circuit 22. The relay 21 is, for example, an electromagnetic mechanical relay. Each of the relays 21-1 to 21-N switches between energizing and de-energizing the corresponding battery pack 23 in accordance with a command from the server 200.

[0015] When DC power is input from the battery pack 23 to the DC / DC conversion circuit 22, the DC / DC conversion circuit 22 outputs DC power to the DC / AC conversion circuit 10 in response to a command from the server 200. The DC / AC conversion circuit 10 outputs AC power to the PCS 300 in response to a command from the server 200. The PCS 300 performs power conversion on the received AC power, and outputs the converted AC power to at least one of the power grid PG and a power load.

[0016] The PCS 300 receives AC power from the power grid PG. The PCS 300 performs power conversion on the received AC power and outputs the converted AC power to at least one of the DC / AC conversion circuit 10 and a power load. The DC / AC conversion circuit 10 converts the AC power input from the PCS 300 into DC power. When AC power is input to the DC / AC conversion circuit 10 from the power grid PG via the PCS 300, the DC / AC conversion circuit 10 outputs DC power in response to a command from the server 200 to each of the DC / DC conversion circuits 22-1 to 22-N. The DC / DC conversion circuit 22 transforms the DC power input from the DC / AC conversion circuit 10 and outputs the DC power in response to the command from the server 200 to the corresponding battery pack 23.

[0017] The server 200 includes a processor 210 and a storage device 220. Battery packs 23-1 to 23-N are registered in the server 200. The storage device 220 stores information about each battery pack (for example, specifications and control information) by distinguishing them by battery pack identification information.

[0018] 2 is a diagram showing the configuration of the battery pack 23. The battery pack 23 corresponds to a stationary power storage device. As shown in FIG. 2, the battery pack 23 includes a power storage device 231, a battery ECU (Electronic Control Unit) 232, a current sensor 233a, a voltage sensor 233b, and a temperature sensor 233c. The detection results of each sensor are input to the battery ECU 232.

[0019] In this embodiment, the power storage device 231 is an assembled battery. The assembled battery includes a plurality of electrically connected secondary batteries. Hereinafter, each secondary battery included in the assembled battery will be referred to as a "cell." The power storage device 231 may include a switch circuit that selectively disconnects some of the cells from the assembled battery. The current sensor 233a detects the current flowing through the power storage device 231. The voltage sensor 233b detects the voltage of each cell included in the power storage device 231. The temperature sensor 233c detects the temperature of the power storage device 231. In this embodiment, a plurality of cells are connected in series in the power storage device 231, and the current value detected by the current sensor 233a is used as a current value common to the plurality of cells included in the power storage device 231. However, this is not limiting. In a configuration in which the power storage device 231 includes a plurality of cells connected in parallel, the battery ECU 232 may calculate the current value of each cell using the current value detected by the current sensor.

[0020] The battery ECU 232 includes a processor and a storage device, and records the detection results of each sensor in the storage device, linking them to the detection time. As will be described in detail later, the battery ECU 232 estimates the SOC (State Of Charge) of each cell from the detection results of each sensor, and links the estimated SOC value to the time and records it in the storage device. The SOC indicates the ratio of the current amount of stored power to the amount of power stored in a fully charged state. In response to a request from the server 200, the battery ECU 232 outputs the data recorded in the storage device to the server 200. In addition, the battery ECU 232 controls the corresponding relays 21 and DC / DC conversion circuits 22 in accordance with commands from the server 200.

[0021] In this embodiment, each cell included in the power storage device 231 (battery pack) is a lithium-ion secondary battery. Specifically, a lithium-ion secondary battery (hereinafter referred to as an "LFP battery") that uses lithium iron phosphate as the positive electrode active material is used as the cell. The relationship between the OCV and SOC of such a cell is represented by, for example, line L1 in FIG. 2.

[0022] Line L1 shows the OCV-SOC curve (horizontal axis: SOC, vertical axis: OCV) of the cell (LFP battery) included in the power storage device 231. OCV stands for open circuit voltage. The higher the SOC, the greater the amount of stored power. Hereinafter, in the OCV-SOC curve, the amount of change in the amount of stored power (SOC) will be represented as "dQ", the amount of change in voltage (OCV) as "dV", and the ratio of the amount of change in voltage to the amount of change in the amount of stored power as "dV / dQ".

[0023] The OCV-SOC curve indicated by line L1 has regions R1 to R3. Region R1 is located near the SOC (0%) in an empty state. Region R3 is located near the SOC (100%) in a fully charged state. Region R2 is located between regions R1 and R3. The OCV-SOC curve is divided into a flat region and a steep region. The flat region is a region where dV / dQ is smaller than a reference value. The steep region is a region where dV / dQ is larger than a reference value. Regions R1 and R3 each correspond to a steep region. Region R2 corresponds to a flat region (plateau region). The reference value may be 0.0001 V / mAh or more and 0.0200 V / mAh or less, or 0.005 V / mAh or more and 0.010 V / mAh or less. However, the reference value is not limited to these numerical ranges and can be set arbitrarily according to the OCV-SOC curve of the battery.

[0024] When a battery is charged from an empty state (for example, when the SOC is "0%), the region to which the battery's SOC belongs shifts from region R1 to region R2. Furthermore, as charging continues, the region to which the battery's SOC belongs shifts from region R2 to region R3. In all of regions R1 to R3, there is a one-to-one correspondence between the OCV and the SOC.

[0025] In this embodiment, the OCV-SOC curve (initial OCV-SOC curve) of each cell included in the power storage device 231 is stored in advance in a storage device of the battery ECU 232. The OCV-SOC curve held by the battery ECU 232 may be an OCV-SOC curve common to multiple cells. The charging characteristics of an LFP battery tend to be an OCV-SOC curve that includes a steep region near the SOC of the fully charged state and a flat region on the low SOC side of the steep region, as shown by line L1, for example. Based on the OCV-SOC curve of the cell, the battery ECU 232 determines whether the SOC of the cell belongs to the flat region or the steep region.

[0026] When the cell's SOC falls within the steep region, the battery ECU 232 references the cell's OCV-SOC curve and estimates the cell's SOC from the cell's OCV. This method makes it easier to estimate the battery's SOC with high accuracy when the battery's SOC falls within the steep region (region where dV / dQ is large) than when the battery's SOC falls within the flat region (region where dV / dQ is small). This is because in the steep region, even a slight change in the amount of stored charge causes a large change in the battery voltage. Hereinafter, the method of estimating the cell's SOC when the cell's SOC falls within the steep region will also be referred to as the "first estimation method." The cell's OCV is detected by, for example, the voltage sensor 233b.

[0027] On the other hand, when the cell SOC belongs to the flat region, the battery ECU 232 estimates the cell SOC using the cell current detected by the current sensor 233a and a correction parameter. The battery ECU 232 estimates the cell SOC by, for example, the coulomb counting method. Hereinafter, the method of estimating the cell SOC when the cell SOC belongs to the flat region will also be referred to as the "second estimation method." The correction parameter in the second estimation method is stored in a storage device of the battery ECU 232 and is updated by a process described later (see S24 in FIG. 4).

[0028] The server 200 sets an upper limit SOC for each of the battery packs 23-1 to 23-N. The set upper limit SOC is associated with the identification information of the corresponding battery pack and stored in the storage device of the battery ECU 232. The storage device of the battery ECU 232 also stores information about each cell (secondary battery) constituting the power storage device 231 for each battery pack, distinguishing the cells by their identification information (cell IDs). The storage device of the battery ECU 232 stores, for each cell, a correction parameter for the output value of the current sensor 233a (hereinafter also referred to as a "first correction parameter") and a correction parameter for the second estimation method described above (hereinafter also referred to as a "second correction parameter"). The first correction parameter may be a correction value (e.g., a correction coefficient) by which the output value of the current sensor 233a is added, subtracted, multiplied, or divided. The second correction parameter may be a correction value (e.g., a correction coefficient) by which the estimated SOC value (SOC estimated value) is added, subtracted, multiplied, or divided.

[0029] Before charging the battery pack (power storage device 231), the server 200 acquires the upper limit SOC set for the battery pack. During charging of the battery pack, the battery ECU 232 in the battery pack estimates the SOC of each cell included in the battery pack. As described above, the battery ECU 232 switches the SOC estimation method (first estimation method and second estimation method) for the cell based on the SOC of the cell. When the SOC of the cell falls within a steep region, the server 200 may update at least one of the first and second correction parameters described above based on the SOC estimate value obtained by the first estimation method. In at least one of the first and second estimation methods, the battery ECU 232 may further use the cell temperature to estimate the SOC of the cell. The server 200 acquires the SOC estimate value of each cell from the battery ECU 232 and performs charging control so that the SOC estimate value of each cell does not exceed the upper limit SOC. FIG. 2 is a flowchart showing charging control according to this embodiment. 2 is repeatedly executed by the server 200. "S" in the flowchart denotes a step.

[0030] 2, in S101, server 200 determines whether or not to charge at least one of battery packs 23-1 to 23-N. If a predetermined charge start condition is met, a YES determination is made in S101, and processing proceeds to S102. As a result, charging is performed in S103. On the other hand, if the charge start condition is not met, a NO determination is made in S101, and processing flow F1 ends. While the charge start condition is not met, the determination in S101 is repeatedly made, and charging is not performed.

[0031] The charge start condition is met, for example, when charging for SOC adjustment (see S23 in FIG. 4), which will be described later, is executed. Alternatively, the charge start condition may be met when the server 200 receives a request for charging for energy management (for example, power adjustment of the power grid PG) by, for example, demand response. When receiving such a request, the server 200 may select one or more battery packs to be charged for energy management.

[0032] In S102, the server 200 acquires the upper limit SOC of the corresponding battery pack and the estimated SOC value of each cell from the battery ECU 232 of each battery pack to be charged.

[0033] In the following S103, the server 200 executes charge control for each battery pack to be charged. Specifically, the server 200 controls the DC / AC conversion circuit 10 so that DC power is supplied from the power grid PG to each battery pack to be charged. Furthermore, for each battery pack to be charged, the server 200 connects the corresponding relay 21 and controls the charging power (charging current and charging voltage) through the corresponding DC / DC conversion circuit 22. In this charge control, the power storage device 231 is charged so that the estimated SOC value of each cell included in the power storage device 231 does not exceed the upper limit SOC set for the corresponding battery pack 23.

[0034] In the next step S104, server 200 determines whether a predetermined charging termination condition is met. For example, the charging termination condition is met when the SOC of power storage device 231 (e.g., the highest SOC value among the estimated SOC values ​​of each cell) reaches a target value. Furthermore, with regard to charging that is started in response to a request, the charging termination condition is met when the requested charging is completed. Furthermore, the charging termination condition is also met when the estimated SOC value of any cell reaches the upper limit SOC. While the charging termination condition is not met (NO in S104), the processes of S102 and S103 are repeatedly executed, and the above-described charging control (S103) is continuously executed. On the other hand, when the charging termination condition is met (YES in S104), processing flow F1 ends. This ends the current charging, and the determination in S101 is executed again.

[0035] 3 is a flowchart showing a process for managing the SOC estimation accuracy of each battery pack. A process flow F2 shown in FIG.

[0036] 3, in S11, server 200 selects an undetermined battery pack from battery packs 23-1 to 23-N as a battery pack to be determined. In this embodiment, first battery pack 23-1 is selected, and then battery packs 23-2, 23-3, ..., 23-N are selected one by one to determine whether or not the N battery packs are to be corrected. However, the determination order can be changed as appropriate.

[0037] In the next step S12, the server 200 acquires predetermined information (hereinafter referred to as "determination information") related to the battery pack selected in step S11 from the battery ECU 232 of the battery pack (target of determination). The determination information includes an OCV-SOC curve, voltage data, and current data. Of these, the current data includes a total charge amount and a zero output value, which will be described later.

[0038] In the next step S13, server 200 uses the determination information acquired in S12 to determine whether the target cell includes a swollen cell. Specifically, server 200 determines, for each cell included in the target cell, whether that cell is swollen. Server 200 acquires the number of swollen cells for the target cell by determining whether each cell is swollen. In this embodiment, server 200 determines whether a cell is swollen based on whether the integrated value of the charging current of the cell (hereinafter also referred to as the "total charge amount") is equal to or greater than a predetermined value. The larger the total charge amount of the cell, the more likely the cell is to swell. However, the method for determining whether or not there is swelling is not limited to this method and is arbitrary. For example, in an embodiment in which each cell is provided with a surface pressure sensor, server 200 may determine whether or not there is swelling based on the surface pressure of the cell.

[0039] If it is determined that one or more cells of the target cell are swollen, YES is determined in S13, and the process proceeds to S131. In S131, the server 200 sets an SOC value (hereinafter referred to as "V2") within the flat region (region R2 in FIG. 2) as the upper limit SOC of the target cell. V2 may be a fixed value within the flat region, or may be variable. The server 200 may lower V2 within the flat region as the total charge amount of the swollen cells increases.

[0040] When the process of S131 is executed, in S14, the server 200 determines whether the error in the SOC estimation of the target cell is large based on the output value of the target cell current sensor 233a when no current is flowing (hereinafter also referred to as the "zero output value"). Specifically, when the cell's SOC is in the flat region, the battery ECU 232 estimates the cell's SOC using the cell current detected by the current sensor 233a. Therefore, if the target cell detects a current value greater than or less than zero (a negative current value) when no current is flowing through the power storage device 231, it is highly likely that a detection error has occurred in the cell's SOC estimation. In this embodiment, the server 200 determines whether the error in the SOC estimation is large based on whether the degree of deviation between the current detected by the current sensor 233a when no current is flowing through the power storage device 231 and zero (0 A) (hereinafter referred to as the "current detection error") is greater than a predetermined threshold. When the output value of current sensor 233a is corrected by the correction parameter (first correction parameter), the corrected current value corresponds to the current detection value. After calculating the current detection error, server 200 uses the current detection error to update the first correction parameter so as to reduce the detection error of current sensor 233a. The updated first correction parameter is transmitted from server 200 to the object to be determined and set in battery ECU 232 of the object to be determined.

[0041] If the current detection error is greater than the threshold, a YES determination is made in S14, and the process proceeds to S15. In S15, the server 200 recognizes the battery pack (determination target) selected in S11 as a target for correction related to SOC estimation (hereinafter also simply referred to as "correction target"). On the other hand, if the current detection error is equal to or less than the threshold, a NO determination is made in S14, and the process skips S15 and proceeds to S16. In this case, the server 200 recognizes that the determination target is not a target for correction.

[0042] If it is determined that none of the cells included in the determination target are swollen (NO in S13), an upper limit SOC is set by the process of S132, and then the process proceeds to S16. In this case, server 200 determines that the determination target is not a correction target. In S132, server 200 sets an SOC value (hereinafter referred to as "V1") within a steep region (region R3 in FIG. 2) on the higher SOC side than the flat region as the upper limit SOC of the determination target. In the initial state of the battery pack, since none of the cells are swollen, V1 is set as the upper limit SOC. V1 corresponds to the initial upper limit SOC. In this embodiment, V1 is a fixed value selected from an SOC range of 90% to 100%. V1 may be 100%. However, V1 does not necessarily have to be a fixed value and may be variable within the steep region (e.g., region R3). The upper limit SOC set in S131 or S132 is transmitted from server 200 to the object to be determined and set in battery ECU 232 of the object to be determined.

[0043] In S16, server 200 determines whether the above-mentioned determination (determination of whether or not a battery pack is a correction target) has been completed for all battery packs 23-1 to 23-N. If the above-mentioned determination has not been completed for any battery pack (NO in S16), the process returns to S11, and the battery pack not yet determined in S11 is set as the determination target. When the above-mentioned determination has been performed for all battery packs, YES is determined in S16, and the process proceeds to S17.

[0044] In S17, server 200 determines whether or not there is a battery pack identified as a correction target in S15 among battery packs 23-1 to 23-N. If there is no battery pack to be corrected (NO in S17), process flow F2 ends. In this case, correction related to SOC estimation (updating of correction parameters) is not performed. However, process flow F2 is repeatedly executed.

[0045] On the other hand, if there are correction targets (YES in S17), the server 200 determines in S18 whether the number of correction targets is two or more. If the number of correction targets is two or more (YES in S18), the server 200 determines the correction order for those correction targets in S19. The server 200 may determine the correction order based on the number of expanded cells. However, the method for determining the correction order is arbitrary. Thereafter, the process proceeds to S20. On the other hand, if there is only one correction target (NO in S18), the process skips S19 and proceeds to S20.

[0046] In S20, the server 200 updates the correction parameters for correcting the SOC estimation error for the swollen cells included in the correction target (battery pack). FIG. 4 is a flowchart showing the details of S20 (the correction parameter update process). In the process flow F3 shown in FIG. 4, the processes from S21 onwards are executed for the target pack. The target pack is the battery pack that was identified as the correction target in S15 of FIG. 3. If there are two or more correction targets, one correction target (uncorrected correction target) is selected according to the correction order determined in S19 of FIG. 3.

[0047] In S21, the server 200 sets the number of expanded cells included in the target pack to a parameter (hereinafter referred to as "m") indicating the uncorrected number of cells. Subsequently, in S22, the server 200 cancels the setting of the upper limit SOC for the target pack. The current upper limit SOC for the target pack is the latest V2 set in S131 of FIG. 3.

[0048] In the next step S23, the server 200 charges the expanded cells included in the target pack until their SOCs reach a first target value higher than the released upper limit SOC (V2). In this embodiment, the initial upper limit SOC (V1 initially set in S132 of FIG. 3) is used as the first target value. Hereinafter, the expanded cells to be charged are referred to as the "target cells." If there are two or more expanded cells in the target pack, one target cell (uncorrected cell) is selected from these cells. The server 200 may select the target cell from the multiple expanded cells in descending order of SOC. However, the method for determining the target cell is arbitrary.

[0049] In S23, the server 200 charges the target cell according to the process flow F1 shown in FIG. 2. However, because the setting of the upper limit SOC was canceled in S22, the upper limit SOC in the charging control is invalidated. Therefore, in S103 of FIG. 2, the charging of the target pack is not limited by the upper limit SOC. The server 200 can charge the target cell up to an initial upper limit SOC (V1), which is higher than the current upper limit SOC (V2). In a configuration in which the power storage device 231 is configured to be able to charge and discharge each cell individually, the server 200 charges only the target cell. However, the target cell may be charged together with other cells.

[0050] When the SOC of the target cell reaches the first target value (V1) through the charging, the server 200 updates a correction parameter (second correction parameter) for correcting the SOC estimation error for the target cell in S24. Specifically, the server 200 acquires the SOC estimate of the target cell obtained by the first estimation method (first SOC estimate) and the SOC estimate of the target cell obtained by the second estimation method (second SOC estimate) from the battery ECU 232 of the target pack, and calculates a correction parameter for the second estimation method (second correction parameter) based on these SOC estimates. Because the SOC of the target cell is in a steep region, the first SOC estimate (SOC estimate based on the OCV-SOC curve) is considered to be closer to the true value than the second SOC estimate (SOC estimate based on the current integration value). Therefore, the server 200 updates the second correction parameter so that the estimate obtained by the second estimation method approaches the first SOC estimate. The updated second correction parameters are transmitted from server 200 to the determination target and set in battery ECU 232 of the determination target, thereby improving the estimation accuracy by the second estimation method.

[0051] In the next S25, the server 200 discharges the target cell in the target pack (first battery pack) so that the SOC of the target cell becomes equal to or less than the upper limit SOC (V2) released in S22, and charges another battery pack (second battery pack) with the discharged power. The first and second battery packs are included in the battery packs 23-1 to 23-N shown in FIG. 1. The server 200 controls the power storage system 100 so that power is exchanged between these battery packs. In a configuration in which the power storage device 231 is configured to be able to charge and discharge each cell individually, the server 200 discharges only the target cell. However, the target cell may be discharged together with other cells. The second target value may be the same value as the upper limit SOC (current upper limit SOC) released in S22. The second battery pack is a battery pack to which the current target cell does not belong. If the number of correction targets is two or more, the next target pack may be the second battery pack.

[0052] Next, in S26, server 200 updates the number of uncorrected cells (m). More specifically, since the correction for the target cell has been completed by the processes of S23 to S25 above, the value obtained by subtracting 1 from the current m is set as the new m. Next, in S27, server 200 determines whether m has become 0. If m is 1 or greater (NO in S27), the target cell is changed and the process returns to S23. Then, the processes of S23 to S25 are executed for the changed target cell. On the other hand, if m has become 0 (YES in S27), the process proceeds to S28. In this embodiment, if the number of expanded cells is two or more, correction is performed for each cell one by one. However, this is not limited to this, and correction may be performed for multiple cells simultaneously.

[0053] In S28, the server 200 resets the upper limit SOC (V2) that was released in S22 for the target pack, thereby validating the upper limit SOC in the charge control (S103 in FIG. 2) for the target pack.

[0054] In the following S29, the server 200 determines whether the above-mentioned correction has been completed for all correction targets. If the above-mentioned correction has not been completed for any of the correction targets (NO in S29), the target pack is changed and the process returns to S21. Then, the processes from S21 onwards are executed for the changed target pack. When the above-mentioned correction has been completed for all correction targets (YES in S29), the process flow F3 (S20 in FIG. 3) ends. This ends the process flow F2 shown in FIG. 3. Thereafter, the process flow F2 starts again.

[0055] As described above, the charging method according to this embodiment includes each process according to process flows F1 to F3 (FIGS. 2 to 4). Each process is performed by one or more processors executing a program stored in one or more memories. However, these processes may also be performed by hardware (electronic circuits) rather than software.

[0056] The charging system according to the above embodiment includes battery packs 23-1 to 23-N and a server 200. Each of the battery packs 23-1 to 23-N includes a plurality of batteries (cells). The server 200 cooperates with the battery ECU 232 of each of the battery packs 23-1 to 23-N to perform charging control for each of the battery packs 23-1 to 23-N. Specifically, the server 200 performs charging control for the corresponding battery pack so that the SOC of each battery included in the corresponding battery pack does not exceed an upper limit SOC set for the battery pack (S103 in FIG. 2). When none of the batteries included in a first battery pack are swollen, the server 200 sets V1 (first SOC value) as an upper limit SOC for the first battery pack (S132 in FIG. 3). When at least one battery included in the first battery pack is swollen, the server 200 sets V2 (a second SOC value lower than the first SOC value) as the upper limit SOC for the first battery pack (S131 in FIG. 3). When the battery swells, the upper limit SOC decreases from V1 to V2. This suppresses the progression of battery swelling.

[0057] Furthermore, if at least one battery included in the first battery pack is determined to be swollen and have a large SOC estimation error, the server 200 increases the SOC of the swollen battery above the second SOC value and calculates a correction parameter for correcting the SOC estimation error for the swollen battery (S13, S14, and S15 in FIG. 3 and S23 and S24 in FIG. 4). This makes it easier to accurately calculate the SOC estimation error, and ultimately to calculate an appropriate correction parameter. Even if the cell's OCV-SOC curve changes due to swelling, it becomes easier to estimate the cell's SOC with high accuracy. Furthermore, because the accuracy of the SOC estimation is improved, it becomes easier to suppress battery swelling using the upper SOC limit.

[0058] After obtaining the correction parameters, the server 200 discharges the swollen battery so that its SOC becomes equal to or less than V2 (second SOC value), and charges the second battery pack with the discharged power (S25 in FIG. 4). In this way, the power discharged from the first battery pack to adjust the SOC of the first battery pack is used to charge another battery pack (second battery pack), thereby improving energy efficiency.

[0059] In the charging system according to the above embodiment, when it is determined that the battery is swollen and the SOC estimation error is large, the server 200 executes a process of canceling the upper limit SOC for the battery (S22 in FIG. 4 ), and then charges the battery so that the SOC of the battery is higher than V2 (second SOC value) (S23 in FIG. 4 ). The server 200 then calculates a second correction parameter when the battery SOC is higher than V2 (S24 in FIG. 4 ). The server 200 then discharges the battery until the SOC of the battery is equal to or lower than V2 (S25 in FIG. 4 ), and sets V2 as the upper limit SOC for the battery (S28 in FIG. 4 ). In this way, temporarily raising the SOC of the battery above the second SOC value makes it easier to calculate an appropriate second correction parameter. Then, by resetting the second SOC value as the upper limit SOC, battery charging control is executed so that the SOC of the battery does not exceed the second SOC value, thereby suppressing battery swelling.

[0060] In addition, in S22 of Fig. 4, instead of the process of canceling the upper limit SOC for the battery, a process of setting the upper limit SOC higher than V2 (second SOC value) may be executed. For example, the server 200 may set the first SOC value as the upper limit SOC in S22 of Fig. 4. Then, the server 200 may return the upper limit SOC to the second SOC value in S28 of Fig. 4.

[0061] In the above embodiment, when it is determined that the battery is swollen and the SOC estimation error is large, the server 200 sets the SOC of the battery to V1 (third SOC value), which is higher than V2 (second SOC value), in S23 of FIG. 4 . In the above embodiment, the first SOC value and the third SOC value are both V1. When the first SOC value falls within the steep slope region, the accuracy of SOC estimation using the first estimation method for a battery in an initial state is increased. Furthermore, when the third SOC value falls within the steep slope region, it becomes possible to calculate correction parameters related to SOC estimation with high accuracy. Furthermore, when the battery is swollen, a second SOC value lower than both the first SOC value and the third SOC value is set as the upper limit SOC, which makes it easier to suppress the progression of swelling. Note that the third SOC value may be higher than V2 and lower than V1.

[0062] The power storage system may include a separate charging circuit and a discharging circuit. FIG. 5 is a diagram showing a modification of the power storage system shown in FIG. 1. In the power storage system 100A shown in FIG. 5, a PCS 310 and a switch circuit 321 are provided instead of the PCS 300 (FIG. 1). The PCS 310 incorporates a charging circuit and a discharging circuit. The charging circuit is connected to the power grid PG and the DC / AC conversion circuit 10, and outputs power supplied from the power grid PG to the DC / AC conversion circuit 10. The discharging circuit is connected to each of the DC / DC conversion circuits 22-1 to 22-N via the switch circuit 321. The switch circuit 321 connects battery packs 23-1 to 23-N that are not being charged to the discharging circuit and disconnects battery packs that are being charged from the discharging circuit. The discharging circuit is configured to be able to supply power to one or more power loads. Specifically, the discharging circuit outputs AC power supplied from the power grid PG and DC power supplied from one or more connected battery packs. The DC power output from the discharge circuit may be converted to AC power by an inverter. Meanwhile, switch circuit 322, which is composed of relays 21-1 to 21-N, connects the battery packs to be charged, among battery packs 23-1 to 23-N, to DC / AC conversion circuit 10, and disconnects the battery packs not to be charged from DC / AC conversion circuit 10. DC / AC conversion circuit 10 charges one or more connected battery packs with power from power system PG. Note that switch circuit 321 may be composed of N relays, similar to switch circuit 322.

[0063] Server 200 shown in FIG. 5 may execute process flow F1A shown in FIG. 6 instead of process flow F1 (FIG. 2). FIG. 6 is a flowchart showing a modification of the process flow shown in FIG. 2. In process flow F1A, when none of the battery packs are to be charged (NO in S101), server 200 connects all of battery packs 23-1 to 23-N to the discharge circuit using switch circuit 321 in S101A. When one or more battery packs are to be charged (YES in S101), server 200 disconnects the battery pack to be charged from the discharge circuit using switch circuit 321 in S101B. According to the above system, while a certain battery pack is being charged, discharged power from other battery packs can be easily supplied to a power load.

[0064] In the above embodiment, the server 200 and the battery ECU 232 cooperate to function as a "control device" according to the present disclosure. However, the present disclosure is not limited to this, and the function of the battery ECU 232 of each battery pack (for example, the SOC estimation function) may be implemented in the server 200.

[0065] In the above-described embodiment and modification, the battery is charged with power from the power grid PG. However, in a configuration in which the charging system includes a power generation device (for example, a solar panel installed on a building), the battery may be charged with power generated by the power generation device.

[0066] In the above embodiment, the charging system includes multiple battery packs. However, this is not limited, and the number of battery packs may be one. Also, instead of a battery pack including multiple secondary batteries, a single secondary battery may be adopted. Also, in the above embodiment, the battery in the charging system is an LFP battery. However, the type of battery in the charging system is arbitrary.

[0067] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the description of the above embodiments, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0068] 23, 23-1 to 23-N battery pack, 100 power storage system, 200 server, 231 power storage device, 232 battery ECU, 233a current sensor, 233b voltage sensor.

Claims

1. A charging system including a control device that executes charging control of the battery so that an estimated SOC value of the battery does not exceed an upper limit SOC, The control device When the battery is not swollen, the upper limit SOC is set to a first SOC value; When the battery swells, the upper limit SOC is set to a second SOC value that is lower than the first SOC value, The control device is configured to, when it is determined that the battery is swollen and the SOC estimation error is large, increase the SOC of the battery above the second SOC value and calculate a correction parameter for correcting the SOC estimation error.

2. The control device When it is determined that the battery is swollen and the SOC estimation error is large, A process of canceling the upper limit SOC for the battery; A process of setting the upper limit SOC higher than the second SOC value; and then charging the battery so that the SOC of the battery is higher than the second SOC value.

2. The charging system according to claim 1, configured to, after determining the correction parameter when the SOC of the battery is higher than the second SOC value, discharge the battery until the SOC of the battery becomes equal to or lower than the second SOC value, and set the second SOC value as the upper limit SOC for the battery.

3. the control device is configured to set the SOC of the battery to a third SOC value higher than the second SOC value when it is determined that the battery has swollen and an SOC estimation error is large; each of the first SOC value and the third SOC value is included in a steep region where dV / dQ of the battery is greater than a reference value; the second SOC value is included in a plateau region where dV / dQ of the battery is smaller than the reference value; 3. The charging system according to claim 1, wherein the dV / dQ of the battery is a ratio of a change in the voltage of the battery to a change in the amount of charge stored in the battery.

4. the charging system further includes a current sensor that detects a current flowing through the battery, and a voltage sensor that detects a voltage of the battery; the control device is configured to determine whether the battery has swollen using an integrated value of a charging current of the battery; The control device When the battery is not swollen, the SOC of the battery is estimated using the voltage of the battery detected by the voltage sensor; When the battery is swollen, the SOC of the battery is estimated using the current of the battery detected by the current sensor and the correction parameter; 4. The charging system according to claim 3, wherein the control device is configured to determine whether an SOC estimation error is large using a detection value of the current sensor when no current flows through the battery.

5. A charging system including a control device that controls charging of a battery, the charging system includes a first battery pack including a plurality of batteries and a second battery pack including a plurality of batteries; the control device is configured to set an upper limit SOC for each of the first battery pack and the second battery pack; the control device is configured to execute charge control of each of the first battery pack and the second battery pack such that an estimated SOC value of each battery included in the corresponding battery pack does not exceed the upper limit SOC set for the corresponding battery pack; The control device When none of the batteries included in the first battery pack is swollen, a first SOC value is set as the upper limit SOC for the first battery pack; a second SOC value lower than the first SOC value is set as the upper limit SOC of the first battery pack when at least one battery included in the first battery pack is swollen, The control device when it is determined that at least one battery included in the first battery pack is swollen and has a large SOC estimation error, increasing the SOC of the swollen battery to be higher than the second SOC value and calculating a correction parameter for correcting the SOC estimation error for the swollen battery; A charging system configured to, after the correction parameter is obtained, discharge the swollen battery so that the SOC of the swollen battery is equal to or less than the second SOC value, and charge the second battery pack with the discharged power.

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