Control method for a charge / discharge circuit, and control program for a charge / discharge circuit

Abstract

To perform charge / discharge control of a secondary battery on the basis of both of inflow current of a string and a deterioration degree of the secondary battery constituting the string.SOLUTION: A charge / discharge device 1 selects cells 7 in order from the one at a higher deterioration degree of the cells 7 for every string 5 to supply power of required power of a load 4 or more to the load 4 in a charge / discharge circuit 2 of the cells 7 in which a plurality of strings 5 of which the number of cells 7 to be connected in series varies by a switch are connected in series with the load 4, estimates inflow current flowing to each string 5 constituted of the selected cells 7, reselects combination of the cells 7 in which the inflow current becomes equal to or less than a permissible value in the strings 5 for every string 5 to include at least one of the selected cells 7, and controls an opening / closing state of the switch of the charge / discharge circuit 2 so that each string 5 is constituted by combination of the cells 7 after reselection.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a control method for a charge / discharge circuit using multiple secondary batteries, and a control program for such a charge / discharge circuit. [Background technology]

[0002] For example, a battery that supplies power to a load that consumes a relatively large amount of electricity, such as a motor, is composed of multiple strings (also called "battery packs") in which secondary batteries are connected in series. For these strings to perform optimally, it is necessary to make the performance characteristics, such as the state of charge (SOC) and voltage, of each secondary battery that makes up the string as uniform as possible.

[0003] Therefore, Patent Document 1 discloses a control method that reduces the capacity difference between secondary batteries by discharging them through the connection of resistors to batteries with different capacities.

[0004] Patent Document 2 discloses a control method that reduces the capacity difference between batteries by charging an inductor with power from a secondary battery with a larger capacity than the other secondary batteries, and then supplying power from the inductor to a secondary battery with a smaller capacity than the other secondary batteries.

[0005] Patent Document 3 discloses a charge / discharge distribution control device that determines the degradation rate of a storage battery and sets the distribution ratio so that the charge / discharge amount is larger for storage batteries with a slower degradation rate.

[0006] Patent Document 4 discloses a capacity adjustment device that detects a degraded secondary battery from among multiple secondary batteries constituting a string, and adjusts the capacity of the degraded secondary battery based on the discharge characteristic distribution of the degraded secondary battery and the normal secondary battery. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 11-299122 [Patent Document 2] International Publication No. 2020 / 049909 [Patent Document 3] Japanese Patent Publication No. 2018-191500 [Patent Document 4] Japanese Patent Publication No. 2003-61257 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] Patent Documents 1 and 2 describe charge / discharge control that focuses on the potential difference between strings in order to reduce the amount of current flowing from one string to the other.

[0009] Patent documents 3 and 4 describe charge / discharge control that focuses on the degree of degradation of the secondary batteries constituting the string.

[0010] However, controlling the charging and discharging of the secondary batteries based on both the incoming current and the degree of degradation of the secondary batteries constituting the string, rather than based on either the incoming current or the degree of degradation of the secondary batteries constituting the string, allows for a more uniform charge state and voltage distribution among the secondary batteries constituting the string, while minimizing wasted energy.

[0011] The present invention has been made in view of the above circumstances, and aims to provide a control method for a charge / discharge circuit and a control program for a charge / discharge circuit that can control the charging and discharging of a secondary battery based on both the current flowing into the string and the degree of degradation of the secondary batteries constituting the string. [Means for solving the problem]

[0012] The first embodiment of the control method for a charge / discharge circuit is a secondary battery charge / discharge circuit in which a plurality of strings, each having a number of secondary batteries connected in series that changes by a switch, are connected in parallel to a load. The method involves a computer performing a process to control the open / closed state of the switch of the charge / discharge circuit so that each string is configured with the re-selected combination of secondary batteries such that the estimated current flowing into each string is less than or equal to the allowable current in the string, and so that each string is configured with the re-selected combination of secondary batteries.

[0013] The control program for a charge / discharge circuit according to the second embodiment is a secondary battery charge / discharge circuit in which a plurality of strings, each having a number of secondary batteries connected in series that changes by a switch, are connected in parallel to a load. The program selects secondary batteries for each string in order from those with the highest degree of degradation, which is expressed based on the size of the charging capacity, in order to supply power to the load that is greater than or equal to the power required by the load. It estimates the current flowing into each string using the voltage of each string composed of the secondary batteries selected with regard to the degree of degradation, the internal impedance of each string, and the internal impedance of the load. It re-selects a combination of secondary batteries for each string such that the estimated current for each string is less than or equal to the allowable value of the current flowing into the string, so as to include at least one of the secondary batteries selected with regard to the degree of degradation. The program causes a computer to execute a process to control the open / closed state of the switch of the charge / discharge circuit so that each string is composed of the re-selected combination of secondary batteries. [Effects of the Invention]

[0014] According to the present invention, there is an effect that a control method for a charge / discharge circuit capable of performing charge / discharge control of a secondary battery based on both the flowing current of a string and the degree of deterioration of the secondary batteries constituting the string, and a control program for the charge / discharge circuit can be provided.

Brief Description of the Drawings

[0015] [Figure 1] FIG. 12 is a diagram showing an example of a charge / discharge system using secondary batteries. [Figure 2] FIG. 15 is a diagram showing an example of a functional block of a control device. [Figure 3] FIG. 18 is a diagram showing an example of a main configuration of an electrical system of a control device. [Figure 4] FIG. 21 is a flowchart showing an example of the flow of charge / discharge processing of cells.

Modes for Carrying Out the Invention

[0016] Hereinafter, the present embodiment will be described with reference to the drawings. Note that the same components and the same processes are denoted by the same reference numerals throughout the drawings, and redundant descriptions are omitted.

[0017] FIG. 33 is a diagram showing an example of a charge / discharge system 100 using secondary batteries. The charge / discharge system 100 is composed of a charge / discharge device 1 and a load 4. In the charge / discharge system 100, the load 4 is connected between the external terminals 8-1 and 8-2 of the charge / discharge device 1, and power is supplied from the charge / discharge device 1 to the load 4.

[0018] The charge / discharge device 1 includes a charge / discharge circuit 2 and a control device 3 that controls the charge / discharge circuit 2. The charge / discharge circuit 2 includes a plurality of cells 7 which are an example of secondary batteries. There is no restriction on the type of the cells 7 included in the charge / discharge circuit 2, and any secondary battery such as, for example, a lithium ion battery, a nickel hydrogen battery, a metal lithium battery, a lithium ion polymer battery, a lead storage battery, a sodium sulfur battery (also referred to as a "NAS battery"), etc. may be used.

[0019] In the charge / discharge circuit 2, multiple strings 5 ​​are formed by connecting at least one cell 7 in series. That is, a string 5 is an example of a battery pack composed of at least one cell 7 connected in series. Each string 5 is connected in parallel to the load 4 by connecting both poles of each string 5 to external terminals 8-1 and 8-2, respectively.

[0020] In the example of the charge / discharge circuit 2 shown in Figure 1, two strings 5 ​​are connected in parallel to the load 4, but the number of strings 5 ​​that make up the charge / discharge circuit 2 can be any number and is not necessarily limited to two.

[0021] For the sake of explanation, one string 5 will be referred to as "string 5A" and the other string 5 as "string 5B". When it is not necessary to distinguish between string 5A and string 5B, both string 5A and string 5B will be collectively referred to as string 5. Accordingly, cell 7 included in string 5A will be referred to as "cell 7A", and cell 7 included in string 5B will be referred to as "cell 7B". Furthermore, since there is at least one cell 7A, when it is necessary to distinguish between each cell 7A, they will be referred to as "cell 7A-N". A This is expressed as "N A " represents an integer greater than or equal to 1. Similarly, when describing each cell 7B separately, use "cell 7B-N B It is expressed as "N B " also represents an integer greater than or equal to 1.

[0022] In the example of the charge / discharge circuit 2 shown in Figure 1, each string 5 contains 5 cells 7, so “N A " and "N B Each of these will be "5". Note that the number of cell 7s in each string 5 does not have to be the same. For example, string 5A may contain 8 cell 7As and string 5B may contain 4 cell 7Bs, so the number of cell 7s in each string 5 may differ.

[0023] Furthermore, each string 5 includes a plurality of switches 6, and by controlling the open / closed states of the switches 6, the cells 7 constituting the string 5 can be selected. For example, semiconductor switches or relays are used for the switches 6.

[0024] For the sake of convenience in explanation, the switch 6 included in the string 5A is represented as "switch 6A", and the switch 6 included in the string 5B is represented as "switch 6B". Also, when distinguishing and explaining each switch 6A, it is represented as "switch 6A-M A ". Here, "M A " represents an integer of 1 or more. Similarly, when distinguishing and explaining each switch 6B, it is represented as "switch 6B-M B ". In the case of the example of the charge / discharge circuit 2 shown in FIG. 1, since each string 5 includes 14 switches 6, "M A " and "M B " are each "14". Similar to the number of cells 7 included in each string 5, the number of switches 6 included in each string 5 does not have to be the same.

[0025] In each string 5, all combinations of the cells 7 are selected, and after connecting the selected cells 7 in series, the switches 6 are arranged so that both ends of the cells 7 connected in series can be connected to both poles of the string 5. That is, in the charge / discharge circuit 2, by controlling the switch 6 to select the cells 7 connected in series, the voltage of each string 5 can be changed. Also, in the charge / discharge circuit 2, by controlling the switch 6, the string 5 connected in parallel to the load 4 can be selected. Note that the cells 7 selected in the string 5 are referred to as "the cells 7 constituting the string 5".

[0026] In the example of the charge / discharge circuit 2 shown in Figure 1, cells 7A-1 to 7A-5 are selected as cells 7A constituting string 5A, and cells 7B-2 to 7B-5 are selected as cells 7B constituting string 5B. Assuming that the voltage of each cell 7 is the same, in this case the voltage of string 5A will be higher than the voltage of string 5B. Therefore, the current of string 5A flowing in the direction of arrow F1 will split in the directions shown by arrows F2 and F3 and flow into load 4 and string 5B. In other words, the charge / discharge device 1 shown in Figure 1 charges the cells 7B constituting string 5B while supplying power to load 4.

[0027] In this way, the charge / discharge device 1 can select the string 5 and cell 7 to be charged or discharged by controlling the open / closed state of switch 6. When the open / closed state of switch 6 changes, current flows from string 5B to string 5A and load 4, supplying power to load 4 while charging cell 7A which makes up string 5A. Hereafter, the current that flows into string 5 due to the potential difference between strings 5 ​​will be referred to as the "inflow current".

[0028] Switches 6-1 and 6-2 are connected between string 5 and external terminals 8-1 and 8-2, respectively. By turning off either switch 6-1 or switch 6-2, the power supply from the charge / discharge device 1 to load 4 can be stopped.

[0029] The control device 3 controls the open / closed state of the switch 6 included in the charge / discharge circuit 2 to select the string 5 and cell 7 to be charged and discharged.

[0030] Figure 2 shows an example of the functional blocks of the control device 3. As shown in Figure 2, the control device 3 is composed of the functional units of a selection unit 3A, an estimation unit 3B, and a control unit 3C.

[0031] The selection unit 3A selects cells 7 in each string 5 in order from the cell with the highest degree of degradation, so that the load 4 is supplied with power equal to or greater than the power required by the load 4 in the charge / discharge circuit 2.

[0032] The degree of degradation of cell 7 is expressed by an index based on the size of the charge capacity, such as SOH (States of Health). SOH is the ratio of the current full charge capacity to the unused full charge capacity of cell 7. A lower SOH value indicates a higher degree of degradation of cell 7.

[0033] If the estimation unit 3B detects variations in the State of Charge (SOC) of cells 7 between strings 5, or in the SOC of cells 7 within a string 5, it uses the voltage and internal impedance of each string 5 composed of cells 7 selected by the selection unit 3A, and the internal impedance of the load 4 to estimate the current flowing into each string 5. SOC is also called the charge rate of cell 7 and is expressed as the ratio of the remaining capacity to the full charge capacity of cell 7.

[0034] The control unit 3C re-selects a combination of cells 7 for each string 5 such that the incoming current estimated by the estimation unit 3B is less than or equal to the allowable value of the incoming current in the string 5 into which the incoming current flows, so that the selection unit 3A selects at least one of the cells 7 for each string 5. The control unit 3C controls the open / closed state of the switch 6 of the charge / discharge circuit 2 so that each string 5 is composed of the re-selected combination of cells 7.

[0035] The control device 3 that performs such processing can be configured using a computer 10. Figure 3 shows an example of the main components of the electrical system of the control device 3 configured using a computer 10.

[0036] Computer 10 includes a CPU (Central Processing Unit) 11, which is an example of a processor that performs the processing of each functional unit shown in Figure 2. Computer 10 also includes a ROM (Read Only Memory) 12 that stores a startup program (Basic Input Output System: BIOS) that performs the startup process of Computer 10, a RAM (Random Access Memory) 13 used as a temporary workspace for the CPU 11, non-volatile memory 14, and an input / output interface (I / O) 15. The CPU 11, ROM 12, RAM 13, non-volatile memory 14, and I / O 15 are connected to each other via a bus 16.

[0037] The non-volatile memory 14 is an example of a storage device that maintains stored information even when the power supplied to the non-volatile memory 14 is cut off. For example, semiconductor memory can be used, but a hard disk may also be used.

[0038] For example, the SOC measurement unit 17, the SOH measurement unit 18, and the internal impedance measurement unit 19 are connected to I / O 15.

[0039] The SOC measurement unit 17 measures the SOC of each cell 7 using a known SOC estimation method, such as the OCV method, which estimates the SOC from the open-circuit voltage of the cell 7.

[0040] The SOH measurement unit 18 measures the SOH of each cell 7 using a known SOH estimation method, such as an inflection point estimation method that estimates the SOH based on the change in SOC-OCV characteristics measured by the SOC measurement unit 17.

[0041] The internal impedance measurement unit 19 measures the internal impedance of each cell 7 by using a known internal impedance estimation method, such as connecting a test resistor to each cell 7 and estimating the internal impedance of cell 7 from the relationship between the current supplied from cell 7, the open-circuit voltage of cell 7, and the resistance value of the test resistor.

[0042] The units connected to I / O15 can be selected or omitted as needed. For example, if the charge / discharge device 1 communicates data with an external device, a communication unit will be connected to I / O15.

[0043] Next, we will describe the charging and discharging process of cell 7 performed by the charging and discharging device 1.

[0044] Figure 4 is a flowchart showing an example of the flow of the charging and discharging process for cell 7 that is executed by the CPU 11 of the control device 3 when a charging and discharging instruction is received from an external source following the connection of load 4 to the charging and discharging device 1.

[0045] The control program that defines the charging and discharging process of cell 7 is pre-stored, for example, in the non-volatile memory 14 of the control device 3. The CPU 11 of the control device 3 reads the control program stored in the non-volatile memory 14 and executes the charging and discharging process of cell 7. The control program is a program that causes the CPU 11 to execute the charging and discharging process of cell 7, which involves controlling the open and closed state of switch 6 in the charging and discharging circuit 2. Therefore, the control program stored in the non-volatile memory 14 is an example of the control program for the charging and discharging circuit 2.

[0046] Furthermore, the non-volatile memory 14 is pre-stored with the correspondence between the switch 6 and its open / closed state for connecting the selected cell 7 in series for each string 5. In addition, the non-volatile memory 14 is pre-stored with the SOC and SOH of each cell 7 measured by the SOC measurement unit 17 and the SOH measurement unit 18, respectively.

[0047] First, in step S10, the CPU 11 calculates the maximum power supply of the charge / discharge device 1 by summing the power supply capabilities of each cell 7 included in the charge / discharge device 1.

[0048] In step S20, the CPU 11 determines whether the maximum power supply calculated in step S10 is equal to or greater than the power requested by load 4. The power requested by load 4 can be, for example, the power requested in advance stored in the non-volatile memory 14, but if a communication unit is connected to I / O 15, the CPU 11 may obtain the power requested by load 4 from an external source via the communication unit. If the maximum power supply of the charge / discharge device 1 is equal to or greater than the power requested by load 4, power can be supplied from the charge / discharge device 1 to load 4, and the process proceeds to step S30.

[0049] In step S30, the CPU 11 calculates the degree of degradation of each cell 7 using the State of Health (SOH) of each cell 7 stored in the non-volatile memory 14, and selects a predetermined number of cells 7 for each string 5 in order from the most degraded to the least degraded. A known calculation method can be used to calculate the degree of degradation of cell 7 using SOH.

[0050] In this way, CPU11 prioritizes selecting the cell 7 with the highest degree of degradation among the cells 7 contained in string 5.

[0051] Hereafter, a cell 7 selected as having a higher degree of degradation than other cells 7 will be referred to as "degraded cell 7" to distinguish it from other cells 7. The CPU 11 may also select a cell 7 as a degraded cell 7 if the value indicating the degree of degradation calculated from the State of Health (SOH) falls within a predetermined range ("degradation range") in which the cell 7 is considered to be degraded. A degraded cell 7 is an example of a secondary battery selected based on its degree of degradation.

[0052] In step S40, the CPU 11 calculates the power supplied by the degraded cells 7 to the charge / discharge device 1 by summing the available power of each degraded cell 7 selected for each string 5.

[0053] In step S50, the CPU 11 determines whether the power supplied, calculated in step S40, is equal to or greater than the power required by load 4. If the power supplied by the charge / discharge device 1 is less than the power required by load 4, load 4 cannot be driven as is. Therefore, the process proceeds to step S60.

[0054] In step S60, the CPU 11 selects a cell 7 from among the cells 7 included in any string 5 that was not yet selected as a degraded cell 7 in step S30, and adds the selected cell 7 to the degraded cell 7 of that string 5. Then, the process proceeds to step S40. In step S40, the CPU 11 sums the available power of each degraded cell 7, including the cell 7 added in step S60, and recalculates the power supplied by the charge / discharge device 1 by the degraded cells 7. That is, the CPU 11 repeatedly executes the processes from steps S40 to S60, adding degraded cells 7, until the power supplied by the degraded cells 7 becomes equal to or greater than the power required by the load 4, as determined by the judgment process in step S50.

[0055] In this case, it is preferable for the CPU 11 to add the cells 7 that have not been selected as degraded cells 7 to the degraded cells 7 in order from the cells with the highest degree of degradation. Also, if a cell 7 that is included in the degradation range is selected as a degraded cell 7 in step S30, it is preferable to add the cells 7 that have a degradation value that is not included in the degradation range to the degraded cells 7 in order from the cells with a degradation value that is closest to the degradation range. However, the CPU 11 is not limited to this, and may add any cell 7 that has not been selected as a degraded cell 7 to the degraded cells 7.

[0056] On the other hand, if the determination process in step S50 determines that the power supplied by the charge / discharge device 1 by the degraded cell 7 is equal to or greater than the power required by the load 4, the process proceeds to step S70.

[0057] In step S70, the CPU 11 determines for each string 5 whether there is variation in the SOC of the selected degraded cell 7. Specifically, the CPU 11 determines whether the difference between the largest and smallest SOCs among the degraded cells 7 constituting string 5 falls within a predetermined range ("equal range") where the SOCs are considered to be uniform. If the difference in SOCs does not fall within the equal range, the CPU 11 determines that there is variation in the SOCs in that string 5. In other words, if the degraded cells 7 constituting string 5 include a degraded cell 7 that shows an extremely high or low SOC compared to other degraded cells 7, the CPU 11 determines that there is variation in the SOCs of the selected degraded cell 7. If it is determined that there is variation in the SOCs of the selected degraded cell 7, the process proceeds to step S80.

[0058] In step S80, the CPU 11 controls the internal impedance measurement unit 19 to measure the internal impedance of each degraded cell 7 that makes up each string 5, thereby calculating the internal impedance of each string 5 when it is composed of degraded cells 7. The CPU 11 also sums the voltages of each degraded cell 7 that make up each string 5 to calculate the voltage of each string 5 when it is composed of degraded cells 7.

[0059] When a potential difference occurs between the strings 5, current flows from the string 5 with the higher voltage to the string 5 with the lower voltage. Therefore, the CPU 11 estimates the current flowing into each string 5 using the voltage of each string 5, the internal impedance of each string 5, and the internal impedance of the load 4.

[0060] On the other hand, each string 5 has an allowable current value that represents the allowable limit of the incoming current. Therefore, in step S90, the CPU 11 re-selects a combination of cells 7 that make up string 5 for each string 5 by adding or removing cells 7 from the degraded cells 7 so that at least one degraded cell 7 is included, so that the incoming current to string 5 is less than or equal to the allowable current value. In other words, the CPU 11 re-selects a combination of cells 7 that make up string 5 for each string 5, taking into account the incoming current.

[0061] However, even if the combination of cells 7 is adjusted based on the degraded cells 7, there may be no combination of cells 7 in which the incoming current is less than or equal to the allowable current value. Therefore, in step S100, the CPU 11 determines whether the incoming current flowing into string 5 is less than or equal to the allowable current value by the re-selected combination of cells 7 selected in step S90. If the incoming current is less than or equal to the allowable current value, the process proceeds to step S120.

[0062] In step S120, the CPU 11 controls the open / closed state of the switch 6 of the charge / discharge circuit 2 so that each string 5 is composed of the re-selected combination of cells 7 that was re-selected in step S90, thereby ending the charge / discharge process of the cells 7 shown in Figure 4. In other words, the control device 3 can perform charge / discharge control of the cells 7 that take into account both the incoming current and the degree of degradation of the cells 7 that constitute the string 5.

[0063] On the other hand, if the determination process in step S100 determines that the incoming current still exceeds the allowable current value of string 5 even after adjusting the combination of cells 7 based on the degraded cells 7, the process proceeds to step S110.

[0064] In step S110, the CPU 11 selects the degraded cell 7 that was re-selected in step S90 as the cell 7 that constitutes string 5 and proceeds to step S120. In this case, in step S120, the CPU 11 controls the open / closed state of the switch 6 of the charge / discharge circuit 2 so that each string 5 is composed of the degraded cell 7 selected so that the power supplied by the charge / discharge device 1 is equal to or greater than the power required by the load 4, and terminates the charge / discharge process of the cell 7 shown in Figure 4.

[0065] Furthermore, if the determination process in step S70 determines that there is no variation in the SOC of the degraded cells 7, the process proceeds to step S120 without executing steps S80 to S110. In this case, similar to the process in step S120 after the execution of step S110, in step S120, the CPU 11 controls the open / closed state of the switch 6 of the charge / discharge circuit 2 so that each string 5 is composed of degraded cells 7 selected so that the power supplied by the charge / discharge device 1 is equal to or greater than the power required by the load 4, thereby terminating the charge / discharge process of the cells 7 as shown in Figure 4.

[0066] On the other hand, if the determination process in step S20 determines that the maximum power supplied by the charge / discharge device 1 is less than the power required by the load 4, the process proceeds to step S130.

[0067] In this case, the charge / discharge device 1 cannot drive the load 4. Therefore, in step S130, the CPU 11 requests a reduction in the power demand of the load 4 and terminates the charge / discharge process of cell 7 shown in Figure 4. Specifically, the CPU 11 requests the user to reduce the power demand of the load 4 by sounding an alarm or lighting an LED. Alternatively, if a communication unit is connected to I / O 15, the CPU 11 may request a reduction in the power demand of the load 4 via the communication unit.

[0068] Furthermore, in step S90, if the combination of cells 7 is re-selected for each string 5 so that the current flowing into string 5 is less than or equal to the allowable current value, the combination of cells 7 may be chosen to minimize the number of cells 7 constituting string 5.

[0069] Furthermore, in step S70, the difference in SOC of the degraded cells 7 constituting string 5 was compared with the equal range to determine whether or not there was variation in the SOC of the selected degraded cells 7. However, this is not the only way to determine whether or not there is variation in SOC. For example, the SOC of each degraded cell 7 constituting string 5 could be summed up to calculate the SOC for the string 5 unit, and if the difference in SOC between the string 5 with the largest SOC and the string 5 with the smallest SOC is not included in the equal range, it could be determined that there is variation in SOC.

[0070] The charge / discharge device 1 of this disclosure allows for the free selection of cells 7 constituting each string 5 by controlling the switch 6 of the charge / discharge circuit 2, thus enabling the full utilization of the capacity of each cell 7 regardless of its degree of degradation. Since cells 7 whose capacity has been used up can be disconnected, it is possible to replace cells 7 while supplying power to the load 4.

[0071] Furthermore, during the discharge of cell 7, cells with a higher degree of degradation reach the discharge termination voltage faster, and during the charging of cell 7, cells with a higher degree of degradation experience a faster voltage increase and complete charging. Also, during the discharge of cell 7, the lower the State of Charge (SOC), the faster the discharge ends, and during the charging of cell 7, the higher the SOC, the faster the charging is completed. Therefore, if such cells are included in the cells 7 that make up string 5, the charging and discharging in the charging / discharging device 1 will end even if the charging and discharging of other cells 7 has not yet been completed. However, since the charging / discharging device 1 of this disclosure can freely select the cells 7 that make up each string 5 by controlling the switch 6 of the charging / discharging circuit 2, charging and discharging can be continued by disconnecting cells 7 whose SOC is approaching 0% or 100%, or cells 7 with a higher degree of degradation compared to other cells 7.

[0072] Furthermore, the charge / discharge device 1 of this disclosure can switch the string 5 being charged by changing the number of cells 7 that make up the string 5, and can also adjust the magnitude of the incoming current. Therefore, in either state of power supply from the charge / discharge device 1 to the load 4, or power supply from the load 4 to the charge / discharge device 1 (referred to as the "charge / discharge state of the load 4"), charging and discharging between the strings 5 ​​can be achieved independently of the charge / discharge state of the load 4.

[0073] In cells 7 with a high degree of degradation, the charge / discharge range is narrower compared to cells 7 that are not degraded, so-called normal cells 7. Therefore, the current drawn from cells 7 with a high degree of degradation cannot be as large as that from normal cells 7. The charge / discharge device 1 of this disclosure can reduce the voltage of string 5 by reducing the number of cells 7 that make up string 5. By reducing the voltage of string 5, the current supplied from string 5 can be reduced, so even cells 7 with a high degree of degradation can be used as cells 7 that make up string 5.

[0074] Furthermore, according to the charge / discharge device 1 of this disclosure, since the cell 7 can be charged using the incoming current, the State of Charge (SOC) of the cell 7 can be increased. Therefore, if a cell 7 with a lower SOC than other cells 7 is selected as the cell 7 constituting the string 5, charging will be performed on that cell 7, thereby suppressing variations in the SOC of the cells 7 included in the string 5. Conversely, if a cell 7 with a higher SOC than other cells 7 is selected as the cell 7 constituting the string 5, discharge will be performed on that cell 7, thereby suppressing variations in the SOC of the cells 7 included in the string 5.

[0075] Furthermore, according to the charge / discharge device 1 of this disclosure, since cells 7 with a high degree of degradation can be prioritized to constitute the string 5, it is possible to handle situations where it is desired to temporarily increase the power supplied from the string 5 to the load 4. Specifically, if power is supplied from a string 5 composed of cells 7 with a high degree of degradation, the voltage of that string 5 will decrease, and the current flowing in from other strings 5 ​​will increase. During charging, cells 7 with a high degree of degradation have the characteristic of their voltage rising in a shorter time compared to normal cells 7. Therefore, since cells 7 with a high degree of degradation complete charging in a shorter time compared to normal cells 7, the power supplied to the load 4 can be temporarily increased.

[0076] Furthermore, if a string 5 composed of cells 7 with a high degree of degradation is charged by the incoming current, the voltage of string 5 will rise more quickly than a string 5 composed of normal cells 7. Consequently, the incoming current to string 5 decreases, and as a result, the current flowing to load 4 increases in a short time, rapidly improving the system efficiency of the charge / discharge system 100. Moreover, in a string 5 with a higher voltage setting than other strings 5, if cells 7 with a high degree of degradation are prioritized for composition of string 5, discharge will occur from the highly degraded cells 7, supplying incoming current to the other strings 5. When discharge occurs from the highly degraded cells 7, the voltage of string 5 will drop more quickly than when discharge occurs from normal cells 7. Consequently, the potential difference between strings 5 ​​decreases, reducing the incoming current to string 5, and as a result, the current flowing to load 4 increases in a short time, rapidly improving the system efficiency of the charge / discharge system 100.

[0077] Although one aspect of the charge / discharge system 100 has been described above using embodiments, the disclosed form of the charge / discharge system 100 is merely an example, and the form of the charge / discharge system 100 is not limited to the scope described in the embodiments. Various modifications or improvements can be made to the embodiments without departing from the spirit of this disclosure, and such modified or improved forms are also included within the technical scope of the disclosure. For example, without departing from the spirit of this disclosure, the internal processing order in the charge / discharge process of cell 7 shown in Figure 4 may be changed.

[0078] Furthermore, in the above embodiment, as an example, a configuration in which the charging and discharging process of cell 7 shown in Figure 4 is implemented by software was described. However, the same process as the flowchart for the charging and discharging process of cell 7 may be performed by hardware. In this case, the processing speed can be increased compared to the case in which the charging and discharging process of cell 7 is implemented by software.

[0079] In the above embodiment, the term "processor" refers to a broad type of processor, including general-purpose processors (e.g., CPU11) and dedicated processors (e.g., GPU: Graphics Processing Unit, ASIC: Application Specific Integrated Circuit, FPGA: Field Programmable Gate Array, programmable logic device, etc.).

[0080] Furthermore, the operation of the processor in the above embodiment may not be performed by a single processor, but may be performed by multiple processors located in physically separate locations working together. Also, the order of the processor operations is not limited to the order described in the above embodiment, but may be changed as appropriate.

[0081] In the above embodiment, an example was described in which the control program is stored in the non-volatile memory 14, but the storage location of the control program is not limited to the non-volatile memory 14. The control program of this disclosure can also be provided in a form recorded on a storage medium readable by the computer 10. For example, the control program may be provided in a form recorded on an optical disc such as a CD-ROM (Compact Disk Read Only Memory), DVD-ROM (Digital Versatile Disk Read Only Memory), or Blu-ray disc. Alternatively, the control program may be provided in a form recorded on a portable semiconductor memory such as a USB (Universal Serial Bus) memory or memory card. ROM 12, non-volatile memory 14, CD-ROM, DVD-ROM, Blu-ray disc, USB, and memory card are examples of non-transitory storage media.

[0082] Furthermore, the control device 3 may download a control program from an external device connected to a communication line via a communication unit and store the downloaded control program in a memory device.

[0083] In this case, the CPU 11 of the control device 3 reads the control program downloaded from the external device from the storage device and executes the charging and discharging process of the cell 7. [Explanation of symbols]

[0084] 1 Charge / discharge device 2 Charge / discharge circuit 3. Control device 3A Selection Section 3B Estimation part 3C Control Unit 4 load 5 (5A, 5B) strings 6 (6A, 6B) switches 7 (7A, 7B) Cells (Degraded Cells) 8-1 (8-2) External terminals 10 Computers 11 CPU 12 ROM 13 RAM 14 Non-volatile memory 15 I / O 16 bus 17 SOC Measurement Unit 18 SOH Measurement Unit 19. Internal Impedance Measurement Unit 100 Charge / Discharge Systems F1 (F2, F3) Arrow

Claims

1. In a secondary battery charging and discharging circuit, where multiple strings, each with a series connection of secondary batteries, are connected in parallel to a load, and the number of secondary batteries connected in series changes via a switch, In order to supply power to the load that is greater than or equal to the load's required power, for each string, secondary batteries are selected in order from those with the highest degree of degradation, which is expressed based on the size of their charging capacity. Using the voltage of each string composed of secondary batteries selected based on the degree of degradation, the internal impedance of each string, and the internal impedance of the load, the current flowing into each string is estimated. The computer performs a process to re-select a combination of secondary batteries for each string such that the estimated incoming current for each secondary battery is less than or equal to the allowable value of the incoming current in the string, including at least one secondary battery selected based on the degree of degradation, and to control the open / closed state of the switch of the charge / discharge circuit so that each string is composed of the re-selected combination of secondary batteries. A method for controlling a charge and discharge circuit.

2. If, among the secondary batteries constituting the string, selected based on their degree of degradation, the difference in charge levels between the secondary battery with the highest charge level and the secondary battery with the lowest charge level does not fall within a predetermined range where the charge levels are considered to have no variation, the computer performs a process to re-select a combination of secondary batteries for each string such that the estimated incoming current of each secondary battery is less than or equal to the allowable value of the incoming current in the string, including at least one of the secondary batteries selected based on their degree of degradation. A method for controlling a charge / discharge circuit according to claim 1.

3. The computer performs a process to re-select a combination of secondary batteries for each string such that the estimated incoming current of each secondary battery, selected based on its degree of degradation, is less than or equal to the allowable value of the incoming current in the string, and the number of secondary batteries constituting the string is kept to a minimum, so that each string includes at least one secondary battery selected based on its degree of degradation. A method for controlling a charge / discharge circuit according to claim 2.

4. If any of the charge levels of the secondary batteries selected based on the degree of degradation fall within the predetermined range, or if, from among the secondary batteries selected based on the degree of degradation, no combination of secondary batteries can be selected such that the estimated incoming current of each battery is less than or equal to the allowable value of the incoming current in the string, the computer executes a process to control the open / closed state of the switch of the charge / discharge circuit so that each string is configured with the combination of secondary batteries selected based on the degree of degradation, without having to re-select the combination of secondary batteries for each string. A method for controlling a charge / discharge circuit according to claim 2 or claim 3.

5. In a secondary battery charging and discharging circuit, where multiple strings, each with a series connection of secondary batteries, are connected in parallel to a load, and the number of secondary batteries connected in series changes via a switch, In order to supply power to the load that is greater than or equal to the load's required power, for each string, secondary batteries are selected in order from those with the highest degree of degradation, which is expressed based on the size of their charging capacity. Using the voltage of each string composed of secondary batteries selected based on the degree of degradation, the internal impedance of each string, and the internal impedance of the load, the current flowing into each string is estimated. The computer is instructed to perform a process to control the open / closed state of the switch of the charge / discharge circuit so that each of the secondary batteries selected based on the degree of degradation is included, and such that the estimated incoming current of each secondary battery is less than or equal to the allowable value of the incoming current in the string, and so that each of the strings is composed of the newly selected combination of secondary batteries. Control program for the charge / discharge circuit.

6. If, among the secondary batteries constituting the string, selected based on their degree of degradation, the difference in charge levels between the battery with the highest charge level and the battery with the lowest charge level does not fall within a predetermined range where the charge levels are considered to have no variation, the computer is instructed to perform a process to re-select a combination of secondary batteries for each string such that the estimated incoming current of each battery is less than or equal to the allowable value of the incoming current in the string, including at least one of the secondary batteries selected based on their degree of degradation. A control program for a charge / discharge circuit according to claim 5.

7. The computer is instructed to perform a process of re-selecting a combination of secondary batteries for each string such that the estimated incoming current of each secondary battery, selected based on its degree of degradation, is less than or equal to the allowable value of the incoming current in the string, and the number of secondary batteries constituting the string is kept to a minimum, so that each string includes at least one secondary battery selected based on its degree of degradation. A control program for a charge / discharge circuit according to claim 6.

8. If any of the charge levels of the secondary batteries selected based on the degree of degradation fall within the predetermined range, or if it is not possible to select a combination of secondary batteries from among those selected based on the degree of degradation such that the estimated incoming current of each battery is less than or equal to the allowable value of the incoming current in the string, the computer will execute a process to control the open / closed state of the switch of the charge / discharge circuit so that each string is composed of the combination of secondary batteries selected based on the degree of degradation, without having to re-select the combination of secondary batteries for each string. A control program for a charge / discharge circuit according to claim 6 or claim 7.

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