Battery pack system

Abstract

To provide a battery pack system that enables matching of a voltage state and / or a charging state of a battery pack system in a short time without passing an excessive current in a secondary battery.SOLUTION: A battery pack system 1 comprises: a unit series battery pack P11 in which a plurality of cells are serially connected; a unit battery pack SP1 in which a plurality of unit series battery packs P11 are parallelly connected; a bypass switch Sw111 that is serially connected to resistances parallelly connected to each cell; a main circuit switch serially connected to each unit series battery; and a balancing control unit 11 that standardizes a voltage state and / or a charging state of each cell in the unit series battery. A standardization target value for the voltage state and / or the charging state of each cell is calculated. If a state of the cell is lower than the standardization target value, the main circuit switch of the unit series battery pack in which that cell is included is turned ON and the bypass switch that is parallelly connected to that cell is turned OFF.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a battery pack system. [Background technology]

[0002] The amount of solar and wind power generation being introduced is increasing. However, the output of solar and wind power generation fluctuates depending on the weather and time of day, making it difficult to adjust supply and demand in the power grid. To solve this problem, it is expected that energy storage systems will be used to adjust supply and demand. In addition, studies are underway to use energy storage systems to supply inertial force to the grid.

[0003] The battery pack system that makes up an energy storage system achieves the required voltage and capacity by connecting multiple secondary batteries in series and parallel. When multiple secondary batteries are connected in series and parallel, there is a possibility that the voltage will vary between the secondary batteries due to individual differences and environmental conditions. When multiple series units each consisting of multiple secondary batteries are connected in series are connected in parallel, the voltage variation can cause excessive current to flow through the secondary batteries, accelerating their degradation.

[0004] As a method for aligning the voltage between series units connected in parallel in a battery pack system without passing excessive current, a method has been proposed in which a switch is used to disconnect a series unit when excessive current flows through it (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2019 / 150836 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the configuration disclosed in Patent Document 1, it may be difficult to equalize the voltages to a target accuracy or less due to variations in characteristics such as resistance and capacity among secondary batteries. , storage In a battery system, the change in charge level due to the circulating current flowing during parallel equalization varies among secondary batteries, which can cause voltage variations even after the equalization operation. To resolve this voltage variation, it is necessary to repeat the equalization operation multiple times in both the series and parallel directions. As the number of secondary batteries in a battery storage system increases, there is a high probability that secondary batteries with large variations in characteristics will exist. Therefore, even if the equalization operation is repeated in both the series and parallel directions, it may not be possible to achieve the target leveling accuracy within the specified time.

[0007] Therefore, the present invention provides a battery pack system that allows the voltage and / or state of charge of the battery pack system to be uniform in a short time. [Means for solving the problem]

[0008] In order to solve the above problems, the battery pack system according to the present invention includes a unit series assembled battery in which a plurality of cells are connected in series, a unit assembled battery in which a plurality of the unit series assembled batteries are connected in parallel, a resistor connected in parallel to each cell, a bypass switch connected in series to the resistor, a main circuit switch connected in series to each unit series assembled battery, and a balancing control unit that equalizes the voltage and / or state of charge between each cell in the unit assembled battery, wherein the balancing control unit Calculate the current value flowing during the leveling operation based on the sum of the internal resistance and the sum of the voltage of each cell, and calculate the current value based on at least one of the voltage or state of charge of each cell before the leveling operation, Equalize the voltage and / or state of charge of each cell for A switch selection unit is provided to calculate a leveling target value and to instruct ON / OFF of the main circuit switch and the bypass switch in the series assembled battery for leveling operation, and the switch selection unit is configured to determine the state of the cells. the voltage and / or state of charge of the cell is lower than the leveling target value, the main circuit switch connected in series to the unit series battery pack including the corresponding cell is instructed to be ON and the bypass switch connected in parallel to the corresponding cell is instructed to be OFF.

[0009] Furthermore, the battery system according to the present invention includes a unit series assembled battery in which a plurality of cells are connected in series, a unit assembled battery in which a plurality of the unit series assembled batteries are connected in parallel, and a battery in which a plurality of the unit assembled batteries are connected in series, wherein the unit series assembled battery includes a resistor connected in parallel to each cell, a bypass switch connected in series to the resistor, a main circuit switch connected in series to each unit series assembled battery, and a balancing control unit that equalizes the voltage and / or state of charge between each cell in the unit assembled battery, Calculate the current value flowing during the leveling operation based on the sum of the internal resistance and the sum of the voltage of each cell, and calculate the current value based on at least one of the voltage or state of charge of each cell before the leveling operation, Equalize the voltage and / or state of charge of each cell for A switch selection unit is provided to calculate a leveling target value and to instruct ON / OFF of the main circuit switch and the bypass switch in the series assembled battery for leveling operation, and the switch selection unit is configured to determine the state of the cells. the voltage and / or state of charge of the cell is lower than the leveling target value, the main circuit switch connected in series to the unit series battery pack including the corresponding cell is instructed to be ON and the bypass switch connected in parallel to the corresponding cell is instructed to be OFF. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a battery pack system that allows the voltage and / or state of charge of the battery pack system to be uniform in a short time. Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram showing the overall configuration of an energy storage system including a battery pack system according to a first embodiment. [Figure 2] 1 is an overall configuration diagram of a battery pack system according to a first embodiment. [Figure 3] FIG. 3 is a functional block diagram showing the overall series balancing control unit shown in FIG. 2. [Figure 4] 3 is a functional block diagram showing a switch selection unit shown in FIG. 2. FIG. [Figure 5] 10 is a flowchart showing a leveling process according to the first embodiment. [Figure 6] 4 is a flowchart showing the operation of a parallel balancing control unit and a switch selection unit that constitute the battery pack system according to the first embodiment. [Figure 7] 5A and 5B are diagrams illustrating voltages, currents, and switch operations when an equalization process is performed in the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same components are designated by the same reference numerals, and detailed descriptions of overlapping parts will be omitted. Hereinafter, an embodiment of the present invention will be described with reference to the drawings. [Example]

[0013] FIG. 1 is a schematic diagram showing the overall configuration of an energy storage system including a battery pack system according to this embodiment. As shown in FIG. 1, an energy storage system 100 supplies active power and reactive power to an AC system 41. The energy storage system 100 may also be connected to industrial equipment or the like to improve the power quality of the industrial equipment or the like. As shown in FIG. 1, the energy storage system 100 includes a transformer 42, a filter 43, an AC / DC converter 44, and a battery pack system 1. The transformer 42 is connected to the AC system 41 and transmits energy between multiple windings using electromagnetic induction. The filter 43 removes a predetermined frequency component.

[0014] When the energy storage system 100 is connected to a power distribution system, it is preferable that the AC / DC converter 44 is a two-level converter or a three-level converter, and that the output voltage of the assembled battery system 1 connected to the AC / DC converter 44 is, for example, 1 kV. When the energy storage system 100 is connected to a power transmission system, it is preferable that the AC / DC converter 44 is a multi-level converter, and that the output voltage of the assembled battery system 1 connected to the AC / DC converter 44 is, for example, 40 kV.

[0015] The battery pack system 1 is charged by application of a DC voltage output by the AC / DC converter 44. The charged battery pack system 1 is then discharged to the AC system 41 via the AC / DC converter 44.

[0016] The details of the battery pack system 1 will be described with reference to Figure 2. The battery pack system 1 is configured with p unit battery packs SP1-SPp connected in series, where p, n, and m are positive integers. Figure 2 shows an example where p=3. Each unit battery pack P1-SPp is configured with m unit series battery packs Pij connected in parallel, each unit battery pack Pij being made up of n replaceable battery cells Bijk (i=1,2,...,p, j=1,2,...,m, k=1,2,...,n) connected in series. 2, the subscript i indicates that the element is included in one unit battery SPi out of the unit batteries SP1-SPp, the subscript j indicates that the element is included in one unit series battery Pij out of the m parallel-connected unit series batteries Pi1-Pim that make up the unit battery SPi, and the subscript k indicates the kth battery cell Bijk out of the n battery cells Bij1-Bijn that make up the unit series battery Pij, or an element connected to battery cell Bijk. For example, the unit series batteries included in unit battery SP1 are P11-P1m, and the n battery cells included in unit series battery P1j are represented as B1j1-B1jn.

[0017] The following describes the elements that make up the first unit battery assembly SP1 shown in Fig. 2. The other unit battery assembly SPp (where p is other than 1) also has a similar configuration. The battery cells may be lithium-ion battery cells, nickel-metal hydride battery cells, lead-acid battery cells, or the like. Hereinafter, this specification will assume an example in which lithium-ion battery cells (nominal voltage: 3.6-4V) are used. The number n of series connections of battery cells B111-B11n in unit series assembled battery P11 included in first unit battery assembled battery SP1 is determined according to the output voltage of unit series assembled battery P11. For example, if the output voltage of unit series assembled battery P11 is approximately 1 kV, approximately n=250 battery cells B111-B11n of lithium-ion batteries are connected in series. Furthermore, the number m of parallel connections of unit series assembled batteries P11-P1m is determined according to the capacity of each battery cell B1jk and the capacity of battery assembled system 1. For example, if the capacity of battery assembled system 1 is 3500 Ah and the capacity of each battery cell B1jk is 100 Ah, approximately m=35 unit series assembled batteries are connected in parallel. Furthermore, the number p of unit battery assemblies SP1-SPp connected in series is determined according to the output voltage of the battery assembly system and the output voltage of the unit series battery assemblies. For example, if the output voltage of the battery assembly system is 40 kV and the output voltage of the unit series battery assemblies is about 1 kV, then about p = 40 unit battery assemblies are connected in series. Therefore, the number of battery cells is n × m × p. Furthermore, although Figure 2 shows an example of three unit battery assemblies, the battery assembly system 1 can have any number of unit battery assemblies connected in series. It is also possible to expand the battery assembly system 1 by connecting multiple battery assemblies in parallel.

[0018] Each battery cell B1jk constituting the unit series battery packs P11-P1m is connected in parallel to a resistor SR1 and a bypass switch Sw1jk. Although not shown in FIG. 2, the unit series battery packs P11-P1m also include a fuse, a fan, a current sensor, and a voltage sensor. Each unit series battery pack P1j also includes a series balancing control unit 1j that manages and controls the state of each battery cell B1jk. FIG. 2 shows the case where j=1 in detail. The series balancing control unit 11 is communicatively connected to the bypass switches Sw111-Sw11n, the switch selection unit 13, and the parallel balancing control unit 12. The series balancing control unit 11 collects information on the state of the battery cells B111-B11n. The states of the battery cells B111-B11n include, for example, the voltage of the battery cell B111, the temperature of the battery cell B111, the life of the battery cell B111, the resistance value of the battery cell B111, and the state of charge of the battery cell B111, i.e., the SOC (State of Charge). The series balancing control unit 11 stores information about the states of the battery cells B111-B11n and outputs the information about the states of the battery cells B111-B11n to the parallel balancing control unit 12 and the switch selection unit 13. The series balancing control unit 11 can be configured, for example, by a microprocessor. It is configured in a similar manner when j is other than 1.

[0019] The unit battery pack SP1 is composed of m unit series batteries P11-P1m connected in parallel. Main circuit switches PW11-PW1m are connected in series to each of the unit series batteries P11-P1m. A parallel balancing control unit 12 and a switch selection unit 13 are connected in parallel to the unit battery pack SP1. While the switch selection unit 13 shown in FIG. 2 is included within the parallel balancing control unit 12, this is not essential and it may be located outside the parallel balancing control unit 13. The parallel balancing control unit 12 is communicatively connected to the switch selection unit 13, the series balancing control units 11-1m, and the overall series balancing control unit 5. The switch selection unit 13 is communicatively connected to the parallel balancing control unit 12, the main circuit switches PW11-PW1m, and the bypass switches Sw111-Sw1mn. The parallel balancing control unit 11 and the switch selection unit 13 can be implemented, for example, by a microprocessor. Furthermore, relays or semiconductor switches can be used for the main circuit switches PW11-PW1m and the bypass switches Sw111-Sw1mn. The battery pack system 1 is configured by connecting unit battery packs SP1-SP3 in series and further connecting them in parallel to an overall series balancing control unit 5. The overall series balancing control unit 5 can be configured, for example, by a microprocessor. The parallel balancing control unit 12 also collects information about the states of battery cells B111-B11n output from the series balancing control unit 11 and outputs this information to the overall series balancing control unit 5. For example, the parallel balancing control unit 12 collects information about the states of battery cells B111-B1mn and outputs the resistance and voltage values ​​of each battery cell B1jk and the resistance and voltage values ​​of each unit series battery pack P1j that includes each battery cell B1jk to the overall series balancing control unit 5.

[0020] Here, parallel balancing control unit 12, switch selection unit 13, series balancing control unit 11-m, and overall series balancing control unit 5 may be configured with a single microprocessor or multiple microprocessors. Components that perform balancing control of battery cells, such as series balancing control unit 11-p1, parallel balancing control unit 12-p2, and overall series balancing control unit 5, are collectively referred to as the balancing control unit.

[0021] Next, the leveling operation according to this embodiment will be described. For generalization, the leveling operation for the battery pack system 1 will be described without being limited to p=3. The resistance and voltage of each battery cell B111-Bpmn included in the battery pack system 1 vary due to aging and the operating environment. For example, if the operating temperatures of each battery cell B111-Bpmn vary, the rate at which aging degradation, such as a decrease in full charge capacity and an increase in resistance value, progresses will vary. As a result, the resistance and SOC of the battery cells will vary, and the voltage corresponding to the SOC will also vary. In response to this, the overall series balancing control unit 5, series balancing control unit 11-p1, parallel balancing control unit 12-p2, and switch selection unit 13-p3 perform a leveling operation to level the voltage and / or SOC of each battery cell B111-B3mn.

[0022] Below, the equalization operation of equalizing the voltage and / or SOC of each battery cell B111-Bpmn by the overall series balancing control unit 5, the series balancing control unit 11-p1, the parallel balancing control unit 12-p2, and the switch selection unit 13-p3 will be explained using Figures 3 and 4.

[0023] FIG. 3 is a functional block diagram of the overall series balancing control unit shown in FIG. 2. The overall series balancing control unit 5 calculates a leveling target value used to level the voltage and / or SOC of each battery cell B111-Bpmn included in the battery pack system 1. The overall series balancing control unit 5 calculates, using a current calculation unit 51, the current that will flow through each of the m-string unit series assembled batteries P11-Ppm when all of the main circuit switches PWp1-PWpm are turned ON and all of the bypass switches Swpm1-Swpmn are turned OFF, based on the resistance and voltage values ​​of each battery cell B111-Bpmn output from the series balancing control unit p1 and integrated by the parallel balancing control unit p2, or the resistance and voltage values ​​of each unit series assembled battery P11-Ppm. Furthermore, the overall series balancing control unit 5 calculates a leveling target value for leveling the voltage and / or SOC of each cell based on the calculated current value and each cell voltage value, in accordance with a leveling target value calculation unit 52, and outputs the calculated value together with the current value.

[0024] The current calculation unit 51 and the leveling target value calculation unit 52 are described below. The current calculation unit 51 calculates the current value flowing through each of the m unit series assembled batteries P11-Ppm based on the resistance and voltage values ​​of each battery cell B111-Bpmn or the resistance and voltage values ​​of each unit series assembled battery P11-Ppm. The current value IPij flowing through the unit series assembled battery Pij (i=1, 2, . . . , p, j=1, 2, . . . , m) can be predicted using the following (Equation 1):

[0025] IPij=(1 / Rj)(1 / (Σ^m_q=1(1 / Rq)))(I+Σ^m_q=1((Vq―Vj) / Rq))···(1) Rj: The sum of the resistance values ​​of the battery cells Bpj1-Bpjn included in the unit series battery Ppj, or the resistance value of the unit series battery Ppj, Vj: The sum of the voltages of the battery cells Bpj1-Bpjn included in the unit series battery Ppj, or the voltage value of the unit series battery Ppj, I: Charge / discharge current value of battery pack system 1, In the above formula (1), Σ^m_q=1 indicates that the subscript q is the sum of 1 to the number m of parallel unit series assembled batteries.

[0026] The leveling target value calculation unit 52 calculates a leveling target value for the voltage or charge amount of each cell based on the current value flowing through each unit series battery pack P11-Ppm and each cell voltage calculated by the current calculation unit 51. The leveling target value can be calculated, for example, by the following method. Based on the current value flowing through each unit series battery pack P11-Ppm calculated by the current calculation unit 51, the amount of change in the charge amount of each battery cell B111-Bpmn is calculated and the voltage of each battery cell is predicted. The minimum value of the predicted voltages of each battery cell B111-Bpmn is then set as the leveling target value. By predicting the battery cell voltages of all battery cells B111-Bpmn included in the battery pack system and setting the leveling target value, it is possible to achieve series and parallel balancing of the battery cells within the unit battery pack as well as series balancing between each unit battery pack.

[0027] The overall series balancing control unit 5 outputs the calculated leveling target value and current calculated value to the parallel balancing control unit p2. The parallel balancing control unit p2 outputs each cell voltage, the leveling target value, and the current calculated value to the switch selection unit p3.

[0028] FIG. 4 is a functional block diagram of the switch selection unit shown in FIG. 2. Note that FIG. 4 shows the operation of the switch selection unit 13-p3. The switch selection unit 13-p3 issues predetermined switch operations to the main circuit switches PWp1-PWpm and the bypass switches Swpm1-Swpmn via the allowable current determination unit p31 and the charge / discharge determination unit p32 based on the cell voltages, leveling target values, and current calculation values ​​output by the parallel balancing control unit 12-p2. The allowable current determination unit p31 compares the current calculation value with the allowable current value of each unit series battery pack P11-Ppm, and outputs a result of the comparison to the charge / discharge determination unit p32 indicating whether the calculated current value exceeds the allowable current value. The allowable current value may be fixed or updateable. Furthermore, the charge / discharge determination unit p32 determines whether to discharge or charge each battery cell B111-B3mn and maintain a constant voltage based on the comparison result between each battery cell, the voltage leveling target value, and the current calculation value and the allowable current value output from the allowable current determination unit p31. Based on the result of the determination by the charge / discharge determination unit p32, the switch selection unit p3 commands the main circuit switches PWp1-PWpm and bypass switches Swpm1-Swpmn to perform the specified switch operation when discharging, charging, or maintaining a constant voltage.

[0029] A specified switch operation during discharge can be, for example, an operation to discharge when the voltage or state of charge of the battery cell Bijk is higher than the leveling target value, and to instruct the bypass switch Swijk connected in parallel to the battery cell Bijk to be ON.

[0030] The predetermined switch operation during charging can be, for example, an operation to instruct the main circuit switch PWij connected in series to the unit series battery pack Pij including the battery cell Bijk to be ON and the bypass switch Swijk connected in parallel to the battery cell Bijk to be OFF when the voltage or charging state of the battery cell Bijk is lower than the leveling target value. The switch operation when the voltage is constant can be, for example, an operation to instruct the main circuit switch PWij connected in series to the unit series battery pack Pij including the battery cell Bijk to be OFF and the bypass switch Swijk connected in parallel to the battery cell Bijk to be OFF.

[0031] 5 is a flowchart showing the voltage leveling process of this embodiment. The flowchart shows the operations of the overall series balancing control unit 5, parallel balancing control unit 12-p2, switch selection unit 13-p3, and series balancing control unit 11-p1 in the voltage and / or SOC leveling process of this embodiment. In step S11, the series balancing control unit 11-p1 detects the voltage of each battery cell B111-Bpmn.

[0032] In the following step S12, the parallel balancing control unit 12-p2 acquires the voltage and internal resistance of the unit series battery P11-Ppm. Here, the voltage of the unit series battery Pij may be the terminal-to-terminal voltage of the unit series battery Pij, or may be the sum of the voltages of the battery cells Bij1-Bijn that make up the unit series battery Pij. Furthermore, the resistance of the unit series battery Pij may be the terminal-to-terminal resistance of the unit series battery Pij, or may be the sum of the resistances of the battery cells Bij1-Bijn that make up the unit series battery Pij.

[0033] In the following step S13, the overall series balancing control unit 5 calculates the current flowing through each unit series battery pack P11-Ppm using the above-mentioned equation (1). In the following step S14, the overall series balancing control unit 5 calculates a target balancing value.

[0034] In the following step S15, the switch selection unit 13-p3 compares the current value flowing through each unit series battery pack P11-Ppm calculated in step S14 with the allowable current value in accordance with the allowable current determination unit p31. In the following step S16, the parallel balancing control unit p2 determines whether to perform charging, discharging, or constant voltage operation for each battery cell B111-Bpmn in accordance with the charging / discharging determination unit p32, and outputs the determined result to the switch selection unit 13-p3.

[0035] In the following step S17, the switch selection unit i3 commands the main circuit switch PWij connected in series to the corresponding cell Bijk and the bypass switch Swijk connected in parallel to the corresponding cell Bijk to perform a predetermined switch operation. In the next step S18, it is determined whether the difference between the voltage and / or SOC of each battery cell B111-Bpmn after the leveling operation and the leveling target value is equal to or less than a tolerance. If the difference between the leveling target value and all battery cells B111-Bpmn is equal to or less than the tolerance, the process ends, the main circuit switches PW11-PWpm are turned ON, and the bypass switches Sw111-Swpmn are turned OFF. If the difference between the leveling target value and at least one of the voltages or SOCs of at least one battery cell Bijk is equal to or greater than the tolerance, the process returns to step S13. The tolerance may be fixed or updateable.

[0036] In this embodiment, the case where only the voltage of each battery cell is detected in step S11 and the like has been described, but this is not limited to this. For example, the same effect can be obtained by detecting the state of charge of each battery cell. Also, instead of the voltage of each battery cell, the voltage and state of charge of each battery cell may be detected. In this case, it is possible to perform the leveling process with even higher accuracy.

[0037] 6 is a flowchart showing the operation of the parallel balancing control unit and switch selection unit that constitute the battery pack system according to this embodiment. This flowchart shows the operation of the parallel balancing control unit 12-p2 and the switch selection unit 13-p3 in the leveling process for leveling the voltage and / or SOC. In step S21, the parallel balancing control unit 12-p2 obtains the calculated value of the current flowing through each unit series assembled battery P11-Ppm, calculated by the overall series balancing control unit 5, based on the voltage and internal resistance of the unit series assembled battery P11-Ppm.

[0038] In the following step S22, the parallel balancing control unit 12-p2 compares the calculated value of the current flowing through each unit series assembled battery P11-Ppm with the allowable current value to see if it is greater than the allowable current value. The next step S23 indicates the operation to be performed when the calculated value of the current flowing through each unit series battery P11-Ppm is greater than the allowable current value, and the switch selection unit i3 commands the main circuit switch PWij connected in series with the corresponding unit series battery Pij to turn OFF. This operation prevents excessive current from flowing through the battery cells due to the leveling operation.

[0039] Step S24 following step S22 indicates the operation to be performed when the calculated value of the current flowing through each unit series assembled battery P11-Ppm is smaller than the allowable current value, and the switch selection unit i3 commands the main circuit switch PWij connected in series to the corresponding unit series assembled battery Pij to turn ON. In the following step S25, the voltage and / or SOC of each battery cell B111-Bpmn is compared with the equalization target value calculated by the overall series balancing control unit 5.

[0040] The following step S26 shows the operation to be performed when the voltage and / or SOC of each battery cell B111-Bpmn is smaller than the leveling target value, and the switch selection unit i3 commands the corresponding bypass switch Swijk connected in parallel to the corresponding battery cell Bijk to be turned OFF. If the main circuit switch PWij is turned ON in step S24, this operation allows the battery cell Bijk to be charged. This operation reduces the power consumed during the leveling operation. If the main circuit switch PWij is turned OFF in step S24, this operation allows the voltage of the battery cell Bijk to be kept constant.

[0041] Step S27 following step S25 indicates an operation to be performed when the voltage and / or SOC of each battery cell B111-Bpmn is greater than the leveling target value, and the switch selection unit i3 commands the corresponding bypass switch Swijk connected in parallel to the corresponding battery cell Bijk to turn ON. This operation allows current to flow through the bypass switch Swijk connected in parallel to the battery cell Bijk, thereby discharging the battery cell Bijk.

[0042] In the next step S28, the voltage and / or SOC of each battery cell B111-Bpmn after the operations of steps S22 to S27 have been performed for a predetermined time is compared with the difference between the voltage and / or SOC and the leveling target value. If the difference between the voltage and / or SOC of at least one battery cell Bijk and the leveling target value is equal to or greater than the allowable value, the process returns to step S21. In the following step S29, if the difference between the voltage and / or SOC of each battery cell B111-Bpmn and the leveling target value is smaller than the allowable value, the switch selection unit 13-p3 commands the bypass switches Sw111-Swpmn to turn OFF, and the process ends. By operating steps S28 and S29, the voltages and / or SOC of all battery cells B111-Bpmn can be leveled so that the difference from the leveling target value is equal to or less than the allowable value.

[0043] In this embodiment, the main circuit switch PWij is checked in steps S22 and S23, and the bypass switches Sw111-Swpmn are checked in steps S26 and S27, but the order may be reversed, and after determining whether to send an ON or OFF command to each switch, the command may be sent to each switch simultaneously.

[0044] According to this embodiment, the switch selection unit issues commands to the main circuit switches PW11-PWpm and the bypass switches Sw111-Swpmn in accordance with the flowchart shown in FIG. 6, thereby making it possible to quickly equalize the voltage and / or state of charge of each battery cell B111-Bpmn that constitutes the battery pack system 1 without passing excessive current through the battery cells. Assume also the case of leveling a large-scale battery system, for example, a battery system consisting of 10 series units, each of which is composed of 10,000 secondary batteries connected in series, connected in parallel. In such a large-scale battery system, the probability of cells with large variations in voltage or SOC increases depending on the number of batteries. In a conventional method of performing parallel balancing after series balancing, different leveling target values ​​are set for each series unit. Therefore, if cells with large variations in voltage or SOC exist, the leveling target values ​​will also vary among the series units. Therefore, with conventional balancing methods, variations in voltage and / or SOC are likely to exist even after balancing. Therefore, to level all cells, multiple balancing operations must be performed, which increases the time required for balancing. In contrast, according to this embodiment, by setting leveling target values ​​taking into account the variations throughout the battery system and issuing appropriate switch operations, the voltage and / or SOC of all cells can be leveled with a single balancing operation. Therefore, even in a large-scale battery system, leveling can be achieved in a short time. Therefore, this embodiment is suitable for application to a large-scale battery storage system.

[0045] FIG. 7 is a diagram showing the voltage, current, and switch operation during the leveling process of this embodiment. The voltage leveling operation of this embodiment will be explained using FIG. 7. The time chart T1-T4 in FIG. 7 shows an example of a time chart showing the voltage and current of battery cells B111 and B121, and the operation of main circuit switches PW11 and PW12, and bypass switches Sw111 and Sw121 when switch operations are performed according to the flowcharts of FIGS. 5 and 6. Here, the voltage leveling operation will be explained using an example of two battery cells with p=1, m=2, and n=1. For simplicity, the series balancing control unit, parallel balancing control unit, switch selection unit, and overall series balancing control unit are omitted from FIG. 7.

[0046] Time chart T1 in Figure 7 shows the voltages of battery cells B111 and B121. At the start of the balancing operation, the voltage of battery cell B111 is higher than that of battery cell B121. The series balancing control unit acquires the voltages and resistance values ​​of battery cells B111 and B121 and outputs them to the parallel balancing control unit. The parallel balancing control unit accumulates the voltages and resistance values ​​of battery cells B111 and B121 and outputs them to the overall series balancing control unit. Based on the voltages and resistance values ​​of battery cells B111 and B121, the overall series balancing control unit calculates the current value and leveling target value flowing through each battery cell and the leveling target value in accordance with the current calculation unit 51 and the leveling target value calculation unit 52, and outputs these values ​​to the parallel balancing control unit. The parallel balancing control unit compares the calculated current value with the allowable current value and outputs the comparison result to the switch selection unit. The switch selection unit commands the main circuit switches PW11 and PW12 to perform the specified switch operation.

[0047] 7, assume that the voltage difference between battery cells B111 and B121 is large at the start of the voltage leveling operation, causing the calculated current value to exceed the allowable current value. In this case, it is necessary to prevent excessive current from flowing to battery cell B112, as shown in time chart T2. To do this, the switch selection unit commands main circuit switch PW11 to be ON and PW12 to be OFF, as shown in time chart T3.

[0048] Next, the parallel balancing control unit compares the voltages of battery cells B111 and B121 with the leveling target value calculated by the overall series balancing control unit, and outputs the comparison result to the switch selection unit. As shown in time chart T1, if the voltage of battery cell B111 is higher than the leveling target value, the switch selection unit commands the bypass switch Sw111 to turn ON. This operation causes battery cell B111 to discharge into the bypass resistor for a predetermined time, lowering the voltage of battery cell B111. The voltage of battery cell B111 decreases while the bypass switch Sw111 is ON. The switch selection unit then commands the bypass switch Sw121 to turn OFF. This operation keeps the voltage of battery cell B121 constant.

[0049] The next switch operation is performed when the current flowing through battery cells B111 and B121, calculated from the voltage difference between battery cells B111 and B121, does not exceed the upper and lower current limits shown in time chart T2. As shown in time chart T1, if it is determined at time t1 that the calculated value of the current flowing through battery cells B111 and B121 does not exceed the lower current limit, the switch selection unit instructs the main circuit switch PW12 to change from OFF to ON, as shown in time chart T3. After the main circuit switch PW12 turns ON, current flows from battery cell B111 to charge battery cell B121, as shown in time chart T2. As a result, the voltage of battery cell B121 rises, as shown in time chart T1.

[0050] The next switch operation is performed a predetermined time after the discharge of the battery cell B111. As shown in time chart T4, at time t2, the switch selection unit commands the bypass switch Sw111 to change from ON to OFF. From time t1 to t2, discharging to the bypass resistor allows the voltage of the battery cell B111 to drop faster. This operation reduces the time required for the voltage leveling operation. Furthermore, by turning the bypass switch Sw111 OFF at time t2, the change in the voltage of the battery cell B111 over time becomes smaller after time t2 compared to before time t2, as shown in time chart T1. This operation reduces the power consumed by the voltage leveling operation.

[0051] According to this embodiment, by following the above flow and issuing commands from the switch selection unit to the main circuit switches PW11, PW12 and the bypass switches Sw111, Sw121 as shown in the time charts T3 and T4, it is possible to perform a leveling operation in a short time and without causing excessive current to flow through the battery cells.

[0052] The present invention is not limited to the above-described embodiment, and includes various modifications. The above-described embodiment has been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to an embodiment having all of the described configurations. [Explanation of symbols]

[0053] 1. Battery pack system 11, 21, 31...Series balancing control section 12, 22, 32...Parallel balancing control section 13, 23, 33...Switch selection section 5... Overall series balancing control section 41…AC system 42...Trans 43...Filter 44...AC / DC converter 51...Current calculation unit 52...Leveling target value calculation unit 100...Energy storage system SP1, SP2, SP3...unit battery pack P11-P1m, P21-P2m, P31-P3m...unit series battery packs B111-B3mn…Battery cells PW11-PW3m...Main circuit switches SR1: Bypass resistor Sw111-Sw3mn...Bypass switches p3...Switch selection section p31...Allowable current judgment section p32...Discharge judgment section T1-T4...Time chart

Claims

1. a unit series assembled battery in which a plurality of cells are connected in series; a unit battery assembly in which a plurality of the unit series battery assemblies are connected in parallel; a resistor connected in parallel to each cell and a bypass switch connected in series to the resistor; a main circuit switch connected in series to each unit series assembled battery; In the battery pack system, a balancing control unit is provided that equalizes the voltage and / or the state of charge among the cells in the unit battery pack, The balancing control unit calculates a current value that flows during a leveling operation based on the sum of the internal resistances and the sum of the voltages of each cell, and calculates a leveling target value for leveling the voltage and / or state of charge of each cell based on the calculated current value and at least one of the voltage or state of charge of each cell before the leveling operation; a switch selection unit that instructs ON / OFF of the main circuit switch and the bypass switch in the series assembled battery for a leveling operation; when a cell's voltage and / or state of charge is lower than the leveling target value, the switch selection unit instructs the main circuit switch connected in series to the unit series assembled battery including the corresponding cell to be turned ON and the bypass switch connected in parallel to the corresponding cell to be turned OFF.

2. a unit series assembled battery in which a plurality of cells are connected in series; a unit battery assembly in which a plurality of the unit series battery assemblies are connected in parallel; In the battery pack in which a plurality of the unit battery packs are connected in series, The unit series battery pack includes a resistor connected in parallel to each cell, and a bypass switch connected in series to the resistor. a main circuit switch connected in series to each unit series assembled battery; In the battery pack system, a balancing control unit is provided that equalizes the voltage and / or the state of charge among the cells in the unit battery pack, The balancing control unit calculates a current value that flows during a leveling operation based on the sum of the internal resistances and the sum of the voltages of each cell, and calculates a leveling target value for leveling the voltage and / or state of charge of each cell based on the calculated current value and at least one of the voltage or state of charge of each cell before the leveling operation; a switch selection unit that instructs ON / OFF of the main circuit switch and the bypass switch in the series assembled battery for a leveling operation; when a cell's voltage and / or state of charge is lower than the leveling target value, the switch selection unit instructs the main circuit switch connected in series to the unit series assembled battery including the corresponding cell to be turned ON and the bypass switch connected in parallel to the corresponding cell to be turned OFF.

3. 3. The battery pack system according to claim 1, the switch selection unit, when maintaining a cell voltage and / or a cell state of charge constant, instructs the main circuit switch connected in series to the unit series assembled battery including the corresponding cell to be turned OFF and the bypass switch connected in parallel to the corresponding cell to be turned OFF.

4. The battery pack system according to claim 3, the switch selection unit instructs the bypass switch connected in parallel to the corresponding cell to be turned ON when the voltage and / or state of charge of the cell is higher than the leveling target value.

5. 5. The battery pack system according to claim 4, The battery pack system is characterized in that the balancing control unit calculates a current value flowing through each of the unit series battery packs based on the internal resistance and voltage of each cell.

6. 6. The battery pack system according to claim 5, the balancing control unit calculates a value of a current flowing through each of the unit series assembled batteries based on a sum of internal resistances and a sum of voltages of the cells constituting the unit series assembled batteries.

7. 7. The battery pack system according to claim 6, the balancing control unit calculates the sum of the internal resistances and the sum of the voltages of the cells constituting each of the unit series assembled batteries, and calculates the value of the current flowing through the unit series assembled battery based on the ratio of the sum of the internal resistances of the unit series assembled battery to the sum of the reciprocals of the sums of the internal resistances of the other unit series assembled batteries and the difference between the sum of the voltages of the unit series assembled battery and the sum of the voltages of the other unit series assembled batteries.

8. The battery pack system according to claim 7, the balancing control unit obtains the internal resistance and voltage of each cell using a measuring device attached to each cell, calculates the sum of the internal resistances and the sum of the voltages of the cells constituting each of the unit series assembled batteries, and calculates the value of current flowing through the unit series assembled battery based on the ratio of the sum of the internal resistances of the relevant unit series assembled battery to the sum of the reciprocals of the sums of the internal resistances of the other unit series assembled batteries and the difference between the sum of the voltages of the relevant unit series assembled battery and the sum of the voltages of the other unit series assembled batteries.

9. The battery pack system according to claim 7, the balancing control unit obtains a sum of internal resistances and a sum of voltages of each cell constituting each of the unit series assembled batteries based on the voltage and current of the unit series assembled battery, and calculates a value of current flowing through the unit series assembled battery based on the sum of internal resistances and sum of voltages of each cell, based on a ratio of the sum of internal resistances of the unit series assembled battery to the sum of reciprocals of the sums of internal resistances of other unit series assembled batteries and a difference between the sum of voltages of the unit series assembled battery and the sum of voltages of the other unit series assembled batteries.

10. The battery pack system according to claim 3, The balancing control unit calculates a current value that will flow during a leveling operation based on the sum of the internal resistances and the sum of the voltages of each cell, predicts the voltage and / or state of charge of each cell after the current value has flowed through it based on the voltage and / or state of charge of each cell before the leveling operation and the calculated current value, and calculates a leveling target value for leveling the voltage and / or state of charge of each cell.

11. The battery pack system according to claim 10, the balancing control unit calculates a current value that will flow during a leveling operation based on the sum of the internal resistances and the sum of the voltages of each cell, predicts the voltage and / or state of charge of each cell after the current value has flowed through it based on the voltage and / or state of charge of each cell before the leveling operation and the calculated current value, and sets the minimum value of the predicted voltage or state of charge as a leveling target value for leveling.

12. The battery pack system according to claim 3, the switch selection unit determines whether to increase, decrease, or keep constant the voltage or state of charge of each cell based on the current value and the leveling target value.

13. The battery pack system according to claim 3, the switch selection unit determines, based on the leveling target value and a current value that flows during a leveling operation calculated from the sum of the internal resistances and the sum of the voltages of each cell constituting each of the unit series assembled batteries, whether to reduce or maintain constant the voltage or state of charge of each cell when the current value is equal to or greater than an allowable current value; determines whether to increase or maintain constant the voltage or state of charge of each cell when the current value is smaller than the allowable current value and the voltage or state of charge of each cell is equal to or less than the leveling target value; and determines whether to reduce or maintain constant the voltage or state of charge of each cell when the current value is smaller than the allowable current value and the voltage or state of charge of each cell is equal to or greater than the leveling target value.

14. The battery pack system according to claim 13, the switch selection unit instructs, when the voltage or state of charge of each cell is to be kept constant, to turn off the main circuit switch connected in series to the unit series battery pack including that cell and to turn off the bypass switch connected in parallel to that cell, based on the current value that flows during a leveling operation and the leveling target value, the current value being calculated based on the sum of the internal resistances and the sum of the voltages of the cells that constitute each of the unit series battery packs; If the current value is equal to or greater than the allowable current value, instruct the bypass switch connected in parallel to the corresponding cell to be turned ON in order to reduce the voltage or state of charge of each cell; and when the current value is smaller than an allowable current value, in order to increase the voltage or state of charge of each cell, the main circuit switch connected in series to the unit series assembled battery including that cell is instructed to be turned ON and the bypass switch connected in parallel to that cell is instructed to be turned OFF.

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