Energy storage system, energy storage system control program, and energy storage system control method

Abstract

Conventional energy storage systems had the problem of low utilization efficiency of secondary batteries. [Solution] The energy storage system according to the present invention comprises a plurality of battery modules, a usage priority determination unit 41 that determines the usage priority of the plurality of battery modules so that the battery module with the best long-term output characteristics is given a higher usage priority, a cell arrangement switching circuit 12 that switches the position of the battery modules in a battery string in which the plurality of battery modules are connected in series based on a cell arrangement switching instruction from the usage priority determination unit, and an AC waveform shaping circuit 13 that generates an AC voltage waveform by periodically switching one terminal voltage selected from a plurality of terminal voltages of a plurality of battery modules B1 to B5 included in the battery string, wherein the usage priority determination unit 41 gives a cell arrangement switching instruction to the cell arrangement switching circuit 12 so that the battery modules with higher usage priority are placed in positions in the battery string where the discharge period is longer.

Description

Technical Field

[0001] The present invention relates to, for example, a power storage system, a power storage system control program, and a method for controlling a power storage system.

Background Art

[0002] In recent years, many power storage systems that output large power using a large number of secondary batteries have been proposed. An example of such a power storage system is disclosed in Patent Document 1.

[0003] The control device for a vehicle battery described in Patent Document 1 is a control device for a vehicle battery that discharges at least a plurality of batteries connected in parallel to each other, detects the remaining capacity charged in each battery, and classifies each battery into a plurality of battery groups based on the remaining capacities, and battery group total remaining capacity calculation means for calculating the total remaining capacity of the maximum charge amount battery group classified as the battery with the most remaining capacity by the classification means, and determination means for determining whether the total remaining capacity of the maximum charge amount battery group is equal to or greater than a predetermined minimum capacity required to run the vehicle, and when it is determined by the determination means that the total remaining capacity of the maximum charge amount battery group is equal to or greater than the predetermined capacity, the maximum charge amount battery group is preferentially used, and when it is determined that the total remaining capacity of the maximum charge amount battery group is less than the predetermined capacity, among the plurality of battery groups, a battery group whose total remaining capacity is less than the maximum charge amount battery group and whose total remaining capacity is greater than the predetermined capacity is preferentially used.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the technology described in Patent Document 1 requires power for cell balancing control, which involves charging and discharging between battery groups to equalize the output voltage of each battery group before switching between battery groups, resulting in a problem of reduced power efficiency.

[0006] This invention has been made in view of the above circumstances, and aims to improve the utilization efficiency of secondary batteries. [Means for solving the problem]

[0007] One embodiment of the energy storage system according to the present invention includes a plurality of battery modules, a usage priority determination unit that estimates at least one of the battery capacity and degradation state of the plurality of battery modules and determines the usage priority of the plurality of battery modules such that the battery module whose estimation result is the best in terms of long-term output characteristics is given the highest usage priority and the battery module whose estimation result is the worst in terms of long-term output characteristics is given the lowest usage priority, a cell arrangement switching circuit that switches the position of the battery modules in a battery string in which the plurality of battery modules are connected in series based on a cell arrangement switching instruction from the usage priority determination unit, and an AC waveform shaping circuit that periodically switches one of the terminal voltages selected from a plurality of terminal voltages of the plurality of battery modules included in the battery string to generate an AC voltage waveform, wherein the usage priority determination unit gives the cell arrangement switching instruction to the cell arrangement switching circuit such that the battery modules with higher usage priority are placed in positions in the battery string where the discharge period is longer.

[0008] One aspect of the control program for an energy storage system according to the present invention is an energy storage system control program that is executed in the calculation unit of an energy storage system having a plurality of battery modules, a cell placement switching circuit that switches the position of the battery modules in a battery string in which the plurality of battery modules are connected in series, and an AC waveform shaping circuit that periodically switches one of the terminal voltages selected from a plurality of terminal voltages of the plurality of battery modules included in the battery string to generate an AC voltage waveform, and gives a cell placement switching instruction to the cell placement switching circuit, wherein the calculation unit is made to perform a usage priority determination process that estimates at least one of the battery capacity and degradation state of the plurality of battery modules and determines the usage priority of the plurality of battery modules such that the battery module whose estimation result is the best in terms of long-term output characteristics is given the highest usage priority and the battery module whose estimation result is the worst in terms of long-term output characteristics is given the lowest usage priority, and a cell placement switching process that gives the cell placement switching circuit a cell placement switching instruction so that the battery modules with higher usage priority are placed in positions in the battery string where the discharge period is longer.

[0009] One aspect of the method for controlling an energy storage system according to the present invention is a method for controlling an energy storage system that provides a cell placement switching instruction to the cell placement switching circuit in an energy storage system having a plurality of battery modules, a cell placement switching circuit for switching the positions of the battery modules in a battery string in which the plurality of battery modules are connected in series, and an AC waveform shaping circuit for generating an AC voltage waveform by periodically switching one of a plurality of terminal voltages of the plurality of battery modules included in the battery string. The method provides a cell placement switching instruction to the cell placement switching circuit, and is performed by computer by an automatic process, comprising: a usage priority determination process that estimates at least one of the battery capacity and degradation state of the plurality of battery modules and determines the usage priority of the plurality of battery modules such that the battery module with the best long-term output characteristics is given the highest usage priority and the battery module with the worst long-term output characteristics is given the lowest usage priority; and a cell placement switching process that provides a cell placement switching instruction to the cell placement switching circuit such that the battery modules with higher usage priority are placed in positions in the battery string where the discharge period is longer. [Effects of the Invention]

[0010] According to the present invention, the energy storage system, the energy storage system control program, and the energy storage system control method can provide an energy storage system that improves the utilization efficiency of secondary batteries. [Brief explanation of the drawing]

[0011] [Figure 1] This is a block diagram of the energy storage system according to Embodiment 1. [Figure 2] This is a flowchart illustrating the operation of the energy storage system according to Embodiment 1. [Figure 3] This figure illustrates an example of a battery string configured in the energy storage system according to Embodiment 1 and the output AC voltage waveform. [Figure 4] This is a circuit diagram illustrating the cell arrangement switching circuit of the energy storage system according to Embodiment 1. [Figure 5]This is a circuit diagram illustrating the cell arrangement switching circuit of the energy storage system according to Embodiment 2. [Figure 6] This figure illustrates an example of a battery string configured in the energy storage system according to Embodiment 2, and the output AC voltage waveform. [Figure 7] This is a circuit diagram illustrating the cell arrangement switching circuit of the energy storage system according to Embodiment 3. [Figure 8] This figure illustrates an example of a battery string configured in the energy storage system according to Embodiment 3, and the output AC voltage waveform. [Figure 9] This figure illustrates an example of a battery string configured in the energy storage system according to Embodiment 3, and the output AC voltage waveform. [Modes for carrying out the invention]

[0012] For clarity of explanation, the following descriptions and drawings have been omitted and simplified as appropriate. Furthermore, each element shown in the drawings as a functional block performing various processes can be composed of a CPU (Central Processing Unit), memory, and other circuits in hardware terms, and implemented in software terms by programs loaded into memory. Therefore, it will be understood by those skilled in the art that these functional blocks can be implemented in various ways using hardware alone, software alone, or a combination thereof, and are not limited to any one of these. In each drawing, the same elements are denoted by the same reference numeral, and redundant explanations have been omitted where necessary.

[0013] Furthermore, the program described above includes, when loaded into a computer, a set of instructions (or software code) for causing the computer to perform one or more of the functions described in the embodiments. The program may be stored in a non-temporary computer-readable medium or a physical storage medium. Examples, but not limited to, include random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technologies, CD-ROM, digital versatile disc (DVD), Blu-ray® disc or other optical disc storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage devices. The program may be transmitted over a temporary computer-readable medium or a communication medium. Examples, but not limited to, include temporary computer-readable medium or a communication medium that includes electrically, optically, acoustically, or otherwise propagating signals.

[0014] Embodiment 1 First, Figure 1 shows a block diagram of the energy storage system 1 according to Embodiment 1. As shown in Figure 1, the energy storage system 1 according to Embodiment 1 includes a plurality of battery modules (for example, battery modules B1 to B5), a battery management device 11, a cell arrangement switching circuit 12, an AC waveform shaping circuit 13, and a transformer 14. In Figure 1, battery modules B1 to B5 are shown as the plurality of battery modules, but the number of battery modules incorporated into the energy storage system 1 is arbitrary as long as there are multiple modules. Also, each battery module only needs to have one or more battery cells incorporated into it.

[0015] And the power storage system 1 according to Embodiment 1 constitutes a battery string in which battery modules B1 to B5 are connected in series using a cell arrangement switching circuit 12, and generates an AC voltage waveform by periodically and sequentially selecting and outputting the voltages of each node of the battery string by an AC waveform shaping circuit 13. Further, the power storage system 1 according to Embodiment 1 generates an AC power signal by driving a transformer 14 with an output signal having this AC voltage waveform. Hereinafter, each functional block constituting the power storage system 1 will be described in detail.

[0016] The battery management device 11 acquires the output voltage value, charge / discharge current value, and battery temperature from each of the battery modules B1 to B5, and calculates an estimated value of at least one of the battery capacity and the deterioration state. Further, the battery management device 11 calculates a usage priority that becomes a higher value in the order of good long-time output characteristics of each battery module based on at least one of the estimated battery capacity and the deterioration state. Then, the battery management device 11 outputs a cell arrangement switching signal Sc for configuring the battery string to the cell arrangement switching circuit 12 so that the battery module with a higher usage priority is the battery module used for a longer time in the generation of the AC voltage waveform.

[0017] The battery management device 11 includes current-voltage measurement units 21 to 25, temperature measurement units 31 to 35, and a usage order determination unit 41. The current-voltage measurement units 21 to 25 are respectively provided corresponding to any one of the battery modules B1 to B5, measure the output voltage value and the charge / discharge current value of the corresponding battery module, and transmit the measured values to the usage order determination unit 41. The temperature measurement units 31 to 35 are respectively provided corresponding to any one of the battery modules B1 to B5, measure the battery temperature of the corresponding battery module, and transmit the measured values to the usage order determination unit 41.

[0018] The usage priority determination unit 41 estimates at least one of the battery capacity and the deterioration state of each of the battery modules B1 to B5 using the output voltage values, charge and discharge current values, and battery temperature acquired from the current-voltage measurement units 21 to 25 and the temperature measurement units 31 to 35. Then, the usage priority determination unit 41 determines the usage priorities of the plurality of battery modules such that the battery module with the best long-term output characteristics in the estimation result has the highest usage priority, and the battery module with the worst long-term output characteristics in the estimation result has the lowest usage priority. Furthermore, the usage priority determination unit 41 gives a cell arrangement switching instruction Sc to the cell arrangement switching circuit 12 so that the battery module with a higher usage priority is arranged at a position where the discharge period is longer in the battery string. Note that the estimation process of the battery capacity and the deterioration state in the usage priority determination unit 41 includes, for example, an estimation process of inputting the output voltage values, charge and discharge current values, and battery temperature acquired from the current-voltage measurement units 21 to 25 and the temperature measurement units 31 to 35 into a battery state estimation model.

[0019] For example, the first to third methods can be considered as the method for determining the usage priority in the usage priority determination unit 41. The first method simply sets a higher usage priority for the battery module with a larger battery capacity based only on the battery capacity. The second method simply sets a higher usage priority for the battery module with less progress of deterioration based only on the deterioration state. The third method defines a plurality of degrees of deterioration each having a predetermined range of deterioration states, classifies the battery modules into any of the degrees of deterioration according to the deterioration state, and sets a higher usage priority for the battery module with a lower degree of deterioration and a larger battery capacity. In the following description, the ranking of the usage priority is determined based on the first method, but it is also possible to adopt the second method or the third method. Also, for the purpose of explaining the operation based on the first method, in FIG. 1, the symbols of the battery modules are shown such that the larger the battery capacity of the battery module, the larger the size on the drawing. Specifically, in FIG. 1, the battery capacities are B3 > B1 > B5 > B2 > B4.

[0020] Furthermore, the usage priority determination unit 41 reviews the state of the switches in the cell arrangement switching circuit 12 at each timing when estimating the battery capacity and degradation state.

[0021] The cell placement switching circuit 12 switches the position of a battery module in a battery string, in which multiple battery modules are connected in series, based on the cell placement switching instruction Sc from the usage order determination unit 41. The AC waveform shaping circuit 13 generates an AC voltage waveform by periodically switching one terminal voltage selected from multiple terminal voltages of multiple battery modules included in the battery string. Specific circuit examples of the cell placement switching circuit 12 and the AC waveform shaping circuit 13 will be described later.

[0022] Next, Figure 2 shows a flowchart illustrating the operation of the energy storage system according to Embodiment 1. Then, referring to Figure 2, the operation of the energy storage system 1 according to Embodiment 1 will be explained. As shown in Figure 2, in the energy storage system 1 according to Embodiment 1, the usage priority determination unit 41 estimates the battery capacity of each battery module, calculates the usage priority based on the ranking of the battery capacities of each battery module, and determines the usage order in descending order of usage priority (step S1). Subsequently, in the energy storage system 1 according to Embodiment 1, the usage priority determination unit 41 outputs a cell arrangement switching instruction Sc to switch the switches in the cell arrangement switching circuit 12 so that the battery module with the highest usage priority (largest battery capacity) has the longest usage time, and the battery module with the lowest usage priority (smallest battery capacity) has the shortest usage time (step S2). Through the processing in step S2, the cell arrangement switching circuit 12 arranges battery module B3 at a position corresponding to the lowest potential of the AC voltage waveform in the battery string, and configures a battery string in which battery modules B1, B5, B2, and B4 are connected in series toward the highest potential side. Subsequently, in the energy storage system 1 according to Embodiment 1, the switches in the AC waveform shaping circuit 13 are sequentially switched to generate an AC voltage waveform (step S3).

[0023] Figure 3 shows an example of a battery string configured in the energy storage system 1 according to Embodiment 1, and illustrates the output AC voltage waveform. The circuit shown on the right side of Figure 3 is the circuit configured after the processing of step S2 in Figure 2 is performed in the energy storage system 1, which includes a battery module having the battery capacity shown in Figure 1. In Figure 3, only the path connecting each battery module and the AC waveform shaping circuit 13 is shown for the cell arrangement switching circuit 12. The cell arrangement switching circuit 12 will be described later with reference to Figure 4.

[0024] As shown in Figure 3, the AC waveform shaping circuit 13 has output switches S0 to S5, which are provided corresponding to the terminal voltages from the lowest potential side to the highest potential side of the battery string. Each of the output switches S0 to S5 is composed of a relay switch that switches the conduction and disconnection of its contacts by mechanical operation, for example. The battery string shown in Figure 3 has a battery module B3 positioned at the position corresponding to the lowest potential of the AC voltage waveform, and battery modules B1, B5, B2, and B4 are connected in series toward the highest potential side. In the energy storage system 1 according to Embodiment 1, the AC waveform shaping circuit 13 increases the voltage of the AC voltage waveform by switching output switch S0 to a conductive state and then exclusively switching the switches that turn on from output switch S1 to output switch S5, and decreases the voltage of the AC voltage waveform by exclusively switching the switches that turn on from output switch S5 to output switch S1.

[0025] Next, Figure 4 shows a circuit diagram illustrating the cell arrangement switching circuit 12 of the energy storage system 1 according to Embodiment 1. In Figure 4, the battery modules B1 to B5 and the AC waveform shaping circuit 13, which are targeted by the cell arrangement switching circuit 12 to switch connection combinations, are shown for reference.

[0026] As shown in Figure 4, the cell arrangement switching circuit 12 has a group of switches for switching the output switch to which each battery module is connected. Specifically, for battery module B1, switch units SW11 to SW15 are provided as a group of switches. Each of the switch units SW11 to SW15 has a first switch that connects the positive terminal of battery module B1 to one of the output switches, and a second switch that connects the negative terminal of battery module B1 to one of the output switches. These first and second switches are configured, for example, as relay switches that switch the conduction and disconnection of contacts by mechanical operation.

[0027] Similar to battery module B1, switch units are also provided for battery modules B2 to B5. Specifically, switch units SW21 to SW25 are provided for battery module B2, switch units SW31 to SW35 for battery module B3, switch units SW41 to SW45 for battery module B4, and switch units SW51 to SW55 for battery module B5.

[0028] In this way, by configuring the switch unit to allow arbitrary switching of which output switch each battery module is connected to, the cell placement switching circuit 12 switches the position of battery modules B1 to B5 in the battery string. For example, to configure the battery string shown in Figure 3, switch unit SW31 connects battery module B3 between output switch S0 and output switch S1, switch unit SW12 connects battery module B1 between output switch S1 and output switch S2, switch unit SW53 connects battery module B5 between output switch S2 and output switch S3, switch unit SW24 connects battery module B2 between output switch S3 and output switch S4, and switch unit SW45 connects battery module B4 between output switch S4 and output switch S5. In the cell placement switching circuit 12, the first and second switches in switch units other than the switch unit that makes the first and second switches conductive remain in the off state.

[0029] Furthermore, the operation of the usage priority determination unit 41 among the above operations is realized by executing the energy storage system control program in the calculation unit within the battery management device 11. In addition, in the control method of the energy storage system 1 according to Embodiment 1, the operation of the usage priority determination unit 41 is also executed by automatic processing in the calculation unit within the battery management device 11.

[0030] As described above, according to the energy storage system 1 of Embodiment 1, an AC voltage waveform is generated by switching the terminal voltages within a battery string in which multiple battery modules are connected in series. As a result, in the energy storage system 1 of Embodiment 1, there is no need to perform cell balance control even if the battery capacity and terminal voltage differ between battery modules, making it possible to achieve high power efficiency. Furthermore, in the energy storage system 1 of Embodiment 1, since the AC voltage waveform is generated directly using the battery string, components such as DC voltage converters and inverters are unnecessary, making it possible to reduce the volume and cost of the system. Moreover, since high-speed switching circuits such as DC voltage converters and inverters are unnecessary, the effects of high-frequency noise can be reduced, thereby improving reliability and stability.

[0031] Furthermore, in the energy storage system 1 according to Embodiment 1, the positions of the battery modules are set so that batteries in good condition are used preferentially when configuring the battery string. As a result, the energy storage system 1 according to Embodiment 1 can output power over a long period of time. In addition, by configuring the battery string to use battery modules in good condition preferentially, differences in the degradation rate between battery modules are absorbed, making it less likely for system malfunctions such as some battery modules reaching the end of their lifespan to occur, and enabling the system to be operated stably over a long period of time.

[0032] Furthermore, in the energy storage system 1 according to Embodiment 1, there is no need to replace a battery module that has deteriorated with another battery module in order to generate an AC voltage waveform, and therefore there is no need to install a spare battery module. By reducing the number of battery modules installed in the system in this way, it becomes possible to prevent the system from becoming overvoltage, over-installing batteries, and becoming overly complex.

[0033] Embodiment 2 Embodiment 2 describes a cell arrangement switching circuit 12a, which is a modified version of the cell arrangement switching circuit 12 of Embodiment 1. In the description of Embodiment 2, components that are the same as those described in Embodiment 1 are denoted by the same reference numerals as in Embodiment 1 and their descriptions are omitted.

[0034] Figure 5 shows a circuit diagram illustrating the cell arrangement switching circuit 12a of the energy storage system according to Embodiment 2. As shown in Figure 5, the cell arrangement switching circuit 12a according to Embodiment 2 has a forward switching unit that incorporates a battery module into the battery string in the forward direction, with the positive terminal facing the final voltage output end of the battery string (for example, the output switch S5 side), and a reverse switching unit that incorporates a battery module into the battery string in the reverse direction, with the negative terminal facing the final voltage output end of the battery string. In the example shown in Figure 5, the positive terminal side wiring to which the positive terminal of the battery module is connected is marked with a "+" sign.

[0035] The forward direction switching section includes a group of switches that switch which output switch the battery module is connected to, consisting of switch units SW11~SW15, SW21~SW25, SW31~SW35, SW41~SW45, SW51~SW55, a forward direction connection switch section 51, and a forward direction short-circuit switch section 52.

[0036] The forward connection switch section 51 has switches SW1p, SW1n, SW2p, SW2n, SW3p, SW3n, SW4p, SW4n, SW5p, and SW5n. Switches SW1p and SW1n switch whether or not to connect battery module B1 to switch units SW11 to SW15. Switches SW1p and SW1n switch whether or not to connect battery module B1 to switch units SW11 to SW15. Switches SW2p and SW2n switch whether or not to connect battery module B2 to switch units SW21 to SW25. Switches SW3p and SW3n switch whether or not to connect battery module B3 to switch units SW31 to SW35. Switches SW4p and SW4n switch whether or not to connect battery module B4 to switch units SW41 to SW45. Switches SW5p and SW5n switch whether or not to connect battery module B5 to switch units SW51 to SW55.

[0037] The positive short-circuit switch section 52 has short-circuit switches SW1s, SW2s, SW3s, SW4s, and SW5s. Short-circuit switch SW1s switches between short-circuiting and disconnecting the positive and negative terminal wiring of switch units SW11, SW21, SW31, SW41, and SW51. Short-circuit switch SW2s switches between short-circuiting and disconnecting the positive and negative terminal wiring of switch units SW12, SW22, SW32, SW42, and SW52. Short-circuit switch SW3s switches between short-circuiting and disconnecting the positive and negative terminal wiring of switch units SW13, SW23, SW33, SW43, and SW53. Short-circuit switch SW4s switches between short-circuiting and disconnecting the positive and negative terminal wiring of switch units SW14, SW24, SW34, SW44, and SW54. The short-circuit switch SW5s switches between short-circuiting and disconnecting the positive and negative terminal wiring of switch units SW15, SW25, SW35, SW45, and SW55.

[0038] The reverse direction switching section includes a group of switches that switch which output switch the battery module is connected to, including switch units SW11r~SW15r, SW21r~SW25r, SW31r~SW35r, SW41r~SW45r, SW51r~SW55r, a reverse direction connection switch section 53, and a reverse direction short-circuit switch section 54.

[0039] The reverse connection switch section 53 has switches SW1pr, SW1nr, SW2pr, SW2nr, SW3pr, SW3nr, SW4pr, SW4nr, SW5pr, and SW5nr. Switches SW1pr and SW1nr switch whether or not to connect battery module B1 to switch units SW11r to SW15r. Switches SW2pr and SW2nr switch whether or not to connect battery module B2 to switch units SW21r to SW25r. Switches SW3pr and SW3nr switch whether or not to connect battery module B3 to switch units SW31r to SW35r. Switches SW4pr and SW4nr switch whether or not to connect battery module B4 to switch units SW41r to SW45r. Switches SW5pr and SW5nr switch whether or not to connect battery module B5 to switch units SW51r to SW55r.

[0040] The reverse short-circuit switch section 54 includes short-circuit switches SW1sr, SW2sr, SW3sr, SW4sr, and SW5sr. Short-circuit switch SW1sr switches between short-circuiting and disconnecting the positive and negative terminal wiring of switch units SW11r, SW21r, SW31r, SW41r, and SW51r. Short-circuit switch SW2sr switches between short-circuiting and disconnecting the positive and negative terminal wiring of switch units SW12r, SW22r, SW32r, SW42r, and SW52r. Short-circuit switch SW3sr switches between short-circuiting and disconnecting the positive and negative terminal wiring of switch units SW13r, SW23r, SW33r, SW43r, and SW53r. The short-circuit switch SW4sr switches between short-circuiting and disconnecting the positive and negative terminal wiring of switch units SW14r, SW24r, SW34r, SW44r, and SW54r. The short-circuit switch SW5sr switches between short-circuiting and disconnecting the positive and negative terminal wiring of switch units SW15r, SW25r, SW35r, SW45r, and SW55r.

[0041] In the cell arrangement switching circuit 12a according to Embodiment 2, when a battery module is incorporated into a battery string in the forward direction, the switch corresponding to the battery module to be incorporated into the battery string in the forward direction is set to conduct in the forward connection switch section 51, to disconnect in the reverse connection switch section 53, to disconnect in the forward short-circuit switch section 52, and to conduct in the reverse short-circuit switch section 54. On the other hand, when a battery module is incorporated into a battery string in the reverse direction, the switch corresponding to the battery module to be incorporated into the battery string in the reverse direction is set to disconnect in the forward connection switch section 51, to conduct in the reverse connection switch section 53, to conduct in the forward short-circuit switch section 52, and to disconnect in the reverse short-circuit switch section 54.

[0042] The cell arrangement switching circuit 12a according to Embodiment 2 makes it possible to incorporate a battery module connected in the reverse direction to the battery string. Therefore, Figure 6 shows an example of a battery string configured in the energy storage system according to Embodiment 2 and a diagram illustrating the output AC voltage waveform.

[0043] The example shown in Figure 6 uses the cell arrangement switching circuit 12a to generate the same AC voltage waveform as the example shown in Figure 3. In the example shown in Figure 6, a battery string is configured in which battery module B4 is connected in the reverse direction during the period when output switch S3 is conducting in Figure 3, and battery module B4 is charged. When performing this operation, output switch S4 is set to conduct instead of output switch S3 during the period when output switch S3 is conducting in Figure 3. Also, when charging battery module B4, three battery modules are connected between output switch S2 and switch S5, and battery module B5 and battery module B3 are connected in the reverse direction to battery module B4. The connection of three battery modules in series between output switch S2 and switch S5 can be achieved by setting switch units SW53, SW35, SW44r, short-circuit switch SW4s, switch SW4pr, and SW4nr to conduct. Furthermore, when the output switch S4 is to be made conductive after charging the battery module B4, the reverse switching unit is disconnected from the battery module, and all switches in the reverse short-circuit switch unit 54 are controlled to be conductive, and the switch control described in Figure 4 is then implemented in the forward switching unit.

[0044] As described above, the cell arrangement switching circuit 12a according to Embodiment 2 has a forward switching section and a reverse switching section, so that when supplemental charging (refresh discharge) is required, it is possible to charge or discharge a specific module by connecting the polarity in reverse.

[0045] Embodiment 3 Embodiment 3 describes a cell arrangement switching circuit 12b, which is a modified version of the cell arrangement switching circuit 12a of Embodiment 2. In the description of Embodiment 3, components that are the same as those described in Embodiments 1 and 2 are denoted by the same reference numerals as in Embodiments 1 and 2, and their descriptions are omitted.

[0046] Figure 7 shows a circuit diagram illustrating the cell arrangement switching circuit 12b of the energy storage system according to Embodiment 3. As shown in Figure 7, the cell arrangement switching circuit 12b is the cell arrangement switching circuit 12a with the addition of a ground position setting unit 55. The ground position setting unit 55 provides a ground voltage as the terminal voltage at any position in the battery string. The ground position setting unit 55 has switches SW0g to SW5g. Switch SW0g switches whether or not to provide a ground voltage to the wiring corresponding to the output switch S0. Switch SW1g switches whether or not to provide a ground voltage to the wiring corresponding to the output switch S1. Switch SW2g switches whether or not to provide a ground voltage to the wiring corresponding to the output switch S2. Switch SW3g switches whether or not to provide a ground voltage to the wiring corresponding to the output switch S3. Switch SW4g switches whether or not to provide a ground voltage to the wiring corresponding to the output switch S4. Switch SW5g switches whether or not to provide a ground voltage to the wiring corresponding to the output switch S5.

[0047] By using this ground position setting unit 55, the ground voltage can be set at any position in the battery string. Next, the operation of the energy storage system according to Embodiment 3 using the cell arrangement switching circuit 12b will be described. As a first example, Figure 8 shows an example of a battery string configured in the energy storage system according to Embodiment 3 and a diagram illustrating the output AC voltage waveform. In the example shown in Figure 8, the energy storage system is shown when a ground fault occurs in the wiring connected to the output switch S2. In such a case, by making the switch SW2g of the ground position setting unit 55 conduct, it becomes possible to make the voltage in the path where the ground fault occurred a stable ground voltage. Also, in the example shown in Figure 8, as the wiring connected to the output switch S2 becomes the ground voltage, the AC voltage waveform takes on a shape that shifts in the direction of decreasing voltage. Specifically, in the example shown in Figure 8, the AC voltage waveform has an amplitude range such that the voltage is 0V during the period when the output switch S2 is in the conduction state.

[0048] As a second example, Figure 9 shows an example of a battery string configured in the energy storage system according to Embodiment 3 and a diagram illustrating the output AC voltage waveform. In the example shown in Figure 9, the voltage during the period when the output switch S2 is in a conductive state is set to the ground voltage by making the switch SW2g of the ground position setting unit 55 conductive. In the example shown in Figure 9, the longest output period is the period when the output switch S2 is in a conductive state, and the period when the output switches S5 and S0 are in a conductive state. Therefore, in the example shown in Figure 9, the battery string is configured by connecting the battery modules in series so that they are B2, B1, B3, B5, and B4 in order from the low potential side. Also, in the example shown in Figure 9, the battery string is configured so that battery modules B2 and B1 are connected in reverse direction using the reverse direction switching unit.

[0049] As described above, by using the cell arrangement switching circuit 12b according to Embodiment 3, it becomes easier to ensure that the voltage to ground is within a safe range in the event of a ground fault. Furthermore, by using the cell arrangement switching circuit 12b according to Embodiment 3, the position to be used as the ground voltage and the polarity of the battery module can be arbitrarily changed to create dual power output, thereby reducing the absolute value of the highest or lowest voltage applied to the transformer 14, and enabling safe operation in a low voltage range.

[0050] It should be noted that the present invention is not limited to the embodiments described above, and can be modified as appropriate without departing from the spirit of the invention. [Explanation of Symbols]

[0051] 1. Energy storage system 11. Battery management device 12-cell configuration switching circuit 13 AC waveform shaping circuit 14 transformers 21-25 Current and voltage measurement section 31~35 Temperature measurement part 41. Order of Use Determination Section 51 Forward connection switch section 52 Forward short-circuit switch section 53 Reverse connection switch section 54 Reverse short-circuit switch section 55 Ground position setting section B1-B5 Battery Modules S0~S5 Output Switch SW11~SW15, SW11r~SW15r Switch Unit SW21~SW25, SW21r~SW25r Switch Unit SW31~SW35, SW31r~SW35r Switch Unit SW41~SW45, SW41r~SW45r Switch Unit SW51~SW55, SW51r~SW55r Switch Unit Sc Cell Placement Switching Instruction

Claims

1. Multiple battery modules, A usage priority determination unit estimates at least one of the battery capacity and degradation state of the plurality of battery modules, and determines the usage priority of the plurality of battery modules such that the battery module with the best long-term output characteristics as determined by the estimation has the highest usage priority, and the battery module with the worst long-term output characteristics as determined by the estimation has the lowest usage priority. A cell arrangement switching circuit that switches the position of the battery modules in a battery string in which the plurality of battery modules are connected in series, based on a cell arrangement switching instruction from the usage order determination unit, The battery string includes an AC waveform shaping circuit that periodically switches one of the terminal voltages selected from a plurality of terminal voltages of the plurality of battery modules to generate an AC voltage waveform, The energy storage system includes a usage priority determination unit that provides a cell arrangement switching instruction to the cell arrangement switching circuit so that the battery modules with higher usage priority are placed in positions in the battery string where the discharge period is longer.

2. The energy storage system according to claim 1, wherein the cell arrangement switching circuit has a group of switches that switch the position on the battery string for each battery module based on the cell arrangement switching instruction.

3. The energy storage system according to claim 2, wherein the group of switches is composed of relay switches.

4. The aforementioned cell arrangement switching circuit is A forward direction switching unit that incorporates the battery module into the battery string in the forward direction, with the positive electrode facing the final voltage output end of the battery string, A reverse switching unit that incorporates the battery module into the battery string in the reverse direction, with the negative terminal facing the final voltage output end of the battery string, The energy storage system according to claim 1, having the following features.

5. The energy storage system according to claim 1, wherein the cell arrangement switching circuit has a ground position setting unit that provides a ground voltage as the terminal voltage at any position of the battery string.

6. Multiple battery modules, A cell arrangement switching circuit that switches the position of the battery modules in a battery string in which the plurality of battery modules are connected in series, A power storage system control program is executed in the calculation unit of a power storage system having an AC waveform shaping circuit that periodically switches one of the terminal voltages selected from a plurality of terminal voltages of the plurality of battery modules included in the battery string to generate an AC voltage waveform, and gives a cell arrangement switching instruction to the cell arrangement switching circuit, A usage priority determination process that estimates at least one of the battery capacity and degradation state of the plurality of battery modules, and determines the usage priority of the plurality of battery modules such that the battery module with the best long-term output characteristics as determined by the estimation has the highest usage priority, and the battery module with the worst long-term output characteristics as determined by the estimation has the lowest usage priority, A cell placement switching process that gives a cell placement switching instruction to the cell placement switching circuit so that the battery modules with higher usage priority are placed in positions in the battery string where the discharge period is longer, A power storage system control program that causes the calculation unit to perform the above-mentioned calculation.

7. Multiple battery modules, A cell arrangement switching circuit that switches the position of the battery modules in a battery string in which the plurality of battery modules are connected in series, A method for controlling an energy storage system, comprising: an AC waveform shaping circuit that periodically switches one terminal voltage selected from a plurality of terminal voltages of a plurality of battery modules included in the battery string to generate an AC voltage waveform, wherein the method provides a cell arrangement switching instruction to the cell arrangement switching circuit in an energy storage system, A usage priority determination process that estimates at least one of the battery capacity and degradation state of the plurality of battery modules, and determines the usage priority of the plurality of battery modules such that the battery module with the best long-term output characteristics as determined by the estimation has the highest usage priority, and the battery module with the worst long-term output characteristics as determined by the estimation has the lowest usage priority, A cell placement switching process that gives a cell placement switching instruction to the cell placement switching circuit so that the battery modules with higher usage priority are placed in positions in the battery string where the discharge period is longer, A method for controlling an energy storage system, which is performed by automated processing using a computer.

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