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

Abstract

Conventional energy storage systems had the problem of requiring a long time to reach their full capacity. [Solution] The energy storage system according to the present invention includes a state estimation unit that calculates a degree of fit indicating how well the state estimation value estimated using a state estimation model matches the actual state of the secondary battery, and a power limit calculation unit that calculates a power limit value for each cartridge which is a limit value for the charging and discharging power of the secondary battery. If the power demand can be met by applying the lowest power limit value among multiple power limit values ​​to all cartridges, the system preferentially selects the cartridge with the lowest degree of fit and outputs the required output voltage (S6). If the power demand cannot be met by applying the lowest power limit value among multiple power limit values ​​to all cartridges, the system generates the required output voltage using only the cartridge with a power limit value that can meet the power demand (S8).

Description

Technical Field

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

Background Art

[0002] In recent years, many power storage systems have been proposed that form a battery string by connecting secondary batteries in series and generate an alternating voltage while switching the secondary batteries that make up the battery string. An example of such a power storage system is described in Patent Document 1.

[0003] The power supply system described in Patent Document 1 includes a plurality of battery modules having batteries, and a power supply circuit capable of connecting the batteries in the plurality of battery modules in series with each other by transferring a gate drive signal from a control controller between the plurality of battery modules. By temporally changing the number of batteries to be connected in series in each of the power supply circuits, alternating voltages having different phases are output. The power supply circuit is divided into a plurality of sub-battery module groups in which the battery modules are connected in series, and has a configuration in which the positive electrode sides or the negative electrode sides of any one sub-battery module group and another sub-battery module group are connected to each other.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in power supply systems (hereinafter referred to as energy storage systems), system maintenance is sometimes performed by replacing battery modules (hereinafter referred to as cartridges). When cartridges are replaced in this way, the state estimation model used to manage the batteries is not optimized and the estimation accuracy is poor, so it becomes necessary to limit the output. This output limit can be relaxed by using the replaced cartridge, but the technology described in Patent Document 1 does not address post-replacement processing, which leads to the problem of a longer period during which the output limit is strictly enforced.

[0006] This invention has been made in view of the above circumstances and aims to shorten the period until the output limit of the energy storage system is relaxed. [Means for solving the problem]

[0007] One aspect of the energy storage system according to the present invention comprises a plurality of cartridges including a secondary battery, a plurality of switch units that switch between incorporating a cartridge corresponding to a string wire or disconnecting a corresponding cartridge from the string wire, a state estimation unit that calculates a degree of fit indicating how well the state estimation value, obtained by estimating the state of the secondary battery for each cartridge using a state estimation model, matches the actual state of the secondary battery, a power limit calculation unit that calculates a power limit value for each cartridge, which is a value that matches the state of the secondary battery estimated by the state estimation unit and serves as a limit value for the charging and discharging power of the secondary battery, and a power demand value provided by a power supply source that supplies power output from the plurality of cartridges, the degree of fit, and the power limit value. The system further comprises a switch control unit that controls the state of the plurality of switch units, wherein the switch control unit operates in a first mode in which, if the power demand can be met by applying the lowest power limit value among the plurality of power limit values ​​to all of the cartridges, it outputs a control signal to the plurality of switch units to preferentially select the cartridge with the lowest suitability and output the required output voltage, and operates in a second mode in which, if the power demand cannot be met by applying the lowest power limit value among the plurality of power limit values ​​to all of the cartridges, it outputs a control signal to the plurality of switch units to generate the required output voltage using only the cartridge having the power limit value that can satisfy the power demand.

[0008] One aspect of the control program for an energy storage system according to the present invention is an energy storage system control program executed in a calculation unit incorporated into an energy storage system having a plurality of cartridges including a secondary battery and a plurality of switch units that switch between incorporating a cartridge corresponding to a string line or disconnecting a corresponding cartridge from the string line, the program comprising: a state estimation process that calculates a degree of fit indicating how well the state estimation value, obtained by estimating the state of the secondary battery for each cartridge using a state estimation model, matches the actual state of the secondary battery; a power limit calculation process that calculates a power limit value for each cartridge, which is a value that matches the state of the secondary battery estimated in the state estimation process and is a limit value for the charging and discharging power of the secondary battery; and a power supply that supplies power output from the plurality of cartridges. The system performs a switch control process that controls the state of the plurality of switch units based on the power demand value provided by the supplier, the suitability, and the power limit value. In the switch control process, if the power demand value can be met by applying the lowest power limit value among the plurality of power limit values ​​to all the cartridges, the system controls the plurality of switch units in a first mode that preferentially selects the cartridge with the lowest suitability and outputs the required output voltage. If the power demand value cannot be met by applying the lowest power limit value among the plurality of power limit values ​​to all the cartridges, the system controls the plurality of switch units in a second mode that generates the required output voltage using only the cartridge having the power limit value that can satisfy the power demand value.

[0009] One aspect of the energy storage system control method according to the present invention is an energy storage system control method in an energy storage system having a plurality of cartridges including a secondary battery and a plurality of switch units that switch between incorporating a cartridge corresponding to a string line or disconnecting a corresponding cartridge from the string line, comprising: a state estimation process that calculates a degree of fit indicating how well the state estimation value obtained by estimating the state of the secondary battery for each cartridge using a state estimation model matches the actual state of the secondary battery; a power limit calculation process that calculates a power limit value for each cartridge, which is a value that matches the state of the secondary battery estimated in the state estimation process and is a limit value for the charging and discharging power of the secondary battery; and power supplied from a power supply source that supplies power to be output from the plurality of cartridges. The calculation unit performs a switch control process that controls the state of the plurality of switch units based on the power demand value, the fitness level, and the power limit value. In the switch control process, if the power demand value can be met by applying the lowest power limit value among the plurality of power limit values ​​to all the cartridges, the plurality of switch units are controlled in a first mode that preferentially selects the cartridge with the lowest fitness level and outputs the required output voltage. If the power demand value cannot be met by applying the lowest power limit value among the plurality of power limit values ​​to all the cartridges, the plurality of switch units are controlled in a second mode that generates the required output voltage using only the cartridge having the power limit value that can satisfy the power demand value. [Effects of the Invention]

[0010] According to the energy storage system, energy storage system control program, and energy storage system control method of the present invention, the period until the output limit of the energy storage system is relaxed can be shortened. [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 diagram illustrates the basic operation of the energy storage system according to Embodiment 1. [Figure 3] This diagram illustrates the operation of the energy storage system according to Embodiment 1 in the first mode. [Figure 4] This diagram illustrates the operation in the second mode of the operation of the energy storage system according to Embodiment 1. [Figure 5] This is a block diagram of the cartridge management unit and switch control unit of the energy storage system according to Embodiment 1. [Figure 6] This is a block diagram of the state estimation unit according to Embodiment 1. [Figure 7] This is a flowchart illustrating the operation of the power limit calculation unit according to Embodiment 1. [Figure 8] This is a flowchart illustrating the operation of the energy storage system according to Embodiment 1. [Figure 9] This figure illustrates the improvement in the suitability of the energy storage system according to Embodiment 1. [Figure 10] This diagram illustrates the operation of the energy storage system according to Embodiment 2 in the first mode. [Figure 11] This is a flowchart illustrating the operation of the energy storage system according to Embodiment 2. [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, FIG. 1 shows a block diagram of the power storage system 1 according to Embodiment 1. The power storage system 1 shown in FIG. 1 is an example of a power storage system using a battery string in which secondary batteries are connected in series, and the method for controlling the power storage system described below is applicable even to power storage systems other than the power storage system 1 shown in FIG. 1.

[0015] In the example shown in FIG. 1, the power storage system 1 according to Embodiment 1 includes an isolation transformer, a global control unit GCU, and strings 10, 11, and 12. The power storage system 1 outputs an AC voltage to the isolation transformer via string lines 13, 14, and 15 by the strings 10, 11, and 12, respectively. The AC voltages generated in the strings 10, 11, and 12 are three-phase AC voltages (U phase, V phase, W phase) having different phases from each other. Here, since the strings 10, 11, and 12 have substantially the same configuration except that the phases of the output AC voltages are different, only the detailed configuration of the string 10 is shown in FIG. 1. Also, in FIG. 1, three strings corresponding to three phases are shown for the string, but other strings that output AC voltages are connected in parallel to the strings corresponding to each phase, and the illustration thereof is omitted in FIG. 1. Although not shown, for example, at least one other string (not shown) that outputs the AC voltage of the U phase is provided so as to be connected in parallel with the string 10.

[0016] The global control unit GCU receives a power demand value from a power supply destination to which the power storage system 1 supplies power, and notifies the power values to be output to the strings 10 to 12. As an example, the global control unit GCU notifies the power demand value to the strings 10 to 12 as it is.

[0017] As shown in FIG. 1, the string 10 includes a switch control unit SCU, a plurality of switch units SU, a plurality of cartridges BC, and a string line 13. Each of the plurality of cartridges BC is provided with a cartridge management unit CMU.

[0018] Cartridge BC contains a battery pack in which at least one secondary battery is connected in series. A switch unit SU is provided for each cartridge BC and switches whether or not to connect cartridge BC to the string wire 13. Specifically, the switch unit SU has switches SWA and SWB. Switch SWA is provided between the positive terminal of cartridge BC and the string wire 13. Switch SWB is inserted in series with the string wire 13. Switch unit SU inserts the corresponding cartridge BC into the string wire 13 by turning switch SWA on and switch SWB off. Switch unit SU also disconnects the corresponding cartridge BC from the string wire 13 by turning switch SWA off and switch SWB on.

[0019] The Cartridge Management Unit (CMU) measures the charge / discharge current, output voltage, and temperature of the secondary battery in the corresponding cartridge BC. It applies the measured values ​​to a state estimation model to estimate the State of Charge (SOC) and outputs the estimated SOC to a higher-level management device such as the Switch Control Unit (SCU). The Cartridge Management Unit (CMU) also calculates a degree of fit, indicating how well the estimated state values ​​(e.g., charge level and output voltage) obtained using the state estimation model match the actual state of the secondary battery. Furthermore, for the corresponding cartridge BC, the Cartridge Management Unit (CMU) calculates a power limit value (PwL) that matches the estimated state of the secondary battery and represents a limit on the charge / discharge power of the secondary battery.

[0020] The switch control unit SCU controls the state of multiple switch units SU based on the power demand value provided by the power supply destination that supplies power output from multiple cartridges BC, and the suitability and power limit value PwL obtained from the cartridge management unit CMU. In other words, in the energy storage system 1, the switch control unit SCU periodically switches the cartridges BC connected to the string wire 13 to output an AC voltage to the isolation transformer via the string wire 13. In addition, the energy storage system 1 selects the cartridge BC to be used to generate the AC voltage according to its suitability.

[0021] Here, the operation of the energy storage system 1 according to Embodiment 1 will be described in more detail. Figure 2 shows a diagram illustrating the basic operation of the energy storage system 1 according to Embodiment 1. As mentioned above, the energy storage system 1 according to Embodiment 1 outputs an AC voltage by periodically switching the number of cartridges BC connected to the string line 13. As shown in Figure 2, the switch control unit SCU outputs a control signal with a duty cycle of 10 to 90% for each switch unit SU, and a delay is provided between each control signal. As a result, the energy storage system 1 according to Embodiment 1 outputs an AC voltage by changing the number of cartridges that are effectively connected on average per unit time. For example, in the example shown in Figure 2, the energy storage system 1 according to Embodiment 1 has 9 out of 10 cartridges effectively connected on average per unit time during periods with a duty cycle of 90%, and 1 out of 10 cartridges effectively connected on average per unit time during periods with a duty cycle of 10%.

[0022] Furthermore, in the energy storage system 1 according to Embodiment 1, it is possible to replace the cartridge BC. When the cartridge BC is replaced in this way, the state estimation model used to estimate the state of the cartridge BC incorporated into the string 10 after replacement does not match the actual secondary battery of the cartridge BC, and the power limit value PwL, which sets the limit on charge and discharge power, is kept low. This is because if the secondary battery of the cartridge BC is used with charge and discharge power exceeding its actual capacity, the secondary battery will deteriorate more quickly, and this measure is taken to suppress this problem. The cartridge management unit CMU improves the fit of the state estimation model by updating the battery parameters so that the state estimation model matches the actual performance of the secondary battery each time the cartridge BC is used. In addition, the power limit value PwL is calculated using the value calculated by the state estimation model, and as the fit of the state estimation model increases, it becomes an appropriate value that can better extract the actual performance of the secondary battery. In other words, in the energy storage system 1 according to Embodiment 1, in order to make the most of the output capacity of the replaced cartridge BC, it is necessary to increase the frequency of use of the replaced cartridge BC. Therefore, in the energy storage system 1 according to Embodiment 1, the cartridge BC connected to the string wire 13 is selected to actively utilize cartridge BC with a low degree of compatibility. Furthermore, in the energy storage system 1 according to Embodiment 1, securing the output voltage from the string 10 is a priority condition for the system, so the use of cartridge BC with a low degree of compatibility is prioritized within the range that satisfies the required power demand value.

[0023] Next, we will explain the selection of cartridges BC in the energy storage system 1 according to Embodiment 1. Figure 3 shows a diagram illustrating the operation of the energy storage system 1 in the first mode of operation according to Embodiment 1. The first mode is the operation of the energy storage system 1 when the upper limit of the charge and discharge power of the string is set to match the lowest power limit value PwL (which is the largest power limit value PwL and the value that restricts charge and discharge power the most strictly). In other words, the operation in the first mode is the operation of the energy storage system 1 when the power limit value PwL is small relative to the power demand value. In the example shown in Figure 3, 15 cartridges BC (cartridges ctrg1 to ctrg15) are incorporated into one string, and 5 of the 15 cartridges BC (cartridges ctrg11 to ctrg15) have been replaced.

[0024] As shown in Figure 3, in the first mode of operation, the energy storage system 1 sets cartridges BC (cartridges ctrg11 to ctrg15) with low suitability and low power limit values ​​PwL as the active cartridges. In the first mode, the system selects cartridges BC with high suitability and high power limit values ​​PwL to make up for any shortage of cartridges needed to generate the output voltage. In the example shown in Figure 3, five of the highly suitable cartridges BC (for example, cartridges ctrg6 to ctrg10) are set as active cartridges, and the remaining five (for example, cartridges ctrg1 to ctrg5) are set as pass-through (i.e., unselected). In this way, when power can be supplied even with low-suitability cartridges BC, the energy storage system 1 prioritizes the use of the low-suitability cartridges, thereby increasing the suitability of the low-suitability cartridges BC and promoting a relaxation of the power limit.

[0025] Next, Figure 4 shows a diagram illustrating the operation of the energy storage system 1 in the second mode of operation according to Embodiment 1. The second mode is the operation of the energy storage system 1 when the power demand value cannot be met when the upper limit of the charging and discharging power of the string is set according to the lowest power limit value PwL. In the example shown in Figure 4, 15 cartridges BC (cartridges ctrg1 to ctrg15) are incorporated into one string, and 5 of the 15 cartridges BC (cartridges ctrg11 to ctrg15) have been replaced.

[0026] As shown in Figure 4, in the second mode of operation, the energy storage system 1 uses cartridges BC (cartridges ctrg1 to ctrg10) that have a high degree of suitability and a high power limit value PwL (i.e., active cartridges). On the other hand, cartridges BC with a low power limit value (for example, cartridges ctrg11 to ctrg15) are set to pass-through. In this way, by generating the output voltage using only cartridges BC with a low power limit value, the energy storage system 1 becomes capable of supplying a large amount of power.

[0027] To perform the above operations, the energy storage system 1 according to Embodiment 1 executes an energy storage system control program in the calculation unit. This energy storage system control program may be executed by the switch control unit SCU alone, for example, but it can also be divided between the switch control unit SCU and the cartridge management unit CMU to perform a single operation. The following description will explain an example in which the processing of the energy storage system control program is divided between the cartridge management unit CMU and the switch control unit SCU. Since a cartridge management unit CMU is provided for each cartridge BC, executing the processing required for each cartridge BC in the cartridge management unit CMU has the effect of increasing the degree of parallelism of processing.

[0028] The following explanation describes an example in which the processing defined by the energy storage system control program is divided and processed by the cartridge management unit (CMU) and the switch control unit (SCU). Furthermore, the following explanation uses hardware as an example, where each processing unit of the energy storage system control program is represented as a processing block. In other words, the implementation method of the control method in energy storage system 1 can be either software or hardware.

[0029] Figure 5 shows a block diagram of the cartridge management unit (CMU) and switch control unit (SCU) of the energy storage system 1 according to Embodiment 1. Although only one cartridge management unit (CMU) is shown in Figure 5, the switch control unit (SCU) receives suitability and power limit value (PwL) from multiple cartridge management units (CMUs). In the example shown in Figure 5, the cartridge management unit (CMU) has a battery measurement value acquisition unit 20, a state estimation unit 21, and a power limit calculation unit 22. Also in the example shown in Figure 5, the switch control unit (SCU) has a power demand determination unit 23 and a switch control signal generation unit 24.

[0030] The battery measurement value acquisition unit 20 acquires the charge / discharge current, output voltage, and temperature information of the secondary battery in the corresponding cartridge BC from the measurement unit (not shown in Figure 5) which measures the state of the battery, and passes this information to the subsequent state estimation unit 21.

[0031] The state estimation unit 21 calculates a degree of fit, which indicates how well the estimated state value, obtained by estimating the state of the secondary battery in the corresponding cartridge BC using the state estimation model, matches the actual state of the secondary battery. The state estimation unit 21 also calculates the charge level of the corresponding cartridge BC using the state estimation model and notifies a higher-level system such as the switch control unit SCU.

[0032] The power limit calculation unit 22 calculates a power limit value PwL for the corresponding cartridge BC, which is a value that matches the state of the secondary battery estimated by the state estimation unit 21 and is the limit value for the charging and discharging power of the secondary battery.

[0033] The switch control unit SCU controls the state of multiple switch units SU based on the power demand value provided by the power supply destination that supplies power output from multiple cartridges BC, the degree of suitability, and the power limit value PwL. More specifically, the power demand determination unit 23 determines whether the power demand value can be met by applying the lowest power limit value among multiple power limit values ​​to all cartridges. Based on the determination result of the power demand determination unit 23, the switch control signal generation unit 24 operates in a first mode, outputting a control signal to the multiple switch units SU to output the required output voltage by preferentially selecting the cartridge BC with the lowest degree of suitability if the power demand value can be met by applying the lowest power limit value among multiple power limit values ​​PwL to all cartridges BC.

[0034] Furthermore, if the power demand cannot be met when the lowest power limit value PwL among the multiple power limit values ​​PwL is applied to all cartridges, the switch control signal generation unit 24 operates in a second mode, outputting control signals to multiple switch units so that only the cartridge BC having a power limit value PwL that can meet the power demand is used to generate the required output voltage.

[0035] Furthermore, the switch control signal generation unit 24, if the power demand cannot be met when the lowest power limit value PwL among the multiple power limit values ​​PwL is applied to all cartridges BC, and the required output voltage cannot be generated using only cartridges BC that have a power limit value PwL that can meet the power demand, outputs a control signal to multiple switch units SU to preferentially select the cartridge BC with the lowest suitability and output an output voltage, and also performs a third mode of operation in which it requests the higher-level control unit (e.g., the global control unit GCU) to output insufficient power to other strings that output AC voltages in the same phase.

[0036] The switch control unit (SCU) determines which cartridge BC to use based on the fit of the state estimation model. This fit will now be explained. In the energy storage system 1 according to Embodiment 1, the cartridge management unit (CMU) calculates the charge level of the secondary battery in the corresponding cartridge BC using the state estimation model. At this time, the cartridge management unit (CMU) takes the charge / discharge current Icd and the temperature of the secondary battery (e.g., battery temperature T) as input and calculates an estimated output voltage value of the secondary battery. Then, the charge level is calculated by fitting the estimated output voltage value to a pre-prepared potential map. Furthermore, if there is an error between the estimated output voltage value and the actual output voltage Vb of the secondary battery obtained by measuring the secondary battery, the cartridge management unit (CMU) updates the correction value given to the state estimation model according to the magnitude of the error to eliminate this error. In other words, the accuracy with which the state estimation model can estimate the actual state of the secondary battery can be determined by the error between the estimated output voltage value and the output voltage Vb. Therefore, in the energy storage system 1 according to Embodiment 1, the error between the estimated output voltage value and the output voltage Vb is used as an indicator of the fit. Furthermore, the metrics that can be used as a measure of fit are not limited to the error between the estimated output voltage and the output voltage Vb; any value that can be used as a metric to determine how well the values ​​that can be calculated by the state estimation model match the actual parameters of the secondary battery is acceptable.

[0037] Here, we will explain the state estimation unit 21, which includes a state estimation model for calculating the degree of fit in the cartridge management unit (CMU), and the power limit calculation unit 22, which includes a power limit model for calculating the power limit value PwL.

[0038] First, Figure 6 shows a block diagram of the state estimation unit 21 according to Embodiment 1. In Figure 6, processing blocks are shown for each processing unit that constitutes the program that realizes the state estimation unit 21. Also, in Figure 6, the program is executed in the calculation unit within the cartridge management unit (CMU).

[0039] As shown in Figure 6, the state estimation unit 21 includes an output voltage estimation unit 30, a correction value estimation processing unit (for example, an extended Kalman filter calculation unit 31), an output voltage error calculation unit 32, and a current sensor correction unit 33.

[0040] The output voltage estimation unit 30 inputs the charge / discharge current and battery temperature obtained from the secondary battery into a state estimation model including an electrochemical model and performs output voltage estimation processing to calculate an estimated output voltage of the secondary battery. In the example shown in Figure 6, the output voltage estimation unit 30 includes, as an electrochemical model in the state estimation model, a solid-phase diffusion model calculation unit 40, a potential map 41, a reaction overvoltage model calculation unit 42, a synthesis processing unit 43, a solid-phase diffusion model calculation unit 44, a potential map 45, a reaction overvoltage model calculation unit 46, a synthesis processing unit 47, a liquid-phase diffusion model calculation unit 48, a liquid-phase potential difference formula 49, and a synthesis processing unit 50.

[0041] The solid-phase diffusion model calculation unit 40 calculates the lithium concentration on the positive electrode surface using the charge / discharge current value Icd and the battery temperature T as inputs. The solid-phase diffusion model calculation unit 40 also corrects the lithium concentration on the positive electrode surface calculated from the charge / discharge current Icd and the battery temperature T using the lithium concentration correction value PLi_ofs. The potential map 41 is a potential map that shows the relationship between the lithium concentration on the positive electrode surface and the positive electrode potential, and outputs the positive electrode potential using the lithium concentration on the positive electrode surface as input. The state of charge (SOC) is calculated by providing an estimated output voltage value to the positive electrode potential map. The reaction overvoltage model calculation unit 42 calculates the positive electrode reaction overvoltage using the charge / discharge current value Icd and the battery temperature T as inputs. The synthesis processing unit 43 adds the positive electrode potential output from the potential map 41 and the positive electrode reaction overvoltage output by the reaction overvoltage model calculation unit 42.

[0042] The solid-phase diffusion model calculation unit 44 calculates the negative electrode surface lithium concentration and the negative electrode average lithium concentration using the charge / discharge current value Icd and the battery temperature T as inputs. The solid-phase diffusion model calculation unit 44 also corrects the negative electrode surface lithium concentration and the negative electrode average lithium concentration calculated from the charge / discharge current Icd and the battery temperature T using the negative electrode lithium concentration correction value NLi_ofs. The potential map 45 is a potential map that shows the relationship between the negative electrode surface lithium concentration and the negative electrode potential, and outputs the negative electrode potential using the negative electrode surface lithium concentration as input. The reaction overvoltage model calculation unit 46 calculates the negative electrode reaction overvoltage using the charge / discharge current value Icd and the battery temperature T as inputs. The synthesis processing unit 47 adds the negative electrode potential output from the potential map 45 and the negative electrode reaction overvoltage output by the reaction overvoltage model calculation unit 46.

[0043] The liquid phase diffusion model calculation unit 48 calculates the salt concentration using the charge / discharge current value Icd and the battery temperature T as inputs. The liquid phase potential difference equation 49 has a liquid phase potential difference equation and calculates the estimated liquid phase potential using the salt concentration as input.

[0044] Electrode resistance Re is a mathematical model of the electrical resistance of the electrodes, liquid resistance Rl is a mathematical model of the resistance component caused by the electrolyte, and coating resistance Rc is a mathematical model of the resistance component caused by the coating applied to the battery components. Electrode resistance Re, liquid resistance Rl, and coating resistance Rc each have temperature characteristics. Therefore, the mathematical models for each resistance are created to take into account the effect of the battery temperature T. Then, by adding the values ​​obtained by applying the charge / discharge current Icd to the mathematical models of each resistance, the potential difference caused by the resistance components is calculated.

[0045] The synthesis processing unit 50 calculates the output voltage estimate by subtracting the negative electrode estimate output from the synthesis processing unit 43 and the resistance component estimate potential calculated by the resistance component mathematical model from the sum of the positive electrode estimate potential output from the synthesis processing unit 47 and the liquid phase estimate potential output from the liquid phase potential difference formula 49.

[0046] The output voltage error calculation unit 32 calculates the output voltage error by subtracting the output voltage estimate value output by the output voltage estimation unit 30 from the measured battery voltage Vb, thereby calculating the error between these two voltages as the output voltage error. Here, the magnitude of the output voltage error indicates the magnitude of the deviation of the electrochemical model held in the output voltage estimation unit 30 from the actual characteristics of the secondary battery, so it is necessary to correct the electrochemical model so that it represents the actual characteristics of the secondary battery. By correcting this deviation, the deviation between the charge level (SOC) and the actual charge level of the secondary battery can be reduced. In the state estimation unit 21 according to Embodiment 1, the electrochemical model is corrected by generating a correction value for the electrochemical model using the correction value estimation unit. In addition, the state estimation unit 21 according to Embodiment 1 outputs the output voltage error as a degree of fit. That is, the closer the degree of fit is to zero, the higher the degree of fit.

[0047] The correction value can be calculated, for example, using an extended Kalman filter. Therefore, in the state estimation unit 21 according to Embodiment 1, an extended Kalman filter calculation unit 31 is used as the correction value estimation unit. In addition, the state estimation unit 21 according to Embodiment 1 generates three correction values, but the correction values ​​that can be generated are not limited to these, and the following description is just one example of correction value application. For example, the extended Kalman filter calculation unit 31 takes the output voltage error as input and performs multiple estimation processes to calculate multiple correction values ​​that minimize the output voltage error and correct the parameters of the electrochemical model of the output voltage estimation unit 30.

[0048] In the example shown in Figure 6, the extended Kalman filter calculation unit 31 includes a measurement estimation unit 51, a first degradation estimation unit 52, and a second degradation estimation unit 53. Each estimation unit performs calculation processing using an extended Kalman filter. The measurement estimation unit 51 takes the output voltage error as input and calculates a current sensor offset correction value Is_ofs to correct the offset amount of the current sensor that detects the charge and discharge current. The first degradation estimation unit 52 takes the output voltage error as input and calculates a positive electrode lithium concentration correction value PLi_ofs, which is used to correct the positive electrode surface lithium concentration in the electrochemical model. The second degradation estimation unit 53 takes the output voltage error as input and calculates a negative electrode lithium concentration correction value NLi_ofs, which is used to correct the negative electrode surface lithium concentration in the electrochemical model.

[0049] The current sensor correction unit 33 outputs a corrected charge / discharge current Icdm, which is obtained by correcting the charge / discharge current Icd, which is obtained by measuring the secondary battery, using the current sensor offset correction value Is_ofs. In the calculation unit, the charge / discharge current Icd that is given to the output voltage estimation unit 30 is this corrected charge / discharge current Icdm.

[0050] The output voltage estimation unit 30 of the state estimation unit 21 described above is also called a battery estimation model that estimates the state of the secondary battery. The power limit calculation unit 22 then uses the measured values ​​obtained by the battery measurement value acquisition unit 20 and the state estimation model of the state estimation unit 21 to calculate a power limit value PwL corresponding to the currently estimated state of the secondary battery. Figure 7 shows a flowchart illustrating the operation of the power limit calculation unit 22 according to Embodiment 1.

[0051] The power limit calculation unit 22 first performs a sample collection process (step S101) if the change in current flowing through the secondary battery during a preset time period is within a predetermined range. If this condition is met, samples are collected as needed during charging and discharging. The preset time is preferably 5 seconds or more, and in Embodiment 1 it is set to 10 seconds. Furthermore, the change in current flowing through the secondary battery is preferably within ±10%, and more preferably within ±5%.

[0052] Furthermore, during the sample collection process, the state of charge (SOC) at the start of measurement is recorded. The sample collection process also integrates the battery voltage and current, as well as the power calculated from the battery voltage and current, over a set period of time. Finally, the sample collection process stores the input / output power calculated by integrating the power, and the charge / discharge termination voltage at the end of the measurement period. During the sample collection process, samples are collected periodically as long as the set time and current change conditions are met.

[0053] In the sample acquisition process, samples of the input / output power at a set time and the charge / discharge termination voltage at the measurement termination time are collected separately for each charge level at the measurement start time. One example of a charge level classification is to divide it into bands of, for example, 10% increments.

[0054] Once a predetermined number of samples have been collected for each pair of input / output power and charge / discharge termination voltage, the power limit calculation unit 22 proceeds with the processing from step S102 onward. An example of a predetermined number is approximately 6 samples.

[0055] The power limit calculation unit 22 performs a power relationship derivation process in steps S102 to S106. In the power relationship derivation process (steps S102 to S106), the power relationship is derived for each charge level from multiple input / output power amounts and charge / discharge termination voltages. Here, "power relationship" refers to the ability to determine how much the battery voltage will drop when a certain amount of input / output power is used at a given charge level. In other words, it indicates the allowable maximum discharge power amount, which is the amount of power that can be discharged, and the allowable maximum charge power amount, which is the amount of power that can be charged, from that charge level state. In Embodiment 1, these are sometimes collectively referred to as "allowable maximum power amount".

[0056] In step S102, the sample points of the actual data are output on a log-log graph (S102). More specifically, in step S102, a graph is generated for each charge level, plotting the combination of input / output power and charge / discharge termination voltage on a log-log graph. Here, a log-log graph is used.

[0057] Next, the power limit calculation unit 22 calculates an extrapolation formula that represents the approximate line of the points plotted on the graph (step S103). The relationship shown by these plotted points is approximated by a straight line L, for example, using the least squares method. In Embodiment 1, a log-log graph is used, but as long as the approximation formula is a straight line, the process can also be carried out on a graph in which either the x-axis or y-axis coordinates are expressed as numerical values. In this case as well, an approximate straight line can be shown.

[0058] In data estimation, "interpolation" refers to obtaining an output within a range based on a relationship derived using certain data. "Extrapolation," on the other hand, refers to obtaining an output outside of that range based on a relationship observed within that range. In other words, "extrapolation" is predicting beyond known values, outside the data domain. In Embodiment 1, the approximation line showing the relationship between the charge / discharge termination voltage and the input / output energy is called the "interpolation formula."

[0059] In Embodiment 1, the interpolation formula is obtained as a straight line from each plotted point using the least squares method. In Embodiment 1, interpolation predicts the input and output power between the maximum and minimum values ​​of the charge / discharge termination voltages collected during the sample collection process. It has been shown that prediction by interpolation is more accurate than prediction by extrapolation. For this reason, it is desirable that the charge / discharge termination voltage of the collected sample be lower than the assumed allowable lower limit voltage.

[0060] Steps S104 and S105 are referred to as the input / output power limit determination process. In the input / output power limit determination process, first, the power that reaches the allowable lower limit voltage within the battery's operating range at the end of charging (discharging) is obtained (step S104). Subsequently, in step S105, the true value of the power is determined using a predetermined formula (for example, exp{In(power)}=power[Ah]) (step S105). What can be derived from this is, for example, the allowable maximum discharge power that can be discharged when the charge rate of secondary battery 1 is 60%.

[0061] Next, the power limit calculation unit 22 performs the allowable upper and lower voltage limit setting process in steps S106 and S107. In the allowable upper and lower voltage limit setting process, the allowable maximum discharge power amount determined in the input / output power limit determination process is given to the state estimation model in the state estimation unit 21 to set the allowable lower voltage and the allowable upper voltage.

[0062] In the process of setting the allowable upper and lower voltage limits, first, the input and output power calculated in step S105 is input to the current state estimation model to calculate the voltage at the end of charging or discharging (step S106). Then, in the process of setting the allowable upper and lower voltage limits, the calculated voltages are set as the allowable upper voltage limit and the allowable lower voltage limit (step S107). After that, the power limit calculation unit 22 updates the power limit value PwL with the power limit values ​​corresponding to the allowable upper and lower voltage limits set in step S107 (step S108).

[0063] In other words, the power limit calculation unit 22 has already derived the actual performance relationship of the secondary battery from the sample in steps S102 and S103. Furthermore, the state estimation unit 21 performs battery model fitting processing through automatic fitting processing of the state estimation model. As a result, the power limit calculation unit 22 can accurately estimate and set the power limit value PwL, i.e., the allowable maximum discharge energy amount and allowable maximum charge energy amount, when set, the allowable lower voltage limit and allowable upper voltage limit. As a result, it is possible to determine the range of battery voltage in which the secondary battery can be used while ensuring smooth charge and discharge control.

[0064] Furthermore, by using a state estimation model, it is possible to first set the allowable lower voltage and allowable upper voltage, and then set the power limit value PwL, i.e., the allowable maximum discharge energy and allowable maximum charge energy.

[0065] Next, Figure 8 shows a flowchart illustrating the operation of the energy storage system 1 according to Embodiment 1. The operation shown in Figure 8 only illustrates the cartridge selection process of selecting the cartridge to be connected to the string line, and explanations of other processes such as AC voltage generation and charging are omitted. Furthermore, the energy storage system 1 executes the process shown in Figure 8 at the timing when the demand power value changes or at predetermined intervals.

[0066] As shown in Figure 8, in the energy storage system 1 according to Embodiment 1, when the cartridge selection process is started, the cartridge management unit CMU first acquires the charge / discharge current, output voltage, and temperature information of the secondary battery from the corresponding cartridge BC (step S1). The cartridge management unit CMU then inputs the acquired charge / discharge current and temperature information to the state estimation unit 21 and performs state estimation processing to estimate the state of the secondary battery in the cartridge BC (step S2). The cartridge management unit CMU also calculates the power limit value PwL of the corresponding cartridge BC from the estimated battery state, and the switch control unit SCU calculates the power limit value PwL of the string based on the power limit values ​​PwL acquired from multiple cartridge management units CMU (step S3). In step S3, the switch control unit SCU determines the lowest power limit value PwL among the multiple power limit values ​​PwL as the power limit value PwL of the string. The cartridge management unit CMU also calculates the degree of fit of the state estimation model (step S4).

[0067] Next, the switch control unit SCU determines whether the power limit value PwL of the string is lower than the power demand value provided by the global control unit GCU (step S5). In step S5, if the power demand value is greater than or equal to the power limit value PwL of the string (the NO branch of step S5), the switch control unit SCU sets the cartridges BC with the highest suitability to pass through in order until the number of cartridges BC can generate the required output voltage (step S6). In other words, if the process in step S6 is performed, the energy storage system 1 operates in the first mode. On the other hand, in step S5, if the power limit value PwL of the string is lower than the power demand value (the YES branch of step S5), it determines whether the required output voltage can be output only by cartridges BC with a power limit value PwL higher than the power demand value (step S7).

[0068] In step S7, if it is determined that the required output voltage can be output only with cartridge BC having a power limit value PwL higher than the power demand value (the YES branch of step S7), the switch control unit SCU sets passthrough to cartridge BC having a low suitability power limit value PwL and controls the switch unit SU to output the output voltage only with cartridge BC having a power limit value PwL higher than the power demand value (step S8). Cartridge BC with a low suitability often has a low power limit value, so in step S8, it is likely that cartridge BC with a low suitability will not be selected. In this step S8, that is, if the process in step S6 is performed, the energy storage system 1 operates in the second mode.

[0069] On the other hand, in step S7, if it is determined that the required output voltage cannot be output using only cartridges BC with a power limit value PwL higher than the power demand value (the NO branch in step S7), the switch control unit SCU preferentially selects cartridges BC with a lower degree of suitability and performs charging and discharging while limiting power with the lowest power limit value PwL among the selected cartridges BC (step S9). The switch control unit SCU also requests the global control unit GCU to redistribute the power that is insufficient in its own string to other strings that are set to output AC voltage in phase with its own string (step S10). In other words, if the processes in steps S9 and S10 are performed, the energy storage system 1 operates in the third mode.

[0070] Here, we will explain the rate of improvement in the fitness level in the energy storage system 1 according to Embodiment 1, to which the control method described above is applied. Figure 9 shows a diagram illustrating the improvement in the fitness level in the energy storage system according to Embodiment 1. In Figure 9, the horizontal axis shows the usage time of cartridge BC, and the vertical axis shows the magnitude of the fitness level. As shown in Figure 9, if the cartridge selection process described above is not performed, the frequency of use of cartridge BC with low fitness level is low, so the improvement in fitness level is slower than in the energy storage system 1 according to Embodiment 1, and it takes a long time for the fitness level to improve sufficiently. On the other hand, in the energy storage system 1 according to Embodiment 1, cartridge BC with low fitness level is used at a high frequency, so the rate of improvement in fitness level is faster.

[0071] As described above, in the energy storage system 1 according to Embodiment 1, the cartridge selection process is performed to actively utilize cartridges BC with low fit. This makes it possible to accelerate the rate of improvement in the fit of the state estimation model in the energy storage system 1 according to Embodiment 1, and to match the power limit value PwL of cartridge BC to the capacity of cartridge BC. In particular, in an energy storage system 1 in which the cartridges of cartridge BC can be replaced, if the usage history of the replacement cartridge BC is unknown, it is important to increase the fit of the state estimation model of the replacement cartridge as early as possible in order to safely use the replacement cartridge BC and fully utilize its capacity. In such cases, the energy storage system 1 according to Embodiment 1 can increase the fit of the state estimation model of the replacement cartridge as early as possible, thus achieving a particularly high effect.

[0072] Embodiment 2 Embodiment 2 describes another form of the cartridge selection process according to 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.

[0073] In the cartridge selection process according to Embodiment 2, when selecting a cartridge BC with a low degree of compatibility in the first mode (step S6 in Figure 8) and the third mode (step S9 in Figure 8), the cartridge BC with the low degree of compatibility is used more actively. Specifically, in Embodiment 2, the selection period is extended for cartridges BC with a lower degree of compatibility in order to extend their usage time. Therefore, Figure 10 shows a diagram illustrating the operation in the first mode of the energy storage system according to Embodiment 2.

[0074] Figure 10 shows an example where, when 10 cartridges BC are selected, the degree of fit decreases from cartridge ctrg1 to cartridge ctrg10. In such a case, in Embodiment 2, the switch control unit SCU generates a control signal such that cartridges BC with lower degrees of fit are connected to the string for a longer period of time.

[0075] Figure 11 shows a flowchart illustrating the operation of the energy storage system according to Embodiment 2. As shown in Figure 11, the control method for the energy storage system according to Embodiment 2 is the same as the flowchart shown in Figure 8, but with step S6 replaced by step S21. In step S21, the duty cycle of the control signal given to the switch unit SU is set so that cartridges with high suitability are used less frequently and cartridges with low suitability are used more frequently. In Figure 11, duty cycle control is shown only in step S21, but the same duty cycle control as in step S9 may also be performed in the processing of step S9.

[0076] As described above, in the cartridge selection method according to Embodiment 2, cartridges BC with low fitness are utilized more actively than in Embodiment 1, making it possible to accelerate the rate of improvement in fitness compared to Embodiment 1.

[0077] 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]

[0078] 1. Energy storage system 10-12 strings 13-15 String wires 20 Battery measurement value acquisition unit 21 State Estimation Unit 22 Power limit calculation unit 23 Electricity demand determination section 24 Switch control signal generation unit 30 Output voltage estimation unit 31 Extended Kalman filter calculation unit 32 Output voltage error calculation unit 33 Current sensor correction unit 40. Solid-phase diffusion model calculation unit 41 Potential Map 42 Reaction Overvoltage Model Calculation Unit 43 Synthesis Processing Unit 44 Solid-phase diffusion model calculation unit 45 Potential Map 46 Reaction Overvoltage Model Calculation Unit 47 Synthesis Processing Unit 48 Liquid-phase diffusion model calculation unit 49 Liquid phase potential difference type 50 Synthesis Processing Unit 51 Measurement and Estimation Unit 52 First Degradation Estimation Unit 53 Second Degradation Estimation Unit 60 Power Limit Model 61 Diffusion Approximation Calculation Unit 62 Power Limit Map 71 Difference calculation part 72. Concentration difference calculation unit during decay 73 Ratio Calculation Unit 74 Diffusion Approximate Lithium Concentration Calculation Unit PwL Power Limit Value Re electrode resistance Rl liquid resistance Rc film resistance PLi_ofs Cathode Lithium Concentration Correction Value NLi_ofs Negative electrode lithium concentration correction value Is_ofs Current sensor offset correction value GCU Global Control Unit SCU Switch Control Unit SU Switch Unit CMU Cartridge Management Department BC Cartridge

Claims

1. Multiple cartridges including a rechargeable battery, Multiple switch units for switching between incorporating the cartridge corresponding to the string wire or disconnecting the corresponding cartridge from the string wire, A state estimation unit calculates a degree of fit indicating how well the state estimate obtained by estimating the state of the secondary battery for each cartridge using a state estimation model matches the actual state of the secondary battery. A power limit calculation unit calculates a power limit value for each cartridge that corresponds to the state of the secondary battery estimated by the state estimation unit and is a limiting value for the charging and discharging power of the secondary battery. The system includes a switch control unit that controls the state of the plurality of switch units based on a power demand value provided by a power supply source that supplies power output from the plurality of cartridges, the suitability, and the power limit value. The switch control unit, If the power demand can be met by applying the lowest power limit value among the multiple power limit values ​​to all the cartridges, the system operates in a first mode in which it outputs control signals to the multiple switch units to preferentially select the cartridge with the lowest suitability and output the required output voltage. A power storage system that operates in a second mode in which, if the power demand cannot be met when the lowest power limit value among the multiple power limit values ​​is applied to all of the cartridges, it outputs a control signal to the multiple switch units so that only the cartridges having the power limit value that can meet the power demand are able to generate the necessary output voltage.

2. The switch control unit, The energy storage system according to claim 1, which operates in a third mode in which, if the power demand value cannot be met when the lowest power limit value among the multiple power limit values ​​is applied to all the cartridges, and the required output voltage cannot be generated with only the cartridges having the power limit value that can meet the power demand value, the system outputs a control signal to the multiple switch units to preferentially select the cartridge with the lower suitability and output the required output voltage, and also requests the higher-level control unit to output insufficient power to other strings that are set to output AC voltage in phase with the string itself.

3. The energy storage system according to claim 1, wherein the switch control unit generates the control signal in the first mode such that the period for which cartridges with lower suitability are selected becomes longer.

4. The energy storage system according to claim 1, wherein the degree of suitability is determined by the magnitude of the estimation error between the output voltage of the secondary battery obtained from the cartridge and the voltage estimate obtained by inputting the charge / discharge current and battery temperature of the secondary battery into the state estimation model.

5. The energy storage system according to claim 4, wherein the state estimation unit calculates a positive electrode lithium concentration correction value, a negative electrode lithium concentration correction value, and a measurement correction value for the charge / discharge current in accordance with the magnitude of the estimation error, and updates the positive electrode lithium concentration correction value, the negative electrode lithium concentration correction value, and the measurement correction value for the charge / discharge current to increase the degree of accuracy.

6. The energy storage system according to claim 1, wherein the switch control unit generates an AC voltage in the string wire by periodically increasing or decreasing the number of cartridges incorporated into the string wire.

7. Multiple cartridges including a rechargeable battery, A power storage system control program executed in a calculation unit incorporated into a power storage system having a plurality of switch units that switch between incorporating the cartridge corresponding to a string line or disconnecting the corresponding cartridge from the string line, A state estimation process that calculates a degree of fit indicating how well the state estimate obtained by estimating the state of the secondary battery for each cartridge using a state estimation model matches the actual state of the secondary battery, A power limit calculation process calculates a power limit value for each cartridge that corresponds to the state of the secondary battery estimated in the state estimation process, and which is a limit value for the charging and discharging power of the secondary battery. A switch control process is performed to control the state of the multiple switch units based on the power demand value provided by the power supply destination that supplies power output from the multiple cartridges, the suitability, and the power limit value. In the aforementioned switch control process, If the power demand can be met by applying the lowest power limit value among the multiple power limit values ​​to all the cartridges, the multiple switch units are controlled in a first mode that preferentially selects the cartridge with the lowest suitability and outputs the required output voltage. A power storage system control program that controls the plurality of switch units in a second mode in which, if the power demand cannot be met when the lowest power limit value among the plurality of power limit values ​​is applied to all of the cartridges, the required output voltage is generated using only the cartridges having the power limit value that can meet the power demand.

8. Multiple cartridges including a rechargeable battery, A method for controlling an energy storage system in an energy storage system having a plurality of switch units that switch between incorporating the cartridge corresponding to a string wire or disconnecting the corresponding cartridge from the string wire, A state estimation process that calculates a degree of fit indicating how well the state estimate obtained by estimating the state of the secondary battery for each cartridge using a state estimation model matches the actual state of the secondary battery, A power limit calculation process calculates a power limit value for each cartridge that corresponds to the state of the secondary battery estimated in the state estimation process, and which is a limit value for the charging and discharging power of the secondary battery. The calculation unit performs a switch control process that controls the state of the multiple switch units based on the power demand value provided by the power supply destination that supplies power output from the multiple cartridges, the suitability, and the power limit value. In the aforementioned switch control process, If the power demand can be met by applying the lowest power limit value among the multiple power limit values ​​to all the cartridges, the multiple switch units are controlled in a first mode that preferentially selects the cartridge with the lowest suitability and outputs the required output voltage. A control method for an energy storage system in which, if the power demand cannot be met when the lowest power limit value among the multiple power limit values ​​is applied to all the cartridges, the system controls the plurality of switch units in a second mode in which the output voltage required is generated using only the cartridges having the power limit value that can meet the power demand.

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