Energy storage system

Abstract

To improve the accuracy of battery charge estimation using a method that is easy to implement. [Solution] The energy storage system comprises a battery (e.g., cell 10-1), one or more capacitors connected in parallel to the battery (e.g., three capacitors 11 included in the energy storage unit 11-1), and a control device. The control device is configured to obtain the amount of energy stored in the battery (e.g., cell 10-1) using the voltage of at least one capacitor (e.g., at least one capacitor 11 included in the energy storage unit 11-1).

Description

Technical Field

[0001] The present disclosure relates to a power storage system.

Background Art

[0002] Japanese Patent Application Laid-Open No. 2017-138128 (Patent Document 1) discloses a technique for estimating the state of a battery (for example, the stored power represented by SOC (State Of Charge)) based on a battery model.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] \ The technique described in Patent Document 1 improves the estimation accuracy of the state of a battery by accurately expressing the non-linear characteristics of the battery using a battery model. Specifically, in the above technique, a DC resistance model, a charge transfer resistance model, an RC equivalent circuit model, and a diffusion resistance model are prepared to create a battery model. Resistance parameters, time constant parameters, and charge parameters are obtained based on the temperature information of the battery and a Kalman filter. Then, the state of the battery is estimated based on the battery model and these parameters.

[0005] However, creating a battery model as described above is not necessarily easy. The technique described in Patent Document 1 has problems from the perspective of ease of implementation.

[0006] The present disclosure has been made to solve the above problems, and an object thereof is to improve the estimation accuracy of the stored power of a battery by a method with high ease of implementation.

Means for Solving the Problems

[0007] According to one embodiment of the present disclosure, an energy storage system is provided. The energy storage system comprises a battery, one or more capacitors connected in parallel with the battery, and a control device. The control device is configured to obtain the amount of energy stored in the battery using the voltage of at least one capacitor. [Effects of the Invention]

[0008] According to this disclosure, it becomes possible to improve the accuracy of estimating the amount of charge stored in a battery using a method that is easy to implement. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows the configuration of a vehicle according to an embodiment of the present disclosure. [Figure 2] This diagram shows the internal configuration of the battery pack shown in Figure 1. [Figure 3] This flowchart shows the external charging control according to this embodiment. [Figure 4] This figure illustrates the operation and effects of the energy storage system according to this embodiment. [Figure 5] This figure shows a modified example of the configuration shown in Figure 2. [Modes for carrying out the invention]

[0010] Embodiments of this disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated.

[0011] Figure 1 shows the configuration of a vehicle 1000 equipped with the energy storage system according to this embodiment. The vehicle 1000 includes a battery pack 100 containing one or more batteries. The battery pack 100 is fixed, for example, under the floor of the vehicle 1000. However, the mounting configuration of the battery pack 100 is arbitrary. The battery pack 100 may be placed on the floor of the vehicle 1000.

[0012] Vehicle 1000 is further equipped with an ECU (Electronic Control Unit) 500 that performs charge and discharge control of the battery pack 100, and various sensors (position sensor, outside temperature sensor, vehicle speed sensor, odometer, etc., not shown) that detect the status of vehicle 1000 in real time. The detection results of the various sensors are output to the ECU 500.

[0013] The ECU 500 includes a processor 510 and a storage device 520. The storage device 520 is configured to store stored information. In the ECU 500, various controls are performed by the processor 510 executing a program stored in the storage device 520. In addition to the program, the storage device 520 also stores various information used by the program. The ECU 500 is an example of a "control device" according to this disclosure.

[0014] The vehicle 1000 further comprises a drive unit 20 for driving the vehicle 1000, an inlet 410, a charger 420, and an HMI (Human Machine Interface) 600.

[0015] The HMI600 includes an input device and a display device. The HMI600 may also include a touch panel display. The input device outputs signals to the ECU500 in response to user input. The display device may include a meter panel and / or a center display.

[0016] The drive unit 20 includes a PCU (Power Control Unit) 21, an MG (Motor Generator) 22, and an engine 23. The vehicle 1000 is configured to run using the power output from the battery pack 100. The vehicle 1000 is, for example, a PHEV (Plug-in Hybrid Electric Vehicle). However, the vehicle 1000 may also be another electric vehicle (xEV), such as a BEV (Battery Electric Vehicle).

[0017] The PCU 21 includes, for example, an inverter. The MG 22 functions as a driving motor and rotates the drive wheels 24 of the vehicle 1000. The MG 22 drives the vehicle 1000 using the electric power output from the battery in the battery pack 100. Specifically, the PCU 21 drives the MG 22 using the electric power supplied from the battery pack 100. As a result, the MG 22 enters a power running state. The MG 22 in the power running state converts electric power into torque. The torque is transmitted to the drive wheels 24. Also, the MG 22 enters a regeneration state during deceleration of the vehicle 1000 and charges each battery included in the battery pack 100 with the generated regenerative electric power.

[0018] The engine 23 functions as an internal combustion engine and drives the vehicle 1000 using the combustion energy of fuel. Specifically, the engine 23 generates power by the combustion energy of fuel supplied from a fuel tank (not shown). The generated power is transmitted to the drive wheels 24. The exhaust pipe 23a is connected to the engine 23 and discharges the exhaust of the engine 23 to the outside of the vehicle.

[0019] The vehicle 1000 is configured to perform external charging (charging of the in-vehicle battery with electric power supplied from outside the vehicle) while parked. The inlet 410 is configured to be connectable to a charging cable of a power supply facility outside the vehicle. The charger 420 is an in-vehicle charger that performs AC / DC conversion. The ECU 500 controls the charger 420 during external charging. The charger 420 converts AC power into DC power according to a command from the ECU 500 and outputs the DC power to the battery pack 100. As a result, each battery included in the battery pack 100 is charged.

[0020] The vehicle 1000 further includes an SMR (System Main Relay) 100b. The SMR 100b is, for example, an electromagnetic mechanical relay. The SMR 100b is located between the battery pack 100 and each of the drive device 20 and the charger 420. During running or external charging of the vehicle 1000, the SMR 100b is maintained in a connected state.

[0021] FIG. 2 is a diagram showing the internal configuration of the battery pack 100. As shown in FIG. 2, the battery pack 100 includes a plurality of cells (power storage cells) each functioning as a secondary battery. In this embodiment, the battery pack 100 includes N cells. N is, for example, 20 or more and 50 or less. However, it is not limited thereto, and N may be 2 or more and less than 20, or may be more than 50. The N cells form a battery stack. The N cells are stacked and constrained in a predetermined direction to form a battery stack. The battery stack is a power storage module in which a plurality of electrically connected cells are modularized. For example, all the cells included in the battery stack are constrained by a pair of end plates (constraint plates). The N cells are electrically connected in series with each other. Hereinafter, each of the N cells will be referred to as "cell 10" when not distinguished. When distinguished, the cells located first, second, ···, Nth from the negative electrode side end of the battery stack are respectively denoted as "cell 10-1", "cell 10-2", ···, "cell 10-N".

[0022] In this embodiment, a liquid-type lithium-ion battery is adopted as the cell 10. More specifically, the cell 10 is an LFP battery in which lithium iron phosphate is adopted as the positive electrode active material. An electrode body and an electrolytic solution are accommodated in a case of the cell 10 (for example, a rectangular battery case). The electrolytic solution includes, for example, an organic solvent and a lithium salt. However, the cell 10 is not limited to an LFP battery, and may be a ternary system battery in which NMC (nickel · manganese · cobalt) is adopted as the positive electrode active material. Further, the cell 10 may be another secondary battery such as a nickel-hydrogen battery or a sodium-ion battery. The type of the secondary battery is not limited to a liquid-type secondary battery, and may be an all-solid-state secondary battery.

[0023] Each of the cells 10-1 to 10-N has multiple capacitors 11 electrically connected in parallel. More specifically, three capacitors 11 are provided for each cell 10. Hereafter, the combination of one cell 10 and the three capacitors 11 connected in parallel to it will be referred to as a "storage block." In addition, with respect to a single storage block, one cell 10 may be referred to as the "first storage unit," and the three capacitors 11 may be referred to as the "second storage unit."

[0024] The three capacitors 11 in the second energy storage unit are electrically connected in parallel with each other. In this embodiment, the three capacitors 11 in the second energy storage unit have the same specifications. That is, these capacitors 11 have the same capacitance.

[0025] The sum of the capacities of the three capacitors 11 in the second energy storage unit is equal to or greater than the capacity of the first energy storage unit (cell 10). This configuration prevents the second energy storage unit (capacitor 11) from becoming overcharged when the first energy storage unit (cell 10) is fully charged. In this embodiment, each of the three capacitors 11 in the second energy storage unit is a lithium-ion capacitor (LIC). By employing a large-capacity lithium-ion capacitor as the second energy storage unit, it becomes easier to secure a capacity for the second energy storage unit that is comparable to that of the first energy storage unit (lithium-ion battery) with a small number of capacitors. However, the type of capacitor 11 is not limited to lithium-ion capacitors; it may also be a supercapacitor. In this embodiment, the sum of the capacities of the three capacitors 11 matches the capacity of cell 10. However, it is not limited to this, and the sum of the capacities of all capacitors 11 included in the second energy storage unit may be greater than the capacity of cell 10. The capacity of an energy storage element (for example, cell 10 or capacitor 11) indicates the amount of energy stored in the energy storage element when fully charged.

[0026] In the battery pack 100, a voltage sensor is provided for each of the 10 cells. Hereinafter, each of these N voltage sensors will be referred to as "voltage sensor Sb" unless otherwise distinguished. If they are distinguished, the voltage sensors located at the 1st, 2nd, ..., Nth positions from the negative terminal end of the battery stack will be referred to as "voltage sensor Sb-1", "voltage sensor Sb-2", ..., "voltage sensor Sb-N", respectively. In addition, the second energy storage units located at the 1st, 2nd, ..., Nth positions from the negative terminal end of the battery stack may be referred to as "energy storage unit 11-1", "energy storage unit 11-2", ..., "energy storage unit 11-N", respectively.

[0027] Voltage sensors Sb-1, Sb-2, ..., and Sb-N detect the voltages of the energy storage units 11-1, 11-2, ..., and 11-N, respectively. Since the multiple capacitors 11 included in the second energy storage unit are connected in parallel with each other, these capacitors 11 have the same voltage (hereinafter also referred to as "capacitor voltage"). In addition, the voltage of the first energy storage unit (cell 10), which is connected in parallel with the second energy storage unit, is the same as the voltage of each capacitor 11 in the second energy storage unit (capacitor voltage). The voltage of the second energy storage unit detected by voltage sensor Sb corresponds to the capacitor voltage.

[0028] Furthermore, the battery pack 100 includes one current sensor Sa and N temperature sensors Sc provided for each cell 10. The detection results of each sensor are output to the ECU 500. The ECU 500 may function as a BMS (Battery Management System) together with these sensors. In this embodiment, all cells 10 included in the battery pack 100 are connected in series, and the same amount of current flows through all cells 10. For this reason, one current sensor Sa is shared by all cells 10.

[0029] Figure 3 is a flowchart illustrating external charging control by the ECU 500. The processing flow F1 shown in Figure 3 is initiated by the ECU 500 when predetermined charging start conditions are met. The charging start conditions are the conditions under which external charging begins. For example, the charging start conditions may be met when the charging cable of the power supply equipment is connected to the inlet 410. If timer charging is reserved in the ECU 500, the charging start conditions may be met when the set start time arrives. In the flowchart, "S" represents a step.

[0030] In processing flow F1, ECU500 obtains the State of Charge (SOC) of cell 10 (hereinafter referred to as "start SOC") in S11 using the capacitor voltage when no current is flowing through cell 10. SOC (State of Charge) indicates the amount of stored energy. SOC is expressed as a percentage from 0 to 100% of the amount of stored energy when fully charged. SOC is also commonly referred to as the "charge rate". The higher the amount of stored energy (the amount of electrical energy stored in the energy storage element), the higher the SOC. The start SOC corresponds to the SOC of cell 10 at the start of external charging.

[0031] In this embodiment, the ECU 500 acquires the capacitor voltage (hereinafter referred to as "VB1") using the voltage sensor Sb when no current is flowing through cell 10. VB1 corresponds to the capacitor voltage at the start of external charging. VB1 also indicates the OCV (Open Circuit Voltage) of cell 10. The OCV corresponds to the voltage of cell 10 when no current is flowing through cell 10. The ECU 500 may correct the capacitor voltage based on the temperature of the first energy storage unit (cell 10) detected by the temperature sensor Sc.

[0032] The memory device 520 pre-stores capacitor information (for example, a map shown by line L1 in Figure 3) that shows the relationship between the capacitor voltage and the State of Charge (SOC) for the second energy storage unit. As shown by line L1, the capacitor information defines a relationship in which the SOC (amount of charge) of the second energy storage unit increases as the capacitor voltage increases. Here, the SOC of the second energy storage unit represents the ratio of the current amount of charge of all capacitors 11 included in the second energy storage unit to the total capacity of all capacitors 11 included in the second energy storage unit. That is, the SOC of the second energy storage unit represents the ratio of the sum of the current amounts of charge of the three capacitors 11 to the sum of the capacities of the three capacitors 11. In this embodiment, all capacitors 11 included in the second energy storage unit have the same characteristics. However, it is not limited to this, and the second energy storage unit may include multiple different types of capacitors.

[0033] In the capacitor information shown by line L1, the capacitor voltage is V1 when the SOC of the second energy storage unit is "0%", and the capacitor voltage is V0 when the SOC of the second energy storage unit is "100%". V0 is higher than V1. Furthermore, there is a linear relationship between the capacitor voltage and the SOC of the second energy storage unit. The capacitor information shows the linear relationship between the capacitor voltage and the SOC of the second energy storage unit (for example, a relationship expressed by slope and intercept). The ECU500 uses this capacitor information to obtain the starting SOC from VB1. The starting SOC is the SOC (amount of stored energy) corresponding to VB1 (capacitor voltage) in the capacitor information. The starting SOC is obtained for each energy storage block (for every 10 cells).

[0034] In the following step S12, the ECU 500 obtains the target SOC for external charging. External charging, which will be started in step S21 (described later), is completed when the SOC of cell 10 rises to the target SOC. The processor 510 may read a target SOC previously set by the user from the storage device 520. Alternatively, the target SOC may be a fixed value (for example, an SOC value indicating full charge). Or, the ECU 500 may request the user to input the target SOC.

[0035] When the target SOC is obtained in S12, the ECU500 obtains the capacitor voltage at the end of external charging based on that target SOC in S13. Hereafter, the capacitor voltage at the end of external charging will be referred to as "VB2". Specifically, the ECU500 uses the aforementioned capacitor information (for example, the map shown by line L1 in Figure 3) to obtain the capacitor voltage corresponding to the target SOC, and the obtained capacitor voltage is referred to as VB2. VB2 is higher than VB1. VB2 is obtained for each energy storage block (for every 10 cells).

[0036] When the process in S13 is executed, the ECU 500 connects the SMR100b and starts external charging control in S21. In S21, with AC power being input to the charger 420 from an external power supply facility via the inlet 410, the ECU 500 controls the charger 420. As a result, power supplied from outside the vehicle is input to each cell 10, and the SOC of each cell 10 increases. In S21, the ECU 500 performs SOC control to raise the SOC of at least one cell 10 to the target SOC.

[0037] In the subsequent S22, the ECU 500 integrates the charging power detected by the current sensor Sa and the voltage sensor Sb. This calculates the total charge amount during external charging (the amount of charging power input to cell 10). The ECU 500 then stores the calculated total charge amount during external charging in the memory device 520.

[0038] In the following S23, the ECU 500 determines whether a predetermined termination condition has been met. For example, the termination condition is met when the user requests the ECU 500 to stop external charging. If it is determined that the termination condition has not been met (NO in S23), the ECU 500 determines in S24 whether the capacitor voltage in at least one energy storage block has become VB2 or higher. The current in cell 10 is detected by the current sensor Sa. External charging (S21) increases the capacitor voltage of each energy storage block.

[0039] If the capacitor voltage of any of the energy storage blocks has not reached VB2 (NO in S24), the process returns to S21. As long as the termination condition is not met and the capacitor voltage of any of the energy storage blocks has not reached VB2 (NO in both S23 and S24), steps S21 to S24 are repeated. As a result, external charging of the battery pack 100 is continuously performed (S21), and the total charge amount during external charging is updated (S22).

[0040] If the termination condition is met during external charging (YES in S23), the ECU 500 terminates the external charging by requesting the power supply equipment to stop supplying power. In this case, after the ECU 500 puts the SMR100b into a shut-off state, processing flow F1 ends. On the other hand, if the capacitor voltage of at least one energy storage block becomes VB2 or higher due to external charging (YES in S24), the ECU 500 determines that the external charging is complete and requests the power supply equipment to stop supplying power. In this case, after the ECU 500 puts the SMR100b into a shut-off state, processing proceeds to S31.

[0041] In S31, the ECU500 calculates the capacity C (battery capacity) of cell 10 according to the following formula.

[0042] C = 100 × dST / |SOC1 - SOC2| In the above formula, "SOC1" represents the starting SOC and "SOC2" represents the target SOC. |SOC1-SOC2| corresponds to the difference (absolute value) between the starting SOC and the target SOC. "dST" represents the total charge amount during the period from when external charging starts until it ends (hereinafter referred to as the "charging period"). During the charging period, the process in S22 is repeated, and the total charge amount during the charging period is stored in the storage device 520. The ECU 500 acquires the capacity C for each cell 10 according to the above formula and stores the capacity C for each cell 10 in the storage device 520. With this method, the capacity of each cell 10 can be detected with high accuracy.

[0043] In the following S32, the ECU 500 calculates the amount of expansion of cell 10 using the total charge and discharge amounts of cell 10 accumulated from the initial state (e.g., at the time of shipment) to the present, and the capacity of cell 10 obtained in S31. The ECU 500 may also accumulate the total charge and discharge amounts while the vehicle 1000 is running and parked. The storage device 520 may pre-store expansion information (e.g., a map) for cell 10 that shows the relationship between the total charge and discharge amount, capacity, and expansion amount. Cell 10 tends to expand as the total charge and discharge amount increases. The larger the capacity of cell 10, the greater the expansion amount of cell 10 tends to be. The larger the expansion amount of cell 10, the greater the constraint load on cell 10. Based on these characteristics of cell 10, the expansion information defines a relationship in which the amount of expansion of cell 10 increases as the total charge and discharge amount of cell 10 increases, and the amount of expansion of cell 10 increases as the capacity of cell 10 increases. The ECU 500 may acquire the amount of expansion of cell 10 using the above expansion information. The ECU 500 may also correct the amount of expansion based on the temperature of cell 10. The amount of expansion is acquired for each cell 10 and stored in the storage device 520.

[0044] In the subsequent S33, the ECU 500 sets the lower and upper limits of the State of Computer (SOC) of cell 10 based on the amount of expansion of cell 10. The lower and upper limits of the SOC set in S33 are used, for example, in the driving control of vehicle 1000. For example, while vehicle 1000 is driving, the ECU 500 controls the SOC of cell 10 within the SOC range from the lower limit to the upper limit of the SOC (hereinafter referred to as the "practical SOC range"). The practical SOC range is updated each time the process in S33 is executed. The practical SOC range is set for each cell 10.

[0045] For example, in S33, ECU500 narrows the practical SOC range as the amount of cell 10 expansion calculated in S32 increases. ECU500 may lower the upper limit of SOC as the amount of cell 10 expansion increases. ECU500 may raise the lower limit of SOC as the amount of cell 10 expansion increases. The practical SOC range corresponds to the amount of usable energy from the capacity C (battery capacity) of cell 10 obtained in S31. The narrower the practical SOC range, the less usable energy there is. On the other hand, the narrower the practical SOC range, the more the expansion of cell 10 is suppressed. Once the processing in S33 is executed, processing flow F1 ends.

[0046] According to the method described above, the amount of expansion of each cell 10 can be detected with high accuracy. Furthermore, the expansion of each cell 10 can be appropriately suppressed by controlling it based on the detected amount of expansion.

[0047] As described above, the energy storage system according to this embodiment comprises a battery (cell 10), one or more capacitors (for example, three capacitors 11) connected in parallel to the battery, and a control device (ECU 500). The control device is configured to acquire the amount of charge stored in the battery using the voltage of at least one capacitor (S11, S13, S24 in Figure 3). The above circuit configuration can be realized by connecting one or more capacitors in parallel to the battery. The above energy storage system can improve the accuracy of estimating the amount of charge stored in the battery by a method that is easy to implement.

[0048] Figure 4 is a diagram illustrating the operation and effects of the energy storage system described above. Line L1 in Figure 4 is the same as line L1 in Figure 3. Line L2 in Figure 4 shows the relationship between OCV and SOC for the first energy storage unit (cell 10). As shown by line L2, in cell 10 (LFP battery), OCV becomes V2 when SOC is "0%" and OCV becomes V0 when SOC is "100%". However, OCV and SOC have a nonlinear relationship. In the OCV-SOC characteristic shown by line L2, there is an SOC region (flat region) where OCV hardly changes even when SOC changes. In such an SOC region, it is difficult to estimate the SOC of cell 10 from the OCV of cell 10 with high accuracy.

[0049] In the capacitor information shown by line L1, the capacitor voltage (V0) when the SOC of the second energy storage unit is "100%" is the same as the OCV when the SOC of cell 10 is "100%". Also, the capacitor voltage (V1) when the SOC of the second energy storage unit is "0%" is lower than V2. In one example, V2 is approximately 2.5V. V0 is, for example, between 4.0V and 5.0V. V1 is, for example, between 0.5V and 2.0V.

[0050] The second energy storage unit (three capacitors 11) is connected in parallel to the first energy storage unit (cell 10). Therefore, during charging or discharging of the energy storage block, the SOC of the first energy storage unit (cell 10) and the SOC of the second energy storage unit (capacitors 11) change similarly. The amount of energy stored in the first energy storage unit (cell 10) and the amount of energy stored in the second energy storage unit (three capacitors 11) can be represented by a common SOC. The ECU 500 then acquires the SOC corresponding to the capacitor voltage detected by the voltage sensor Sb, based on the capacitor information indicated by line L1. In the capacitor information, the capacitor voltage changes linearly in response to the change in SOC. The capacitor information does not have the flat region mentioned above. Therefore, the ECU 500 can estimate the SOC of the first energy storage unit (cell 10) and the SOC of the second energy storage unit (three capacitors 11) with high accuracy.

[0051] In the above embodiment, all capacitors 11 included in the second energy storage unit have the same characteristics. Therefore, the State of Charge (SOC) of the second energy storage unit, as indicated by the capacitor information, basically matches the SOC of one capacitor 11 included in the second energy storage unit. The capacitor information may include information about individual capacitors, rather than information about the entire second energy storage unit. The capacitor information may also show the relationship between the capacitor voltage and the SOC for each individual capacitor. Capacitor information for each capacitor 11 included in the second energy storage unit (for example, three maps) may be stored in the storage device 520.

[0052] In the above embodiment, an example is shown in which the amount of charge stored in the battery is estimated using the capacitor voltage in SOC control (S21) to raise the SOC of the battery to a target SOC. However, it is also possible to estimate the amount of charge stored in the battery (cell 10) using the capacitor voltage in SOC control to lower the SOC of the battery (cell 10) to a target SOC. For example, the vehicle 1000 may be configured to perform external power supply (power supply that outputs the power of the on-board battery to the outside of the vehicle). Furthermore, the ECU 500 may estimate the change in the amount of charge stored in the battery (cell 10) (discharge amount) using the capacitor voltage while the vehicle 1000 is running using the power of the battery (cell 10). Furthermore, the ECU 500 may estimate the change in the amount of charge stored in the battery (cell 10) (charge amount) using the capacitor voltage when the battery (cell 10) is charged by regenerative power.

[0053] The number of capacitors 11 in the second energy storage unit is not limited to three; it may be two, four or more, or even just one.

[0054] Figure 5 shows a modified version of the configuration shown in Figure 2. In the modified version shown in Figure 5, energy storage units 11-1, 11-2, ..., 11-N are connected in parallel to cells 10-1, 10-2, ..., 10-N, respectively. Each of the energy storage units 11-1 to 11-N is a single capacitor. The total capacity of each of the energy storage units 11-1 to 11-N corresponds to the capacity of the corresponding single capacitor. The capacities of the energy storage units 11-1, 11-2, ..., 11-N may be the same as the capacities of cells 10-1, 10-2, ..., 10-N, respectively. By making the capacities of the first energy storage unit the same as the capacities of the second energy storage unit, it becomes easier to accurately estimate the amount of energy stored in the first energy storage unit based on the voltage of at least one capacitor included in the second energy storage unit.

[0055] The processing flow shown in Figure 3 can be modified as needed. For example, the order of processing may be changed, or unnecessary steps may be omitted depending on the purpose. Furthermore, the content of any of the processing steps may be changed.

[0056] The vehicle configuration shown in Figure 1 can be modified as needed. The application of the energy storage system is arbitrary. The energy storage system may be applied to stationary batteries rather than on-board batteries.

[0057] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the description of the embodiments above, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of Symbols]

[0058] 10, 10-1 to 10-N cells, 11 capacitors, 11-1 to 11-N energy storage units, 100 battery packs, 500 ECUs, 520 memory devices, 1000 vehicles, Sb, Sb-1 to Sb-N voltage sensors.

Claims

1. A power storage system comprising a battery, one or more capacitors connected in parallel to the battery, and a control device, The control device is configured to obtain the amount of charge stored in the battery using the voltage of at least one of the capacitors, in an energy storage system.

2. The control device further includes a storage device that stores capacitor information showing a linear relationship between the voltage of the capacitor and the amount of charge stored in the capacitor for at least one of the capacitors. The control device is For at least one of the capacitors, the amount of charge stored in the capacitor is obtained from the voltage of the capacitor using the capacitor information. The energy storage system according to claim 1, configured to obtain the amount of energy stored in the battery using the amount of energy stored in at least one of the capacitors obtained.

3. The aforementioned battery is a lithium-ion battery, The energy storage system according to claim 1, wherein each of the one or more capacitors is a lithium-ion capacitor.

4. The one or more capacitors include multiple capacitors, The aforementioned plurality of capacitors have the same capacitance to each other. The energy storage system according to any one of claims 1 to 3, wherein the total capacity of the plurality of capacitors is equal to or greater than the capacity of the battery.

5. The energy storage system according to any one of claims 1 to 3, wherein the total capacity of the one or more capacitors is the same as the capacity of the battery.

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