Energy storage device, energy storage system, internal resistance estimation method, and computer program

Abstract

This electric storage device comprises an electric storage element and a management unit. The management unit acquires a current and a voltage of the electric storage element while the SOC of the electric storage element is in a predetermined SOC range in a process where the SOC of the electric storage element is reduced by discharging the electric storage element and the SOC of the electric storage element is increased by charging the electric storage element. The management unit calculates the internal resistance of the electric storage element on the basis of the acquired current and voltage. In the SOC range, fluctuation in the voltage of the electric storage element is larger than a change of the SOC of the electric storage element as compared with a range where the value of the SOC is larger than the SOC range.

Description

[Technical Field]

[0001] The present invention relates to a power storage device, a power storage system, an internal resistance estimation method, and a computer program that perform processing for estimating internal resistance. [Background technology]

[0002] A vehicle is equipped with an electric storage device such as a lead-acid battery or a lithium-ion secondary battery. Because the degradation state of the electric storage device affects the operation of the vehicle, it is desirable to determine the degradation state of the electric storage device at any time. In order to determine the degradation state of the electric storage device, it is necessary to estimate the internal resistance of the electric storage device. When starting the engine of a vehicle, cranking is performed in which the engine crankshaft is rotated by an electric motor external to the engine. During cranking, the electric storage device discharges to supply power to the electric motor, and a large current flows through the electric storage device. Patent Document 1 discloses a technology for estimating the internal resistance of the electric storage device by utilizing the large current that flows during cranking. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-117413 Summary of the Invention [Problem to be solved by the invention]

[0004] Some electric storage devices installed in vehicles are not used to drive the vehicle or start the engine, but are used to supply power to electrical devices inside the vehicle. Such electric storage devices do not draw large current during cranking, draw only small current during discharge, and have small voltage fluctuations. As a result, current and voltage measurement errors have a significant impact on the estimation of internal resistance, resulting in low accuracy in estimating the internal resistance. Therefore, a method for improving the accuracy of estimating the internal resistance of an electric storage device is desired.

[0005] An object of the present invention is to provide an electricity storage device, an electricity storage system, an internal resistance estimation method, and a computer program that can estimate internal resistance with high accuracy even when there is no opportunity for a large current to flow due to discharge. [Means for solving the problem]

[0006] According to one aspect of the present invention, an energy storage device includes an energy storage element and a management unit. The management unit acquires the current and voltage of the energy storage element while the SOC of the energy storage element is within a predetermined SOC range during the process of lowering the SOC (State of Charge) of the energy storage element by discharging the energy storage element and increasing the SOC of the energy storage element by charging the energy storage element, and calculates the internal resistance of the energy storage element based on the acquired current and voltage. The SOC range is a range in which the change in voltage of the energy storage element relative to a change in the SOC of the energy storage element is larger than a range in which the SOC value is higher than the SOC range.

[0007] According to one aspect of the present invention, there is provided a power storage system including a first power storage device, a second power storage device that supplies power to a second load different from a first load supplied by the first power storage device, and a power transmission circuit for supplying power from the first power storage device to the second power storage device. The second power storage device includes a power storage element and a management unit. The management unit discharges the power storage element to reduce its SOC, supplies power from the first power storage device to the second power storage device via the power transmission circuit, and charges the power storage element to increase its SOC. During this process, the management unit acquires the current and voltage of the power storage element while the SOC of the power storage element is within a predetermined SOC range, and calculates the internal resistance of the power storage element based on the acquired current and voltage. The SOC range is a range in which the change in voltage of the power storage element relative to a change in SOC of the power storage element is greater than a range in which the SOC value is greater than the SOC range.

[0008] In a method for estimating the internal resistance of a storage element according to one aspect of the present invention, the SOC of the storage element is lowered by discharging the storage element and increased by charging the storage element, and the current and voltage of the storage element are acquired while the SOC of the storage element is within a predetermined SOC range, and the internal resistance of the storage element is calculated based on the acquired current and voltage. The SOC range is a range in which the change in voltage of the storage element relative to a change in SOC of the storage element is larger than a range in which the SOC value is higher than the SOC range.

[0009] A computer program according to one aspect of the present invention causes a computer to execute a process of acquiring the current and voltage of a storage element while the SOC of the storage element is within a predetermined SOC range in which the change in voltage of the storage element relative to the change in SOC of the storage element is greater than in other ranges, during the process of lowering the SOC of the storage element by discharging the storage element and increasing the SOC of the storage element by charging the storage element, and calculating the internal resistance of the storage element based on the acquired current and voltage. [Effects of the Invention]

[0010] With the above configuration, the power storage device can estimate the internal resistance of the power storage element with high accuracy even when there is no opportunity for a large current to flow due to discharge. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a conceptual diagram illustrating an example of the configuration of a power storage system. [Figure 2] FIG. 4 is a block diagram showing an example of the internal configuration of a second power storage device. [Figure 3] FIG. 2 is a block diagram showing an example of the internal functional configuration of a BMU. [Figure 4] 6 is a flowchart showing a procedure for processing an internal resistance estimation performed by a second power storage device. [Figure 5] FIG. 1 is a block diagram showing an example of the configuration of a BMU that can pass a current therethrough. [Figure 6]1 is a graph showing an example of the relationship between SOC and voltage during charging. [Figure 7] 6 is a timing chart showing the timing of each process performed by the second power storage device. DETAILED DESCRIPTION OF THE INVENTION

[0012] The energy storage device includes an energy storage element and a management unit. The management unit discharges the energy storage element to lower its SOC (State of Charge) and charges the energy storage element to increase its SOC. During this process, the management unit acquires the current and voltage of the energy storage element while the SOC of the energy storage element is within a predetermined SOC range, and calculates the internal resistance of the energy storage element based on the acquired current and voltage. The SOC range is a range in which the change in voltage of the energy storage element relative to a change in the SOC of the energy storage element is larger than a range in which the SOC value is higher than the SOC range.

[0013] The energy storage device discharges the energy storage element to lower its SOC, then charges it to raise the SOC, and acquires the current and voltage of the energy storage element while the SOC is rising within a predetermined SOC range. Furthermore, the energy storage device estimates the internal resistance of the energy storage element by calculating the internal resistance based on the acquired current and voltage. Within the predetermined SOC range, the voltage changes more significantly with respect to changes in SOC than in higher SOC ranges. Therefore, the change in voltage acquired during charging is greater, and the accuracy of estimating the internal resistance is improved when the internal resistance is calculated using the current and voltage. Since the internal resistance is calculated after adjusting the SOC to increase the change in voltage, the accuracy of estimating the internal resistance is always high, enabling stable and highly accurate estimation of the internal resistance of the energy storage element. Furthermore, since the energy storage device charges the energy storage element after temporarily lowering its SOC, there is little chance of the energy storage element being overcharged, even if a large current is passed through it. Therefore, a large current can be passed through the energy storage element. Passing a large current increases the change in the measured voltage over time. By calculating the internal resistance from the voltage value, which varies greatly over time, the accuracy of estimating the internal resistance is improved.

[0014] The management unit may reduce the SOC of the storage element to below a lower limit of the SOC range during discharging, and may increase the SOC of the storage element to a value that exceeds at least the lower limit during charging. The energy storage device temporarily reduces the SOC of the storage element to below the lower limit of a predetermined SOC range, and then charges the storage element until the SOC exceeds at least the lower limit of the SOC range. During charging, the SOC falls within the predetermined SOC range. By acquiring the current and voltage of the storage element while charging is being performed with the SOC within the predetermined SOC range, it is easy to acquire the current and voltage in a state where the voltage value changes significantly.

[0015] The management unit may receive status information indicating a state outside the power storage device, and determine whether to start processing to reduce the SOC of the power storage element based on the status information. Depending on the state outside the power storage device, such as when there is a high demand for power in a power storage system including the power storage device, reducing the SOC of the power storage element may result in a power shortage. By reducing the SOC of the power storage element when no power shortage will occur based on the state outside the power storage device, a power shortage is prevented.

[0016] The management unit may discharge the energy storage element by supplying power from the energy storage element to a load external to the energy storage device. Since the load to which power is supplied is external to the energy storage device, it is easy to configure the load to consume power efficiently, for example by increasing power consumption. By supplying power to a load that consumes power efficiently, the power of the energy storage element is consumed efficiently and discharge is reliably performed.

[0017] The energy storage device may further include a load circuit. The management unit may discharge the energy storage elements by supplying power from the energy storage elements to the load circuit. Regardless of the state outside the energy storage device, such as a state in which the energy storage device is not connected to an external load, the energy storage device can discharge the energy storage elements by itself by supplying power to an internal load circuit.

[0018] The power storage device may be a device provided in an electric vehicle and supplying power to a 12V load of the electric vehicle. The power storage device does not discharge a large current when the vehicle is driven or started. However, by charging under conditions that cause large changes in voltage value, it becomes possible to estimate the internal resistance of the storage elements with high accuracy even in a power storage device that does not experience a large current flow due to discharge.

[0019] The power storage system includes a first power storage device, a second power storage device that supplies power to a second load different from a first load supplied by the first power storage device, and a power transmission circuit for supplying power from the first power storage device to the second power storage device. The second power storage device includes a power storage element and a management unit. The management unit discharges the power storage element to reduce its SOC, supplies power from the first power storage device to the second power storage device via the power transmission circuit, and charges the power storage element to increase its SOC. During this process, the management unit acquires the current and voltage of the power storage element while the SOC of the power storage element is within a predetermined SOC range, and calculates the internal resistance of the power storage element based on the acquired current and voltage. The SOC range is a range in which the change in voltage of the power storage element relative to a change in SOC of the power storage element is greater than a range in which the SOC value is greater than the SOC range. The second storage device temporarily lowers the SOC of the storage element by discharging, and then charges the storage element by receiving power from the first storage device, thereby increasing the SOC. During the SOC increase process, the internal resistance of the storage element is estimated based on the current and voltage measured within a predetermined SOC range in which voltage changes significantly with changes in SOC. The second storage device can estimate the internal resistance of the storage element by charging using power from the first storage device, without discharging to allow a large current to flow. In the second storage device, the SOC is adjusted so that voltage changes significantly in response to changes in SOC due to charging, and then the internal resistance is calculated. This increases the accuracy of internal resistance estimation, enabling stable and highly accurate internal resistance estimation.

[0020] The power storage system may further include a control device. The first power storage device is connected to the second load or the second power storage device via the power transmission circuit, and the control device inputs status information indicating whether the first power storage device and / or the power transmission circuit are in a state where power can be supplied from the first power storage device to the second load or the second power storage device to the management unit, and the management unit may determine whether to start processing to reduce the SOC of the power storage element based on the status information. If there is a malfunction in the first power storage device or the power transmission circuit, it is difficult to charge the second power storage device with power from the first power storage device or to supply power from the first power storage device to the second load. By reducing the SOC of the power storage element when the first power storage device or the power transmission circuit is in good condition, it is possible to prevent the second power storage device from becoming unable to be charged or a shortage of power supplied to the second load.

[0021] The power storage system may be provided in a vehicle. The control device may input information indicating whether the vehicle is parked or not to the management unit as the state information. When the vehicle is not parked, the demand for power in the vehicle is high, and if the SOC of the power storage element in the second power storage device is lowered, there is a possibility that the power to be supplied will be insufficient. By lowering the SOC of the power storage element while the vehicle is parked, a power shortage is prevented.

[0022] The power storage system may be provided in a vehicle, the first load may include an electrical device used to drive or start the vehicle, the second load may not include any electrical device used to drive or start the vehicle, and the second power storage device may be a device that does not supply power to the first load. The first power storage device is used to drive or start the vehicle, and a large current flows through it when it is discharged. On the other hand, the second power storage device does not flow a large current when it is discharged when the vehicle is driven or started. However, by charging the second power storage device using power from the first power storage device under conditions that cause large changes in voltage value, it is possible to estimate the internal resistance of the power storage element with high accuracy even when there is no opportunity for a large current to flow through it when it is discharged.

[0023] In a method for estimating the internal resistance of a storage element, the SOC of the storage element is lowered by discharging the storage element and then increased by charging the storage element. During this process, the current and voltage of the storage element are acquired while the SOC of the storage element is within a predetermined SOC range, and the internal resistance of the storage element is calculated based on the acquired current and voltage. The SOC range is a range in which the voltage of the storage element changes more significantly with respect to changes in the SOC of the storage element than in a range in which the SOC value is higher than the SOC range. The SOC of the storage element temporarily decreases with discharging and increases with charging. The internal resistance of the storage element is estimated based on the current and voltage measured within the predetermined SOC range, in which the voltage change with respect to changes in SOC is larger. The voltage value acquired during charging changes more significantly, and the accuracy of estimating the internal resistance is improved when the internal resistance is calculated using the current and voltage. The internal resistance is calculated after adjusting the SOC to increase the voltage change. This enables stable and highly accurate estimation of the internal resistance.

[0024] A computer program for causing a computer to execute a process for estimating the internal resistance of a storage element causes the computer to execute a process for acquiring the current and voltage of the storage element while the SOC of the storage element is within a predetermined SOC range in which the change in voltage of the storage element relative to a change in SOC of the storage element is larger than in other ranges during the process of lowering the SOC of the storage element by discharging the storage element and increasing the SOC of the storage element by charging the storage element, and then calculating the internal resistance of the storage element based on the acquired current and voltage. The computer temporarily lowers the SOC of the storage element by discharging, then increases the SOC of the storage element by charging, and estimates the internal resistance of the storage element based on the current and voltage measured within the predetermined SOC range in which the change in voltage relative to a change in SOC is large. Since the change in voltage value acquired during charging is large, the accuracy of estimating the internal resistance is improved when the internal resistance is calculated using the current and voltage. The internal resistance is calculated after adjusting the SOC to increase the change in voltage value, allowing the computer to stably and accurately estimate the internal resistance of the storage element.

[0025] The present invention will now be described in detail with reference to the drawings showing embodiments thereof. <Embodiment> FIG. 1 is a conceptual diagram showing an example of the configuration of a power storage system 1. The power storage system 1 is provided in a vehicle 4. The power storage system 1 executes an internal resistance estimation method. The power storage system 1 includes a first power storage device 11, a DC-DC converter 13, a second power storage device 2, and a control device 3. For example, the first power storage device 11 is a 48V power supply, and the second power storage device 2 is a 12V power supply. The first power storage device 11 is connected to a first load 12 and supplies power to the first load 12. The first load 12 includes an electric device, such as an electric motor, used to drive or start the vehicle 4. Driving the vehicle 4 means running the vehicle 4 by operating the engine, or running the vehicle 4 by operating the electric motor. Starting the vehicle 4 means starting the operation of the engine that runs the vehicle 4. The vehicle 4 is driven and started by supplying power from the first power storage device 11 to the first load. That is, when the vehicle 4 is driven or started, the first power storage device 11 discharges, and a large current flows through the first power storage device 11. For example, when the vehicle 4 is started, cranking is performed, and a large current flows through the first power storage device 11. The internal resistance of the first power storage device 11 can be estimated during cranking. The first power storage device 11 is supplied with power from an alternator (not shown) or from outside the vehicle 4, and is charged. The vehicle 4 may be an electric vehicle that runs by operating an electric motor, such as an electric vehicle (EV), a hybrid electric vehicle (HEV), or a plug-in hybrid electric vehicle (PHEV). The power storage system 1 shown in FIG. 1 may be, for example, a power supply system for a PHEV.

[0026] The second power storage device 2 is connected to a second load 14 and supplies power to the second load 14. The second load 14 is an electrical device different from the first load 12. The second load 14 does not include any electrical device used to drive or start the vehicle 4. The second load 14 is an electrical device that consumes less power than the first load 12, such as a lamp or an air conditioner. For example, the second load 14 is a 12V load. The second power storage device 2 does not supply power to the first load 12. The second power storage device 2 is not used to drive or start the vehicle 4, and does not flow a large current due to discharge for driving or starting the vehicle 4. For example, the second power storage device 2 does not flow a large current during cranking. Therefore, there is no opportunity for a large current to flow through the second power storage device 2 due to discharge. For example, the first power storage device 11 has a higher voltage than the second power storage device 2. For example, the second power storage device 2 is a so-called auxiliary battery.

[0027] The DCDC converter 13 is connected to the first power storage device 11 and the second power storage device 2. The first power storage device 11 is connected to the second power storage device 2 and the second load 14 via the DCDC converter 13. The DCDC converter 13 converts the voltage of the first power storage device 11 and supplies power from the first power storage device 11 to the second power storage device 2 and the second load 14. The DCDC converter 13 corresponds to a power transmission circuit. The first power storage device 11 can supply power to the second load 14 through the DCDC converter 13. In addition, the first power storage device 11 supplies power to the second power storage device 2 through the DCDC converter 13, causing the second power storage device 2 to be charged.

[0028] The control device 3 is connected to each part of the power storage system 1 and controls each part. The control device 3 is configured using, for example, an ECU (engine control unit). The control device 3 may control the first load 12 or the second load 14. The control device 3 may receive signals from outside the power storage system 1. For example, the control device 3 may receive signals from various sensors provided in the vehicle 4.

[0029] 2 is a block diagram showing an example of the internal configuration of the second power storage device 2. The second power storage device 2 includes a plurality of power storage cells 21. The plurality of power storage cells 21 are connected in series. The plurality of power storage cells 21 correspond to power storage elements. For example, the power storage cells 21 are lithium ion secondary batteries. The power storage cells 21 may also be other secondary batteries such as lead storage batteries.

[0030] One end of the plurality of serially connected storage cells 21 is connected to a positive terminal 25 via a power line, and the other end is connected to a negative terminal 26 via a power line. The positive terminal 25 and the negative terminal 26 are connected to the outside of the second storage device 2 via power lines. For example, one of the positive terminal 25 and the negative terminal 26 is connected to the second load 14 and the DC-DC converter 13, and the other is connected to ground. A current flows through the plurality of storage cells 21 via the positive terminal 25 and the negative terminal 26, and the plurality of storage cells 21 discharge or charge. When the plurality of storage cells 21 discharge, power is supplied to the second load 14 via the positive terminal 25 and the negative terminal 26. When power is supplied to the second storage device 2 from the outside of the second storage device 2 via the positive terminal 25 and the negative terminal 26, the plurality of storage cells 21 charge.

[0031] A current sensor 23 and a current interruption device 24 are provided in the middle of an electric path between the plurality of storage cells 21 and the positive terminal 25 or the negative terminal 26. The current sensor 23 measures a current flowing through the plurality of storage cells 21. The current interruption device 24 interrupts the current flowing through the plurality of storage cells 21 to stop discharging or charging. The second storage device 2 includes a BMU (Battery Management Unit) 22. The BMU 22 corresponds to a management unit. The BMU 22 is connected to both ends of the plurality of storage cells 21 and is connected to the current sensor 23 and the current interruption device 24 by communication lines. The both ends of the plurality of storage cells 21 correspond to both ends of a storage element when the plurality of storage cells 21 connected in series are combined into one storage element. The BMU 22 controls the current sensor 23 and the current interruption device 24. The second storage device 2 includes a communication connector 27 connected to a device external to the second storage device 2 by a communication line. For example, the communication connector 27 is connected to the control device 3. The BMU 22 is connected to a communication connector 27 via a communication line.

[0032] 3 is a block diagram showing an example of the internal functional configuration of the BMU 22. The BMU 22 manages the states of the plurality of power storage cells 21 and controls each unit of the second power storage device 2. The BMU 22 includes a calculation unit 221, a memory 222, a storage unit 223, a voltage acquisition unit 224, an interface unit 225, and a communication unit 226. The calculation unit 221 is, for example, a CPU (Central Processing Unit). The memory 222 stores information necessary for calculations in the calculation unit 221. The storage unit 223 is nonvolatile and stores various types of data. For example, the storage unit 223 is a nonvolatile semiconductor memory.

[0033] The storage unit 223 stores a computer program 51. The computer program 51 is read from a storage medium 50, such as an optical disk, that stores the computer program 51 by a recording device (not shown), and written to the storage unit 223, thereby being stored in the storage unit 223. The BMU 22 is a computer that causes the computer program 51 to execute processing. The calculation unit 221 executes processing required for the BMU 22 in accordance with the computer program 51. Alternatively, some or all of the processing executed by the BMU 22 may be executed by a method other than a method that uses the computer program 51.

[0034] The voltage acquisition unit 224 acquires the voltage between both ends of the plurality of storage cells 21 connected in series. The voltage acquisition unit 224 measures the voltage or acquires a voltage value measured elsewhere. The voltage acquisition unit 224 may acquire the voltage of each storage cell 21. The interface unit 225 is connected to the current sensor 23 and the current interruption device 24. The interface unit 225 receives a signal related to the current measured by the current sensor 23, and the BMU 22 acquires a current value corresponding to the received signal. The BMU 22 outputs a control signal from the interface unit 225 to the current interruption device 24 to control the current interruption device 24. The communication unit 226 is connected to the communication connector 27 via a communication line. The communication unit 226 communicates with the outside of the second storage device 2 through the communication connector 27. For example, the BMU 22 communicates with the control device 3 through the communication connector 27 using the communication unit 226.

[0035] The second power storage device 2 performs a process of estimating the internal resistance of the plurality of power storage cells 21. The second power storage device 2 lowers the SOC (State of Charge) of the plurality of power storage cells 21, and estimates the internal resistance of the plurality of power storage cells 21 by utilizing the current that flows through the plurality of power storage cells 21 when charging is performed from a low SOC state. The SOC is a charging rate, and is expressed as a ratio of the amount of electricity charged in the power storage cells 21 to the full charge capacity of the power storage cells 21.

[0036] 4 is a flowchart showing the steps of the process of estimating internal resistance performed by the second power storage device 2. Hereinafter, step is abbreviated as S. The control device 3 determines the states of the vehicle 4 and the power storage system 1 as needed, and transmits state information indicating the states of the vehicle 4 and the power storage system 1. The state information is input to the BMU 22 via the communication connector 27, and the BMU 22 receives the state information at the communication unit 226 (S1).

[0037] For example, the control device 3 determines whether the vehicle 4 is parked based on information about the operation of the engine or the electric motor, or information about the operation of the vehicle 4, such as the speed, and transmits status information including information indicating whether the vehicle 4 is parked. For example, the control device 3 determines whether there is a malfunction in the first power storage device 11, and transmits status information including information indicating whether there is a malfunction in the first power storage device 11. The control device 3 determines whether there is a malfunction in the first power storage device 11 based on a signal output from the first power storage device 11 when a malfunction occurs in the first power storage device 11, a voltage applied from the first power storage device 11 to the first load 12, or the like.

[0038] For example, the control device 3 determines whether the first storage device 11 is sufficiently charged to supply power to the second load 14 or the second storage device 2, and transmits status information including information indicating whether the first storage device 11 is sufficiently charged. The control device 3 determines whether the first storage device 11 is sufficiently charged by, for example, estimating the SOC of the first storage device 11 according to the OCV (Open Circuit Voltage) of the first storage device 11. Furthermore, the control device 3 determines whether there is a malfunction in the DC-DC converter 13 based on a signal output from the DC-DC converter 13 when the DC-DC converter 13 fails, and transmits status information including information indicating whether there is a malfunction in the DC-DC converter 13. The control device 3 transmits the status information periodically or as needed. Alternatively, the BMU 22 may request the status information from the control device 3 periodically or as needed, and the control device 3 may transmit the status information in response to the request.

[0039] The calculation unit 221 of the BMU 22 determines whether or not it is possible to estimate the internal resistance of the plurality of power storage cells 21 based on the received state information (S2). Through the process of S2, the calculation unit 221 determines whether or not to start processing to lower the SOC of the plurality of power storage cells 21. For example, if the state information indicates that the vehicle 4 is not parked, the calculation unit 221 determines that it is not possible to estimate the internal resistance. When the vehicle 4 is not parked, the demand for power is high, and lowering the SOC of the plurality of power storage cells 21 may result in a shortage of power to be supplied. For example, if the state information indicates that the first power storage device 11 has a malfunction or is not sufficiently charged, the calculation unit 221 determines that it is not possible to estimate the internal resistance. When the first power storage device 11 has a malfunction or is not sufficiently charged, there is a risk that charging using power from the first power storage device 11 may not be possible. Furthermore, when a demand for power arises in the second load 14 while the SOC of the plurality of power storage cells 21 is lowered, there is a risk that power cannot be supplied from the first power storage device 11 to the second load 14.

[0040] For example, when the state information indicates that the DC-DC converter 13 has a malfunction, the calculation unit 221 determines that it is not possible to estimate the internal resistance. When the DC-DC converter 13 has a malfunction, there is a risk that power cannot be supplied from the first power storage device 11 to the second power storage device 2 or the second load 14 through the DC-DC converter 13. For example, when the vehicle 4 is parked, the first power storage device 11 and the DC-DC converter 13 have no malfunctions, and the first power storage device 11 is sufficiently charged, the calculation unit 221 determines that it is possible to estimate the internal resistance. Note that in S1, the control device 3 may determine whether it is possible to estimate the internal resistance based on the states of the vehicle 4 and the power storage system 1 and input determination information indicating the determination result to the BMU 22, and in S2, the calculation unit 221 may make a determination based on the determination information.

[0041] If it is determined that estimation of the internal resistance is not possible (S2: NO), the calculation unit 221 ends the process. If it is determined that estimation of the internal resistance is possible (S2: YES), the BMU 22 discharges the multiple storage cells 21 (S3). For example, the BMU 22 sends a control signal to the second load 14 to connect the second load 14 to the second power storage device 2, and supplies power from the multiple storage cells 21 to the second load 14, thereby discharging the multiple storage cells 21. The power storage system 1 may have a load that receives power from the second power storage device 2, separate from the second load 14, and the BMU 22 may supply power from the second power storage device 2 to a load separate from the second load 14. Power is consumed by a load external to the second power storage device 2, and the multiple storage cells 21 are discharged. Because the load is external to the second power storage device 2, it is easy to configure the load to consume power efficiently, for example, by increasing power consumption or heat dissipation efficiency. By supplying power to a load that efficiently consumes power, the power of the plurality of power storage cells 21 is efficiently consumed and the plurality of power storage cells 21 is reliably discharged. In addition, the time required to discharge the plurality of power storage cells 21 is shortened.

[0042] The second power storage device 2 may be configured to discharge the plurality of power storage cells 21 by causing a current to flow inside the BMU 22. FIG. 5 is a block diagram showing an example configuration of a BMU 22 that can cause a current to flow inside. The BMU 22 has a load 227a connected to both ends of the plurality of power storage cells 21 by a power line. A switch 227b is provided on the power line connecting the plurality of power storage cells 21 and the load 227a. The load 227a and the switch 227b form a load circuit 227. When the switch 227b is in an on state, a current flows from the plurality of power storage cells 21 to the load 227a. In S3, the calculation unit 221 turns the switch 227b on. By causing a current to flow from the plurality of power storage cells 21 to the load 227a, power is supplied from the plurality of power storage cells 21 to the load circuit 227. Power is consumed in the load circuit 227 inside the second power storage device 2, and the plurality of power storage cells 21 discharge. Even when the second power storage device 2 is not connected to an external load, the second power storage device 2 can discharge the plurality of power storage cells 21 by supplying power to the load circuit 227. Regardless of the state outside the second power storage device 2, the second power storage device 2 can discharge the plurality of power storage cells 21 by itself. Furthermore, since the second power storage device 2 discharges power without flowing current to an external load, the second power storage device 2 can reduce the external impact of the discharge.

[0043] The calculation unit 221 then determines the SOC of the multiple storage cells 21 and determines whether the SOC of the multiple storage cells 21 is less than the lower limit of a predetermined SOC range (S4). The predetermined SOC range is a range of the SOC of the multiple storage cells 21 used to estimate the internal resistance of the multiple storage cells 21 while charging. The upper and lower limit values ​​of the predetermined SOC range are the upper and lower limit values ​​of the SOC included in the predetermined SOC range. As will be described later, the predetermined SOC range is a range in which the change in OCV between both ends of the multiple storage cells 21 in response to a change in SOC is large. The predetermined SOC range is determined in advance. For example, the upper and lower limit values ​​of the SOC range are stored in advance in the storage unit 223.

[0044] For example, the calculation unit 221 estimates the SOC of the multiple storage cells 21 using a current integration method and compares the estimated SOC with the lower limit of a predetermined SOC range. The calculation unit 221 may estimate the SOC of the multiple storage cells 21 using other methods, such as the current integration method. The calculation unit 221 may estimate the SOC of the multiple storage cells 21 using methods other than the current integration method, such as a method based on a relationship between the SOC and the voltage during discharging, which is stored in advance in the storage unit 223. The calculation unit 221 may determine whether the SOC is equal to or lower than the lower limit of the SOC range. Alternatively, the calculation unit 221 may perform the process of S4 by comparing the acquired voltage with a voltage corresponding to the lower limit of the SOC range and determining whether the acquired voltage is lower than the voltage corresponding to the lower limit. The calculation unit 221 may determine whether the acquired voltage is equal to or lower than the voltage corresponding to the lower limit. Alternatively, the calculation unit 221 may determine whether the SOC is equal to or higher than the lower limit and equal to or lower than the upper limit of the SOC range. The calculation unit 221 may perform the process of S4 by comparing the acquired voltage with voltages corresponding to the upper and lower limits of the SOC range and determining whether the acquired voltage is equal to or greater than the voltage corresponding to the lower limit and less than the voltage corresponding to the upper limit. The calculation unit 221 may also determine whether the acquired voltage is equal to or greater than the voltage corresponding to the lower limit and less than the voltage corresponding to the upper limit.

[0045] If the SOC of the plurality of storage cells 21 is equal to or greater than the lower limit of the predetermined SOC range (S4: NO), the calculation unit 221 returns the process to S3, and the discharging of the plurality of storage cells 21 continues. If the SOC of the plurality of storage cells 21 is less than the lower limit of the predetermined SOC range (S4: YES), the calculation unit 221 ends the discharging and starts charging the plurality of storage cells 21 (S5). For example, the calculation unit 221 causes the communication unit 226 to transmit a control signal for starting charging to the control device 3. The control device 3 receives the control signal and controls the first storage device 11 and the DC-DC converter 13 in accordance with the control signal, thereby causing the first storage device 11 to supply power to the second storage device 2 through the DC-DC converter 13. The BMU 22 charges the plurality of storage cells 21 with power from the first storage device 11. The SOC of the plurality of storage cells 21 increases as a result of charging. At this time, the BMU 22 charges the plurality of storage cells 21 at least until the SOC of the plurality of storage cells 21 exceeds the lower limit of a predetermined SOC range. During charging, the SOC of the plurality of storage cells 21 falls within the predetermined SOC range. Therefore, charging is performed with the SOC of the plurality of storage cells 21 falling within the predetermined SOC range. During charging, the BMU 22 passes a large current through the plurality of storage cells 21. For example, the absolute value of the current flowing through the plurality of storage cells 21 during charging is greater than the absolute value of the current flowing during discharging. By passing a large current through the plurality of storage cells 21, charging progresses quickly, and the change over time in the voltage of the plurality of storage cells 21 increases.

[0046] FIG. 6 is a graph showing an example of the relationship between SOC and OCV. The horizontal axis of FIG. 6 represents the SOC of the multiple storage cells 21, in %, and the vertical axis represents the OCV across the multiple storage cells 21, in volts. FIG. 6 also shows an example of a predetermined SOC range. The range in which the SOC changes from 0% to 100% includes a range in which the OCV changes significantly with respect to changes in SOC, and a range in which the OCV changes only slightly with respect to changes in SOC. The SOC range in which the OCV changes significantly has a smaller SOC value than the SOC range in which the OCV changes only slightly.

[0047] As shown in FIG. 6 , the predetermined SOC range for estimating internal resistance is a range in which the OCV changes more significantly with respect to changes in SOC than a range with a higher SOC value. The upper and lower limits of the SOC range are predetermined so that the SOC range is a range in which the OCV changes more significantly with respect to changes in SOC. For example, the upper limit is the SOC value at which the rate of increase in OCV decreases to a predetermined value or less when the SOC is increased from zero. The lower limit is a value that exceeds zero but is less than the upper limit. The lower limit is preferably a value of a certain magnitude so that the storage cells 21 do not over-discharge when discharged. The SOC values ​​included in the predetermined SOC range are relatively small. The upper and lower limits of the SOC range may be set so that the SOC range is a range in which the OCV changes more significantly with respect to changes in SOC. The SOC range shown in FIG. 6 is an example. For example, the upper limit may be a value of 25% SOC and the lower limit may be a value of 5% SOC. The voltage generated across the multiple storage cells 21 during charging increases or decreases depending on the increase or decrease in OCV. If the change in OCV relative to the change in SOC is small, the voltage measured during charging will change little in response to the change in SOC due to charging. Because the change in the measured voltage is small, the effect of measurement error on the change in voltage will be large, and the estimation accuracy will be low when the internal resistance is calculated from the measured current and voltage values. If the change in OCV relative to the change in SOC is large, the voltage measured during charging will change little in response to the change in SOC due to charging. Because the effect of measurement error on the change in voltage will be small, the estimation accuracy will be high when the internal resistance is calculated from the measured current and voltage values.

[0048] While the multiple storage cells 21 are being charged with their SOCs within a predetermined SOC range, the BMU 22 acquires the current measured by the current sensor 23 via the interface unit 225 and acquires the voltage via the voltage acquisition unit 224, thereby measuring the current and voltage (S6). In S6, the BMU 22 measures the current flowing through the multiple storage cells 21 during charging and the voltage generated across the multiple storage cells 21 during charging. The BMU 22 measures the current and voltage at least once while the SOC is within the predetermined SOC range. It is desirable that the BMU 22 measure the current and voltage multiple times while the SOC is within the predetermined SOC range. While the SOC is within the predetermined SOC range, the voltage changes significantly in response to changes in SOC, so the current and voltage can be acquired in a state where the voltage changes significantly. The BMU 22 stores the measured current and voltage values ​​in the memory 222 or the storage unit 223. That is, the BMU 22 measures the current and voltage multiple times while the SOC is within the SOC range as the SOC increases. For example, the calculation unit 221 estimates the SOC using a current integration method, and when the estimated SOC is within the SOC range, stores the current and voltage values ​​in the memory 222 or the storage unit 223. When the multiple storage cells 21 are sufficiently charged, the BMU 22 ends charging. For example, when the SOC reaches a predetermined value between 80% and 100%, the BMU 22 ends charging.

[0049] The calculation unit 221 then calculates the internal resistance of the multiple storage cells 21 based on the measured current and voltage (S7). In S7, the calculation unit 221 calculates the value of the internal resistance based on the multiple current and voltage values ​​measured while the SOC is within the SOC range. For example, the calculation unit 221 estimates the SOC using a current integration method, and calculates the internal resistance using a least-squares method that utilizes the relationship between the OCV and the voltages and currents generated across the multiple storage cells 21 based on the OCV, measured voltages, and measured currents corresponding to the SOC. Through the calculation in S7, the BMU 22 estimates the internal resistance of the multiple storage cells 21. In S7, the calculation unit 221 may calculate the internal resistance using the current or voltage measured before the start of charging or the voltage estimated from the SOC, in addition to the current and voltage values ​​measured while the SOC is within the SOC range. The calculation unit 221 may calculate the internal resistance using the current and voltage values ​​measured once while the SOC is within the SOC range, and the current or voltage measured before the start of charging, or the voltage estimated from the SOC.

[0050] The calculation unit 221 stores the calculated value of internal resistance in the storage unit 223 (S8), and ends the process of estimating internal resistance. In S8, the calculation unit 221 may update the value of internal resistance stored in the storage unit 223. The BMU 22 executes the processes of S1 to S8 as needed. The value of internal resistance stored in the storage unit 223 can be used to estimate the full charge capacity of the multiple storage cells 21 or to determine the degradation state of the multiple storage cells 21.

[0051] FIG. 7 is a timing chart showing the timing of each process performed by the second power storage device 2. The horizontal axis represents elapsed time. FIG. 7 also shows the time changes of the SOC and current of the multiple power storage cells 21. Of the currents flowing through the multiple power storage cells 21, charging currents are shown as positive values, and discharging currents are shown as negative values. Initially, the current value is zero. The BMU 22 determines whether or not to perform internal resistance estimation and starts discharging. During discharging, a discharge current flows through the multiple power storage cells 21, and the SOC decreases. After determining that the SOC has fallen below the lower limit of the SOC range, the BMU 22 ends discharging. The decrease in SOC stops, and the current becomes zero. Next, the BMU 22 starts charging. During charging, a charging current flows through the multiple power storage cells 21, and the SOC increases. The absolute value of the charging current is greater than the absolute value of the discharging current. As the SOC increases, the BMU 22 measures the current and voltage multiple times while the SOC is increasing within the SOC range. When the plurality of storage cells 21 are fully charged, the BMU 22 terminates charging and calculates and stores the internal resistances of the plurality of storage cells 21.

[0052] As described above in detail, the second storage device 2 measures the current and voltage during the process of discharging to reduce the SOC of the multiple storage cells 21 and then charging to increase the SOC of the multiple storage cells 21. The second storage device 2 estimates the internal resistance by calculating the internal resistance of the multiple storage cells 21 based on the current and voltage measured while the SOC is increasing within a predetermined SOC range during charging. Within the predetermined SOC range, the voltage changes significantly with changes in SOC. Therefore, the voltage measured during charging changes significantly, and when the internal resistance is calculated using the measured current and voltage, the accuracy of estimating the internal resistance increases. Because the internal resistance is calculated after adjusting the SOC so that the change in voltage is large, the accuracy of estimating the internal resistance is always high, making it possible to estimate the internal resistance with stable high accuracy.

[0053] Furthermore, since the second storage device 2 is charged after lowering the SOC of the multiple storage cells 21, even if a large current is passed through the multiple storage cells 21 during charging, the multiple storage cells 21 are unlikely to be overcharged. Simply passing a large current through a storage element can result in overcharging or overdischarging. However, passing a large current through the storage element for charging when the SOC of the storage element is low reduces the likelihood of overcharging or overdischarging. Therefore, a large current can be passed through the second storage device 2, which does not experience a large current during cranking. By passing a large current through the multiple storage cells 21, charging progresses quickly, resulting in a large change in the measured voltage over time. This further increases the change in the voltage measured during charging, further improving the accuracy of estimating the internal resistance when calculating the internal resistance from the measured current and voltage values. In this way, the second storage device 2 can accurately estimate the internal resistance of the multiple storage cells 21 even when a large current does not flow due to discharging.

[0054] In the present embodiment, a configuration has been shown in which the internal resistance of a single energy storage element is estimated when a plurality of energy storage cells 21 connected in series are grouped together. Alternatively, the second energy storage device 2 may be configured to estimate the internal resistance of each of the energy storage cells 21. Alternatively, the energy storage element may include energy storage cells 21 connected in parallel.

[0055] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. In other words, embodiments obtained by combining technical means modified appropriately within the scope of the claims are also included in the technical scope of the present invention. [Explanation of symbols]

[0056] 1. Energy storage system 11 First power storage device 12 1st load 13 DC-DC converter (power transmission circuit) 14 2nd load 2 Second storage device 21 Energy storage cell (energy storage element) 22 BMU (Management Department) 227 Load circuit 227a load 227b switch 3. Control device 4 vehicles 50 Recording Media 51 Computer Programs

Claims

1. A power storage device including a power storage element and a management unit, the power storage device is an auxiliary battery that is not used to drive the vehicle or start the engine, but supplies power to electrical devices in the vehicle; The management unit By discharging the storage element, the SOC (State of Charge) of the storage element is reduced, In the process of increasing the SOC of the storage element by charging the storage element, a current and a voltage of the storage element are acquired while the SOC of the storage element is within a predetermined SOC range; Calculating the internal resistance of the energy storage element based on the acquired current and voltage; The SOC range is: A range in which the change in voltage of the storage element relative to the change in SOC of the storage element is larger than a range in which the SOC value is larger than the SOC range. Energy storage device.

2. The management unit reduces the SOC of the storage element to below a lower limit value of the SOC included in the SOC range during discharging, and increases the SOC of the storage element to a value that exceeds at least the lower limit value during charging. The power storage device according to claim 1 .

3. The management unit receives state information indicating an external state of the power storage device, and determines whether to start a process of reducing the SOC of the power storage element according to the state information. The power storage device according to claim 1 or 2.

4. The management unit causes the power storage element to discharge by supplying power from the power storage element to a load external to the power storage device. The electricity storage device according to claim 1 .

5. a load circuit; The management unit causes the storage element to discharge by supplying power from the storage element to the load circuit. The electricity storage device according to claim 1 .

6. The power supply is provided in an electric vehicle and supplies power to a 12V load of the electric vehicle. The power storage device according to claim 1 .

7. a first power storage device; a second power storage device that supplies power to a second load different from a first load to which the first power storage device supplies power; a power transmission circuit for supplying power from the first power storage device to the second power storage device, the second power storage device is an auxiliary battery that is not used to drive the vehicle or start the engine, but supplies power to electrical devices in the vehicle; The second power storage device is A storage element; and a management department. The management unit The SOC of the storage element is reduced by discharging the storage element; a process of increasing the SOC of the power storage element by supplying power from the first power storage device to the second power storage device via the power transmission circuit and charging the power storage element, acquiring a current and a voltage of the power storage element while the SOC of the power storage element is within a predetermined SOC range, and calculating an internal resistance of the power storage element based on the acquired current and voltage; The SOC range is: A range in which the change in voltage of the storage element relative to the change in SOC of the storage element is larger than a range in which the SOC value is larger than the SOC range. Energy storage system.

8. Further comprising a control device, the second load is connected to the second power storage device; the first power storage device is connected to the second load or the second power storage device via the power transmission circuit; the control device inputs, to the management unit, state information indicating whether a state of the first power storage device and / or the power transmission circuit is in a state in which power can be supplied from the first power storage device to the second load or the second power storage device; The management unit determines whether to start a process of reducing the SOC of the power storage element according to the state information. The power storage system according to claim 7 .

9. The power storage system is provided in a vehicle, The control device inputs, as the state information, information indicating whether the vehicle is parked or not to the management unit. The power storage system according to claim 8 .

10. The power storage system is provided in a vehicle, the first load includes an electric device used to drive or start the vehicle, the second load does not include any electrical equipment used to drive or start the vehicle; The second power storage device does not supply power to the first load. The power storage system according to any one of claims 7 to 9.

11. A method for estimating the internal resistance of a storage element provided in an auxiliary battery that is not used to drive a vehicle or start an engine but supplies power to electrical devices in a vehicle, comprising: The SOC of the storage element is reduced by discharging the storage element; In the process of increasing the SOC of the storage element by charging the storage element, a current and a voltage of the storage element are acquired while the SOC of the storage element is within a predetermined SOC range; Calculating the internal resistance of the energy storage element based on the acquired current and voltage; The SOC range is a range in which the change in voltage of the storage element relative to the change in SOC of the storage element is larger than a range in which the SOC value is higher than the SOC range. Internal resistance estimation method.

12. A computer program that causes a computer to execute a process for estimating the internal resistance of a storage element provided in an auxiliary battery that is not used to drive a vehicle or start an engine but that supplies power to electrical devices in a vehicle, comprising: The SOC of the storage element is reduced by discharging the storage element; acquiring a current and a voltage of the storage element while the SOC of the storage element is within a predetermined SOC range in which a change in voltage of the storage element relative to a change in SOC of the storage element is larger than in other ranges during the process of increasing the SOC of the storage element by charging the storage element; Calculating the internal resistance of the storage element based on the acquired current and voltage A computer program that causes a computer to perform a process.

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