Voltage calculation system

Abstract

The present invention provides a voltage calculation system that can suppress the time required to complete the estimation of the open-circuit voltage of an energy storage device while also suppressing inaccuracies in the estimation of the open-circuit voltage. [Solution] The OCV calculation system 100 includes a charger / discharger 20 connected to the battery 40 and configured to generate a ripple current in the battery 40, and a BMS 30 and ECU 10 that detect the voltage of the battery 40. The ECU 10 acquires an IV plot that includes current IB information of the ripple current and information of the CCV voltage VB when the ripple current is being generated, and calculates the internal resistance value R of the battery 40 based on the acquired IV plot. The ECU 10 calculates the OCV of the battery 40 based on the calculated internal resistance value R.

Description

Technical Field

[0001] The present disclosure relates to a voltage calculation system.

Background Art

[0002] Japanese Patent Application Laid-Open No. 2016-201984 (Patent Document 1) discloses a method for estimating the open circuit voltage (OCV) of a power storage device. In Patent Document 1, it is described that after charging or discharging of the power storage device is completed, the open circuit voltage is estimated after the elapse of a polarization dissipation time during which polarization can be considered to have disappeared.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As described in Patent Document 1 above, when estimating the open circuit voltage after the elapse of the polarization dissipation time of the power storage device, it is considered that the time required to complete the estimation of the open circuit voltage becomes long. On the other hand, it is conceivable to calculate the open circuit voltage based on the internal resistance value of the power storage device. In this case, the internal resistance value is calculated based on the change in the closed circuit voltage when the current value supplied to the power storage device is changed. However, at this time, there is a risk that further polarization may occur in the power storage device due to the supply of current to the power storage device. Due to this, since the electromotive force of the power storage device fluctuates, it is considered that the calculated internal resistance value becomes inaccurate. In this case, the calculated open circuit voltage becomes inaccurate.

[0005] This disclosure was made to solve the above-mentioned problems, and its purpose is to provide a voltage calculation system that can suppress inaccuracies in the estimation of the open-circuit voltage of an energy storage device while suppressing the time required to complete the estimation of the open-circuit voltage of the energy storage device. [Means for solving the problem]

[0006] A voltage calculation system according to one aspect of this disclosure comprises a ripple generation device connected to a power storage device and configured to generate a ripple current in the power storage device, a voltage detection device for detecting the voltage of the power storage device, and a calculation device. The voltage when no load is connected to the power storage device is defined as the open-circuit voltage, and the voltage of the power storage device when a load is connected is defined as the closed-circuit voltage. The voltage detection device detects the closed-circuit voltage. The calculation device acquires current-voltage information including information on the current value of the ripple current and information on the voltage value of the closed-circuit voltage when the ripple current is being generated, and calculates the internal resistance value of the power storage device based on the acquired current-voltage information. The calculation device calculates the open-circuit voltage of the power storage device based on the calculated internal resistance value.

[0007] In a voltage calculation system relating to one aspect of this disclosure, as described above, the internal resistance value is calculated based on current-voltage information acquired when a ripple current is flowing, and the open-circuit voltage is calculated based on the calculated internal resistance value. As a result, supplying a ripple current (alternating current) to the energy storage device suppresses polarization in the energy storage device compared to when a direct current is supplied to the energy storage device. Consequently, inaccuracies in the calculated internal resistance value can be suppressed, and therefore inaccuracies in the open-circuit voltage calculated based on the internal resistance value can be suppressed. Furthermore, by calculating the open-circuit voltage using the internal resistance value, the open-circuit voltage can be estimated more quickly than waiting for the polarization to be resolved before estimating the open-circuit voltage. Therefore, the open-circuit voltage can be accurately estimated while suppressing the time required to complete the estimation of the open-circuit voltage of the energy storage device.

[0008] In the voltage calculation system relating to the first aspect described above, preferably, the calculation device calculates a converged value of the closed-circuit voltage based on the fluctuation of the closed-circuit voltage after the ripple current has stopped, and determines the open-circuit voltage based on at least one of the converged value and the open-circuit voltage calculated based on the ripple current when the magnitude of the difference between the converged value and the open-circuit voltage calculated based on the ripple current is smaller than a predetermined threshold. Here, the converged value of the closed-circuit voltage after the ripple current has been applied is a value based on the magnitude of the open-circuit voltage. Therefore, when the open-circuit voltage predicted based on the converged value and the open-circuit voltage calculated based on the internal resistance value are relatively close, it is considered that each value is relatively close to the open-circuit voltage. Therefore, when the magnitude of the difference is smaller than a predetermined threshold, it is easy to suppress inaccuracies in the estimation of the open-circuit voltage by determining the open-circuit voltage based on at least one of the converged value and the open-circuit voltage calculated based on the ripple current.

[0009] In this case, preferably, the ripple generation device supplies a re-ripple current with an amplitude different from the amplitude of the ripple current to the energy storage device when the difference is greater than or equal to a predetermined threshold. The calculation device acquires re-current voltage information, which includes information on the current value of the re-ripple current and information on the voltage value of the closed-circuit voltage when the re-ripple current is being generated, and calculates the internal resistance value of the energy storage device based on the acquired re-current voltage information. The calculation device calculates the open-circuit voltage of the energy storage device based on the internal resistance value calculated based on the re-current voltage information. With this configuration, the internal resistance value can be recalculated using the re-ripple current when the difference is greater than or equal to a predetermined threshold. This makes it possible to further suppress inaccuracies in the estimation of the open-circuit voltage compared to when the open-circuit voltage is estimated using only the internal resistance value calculated when the difference is less than a predetermined threshold.

[0010] In a voltage calculation system that calculates the open-circuit voltage using the above-described re-ripple current, preferably, the ripple generation device sets the frequency of the re-ripple current to be different from the frequency of the ripple current. With this configuration, it is possible to suppress the re-current voltage information obtained when the re-ripple current is flowing from being the same as the current voltage information obtained when the ripple current is flowing. As a result, the amount of information used to estimate the open-circuit voltage can be increased.

[0011] In the voltage calculation system relating to the first aspect described above, preferably, the calculation device estimates that the acquired closed-circuit voltage is the open-circuit voltage when a predetermined time has elapsed since the battery-mounted device equipped with the energy storage device was last turned off, and performs a process to calculate the open-circuit voltage using ripple current when the predetermined time has not elapsed since the battery-mounted device was last turned off. Here, when a predetermined time has elapsed since the battery-mounted device was last turned off, there is a higher probability that the polarization of the energy storage device has been resolved compared to when the predetermined time has not elapsed since the battery-mounted device was last turned off. Therefore, the process of calculating the open-circuit voltage using ripple current when there is a high probability that the polarization of the energy storage device has been resolved can be suppressed. This reduces the processing load on the voltage calculation system. [Effects of the Invention]

[0012] According to this disclosure, it is possible to suppress the inaccuracy of the open-circuit voltage estimation while suppressing the time required to complete the estimation of the open-circuit voltage of the energy storage device. [Brief explanation of the drawing]

[0013] [Figure 1] This figure shows a vehicle equipped with the OCV calculation system according to this embodiment. [Figure 2] This figure shows the ripple current and the CCV when a ripple current is being generated. [Figure 3] This is a flowchart illustrating the control used by the ECU to calculate OCV according to this embodiment. [Figure 4] This figure shows an example of an IV plot. [Figure 5] This flowchart shows a modified example of the control method used by the ECU to calculate OCV. [Modes for carrying out the invention]

[0014] 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.

[0015] Figure 1 shows a vehicle 200 equipped with an OCV calculation system 100 according to an embodiment of this disclosure. The vehicle 200 and the OCV calculation system 100 are examples of the "battery mounting device" and "voltage calculation system" of this disclosure, respectively.

[0016] Vehicle 200 is electrically connected to power stand 300 via cable 310, enabling power exchange (charging and discharging) between the vehicle and power stand 300. This power exchange takes place with a plug 311 at the end of cable 310 connected to the inlet 210 of vehicle 200. Alternating current flows between power stand 300 and vehicle 200. Power stand 300 exchanges power with the power grid PG.

[0017] Vehicle 200 is equipped with an OCV calculation system 100, an MG (Motor Generator) 220, and a PCU (Power Control Unit) 230.

[0018] The OCV calculation system 100 includes an ECU (Electronic Control Unit) 10, a charger 20, a BMS (Battery Management System) 30, a battery 40, an SMR (System Main Relay) 50, and a relay 60. Note that the ECU 10 and the battery 40 are examples of the "calculation device" and the "power storage device" of the present disclosure, respectively. Also, the BMS 30 and the charger 20 are examples of the "voltage detection device" and the "ripple generation device" of the present disclosure, respectively.

[0019] The ECU 10 includes a processor 11, a RAM (Random Access Memory) 12, and a storage device 13. The storage device 13 is configured to be able to store the stored information. In addition to the program, information used in the program (for example, maps, mathematical formulas, and various parameters) is stored in the storage device 13. In the present embodiment, by the processor 11 executing the program stored in the storage device 13, various processes (for example, OCV calculation process) by the ECU 10 are executed. However, these processes may be executed only by hardware (electronic circuit) without using software.

[0020] The vehicle 200 is configured to be able to run using the electric power stored in the battery 40. The vehicle 200 is, for example, a battery electric vehicle (BEV) without an engine (internal combustion engine). However, it is not limited to this, and the vehicle 200 may be a PHEV (plug-in hybrid vehicle) with an internal combustion engine, or may be another electric vehicle (xEV).

[0021] The battery 40 includes a power storage cell 41 that is a secondary battery, an internal resistance 42, a capacitor 43, a first terminal 44, and a second terminal 45. The power storage cell 41 is, for example, a lithium-ion battery. Each of the first terminal 44 and the second terminal 45 is connected to the SMR 50. Note that the configuration of the battery 40 is not limited to the above example.

[0022] The BMS30 monitors the status of the battery 40. Specifically, the BMS30 includes various sensors that detect the status of the battery 40 (e.g., voltage, current, and temperature), and a monitoring IC (integrated circuit) that receives the detection signals from the various sensors.

[0023] The BMS30 can detect the terminal voltage between the first terminal 44 and the second terminal 45. In the following, the terminal voltage when no load is connected to the battery 40 will be referred to as the open circuit voltage (OCV). The terminal voltage when a load is connected to the battery 40 will be referred to as the closed circuit voltage (CCV).

[0024] The charger / discharger 20 and relay 60 are located between the inlet 210 and the battery 40. Each of the charger / discharger 20 and relay 60 is controlled by the ECU 10. In this embodiment, the charge / discharge line, including the inlet 210, charger / discharger 20, and relay 60, is connected between the SMR 50 and the PCU 230. However, it is not limited to this, and the charge / discharge line may be connected between the battery 40 and the SMR 50.

[0025] The charger / discharger 20 charges the battery 40 using power input to the inlet 210 from outside the vehicle. The charger / discharger 20 includes a power conversion circuit (e.g., an inverter and converter) and is configured to adjust the charging current. The relay 60 switches the connection / disconnection of the circuit from the inlet 210 to the battery 40.

[0026] In the plugged-in vehicle 200, external charging (i.e., charging of the battery 40 with power from outside the vehicle) and external discharging (i.e., discharging of power from the battery 40 to the outside of the vehicle) are possible. Note that the vehicle 200 may also be capable of performing only external charging. When external charging and external discharging are performed, the relay 60 is set to a closed state (connected state), and when external charging and external discharging are not performed, the relay 60 is set to an open state (disconnected state).

[0027] The MG220 is, for example, a three-phase AC motor generator. The MG220 functions as a drive motor for the vehicle 200. The MG220 is driven by the PCU230 and rotates the drive wheels of the vehicle 200. The MG220 also performs regenerative power generation and outputs the generated power to the battery 40. The number of drive motors equipped on the vehicle 200 is arbitrary.

[0028] The PCU230 includes a circuit (e.g., an inverter and converter) that drives the MG220 using power supplied from the battery 40. The SMR50 switches the connection / disconnection of the circuit from the battery 40 to the PCU230. Both the SMR50 and the PCU230 are controlled by the ECU10. The SMR50 is closed (connected) when the vehicle 200 is running. The SMR50 is also closed when power is exchanged between the battery 40 and the inlet 210 (and thus outside the vehicle).

[0029] Figure 2 shows the current applied to the battery 40 (including the ripple current described later) and the CCV when this current is being generated. Figure 2 shows an example in which a ripple current is flowing while the charging current is being applied to the battery 40. The ripple current shown in Figure 2 is a rectangular wave AC current in which the maximum value of the current value (hereinafter referred to as current IB) is Ia and the minimum value of current IB is 0.

[0030] The ripple current may be generated by the ECU 10 controlling the charger / discharger 20. For example, the ripple current may be generated by switching the on / off state of a switching element of a converter (not shown) provided in the charger / discharger 20. However, the method of generating the ripple current is not limited to this example.

[0031] Figure 2 illustrates an example in which a ripple current is generated at time t1, and then the ripple current is stopped at time t2. The voltage value of the CCV (hereinafter referred to as voltage VB) repeatedly increases and decreases in conjunction with the fluctuations of the ripple current while the ripple current is applied to the battery 40.

[0032] In conventional systems, OCV (Operating Curve Value) is estimated after the depolarization time of the energy storage device has elapsed. In this case, it is thought that the time required to complete the OCV estimation will be long. In contrast, it is conceivable to calculate the OCV based on the internal resistance value of the energy storage device. In this case, the internal resistance value is calculated based on the change in the magnitude of the CCV (Control Curve Value) when the magnitude of the current (DC current) supplied to the energy storage device is changed. However, in this case, there is a risk that further polarization will occur in the energy storage device due to the supply of current. As a result, the electromotive force of the energy storage device will fluctuate, and it is thought that the calculated internal resistance value will be inaccurate. In this case, the calculated OCV will be inaccurate.

[0033] Therefore, in this embodiment, the ECU 10 calculates the internal resistance value R of the battery 40 (resistance value of internal resistance 42) based on the current IB information of the ripple current and the voltage VB information of the CCV when the ripple current is being generated. Then, the ECU 10 calculates the OCV of the battery 40 based on the calculated internal resistance value R.

[0034] Specifically, if battery 40 is being charged, the OCV is calculated based on the following formula (1). If battery 40 is being discharged, the OCV is calculated based on the following formula (2). OCV = VB - IB × R ... (1) OCV = VB + IB × R ... (2)

[0035] (Control flow) Referring to Figure 3, an example of a control flow showing how the ECU 10 calculates the OCV will be explained. The flow shown in Figure 3 may be executed at predetermined intervals while the battery 40 is charging (or discharging).

[0036] In step S1, the ECU 10 determines whether a predetermined time (for example, several hours) has elapsed since the last time the vehicle 200 was turned off. Turning off the vehicle 200 may include, for example, turning off the SMR50. The time when the vehicle 200 (SMR50) was last turned off may be stored in the storage device 13 of the ECU 10. If a predetermined time has elapsed since the last time the vehicle 200 was turned off (Yes in S1), the process proceeds to step S17. If a predetermined time has not elapsed since the last time the vehicle 200 was turned off (No in S1), the process proceeds to step S2.

[0037] In step S2, the ECU 10 controls, for example, the charger / discharger 20 to generate a ripple current (Figure 2). This generated ripple current is then applied to the battery 40. At this time, the frequency and amplitude of the ripple current are fixed to a constant value.

[0038] In step S3, the ECU 10 acquires information on the current IB of the ripple current and information on the voltage VB of the CCV while the ripple current is flowing. The ECU 10 may acquire information on the current IB and voltage VB at a frequency shorter than the frequency of the ripple current while the ripple current is applied to the battery 40. Based on the acquired information, the ECU 10 creates an IV plot (Figure 4) showing the relationship between the current IB and the voltage VB. The number of measurement points in the IV plot acquired in step S3 may be 1 or 2 or more. The IV plot is an example of the "current-voltage information" in this disclosure.

[0039] In step S4, the ECU 10 determines whether the number of measurement points in the IV plot acquired in step S3 is 300 or more. If the number of measurement points is 300 or more (Yes in S4), the process proceeds to step S5. If the number of measurement points is less than 300 (No in S4), the process returns to step S3.

[0040] In step S5, the ECU 10 calculates the internal resistance R of the battery 40 based on the IV plot obtained in step S3. Specifically, as shown in Figure 4, the ECU 10 calculates a linear function f1 using the least squares method based on the current IB and voltage VB at each measurement point. The ECU 10 determines that the value of the slope of the linear function f1 is the internal resistance R.

[0041] In step S6, the ECU10 calculates the OCV based on the internal resistance value R calculated in step S5. The OCV is calculated using equations (1) and (2) above.

[0042] In step S7, the ECU 10 stops applying the ripple current. Specifically, the ECU 10 controls the charger / discharger 20 so that the current IB is maintained at 0. In the example shown in Figure 2, the ECU 10 maintains the current IB at 0 from time t2 to time t3. The length between time t2 and time t3 may be greater than, for example, the length of half a cycle of the ripple current (for example, more than twice as long).

[0043] In step S8, the ECU10 calculates the converged value of the CCV (voltage VB). Specifically, the ECU10 calculates (predicts) the converged value of the CCV based on the fluctuation of voltage VB after the ripple current has stopped in step S7. More specifically, the ECU10 calculates the converged value based on a function f2 (Figure 2) that shows the change in voltage VB with respect to time from time t2 to time t3 when the ripple current has stopped. For example, the ECU10 may calculate the converged value by using the least squares method based on the function f2. Note that the method for calculating the converged value is not limited to this example.

[0044] In step S9, the ECU 10 determines whether the magnitude (absolute value) of the difference D between the OCV calculated in step S6 and the converged CCV calculated in step S8 is less than threshold A. If the magnitude of the difference D is less than threshold A (Yes in S9), the process proceeds to step S17. If the magnitude of the difference D is greater than or equal to threshold A (No in S9), the process proceeds to step S10. Threshold A may be, for example, a predetermined percentage (e.g., 5%) of the OCV calculated in step S6 (or the CCV calculated in step S8), or a pre-set fixed value. Threshold A is an example of a "predetermined threshold" in this disclosure.

[0045] In step S10, the ECU 10 generates a ripple current again and applies the ripple current to the battery 40 again. The ripple current generated in step S10 is an example of the "re-ripple current" as defined in this disclosure.

[0046] In step S11, the ECU 10 changes the frequency of the ripple current in step S10 from the frequency of the ripple current applied to the battery 40 in step S2. The ECU 10 may also change the frequency of the ripple current by adjusting the switching period of the switching element included in the charger / discharger 20 (for example, the converter). If the process in step S11 is executed multiple times, the ripple current frequencies set in each step S11 may be adjusted to be different from each other.

[0047] In step S12, the ECU 10 changes the amplitude of the ripple current in step S10 from the amplitude of the ripple current applied to the battery 40 in step S2. The ECU 10 may also change the amplitude of the ripple current by controlling the charger / discharger 20 (for example, a converter). If the process in step S12 is executed multiple times, the amplitudes of the ripple current set in each step S12 may be adjusted to be different from each other.

[0048] In step S13, the ECU 10 acquires an IV plot based on the ripple current applied to the battery 40 in step S10, similar to step S3. The IV plot acquired in step S13 is an example of the "recurrent voltage information" in this disclosure.

[0049] In step S14, the ECU 10, similar to step S4, determines whether the number of measurement points in the IV plot acquired in step S13 is 300 or more. If the number of measurement points is 300 or more (Yes in S14), the process proceeds to step S15. If the number of measurement points is less than 300 (No in S14), the process returns to step S11. Alternatively, if the number of measurement points is less than 300 (No in S14), the process may return to step S12 or S13.

[0050] In step S15, the ECU 10 calculates the internal resistance R of the battery 40 based on the IV plot obtained in step S13. Specifically, the ECU 10 uses the IV plot obtained in step S3 and the IV plot obtained in step S13 to calculate a linear function f1 (Figure 4) based on the least squares method. The ECU 10 determines that the value of the slope of the linear function f1 is the internal resistance R.

[0051] In step S16, the ECU10 calculates the OCV based on the internal resistance value R calculated in step S15, similar to step S6.

[0052] In step S17, the ECU10 determines the OCV. Specifically, if the answer in step S1 was "Yes," the ECU10 determines that the OCV is the CCV (OCV = CCV).

[0053] Furthermore, in step S17, if the ECU 10 determines Yes in step S9, it determines the OCV based on the converged value of the OCV calculated in step S6 and the CCV calculated in step S8. For example, the ECU 10 may determine that the OCV is the average value of the OCV calculated in step S6 and the converged value of the CCV calculated in step S8. Alternatively, the ECU 10 may determine that the OCV is the converged value of the OCV calculated in step S6 or the CCV calculated in step S8.

[0054] Furthermore, in step S17, if the process in step S16 has been executed, the ECU 10 may determine that the value calculated in step S16 is the OCV.

[0055] As described above, in this embodiment, the ECU 10 calculates the internal resistance R of the battery 40 based on an IV plot that includes information on the ripple current IB and the voltage VB of the CCV when the ripple current is being generated, and calculates the OCV of the battery 40 based on the calculated internal resistance R. As a result, supplying a ripple current (alternating current) to the battery 40 suppresses polarization in the battery 40 compared to when a DC current is supplied to the battery 40. Consequently, it is possible to suppress changes in the electromotive force of the battery 40 due to polarization while the ripple current is flowing. This prevents the internal resistance R calculated using the IV plot from becoming an inappropriate value.

[0056] This method helps prevent inaccuracies in the calculated internal resistance value, thus preventing inaccuracies in the open-circuit voltage calculated based on the internal resistance value. Furthermore, calculating the open-circuit voltage using the internal resistance value allows for faster estimation than waiting for polarization to dissipate before estimating the open-circuit voltage. Therefore, it is possible to accurately estimate the open-circuit voltage while minimizing the time required to complete the estimation of the open-circuit voltage of the energy storage device. This also helps prevent inaccuracies in the OCV calculated based on the internal resistance value R. Consequently, it is possible to accurately estimate the OCV of battery 40 while minimizing the time required to complete the estimation of the OCV.

[0057] <Variation> Figure 5 shows a modified version of the flow in Figure 3. The control flow shown in Figure 5 differs from the control flow in Figure 3 in that steps S21 to S24 are provided instead of step S17 in Figure 3.

[0058] First, in the flow chart of Figure 5, if step S1 is Yes, and if step S9 is Yes, the process proceeds to step S24. Also, the process of step S21 is executed after step S16.

[0059] In step S21, the ECU 10, similar to step S7, stops the ripple current applied to the battery 40 in step S10.

[0060] In step S22, the ECU10 calculates the converged value of the CCV (voltage VB) based on the fluctuation of the CCV after the ripple current has been stopped, similar to step S8.

[0061] In step S23, the ECU 10, similar to step S9, determines whether the magnitude (absolute value) of the difference D between the OCV calculated in step S16 and the converged CCV calculated in step S22 is less than the threshold B. If the magnitude of the difference D is less than the threshold B (Yes in S23), the process proceeds to step S24. If the magnitude of the difference D is greater than or equal to the threshold B (No in S23), the process returns to step S11. Note that the threshold B may be different from (for example, smaller than) or equal to the threshold A.

[0062] In step S24, the ECU 10 determines the OCV. Specifically, if the answer in step S23 is Yes, the ECU 10 determines the OCV based on the OCV calculated in step S16 and the converged value of the CCV calculated in step S22. Note that the processing in step S24 when step S1 is Yes and when step S9 is Yes is the same as in step S17 in Figure 3.

[0063] In the above embodiment, an example was shown in which it is determined whether or not to supply ripple current to the battery 40 again based on the magnitude of the difference between the OCV calculated from the internal resistance value R and the converged CCV, but the disclosure is not limited thereto. In step S6, the OCV calculated from the internal resistance value R may be determined as the OCV of the battery 40. In other words, steps S7 to S16 may not be provided.

[0064] In the above embodiment, an example was shown in which the frequency of the ripple current is changed in step S11 and the amplitude of the ripple current is changed in step S12, but the disclosure is not limited thereto. For example, either one or both of steps S11 and S12 may not be performed.

[0065] In the above embodiment, an example was shown in which the measured CCV is determined to be OCV if a predetermined time has elapsed since the last time the vehicle 200 (SMR50) was turned off, but the disclosure is not limited thereto. Regardless of the elapsed time since the last time the vehicle 200 (SMR50) was turned off, a process may be performed to calculate the OCV using the internal resistance value R calculated from the ripple current.

[0066] In the above embodiment, an example was shown in which a ripple current is generated using the current (charging current or discharging current) flowing between the inlet 210 and the battery 40, but the disclosure is not limited thereto. For example, by turning off the inverter provided in the charger / discharger 20 or PCU 230, a closed circuit including the converter provided in the charger / discharger 20 or PCU 230 and the battery 40 may be formed. In this state, a ripple current may be generated in the closed circuit by switching the switching element of the converter. The ripple current generated in this way may also be used to heat the battery (for example, to raise the temperature of the battery before charging).

[0067] In the above embodiment, an example was shown in which the OCV calculation system 100 is mounted on a vehicle, but the disclosure is not limited thereto. The OCV calculation system 100 may be mounted on a device other than a vehicle (for example, a stationary energy storage device).

[0068] In the above embodiment, an example was shown in which the device (ECU10) for calculating OCV is provided in the vehicle 200, but the disclosure is not limited thereto. The device for calculating OCV may be provided outside the vehicle. In this case, the device obtains information such as current IB and voltage VB from the vehicle by communication.

[0069] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure 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]

[0070] 10 ECU (Calculation Unit), 20 Charger / Discharger (Ripple Generation Device), 30 BMS (Voltage Detection Device), 40 Battery (Energy Storage Device), 100 OCV Calculation System (Voltage Calculation System), 200 Vehicle (Battery Mounting Device).

Claims

1. A ripple generation device connected to a power storage device and configured to generate a ripple current in the power storage device, A voltage detection device for detecting the voltage of the aforementioned energy storage device, A calculation device is provided, If we define the voltage when no load is connected to the energy storage device as the open-circuit voltage, and the voltage of the energy storage device when the load is connected as the closed-circuit voltage, The voltage detection device detects the closed-circuit voltage, The calculation device is, The current-voltage information is obtained, which includes information on the current value of the ripple current and information on the voltage value of the closed-circuit voltage when the ripple current is being generated. Based on the acquired current and voltage information, the internal resistance value of the energy storage device is calculated. The calculation device is a voltage calculation system that calculates the open-circuit voltage of the energy storage device based on the calculated internal resistance value.

2. The calculation device is, Based on the fluctuation of the closed-circuit voltage after the ripple current has stopped, the convergence value of the closed-circuit voltage is calculated. The voltage calculation system according to claim 1, wherein, when the magnitude of the difference between the convergence value and the open-circuit voltage calculated based on the ripple current is smaller than a predetermined threshold, the open-circuit voltage is determined based on at least one of the convergence value and the open-circuit voltage calculated based on the ripple current.

3. The ripple generation device, when the difference is greater than or equal to the predetermined threshold, supplies a re-ripple current with an amplitude different from the amplitude of the ripple current to the energy storage device. The calculation device is, Recurrent voltage information is obtained, which includes information on the current value of the re-ripple current and information on the voltage value of the closed-circuit voltage when the re-ripple current is being generated. Based on the acquired recurrent voltage information, the internal resistance value of the energy storage device is calculated. The voltage calculation system according to claim 2, wherein the calculation device calculates the open-circuit voltage of the energy storage device based on the internal resistance value calculated based on the recurrent voltage information.

4. The voltage calculation system according to claim 3, wherein the ripple generation device makes the frequency of the re-ripple current different from the frequency of the ripple current.

5. The calculation device is, If a predetermined time has elapsed since the battery-mounted device equipped with the aforementioned energy storage device was last turned off, the acquired closed-circuit voltage is estimated to be the open-circuit voltage. A voltage calculation system according to any one of claims 1 to 4, wherein if the predetermined time has not elapsed since the battery-mounted device was last turned off, a process is executed to calculate the open-circuit voltage using the ripple current.

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