State of charge estimation device, power grid system

Abstract

To provide a technique capable of identifying a variation in hysteresis shape due to the deterioration state of a storage battery, and precisely estimating the state of charge of the storage battery based on the same.SOLUTION: A charge state estimation device in an embodiment is configured to calculate the virtual resistance component that affects the output voltage of the storage battery and the hysteresis characteristics of the state of charge and fluctuates due to the deterioration state of the storage battery, calculate the open circuit voltage of the storage battery by using the internal resistance of the storage battery and the virtual resistance component, and estimate the state of charge of the storage battery using the open circuit voltage.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a technique for estimating the state of charge of a storage battery. [Background technology]

[0002] In recent years, with the spread of renewable energy, battery storage systems are expected to make a significant contribution to solving environmental problems from the perspective of energy storage and adjustment. In microgrids that use photovoltaic power generation and battery storage systems as power sources, a stable power supply is an issue. The amount of power generated by photovoltaic power generation fluctuates greatly depending on the time and weather. It is necessary to accurately control the charging and discharging from the battery storage system to compensate for this fluctuation.

[0003] The following non-patent document 1 describes a method for estimating the state of charge (SOC) of a storage battery system. The document describes a method for calculating the SOC based on the integral value of the current flowing through the storage battery system. The document also describes a method for calculating the SOC based on the voltage and resistance of the storage battery system. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Martin Murnane, et al. “A Closer Look at State of Charge (SOC) and State of Health (SOH)Estimation Techniques for Batteries”, Analog Devices, pp. 2-9, May 2017 Summary of the Invention [Problem to be solved by the invention]

[0005] It is known that the relationship between the output voltage and the state of charge of a storage battery has a hysteresis characteristic during charging and discharging. For example, this hysteresis characteristic is formed so that the output voltage during discharging is lower than the open circuit voltage. Until now, it was thought that such a difference between the open circuit voltage and the hysteresis voltage was caused by the internal resistance of the storage battery. However, the present inventor has found that this difference varies depending on the deterioration state of the storage battery, and that a drop in the hysteresis voltage occurs due to the deterioration state, in addition to the difference that has been thought of as a voltage drop from the open circuit voltage.

[0006] Conventional techniques such as those described in Non-Patent Document 1 do not recognize the voltage drop of the hysteresis voltage caused by such a deterioration state, and therefore may inaccurately identify the output voltage of the battery, which is believed to reduce the accuracy of estimating the state of charge.

[0007] The present invention has been made based on the above-mentioned findings, and aims to provide a technology that can identify fluctuations in the hysteresis shape caused by the deterioration state of a storage battery and, based on this, can accurately estimate the state of charge of the storage battery. [Means for solving the problem]

[0008] The state of charge estimation device of the present invention calculates a virtual resistance component that affects the output voltage and hysteresis characteristics of a storage battery and fluctuates due to the deterioration state of the storage battery, calculates the open circuit voltage of the storage battery using the internal resistance of the storage battery and the virtual resistance component, and estimates the state of charge of the storage battery using the open circuit voltage. Effect of the Invention

[0009] According to the state-of-charge estimating device of the present invention, even if the hysteresis shape fluctuates due to the deterioration state of the storage battery, the fluctuation can be identified and the state of charge of the storage battery can be accurately estimated based on the fluctuation. [Brief description of the drawings]

[0010] [Figure 1] 1 is a graph illustrating the hysteresis characteristics of a storage battery. [Diagram 2] 2 is an enlarged view of the vicinity of the end of the discharge operation (near the left end of the discharge operation in FIG. 1) in the hysteresis characteristic of FIG. 1. [Diagram 3] 1 is a configuration diagram of a state-of-charge estimating device 100 according to a first embodiment. [Figure 4] 1 is a graph plotting the relationship between the virtual resistance component Rbat and SOH. [Diagram 5] 1 is a graph illustrating the relationship between the open circuit voltage Vocv and the SOC of the storage battery system 200. [Figure 6] FIG. 2 is a diagram showing the module configuration of a calculation unit 110. [Figure 7] 1 shows an example of a module configuration of a calculation unit 110 in the second embodiment. [Figure 8] 11 is a diagram for explaining a procedure in which the SOH-Rbat conversion unit 111 calculates Rbat. FIG. [Figure 9] 11 is a diagram for explaining a procedure in which a Vocv-SOC conversion unit 113 acquires an SOC. FIG. [Figure 10] 1 shows the hysteresis characteristics between Vbat and SOC during charging and discharging operations of the storage battery system 200. [Figure 11] 11 is a graph illustrating changes in Vbat and Ibat when a current command is changed. [Figure 12] 10 is a flowchart illustrating an operation of the state-of-charge estimating device 100 in the fourth embodiment. [Figure 13] 1 is a graph illustrating the difference between measured and estimated Vocv values. [Figure 14] 13 is a flowchart illustrating the operation of the state-of-charge estimating device 100 in the fifth embodiment. [Figure 15] A concrete example of correcting the function describing the relationship between Rbat and SOH is given. [Figure 16] 10 is a flowchart illustrating a procedure for calculating the SOH by a calculation unit 110. [Figure 17] 1 is a graph showing changes over time in the current and voltage output by the storage battery system 200 during a rest period after discharging. [Figure 18] 1 is a graph showing changes over time in the current and voltage output by the storage battery system 200 during a rest period after charging. [Figure 19] 13 is a diagram showing a configuration of a relational table 121 and an example of data. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] <About the hysteresis characteristics of storage batteries> In order to facilitate understanding of the present invention, the hysteresis characteristics of the output voltage and state of charge of the storage battery will be described below first, and then the fluctuation of the hysteresis voltage due to the deterioration state of the storage battery will be described.

[0012] Fig. 1 is a graph illustrating the hysteresis characteristic of a storage battery. It is generally known that a storage battery has a hysteresis characteristic as shown in Fig. 1 in the output voltage Vbat and the state of charge SOC during the charging and discharging operations.

[0013] Figure 2 is an enlarged view of the hysteresis characteristic in Figure 1 near the end of the discharge operation (near the left end of the discharge operation in Figure 1). The output voltage Vbat in the discharge operation is lower than the open circuit voltage Vocv of the storage battery. This is thought to be due to a voltage drop caused by the internal resistance of the storage battery. In Figure 2, the voltage drop is indicated by an arrow.

[0014] The inventor further discovered that the amount of drop in the hysteresis voltage varies depending on the state of deterioration (SOH) of the storage battery. For example, in the discharge operation shown in Figure 2, it was found that the output voltage further drops as the SOH decreases (deterioration progresses). In Figure 2, the voltage drop due to the SOH is indicated by an arrow.

[0015] Conventionally, both voltage drops indicated by the two arrows in Figure 2 have been considered to be caused by the internal resistance of the storage battery. Therefore, it is common to treat the two voltage drops together as a voltage drop caused by internal resistance, regardless of the value of SOH. However, according to the knowledge gained by the present inventor, it has been found that there is a voltage drop caused by SOH in addition to the voltage drop caused by internal resistance, as shown in Figure 2.

[0016] The cause of the voltage drop due to SOH is considered to be a characteristic similar to the electrical resistance inside the storage battery. Therefore, in the present invention, the characteristic of the storage battery that causes the voltage drop due to SOH is treated as a virtual resistance component (called the virtual resistance component Rbat). Therefore, the voltage drop due to SOH can be expressed as Rbat x output current.

[0017] It is believed that by calculating Vocv using the voltage drop caused by this SOH, Vocv can be obtained more accurately. Therefore, when estimating SOC using Vocv, the estimation accuracy is improved. Below, an embodiment of the present invention that estimates SOC using this principle will be described.

[0018] <Embodiment 1> 3 is a configuration diagram of a state-of-charge estimating device 100 according to the first embodiment of the present invention. The state-of-charge estimating device 100 is a device that estimates the state of charge of a storage battery system 200. The state-of-charge estimating device 100 is connected to each of the storage battery system 200 and a DC / DC converter 300. As a result, each device forms a power grid system.

[0019] The storage battery system 200 is configured by connecting one or more storage battery modules. The storage battery system 200 includes a storage battery management unit 210 and a voltage sensor 220. The voltage sensor 220 measures the output voltage Vbat of the storage battery system 200. The storage battery management unit 210 outputs the measurement result. The output current Ibat of the storage battery system 200 may be measured by an appropriate ammeter or the like, and the measurement result may be output together.

[0020] The DC / DC converter 300 controls the output (current or voltage) of the storage battery system 200 to control its operation. The DC / DC converter 300 includes a control unit 310, a voltage sensor 320, and an AD conversion unit 330. The control unit 310 controls the overall operation of the DC / DC converter 300 according to commands from the calculation unit 110. The voltage sensor 320 measures the output voltage Vbat of the storage battery system 200. The AD conversion unit 330 converts the measurement result into a digital value and outputs it. The output current Ibat of the storage battery system 200 may also be measured in a similar manner and the measurement result may be output.

[0021] The state-of-charge estimation device 100 includes a calculation unit 110 and a storage unit 120. The calculation unit 110 acquires the measurement results of the output voltage Vbat and the output current Ibat from at least one of the storage battery management unit 210 and the AD conversion unit 330. The calculation unit 110 estimates the SOC of the storage battery system 200 using these values. The estimation procedure will be described later. The storage unit 120 stores data used by the calculation unit 110. The details of the data will be described later.

[0022] FIG. 4 is a graph plotting the relationship between the virtual resistance component Rbat and the SOH. According to the knowledge of the present inventor, the virtual resistance component Rbat and the SOH have a correlation, and the relationship can be expressed by a function. In FIG. 4, an example of expressing the relationship by a linear function is shown, but the relationship may be expressed by using other functions. The storage unit 120 stores data describing the relationship shown in FIG. 4 in advance. The calculation unit 110 can obtain Rbat by acquiring the SOH of the storage battery system 200 and applying the value to the function shown in FIG. 4. Alternatively, the function representing the relationship in FIG. 4 is implemented in a program in advance, and the calculation unit 110 executes this to perform a similar calculation.

[0023] 5 is a graph illustrating the relationship between the open circuit voltage Vocv and the SOC of the storage battery system 200. The relationship between Vocv and the SOC can be acquired in advance. The storage unit 120 stores data describing this relationship in advance. The calculation unit 110 can acquire the SOC of the storage battery system 200 by referring to this data using Vocv.

[0024] 6 is a diagram showing the module configuration of the calculation unit 110. The calculation unit 110 includes a SOH-Rbat conversion unit 111, a Vocv calculation unit 112, and a Vocv-SOC conversion unit 113. The calculation unit 110 and these modules can be configured by hardware such as a circuit device that implements the functions, or can be configured by a calculation device executing software that implements the functions.

[0025] The SOH-Rbat conversion unit 111 acquires the SOH of the storage battery system 200. The SOH may be acquired from the storage battery management unit 210 or the DC / DC converter 300, or may be acquired by estimation by the calculation unit 110. An example of an estimation method will be described separately in the embodiment described later. The SOH-Rbat conversion unit 111 acquires the virtual resistance component Rbat by using the acquired SOH and referring to the data in FIG. 4.

[0026] The Vocv calculation unit 112 acquires the output current Ibat of the storage battery system 200 and the output voltage Vbat of the storage battery system 200. These values ​​can be acquired from the storage battery management unit 210 or the DC / DC converter 300. The Vocv calculation unit 112 calculates the open circuit voltage Vocv of the storage battery system 200 according to Equation 1 below.

[0027] Vbat=Vocv+R IR ·Ibat+Rbat·Ibat (1)

[0028] The output voltage Vbat in the hysteresis characteristic is determined by the internal resistance R IRand the virtual resistance component Rbat. IR Ibat is the internal resistance R of the battery storage system 200 IR In equation 1, Rbat·Ibat is the voltage drop caused by the virtual resistance component Rbat.

[0029] The Vocv-SOC conversion unit 113 obtains the SOC of the storage battery system 200 by referring to the data in Fig. 5 using the Vocv calculated by the Vocv calculation unit 112. If there is a possibility that the Vocv calculated by the Vocv calculation unit 112 does not correspond one-to-one to the SOC, a voltage corresponding to the SOC may be calculated by correcting the Vocv using an appropriate correction formula. The SOC can be obtained by referring to the data in Fig. 5 using the calculation result.

[0030] <First embodiment: Summary> The state-of-charge estimating device 100 according to the first embodiment calculates a virtual resistance component Rbat that affects the hysteresis characteristics in the process of charging and discharging operations of the storage battery system 200 and fluctuates due to the SOH of the storage battery system 200. The state-of-charge estimating device 100 calculates the open circuit voltage Vocv of the storage battery system 200 using Rbat, and acquires the SOC of the storage battery system 200 using the Vocv. By using the virtual resistance component Rbat, it is possible to accurately estimate the SOC by taking into account the component that affects the hysteresis characteristics.

[0031] <Embodiment 2> In the first embodiment, it has been described that Rbat changes for each value of SOH. The present inventor has discovered that Rbat changes not only with SOH but also with the temperature Tbat of the storage battery system 200. Therefore, in the second embodiment of the present invention, a configuration example in which Rbat is calculated according to Tbat will be described. The configuration of each device is the same as that of the first embodiment.

[0032] 7 shows an example of a module configuration of the calculation unit 110 in the present embodiment 2. In addition to the configuration described in the embodiment 1, the SOH-Rbat conversion unit 111 and the Vocv-SOC conversion unit 113 each acquire a temperature Tbat of the storage battery system 200. For example, Tbat can be acquired from the storage battery management unit 210, but this is not limiting, and the calculation unit 110 may estimate Tbat using changes over time in the output voltage Vbat and the output current Ibat of the storage battery system 200.

[0033] FIG. 8 is a diagram for explaining the procedure by which the SOH-Rbat conversion unit 111 calculates Rbat. The SOH-Rbat conversion unit 111 acquires Rbat in the same manner as in the first embodiment, and further corrects the Rbat using the battery temperature Tbat. For example, a function describing the relationship between SOH and Rbat may be stored in the storage unit 120 in advance for each value of Tbat, and Rbat may be calculated using the function corresponding to the acquired Tbat. Alternatively, the parameters of the function describing the relationship between SOH and Rbat may be corrected according to Tbat. For example, if it is known in advance that the intercept and slope of the linear function change according to Tbat, these parameters may be corrected according to Tbat. The SOH-Rbat conversion unit 111 acquires Rbat by applying SOH to the corrected data. As in FIG. 4, the relationship in FIG. 8 may be implemented by a program for each value of Tbat.

[0034] FIG. 9 is a diagram for explaining the procedure by which the Vocv-SOC conversion unit 113 acquires the SOC. The relationship between SOC and Vocv may also vary according to the battery temperature Tbat. In this case, the relationship in FIG. 5 may be corrected according to Tbat, as in FIG. 8. For example, data describing the relationship between SOC and Vocv for each value of Tbat is stored in advance in the storage unit 120, and the Vocv-SOC conversion unit 113 can acquire the SOC by referring to this data using Tbat. As in FIG. 8, the data may be corrected by other procedures.

[0035] <Embodiment 3> FIG. 10 shows the hysteresis characteristic between Vbat and SOC in the process of charging and discharging operations of the storage battery system 200. When the wiring resistance Rser of the storage battery system 200 is large, the difference ΔVhys between Vbat during charging and Vbat during discharging also becomes large accordingly. In the third embodiment of the present invention, a configuration example is described in which Rbat is calculated taking into account such an influence of the wiring resistance Rser on the hysteresis characteristic. The configuration of each device is the same as that of the first embodiment.

[0036] The Vocv calculation unit 112 can calculate the wiring resistance Rser according to the following formula 2. Alternatively, data describing the value of Rser may be stored in the storage unit 120 in advance.

[0037] ΔVhys=2×(R IR ·Ibat+Rbat・Ibat+Rser・Ibat) (2)

[0038] During the discharge operation, Vbat is affected by the voltage drop due to the wiring resistance in addition to the voltage drop due to the internal resistance and the voltage drop due to the virtual resistance component. Therefore, Vbat can be calculated by the following formula 3. The Vocv calculation unit 112 can calculate Vocv according to formula 3. The subsequent operations are the same as those in the first and second embodiments.

[0039] Vbat=Vocv+R IR ·Ibat+Rbat・Ibat+Rser・Ibat (3)

[0040] <Fourth embodiment> In the above embodiment, the method of estimating the SOC has been described using the virtual resistance component Rbat that causes a fluctuation in the hysteresis characteristic during the discharging operation of the storage battery system 200. Therefore, as long as the voltage drop caused by the virtual resistance component Rbat can be measured, it is considered that the timing for estimating the SOC can be freely set. Therefore, in the fourth embodiment of the present invention, a configuration example will be described in which a voltage drop caused by the virtual resistance component Rbat is intentionally caused in an arbitrary period in which the voltage drop is expected to occur, and Rbat is calculated at that timing. The configuration of each device is the same as that of the first embodiment.

[0041] Fig. 11 is a graph illustrating the changes in Vbat and Ibat when the current command is changed. At any time during a period during which a voltage drop due to the virtual resistance component Rbat is expected to occur in the hysteresis characteristic (for example, near the end of a discharging operation), the calculation unit 110 changes the current command for the storage battery system 200 as shown in the lower part of Fig. 11. This period can be determined by either the SOC or Vbat value. Due to the change in the current command, Ibat changes by ΔIbat, and Vbat also changes by ΔVbat following this.

[0042] 11, the output voltages before and after the change in the current command are Vbat1 and Vbat2, and the output currents are Ibat1 and Ibat2. The calculation unit 110 can calculate Rbat according to the following formula 4. When formula 4 is used, it is not necessary to obtain SOH in advance to calculate Rbat.

[0043] Vbat1=Vocv+R IR ·Ibat1+Rbat·Ibat1 Vbat2=Vocv+R IR ·Ibat2+Rbat·Ibat2 ΔVbat = Vbat1 - Vbat2 =(Ibat1-Ibat2)(R IR +Rbat) =ΔIbat(R IR +Rbat) (4)

[0044] Fig. 12 is a flowchart illustrating the operation of the state-of-charge estimating device 100 in the embodiment 4. Each step in Fig. 12 will be described below.

[0045] (FIG. 12: Step S1201) At any time point within a period during which a voltage drop due to the virtual resistance component Rbat is assumed to occur in the hysteresis characteristic, the calculation unit 110 changes the current command for the storage battery system 200 as shown in the lower part of Fig. 11. The calculation unit 110 calculates ΔVbat and ΔIbat by acquiring the measurement results of Vbat and Ibat over time.

[0046] (FIG. 12: Steps S1202 to S1203) The calculation unit 110 calculates Rbat according to Equation 4 (S1202). The calculation unit 110 can further estimate the SOH of the storage battery system 200 by using the calculated Rbat and referring to the data in Fig. 4 (S1203).

[0047] (FIG. 12: Steps S1204 to S1206) The calculation unit 110 acquires the measurement results of Vbat and Ibat (S1204). The calculation unit 110 calculates Vocv according to Equation 1 (S1205). The calculation unit 110 acquires the SOC of the storage battery system 200 by using the calculated Vocv and referring to the data in FIG. 5 (S1206). These steps are the same as those in the first embodiment.

[0048] <Fifth Preferred Embodiment> In the above embodiment, it has been described that the SOC is obtained using the open circuit voltage Vocv of the storage battery system 200. Also, Vocv is calculated according to Equation 1. If the calculated Vocv contains an error, the estimation accuracy of the SOC will also decrease. Therefore, in the fifth embodiment of the present invention, a configuration example will be described in which the relational expression for SOC estimation is corrected using the difference between the actual measurement value and the calculated value of Vocv. The configuration of each device is the same as that of the first embodiment.

[0049] FIG. 13 is a graph illustrating the difference between the measured value and the estimated value of Vocv. To obtain the actual value of the open circuit voltage, Ibat is shut off and the measurement result of Vbat is obtained. The estimated value of Vocv, Vocv_est, can be calculated by Vocv in Equation 1. There may be a difference between the actual measured value of Vocv, Vocv_act, and the estimated value, Vocv_est, as shown in FIG. 13.

[0050] Fig. 14 is a flowchart illustrating the operation of the state-of-charge estimating device 100 in the embodiment 5. Each step in Fig. 14 will be described below.

[0051] (FIG. 14: Step S1401) The calculation unit 110 sets an upper limit voltage Vbat_th of the storage battery system 200. Vbat_th can be calculated, for example, by the following formula: Vbat_th=Vocv_est+Rbat·Ibat. Vocv_est is the same as Vocv in formula 1.

[0052] (FIG. 14: Steps S1402 to S1403) The calculation unit 110 acquires the SOH of the storage battery system 200 (S1402), and acquires Rbat by using the SOH and referring to the data in Fig. 4 (S1403). These steps are the same as those in the first embodiment.

[0053] (FIG. 14: Steps S1404 to S1405) When the output voltage Vbat of the storage battery system 200 reaches the upper limit voltage Vbat_th, the calculation unit 110 cuts off the output current Ibat of the storage battery system 200 (S1404). The calculation unit 110 calculates Vocv_est (i.e., Vocv) according to Equation 1 (S1405). The order of these steps may be reversed.

[0054] (FIG. 14: Step S1406) After Ibat is shut off, when Vbat becomes stable (when the time rate of change of Vbat becomes less than the threshold), the calculation unit 110 acquires the actual measurement value Vocv_act of the open circuit voltage of the storage battery system 200. For example, this step can be performed when 5 minutes have elapsed since Ibat was shut off.

[0055] (FIG. 14: Step S1407) The calculation unit 110 corrects the function describing the relationship between Rbat and SOH (the data in FIG. 4) according to the difference between Vocv_est and Vocv_act. A specific example of the correction is shown in FIG.

[0056] FIG. 15 shows a specific example of correcting a function describing the relationship between Rbat and SOH. As an example of the correction procedure, data describing the relationship between Rbat and SOH for each value of Vocv is stored in advance in the storage unit 120, and Rbat can be obtained using a relational expression corresponding to the actual measurement value Vocv_act. Alternatively, the parameters of the function describing the relationship between SOH and Rbat may be corrected according to Vocv. For example, if it is known in advance that the intercept and slope of the linear function change according to Vocv, these parameters may be corrected according to Vocv. The SOH-Rbat conversion unit 111 obtains Rbat by applying SOH to the corrected data. The subsequent operations are the same as those in the first embodiment.

[0057] <Sixth embodiment> In the above embodiments, the SOH of the storage battery system 200 may be estimated by the calculation unit 110. However, in order to estimate the SOH, it may take a long time until the measured value stabilizes. Therefore, in the sixth embodiment of the present invention, a configuration example in which the SOH is measured by a simple means in a short time will be described. The configuration of each device is the same as that of the first embodiment.

[0058] Fig. 16 is a flowchart explaining the procedure for calculating the SOH by the calculation unit 110. The calculation unit 110 starts this flowchart at an appropriate timing, for example, when the state-of-charge estimating device 100 is started, when instructed to start this flowchart, or at a predetermined interval. Each step in Fig. 16 will be explained below.

[0059] (FIG. 16: Step S1601) The calculation unit 110 determines whether or not it is a rest period after charging or a rest period after discharging. If it is not currently in a rest period, this flowchart ends. If it is currently in a rest period, proceed to S1602. For example, a rest period after discharging can be determined by (a) the current output by the storage battery system 200 changing from a negative value (I<0) toward zero, or (b) changing from a negative value to a value close to zero and stabilizing (|I|<threshold value), etc.

[0060] (FIG. 16: Step S1602) The calculation unit 110 calculates ΔVa and ΔVb. ΔVa is the amount of change in the output voltage of the storage battery system 200 from a first calculation start point after the end of the suspension period to a first time when a first period ta has elapsed. ΔVb is the amount of change in the output voltage of the storage battery system 200 from a second calculation start point after the first time to a second time when a second period tb has elapsed. The calculation procedure will be described later.

[0061] (FIG. 16: Step S1603) The calculation unit 110 calculates the internal resistance Ri and the SOH of the storage battery system 200 according to the following formulas 5 and 6. Ri defines Ri as a function of ΔVa. Ri has a parameter (c_Ri_T) that varies with the temperature of the battery system 200 and a parameter (c_Ri_I) that varies with the output current of the battery system 200. SOH defines SOH as a function of ΔVb. SOHhas a parameter (c_SOH_T) that varies with the temperature of the battery system 200 and a parameter (c_SOH_I) that varies with the output current of the battery system 200. These parameters are defined by a relationship table 121 stored in the storage unit 120. Specific examples of each function and the relationship table 121 will be described later. Ri and f SOH is an equation formed based on experimental data for each lot, for example.

[0062] (Figure 16: Step S1603: Calculation formula) Ri=f Ri (ΔVa,c_Ri_T_1,c_Ri_T_2,···,c_Ri_I_1,c_Ri_I_2,···) (5) SOH=f SOH (ΔVb,c_SOH_T_1,c_SOH_T_2,···,c_SOH_I_1,c_SOH_I_2,···) (6)

[0063] FIG. 17 is a graph showing the change over time of the current and voltage output by the storage battery system 200 during the pause period after discharge. ΔVa in S1602 is the fluctuation of the output voltage of the storage battery system 200 from the first calculation point at or after the end of discharge to the first time when the first period ta has elapsed. The present inventor found that the voltage fluctuation due to the internal resistance of the storage battery system 200 is well reflected in the output voltage immediately after the end of discharge. In other words, it can be said that the fluctuation of the output voltage (ΔVa) during this period has a strong correlation with Ri. In this embodiment, this fact is utilized to estimate Ri by ΔVa. The optimal values ​​of the start time and duration of ta can be obtained based on the section from the end of discharge to the maximum point of the slope change rate in the voltage change over time curve. In addition, when specifying the above-mentioned section, it is only necessary to appropriately operate it in a preferable manner, such as near both ends of the above-mentioned section or including both ends, depending on the type of battery, device, accuracy, etc.

[0064] The start time of ta does not necessarily have to be the same as the end time of discharge, but it is preferably close to the end time of discharge. The start time of tb does not necessarily have to be the same as the end time of ta. In any case, ta and tb have the relationship ta < tb. Regarding the magnitudes of ΔVa and ΔVb, there may be cases where ΔVa is larger, or there may be cases where ΔVb is larger. Here, ta < tb is assumed, but depending on the type of battery, device, accuracy, etc., there may also be cases where ta > tb or ta = tb, so an appropriate preferable relationship may be set as needed.

[0065] It has been found from the experimental results of the present inventor that Ri and SOH can be accurately estimated even if the total of ta and tb is, for example, about several seconds. Therefore, according to the present embodiment, both Ri and SOH can be quickly estimated during the rest period.

[0066] FIG. 18 is a graph showing the change over time of the current and voltage output by the storage battery system 200 during the rest period after charging. ΔVa in S1602 may be the variation in the output voltage of the storage battery system 200 from the time when charging ends or a later first starting point until the first time when the first period ta has elapsed. In this case, ΔVb in S1602 is the variation in the output voltage of the storage battery system 200 from the time when the period ta has elapsed or a later second starting point until the second time when the second period tb has elapsed. The present inventor has found that even during the rest period after charging, ΔVa has a correlation with Ri and ΔVb has a correlation with SOH. Therefore, in the present embodiment, ΔVa and ΔVb in S1602 may be obtained after either charging or discharging.

[0067] 19 is a diagram showing a configuration of the relationship table 121 and an example of data. The relationship table 121 is a data table that defines each parameter in Equation 5 and Equation 6. c_Ri_I and c_SOH_I vary depending on the output current of the storage battery system 200, and are therefore defined for each output current value. c_Ri_T and c_SOH_T vary depending on the temperature of the storage battery system 200, and are therefore defined for each temperature. These parameters may have different characteristics between a rest period after discharging and a rest period after charging, and therefore the relationship table 121 defines each parameter for each of these periods.

[0068] f Ri When is a linear function of ΔVa, Ri can be expressed by, for example, the following formula 7. This is because the slope of Ri is affected by temperature and the intercept is affected by current. In this case, c_Ri_T and c_Ri_I are each one.

[0069] Ri=c_Ri_T_1×ΔVa+c_Ri_I_1 (7)

[0070] f SOH When is a linear function of ΔVb, SOH can be expressed by, for example, the following formula 8. This is because the slope of SOH is affected by temperature and the intercept is affected by current. In this case, c_SOH_T and c_SOH_I are each one.

[0071] SOH=c_SOH_T_1×ΔVb+c_SOH_I_1 (8)

[0072] <Embodiment 6: Summary> The state-of-charge estimating device 100 according to the sixth embodiment estimates Ri using a voltage fluctuation ΔVa during a period ta during a pause period after the end of discharging or a pause period after the end of charging, and estimates SOH using a voltage fluctuation ΔVb during a period tb. This makes it possible to estimate both Ri and SOH in a shorter time than in the past.

[0073] In the state-of-charge estimating device 100 according to the sixth embodiment, the relationship table 121 includes a function f Ri The internal resistance parameters include c_Ri_I, which varies with the output current of the battery storage system 200, and c_Ri_T, which varies with the temperature of the battery storage system 200. Ri Even if fluctuates due to the temperature of the battery system 200 or the output current of the battery system 200, it is possible to accurately estimate Ri. SOH The same is true for the deterioration state parameters that define

[0074] In the state-of-charge estimating device 100 according to the sixth embodiment, the relationship table 121 describes the internal resistance parameters and the degradation state parameters for each of the rest periods after charging and after discharging. This makes it possible to accurately estimate Ri and SOH even if the functions (i.e., the characteristics of the storage battery system 200) are different between the rest periods after charging and the rest periods after discharging.

[0075] <Modifications of the present invention> The present invention is not limited to the above-described embodiment, and includes various modified examples. For example, the above-described embodiment has been described in detail to clearly explain the present invention, and is not necessarily limited to those having all of the configurations described. In addition, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. In addition, it is possible to add, delete, or replace a part of the configuration of each embodiment with another configuration.

[0076] In the above embodiment, it has been described that the hysteresis shape during the discharge operation is influenced by the virtual resistance component due to SOH, but similar fluctuations in the hysteresis shape due to SOH may occur in other parts of the hysteresis process. It is considered that which part of the hysteresis this occurs in depends on the characteristics of the storage battery. In either case, as in the above embodiment, Vocv can be calculated using the virtual resistance component Rbat, and the SOC can be estimated using this. For example, when there is a voltage fluctuation due to SOH near the end of the charging operation, the SOC can be estimated as in the first embodiment. Also, in the fourth embodiment, the Ibat can be shut off during the charging operation to perform a similar operation.

[0077] In the above embodiment, the state of charge estimating device 100 has been described as estimating the state of charge of the storage battery system 200, but the invention is not limited thereto and may estimate, for example, the state of charge of a storage battery module or the state of charge of a storage battery cell. In this case, the output current, output voltage, deterioration state, etc. of the storage battery to be estimated may be acquired, and the SOC may be estimated by the same procedure as in the above embodiment. [Explanation of symbols]

[0078] 100: Charge state estimation device 110: Arithmetic section 120: Storage section 200: Battery storage system 300: DC / DC converter

Claims

1. A state-of-charge estimation device that estimates a state of charge of a storage battery, A calculation unit that estimates a state of charge of the storage battery; a memory unit for storing data describing a relationship between an open circuit voltage of the battery and a state of charge of the battery; Equipped with The output voltage of the storage battery and the state of charge of the storage battery have a hysteresis characteristic during a charging operation of the storage battery and a discharging operation of the storage battery, The calculation unit calculates a characteristic of the storage battery that affects a shape of the hysteresis and varies due to a deterioration state of the storage battery as a virtual resistance component of the storage battery; the calculation unit calculates the open circuit voltage by calculating a difference between the output voltage and the open circuit voltage in the hysteresis characteristic using an internal resistance of the storage battery and the virtual resistance component; The calculation unit estimates the state of charge by referring to the data using the calculated open circuit voltage; The calculation unit obtains a first difference in output current of the storage battery before and after the storage battery stops a charging operation or a discharging operation, and a second difference in the output voltage of the storage battery before and after the storage battery stops a charging operation or a discharging operation, The calculation unit calculates the virtual resistance component by using the first difference, the second difference, and the internal resistance. A state-of-charge estimating device comprising:

2. A state-of-charge estimation device that estimates a state of charge of a storage battery, A calculation unit that estimates a state of charge of the storage battery; a memory unit for storing data describing a relationship between an open circuit voltage of the battery and a state of charge of the battery; Equipped with The output voltage of the storage battery and the state of charge of the storage battery have a hysteresis characteristic during a charging operation of the storage battery and a discharging operation of the storage battery, The calculation unit calculates a characteristic of the storage battery that affects a shape of the hysteresis and varies due to a deterioration state of the storage battery as a virtual resistance component of the storage battery; the calculation unit calculates the open circuit voltage by calculating a difference between the output voltage and the open circuit voltage in the hysteresis characteristic using an internal resistance of the storage battery and the virtual resistance component; The calculation unit estimates the state of charge by referring to the data using the calculated open circuit voltage; The calculation unit acquires a measurement result of the deterioration state, the calculation unit approximates a relationship between the degradation state and the virtual resistance component using a function, and calculates the virtual resistance component by applying the acquired degradation state to the function; the calculation unit cuts off a current flowing through the storage battery when the output voltage reaches a threshold value, and estimates the output voltage at a reference point in time after the cutoff; The calculation unit acquires a measurement result of the output voltage at the reference time point, The calculation unit corrects the function according to a difference between the estimated output voltage and the measurement result, and calculates the virtual resistance component using the corrected function. A state-of-charge estimating device comprising:

3. A state-of-charge estimation device that estimates a state of charge of a storage battery, A calculation unit that estimates a state of charge of the storage battery; a memory unit for storing data describing a relationship between an open circuit voltage of the battery and a state of charge of the battery; Equipped with The output voltage of the storage battery and the state of charge of the storage battery have a hysteresis characteristic during a charging operation of the storage battery and a discharging operation of the storage battery, The calculation unit calculates a characteristic of the storage battery that affects a shape of the hysteresis and varies due to a deterioration state of the storage battery as a virtual resistance component of the storage battery; the calculation unit calculates the open circuit voltage by calculating a difference between the output voltage and the open circuit voltage in the hysteresis characteristic using an internal resistance of the storage battery and the virtual resistance component; The calculation unit estimates the state of charge by referring to the data using the calculated open circuit voltage; the calculation unit obtains a first difference between the output voltage at a first calculation point after a termination point at which charging or discharging of the storage battery is terminated and the output voltage at a first point when a first period has elapsed from the first calculation point; The calculation unit obtains a second difference between the output voltage at a second starting point after the first point in time and the output voltage at a second point in time when a second period has elapsed from the second starting point in time, the calculation unit acquires relationship data describing a relationship between the first difference and the internal resistance and a relationship between the second difference and the degradation state; the calculation unit estimates the internal resistance by referring to the relationship data using the first difference; The calculation unit estimates the deterioration state by referring to the relationship data using the second difference. A state-of-charge estimating device comprising:

4. The calculation unit acquires a measurement result of the deterioration state, The calculation unit approximates a relationship between the deterioration state and the virtual resistance component using a function, and calculates the virtual resistance component by applying the acquired deterioration state to the function.

4. The device for estimating a state of charge according to claim 1 or 3.

5. the data describing a relationship between an internal resistance of the storage battery and a state of deterioration of the storage battery for each temperature of the storage battery; The calculation unit acquires a temperature of the storage battery, The calculation unit obtains the internal resistance corresponding to the temperature by referring to the data using the obtained temperature.

4. The device for estimating a state of charge according to claim 1.

6. the data describing a relationship between an open circuit voltage of the battery and a state of charge of the battery for each temperature of the battery; The calculation unit acquires a temperature of the storage battery, The calculation unit obtains the state of charge corresponding to the temperature by referring to the data using the obtained temperature.

4. The device for estimating a state of charge according to claim 1.

7. The calculation unit acquires a wiring resistance of the storage battery, The calculation unit calculates the open circuit voltage by calculating a difference between the output voltage and the open circuit voltage in the hysteresis characteristic using the wiring resistance in addition to the internal resistance and the virtual resistance component.

4. The device for estimating a state of charge according to claim 1.

8. the hysteresis characteristic has a voltage difference between the output voltage in a charging operation and the output voltage in a discharging operation, The calculation unit calculates the wiring resistance using the voltage difference.

8. The device for estimating a state of charge according to claim 7.

9. The calculation unit approximates a relationship between the deterioration state and the virtual resistance component using a function, and estimates the deterioration state by applying the calculated virtual resistance component to the function.

2. The device for estimating a state of charge according to claim 1.

10. The calculation unit estimates the output voltage at the reference time by calculating the open circuit voltage using the internal resistance and the virtual resistance component.

3. The device for estimating a state of charge according to claim 2.

11. The calculation unit uses, as the reference time point, a time point at which a time rate of change of the output voltage reaches a threshold value or less after a current flowing through the storage battery is interrupted.

3. The device for estimating a state of charge according to claim 2.

12. The device for estimating a state of charge according to any one of claims 1 to 3, a power grid configured by connecting a plurality of the storage batteries; 1. A power grid system comprising:

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