Battery system and operation method for battery system

Abstract

A battery system according to the present invention comprises a battery module in which a plurality of battery units that each include at least one battery cell are electrically connected in series. The battery system has a current meter that measures a current value I for the battery module, a voltage meter that measures respective voltage values Vi for the plurality of battery units, a determination device that can determine at least one of whether there is an abnormality in respective open circuit voltages OCVi for the plurality of battery units and whether there is an abnormality in an internal resistance value Ri, and a reporting device that reports determination results from the determination device.

Description

Battery system and method for operating the battery system

[0001] This application claims priority to Japanese Patent Application No. 2024-105591, filed June 28, 2024, and incorporates by reference all of the contents of said Japanese application.

[0002] Patent Literature 1 discloses a method for detecting the degradation state of a redox flow battery in a battery system including the redox flow battery. In this detection method, the voltage of each module, each cell stack, or each battery cell is measured while an electrolyte is circulating through the module when charging or discharging is not being performed. Then, performance degradation of each unit component, such as the module, cell stack, or battery cell, is detected based on the measured voltage.

[0003] Japanese Patent Application Laid-Open No. 2007-311210

[0004] a voltmeter for measuring a voltage value Vi of each of the plurality of battery units; a determination device capable of determining whether or not there is an abnormality in an open circuit voltage OCVi of each of the plurality of battery units and whether or not there is an abnormality in an internal resistance value Ri of each of the plurality of battery units; and a notification device for notifying a result of the determination by the determination device, wherein the determination device includes a calculation unit and at least one of a first determination unit and a second determination unit, wherein the i is a natural number and is a unique number assigned to each of the plurality of battery units, and the calculation unit is configured to calculate battery data including the current value I and the voltage value Vi of each of the plurality of battery units measured at the same time, in a manner that the calculation unit calculates the battery data ... the first determination unit determines whether an absolute value of the intercept ΔOCVi is larger than a first threshold value; the second determination unit determines whether an absolute value of the slope ΔRi is larger than a second threshold value; the equation of the linear function is ΔVi=ΔRi×I+ΔOCVi, where ΔVi is a difference between the voltage value Vi in the battery data and a reference voltage value V0, and the reference voltage value V0 is one of a mode, a median, and an average value determined from voltage values ​​excluding the voltage value Vi in the battery data acquired at each of the plurality of times.

[0005] Fig. 1 is a schematic diagram of a battery system described in an embodiment. Fig. 2 is a schematic diagram of a battery module provided in the battery system shown in Fig. 1. Fig. 3 is a graph showing the relationship between the current value flowing through the battery module shown in Fig. 2 and the difference between the voltage value of a battery unit provided in the battery module and the voltage value of a hypothetical battery unit that is not deteriorated. Fig. 4 is a schematic diagram of a redox flow battery described in an embodiment. Fig. 5 is a schematic diagram of a cell stack provided in the redox flow battery shown in Fig. 4.

[0006] Redox flow batteries charge or discharge by circulating an electrolyte. Redox flow batteries include a module containing multiple cell stacks. A module is formed by connecting multiple cell stacks in series. Each cell stack is formed by connecting multiple battery cells in series. A common electrolyte is supplied to the positive or negative electrodes of each battery cell in the module. In this specification, a unit component smaller than a module is called a battery unit.

[0007] In the conventional configuration, the degradation of the battery units is measured when the battery system is not in operation, i.e., when no charging or discharging is being performed as part of the power grid. Therefore, in an environment where the battery system is frequently charged and discharged, it is not possible to adequately monitor the status of the battery units of the battery system.

[0008] An object of the present disclosure is to provide a battery system that can monitor the state of a battery unit at any time during operation of the battery system.

[0009] The battery system of the present disclosure can monitor the state of the battery units at any time during operation of the battery system.

[0010] The inventors hypothesized that in a battery system including a battery module in which multiple battery units are connected in series, the voltage value Vi, open-circuit voltage OCVi, internal resistance value Ri, and current value I flowing through the battery module can be expressed by the following equations, assuming that the direction of current flowing during charging is positive. The voltage value Vi is the potential difference between the positive and negative electrodes of each battery unit when the battery module is connected to a load and current is flowing. The open-circuit voltage OCVi is the potential difference between the positive and negative electrodes of each battery unit when the battery module is not connected to a load, i.e., in an open state. The state of charge (SOC) of the battery unit can be estimated based on the open-circuit voltage OCVi of the battery unit. Ri × I is the overvoltage caused by the internal resistance of the battery unit. Vi = Ri × I + OCVi, where "i" is a natural number indicating the number of the battery unit, and is a unique number assigned to each of the multiple battery units and used to distinguish each battery unit. For example, "V1" is the voltage value of battery unit No. 1. Similarly, "OCV1" is the open circuit voltage of battery unit No. 1, and "R1" is the internal resistance value of battery unit No. 1.

[0011] Furthermore, the inventors have come up with the idea that the degree of degradation of a battery unit can be evaluated by determining the difference ΔVi between the voltage value Vi of the battery unit and the reference voltage value V0 of a hypothetical battery unit that is not degraded. For example, if the battery unit is not degraded, ΔVi is considered to approach zero. The difference ΔVi can be expressed by the following formula. In the formula below, R0 is the internal resistance value of the hypothetical battery unit, and OCV0 is the open circuit voltage of the hypothetical battery unit. ΔVi = Vi - V0 = (Ri x I + OCVi) - (R0 x I + OCV0) = (Ri - R0) x I + (OCVi - OCV0) = ΔRi x I + ΔOCVi

[0012] The above equation ΔVi = ΔRi × I + ΔOCVi can be interpreted as a linear function equation with ΔRi as the slope and ΔOCVi as the intercept. The slope ΔRi is the difference between the internal resistance value Ri of the battery unit and the internal resistance value R0 of the virtual battery unit, and is considered to represent the degree of increase in the internal resistance of the battery unit. Furthermore, the intercept ΔOCVi is the difference between the open circuit voltage OCVi of the battery unit and the open circuit voltage OCV0 of the virtual battery unit, and is considered to represent the change in the SOC of the battery unit. If the battery unit is not degraded as ΔVi approaches zero, then it can be determined that the battery unit is not degraded as the slope ΔRi and intercept ΔOCVi approach zero. In other words, if the slope ΔRi and intercept ΔOCVi can be calculated based on battery data obtained from the battery system, the degree of degradation of the battery unit can be monitored. Based on these findings, the inventors have completed the battery system and battery system operating method of the present disclosure. First, embodiments of the present disclosure will be listed and described.

[0013] <1> A battery system according to an embodiment of the present disclosure includes a battery module in which a plurality of battery units are electrically connected in series, each of the plurality of battery units including at least one battery cell. The battery system includes an ammeter that measures a current value I flowing through the battery module, a voltmeter that measures a voltage value Vi of each of the plurality of battery units, a determination device that can determine whether or not there is an abnormality in the open circuit voltage OCVi or the internal resistance value Ri of each of the plurality of battery units, and a notification device that notifies the determination result by the determination device. The determination device includes a calculation unit and at least one of a first determination unit and a second determination unit. The i is a natural number and is a unique number assigned to each of the plurality of battery units. The calculation unit acquires battery data at multiple different times, including the current value I and the voltage value Vi of each of the multiple battery units measured at the same time, and at each of the multiple times, calculates an equation of a linear function having a slope ΔRi and an intercept ΔOCVi for each of the multiple battery units based on the battery data acquired at each of the multiple times, and calculates the slope ΔRi and the intercept ΔOCVi using the multiple equations of the linear function calculated at different times. The first determination unit determines whether the absolute value of the intercept ΔOCVi is larger or smaller than a first threshold, and the second determination unit determines whether the absolute value of the slope ΔRi is larger or smaller than a second threshold, and the equation of the linear function is ΔVi = ΔRi × I + ΔOCVi, where ΔVi is the difference between the voltage value Vi in the battery data and a reference voltage value V0. The reference voltage value V0 is one of a mode, a median, and an average value obtained from voltage values ​​excluding the voltage value Vi in the battery data acquired at each of the plurality of timings.

[0014] In the battery system of the present disclosure, multiple pieces of battery data are acquired at different times. Each piece of battery data includes a current value I(t) and a voltage value Vi(t) (i ⊂ {1, 2, ..., n}, where n is a natural number) at time t. To solve the equation of the linear function above, two or more pieces of battery data acquired at different times are required. Furthermore, the reference voltage value V0 is calculated from all voltage values ​​in each piece of battery data except for the voltage value Vi of the battery unit being evaluated. For example, if there are four battery units and the slope ΔR1 and intercept ΔOCV1 of the number 1 battery unit are to be examined, the reference voltage value V0 is one of the mode, median, and mean of the number 2 voltage value V2, the number 3 voltage value V3, and the number 4 voltage value V4.

[0015] The battery system described above allows for the monitoring of the degree of deterioration of the battery units included in the battery system. Here, "constantly" includes not only standby mode, in which the battery system is neither charging nor discharging, but also operation mode, in which the battery system is charging or discharging. For example, if the first determination unit determines that |ΔOCVi| ≧ the first threshold value, the open circuit voltage Vi of the battery unit deviates from the open circuit voltages of the other battery units. In other words, the SOC of the battery unit deviates from the SOC of the other battery units. From this determination result, the system administrator can recognize that an abnormality has occurred that may cause a difference in SOC. Possible abnormalities that may cause a difference in SOC include, for example, damage to the diaphragm separating the positive and negative electrodes. Furthermore, if the second determination unit determines that |ΔRi| ≧ the second threshold value, the internal resistance Ri of the battery unit deviates from the internal resistances of the other battery units. From this determination result, the system administrator can recognize that an abnormality has occurred in the battery unit that may cause a difference in internal resistance. An abnormality that causes a difference in internal resistance can be attributed to, for example, deterioration of the components of the battery unit due to oxidation, etc. The system administrator can quickly take action, such as replacing the battery unit in which the abnormality occurred.

[0016] Here, when determining ΔRi, at least one of the plurality of battery data must be battery data during charging or battery data during discharging. This is because when the battery system is neither charging nor discharging, the current value I becomes zero, and ΔRi×I in the equation of the linear function also becomes zero. On the other hand, when determining ΔOCVi, all of the plurality of battery data may be standby battery data.

[0017] <2> In the battery system described in <1> above, the first judgment unit may determine that there is an abnormality in the open circuit voltage OCVi when the absolute value of the intercept ΔOCVi is greater than or equal to the first threshold value, and the second judgment unit may determine that there is an abnormality in the internal resistance value Ri when the absolute value of the slope ΔRi is greater than or equal to the second threshold value.

[0018] According to the battery system, it is possible to warn a system administrator of an abnormality in a battery unit, thereby urging the system administrator to take action such as replacing the abnormal battery unit.

[0019] <3> The battery system according to the above item <1> or <2> may not include a monitor cell that measures the open circuit voltage OCVi.

[0020] The battery system according to the embodiment of the present disclosure can evaluate the degree of deterioration of each battery unit even without a monitor cell. The absence of a monitor cell in the battery system provides the advantages of reducing the number of parts in the battery system, reducing the assembly process, and reducing costs.

[0021] <4> In the battery system according to any one of <1> to <3> above, the reference voltage value V0 may be the mode value.

[0022] The mode of voltage values ​​in the battery data is more reliable as the reference voltage value V0 than the median or average. For example, if the battery data includes voltage values ​​that deviate significantly from the other voltage values, the reference voltage value V0, which is the average, may deviate significantly from the voltage value of a non-degraded battery unit. Therefore, a battery system that uses the mode to calculate the slope ΔRi and the intercept ΔOCVi can more accurately evaluate the degree of degradation of each battery unit.

[0023] <5> In the battery system according to any one of <1> to <4> above, the battery cells may be redox flow battery cells.

[0024] According to the battery system described in <5> above, it is possible to constantly monitor the battery units in the redox flow battery, and it is possible to easily identify a battery unit in which an abnormality has occurred.

[0025] <6> A method for operating a battery system according to an embodiment of the present disclosure includes a battery module including multiple battery units electrically connected in series, each of the multiple battery units including at least one battery cell. The method includes: a step A for acquiring battery data at different times, the battery data including a current value I flowing through the battery module and a voltage value Vi of each of the multiple battery units, the current values ​​being acquired at the same time; a step B for determining, based on the multiple battery data acquired at each of the multiple times, whether or not there is an abnormality in the open circuit voltage OCVi or the internal resistance value Ri of each of the multiple battery units; and a step C for reporting the determination result. The i is a natural number and is a unique number assigned to each of the multiple battery units. The step B includes a step B1 and at least one of a step B2 and a step B3. In step B1, an equation of a linear function having a slope ΔRi and an intercept ΔOCVi is calculated for each of the plurality of battery units based on the battery data acquired at each of the plurality of timings. The slope ΔRi and the intercept ΔOCVi are calculated using the equations of the linear function calculated at different timings. In step B2, a magnitude relationship between the absolute value of the intercept ΔOCVi and a first threshold value is determined. In step B3, a magnitude relationship between the absolute value of the slope ΔRi and a second threshold value is determined. The equation of the linear function is ΔVi = ΔRi × I + ΔOCVi. ΔVi is the difference between the voltage value Vi in the battery data and a reference voltage value V0. The reference voltage value V0 is one of the mode, median, and average calculated from voltage values ​​excluding the voltage value Vi in the battery data acquired at each of the plurality of timings.

[0026] According to the battery system operation method of the present disclosure, a system administrator can quickly recognize that an abnormality has occurred in a battery unit provided in the battery system, and can therefore quickly take action such as replacing the abnormal battery unit, making it easier to maintain the performance of the battery system over the long term.

[0027] <7> The operating method of the battery system described in <6> above may determine in step B2 that there is an abnormality in the open circuit voltage OCVi if the absolute value of the intercept ΔOCVi is greater than or equal to the first threshold value, and may determine in step B3 that there is an abnormality in the internal resistance value Ri if the absolute value of the slope ΔRi is greater than or equal to the second threshold value.

[0028] According to the battery system operation method described in <7> above, it is possible to warn a system administrator of an abnormality in a battery unit, thereby urging the system administrator to take action such as replacing the abnormal battery unit.

[0029] <8> In the method for operating a battery system according to the above item <6> or <7>, the reference voltage value V0 may be the mode value.

[0030] The mode of the voltage values ​​in the battery data is more reliable as the reference voltage value V0 than the median or average value. Therefore, a battery system that uses the mode to calculate the slope ΔRi and the intercept ΔOCVi can more accurately evaluate the degree of deterioration of each battery unit.

[0031] <9> In the method for operating a battery system described in any one of <6> to <8> above, the slope ΔRi and the intercept ΔOCVi may be determined by linear regression analysis using a plurality of pieces of battery data acquired over a predetermined period of time.

[0032] The linear regression analysis method is, for example, the least squares method. The slope ΔRi and intercept ΔOCVi can be calculated by the linear regression analysis. The more battery data there is, the more easily the influence of measurement errors can be eliminated. For example, the degree of deterioration of a battery unit can be evaluated using one day's worth of battery data.

[0033] <10> In the method for operating a battery system according to any one of <6> to <9> above, the battery cells may be redox flow battery cells.

[0034] The battery units in the redox flow battery can be monitored at any time, and any battery unit in which an abnormality has occurred can be easily identified.

[0035] [Details of the embodiment of the present disclosure] Specific examples of a battery system and a method of operating the battery system according to an embodiment of the present disclosure will be described below with reference to the drawings. The same reference numerals in the drawings indicate the same or corresponding parts.

[0036] 1 includes a battery module 2, an ammeter 5, a voltmeter 6, a determination device 7, and an alarm device 8. The battery module 2 includes a plurality of battery units 3 electrically connected in series. One of the features of this battery system 1 is that it is possible to monitor each battery unit 3 for abnormalities regardless of the operating state of the battery system 1. Each component of the battery system 1 will be described in detail below.

[0037] <Battery Module> The number of battery modules 2 each having a plurality of battery units 3 may be one or more. The battery system 1 of this example includes a plurality of battery modules 2. The plurality of battery modules 2 are electrically connected in parallel. Each battery module 2 includes a plurality of battery units 3 electrically connected in series. Each battery unit 3 is assigned a number, and the determination device 7 has information about this number. Therefore, the determination device 7 can distinguish between each battery unit 3. In FIG. 1, the number of each battery unit 3 is indicated by a circled number. "n" in the figure is a natural number. In the following description, "i" means any natural number equal to or less than "n".

[0038] As shown in Fig. 2, each battery unit 3 includes at least one battery cell 4. In Fig. 2, the battery cell 4 is represented by a battery symbol and a resistor symbol, which are electrical symbols. The resistor symbol indicates the internal resistance of the battery cell 4. In the example shown in Fig. 2, one battery unit 3 includes one battery cell 4. In practice, the battery unit 3 includes multiple battery cells 4.

[0039] <<Ammeter>> The ammeter 5 is connected in series to the battery modules 2 and measures the current value I flowing through the battery modules 2. In FIG. 1 , only the ammeter 5 corresponding to the top battery module 2 is shown. In reality, one ammeter 5 is provided for each battery module 2. The current value I measured by the ammeter 5 is output to the determination device 7.

[0040] <Voltmeter> The voltmeter 6 measures the voltage value Vi of each battery unit 3. One voltmeter 6 is provided for each battery unit 3. Therefore, the number of voltmeters 6 provided in one battery module 2 is the same as the number of battery units 3 included in that battery module 2. The voltage value Vi measured by the voltmeter 6 is the sum of the open circuit voltage of the battery and the back electromotive force caused by the internal resistance. Although only the voltmeter 6 corresponding to the top battery module 2 is shown in FIG. 1 , voltmeters 6 are similarly provided in the other battery modules 2. The voltage value Vi measured by each voltmeter 6 is output to the determination device 7.

[0041] <Determination Device> As shown in Fig. 1 , the determination device 7 can determine at least one of the presence or absence of an abnormality in the open circuit voltage OCVi and the presence or absence of an abnormality in the internal resistance value Ri of each battery unit 3. More specifically, the determination device 7 of this example includes a calculation unit 70, a first determination unit 71, and a second determination unit 72. Unlike this example, the determination device 7 may be configured to include the calculation unit 70 and the first determination unit 71, but not the second determination unit 72. Alternatively, the determination device 7 may be configured to include the calculation unit 70 and the second determination unit 72, but not the first determination unit 71.

[0042] The calculation unit 70 calculates a physical quantity related to the degree of deterioration of each battery unit 3 based on multiple pieces of battery data acquired at different times. These physical quantities will be described later. Each piece of battery data includes a current value I measured at the same time and n voltage values ​​Vi, the same number as the number of battery units 3. For example, given battery data A and battery data B acquired at different times, battery data A includes a current value I(t1) measured at time t1 and n voltage values ​​Vi(t1). The n voltage values ​​Vi(t1) are the voltage value V1(t1) of the number 1 battery unit, the voltage value V2(t1) of the number 2 battery unit, ..., and the voltage value Vn(t1) of the number n battery unit. Battery data B includes a current value I(t2) measured at time t2, which is different from time t1, and n voltage values ​​Vi(t2). The n voltage values ​​Vi(t2) are the voltage value V1(t2) of the battery unit number 1, the voltage value V2(t2) of the battery unit number 2, ..., the voltage value Vn(t2) of the battery unit number n. The interval at which the battery data is acquired is not particularly limited. For example, the interval at which the battery data is acquired is 1 second or more and 300 seconds or less.

[0043] The calculation unit 70 calculates the slope ΔRi and intercept ΔOCVi of the following linear function equation as a physical quantity related to the degree of deterioration of each battery unit 3: ΔVi=ΔRi×I+ΔOCVi

[0044] As already explained, the above linear function equation shows the relationship between each battery unit 3 and a hypothetical, undegraded battery unit. The difference ΔVi is the difference between the voltage value Vi of the battery unit 3 numbered i and the reference voltage value V0 of a hypothetical, undegraded battery unit. If the battery unit 3 numbered i is not degraded, ΔVi approaches zero. The slope ΔRi is the difference between the internal resistance value Ri of the battery unit 3 numbered i and the internal resistance value R0 of the hypothetical battery unit, and indicates the degree of increase in the internal resistance of the battery unit 3 numbered i. The intercept ΔOCVi is the difference between the open circuit voltage OCVi of the battery unit 3 numbered i and the open circuit voltage OCV0 of the hypothetical battery unit, and indicates the change in SOC of the battery unit 3 numbered i.

[0045] The current value I is the actual value measured by the ammeter 5. The difference ΔVi is calculated from the actual values ​​measured by the multiple voltmeters 6. As already mentioned, ΔVi = Vi - V0. The reference voltage value V0 may be the average value, median, or mode of all voltage values ​​other than the voltage value Vi. For example, when calculating the difference ΔV1, the reference voltage value V0 is one of the average value, median, and mode of the voltage values ​​V2, V3, V4, ..., and Vn other than the voltage value V1. The mode is calculated from a frequency distribution table. Specifically, all voltage values ​​other than the voltage value V1 are divided into multiple classes with a predetermined voltage range, and the class value of the class with the most voltage values ​​is the mode. The classes are, for example, ranges such as 1.3 V or more and less than 1.4 V, or 1.4 V or more and less than 1.5 V. The class value is the median of the range. The average value is the sum of n-1 voltage values ​​divided by n-1. The median value is the (n-1) / 2th smallest voltage value among the n-1 voltage values. If (n-1) / 2 is not a natural number, the median is the average of the voltage values ​​before and after (n-1) / 2. The most suitable value for this reference voltage value V0 is the mode. For example, if the battery data contains a voltage value that is extreme compared to other voltage values, the reference voltage value V0 formed from the average value may deviate significantly from the voltage value of an undegraded battery unit. The reference voltage value V0 formed from the mode value eliminates the influence of the extreme voltage value, making the reference voltage value V0 highly reliable.

[0046] The calculation unit 70 calculates the slope ΔRi and the intercept ΔOCVi using a linear regression analysis technique such as the least squares method. The procedure for linear regression analysis will be described with reference to the graph in FIG. 3 . The horizontal axis of the graph in FIG. 3 represents the current value I of the battery module 2. When charging the battery module 2, the current value I is positive, and when discharging from the battery module 2, the current value I is negative. The vertical axis of FIG. 3 represents the difference ΔVi. The current values ​​I and ΔVi in FIG. 3 are unitless numerical values ​​normalized by a predetermined value. In FIG. 3 , the difference ΔVi(t) corresponding to the current value I(t) for each battery data is plotted as a white circle. In other words, one plot corresponds to one battery data.

[0047] In this example, the least squares method is used to calculate the slope ΔRi and intercept ΔOCVi of ΔVi = ΔRi × I + ΔOCVi, which is shown as a straight line in FIG. 3 . The number of battery data items required to calculate the slope ΔRi and intercept ΔOCVi is three or more. The greater the number of battery data items, the more effectively the influence of battery data containing suddenly measured extreme values ​​can be reduced. FIG. 3 plots multiple battery data items measured over the course of a day. As shown in FIG. 3 , the battery data items are plotted in both positive and negative current value I areas. This indicates that battery data is acquired during both charging and discharging. In this example, the slope ΔRi and intercept ΔOCVi of each battery unit 3 are calculated based on one day's worth of battery data. By calculating the slope ΔRi and intercept ΔOCVi of each battery unit 3 based on the battery data items for the next day, the degree of deterioration of each battery unit 3 can be confirmed on a daily basis.

[0048] The interval for calculating the slope ΔRi and the intercept ΔOCVi is not limited to one day. If the interval is short, the system administrator can quickly recognize sudden changes in the slope ΔRi and the intercept ΔOCVi. The slope ΔRi and the intercept ΔOCVi may be calculated every time a predetermined number of new battery data, for example, five new battery data, are obtained. Of course, the slope ΔRi and the intercept ΔOCVi may also be calculated every time one new battery data is obtained. The slope ΔRi and the intercept ΔOCVi may be calculated, for example, based on the battery data for the past one day from the latest battery data.

[0049] The method described above makes it possible to obtain the slope ΔRi and intercept ΔOCVi for all battery units 3 included in the battery module 2. Therefore, the battery system 1 of this example makes it possible to obtain information regarding the degree of deterioration of all battery units 3. This information can be obtained both when the battery system 1 is in standby mode, i.e., not charging or discharging, and when the battery system 1 is in operation, charging or discharging.

[0050] The first determination unit 71 determines whether the absolute value of the intercept ΔOCVi is greater than or equal to the first threshold. For example, the first determination unit 71 determines whether the absolute value of the intercept ΔOCVi is greater than or equal to the first threshold. Furthermore, the first determination unit 71 determines that an abnormality exists when the absolute value of the intercept ΔOCVi is greater than or equal to the first threshold. The first threshold is a value determined in advance based on a preliminary test or the like. If the determination result of the first determination unit 71 is YES, i.e., |ΔOCVi| ≧ the first threshold, it is determined that the SOC of the battery unit 3 with the number i deviates from the SOC of the other battery units 3. Conversely, the first determination unit 71 may be configured to determine that no abnormality exists when the absolute value of the intercept ΔOCVi is less than the first threshold. If |ΔOCVi| < the first threshold, it is determined that the SOC of the battery unit 3 with the number i does not deviate from the SOC of the other battery units 3. The first threshold may vary depending on the composition of the electrolyte, for example, in the case of a redox flow battery. Therefore, it is advisable to determine the first threshold value through a preliminary test as described above.

[0051] The first determination unit 71 outputs the determination result for the battery unit 3 with number i to the notification device 8. This determination result is the result of comparing the intercept ΔOCVi for the battery unit 3 with number i with a first threshold. The system administrator can check the determination result through the notification device 8. If |ΔOCVi| is greater than or equal to the first threshold, the system administrator can recognize that an abnormality that causes a difference in SOC has occurred in the battery unit 3 with number i. In addition to comparing the intercept ΔOCVi with the first threshold, the first determination unit 71 may also determine that an abnormality exists in the open circuit voltage OCVi if the absolute value of the intercept ΔOCVi is greater than or equal to the first threshold. In this case, the determination result that an abnormality exists in the open circuit voltage OCVi is output to the notification device 8.

[0052] The second determination unit 72 determines whether the absolute value of the slope ΔRi is greater than or equal to a second threshold value. For example, the second determination unit 72 determines whether the absolute value of the slope ΔRi is greater than or equal to a second threshold value. Furthermore, if the absolute value of the slope ΔRi is greater than or equal to the second threshold value, the second determination unit 72 determines that an abnormality exists. The second threshold value is a value determined in advance based on a preliminary test or the like. If the determination result of the second determination unit 72 is YES, i.e., |ΔRi| ≧ the second threshold value, it is determined that the internal resistance value of the battery unit with the number i deviates from the internal resistance values ​​of the other battery units 3. Conversely, the second determination unit 72 may be configured to determine that no abnormality exists if the absolute value of the slope ΔRi is less than the second threshold value. If |ΔRi| < the second threshold value, it is determined that the internal resistance value of the battery unit with the number i does not deviate from the internal resistance values ​​of the other battery units 3. The second threshold value may also vary depending on the composition of the electrolyte, for example, in the case of an RF battery.

[0053] The second determination unit 72 outputs the determination result for the battery unit 3 with number i to the alarm device 8. This determination result is the result of comparing the slope ΔRi for the battery unit 3 with number i and a second threshold value. The system administrator can check the determination result through the alarm device 8. If |ΔRi| is greater than or equal to the second threshold value, the system administrator can recognize that deterioration has occurred in the components of the battery unit 3 with number i. In addition to comparing the slope ΔRi with the second threshold value, the second determination unit 72 may also determine that there is an abnormality in the internal resistance value Ri if the absolute value of the slope ΔRi is greater than or equal to the second threshold value. In this case, the determination result that there is an abnormality in the internal resistance value Ri is output to the alarm device 8.

[0054] Each process performed by the determination device 7 is implemented by a processing circuit (circuitry) including one or more processors. The processing circuit may be configured as an integrated circuit or the like that combines one or more memories, various analog circuits, and various digital circuits in addition to the one or more processors. The one or more memories store programs (instructions) that cause the one or more processors to execute each process. The memory also stores first and second thresholds used in the process. The one or more processors may execute each process according to the program read from the one or more memories, or according to a logic circuit pre-designed to execute each process. The processor may be a CPU, GPU, DSP, FPGA, ASIC, or any other processor suitable for computer control. The physically separated processors may cooperate with each other to execute each process. For example, the processors installed in each of physically separated computers may cooperate with each other via a network such as a LAN, WAN, or the Internet to execute each process. The program may be installed into the memory via the network from an external server device, or may be distributed stored on a recording medium such as a CD-ROM, DVD-ROM, or semiconductor memory, and installed into the memory from the recording medium.

[0055] <<Notification Device>> The notification device 8 may be any medium that allows the system administrator to recognize the determination result of the determination device 7. For example, the notification device 8 is a monitor. If the determination result is displayed on the monitor as characters or symbols, the system administrator can check the status of the battery unit 3.

[0056] The alarm device 8 may further include an alarm lamp or an alarm buzzer. The alarm lamp, for example, emits red light when an abnormality occurs in the battery unit 3. The alarm buzzer emits an alarm sound when an abnormality occurs in the battery unit 3. The alarm lamp or alarm buzzer reduces the possibility that the system administrator will overlook the judgment result on the monitor. The alarm lamp or alarm buzzer also contributes to notifying that there is no abnormality in the battery unit 3. For example, if the alarm lamp is configured to emit blue light when there is no abnormality in the battery unit 3, the alarm lamp can notify that there is no abnormality in the battery unit 3.

[0057] The notification device 8 allows the system administrator to identify the battery unit 3 that may be experiencing an abnormality. The system administrator can maintain the battery system 1 in an undegraded state by, for example, replacing the battery unit 3 as necessary.

[0058] The battery system 1 of this example can obtain information from the battery module 2 itself to identify any abnormalities that may occur in the battery module 2. Therefore, the battery system 1 of this example does not have a monitor cell that measures the open circuit voltage. The absence of a monitor cell in the battery system 1 provides the advantages of reducing the number of parts in the battery system 1, reducing the assembly process, and reducing costs.

[0059] <Operation Method of Battery System> A method of operating a battery system using the battery system 1 of this example includes the following steps A, B, and C.

[0060] In step A, a plurality of battery data are acquired. Each of the plurality of battery data is acquired at a plurality of different timings. Each battery data includes a current value I flowing through the battery module 2 and a voltage value Vi of each of the plurality of battery units 3 acquired at the same timing as the current value I. Step A is performed by the determination device 7 acquiring the battery data.

[0061] The current value I is measured by the ammeter 5 and output to the determination device 7. The voltage value Vi is measured by the voltmeter 6 and output to the determination device 7. The output current value I and the multiple voltage values ​​Vi are used as battery data for processing in the determination device 7.

[0062] In step B, a determination result is obtained based on the plurality of battery data acquired at each of the plurality of timings to determine whether or not there is an abnormality in the open circuit voltage OCVi and / or the internal resistance value Ri of each of the plurality of battery units 3. Step B includes step B1 and at least one of step B2 and step B3.

[0063] In step B1, the slope ΔRi and the intercept ΔOCVi are calculated for each of the battery units 3 based on a plurality of pieces of battery data acquired at different times. Step B1 is performed by the calculation unit 70 of the determination device 7. The slope ΔRi and the intercept ΔOCVi are the same as those described in the description of the battery system 1.

[0064] In step B2, it is determined whether the absolute value of the intercept ΔOCVi is equal to or greater than a first threshold value. This determination is made by the first determination unit 71 of the determination device 7. On the other hand, in step B3, it is determined whether the absolute value of the slope ΔRi is equal to or greater than a second threshold value. This determination is made by the second determination unit 72 of the determination device 7. The first threshold value and the second threshold value are the same as those described in the description of the battery system 1.

[0065] In step C, the determination result obtained in step B is notified. The notification is performed by the notification device 8. The notified determination result may be only whether or not the slope ΔRi is equal to or greater than the first threshold value, or may be only whether or not the intercept ΔOCVi is equal to or greater than the second threshold value. The determination result may also refer to abnormalities in the slope ΔRi and the intercept ΔOCVi.

[0066] <Redox Flow Battery> The battery system 1 of this example is suitable for a battery system including a large-capacity secondary battery in which a large number of battery cells are electrically connected. The large-capacity battery is, for example, a redox flow battery or a lithium-ion battery. Hereinafter, the redox flow battery will be referred to as an RF battery. Hereinafter, the configuration of the RF battery 9 will be described with reference to FIGS. 4 and 5. The RF battery 9 in FIG. 4 is shown in the form of a sub-stack 90s, which will be described later. The RF battery 9 in FIG. 5 is shown in the form of a cell stack 90, which will be described later.

[0067] The RF battery 9 illustrated in Fig. 4 is a secondary battery with a circulating electrolyte. The RF battery 9 is used, for example, for load leveling, compensation for momentary voltage drops, emergency power supplies, and output smoothing of natural energy power generation. The RF battery 9 is charged and discharged by utilizing the difference between the oxidation-reduction potential of the positive electrode active material contained in the positive electrode electrolyte and the oxidation-reduction potential of the negative electrode active material contained in the negative electrode electrolyte. The positive electrode active material and the negative electrode active material are, for example, vanadium ions.

[0068] The RF battery 9 typically includes a plurality of battery cells 40. Each battery cell 40 includes a positive electrode cell 42, a negative electrode cell 43, and a diaphragm 41. The diaphragm 41 is disposed between the positive electrode cell 42 and the negative electrode cell 43. The positive electrode cell 42 is provided with a positive electrode 44. The negative electrode cell 43 is provided with a negative electrode 45. Known configurations can be used as appropriate for each configuration of the battery cells 40.

[0069] A cathode electrolyte is supplied to each of the cathode cells 42 of the plurality of battery cells 40 from a cathode tank (not shown) through an outward piping 421. A pressure pump (not shown) is disposed in the outward piping 421. The cathode electrolyte discharged from the cathode cell 42 is returned to the cathode tank through a return piping 422. In other words, the cathode electrolyte circulates between the cathode tank and the cathode cell 42. Anode electrolyte is supplied to each of the anode cells 43 of the plurality of battery cells 40 from a cathode tank (not shown) through an outward piping 431. A pressure pump (not shown) is disposed in the outward piping 431. The anode electrolyte discharged from the anode cell 43 is returned to the anode tank through a return piping 432. In other words, the anode electrolyte circulates between the anode tank and the anode cell 43. In FIG. 4 , the flows of the cathode electrolyte and the anode electrolyte are indicated by arrows with arrowheads. Known cathode electrolytes and anode electrolytes can be used.

[0070] The RF battery 9 of this example is usually used in a configuration called a cell stack 90 shown in Fig. 5. The cell stack 90 is configured by sandwiching a plurality of sub-stacks 90s between two end plates 91, 91. The end plates 91, 91 are fastened together by a fastening mechanism 92. The sub-stack 90s is a stack sandwiched between two supply / discharge plates 95. As shown in Fig. 4, the stack has a structure in which a cell frame 49, a positive electrode 44, a diaphragm 41, and a negative electrode 45 are repeatedly stacked in this order.

[0071] The cell frame 49 has a bipolar plate 49b and a frame body 49f. The bipolar plate 49b faces at least one of the positive electrode 44 and the negative electrode 45. The frame body 49f holds the outer edge of the bipolar plate 49b. The bipolar plate 49b and the frame body 49f form a recess inside the frame body 49f. The recess houses the positive electrode 44 or the negative electrode 45, sandwiching the bipolar plate 49b between them. A single battery cell 40 is formed by disposing the positive electrode 44 and the negative electrode 45 between the bipolar plates 49b of adjacent cell frames 49, with the diaphragm 41 sandwiched between them.

[0072] When the above-described RF battery 9 is applied to the battery system 1 of FIG. 1 , the cell stack 90 or sub-stack 90s of the RF battery 9 can become either a battery module 2 or a battery unit 3. For example, when the battery module 2 is formed by the cell stack 90, the sub-stack 90s can become the battery unit 3. Furthermore, the battery module 2 may be formed by electrically connecting multiple cell stacks 90 in series. In this case, each of the multiple cell stacks 90 can become a battery unit 3.

[0073] Even in a battery system 1 equipped with an RF battery 9, the state of the battery unit 3 including the battery cells 40, i.e., ΔRi and ΔOCVi related to the battery unit 3, can be monitored regardless of the operating state of the RF battery 9. This allows a system administrator to quickly take action such as replacing a battery unit 3 that may have developed a malfunction. For example, if the battery module 2 is made up of multiple cell stacks 90, the system administrator can quickly replace only the cell stack 90 that may have developed a malfunction. As a result, the performance of the battery system 1 is maintained over a long period of time.

[0074] As shown by the arrowheads in FIG. 4 , in the RF battery 9, the positive electrode electrolyte supplied to each of the multiple battery cells 40 is supplied from a common positive electrode tank. The negative electrode electrolyte supplied to each of the multiple battery cells 40 is also supplied from a common negative electrode tank. Therefore, the SOCs of the multiple battery cells 40 are usually approximately the same. However, there are cases where the SOC of some battery cells 40 varies significantly compared to the SOC of the other battery cells 40. For example, if a hole or the like occurs in the membrane 41 of the leftmost battery cell 40, the positive electrode electrolyte and the negative electrode electrolyte will mix within the battery cell 40, causing a significant change in the SOC of that battery cell 40. In the battery system 1 of this example, the change in SOC can be detected as ΔOCVi. Therefore, a battery unit 3 ( FIG. 1 ) including a battery cell 40 in which an abnormality such as a change in SOC has occurred can be quickly detected.

[0075] The embodiments disclosed herein should be considered illustrative in all respects and not restrictive. The present disclosure is not limited to these examples, but is defined by the claims, and all modifications within the meaning and scope of the claims are intended to be included. For example, in the above-described embodiment, the reference voltage value V0 determined at multiple timings was one of the mode, median, and average. That is, if the reference voltage value V0(t1) was the mode at time t1, the reference voltage value V0(t2) was also the mode at time t2, and the reference voltage value V0(t) was also the mode at other times t. Depending on the deterioration state of the battery unit, it is considered that the degree of deterioration of the battery unit can be more appropriately determined by combining two or three selected from the mode, median, and average. For example, the reference voltage value V0(t1) may be the mode at time t1, and the reference voltage value V0(t) may be the median or average at other times t. For example, the reference voltage value V0 may be set as the average value at all times, and the reference voltage value V0 may be set as the mode value intermittently at predetermined time intervals.

[0076] REFERENCE SIGNS LIST 1 Battery system 2 Battery module 3 Battery unit 4, 40 Battery cell 41 Diaphragm 42 Positive electrode cell 43 Negative electrode cell 44 Positive electrode 45 Negative electrode 49 Cell frame 49b Bipolar plate 49f Frame 421, 431 Outward piping 422, 432 Return piping 5 Ammeter 6 Voltmeter 7 Determination device 70 Calculation unit 71 First determination unit 72 Second determination unit 8 Notification device 9 RF battery 90 Cell stack 90s Substack 91 End plate 92 Clamping mechanism 95 Supply and discharge plate

Claims

1. A battery system comprising a battery module in which a plurality of battery units are electrically connected in series, each of the plurality of battery units including at least one battery cell, the battery system comprising: an ammeter for measuring a current value I flowing through the battery module; a voltmeter for measuring a voltage value Vi of each of the plurality of battery units; a determination device capable of determining whether or not there is an abnormality in the open circuit voltage OCVi and / or the internal resistance value Ri of each of the plurality of battery units; and a notification device for notifying the determination result by the determination device, the determination device comprising a calculation unit and at least one of a first determination unit and a second determination unit, the i being a natural number and a unique number assigned to each of the plurality of battery units, the calculation unit acquires, at a plurality of different timings, battery data including the current value I measured at the same timing and the voltage value Vi of each of the plurality of battery units, and at each of the plurality of timings, calculates an equation of a linear function having a slope ΔRi and an intercept ΔOCVi for each of the plurality of battery units based on the battery data acquired at each of the plurality of timings, and calculates the slope ΔRi and the intercept ΔOCVi using the plurality of equations of the linear function calculated at different timings; the first determination unit determines whether an absolute value of the intercept ΔOCVi is larger or smaller than a first threshold; the second determination unit determines whether the absolute value of the slope ΔRi is larger or smaller than a second threshold; the equation of the linear function is ΔVi=ΔRi×I+ΔOCVi, and ΔVi is a difference between the voltage value Vi in the battery data and a reference voltage value V0; the reference voltage value V0 is one of a mode, a median, and an average value calculated from voltage values ​​excluding the voltage value Vi in the battery data acquired at each of the plurality of timings.

2. The battery system of claim 1, wherein the first determination unit determines that there is an abnormality in the open circuit voltage OCVi when the absolute value of the intercept ΔOCVi is greater than or equal to the first threshold value, and the second determination unit determines that there is an abnormality in the internal resistance value Ri when the absolute value of the slope ΔRi is greater than or equal to the second threshold value.

3. The battery system according to claim 1 or 2, which does not include a monitor cell for measuring the open circuit voltage OCVi.

4. The battery system according to any one of claims 1 to 3, wherein the reference voltage value V0 is the most frequent value.

5. The battery system according to any one of claims 1 to 4, wherein the battery cells are redox flow battery cells.

6. A method for operating a battery system comprising a battery module in which a plurality of battery units are electrically connected in series, each of the plurality of battery units including at least one battery cell, comprising: step A of acquiring, at different times, battery data including a current value I flowing through the battery module and a voltage value Vi of each of the plurality of battery units, the data being acquired at the same time; step B of determining, based on the plurality of battery data acquired at each of the plurality of times, whether or not there is an abnormality in the open circuit voltage OCVi and the internal resistance value Ri of each of the plurality of battery units; and step C of notifying the determination result, wherein i is a natural number and is a unique number assigned to each of the plurality of battery units, and step B includes step B1 and at least one of step B2 and step B3, a first threshold value for determining whether the absolute value of the intercept ΔOCVi is larger than a first threshold value; and a second threshold value for determining whether the absolute value of the slope ΔRi is larger than a second threshold value. The method for operating a battery system includes: determining, at each of the plurality of timings, an equation of a linear function having a slope ΔRi and an intercept ΔOCVi for each of the plurality of battery units based on the battery data acquired at each of the plurality of timings; determining, at each of the plurality of timings, an equation of a linear function having a slope ΔRi and an intercept ΔOCVi for each of the plurality of battery units based on the battery data acquired at each of the plurality of timings; determining, at each of the plurality of timings, an equation of the linear function having a slope ΔRi and an intercept ΔOCVi for each of the plurality of battery units; determining, at each of the plurality of timings, an equation of the linear function 7. The method of operating a battery system described in claim 6, wherein in step B2, if the absolute value of the intercept ΔOCVi is greater than or equal to the first threshold value, it is determined that there is an abnormality in the open circuit voltage OCVi, and in step B3, if the absolute value of the slope ΔRi is greater than or equal to the second threshold value, it is determined that there is an abnormality in the internal resistance value Ri.

8. The method for operating a battery system according to claim 6 or 7, wherein the reference voltage value V0 is the mode value.

9. A method for operating a battery system according to any one of claims 6 to 8, wherein the slope ΔRi and the intercept ΔOCVi are determined by linear regression analysis using a plurality of pieces of battery data acquired over a predetermined period of time.

10. A method for operating a battery system according to any one of claims 6 to 9, wherein the battery cells are redox flow battery cells.

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