Battery storage system, railway vehicle equipped with same, and abnormal battery detection method

Abstract

To provide a method of detecting an abnormal battery capable of early detecting an abnormal cell.SOLUTION: A storage battery system operates an assembled battery while adjusting the capacity, in which a plurality of battery cells are connected in series in the assembled battery and is provided with a controller capable of adjusting the capacity. The controller obtains the battery status from each of the plurality of batteries, generates a control command based on the obtained battery status, and in the process of adjusting the capacity of the battery cell whose voltage is outside an allowable range by the control command from the assembled battery, determines a battery cell having a voltage deviation of a predetermined value or more with respect to the average voltage of the assembled battery as an abnormal battery. In addition, the deviation between the voltage of each battery cell and the average voltage of the assembled battery may be calculated. For example, if there is a deviation of 3σ or more in a normal distribution, it may be determined that the battery is abnormal.SELECTED DRAWING: Figure 11

Description

[Technical Field]

[0001] The present invention relates to a storage battery system useful for efficient operation of storage batteries, a railway vehicle equipped with the same, and an abnormal battery detection method. [Background technology]

[0002] Battery deterioration can lead to self-discharge. In a storage battery system where batteries are connected in series, if even one of the series-connected battery cells self-discharges, the performance of the entire storage battery system, i.e., its energy efficiency, will decrease. Therefore, it is necessary to detect such self-discharge before it adversely affects the performance of the battery system.

[0003] Furthermore, the rate of self-discharge is on the order of a few mV / day in the initial stage of degradation, and does not have much of an impact, but once this stage is passed, the rate of self-discharge rises rapidly to the order of several tens of mV / day, significantly reducing energy efficiency. To avoid this, the rate of self-discharge needs to be detected at a stage on the order of a few mV / day. However, the voltage sensor installed in the battery controller only has an accuracy of around 10 mV.

[0004] In addition, because storage battery systems are equipped with a control device that equalizes the voltages of each battery cell connected in series, i.e., adjusts the battery capacity of each battery cell, it is difficult to detect minute self-discharges of individual battery cells. In other words, this battery capacity adjustment makes it difficult to detect self-discharges early. Therefore, a method is known in which, if the battery with the lowest voltage that is the capacity adjustment target deviates from the average voltage even after capacity adjustment, it is determined to be an abnormal battery (Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-10512 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the abnormal battery determination method described in Patent Document 1 had the following two problems. First, simply monitoring the voltage before and after capacity adjustment made it difficult to capture changes of several mV / day. Second, it was not possible to identify the cause of the abnormality, such as whether the deviation from the average voltage was due to self-discharge or other causes such as capacity degradation. The present invention was made in light of the above problems, and its purpose is to provide a storage battery system capable of early detection of abnormal cells. [Means for solving the problem]

[0007] The present invention, which solves the above-mentioned problems, is a storage battery system that operates while adjusting the capacity of a battery pack, in which the battery pack has multiple battery cells connected in series and is equipped with a controller that can also adjust the capacity, and the controller acquires the battery status from each of the multiple batteries and generates a control command based on the acquired battery status, and in the process of adjusting the capacity of battery cells in the battery pack whose voltage is outside the allowable range using the control command, battery cells whose voltage deviation from the average voltage of the battery pack is greater than a predetermined value are determined to be abnormal batteries. [Effects of the Invention]

[0008] The present invention provides a storage battery system that is capable of detecting abnormal cells early. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a functional block diagram showing a schematic configuration of a storage battery system (hereinafter also referred to as "the system") according to a first embodiment of the present invention. [Figure 2]FIG. 1 is a circuit diagram for explaining an individual capacity adjustment circuit for a battery pack in which n cells are connected in series. [Figure 3] FIG. 1 is a schematic diagram for explaining passive balancing control. [Figure 4] 10 is a flowchart showing a procedure for detecting a self-discharge abnormality. [Figure 5] 10 is a graph for explaining an abnormal battery detection method (hereinafter also referred to as "detection method") based on threshold determination of target designation count / time. [Figure 6] 10 is a graph for explaining a detection method based on variance determination of target designation count / time. [Figure 7] 10 is a graph for explaining a detection method based on balancing time / time threshold determination. [Figure 8] 10 is a graph illustrating a detection method based on a balancing time and capacity distribution determination. [Figure 9] 10 is a graph for explaining determination of variations in capacity deterioration rate (SOHQ). [Figure 10] 10 is a graph illustrating a detection method by measuring a voltage deviation, which is the voltage of each cell minus the average voltage. [Figure 11] 10 is a graph for explaining a detection method based on deviation determination of each cell voltage. [Figure 12] 10 is a graph for explaining a detection method based on maximum / average / minimum voltages. [Figure 13] FIG. 1 is a schematic diagram for explaining active balancing control. [Figure 14] FIG. 10 is a schematic diagram for explaining a detection method based on threshold determination of the designated number of balancing charge times / time and the capacity / time. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings etc. Example 1 will be described with reference to Figs. 1 to 6. Example 2 will be described with reference to Figs. 7 and 8. Example 3 will be described with reference to Figs. 9. Example 4 will be described with reference to Figs. 10 and 11. Example 5 will be described with reference to Fig. 12. Example 6 will be described with reference to Figs. 13 and 14.

[0011] The present invention is not limited to the following description of specific examples, and various changes and modifications can be made by those skilled in the art within the scope of the technical ideas disclosed in this specification. Furthermore, in all drawings used to explain the present invention, components having the same function are given the same reference numerals, and redundant descriptions may be omitted. Furthermore, in all Examples 1 to 6, battery cells with cell numbers 1 to 6 (hereinafter simply referred to as "batteries" or "cells") are clearly shown, and descriptions of the other battery cells 7 to n are omitted, but these battery cells 7 to n are also within the scope of the present invention. [Example]

[0012] Figure 1 is a functional block diagram showing the general configuration of this system. The system in Figure 1 is composed of a host controller 19 and a battery pack (hereinafter also referred to as a "battery pack") 10, which transmits information and controls input and output via a communication line 18. To ensure the required voltage and capacity, a large number of battery packs 10 are connected in series, and the battery packs 10 are equipped with battery cell controllers 12 and a battery control device 15 for adjusting the voltage and capacity.

[0013] The host controller 19 may be considered an ECU (Electronic Control Unit) installed in an automobile or an electronic control device provided to assist the driving operation of a railway vehicle, and is a general term for a device (unit) that controls a system using electronic circuits. Here, the host controller 19 transmits information to the battery control device 15 and its subordinate cell control 12 via the communication line 18 to monitor the battery pack 10 and control input and output by executing advanced control, which will be described later, in accordance with the application of the battery pack 10.

[0014] The battery control device 15 is located below the upper controller 19, with one battery control device provided for each battery pack 10. The battery control device 15 is hierarchically structured so that multiple cell controllers 12 are subordinate to it, and each cell controller 12 monitors and controls (hereinafter referred to as "monitoring control" or simply "control") multiple battery cells 11. To monitor the status of each battery cell 11 under its supervision, the cell controller 12 detects voltage using a voltage detection line 13 and also detects temperature using a thermocouple 14.

[0015] Based on these detection results, if there is a capacity imbalance between the many series-connected battery cells 11, the cell control 12 performs balancing control to adjust the imbalance. As an example, with regard to temperature detection, one cell control 12 monitors only one point.

[0016] The cell controller 12 can simultaneously control a large number of battery cells 11 that are linked to each other in advance. As shown in Fig. 2 (omitted from Fig. 1) and exemplified in Fig. 2, the cell controller 12 can monitor not only an assembled battery in which six cells are connected in series (hereinafter also referred to as "6-series"), but also an assembled battery in which twelve cells are connected in series (hereinafter also referred to as "12-series").

[0017] It is preferable that the number of cell controllers 12 is proportional to the number of battery cells 11 connected in series. The cell controllers 12 perform balancing control and the like by receiving commands from the battery control device 15 via communication lines 16. For example, CAN may be used as a communication method for this purpose in the case of a mobile object.

[0018] Furthermore, by connecting the multiple cell controllers 12 with each other through communication lines 16, it becomes possible to simultaneously send communication commands from the battery control device 15 to all of the cell controllers 12. Based on the voltage information and temperature information of each cell sent from the cell controllers 12 and the current information of the current sensor 17, the battery control device 15 estimates the state of charge (SOC), estimates and controls the deterioration rate (capacity maintenance rate: SOH: State of Health), and calculates the allowable power.

[0019] At the same time, the battery control device 15 transmits information to the host controller 19 via a communication line 18 to control the input and output of the battery. As shown in FIG. 1, the battery pack 10 and the host controller 19 function in cooperation with each other via the communication line 18, but they are independent components that can be procured separately. Here, the capacity adjustment circuit 23, the cell control unit 12, and the battery control device 15 are collectively referred to as the controller. This controller can also be considered to include the host controller 19. The control hierarchy shown in FIGS. 1 and 2 is configured in the reverse order described here, i.e., in the order of the host controller 19, battery control device 15, cell control unit 12, and capacity adjustment circuit 23.

[0020] An example of a circuit for performing balancing control and an example of control are shown using Figures 2 and 3. Figure 2 is a circuit diagram for explaining an individual capacity adjustment circuit for a battery pack in which n cells are connected in series. As shown in Figure 2, a capacity adjustment (balancing) circuit 23 is located between six battery cells 1 to 6 connected in series and a cell control circuit 12 that monitors them all together. This balancing circuit 23 is mainly composed of transistors 21 such as MOSFETs and balancing resistors 22, and one transistor 21 and one balancing resistor 22 are connected in parallel to each battery cell 11.

[0021] An example of balancing operation is explained with reference to FIG. 3. FIG. 3 is a schematic diagram for explaining passive balancing control. As shown in FIG. 3, among the cells identified by cell numbers 1 to n, cell number 4 (cell 4) has the lowest voltage. In this way, the battery with the lowest voltage is called the balancing target cell. For example, when the voltage difference between each of cells 1 to n and the balancing target cell is equal to or greater than the voltage threshold Vth, it is determined that capacity adjustment is necessary, and balancing control is performed on the target cell 4.

[0022] In this case, this applies to cell number 1 and cell number 3. By turning on transistor 21 connected in parallel to these cells 1 and 3 and passing current through balancing resistor 22 connected in parallel, the target cells are discharged and their capacity is matched to that of cell 4, the balancing target cell. Balancing control that adjusts capacity by discharging into balancing resistor 22 in this way is called passive balancing control and is a commonly used method of adjusting battery capacity.

[0023] In this system, the battery with the lowest voltage among the n batteries connected in series in the battery pack 10 is targeted, and all of the other n-1 batteries are subjected to balancing operation. In the battery pack 10, it is necessary to monitor all of the battery cells 11 connected in series in this way and make appropriate adjustments.

[0024] Therefore, the cell controller 12 communicates information that is linked to all cell numbers 1 to n and that allows the voltage of each cell to be determined to the battery control device 15. The battery control device 15 is higher-level than the cell controller 12 and has a wider control range, and is able to aggregate all cell information obtained from the cell controller 12, and uses this information to determine the target voltage of the battery pack 10. Meanwhile, the cell controller 12 only performs balancing operations for each battery cell 11.

[0025] In the system of the first embodiment, a detection method based on the number of times a target cell is specified for capacity adjustment will be described. Here, a control flow of balancing control by the battery control device 15 and a method for detecting an abnormal cell will be described. FIG. 4 is a flowchart showing the procedure for detecting a self-discharge abnormality. As shown in FIG. 4, the procedure for detecting a self-discharge abnormal cell is executed by the battery control device 15 through steps S10 to S17.

[0026] First, step S10 is reached, with a calculation cycle of, for example, every second, and control is initiated. Next, in step S11, the battery control device 15 detects each cell voltage and each cell number. When the battery control device 15 performs this control, it obtains each cell voltage and each cell number through communication from the cell control 12. At this time, the cell with the lowest voltage among all voltages is detected and set as the minimum voltage value Vmin.

[0027] Next, in step S12, the battery control device 15 determines whether Vmin + voltage threshold < cell voltage for all cells. If there is a corresponding cell, the process proceeds to step S13; if there is no corresponding cell, the process proceeds to step S17, where the calculation ends. In step S13, the battery control device 15 starts a balancing operation for the corresponding cell so that the capacity is adjusted by (cell voltage - Vmin), and then proceeds to step S14. In step S14, the battery control device 15 counts up the target specified number of times / time, which is the number of times specified as the balancing target within a certain period of time for the cell number that has the lowest voltage, and then proceeds to step S15.

[0028] In step S15, the battery control device 15 determines whether this target specified count value / time is equal to or less than the target specified count threshold. If this determination is equal to or less than the threshold (Yes), the cell is not a self-discharge abnormal cell, and the process proceeds to step S17, where the calculation ends. If, in step S15 (No), there is a cell with a count equal to or greater than the threshold, the battery control device 15 determines that the cell is a self-discharge abnormal cell in S16, and then proceeds to step S17, where the calculation ends. The control content of steps S14 and S15 will be described in detail using FIG. 5.

[0029] Figure 5 is a graph illustrating a detection method using a threshold value judgment of target designation count / time. In Figure 5, the horizontal axis represents the cell number, and the vertical axis represents a time interval, for example, the number of target designation counts per year. As shown in Figure 5, the target designation count is the number of times a cell has reached the lowest voltage and been designated as a target cell during balancing control in battery control device 15. As in Figure 3, it can be seen that cell 4 has been designated as a target cell more times than the other cells.

[0030] If this target designation count is greater than the target designation count threshold B, i.e., if the battery control device 15 determines in step S15 that it has exceeded the threshold (No), it determines that the cell is abnormal in step S16. In this way, the battery control device 15 can detect abnormalities such as self-discharge. The target designation count threshold is determined taking into consideration variations in power consumption of the cell controller 12 and variations in expected deterioration.

[0031] Originally, balancing control is a capacity adjustment function that corrects the aforementioned variations in power consumption and deterioration. For example, if the aforementioned variation occurs by A% of capacity and the purpose of balancing control is to correct this, and the number of balancing operations estimated from A% is B, the target specified number of operations must be greater than threshold B.

[0032] In this way, the target specification count threshold B is determined based on the expected number of balancing operations. While FIG. 5 shows only cell 4 as being affected, multiple cells may be affected. If the battery control device 15 determines in step S16 that the cell is experiencing a self-discharge abnormality, it sends an alarm signal to the host system 19 or warns the system manager. This is to prompt battery replacement and to inform the system manager that operation should be stopped.

[0033] If a self-discharge abnormal cell does not pose an immediate danger but protection control is necessary, the host system 19 and the battery control device 15 will execute such control. For example, this system is usually monitored and controlled using the average value of the charging rates obtained from the SOCs of all cells 1 to n.

[0034] However, if the occurrence of this self-discharge abnormal cell is determined, it is advisable to use the SOC calculated from the voltage of this cell 4 as a control value to protect and operate the abnormal cell 4. This is particularly true in special cases such as discharging to a 0% charge rate, in order to enable optimal control while grasping the SOC of the abnormal battery that is estimated to be the most deteriorated. In steps S14 and S15, the battery control device 15 determines whether the target specified count value / time is equal to or greater than a certain threshold, but there is also a method that takes variance into consideration.

[0035] Figure 6 is a graph illustrating a detection method based on variance judgment of target specification count / time. In Figure 6, the horizontal axis shows the target specification count / time, and the vertical axis shows the number of applicable cells. Here, the number of applicable cells is the sample size considered to be the statistical significance level, and if the variance is ideal, the target specification count should follow a normal distribution centered on a median with a variance of 0. As shown in Figure 6, distribution C of the balancing target specification count follows this normal distribution, and variance judgment is performed based on this assumption. In an actual system, due to complex variations in operating conditions and components, this distribution does not follow this normal distribution, but it can be used as a judgment criterion.

[0036] In Example 1, the variance threshold D is assumed to be a value of 3σ. When following a normal distribution, the target designation count with a variance of 3σ or more exists in only about 0.1%, so if the number of batteries in series is 96, there is a high probability that not a single cell will fall into this category. However, as shown in Figure 6, if a cell falls into this category with a target designation count of 3σ or more, it is statistically reasonable to determine that this is an abnormal cell that deviates significantly from the standard. Note that the variance threshold D does not need to be 3σ, as it should be determined depending on the extent of variance that is considered abnormal.

[0037] Furthermore, in addition to the criteria shown in step S15, the following criteria can be added as criteria for determining whether a cell is a self-discharge abnormal cell. That is, a cell may be determined to be abnormal when both the target specified count threshold B, which is determined by the absolute value of the count as explained in Fig. 5, and the variance threshold D, which is determined by the variance from the median as explained in Fig. 6, are satisfied (AND condition). Alternatively, a cell may be determined to be abnormal when only one of the target specified count threshold B and the variance threshold D is satisfied (OR condition).

[0038] In conventional battery pack systems, the well-known method of detecting self-discharge of any of the multi-series connected cells is to monitor the voltage after balancing, but it is difficult to take into account the capacity adjusted by the balancing operation. This method also has the following two issues. First, simply monitoring the voltage before and after capacity adjustment makes it difficult to capture changes of a few mV / day. Second, when a battery is detected as abnormal due to a deviation from the average voltage, it is impossible to identify the cause of the abnormality: whether it is self-discharge or other causes such as capacity degradation.

[0039] The method for detecting an abnormal battery in this system is to determine whether a battery is abnormal based on the specified number of times for a target cell using battery control device 15, which can aggregate all cell information. That is, battery control device 15 calculates the self-discharge of battery pack (assembled battery) 10, in which multiple battery cells 1 to n are connected in series, and the deviation between the voltage of each battery cell and the average voltage of the assembled battery, and determines that self-discharge has occurred if the deviation exceeds a predetermined value.

[0040] In other words, if the number of times that the open circuit voltage (OCV) of any of the battery cells 1 to n reaches the lowest cell voltage (balancing target cell) exceeds a predetermined value during balancing of the cell's open circuit voltage (OCV), the system determines that the OCV of that battery cell has decreased. By utilizing the specified target number of balancing attempts, the system can detect differences based on the cell's original performance before the balancing operation. Therefore, the system can achieve higher detection accuracy than conventional methods that evaluate the voltage value after balancing.

[0041] As a result, this system can detect that the problem is self-discharge, rather than capacity degradation due to other causes. In this way, when the battery control device 15 determines in step S16 that the cell is abnormal due to self-discharge, it sends an alarm signal to the host system 19 or warns the system manager. This allows the battery control device 15 to prompt the replacement of the abnormal battery and to inform the system manager that operation should be stopped. [Example]

[0042] In the first embodiment, the target number of balancing operations was used as the control value, but similar information includes the balancing time and the capacity adjusted (discharged) by balancing. As explained in the first embodiment, such balancing time and the capacity used for the adjustment can be applied to the process for detecting the difference based on the original performance of the cells before the balancing operation. However, such balancing time and the capacity used for the adjustment are usually not known in the cell controller 12 or the battery control device 15, and therefore are not as versatile as the target number of balancing operations in the first embodiment.

[0043] Figure 7 is a graph to explain the detection method based on balancing time / time threshold judgment, with the horizontal axis showing the cell number and the vertical axis showing the balancing time or balancing capacity within a certain period. Normally, the current value flowing through the balancing resistor during balancing is almost constant, and since there is a correlation between balancing capacity and time, the two are considered to be equivalent indicators and are displayed on the vertical axis in Figure 7.

[0044] In Figure 5, the higher the balancing target specified count value, the closer it is to the lowest cell voltage, and the more likely the cell is to self-discharge. In contrast, in Figure 7, the lower the balancing time or capacity, the closer it is to the lowest cell voltage, indicating that the cell is not subject to balancing adjustment. If the value is smaller than the balancing capacity threshold E, the cell is determined to be abnormal.

[0045] Furthermore, similar to the example of applying 3σ variance to the target specification count in Figure 6, it is possible to reach a similar conclusion by applying 3σ variance to the numerical value of balancing time or capacity. Here, Figure 8 is a graph for explaining a detection method based on variance determination of balancing time and capacity. As shown in Figure 8, when the balancing time or capacity is extremely small, that is, when the variance is below the negative variance threshold G, an abnormality is determined in the same way as in Figure 7. [Example]

[0046] As in Examples 1 and 2, it is possible to identify self-discharge cells based on the target number of balancing control attempts, time, and capacity. However, because the balancing control is intended to protect cells experiencing capacity degradation, there is a possibility that capacity degradation may be erroneously detected instead of self-discharge. Therefore, as shown in Figure 9, it is possible to improve the accuracy of self-discharge detection by detecting that there is no difference in the capacity degradation rate. Figure 9 is a graph for explaining the determination of variations in capacity degradation rate (SOHQ), with the horizontal axis representing cell number and the vertical axis plotting capacity degradation rate (SOHQ).

[0047] The capacity degradation rate is estimated for each cell by the battery control device 15. In FIG. 9, it can be seen that there are cells with SOHQs that deviate from the degradation tolerance H from the average SOHQ. As an example, if the balancing operation is performed with no difference in SOHQ despite the number of times the target is specified in the balancing control being high, it can be estimated that this is due to self-discharge rather than capacity degradation. As a result, the battery pack system of Example 3 (also referred to as "this system") can improve the accuracy of detecting self-discharge.

[0048] The control flow is as follows: if the target specified count threshold B in Figure 5 is exceeded and the SOHQ of the cell that has reached target specified count threshold B is exceeded by the degradation tolerance value H, a self-discharge abnormality is detected. If the SOHQ of each cell has not been determined, it is also effective to use the resistance degradation rate (SOHR) of each cell as a substitute. Also, if neither the SOHQ nor the SOHR of each cell has been estimated, it is also possible to use the voltage information of each cell as a substitute.

[0049] For example, a cell with more advanced capacity degradation than others often has the lowest voltage and is therefore designated as the target for balancing control. However, if such a degraded cell is subjected to regulated charging using this system, its voltage will be the maximum due to its small capacity. By detecting this phenomenon, it is possible to determine whether the cell is designated as the target for balancing control due to variations in capacity degradation. The control flow is as follows: if the target designation count threshold B in Figure 5 is exceeded and the cell that has reached target designation count threshold B does not become the maximum voltage cell, a self-discharge abnormality is detected. [Example]

[0050] In the fourth embodiment, a method for detecting an abnormality from the deviation of the voltage of the battery cells 11, rather than from values ​​related to balancing control, will be described. When it is not possible to grasp information related to balancing control and only the voltage of each cell can be obtained by the battery control device 15, it is necessary to detect a self-discharge abnormality from the cell voltage.

[0051] The detection method in this case will be explained using Figures 10 and 11. Figure 10 is a graph for explaining the detection method by measuring the voltage deviation Vd, which is the voltage of each cell minus the average voltage. Figure 10 shows the voltage of each cell 1 to n. Figure 10 also shows the average cell voltage (hereinafter simply referred to as "average voltage") V, which is the average value of the voltages of all cells 1 to n.

[0052] In Example 4, detection is performed by measuring the voltage deviation Vd, which is the cell voltage minus the average voltage, for each cell. This voltage deviation Vd is calculated by taking a moving average of, for example, one month's worth of data, to obtain a voltage deviation moving average Vd', as shown in FIG. 11. FIG. 11 is a graph illustrating a detection method based on determining the deviation of each cell voltage. As shown in FIG. 11, a simple moving average is assumed here, but the averaging process can be performed using a low-pass filter or any other method.

[0053] In Figure 11, only cell 4 is below the voltage deviation threshold J. By setting the voltage deviation threshold J to a value close to the voltage threshold A, which is the balancing control threshold, it is possible to determine that there is a high possibility that balancing control is being performed with cell 4 as the target.

[0054] The control flow is such that a self-discharge abnormality is detected when the voltage deviation moving average Vd' is equal to or greater than the voltage deviation threshold J. Normally, the capacity is adjusted by balancing at the voltage threshold A, so it is unlikely that the voltage deviation moving average Vd' will be equal to or greater than the voltage threshold A. Therefore, the voltage deviation threshold J is set to a value smaller than the voltage threshold A. By doing so, detection equivalent to that in Examples 1 and 2 can be achieved from voltage information as well. [Example]

[0055] Example 5 illustrates a detection method (hereinafter also referred to as "this detection method") in this system that determines an abnormality based only on limited information such as the maximum cell voltage, the minimum cell voltage, and the average voltage. Up to this point, Examples 1 to 4 have been described on the assumption that software for this detection method is implemented in the battery control device 15. Since the procedure for this detection method may be implemented as a program in the upper controller 19, Example 5 assumes that this detection method is implemented in this upper controller 19. Generally, all voltage information for each cell can be obtained up to the battery control device 15, but the upper controller 19 can only obtain limited information.

[0056] That is, only information such as the maximum, average, and minimum voltage values, which are representative values ​​of the cell voltages, is transmitted to the upper controller 19. Therefore, the upper controller 19 needs a method for detecting self-discharge abnormalities from these limited representative values. Here, we consider a case where self-discharge occurs on a scale of several cells. In this system, if several cells, such as cells 1 and 3 in Figure 3, deviate from the average voltage value by the voltage threshold Vth, after the balancing operation, the balancing will stop when the voltages of all cells 1 to n fall below the voltage threshold Vth.

[0057] In such a case, the deviation between the maximum voltage value and the average voltage value is small, but the deviation between the minimum voltage value and the average voltage value is large, as will be described later with reference to Figure 12. To detect this situation, the condition that both of the following determination formulas (a) and (b) are satisfied simultaneously must be met, and if this is met, self-discharge can be detected.

[0058] (a) Maximum voltage value - average voltage value < maximum voltage deviation threshold M (b) Average voltage value - minimum voltage value > minimum voltage deviation threshold L Furthermore, although it is possible to use only the above judgment formulas (a) and (b), this alone may result in incorrect operation, such as excessively determining an abnormality even when the judgment formulas (a) and (b) are temporarily established. To avoid such incorrect operation, accuracy can be improved by determining an abnormality only when the above judgment formulas (a) and (b) are established consecutively.

[0059] This can be achieved by introducing an abnormality notification counter that satisfies the following conditions (1) and (2).

[0060] If condition (1), judgment formulas (a) and (b) are both true, and if the abnormality notification counter is greater than or equal to the abnormality notification counter threshold K,

[0061] Regarding the issuance of an abnormality Condition (2), if both the judgment formulas (a) and (b) are true, and if the abnormality notification counter is less than the abnormality notification counter threshold K.

[0062] Abnormality Notification Counter = Abnormality Notification Counter + 1 Condition (3) Other than the above (when either the judgment formula (a) or (b) is false) Abnormality counter = 0

[0063] This detection operation is explained in Figure 12. Figure 12 is a graph for explaining the detection method from the maximum / average / minimum voltage. As shown in the legend at the top of Figure 12, <circles> indicate the progress of the maximum voltage value, <triangles> indicate the progress of the average voltage value, and <squares> indicate the progress of the minimum voltage value.

[0064] The coarse dashed line indicates the transition of the average voltage value + maximum voltage deviation threshold M, and the fine dotted line indicates the transition of the average voltage value - minimum voltage deviation threshold L. The presence of a circle inside the coarse dashed line and the presence of a square outside the fine dashed line correspond to the cases where the judgment formulas (a) and (b) are true, respectively. At the condition satisfaction time T, both the conditions of the judgment formulas (a) and (b) are satisfied. At this timing, the abnormality announcement counter at the bottom of Figure 12 begins counting up.

[0065] This indicates that the judgment expressions (a) and (b) are satisfied, and the state has transitioned from condition (3) to condition (2). Even after the condition satisfaction time T, the judgment expressions (a) and (b) are satisfied, so the counting continues. This indicates that the state of condition (2) continues. At the abnormality notification time N, the abnormality notification counter becomes equal to or exceeds the abnormality notification counter threshold K, so at this point the detection of an abnormality is notified to the upper controller 19 (Figure 1). This indicates that the state has transitioned from condition (2) to condition (1). By using the duration time for judgment in this way, it is possible to improve the accuracy of abnormality detection. [Example]

[0066] In the first and second embodiments, passive balancing control has been described as a premise, but there are cases where the minimum voltage value is not set as a target in active balancing control, etc. Such a case will be described in the sixth embodiment.

[0067] Active balancing control is a control that can adjust the capacity without energy loss by transferring energy from a battery with a higher-than-average SOC and voltage to a battery with a lower-than-average SOC and voltage. Figure 13 is a schematic diagram for explaining active balancing control. In Figure 13, the energy transfer target voltage P is set to, for example, an average voltage value.

[0068] As shown in Figure 13, the battery control device 15 performs balancing discharge Z on balancing discharge designated cell Q, which is a battery with a voltage higher than the energy transfer target voltage P, until the voltage reaches the energy transfer target voltage P. Next, the battery control device 15 performs balancing charge U on balancing charge designated cell S, which is a battery with a voltage lower than the energy transfer target voltage P, until the voltage reaches the energy transfer target voltage P.

[0069] This method of transferring energy from a battery with a high SOC and voltage to a battery with a low SOC and voltage is called active balancing control. In Example 6 shown in Figure 13, all cells are designated for discharge if their voltage is higher than the energy transfer target voltage. However, this does not have to be the case for all cells, and a control threshold may be set if there is a deviation of more than a certain amount.

[0070] Similarly, if the voltage is lower than the energy transfer target voltage, all cells are designated for charging. However, if the deviation exceeds a certain level, a control threshold may be set. To achieve this, for example, a system configuration may be provided that transfers energy via a transformer. This requires a system configuration that transfers energy using the hardware of the cell controller 12, which is added to the circuit in Figure 2.

[0071] As mentioned above, in the case of active balancing control, there are cases where the target voltage is not the minimum voltage value but the average voltage value. In this case, counting up the target specification count is not appropriate because it would result in counting up the average voltage cell.

[0072] Therefore, the method using the deviation of each cell voltage as shown in Examples 4 and 5, or the method described in Example 6, is preferable. In active balancing control, energy is transferred by specifying the cell with the lowest SOC, i.e., the cell to which energy is to be transferred. In this case, the cell controller 12 must determine and process this, so the balancing charge specified cell and balancing charge capacity are used as control values.

[0073] By tallying up the number of balancing target designations using this control value by the battery control device 15 or the upper controller 19, it is possible to perform processing equivalent to passive balancing control. In this case, the number of balancing charge designations can be substituted for the value corresponding to the number of balancing target designations for the minimum voltage used in Figure 5. Also, the balancing charge capacity can be substituted for the values ​​corresponding to the balancing time and balancing capacity used in Figure 7.

[0074] This will be explained using Figure 14. In Figure 14, the horizontal axis represents the cell number, and the vertical axis represents the specified number of balancing charge times / time within a certain period and the balancing charge capacity [Ah] / hour. In Figure 14, if the specified number of balancing charge times or the balancing charge capacity is greater than the balancing charge threshold Y, an abnormal cell is determined. By using this detection method, active balancing control can perform detection equivalent to that of passive balancing control.

[0075] [Supplementary Note 1] Self-discharge is caused by a decrease in the insulation resistance between the positive and negative electrodes inside the cell. This self-discharge is a phenomenon in which the no-load voltage drops from 4V to 3.9V even when no power is consumed, and is caused by poor internal insulation, etc. Capacity degradation is a performance degradation phenomenon in which the discharge process under load, such as the voltage changing from 4V (100%) to 3.7V (40%) to 2.7V (0%), occurs more quickly than normal, resulting in a decrease in energy capacity.

[0076] Passive balancing equalizes the voltage of each cell by resistively discharging the higher cell if it is about 40mV off the average. Active balancing equalizes the voltage by replenishing the excess power to the deficient cell without resistively discharging.

[0077] [Supplementary Note 2] In recent years, improvements in the energy density of lithium-ion batteries have led to the gradual expansion of the use of electric vehicles (EVs). Passenger-type EVs can travel over 400 km on a single charge. On the other hand, railway cars weigh 30 to 40 tons, and the space available for on-board equipment is limited. In response to these constraints, electric trains (EMUs: Electric Multiple-Units) have been introduced that incorporate on-board storage battery systems using lithium-ion batteries that combine high energy density and high power density.

[0078] In other words, the regenerative energy absorption system, which absorbs part of the train's regenerative energy and prevents regeneration lapse, will be improved. As a result, it will be possible to travel more than 100 km on a single charge. Furthermore, progress is being made on hybrid diesel railcars equipped with lithium-ion batteries to absorb the regenerative energy of electric diesel railcars (DEMU: Diesel-Electric Multiple-Unit) and assist with power generation.

[0079] Compared to conventional train systems, trains equipped with onboard battery systems can run on non-electrified sections that do not have overhead lines, substations, or other ground facilities by installing charging facilities only at the starting and terminal stations, and possibly at several intermediate stations, and charging the batteries at each charging facility.

[0080] Even on electrified lines, introducing trains equipped with onboard battery systems and eliminating overhead lines, substations, and other ground facilities on infrequently used lines such as branch lines can reduce maintenance costs. In such trains equipped with onboard battery systems, they are typically charged to a high storage rate to maintain SOC, allowing them to travel a specified distance on a single charge.

[0081] On the other hand, there is a growing need for the introduction of battery storage systems, which allow trains to travel a certain distance in the event of a breakdown in wayside equipment, particularly in the event of a power outage on the overhead lines, to avoid getting stranded in sections where it is difficult for passengers to evacuate, such as on bridges or in tunnels.When using battery storage systems to prevent trains from getting stranded in the event of a wayside equipment failure, it is necessary to maintain a high storage rate for an extended period of time in preparation for the unlikely event of a breakdown.

[0082] The storage battery system according to the embodiment of the present invention (the present system) can be summarized as follows. [1] The system described in Example 4 operates a battery pack while controlling its capacity adjustment (balancing). This system includes a battery pack, a capacity adjustment circuit 23, a battery cell controller 12, and a battery control device 15. The capacity adjustment circuit 23, the cell controller 12, and the battery control device 15 are collectively referred to as a controller. This controller may be considered to further include a higher-level controller 19. The control hierarchy shown in Figures 1 and 2 is configured in the reverse order of that described here.

[0083] The assembled battery (battery pack) 10 has multiple battery cells 11 connected in series to provide the desired voltage and capacity. The capacity adjustment circuit 23 is a lower function of the controller, and adjusts the capacity to correct imbalances between the multiple battery cells 11 that make up the assembled battery 10. The cell control unit 12 controls the capacity adjustment circuit 23. This cell control unit 12 can aggregate information from all cells 1 to n, constantly monitors the difference from the average voltage of each cell, and determines that cell 4 that is constantly protruding from the bottom is abnormal. The battery control device 15 is configured hierarchically above the cell control unit 12, and monitors and controls the battery cells 11 while exchanging acquired information indicating the battery state and control commands.

[0084] The battery control device 15 adjusts the capacity of a battery cell 11 (cell 4) in the battery pack 10 whose voltage exceeds the allowable range indicated by the voltage deviation threshold J. That is, as shown in FIG. 11 of Example 4, if there is a battery cell 11 (cell 4) whose voltage deviation from the average voltage of the battery pack 10 is equal to or exceeds a predetermined value, the battery control device 15 determines that this is an abnormal battery in which self-discharge has occurred. This system makes it possible to early detect abnormal cells with excessive self-discharge by making an estimation from the voltage information of each cell.

[0085] [2] In the above [1], it is preferable that the system detects an abnormal battery using statistical information on the voltage collected from each battery cell 11. That is, the system calculates the deviation between the voltage of each battery cell 11 and the average voltage of the battery pack 10, and if the variance of the deviation distribution is equal to or greater than a predetermined value, it determines that the battery is abnormal due to self-discharge. For example, if there is a deviation of 3σ or more in what is called a normal distribution in statistics, it may be determined that the battery is abnormal. In this way, by realizing a rational quality control system based on statistics, it is possible to reduce the waste of replacing still usable products, as well as the waste that occurs when it is too late to correct the problem and thereby impair availability.

[0086] [3] In the present system described in [1] or [2] above, the capacity adjustment circuit 23 may perform passive balancing control to adjust the short circuit of a battery cell 11 that is higher than the others, thereby correcting imbalances among the multiple battery cells 11 that make up the battery pack 10. In this case, the battery control device 15 counts the number of times the minimum voltage is reached per unit time while this passive balancing control is being performed. The number of times the minimum voltage is reached thus counted may be used as a criterion for determining whether a battery is abnormal.

[0087] This criterion replaces the deviation of the voltage of each battery cell 11 from the average voltage of the battery pack 10, which was applied in [1] or [2] above. This system, which applies this criterion, makes it possible to detect differences based on the original performance of the cells before the balancing operation by utilizing the target number of balancing operations. Therefore, this system can achieve higher detection accuracy than the conventional method of evaluating the voltage value after balancing.

[0088] [4] In the above [1] or [2], the execution time per unit time in capacity adjustment or the adjustment capacity value may be applied instead of the deviation of the voltage of each battery cell 11 from the average voltage of the battery pack 10. According to the present system that applies such a criterion, as in the above [3], by utilizing the target number of balancing operations, it becomes possible to detect the difference based on the original performance of the cells before the balancing operation. Therefore, the present system can improve the detection accuracy compared to the conventional method that evaluates the voltage value after balancing.

[0089] [5] In the above [1] or [2], the system described in the fifth embodiment may apply the deviation of the maximum cell voltage and the minimum cell voltage from the average voltage during capacity adjustment instead of the deviation of the voltage of each battery cell 11 from the average voltage of the battery pack 10. In this case, if there is a battery cell 11 whose deviation between the maximum cell voltage and the average voltage is equal to or less than a predetermined value and whose minimum cell voltage deviation from the average voltage is equal to or greater than a predetermined value, it is determined to be an abnormal battery in which self-discharge has occurred.

[0090] This system can achieve good judgment performance even when judgment is made by the cell control 12 or its higher-level controller 19, which cannot collect all information. For example, this applies to cases where judgment is required based on limited information such as minimum, average, and maximum voltages. In addition, if there is a battery cell 11 in which the minimum voltage target cell does not change even after passive balancing control and a deviation of about the voltage threshold continues for a long period of time, it is determined to be an abnormal battery in which self-discharge has occurred.

[0091] [6] In the above [1] or [2], as described in the sixth embodiment, the capacity adjustment circuit 23 may perform active balancing control by adjusting the charge of the battery cell 11 with a lower capacity than the others in order to adjust the capacity. During the execution of this active balancing control, if there is a battery cell 11 for which at least one of the number of times charged per unit time and the charged capacity is equal to or greater than a predetermined value, it is determined to be an abnormal battery in which self-discharge has occurred.

[0092] This replaces the deviation of the voltage of each battery cell 11 from the average voltage of the battery pack 10, which was used as the criterion in [1] or [2] above. Passive balancing control wastes power by short-circuiting healthy cells. In contrast, the active balancing control of this system supports weaker cells, so if the system is configured optimally for this purpose, it can reduce unnecessary power consumption during adjustment.

[0093] [7] In the above [1], as described in the third embodiment, it is preferable that the battery control device 15 is capable of estimating the state of health (SOHQ) of each battery cell 1-n based on the acquired information indicating the battery state, and calculating an average capacity degradation rate (average SOHQ) by averaging these values ​​for the entire battery pack. It is preferable that the battery control device 15 determines that self-discharge has occurred in one of the battery cells 1-n when the estimated state of health (SOHQ) of each battery cell 1-n is within the range of the degradation tolerance value H.

[0094] According to the system of the third embodiment, only when there is a small difference in the state of health quality (SOHQ) of each battery 1 to n in the battery pack, it is determined that the battery is an abnormal battery in which self-discharge has occurred, as in [1] above, thereby improving the accuracy of abnormality detection. In other words, if the difference in state of health quality (SOHQ) is large enough to exceed the range of the degradation tolerance value H, it is determined that the voltage drop is not due to self-discharge, as in [1] above, thereby improving the accuracy of abnormality detection. In other words, it is possible to eliminate the waste of false alarms about self-discharge, which requires earlier response.

[0095] This system can detect self-discharge, which is more harmful than a deterioration in State of Health Quotient (SOHQ), for the series-connected battery pack 10. SOHQ is a phenomenon that is expected as a part of the lifespan of a storage battery, such as a decrease in charge / discharge efficiency under load due to aging and frequency of use, and can be addressed with appropriate operation.

[0096] However, self-discharge is a deterioration of the insulation inside the cell that should never occur, and if left unchecked for a long period of time, serious problems such as increased heat generation and breakdowns due to discharge when no load is present can be expected. In this way, this system, which distinguishes self-discharge, which should never occur, from inevitable SOHQ and can detect it early even when no load is present, is advantageous in terms of safety.

[0097] The battery control device 15 is a computer such as a single-chip microcomputer, and may execute a program stored in a memory (not shown) to operate an algorithm for estimating the state of health (SOHQ) and resistance degradation. The estimated SOHQ may be supplemented with voltage information to improve accuracy. For example, if the battery cell with the maximum voltage is the same as the balancing target, the SOHQ can be estimated more reliably. Furthermore, the computer may have any shape, and part of a computer for other purposes may be used for this purpose.

[0098] [8] It is preferable that the battery storage system described in [1] to [7] above is installed in a railway vehicle. Such a battery storage system for a railway vehicle can detect abnormal cells with high self-discharge rates early, so availability can be improved by performing maintenance without delay, such as replacing only the detected abnormal batteries. [Explanation of symbols]

[0099] 10: Battery pack, 11: Battery cell, 12: Battery cell controllers, 13: Voltage detection line, 14: Thermocouple, 15: Battery control device, 16: Communication line, 17: Current sensor, 18: Communication line with higher level, 19: Upper controller, 23: Balancing circuit, 21: Transistor, 22: Balancing resistor, B: Target specified number of times threshold, C: Distribution of the number of times the balancing target is specified, D: Variance threshold of the number of times the balancing target is specified specified), E: Balancing capacity threshold, F: Balancing time distribution, G: Balancing time variance threshold, H: Deterioration tolerance, J: Voltage deviation threshold, K: Abnormal announcement counter threshold, L: Minimum voltage deviation threshold, M: Maximum voltage deviationthreshold), N: Abnormal announcement time, P: Energy transfer target voltage, Q: Balancing discharge designated cell, S: Balancing charge designated cell, T: Condition fulfillment time, U: Balancing charging, V: Average cell voltage, Vd: Voltage deviation, Vd': Voltage deviation moving average, Vth: Voltage threshold, Y: Balancing charge threshold, Z: Balancing discharge

Claims

1. A storage battery system that operates while adjusting the capacity of a battery pack, The battery pack has a plurality of battery cells connected in series, a controller capable of adjusting the capacity, The controller acquiring a battery state from each of the plurality of battery cells, and generating a control command based on the acquired battery state; During the execution of capacity adjustment to adjust the capacity of the battery cells in the battery pack whose voltage is outside the allowable range in accordance with the control command, if there is a battery cell whose highest cell voltage has a deviation from the average voltage of the battery pack that is equal to or smaller than a predetermined value and whose lowest cell voltage has a deviation from the average voltage that is equal to or larger than a predetermined value, the battery is determined to be an abnormal battery in which self-discharge has occurred. Battery storage system.

2. A storage battery system that operates while adjusting the capacity of a battery pack, The battery pack has a plurality of battery cells connected in series, The controller is capable of adjusting the capacitance, and a capacitance adjustment circuit is a lower function of the controller. The controller acquiring a battery state from each of the plurality of battery cells, and generating a control command based on the acquired battery state; By the control command, the capacity adjustment circuit performs passive balancing control by short-circuiting higher-voltage battery cells to adjust the capacity; During the passive balancing control, a battery cell that has reached the minimum voltage a predetermined number of times per unit time is determined to be an abnormal battery; To adjust the capacity, the charge of the battery cell having a lower capacity than the other cells is adjusted to perform active balancing control; During execution of the active balancing control, if there is a battery cell for which at least one of the number of times charged per unit time and the charged capacity is equal to or greater than a predetermined value, the battery is determined to be an abnormal battery in which self-discharge has occurred. Battery storage system.

3. A storage battery system that operates while adjusting the capacity of a battery pack, The battery pack has a plurality of battery cells connected in series, a controller capable of adjusting the capacity, The controller acquiring a battery state from each of the plurality of battery cells, and generating a control command based on the acquired battery state; In the process of adjusting the capacity of a battery cell in the assembled battery whose voltage is outside the allowable range according to the control command, a battery cell whose voltage deviation from the average voltage of the assembled battery is equal to or exceeds a predetermined value is determined to be an abnormal battery; The capacity deterioration rate of each battery cell can be estimated based on the acquired information indicating the battery state, determining that an abnormality has occurred in any of the battery cells when the capacity deterioration rate of each of the battery cells is within a range of a deterioration tolerance defined as a deviation from an average capacity deterioration rate of the battery cells being equal to or less than a predetermined value; Battery storage system.

4. the controller is capable of estimating a capacity deterioration rate of each battery cell based on the acquired information indicating the battery state; determining that an abnormality has occurred in any of the battery cells when the capacity deterioration rate of each of the battery cells is within a range of a deterioration tolerance defined as a deviation from an average capacity deterioration rate of the battery cells being equal to or less than a predetermined value; The battery system according to claim 1 or 2.

5. A railway vehicle equipped with the storage battery system according to any one of claims 1 to 4.

6. An abnormal battery detection method in which a controller operates a battery pack in which a plurality of battery cells are connected in series while adjusting the capacity, comprising: The controller monitor and control the battery cells while exchanging the acquired information indicating the battery state and control commands; The controller adjusts the capacity of a battery cell in the assembled battery that has a voltage outside an allowable range, and During the capacity adjustment, if there is a battery cell whose deviation between the highest cell voltage and the average voltage of the battery pack is equal to or less than a predetermined value and whose lowest cell voltage whose deviation from the average voltage is equal to or greater than a predetermined value, the battery is determined to be an abnormal battery in which self-discharge has occurred. Abnormal battery detection method.

7. An abnormal battery detection method in which a controller operates a battery pack in which a plurality of battery cells are connected in series while adjusting the capacity, comprising: The controller monitor and control the battery cells while exchanging the acquired information indicating the battery state and control commands; The controller adjusts the capacity of a battery cell in the assembled battery that has a voltage outside an allowable range, and The capacity adjustment circuit, which is a lower function of the controller, performs passive balancing control by short-circuiting higher battery cells to adjust the capacity, and During the passive balancing control, if there is any battery cell that has reached the minimum voltage a predetermined number of times per unit time, the battery cell is determined to be an abnormal battery that has self-discharged, To adjust the capacity, the charge of the battery cell having a lower capacity than the other cells is adjusted to perform active balancing control; During execution of the active balancing control, if there is a battery cell for which at least one of the number of times charged per unit time and the charged capacity is equal to or greater than a predetermined value, the battery is determined to be an abnormal battery in which self-discharge has occurred. Abnormal battery detection method.

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