Monitoring system and monitoring method

Abstract

Provided are a monitoring system and a monitoring method that can protect a storage battery system for driving a railway vehicle from failure due to self-discharge deterioration. The monitoring system

Description

Monitoring system and monitoring method

[0001] The present invention relates to a monitoring system and a monitoring method for monitoring a battery system that is used to drive railway vehicles and includes a battery in which a plurality of battery cells are connected in series.

[0002] Railway lines include electrified sections where rolling stock receives power from overhead lines, and non-electrified sections where there are no overhead lines and rolling stock cannot receive power. Traditionally, rolling stock on non-electrified sections was powered by diesel engines. In recent years, advances in lithium-ion battery technology have led to the introduction of vehicles powered by batteries, such as hybrid diesel railcars and battery-powered trains.

[0003] Hybrid diesel railcars are conventional diesel railcars equipped with storage batteries, which are charged with regenerative electricity during braking and assisted by the storage battery and motor during power running. Battery-powered electric railcars use the storage battery as their driving energy source. In electrified sections, battery-powered electric railcars charge the storage battery while using power from the overhead lines as driving energy, and in non-electrified sections, they run using the storage battery as their energy source.

[0004] The voltage of a chemical battery is usually several volts per battery cell, with the upper limit for a lithium-ion battery cell being around 4.2 V. Railway storage batteries are typically operated at a DC voltage of several hundred to several thousand volts, so several hundred or more battery cells are connected in series to ensure this voltage.

[0005] The amount of charge (Ah) that a battery can discharge is proportional to the number of battery cells connected in parallel. To ensure the required capacity, battery cells are connected in parallel. Due to the nature of electrical circuits, when multiple battery cells are connected in series or parallel, the parallel sections have the same voltage and the series sections have the same current. Because the series sections have the same current, if the state of all battery cells is uniform, even if the charge rate fluctuates, all battery cells will have the same charge rate and the same voltage.

[0006] However, variations in the state of the battery cells within a series connection can lead to uneven voltages among the cells. There are four causes of voltage variations among multiple battery cells: self-discharge, capacity degradation, resistance degradation, and temperature differences. Because a battery system controls the charging and discharging of each battery cell to maintain upper and lower voltage limits, if there is voltage variation, charging is restricted to the cell with the highest voltage, and discharging is restricted to the cell with the lowest voltage, limiting the overall operation of the battery system.

[0007] To correct voltage variations, the battery system is equipped with a passive balancing circuit such as that disclosed in Patent Document 1. The balancing circuit discharges the voltage of each of the multiple series-connected storage batteries via a switch to a balancing resistor installed in parallel, thereby making it possible to align the voltage of each of the multiple storage battery cells to that of the storage battery cell with the lowest voltage.

[0008] Self-discharge occurs due to internal short circuits caused by manufacturing defects or a deterioration in the insulation of the insulating structure inside the battery cell. The ability of the balancing circuit to correct voltage variations is limited by the discharge rate, which depends on the value of the balancing resistor. Therefore, if the self-discharge rate of the battery cells, i.e., the maximum difference in self-discharge rate within a series, exceeds the capacity of the balancing circuit, the voltage variations will continue to increase. Since self-discharge of battery cells is an irreversible degradation event, the battery cells should be replaced with ones that do not self-discharge.

[0009] Patent Document 2 discloses a technique for obtaining the voltage of each battery cell, and obtaining the open-circuit voltage when at least one battery cell exceeds a threshold voltage.

[0010] JP 2022-179015 A JP 2016-075567 A

[0011] Even if voltage variations occur among multiple series-connected storage battery cells, these variations are constantly corrected by the balancing circuit described above. Therefore, by the time voltage variations occur, the balancing circuit's correction capability has already been exceeded. Because the rate of self-discharge degradation progresses nearly 10 times faster than the rates of resistance degradation and capacity degradation, if the problematic storage battery cell is not immediately replaced, the storage battery system may rapidly become unusable. However, conventional technology has not been able to distinguish self-discharge of storage battery cells from other causes of degradation.

[0012] The voltage of a storage battery for traction of railway vehicles is approximately 2000 V, which is several to several tens of times higher than the approximately 200 to 400 V of an automobile storage battery, and the capacity is also several to several tens of times higher, so a storage battery for traction of railway vehicles uses several tens to several hundred times as many series-connected storage battery cells as an automobile storage battery. Therefore, the impact of self-discharge of the storage battery system is magnified accordingly.

[0013] To summarize, the prior art has the following problems: first, in the field of traction battery systems for railway vehicles, there has been little awareness of the problem of system failure due to self-discharge of storage battery cells; second, it has been difficult to distinguish self-discharge degradation of storage battery cells from other causes of degradation; and third, when self-discharge occurs, failure of storage battery cells progresses quickly, causing failure of the traction battery system for railway vehicles in a short period of time. Therefore, an object of the present invention is to provide a monitoring system and monitoring method that can protect traction battery systems for railway vehicles from failure due to self-discharge degradation.

[0014] To achieve the above object, the present invention provides a monitoring system for monitoring a battery system used as a drive source for a traction system of a railway vehicle, the battery system including a battery having a plurality of series-connected storage battery cells, the monitoring system including: an acquisition unit that acquires voltages of the plurality of storage battery cells; and a determination unit that determines, based on the acquired voltages, a storage battery cell that is experiencing self-discharge from among the plurality of storage battery cells. Furthermore, the present invention also provides a similar monitoring method.

[0015] It is possible to provide a monitoring system and a monitoring method that can protect a traction storage battery system for a railway vehicle from failure due to self-discharge degradation.

[0016] FIG. 10 is a block diagram of a monitoring system according to a first embodiment of the present invention, and is a combined block diagram of a drive system and monitoring system for a battery-powered electric railcar. FIG. 11 is a combined block diagram of a drive system and monitoring system for a hybrid diesel railcar. FIG. 12 is an example of an arrangement structure of batteries in a battery system. FIG. 13 is an example of a block diagram of a battery box. FIG. 14 is an example of a block diagram of a battery module. FIG. 15 is an example of a balancing circuit block diagram. FIG. 16 is a graph illustrating the SOCOCV curve of a typical lithium-ion battery. FIG. 17 is a graph illustrating changes in cell voltage related to balancing circuit operation when some cells self-discharge quickly. FIG. 18 is a graph illustrating changes in cell voltage related to balancing circuit operation when most cells self-discharge quickly. FIG. 19 is a graph illustrating the operation of a means for identifying an abnormal cell. FIG. 11 is a table illustrating causes and properties of voltage variations in a battery. FIG. 12 is an example of a DCR curve when a lithium-ion battery is discharging. FIG. 13 is a DCR curve when a lithium-ion battery is charging. FIG. 14 is a diagram illustrating the cell voltage distribution of each battery cell before self-discharge variations occur. FIG. 15 is a diagram illustrating the cell voltage distribution of each battery cell after self-discharge variations have progressed. FIG. 16 is a block diagram of a self-discharge battery countermeasure unit. FIG. 1 is a block diagram of a timing instruction unit. FIG. 2 is a block diagram of a self-discharge cell addition determination unit that performs a self-discharge cell addition determination based on usage history. FIG. 3 is a block diagram of a self-discharge battery treatment unit that performs a self-discharge cell addition determination based on usage history. FIG. 4 is a flowchart according to embodiment 1. FIG. 5 is a flowchart according to embodiment 2. FIG. 6 is a block diagram of a self-discharge battery treatment unit according to embodiment 2. FIG. 7 is a graph explaining the calculation principle of self-discharge current according to embodiment 3. FIG. 8 is a block diagram of a self-discharge battery treatment unit according to embodiment 3. FIG. 9 is a control flowchart according to embodiment 3.

[0017] An embodiment of the present invention will be described with reference to the accompanying drawings. The same elements are designated by the same numbers throughout the embodiments. The embodiment described below relates to a monitoring system for monitoring faults caused by self-discharge in a storage battery system installed in a railway vehicle. The storage battery cells are lithium-ion batteries, but other storage elements such as lead batteries, nickel-metal hydride batteries, or capacitors may also be used. In the mathematical formulas described below, charging current is positive and discharging current is negative.

[0018] (Embodiment 1) Fig. 1 is a block diagram combining a traction system 1A and a monitoring system 2A for a battery-powered electric railcar. In the figure, solid lines indicate power transmission paths, double lines indicate torque transmission paths, and dotted lines indicate transmission paths for information such as control signals and sensor values. In electrified sections, the traction system 1A runs the railcar using power from the overhead lines and charges the storage battery, and in non-electrified sections, it drives the railcar using power from the storage battery. The configuration of each block in the traction system 1A will be described.

[0019] The drive system 1A includes a pantograph 2 connected to the overhead line, a converter 5 that converts overhead line power into required DC power, a motor inverter 6 that converts DC power into AC power, a motor 7 that drives the railway vehicle, a reducer 8 that reduces the output of the motor 7 and transmits it to the wheel set 9, an auxiliary inverter 10, auxiliary equipment 11 used for services such as vehicle lighting and air conditioning, a storage battery system 20 that drives a storage battery to which multiple storage battery cells are connected, a driver's cab 12 that has a display and generates driving commands in response to notch operation by the driver, a vehicle control device 13 that generates control commands for the converter 5, the motor inverter 6, and the auxiliary inverter 10 based on the driving commands transmitted from the driver's cab 12 and the state of the storage battery system 20, and a data transmission / reception device 60 that wirelessly transmits and receives data and signals from the storage battery system 20 and the vehicle control device 13 to and from a server 70 outside the vehicle.

[0020] The pantograph 2 is an electric switch that moves up and down, and when it rises and comes into contact with the overhead wire 14, the DC or AC power supplied by the overhead wire 14 is supplied to the converter 5. When the pantograph 2 is in contact with the overhead wire 14, the battery electric train runs on power from the overhead wire and charges the storage battery, and when the pantograph 2 is not in contact with the overhead wire 14, it uses power from the storage battery. The converter 5 receives the DC or AC power output from the pantograph 2 as input, converts it into DC power corresponding to a commanded amount of power, and outputs it. The motor inverter 6 converts the DC power supplied via the converter 5 into three-phase AC power to drive the electric motor 7.

[0021] The electric motor 7 receives three-phase AC power output by the electric motor inverter 6, converts it into axle torque, and outputs it. The speed reducer 8 reduces the rotational speed of the electric motor 7 by combining gears with different numbers of teeth, and the axle torque thus amplified drives the wheel set 9, accelerating and decelerating the vehicle. A tachograph (not shown) for measuring vehicle speed is also attached to the wheel set 9.

[0022] The auxiliary inverter 10 receives DC power between the converter 5 and the motor inverter 6, converts it into three-phase AC power, and outputs it. The auxiliary equipment 11 is service equipment such as lighting and air conditioning for the vehicle, and operates on the power supplied from the auxiliary inverter 10.

[0023] The driver's cab 12 is equipped with a display that displays the time, vehicle speed, battery information, etc., and an input device through which the driver inputs driving commands, etc., into the control device 13. The storage battery is a device that stores energy to drive the railway vehicle. The storage battery of the storage battery system 20 is charged with DC charging power output from the converter 5 and discharges to the motor inverter 6 and the auxiliary inverter 10. When the vehicle is applying regenerative braking, the storage battery system 20 is charged with DC charging power output from the motor inverter 6. The storage battery system 20 has a battery control device (battery box control board) 212 that measures the state of the storage battery contained therein, calculates the charging rate and allowable current, and communicates with the vehicle control device 13.

[0024] The vehicle control device 13 outputs control signals to the converter 5, the motor inverter 6, and the auxiliary inverter 10 based on driving commands, the state of the battery system 20, the state of the pantograph 2, etc., and controls the entire drive system 1A for railway vehicles.

[0025] The data transmitter / receiver 60 receives data from the vehicle control device 13 and the battery box control board 212, transmits it wirelessly to a server 70 outside the vehicle, and receives control commands and display contents for the driver's cab from the server 70. The server 70 has a monitoring unit 30 that monitors the storage battery system 20. The monitoring unit 30 detects self-discharge of the storage battery based on the data received from the vehicle, and notifies the operation control center 40 of any abnormalities and issues replacement instructions. The operation control center 40 may be a manufacturer that manages the battery system.

[0026] As long as a battery storage system is included, the railway vehicle is not limited to the form of a battery-powered electric train. Another form is, for example, a hybrid diesel railcar. Figure 2 is a block diagram showing the system configuration of a railway vehicle drive system 1B for a hybrid diesel railcar. A hybrid diesel railcar is a railway vehicle that does not use power from overhead lines, but runs on power generated by an engine and power from a storage battery. The engine is started when continuous acceleration commands are input or when the storage battery's charge rate drops.

[0027] The hybrid diesel railcar traction system 1B has an engine 3 and a generator 4 instead of the overhead wires 14 and pantograph 2. The engine 3 outputs shaft torque according to an engine speed command value from a vehicle control device 13. The generator 4 receives the shaft torque of the engine 3 as input, converts it into three-phase AC power, and outputs it. The converter 5 receives the three-phase AC power output from the generator 4 as input, converts it into DC power corresponding to the commanded amount of power, and outputs it. The rest of the system configuration is the same as the traction system 1A for battery-powered railcars. The following explanation will be given assuming a battery-powered railcar, but this does not exclude hybrid diesel railcars.

[0028] Next, the configuration of the storage battery system 20 will be described. Fig. 3 shows an example of the arrangement of storage batteries in the storage battery system 20. The storage battery system 20 exists as a drive source for the drive system 1A. Inside the storage battery system 20, storage battery boxes 21 are connected in series and in parallel. Each storage battery box 21 has a structure covered by a box casing. The storage battery system 20 is composed of multiple storage battery boxes 21.

[0029] 4 is a block diagram of the battery box 21. The battery box 21 includes a battery module 211, a battery box control board 212, a box voltmeter 213, and a group ammeter 214. Within the battery box 21, multiple battery modules 211 are connected in series and in parallel.

[0030] The battery replacement unit 23 is a hardware division that allows for easy work during battery manufacturing and replacement, with multiple battery modules fixed and wired to a rack or the like, and can be removed unit by unit from the battery box 21. Replacement of each battery replacement unit 23 is quicker than replacing each battery module 211 individually. The range in which the battery modules 211 are connected in series is called a battery series group 22. The group ammeter 214 measures current for each series group.

[0031] The box voltmeter 213 measures the box voltage. The battery box 21 includes at least one battery box control board 212. The battery box control board 212 is a battery monitoring device. The battery box control board 212 performs various functions, such as monitoring the battery status, calculating the battery status, sending signals to and receiving signals from a higher-level control board, and controlling the battery box 21.

[0032] To monitor the status of the storage battery, the battery box control board 212 receives current signals from the group ammeter 214, voltage signals from the box voltmeter 213, and battery temperature signals and cell voltage signals obtained from cell controller boards 2112 (FIG. 5) mounted on the storage battery modules 211 inside the box. From these signals, the battery box control board 212 calculates the storage battery's charging rate, capacity degradation degree, resistance degradation degree, allowable current, and box balancing target cell voltage, detects self-discharging cells, and performs status calculations to detect abnormal states, in order to calculate the status of the storage battery.

[0033] The battery box control board 212 transmits the detection signals and calculated values ​​to the upper control boards, such as the vehicle control device 13 and the data transceiver device 60. The battery box control board 212 receives the system balancing target cell voltage and the battery box circuit breaker operation signal from the upper control board. The box balancing target value is the minimum cell voltage obtained by the battery box control board monitoring the voltage information of the storage battery cells in each box, and the system balancing target value is the minimum cell voltage among the multiple box voltage balancing target values.

[0034] The battery box control board 212 transmits circuit breaker control and system balancing target values ​​to each cell controller board 2112 (Figure 5). The balancing target cell voltage is usually the same value at least within the series range within the battery system. Since the parallel range has the same voltage, the balancing target cell voltage does not necessarily need to be shared, but for simplicity's sake, in this embodiment, the battery boxes are connected in parallel and there is only one target cell voltage within the battery system. When multiple battery boxes 21 are connected in series within the battery system 20 as shown in Figure 3, the battery box control board 212 transmits the balancing target value for each battery box to the vehicle control device 13, and the vehicle control device 13 transmits the lowest value of these to each box as the system balancing target value.

[0035] 5 is a block diagram of the storage battery module 211. The storage battery module 211 includes storage battery cells 2111, a cell controller board 2112, a high-voltage connector, a communication connector, and a sensor. The storage battery module 211 is the smallest unit of battery procurement. The cell controller board 2112 monitors the status of the storage battery module 211.

[0036] The cell controller board 2112 has a balancing circuit 2113 (Figure 6) and also has a function for communicating with sensors. The storage battery cells have voltage sensors. A temperature sensor is provided at a representative point within the storage battery module 211. The cell controller board 2112 detects the state of the storage battery cells. The cell controller board 2112 detects the voltage of each of the multiple storage battery cells using the voltage sensor. The cell controller board 2112 detects the temperature of each storage battery cell using the temperature sensor.

[0037] 6 is an example of a circuit diagram of the balancing circuit 2113. The balancing circuit 2113 is mounted on a cell controller board 2112. The balancing circuit 2113 includes a balancing controller 2114, a balancing resistor 2115, a balancing switch 2116, and a cell voltmeter 2117.

[0038] Each storage battery cell 2111 is provided with a set of a balancing resistor 2115, a balancing switch 2116, and a cell voltmeter 2117. The cell voltage (SG2) acquired by the balancing controller 2114 using the cell voltmeter 2117 is sent to the battery box control board 212 via communication.

[0039] The voltage of the storage battery cell detected by the balancing controller 2114 corresponds to the closed circuit voltage CCVi(t) in Equation 1. The battery box control board 212 calculates the lowest cell voltage of the multiple storage battery modules 211 in the box as the box balancing target value and transmits it to the vehicle control device 13. The vehicle control device 13 returns the lowest voltage from the multiple box balancing target values ​​to the balancing controller 2114 as the system balancing target value (SG1). The balancing controller 2114 calculates the voltage CCV of each storage battery cell. ｉ (t) is compared with the system balancing target value, and the discharge time of each storage battery cell required to reduce the voltage of each storage battery cell to the system balancing target value is calculated.

[0040] The balancing controller 2114 controls the balancing resistor R ｂａｌ and a balancing current (self-discharge current) I, which is a current flowing through the balancing circuit 2113 based on the resistance Ri of each storage battery cell i. ｂａｌ，ｉ (A) is predicted using Equation 2, and the discharge time is adjusted so that the SOC of each storage battery cell 2111 after discharge is the same.

[0041] When the SOC is the same, the OCV of the battery is the same according to the SOC-OCV curve in Figure 7. The balancing controller 2114 closes the balancing switch 2116 for the discharge time given to each battery cell, and discharges each battery cell for an individual time. Generally, the balancing current i ｂａｌ，ｉ is small, the balancing circuit operates for several hours, and continues to operate even when the battery system 20 starts normal charging and discharging.

[0042] Figure 8 shows the change in battery cell voltage reflecting the operation of the balancing circuit. The vertical axis of each graph represents cell voltage, and the horizontal axis represents cell ID. Cell voltage is the voltage when the system current is zero and the system voltage is within the reference threshold. Cell ID is the identification number of each battery cell in the battery system. Identification numbers are assigned according to rules such as voltage order or position order.

[0043] During normal battery operation (1), the cell voltages of the battery system are uniform. When self-discharge of at least one battery causes variations in cell voltage among multiple battery cells (2), the lowest-voltage cell C1 (black circle in the figure) is the battery cell with the most advanced self-discharge. This battery cell self-discharges faster than the other battery cells, resulting in an outlier-low voltage.

[0044] At this time, the voltage difference ΔV between the plurality of storage battery cells is proportional to the maximum difference in the self-discharge current of each storage battery cell. In other words, all the cells deteriorate uniformly, and the self-discharge current (I ｓｅｌｆ，ｉ ) increases uniformly, no voltage variations occur. The balancing circuit 2113 sets this cell as the balancing target value and starts the balancing operation.

[0045] If the performance of the balancing circuit exceeds the difference in self-discharge rates, balancing is achieved. After balancing, in (3), the multiple cell voltages are equalized to the lowest voltage cell. On the other hand, if the difference in self-discharge rates exceeds the performance of the balancing circuit 2113, the rate of voltage drop of the storage battery cell (●) with the fastest self-discharge rate is greater than the balancing voltage correction capability, and the cell voltages do not become equal, and the voltage difference increases, as shown in (4).

[0046] The voltages of the battery cells other than the lowest voltage cell (●) are reduced to the minimum voltage range, which is the sum of their own self-discharge rate and the maximum balancing possible amount ((4)a). As a result, the voltages of the cells other than the lowest voltage cell also vary. In this state, the low-voltage battery (●) with a fast self-discharge rate must be replaced quickly.

[0047] Rapid self-discharge in battery cells can occur, for example, when a manufacturing defect causes metal pieces to get mixed into the battery cell, resulting in a micro-short circuit; when the temperature distribution within the battery system causes localized deterioration that reduces the insulating properties of the insulating structure within the battery cell; or when battery modules within the battery system are partially replaced, resulting in variations in insulation properties.

[0048] Whether the performance of the balancing circuit exceeds the self-discharge performance is determined according to the following formulas 3A and 3B, taking into consideration that self-discharge occurs all the time and that the balancing circuit 2113 operates while the railway system is powered on. ｓｅｌｆ，ｍａｘ [A] is the self-discharge current (absolutely largest) of the battery cell with the largest self-discharge, I ｓｅｌｆ，ｍｉｎ [A] is the self-discharge current of the cell with the smallest self-discharge (the smallest absolute value), t ｏｎ [h] is the average daily time that the balancing circuit operates, which in a railway vehicle is the maximum time that the drive system is on.

[0049] (The performance of the balancing circuit is equal to or exceeds the self-discharge) |(I ｓｅｌｆ，ｍａｘ -I ｓｅｌｆ，ｍｉｎ ) × 24 |≦| I ｂａｌ，ｉ ×t ｏｎ|... (Equation 3A) (the performance of the balancing circuit is below the self-discharge) |(I ｓｅｌｆ，ｍａｘ -I ｓｅｌｆ，ｍｉｎ ) x 24 |>|I ｂａｌ，ｉ ×t ｏｎ |・・・(Formula 3B)

[0050] Figure 9 shows the change in battery cell voltage related to the operation of the balancing circuit when the majority of battery cells self-discharge quickly (Figure 8). The difference from the results when some battery cells self-discharge quickly (Figure 8) is that in the case of variation (2) compared to normal (1), the lowest voltage cell (●) is the one with the most advanced self-discharge, while most of the other battery cells (◯) also have fast self-discharge rates, so the cell voltages on the low-voltage side are generally uniform. The battery cell with the slowest self-discharge rate and the highest voltage (◎) exhibits a high voltage that appears to be an outlier, even though the internal state of the battery is actually the healthiest.

[0051] After this, according to the above-mentioned formulas 3A and 3B, it is possible to determine a state (3) in which the performance of the balancing circuit 2113 exceeds the self-discharge rate difference, and an abnormal state (4) in which the self-discharge rate difference exceeds the performance of the balancing circuit. In state (3), as in the case where some cells self-discharge quickly (FIG. 8), the cell voltages are equalized to the lowest voltage cell (●) by voltage equalization by the balancing circuit.

[0052] In state (4), as in Figure 8, the difference in self-discharge rates exceeds the performance of the balancing circuit, so the rate of voltage drop of the battery cell (●) with the fastest self-discharge is greater than the balancing's voltage correction ability, and the voltages do not become uniform, resulting in an increase in the voltage difference. Unlike Figure 8, most cells other than the battery cell (●) with the most advanced self-discharge also have fast self-discharge rates, so within the range of their self-discharge rates and the maximum balancing capacity, the voltages of the multiple battery cells will be aligned with the battery cell with the fastest self-discharge. The voltage of the battery cell (◎) with the slowest self-discharge behaves as an outlier.

[0053] In an actual battery system, cases where some battery cells self-discharge quickly (FIG. 8) and cases where some battery cells self-discharge slowly (FIG. 9) can occur simultaneously. FIG. 10 is a graph explaining the operation of the abnormal cell identification means. A battery cell (◇) whose voltage is lower than the threshold voltage difference ΔVth from the highest voltage battery cell (◎) is determined to be a self-discharging cell. This means is superior to determining that a battery cell (●) whose voltage drops below the average cell voltage in the battery system by more than the threshold voltage is a self-discharging cell, in that it can detect cases where the majority of cells self-discharge quickly. The cell voltage (◎) is V ｍａｘ Then, the cell voltage V ｉ The battery cells are Here, the threshold voltage difference ΔVth is a value that can separate a self-discharge cell from measurement noise of the cell voltage, and is usually a value of several tens of mV.

[0054] Typically, the cell controller board 2112 can directly measure the closed-circuit voltage of each storage battery cell, and detects variations in closed-circuit voltage by separating those caused by self-discharge. There are generally four causes of voltage variation: self-discharge, capacity degradation, resistance degradation, and temperature. Figure 11 is a table showing the causes and characteristics of voltage variation. Voltage variation is undesirable regardless of its cause, since the entire system is rate-determined by the cells at the upper and lower limits of voltage variation. Temperature variation generally does not improve even if the battery is replaced. Self-discharge variation, capacity degradation variation, and resistance degradation variation are all caused by battery degradation, and if the variation exceeds a certain level, battery replacement is required.

[0055] Of these, detection of self-discharge variation is important. This is because, although self-discharge variation is corrected by the balancing circuit 2113, the correction capability of the balancing circuit is exceeded when variation first appears, and unless immediate action is taken after detection, voltage variation rapidly progresses to the point where the battery system becomes unusable. The rate at which problems caused by self-discharge variation progress is nearly 10 times faster than the rate at which resistance degradation and capacity degradation progress.

[0056] The causes of voltage variations will be explained using formulas. Formulas 1, 2, and 5 represent the closed-circuit voltage of a storage battery. Formula 1 represents the closed-circuit voltage of a storage battery cell. The first term represents the open-circuit voltage of the battery cell, and the second term represents polarization (also called IR drop), which is the voltage change due to current. i represents the cell number, t represents the time, CCVi (Closed Circuit Voltage) represents the closed-circuit voltage [V] of cell i, OCVi (Open Circuit Voltage) represents the open-circuit voltage [V] of cell i, SOCi (State of Charge) represents the charge rate [%] of cell i, and I represents the current [A] flowing through the series group including cell i.

[0057] SOHRi (State of Health of Resistance) is the amplification ratio [%] of the resistance of cell i from the time of shipment, DCRi (Direct Current Resistance) is the DC resistance [Ω] of cell i, Ti is the cell temperature [°C] of cell i, and C1 is a coefficient for ensuring dimensional consistency. The OCV in Equation 1 is determined as a function of the SOC-OCV curve as shown in Figure 7. The shape of the SOC-OCV curve varies depending on the cell design, but it is generally a nonlinear function such that the higher the SOC, the higher the OCV.

[0058] Figure 12A shows the DCR curve for a lithium-ion battery during discharge. Figure 12B shows the DCR curve for a lithium-ion battery during charge. The DCR in Equation 1 is often determined as a function of SOC, temperature (T), and current, as shown in the figure. Current often divides the DCR into charge and discharge. The shape of the DCR map varies depending on the cell design, but it is generally a nonlinear function such that the higher the temperature, the lower the DCR (Figure 12A: T1 < T2 < T3).

[0059] Equation 5 defines the SOC at a certain time t. The first term is the SOC of cell i at the start, and the second term indicates how much the integrated current value from the start to the present corresponds to the change in the charging rate. t0 is the start time, I ｓｅｌｆ，ｉ is the self-discharge current of cell i, I ｂａｌ，ｉis the balancing current of cell i, Q0 is the initial cell charge capacity [Ah], SOHQ (State of Health of Capacity) is the rate of decrease in charge capacity from the time of shipment [%], and C2 is a coefficient for ensuring dimensional consistency. The second term in Equation 5 represents the change in SOC due to the current flowing through the battery cell, and the proportional part of I(t) is the SOC change ΔSOC due to battery use. ｕｓｅ means I ｓｅｌｆ，ｉ The proportional part of ΔSOC is the SOC change caused by self-discharge. ｓｅｌｆ means I ｂａｌ，ｉ The proportional part of ΔSOC is the SOC change caused by the balancing circuit discharge. ｂａｌ This means:

[0060] Voltage variation refers to the variation in CCVi in Equation 1 between multiple storage battery cells i, and the second term, the polarization term, will cause voltage variation due to variations in SOHRi, variations in Ti due to temperature distribution inside the box, and variations in SOCi, even if the battery cells are connected in series and the current I is the same value.

[0061] Because the second term is proportional to the current, the resistance degradation variation and temperature variation become larger when the current is large, as shown in Figure 11. The DCR of a normal battery due to temperature variation increases at lower temperatures, as shown in Figure 12B, so the second term generally varies more at lower temperatures.

[0062] This second term can be made closer to 0 by bringing the timing of acquiring each battery cell voltage CCVi closer to I=0. Generally, the second term, which is polarization, has a time constant in its change, so in order to bring the term closer to 0, it is desirable that the period during which I=0 is long. In other words, the condition is as shown in Equation 6.

[0063] t ｎｏｗ is the current time, Δt ｔｈ is the threshold time for which the current remains zero, I ｓｙｓ is the system current, ΔI ｓｙｓ、ｔｈ is the threshold current at which the current is judged to be 0. ｔｈ is the waiting time until the polarization of the battery settles down and the closed circuit voltage of each cell can be considered to be equal to the open circuit voltage, which is usually several minutes to several tens of minutes.ｓｙｓ、ｔｈ It is desirable that the error of the current sensor is within the range of error. However, depending on the configuration of the drive system, the current consumed by the auxiliary device 11 may flow constantly even when the vehicle is not running. In this case, the current in the low current state where only the auxiliary device is used is set as ΔI ｓｙｓ、ｔｈ Let's say.

[0064] However, it should be noted that even if the second term in Equation 1 is canceled, the first term, SOCi, varies according to Equation 5. The second term in Equation 5 represents the change in SOC due to the current flowing through the battery cell. The voltage variation phenomenon due to self-discharge is caused by the self-discharge current I of each battery cell. ｓｅｌｆ，ｉ and the balancing current I ｂａｌ，ｉ After the SOC of each cell changes due to the change, the OCVi(SOCi) corresponding to the SOCi of each cell varies.

[0065] At this time, the current I that the battery cell flows to the external device is usually the self-discharge current I ｓｅｌｆ，ｉ and the balancing current I ｂａｌ，ｉ is several orders of magnitude larger than the self-discharge current I(t), so if the integral value of I(t) is not zero, the second term is approximately the self-discharge current I ｓｅｌｆ，ｉ and the balancing current I ｂａｌ，ｉ The SOC change ΔSOC due to the use of the storage battery is the same as when ｕｓｅ If we use the assumption that multiple storage battery cells are connected in series and I(t) is common, the second term is proportional to the inverse of SOHQi, so the smaller the SOHQi (the more deteriorated the storage battery), the larger the term becomes, and variation in SOHQi is observed.

[0066] The voltage of a battery with degraded capacity is maximum when the integral value of I(t) is positive (the integral period is overcharged) and is minimum when the integral value is negative (the integral period is overcharged), so if a low-voltage battery cell in a battery system is simply determined to be a degraded battery, a relatively healthy battery will be mistakenly identified as a degraded battery. Due to this characteristic, it is desirable that the timing at which the balancing circuit 2113 obtains the target minimum cell voltage is also the timing at which the integral value of current I relative to the reference voltage is 0.

[0067] From the viewpoint of accuracy, the timing at which the balancing circuit 2113 operates is excellent in the region (low SOC region) where dOCV / dSOC shown in FIG. 7 is most sensitive, because the voltage fluctuates greatly due to minute self-discharge and balancing discharge. However, in general railway vehicle applications, the low SOC region, which carries the risk of running out of power, is used less frequently.

[0068] A voltage used as the standard charge rate for a railway vehicle in standby mode is desirable in order to ensure the operation frequency of the balancing circuit 2113. The target charge rate is near full charge for the drive system 1A of a battery-powered electric railcar, and an SOC of 50% for the drive system 1B of a hybrid diesel railcar.

[0069] When the battery box control board 212 detects capacity degradation separately, the integrated value of the current I is not 0, and if the cell voltage OCVi (SOCi) is obtained when the current is 0, the SOHQi of each cell can be calculated.

[0070] In order for the battery box control board 212 to detect voltage variations due to self-discharge, it is desirable that the integral value of current I is 0. If the detection accuracy of current I is sufficiently high, the timing when the integral value of current I is 0 can be calculated using the actual current detection value. However, if self-discharge is determined every day from the start time t0, it is generally difficult to detect the daily current integral value with an accuracy that can be ignored relative to the battery capacity. For this reason, the battery box control board 212 uses the relationship in which the OCV of the battery cell is a function of the SOC, as shown in Figure 7. The voltage of the battery system is V ｓｙｓ , the tolerance is ΔV ｓｙｓ，ｔｈ , the battery system voltage V ｓｙｓ (t ｎｏｗ ) satisfies the following relationship:

[0071] Here, V ｓｙｓ (t ０ ) is preferably the system voltage at which the balancing circuit operates. ｓｙｓ、ｔｈ Similarly, the voltage tolerance of the system over which the balancing circuit operates is matched.

[0072] 13A shows the voltage distribution of each storage battery cell before the occurrence of self-discharge variation. FIG. 13B shows the voltage distribution of each cell after the self-discharge variation has progressed. ｓｙｓ (t ０ ) and when the number of storage battery cells is N, the average voltage of the storage battery cells is V ｃａｌｌ，ａｖｅ The voltage distribution of each cell varies depending on the balance between the individual self-discharge current and the balancing current, and the battery cell with the most self-discharge (●) appears as the lowest voltage. The cell with the slowest self-discharge is V ｃｅｌｌ，ａｖｅ This results in a higher voltage (Fig. 13B).

[0073] The operation of the monitoring unit of the server 70 will be described. The monitoring unit includes a self-discharge battery countermeasure unit 31 shown in the functional block diagram of FIG. 14. The self-discharge battery countermeasure unit 31 analyzes signals from the battery system, identifies self-discharged cells, and instructs the operation control center 40 (FIG. 1) on the location of replacement. The server 70 realizes the monitoring unit based on computer hardware control resources such as a processor or a controller. A "unit" is a function realized by a processor executing a program in the memory of the server 70. The term "unit" may also be replaced with terms such as module, circuit, unit, or means. While the monitoring unit has been described as existing in the server 70, the monitoring unit may also be located in the traction system 1A, or may be separated from the server 70 and exist in the traction system 1A.

[0074] The self-discharge battery countermeasure unit 31 controls the system current I １ , system voltage V １ , each battery cell closed circuit voltage V ｃｅｌｌ is taken as input, and the replacement unit ID (ID-1), the abnormal module ID (ID-2), and the self-discharging cell ID (ID-3) are output.

[0075] The self-discharge battery treatment unit 31 has a timing instruction unit 301, a self-discharge cell determination unit 302, and a replacement instruction unit 303. The timing instruction unit 301 controls the system current I １ and system voltage V １ and outputs a calculation execution flag F1 to the self-discharge cell determination unit 302.

[0076] The self-discharge cell determination unit 302 calculates the self-discharge cell ID (ID-3) from the voltage of each storage battery cell and makes a determination. The self-discharge cell determination unit 302 calculates the self-discharge cell ID (ID-3) from the execution flag F1 and each cell closed circuit voltage V ｃｅｌｌ The self-discharge cell ID (ID-3) is determined and output (the determination unit of claim 1). The self-discharge cell ID is the ID of the storage battery cell (◇, ●) whose maximum cell voltage is different from the threshold voltage by more than the threshold voltage, as shown in FIG. 10 .

[0077] The replacement instruction unit 303 specifies the abnormal module ID (ID-2) including the self-discharge cell ID (ID-3) and the replacement unit ID (ID-1). The replacement instruction unit 303 receives the self-discharge cell ID as input and outputs the IDs of the battery module 211 and battery replacement unit 23 corresponding to the self-discharge cell ID.

[0078] The train operation control center 40, or a manufacturer requested by the train operation control center 40, replaces the battery replacement unit 23 with one in better condition according to the output replacement unit ID. The manufacturer removes the storage battery module associated with the abnormal module ID from the collected battery replacement unit 23, replaces it with a non-defective unit, and then reuses it. The railway operator can quickly replace defective cells in units of battery replacement units 23.

[0079] 15 is a detailed functional block diagram of the timing instruction unit 301. The timing instruction unit 301 has a current condition determination unit 3011 and a voltage condition determination unit 3012. The current condition determination unit 3011 determines the battery system current I １ and outputs flag F1a if the low current state continues for a threshold time or longer according to Equation 6. A voltage condition determination unit 3012 receives system voltage V1 and outputs flag F1b if the voltage is within a certain range according to Equation 7. An AND processing unit 3013 outputs the execution flag F1 described above if flags F1a and F1b are established.

[0080] The problem with identifying self-discharge cells using this type of processing is that the function for identifying self-discharge cells shown in Figure 10 is based on the difference in self-discharge rate among the storage battery cells in the system, and therefore storage battery cells with relatively slow self-discharge rates and high voltages are not determined to be self-discharge cells.

[0081] In this case, even if a battery cell had a relatively slow self-discharge rate before replacement, its self-discharge rate will be faster than that of a newly replaced battery cell in good condition, which could cause the unreplaced battery to have the lowest voltage and increase voltage variation within the system. If the self-discharge cell is due to a manufacturing defect, the unreplaced cell will not self-discharge, but because a decrease in internal insulation due to deterioration can occur in all batteries, even a battery cell in relatively good condition will experience some insulation deterioration due to factors such as manufacturing variation and temperature variation. Therefore, if the self-discharge is due to deterioration, it is acceptable to replace not only the cell determined to be self-discharged, but also a battery that has been used to a similar extent and is currently in good condition.

[0082] Fig. 16 is a functional block diagram of a self-discharge battery countermeasure unit 31 that determines whether a self-discharge cell has been added based on the usage history of the storage battery cells. In addition to the block diagram of Fig. 14, Fig. 16 includes a usage history calculation unit 304 and a self-discharge cell addition determination unit 305. The other blocks operate in the same way as those in Fig. 14.

[0083] The usage history calculation unit 304 calculates the closed circuit voltage V ｃｅｌｌ and each cell current (current sensor value for each series group) I ｃｅｌｌ The "accumulated absolute value of the power of each battery cell (VAL1)" is calculated by multiplying the above values ​​by the sum of the accumulated absolute values ​​of the power of each battery cell. The "accumulated value of each cell Wh (VAL1)" is the accumulated value from the time when each battery cell began to be used in the battery system, and in the case of a second-hand battery, it is the sum of the accumulated values ​​before it was installed in the battery system.

[0084] 17 is a functional block diagram showing details of the self-discharge cell addition determination unit 305. The self-discharge cell addition determination unit 305 has a multiple cell self-discharge determination unit 3051 and a self-discharge cell addition unit 3052. The self-discharge cell addition determination unit 305 outputs an ID (ID-4) obtained by adding the ID of a storage battery cell that has a relatively slow self-discharge rate within the storage battery system but has been newly determined to be a self-discharge cell based on the usage history of the storage battery cell to the self-discharge cell ID (ID-3).

[0085] The multiple cell self-discharge determination unit 3051 determines the number of self-discharge cell IDs, and if the number of self-discharge cell IDs is equal to or less than a threshold, it determines that self-discharge is due to a manufacturing defect. On the other hand, if the number exceeds the threshold, it determines that self-discharge is due to deterioration, and outputs the determination result as flag F2. This threshold is normally small because it corresponds to a manufacturing defect, and is set to several cells per storage battery system. The self-discharge cell addition unit 3052 receives flag F2, the self-discharge cell ID (ID-3), and each cell Wh cumulative value VAL1 as input, and outputs the self-discharge cell ID (ID-4).

[0086] If flag F2 indicates a manufacturing defect, the input self-discharge cell ID (ID-3) is output as ID-4. If flag F2 indicates deterioration, the minimum value of the cell Wh accumulation value VAL1 corresponding to the input self-discharge cell ID (ID-3) is taken, and the storage battery cell ID with the least usage history up to the threshold Wh accumulation amount is added to ID-3 and output as the self-discharge cell ID (ID-4).

[0087] The operation of the battery monitoring unit will be described in relation to the operation of the drive system 1A using the flowchart in Figure 18. Step S1 starts the flowchart. Step S2 turns on the drive system. At this time, various control boards and accessories for the entire drive system 1A are turned on, and the system voltage, system current, cell voltage, etc. of the battery system 20 are measured and transmission and reception of signals begins (step S3).

[0088] In step S4, the AND processing unit 3013 (FIG. 15) checks whether F2 is set, and in step S4, the AND processing unit 3013 checks whether F1 is set. The AND processing unit 3013 repeats steps S4 and S5 until both flags are set. Note that the order of steps S4 and S5 may be reversed.

[0089] In step S6, the self-discharge cell determination unit 302 acquires the voltages of all storage battery cells in the storage battery system. In step S7, the self-discharge cell determination unit 302 determines whether or not there is an abnormal cell according to the method of Fig. 10. If the self-discharge cell determination unit 302 determines an abnormal cell, it identifies the ID of the cell, and if it does not determine an abnormal cell, it sets the cell ID to NULL (no abnormal cell).

[0090] In step S8, if no abnormal cells are found in step S7, the self-discharge cell determination unit 302 proceeds to step S11, and if abnormal cells are found, the process proceeds to step S9. In step S9, the self-discharge cell addition determination unit 305 adds a self-discharge cell ID according to the cell usage history. In step S10, the replacement instruction unit 303 notifies the operation control center 40 of the replacement unit ID, abnormal module ID, and self-discharge cell ID. In step S11, the vehicle is used in the normal manner, and the battery system 20 supplies power to the traction system 1A of the battery train and absorbs and charges regenerative current.

[0091] In step S12, the driver inputs an operation to turn off the drive system 1A from the cab 12. In step S13, the vehicle control device 13 shuts down each device in the system. At this time, data transmission from the remote monitoring device is also completed. In step S14, this flowchart ends.

[0092] The advantages of the above-described embodiments are as follows. In the technical field of railway vehicles that use storage batteries as drive sources, the impact of self-discharge degradation of storage batteries has not been considered in the past. However, the embodiments can distinguish self-discharge degradation from other causes of degradation and identify it early. Self-discharge degradation of storage batteries progresses faster than other causes of degradation, and by the time voltage variations appear in the balancing circuit, the capacity of the balancing circuit is exceeded, which may progress in a short period of time due to a power generation system failure. However, according to the embodiments, self-discharge degradation of storage batteries can be detected early, so that storage batteries that have deteriorated due to self-discharge can be replaced in advance, thereby preventing system failures and associated vehicle operation disruptions.

[0093] (Embodiment 2) In the flowchart of FIG. 18 , steps S4 and S5 are determined to be positive, and the cell voltage is acquired (step S6). This method has three problems. First, the timing of the determinations in steps S4 and S5 is unstable. Second, because the balancing circuit 2113 operates when the drive system is turned on, if the balancing circuit 2113 is operating sufficiently at the start of the flowchart of FIG. 18 , voltage variations are corrected, and the detection of self-discharge is delayed. Third, the data processing required to perform the determinations in steps S4 and S5 becomes state-dependent, resulting in a large computational load. Therefore, embodiment 2 relates to an operation method in which steps S4 and S5 are determined to be positive when the drive system is started.

[0094] In step S5, current I exists for several hours after the drive system is turned off. When the vehicle is started, the vehicle is not running and charging has not yet begun, so the current is at a minimum value for the operation of the control board and auxiliary equipment 11. When the drive system 1A is turned on, it starts only the battery control board, battery-related sensors, and data transmission / reception device, and operates other auxiliary equipment such as the air conditioner and lighting, as well as the inverter 6, and other devices that are not related to the execution of steps S4 and S5, after obtaining the battery cell voltage, which is desirable because it allows the battery cell voltage to be obtained with a low current.

[0095] Since step S4 is answered affirmatively when the drive system is started, a function is added to adjust the voltage by charging or discharging when the drive system is off. In battery-powered railcars, this is done by charging via the pantograph, and in hybrid diesel railcars, this is done by charging using the engine or discharging using auxiliary machinery.

[0096] Figure 19 is a flowchart according to the second embodiment. The same parts as those in the flowchart of Figure 18 are designated by the same reference numerals, and their description will be omitted. In step S2, the drive system is turned on. At this time, only the control board, sensor data transmission / reception device, etc., necessary for detecting the state of the battery system, are activated.

[0097] In step 15, the voltage of each storage battery cell is acquired. At this time, the determinations in steps S4 and S5 are affirmative. In step 16, since the voltage has been acquired, the vehicle control device 13 starts up all the devices. Steps S7 to S12 are the same as those in FIG. 18. In step S12, after the driver inputs the drive system off operation in the cab 12, the vehicle control device 13 notifies the storage battery system 20 that the storage battery is at a predetermined voltage V ｓｙｓ (t ０ ) until the battery level reaches 100%. For example, in a battery train, the vehicle control device 13 raises the pantograph 2 and activates the converter. In step S13, the vehicle control device 13 shuts down each device in the traction system.

[0098] Fig. 20 is a functional block diagram of the self-discharge battery countermeasure unit 31 according to the flowchart of Fig. 19. The difference from Fig. 14 is that the timing instruction unit 301 is executed by the start flag (S1) of the drive system.

[0099] The second embodiment provides the following three advantages. First, self-discharge detection is stably established day by day. Second, the voltage of each of the multiple storage batteries is acquired before and during the start-up of the balancing circuit, which is the timing when the cell voltage variation due to self-discharge is greatest, so the self-discharge battery countermeasure unit 31 can detect self-discharge at an early stage. Third, since there is no need to perform steps S4 and S5, the calculation load is small.

[0100] (Embodiment 3) In embodiment 1, the self-discharge rate difference was obtained from the closed-circuit voltage difference between multiple storage battery cells, which resulted in two problems. First, even a storage battery cell with a relatively low self-discharge rate could have a higher self-discharge rate than the storage battery cell being replaced. Therefore, when the self-discharge of multiple cells is detected, the self-discharge battery countermeasure unit 31 adds the cells with a similar cumulative Wh usage to self-discharge cell ID-4, assuming that the self-discharge rate may also be increasing. However, this is the result of assuming that the self-discharge rate follows the usage history, and in reality, there is a possibility of erroneous determination.

[0101] The second point is that in order to eliminate the variation in capacity degradation caused by the voltage variation, it is necessary to limit the system voltage during daily measurements to a certain voltage range. In the first embodiment, this is addressed by waiting for the timing, while in the second embodiment, the charging rate is controlled in accordance with the system off operation on the previous day.

[0102] The configuration of embodiment 2 has the problem that it takes time from when the driver performs the system-off operation in step S12 until the drive system actually turns off (step S15), and also has the problem that it cannot handle cases where the system is turned off in a location where a battery-powered train cannot be charged.

[0103] Therefore, in the second embodiment, the self-discharge rate of each cell is measured to make a determination that does not depend on the relative voltage difference between the cells. The self-discharge rate is the amount of change in cell voltage per unit time [V / cell·hour] or the self-discharge current I ｓｅｉｆ，ｉ The amount of change in cell voltage per unit time and the self-discharge current can be converted into each other using Equation 5 and Fig. 7. In the third embodiment, an example of calculating the self-discharge current will be shown.

[0104] 21 is a graph illustrating the calculation principle of the self-discharge current according to embodiment 3. The self-discharge current is obtained by dividing the difference between the voltage of the storage battery cell when the system was off the previous day (dotted circle in the figure) and the battery cell voltage on the day the system was on (solid circle in the figure) by the time of the system-off period.

[0105] In the first embodiment, the cell C1 with the lowest voltage was determined to be the most self-discharged, but in the third embodiment, the cell C4 with the largest voltage difference from the previous day (the highest self-discharge rate) is determined to be the self-discharged cell. The formula for calculating the self-discharge current is shown in Equation 8. Ｓ is the time on the day the system is turned on, t Ｅ is the system off time on the previous day, SOHQ is the capacity degradation rate [%] of the entire battery system, Q0 is the initial cell charge capacity [Ah / cell], C ２ is a coefficient to ensure dimensional consistency.

[0106] SOHQ is preferably the capacity degradation rate SOHQi of each cell, but since it is generally difficult to calculate, it may be approximated by the capacity degradation rate of the entire system. Since dSOC / dOCV changes according to the curve in Figure 2, OCV is OCV ｉ (t Ｓ ) ~ OCV ｉ (t Ｅ ) The average value of the range of OCVi is set to CCVi=OCVi by setting the current at the time of measurement to 0 continuation.

[0107] The self-discharge abnormality cell is judged by, for example, calculating the self-discharge current of a new battery by I ｓｅｌｆ，０ [A / cell], and the balancing current defined by Equation 2 is I ｂａｌ，ｉ [A / cell], the average daily time the balancing circuit operates t ｏｎ [h], we define this as the case where Equation 9 holds. If this equation holds, it means that if cell i is incorporated into the same battery system as a new cell, the voltage difference will continue to increase due to self-discharge.

[0108] Unlike the determination method of the first embodiment (FIG. 10, Equations 3A and 3B), this determination method does not evaluate the voltage difference between different cell IDs in the system, and therefore can evaluate the self-discharge rate regardless of the voltage variation due to the capacity variation between cells shown in Equation 5. This makes it possible to omit the determination of Equation 6 in the first embodiment and the system voltage adjustment step S18 in the second embodiment.

[0109] 22 is a functional block diagram of a self-discharge battery countermeasure unit 31 that calculates a self-discharge rate according to a third embodiment of the present invention. A timing instruction unit 301 receives a system-on flag S1 and a system-off flag S2, and outputs an execution flag F1 based on the received flags. After receiving the system-off flag, the timing instruction unit 301 executes system voltage adjustment (FIG. 23, step S13) and turns off other devices (FIG. 23, step S18), and outputs the execution flag F1.

[0110] Since the closed circuit voltage of the storage battery has a polarization term, which is the second term in Equation 1, it is ideally desirable to set the system current to 0. If the system current cannot be set to 0 due to system constraints, the system current can be set to the same value at the two cell voltage acquisition timings. Since the voltage difference is taken at the two acquisition timings as in Equation 8, the effects of polarization can be canceled out if the polarization is set to the same value. In embodiment 3, in order to set the system current to the same value, devices not required for cell voltage acquisition are turned off at the two cell voltage acquisition timings.

[0111] Even if the voltage is acquired while the auxiliary equipment is on, the timing instruction unit 301 may determine whether the system current when the system is on is the same as the system current when the system is off, and output the execution flag. ｃｅｌｌ The self-discharge rate (self-discharge current in the third embodiment) of each cell is calculated according to Equation 8 using the time difference of the execution flag, and cells that meet the conditions of Equation 8 are identified as self-discharge cells, and the self-discharge cell ID (ID-3) is output.

[0112] 23 is a flowchart according to the third embodiment. In step S2, the drive system is turned on. At this time, only the minimum control board, sensors, data transmission / reception device, etc. required for detecting the state of the storage battery system 20 are activated. In step S15, the voltage of each cell at the time of system activation is acquired. At this time, other devices such as auxiliary machinery are not operating, so the system current is approximately the same as the voltage acquired when the drive system was shut down (step S19).

[0113] In step S16, since voltage acquisition is complete, the vehicle control device 13 starts up all devices in the traction system 1A. In step S17, the self-discharge rate calculation unit 306 calculates the self-discharge rate of each cell and outputs the ID of the self-discharge cell. Steps S7 to S12 are the same as those in the flowchart of FIG. 18, except that the usage history determination step S9 is unnecessary. After receiving a drive system off command from the driver's cab in step S12, the vehicle control device 13 first turns off devices not required for self-discharge rate calculation in step S18. That is, the process is the same as step S15. This significantly reduces the auxiliary current flowing through the battery storage system 20, and the minute current flow can be made the same between step S15 and step S19, the two voltage acquisition timings. In step S19, measurement data of each cell voltage at system shutdown is transmitted to the server 70 via the data transmission / reception device 60. In step S13, the vehicle control device 13 shuts down each device in the traction system.

[0114] This embodiment has two advantages. First, it directly calculates the self-discharge current of each cell without estimating it from the usage history, enabling replacement of cells with high self-discharge currents. Therefore, even if a cell with a relatively low self-discharge current remains after replacement in the first embodiment, it is possible to avoid a situation in which the self-discharge current is higher than that of the replaced cell, resulting in an increase in voltage difference. Since an increase in the self-discharge rate can be detected even when there is no difference in self-discharge current between cells, it is possible to address the issue at an early stage of self-discharge occurrence. Second, because it is possible to determine self-discharge of each cell even when the system voltage is not within a certain range, it is possible to solve the problems of the first embodiment, where the voltage condition is not met and self-discharge determination is not established, the second embodiment, where voltage adjustment time is required until the traction system is turned off, and the second embodiment, where voltage adjustment is not possible when the battery-powered train is turned off in a location where charging is not possible.

[0115] Servers, personal computers, and other computer equipment equipped with the above-mentioned monitoring system, storage battery systems monitored by the monitoring system, drive systems or storage battery systems equipped with part or all of the monitoring system, railway vehicles equipped with this drive system, vehicle operation systems that use the monitoring system, computer programs for executing the monitoring system, portable storage media on which the program is recorded, and integrated circuits on which the monitoring system is mounted are inventions supported by the above-mentioned embodiments.

[0116] The embodiments described so far have been directed to monitoring systems for storage battery systems mounted on the drive systems of railway vehicles, but storage battery systems are not limited to those on railway vehicles, and are not limited to the railway field, in particular, as long as they are used in fields where a relatively large number of storage batteries are connected in series and self-discharge issues can occur.

[0117] Although the present invention has been described above using embodiments, it goes without saying that the technical scope of the present invention is not limited to the scope described in the above embodiments. It will be apparent to those skilled in the art that various modifications and improvements can be made to the above embodiments. Furthermore, it is clear from the claims that such modifications and improvements can also be included within the technical scope of the present invention.

[0118] DESCRIPTION OF SYMBOLS 1A... Drive system (for battery-powered electric railcars) 1B... Drive system (for hybrid diesel railcars) 2... Pantograph 3... Engine 4... Generator 5... Converter 6... Motor inverter 7... Motor 8... Reducer 9... Wheelset 10... Auxiliary inverter 11... Auxiliary 12... Cab 13... Vehicle control device 14... Overhead line 20... Battery system 21... Battery box 22... Battery series group 23... Battery replacement unit 30... Monitoring unit 40... Operation control center 60... Data transmitter / receiver 70... Server 211... Battery module 212... Battery box control board 213... Box voltmeter 214... Group voltmeter 2111... Battery cell 2112... Cell controller board 2113... Balancing circuit 2114... Balancing controller 2115... Balancing resistor 2116... Balancing switch 2117... Cell voltmeter 31... Self-discharge battery handling unit 301... Timing instruction unit 302... Self-discharge cell determination unit 303... Replacement instruction unit 304... Usage history calculation unit 305... Self-discharge cell addition determination unit 306... Self-discharge rate calculation unit 3011... Current condition determination unit 3012... Voltage condition determination unit 3051... Multiple cell self-discharge determination unit 3052... Self-discharge cell addition unit

Claims

1. A monitoring system for monitoring a storage battery system used as a power source for a railway vehicle drive system, the storage battery system having a plurality of storage battery cells connected in series, the monitoring system comprising: an acquisition unit that acquires voltages of the plurality of storage battery cells; and a determination unit that determines which of the plurality of storage battery cells is self-discharging based on the acquired voltage.

2. The monitoring system of claim 1, wherein the acquisition unit acquires the voltages of the multiple storage battery cells when the current of the storage battery system approaches zero and when the integrated value of the current of the storage battery system is zero.

3. The monitoring system of claim 1 or 2, characterized in that the acquisition unit acquires the voltages of the multiple storage battery cells when the current of the storage battery system approaches zero and when the charging rate of the storage battery system is within a predetermined range.

4. The monitoring system of any one of claims 1 to 3, characterized in that the acquisition unit acquires the voltages of the multiple storage battery cells when the current of the storage battery system approaches zero and when the average voltage of each storage battery cell in the storage battery system is within a predetermined range.

5. A monitoring system as described in any one of claims 1 to 4, characterized in that the acquisition unit acquires the voltages of the multiple storage battery cells when the absolute current value of the storage battery system is below a threshold value and the voltage of the storage battery system is within a voltage threshold value from a reference system voltage.

6. The monitoring system according to any one of claims 1 to 5, characterized in that the determination unit determines that, among the acquired voltages of the multiple storage battery cells, a storage battery cell whose voltage is lower than a voltage threshold value, starting from the storage battery cell with the highest voltage, is a storage battery cell that has self-discharged.

7. The monitoring system of any one of claims 1 to 6, characterized in that, when a signal to turn off the drive system is input, the drive system charges or discharges the storage battery system, adjusts the storage battery system to within a voltage threshold from a reference system voltage, and is turned off after the adjustment is completed.

8. The monitoring system of any one of claims 1 to 7, characterized in that, when a signal to turn off the drive system is input, the drive system charges or discharges the storage battery system, adjusts the storage battery system from a reference system charging rate to within a charging rate threshold, and is turned off after the adjustment is completed.

9. The monitoring system according to any one of claims 1 to 8, wherein the acquisition unit acquires the voltages of the plurality of storage battery cells after the drive system of the railway vehicle is turned on and before the railway vehicle starts moving.

10. The monitoring system of any one of claims 1 to 9, characterized in that when the drive system is turned on, it starts up first with the equipment required to acquire the voltages of the multiple storage battery cells, and after acquiring the voltages of the multiple storage battery cells, it turns on the other equipment.

11. The monitoring system of any one of claims 1 to 10, characterized in that the acquisition unit acquires the voltages of the multiple storage battery cells after the railway vehicle's drive system has stopped running the railway vehicle and before the drive system is turned off.

12. The monitoring system according to any one of claims 1 to 11, characterized in that the drive system is turned off except for devices necessary for acquiring the voltages of the plurality of storage battery cells, and after the voltages of the plurality of storage battery cells have been acquired, the necessary devices are turned off.

13. The monitoring system according to any one of claims 1 to 12, characterized in that the determination unit determines a storage battery cell to be a self-discharging cell by adding storage battery cells with an equivalent usage history to the storage battery cell determined to be a self-discharging cell.

14. A monitoring system as described in any one of claims 1 to 13, characterized in that the judgment unit performs the judgment based on the self-discharge rate of each of the plurality of storage battery cells, and the self-discharge rate of each of the storage battery cells is calculated based on the cell voltage when the drive system is off, the cell voltage when the system is on, and the elapsed time from when the system is off to when the system is on.

15. The monitoring system of any one of claims 1 to 14, characterized in that the storage battery system includes a balancing circuit that balances the voltages of the multiple storage battery cells, and the determination unit determines which storage battery cell is self-discharging based on the self-discharge rate of each of the multiple storage batteries and the voltage adjustment rate of the balancing circuit.

16. A monitoring system as claimed in any one of claims 1 to 15, characterized in that the storage battery system controls the system current to be the same when the system is off and when the system is on.

17. A monitoring system as claimed in any one of claims 1 to 16, further comprising an indicating unit that indicates a storage battery cell that has been determined to be self-discharging.

18. The monitoring system of any one of claims 1 to 17, characterized in that the determination unit determines that a storage battery cell has self-discharged when the difference in self-discharge rate between the storage battery cell and a storage battery cell to be replaced that has a daily cumulative difference is greater than the adjustment speed of a balancing circuit that balances the voltages of the multiple storage battery cells multiplied by the average operating time of the drive system.

19. A monitoring system as described in any one of claims 1 to 18, characterized in that the instruction unit that indicates a storage battery cell determined to be self-discharging specifies a battery module that includes the storage battery cell that is self-discharging, and instructs replacement of that storage battery cell.

20. A monitoring system as described in any one of claims 1 to 19, characterized in that the instruction unit that indicates a storage battery cell determined to be self-discharging specifies a replacement unit including the battery module and instructs replacement of the storage battery cell.

21. A monitoring method in which a computer monitors a battery system that is used as a power source for a railway vehicle drive system and has a battery with multiple battery cells connected in series, the monitoring method being characterized in that the computer acquires voltages of the multiple battery cells, and determines which of the multiple battery cells is self-discharging based on the acquired voltages.

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