Battery monitoring device, program, and battery monitoring method

Abstract

To provide a battery monitoring device capable of appropriately determining whether to energize a storage battery, the storage battery comprising a plurality of battery cells connected to each other.SOLUTION: A battery monitoring device monitors a state of a storage battery 20 comprising a plurality of battery cells 21 connected to each other. The battery monitoring device obtains, for each battery cell, a response signal of the battery cell to an AC signal in a state in which a predetermined AC signal is applied to the battery cell, calculates the impedance of the battery cell based on the response signal, and based on the impedance, determines insulation deterioration between electrode terminals of each battery cell.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a battery monitoring device for monitoring the state of a storage battery. , program, and battery monitoring method - Patents.com Regarding. [Background technology]

[0002] Conventionally, a storage battery having a plurality of battery cells connected to each other has been used as a power source mounted on a vehicle. For example, Patent Document 1 discloses an air-cooled storage battery in which a plurality of battery cells are housed in a housing provided with an air supply / intake duct and an air exhaust duct. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5953925 Summary of the Invention [Problem to be solved by the invention]

[0004] In a storage battery having a plurality of battery cells connected to each other, if a conductive foreign object generated in the housing adheres between the electrode terminals of one of the battery cells, the capacity of the battery cell may decrease due to localized discharge through the conductive foreign object, and the terminal voltage of the battery cell may decrease. If this causes a large variation in the terminal voltage of the battery cells in the storage battery, there is a concern that the storage battery may not be able to be energized properly.

[0005] The present invention has been made in consideration of the above problems, and provides a battery monitoring device that can appropriately determine whether or not current is passed through a storage battery having a plurality of battery cells connected to each other. , program, and battery monitoring method - Patents.com The purpose of this invention is to provide [Means for solving the problem]

[0006] A first means for solving the above problem is a battery monitoring device that monitors the state of a storage battery having a plurality of battery cells connected to each other, and includes an impedance calculation unit that, for each battery cell, acquires a response signal of the battery cell to a predetermined AC signal while applying the AC signal to the battery cell, and calculates the impedance of the battery cell based on the response signal, and an insulation determination unit that determines a deterioration in insulation between the electrode terminals of each battery cell based on the impedance.

[0007] In a storage battery having multiple battery cells connected to each other, if the insulation between the electrode terminals of one of the multiple battery cells deteriorates and the terminal voltage of that battery cell decreases, the terminal voltage of the battery cells will vary greatly within the battery, raising concerns that the storage battery may not be able to properly supply electricity.

[0008] In this regard, in the above-described configuration, the impedance of each battery cell is calculated, and the deterioration of the insulation between the electrode terminals of each battery cell is judged based on the impedance, so that it is possible to appropriately judge whether or not the storage battery is energized based on the result of the judgment of the deterioration of the insulation of each battery cell.

[0009] In a second aspect, each of the battery cells is cooled by being immersed in an insulating liquid coolant, and the insulation determining unit determines the deterioration of the insulation based on the impedance.

[0010] In a storage battery in which each battery cell is immersed in an insulating liquid refrigerant for cooling, the liquid refrigerant may deteriorate the insulation between the electrode terminals of each battery cell. For example, conductive foreign matter may be mixed into the liquid refrigerant. The insulating properties of the liquid refrigerant may also deteriorate.

[0011] In this regard, in the above-described configuration, the deterioration of insulation is judged based on the impedance of each battery cell, which makes it possible to appropriately judge whether or not current is allowed to flow through the storage battery in which each battery cell is cooled by being immersed in a liquid refrigerant.

[0012] In a third method, the insulation determination unit determines whether the insulation degradation is a foreign-matter-induced degradation caused by the introduction of conductive foreign matter into the liquid refrigerant, or a refrigerant-induced degradation caused by deterioration or reduction of the liquid refrigerant, based on the number of degraded cells, which are battery cells whose impedance has dropped below a predetermined threshold value.

[0013] For example, in a foreign object-induced degradation, only one of the battery cells immersed in the liquid coolant may be a degraded cell. On the other hand, in a coolant-induced degradation, all of the battery cells immersed in the liquid coolant may be degraded. Thus, the number of degraded cells differs between a foreign object-induced degradation and a coolant-induced degradation.

[0014] In this regard, in the above-described configuration, it is determined whether the insulation deterioration is due to a foreign object or a refrigerant based on the number of deteriorated cells, so that the type of insulation deterioration occurring in the storage battery can be properly understood.

[0015] In a fourth method, the multiple battery cells are arranged in a predetermined arrangement direction, and when the battery cell whose impedance has dropped below a predetermined threshold is determined to be a degraded cell, the insulation determination unit determines, based on the position of the degraded cell in the arrangement direction, whether the degradation in insulation due to the liquid refrigerant is a foreign-matter-induced degradation due to the introduction of a conductive foreign matter into the liquid refrigerant, or a refrigerant-induced degradation due to deterioration or reduction of the liquid refrigerant.

[0016] For example, in a foreign object-induced degradation, only the battery cell located in the middle of the battery arrangement direction may be a degraded cell. On the other hand, in a refrigerant-induced degradation, battery cells within a predetermined range from one end in the arrangement direction may be degraded cells. Thus, the position of the degraded cell in the arrangement direction differs between a foreign object-induced degradation and a refrigerant-induced degradation.

[0017] In this regard, in the above-described configuration, it is determined whether the insulation deterioration is due to a foreign object or a refrigerant based on the position of the deteriorated cell in the arrangement direction, so that the type of insulation deterioration occurring in the storage battery can be properly grasped.

[0018] The fifth means includes a change unit that changes a subsequent usage mode of the storage battery based on a determination result of whether the deterioration is due to the foreign matter or the refrigerant.

[0019] For example, in the case of deterioration caused by foreign object, the number of battery cells that become deteriorated cells is small, and there is a possibility that the foreign object will separate from the deteriorated cells with use, so it may be acceptable to continue using the storage battery. On the other hand, in the case of deterioration caused by refrigerant, the number of battery cells that become deteriorated cells is large, and there is a small possibility that the insulating properties of the liquid refrigerant will recover with use, so it may be better to stop using the storage battery. In this way, the preferable manner of using the storage battery after deterioration caused by foreign object and deterioration caused by refrigerant may differ.

[0020] In this regard, in the above-mentioned configuration, the subsequent usage of the storage battery is changed based on the result of the determination of whether the deterioration in insulation of the storage battery is due to a foreign object or due to a refrigerant, so that the subsequent usage of the storage battery can be appropriately determined according to the state of the deterioration in insulation of the storage battery. [Brief description of the drawings]

[0021] [Figure 1] Overall configuration diagram of the power supply system. [Diagram 2] FIG. [Diagram 3] 1 is a graph showing a complex impedance plane plot of a battery cell. [Figure 4] 1A and 1B are diagrams showing a state in which insulation between electrode terminals of a battery cell is deteriorated. [Diagram 5] 5 is a flowchart showing the procedure of a determination process in the first embodiment. [Figure 6] 4 is a graph showing the relationship between the real part of the complex impedance and the temperature of a battery cell. [Figure 7] FIG. 11 is a configuration diagram of a storage battery according to a second embodiment. [Figure 8] 10 is a flowchart showing the procedure of a determination process in the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] (First embodiment) DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment in which a battery monitoring device according to the present invention is applied to a power supply system of a vehicle (for example, a hybrid vehicle or an electric vehicle) will be described with reference to the drawings.

[0023] As shown in FIG. 1, the power supply system 10 is a system that supplies power to an electrical load such as a rotating machine (motor generator), and includes a storage battery 20 and a refrigerant supply unit 30 that supplies a liquid refrigerant 31 to the storage battery 20.

[0024] The storage battery 20 has an output voltage of, for example, several hundred volts, and is configured by connecting a plurality of battery cells 21 in series with one another. In this embodiment, the inter-terminal voltages (for example, rated voltages) of the battery cells 21 constituting the storage battery 20 are set to be the same. For example, a lithium ion battery or a nickel metal hydride battery can be used as the battery cells 21.

[0025] The battery cell 21 is formed, for example, in the shape of a flattened rectangular parallelepiped, and has electrode terminals 22 (positive electrode terminal 22a, negative electrode terminal 22b) provided on both ends of the longitudinal direction on its top surface (vertically upper surface). The positive electrode terminal 22a and the negative electrode terminal 22b protrude upward from the top surface of the battery cell 21 to the same extent. The multiple battery cells 21 are arranged side by side in the short side direction so that their side surfaces overlap each other. In this case, adjacent battery cells 21 are arranged so that the positive electrode terminals 22a and the negative electrode terminals 22b are staggered. In this embodiment, the short side direction corresponds to the "arrangement direction".

[0026] In order to connect the battery cells 21 in series, the positive electrode terminal 22a of the battery cell 21 is connected to the negative electrode terminal 22b of the battery cell 21 on one side adjacent to it in the short side direction by a lid 23 that functions as a bus bar. Also, the negative electrode terminal 22b of the battery cell 21 is connected to the positive electrode terminal 22a of the battery cell 21 on the other side adjacent to it by the lid 23.

[0027] The lid 23 covers an opening 24a provided on the upper surface of a battery casing 24 that houses a plurality of battery cells 21, and its lower surface functions as a bus bar that connects adjacent battery cells 21 in the short side direction. A connector 23a for connecting the storage battery 20 to an electrical load is provided on the upper surface of the lid 23, and the storage battery 20 is connected to the electrical load by power supply paths L1, L2 connected to the connector 23a. Note that a bus bar may be provided separately from the lid 23.

[0028] The lid 23 is provided with a battery measuring device 40 that measures the state of the storage battery 20. The battery measuring device 40 is a device that measures the complex impedance Zm of each battery cell 21 as the state of the storage battery 20. Note that the battery measuring device 40 may be provided separately from the lid 23.

[0029] 2 shows an equivalent circuit model of the complex impedance Zm of the battery cell 21. In this equivalent circuit model, the complex impedance Zm of the battery cell 21 is composed of a series connection of an ohmic resistance RA and a reaction resistance Rct. The ohmic resistance RA is a current resistance in the electrodes and electrolyte that constitute the battery cell 21. The reaction resistance Rct represents a resistance due to an electrode interface reaction in the electrodes, and is represented as a parallel connection of a resistance component RB and a capacitance component CB.

[0030] 2 also shows a battery measurement device 40. The battery measurement device 40 is provided for each battery cell 21, and includes a current modulation circuit 41, a voltmeter 42, and a control device 43 as a battery monitoring device.

[0031] The current modulation circuit 41 is a circuit that applies a predetermined AC signal to the battery cell 21 that is the measurement target. The current modulation circuit 41 has a semiconductor switch element 41a (e.g., a MOSFET) and an ammeter 41b connected in series to the semiconductor switch element 41a, and is connected to the battery cell 21 by a first electrical path 44.

[0032] A gate terminal of the semiconductor switch element 41a is connected to the control device 43. Based on a gate signal input from the control device 43, the semiconductor switch element 41a causes the battery cell 21 to output a current signal as an AC signal corresponding to the gate signal. The AC signal is, for example, a sine wave signal or a square wave signal. The ammeter 41b measures the current signal generated in the first electrical path 44, and outputs the measured current signal data to the control device 43.

[0033] The voltmeter 42 is connected to the battery cell 21 by a second electrical path 45 different from the first electrical path 44. When the voltmeter 42 outputs a current signal, a response signal (voltage fluctuation) reflecting the complex impedance Zm of the battery cell 21 is generated. The voltmeter 42 measures this response signal and outputs the measured response signal data to the control device 43.

[0034] The first electrical path 44 and the second electrical path 45 are both connected between the positive electrode terminal 22a and the negative electrode terminal 22b of the battery cell 21, and are wired so as to be separated in the immediate vicinity of the positive electrode terminal 22a and the negative electrode terminal 22b.

[0035] The control device 43 is mainly configured with a microcomputer, and realizes various control functions by executing programs stored in a storage device provided in the control device 43. The control device 43 has a function of monitoring the state of the storage battery 20. Specifically, the control device 43 calculates the complex impedance Zm of each battery cell 21, that is, the real part ReZm and the imaginary part ImZm of the complex impedance Zm, based on the response signal and the current signal. The control device 43 creates, for example, a complex impedance plane plot (Cole-Cole plot) based on the calculation result.

[0036] 3 shows a complex impedance planar plot of the battery cell 21. In the complex impedance planar plot, in order to show a vector locus focusing on the capacitance component in the first quadrant, the upper side of the vertical axis is drawn to be "-ImZm", that is, the imaginary part is inverted.

[0037] On the complex impedance plane plot, the complex impedance Zm changes depending on the frequency of the gate signal input from the control device 43 to the semiconductor switch element 41a, and a semicircular arc Cr appears in the low frequency region. At the end point PA on the high frequency side of the arc Cr, the imaginary part ImZm of the complex impedance Zm becomes zero. The value of the real part ReZm of the complex impedance Zm at this end point PA represents the ohmic resistance RA.

[0038] A straight line Dr appears on the low frequency side of the arc Cr. On a virtual line (dash line) extending from the connection point PB between the arc Cr and the straight line Dr along the arc Cr, a virtual point PC is defined as a point where the imaginary part ImZm of the complex impedance Zm becomes zero. The value of the real part ReZm of the complex impedance Zm at this virtual point PC represents the sum of the ohmic resistance RA and the resistance component RB of the reactive resistance Rct.

[0039] The control device 43 is also connected to the notification unit 46 and controls the notification unit 46. The notification unit 46 is a device that notifies the driver visually or audibly, and is, for example, a display or a speaker installed in the vehicle cabin.

[0040] Returning to FIG. 1, the coolant supply unit 30 is connected to the storage battery 20 via a pair of communication holes 24b, 24c provided on the lower side surface of the battery housing 24. The coolant supply unit 30 has a circulation pump 32 that circulates the liquid coolant 31 and a heat exchanger 33 such as a radiator that cools the liquid coolant 31, and these components are arranged in series via a coolant passage 34 through which the liquid coolant 31 passes. The liquid coolant 31 is an insulating coolant, such as an insulating LLC (long life coolant). The liquid coolant 31 cooled by the heat exchanger 33 circulates between the coolant passage 34 and the battery housing 24 by the operation of the circulation pump 32, thereby cooling the storage battery 20.

[0041] The inside of the battery casing 24 is filled with liquid refrigerant 31, and each battery cell 21 is provided in a cooled state by being immersed in the liquid refrigerant 31. In this embodiment, the amount of liquid refrigerant 31 inside the battery casing 24 is adjusted so that the electrode terminals 22 of each battery cell 21 are not immersed in the liquid refrigerant 31.

[0042] Incidentally, in a storage battery 20 in which the battery cells 21 are immersed in and cooled by a liquid refrigerant 31, the liquid refrigerant 31 may cause a decrease in insulation between the electrode terminals 22 of each battery cell 21. For example, as shown in FIG. 4(A), conductive foreign matter 50 generated inside the battery casing 24 or the refrigerant supply unit 30 may become mixed into the liquid refrigerant 31. When the foreign matter 50 adheres between the electrode terminals 22 of one battery cell 21 due to circulation of the liquid refrigerant 31, the foreign matter 50 causes a decrease in insulation between the electrode terminals 22 of each battery cell 21. Hereinafter, the decrease in insulation between the electrode terminals 22 of the battery cells 21 due to the inclusion of the foreign matter 50 is referred to as a decrease caused by foreign matter.

[0043] Furthermore, as shown in Fig. 4(B), depending on the driving conditions of the vehicle in which the storage battery 20 is mounted, the storage battery 20 may tilt by an angle θ, and among the multiple battery cells 21 arranged side by side in the short side direction, the electrode terminals 22 of two battery cells 21 at one end side (the right end side in Fig. 4(B)) may become immersed in the liquid refrigerant 31. The liquid refrigerant 31 is an insulating refrigerant, but its insulating properties may deteriorate due to deterioration over time. In this case, the insulation between the electrode terminals 22 of each battery cell 21 decreases due to the deterioration of the insulating properties of the liquid refrigerant 31. Hereinafter, the decrease in insulation between the electrode terminals 22 of the battery cells 21 due to the deterioration of the liquid refrigerant 31 is referred to as a refrigerant-induced decrease.

[0044] If the insulation between the electrode terminals 22 of the battery cells 21 is degraded due to a foreign object-induced degradation or a refrigerant-induced degradation, the capacity of the battery cell 21 is reduced due to local discharge through the foreign object 50 or the liquid refrigerant 31, and the terminal voltage of the battery cell 21 is reduced. As a result, if the terminal voltages of the battery cells 21 in the storage battery 20 vary widely, there is a concern that the storage battery 20 may not be able to be energized appropriately. Therefore, in this embodiment, the control device 43 performs a determination process to determine whether the insulation between the electrode terminals 22 of each battery cell 21 has been degraded.

[0045] A flowchart of the determination process of this embodiment is shown in Fig. 5. The control device 43 performs the determination process when the vehicle is started or when an abnormality such as a vehicle impact is detected.

[0046] When the determination process is started, in step S11, the complex impedance Zm of each battery cell 21 is calculated. In the following step S12, a decrease in insulation between the electrode terminals 22 of each battery cell 21 is determined based on the complex impedance Zm calculated in step S11, and the process proceeds to step S13. Note that in this embodiment, the process of step S11 corresponds to an "impedance calculation unit", and the process of step S12 corresponds to an "insulation determination unit".

[0047] A predetermined threshold value Zth for determining whether or not an insulation property has decreased is stored in the control device 43. In step S12, it is determined that an insulation property decrease has occurred in the battery cell 21 based on the fact that the complex impedance Zm calculated in step S11 has decreased below the threshold value Zth.

[0048] Here, the threshold value Zth is set based on the complex impedance Zm of each battery cell 21 in a normal state where no deterioration in insulation occurs. FIG. 6 shows the relationship between the real part ReZm of the complex impedance Zm in the normal state and the temperature of the battery cell 21. As shown in FIG. 6, the real part ReZm of the complex impedance Zm decreases as the temperature of the battery cell 21 increases. The same is true for the imaginary part ImZm of the complex impedance Zm. In other words, the complex impedance Zm of each battery cell 21 in the normal state changes depending on the temperature of the battery cell 21.

[0049] Fig. 6 shows the above relationship in three states where the SOC (State Of Charge) of the battery cells 21 is different from one another. In the example shown in Fig. 6, the SOC decreases in the order of white circles, white triangles, and white squares. As shown in Fig. 6, the real part ReZm of the complex impedance Zm increases as the SOC decreases. The same is true for the imaginary part ImZm of the complex impedance Zm. In other words, the complex impedance Zm of each battery cell 21 in the normal state changes depending on the SOC of the battery cell 21.

[0050] Therefore, in the present embodiment, the threshold value Zth is set for each temperature and SOC of the battery cell 21. Therefore, it is possible to determine that a deterioration in the insulation property of the battery cell 21 has occurred, regardless of the temperature and SOC of the battery cell 21.

[0051] In step S13, it is determined whether or not the determination of insulation deterioration has been completed for all of the battery cells 21. If the determination has not been completed for all of the battery cells 21, the process returns to step S11. On the other hand, if the determination has been completed for all of the battery cells 21, the process proceeds to step S14.

[0052] In step S14, it is determined whether or not there is a degraded cell, which is a battery cell 21 determined to have deteriorated insulation in step S12. If there is no degraded cell, this process ends. On the other hand, if there is a degraded cell, the process proceeds to steps S15 and S16.

[0053] In steps S15 and S16, the position of the degraded cell in the short-side direction is determined. Specifically, in step S15, it is determined whether or not the multiple battery cells 21 determined to be degraded cells are continuous in the short-side direction. If there is one battery cell 21 determined to be a degraded cell, or if there are multiple battery cells 21 determined to be degraded cells and there are battery cells 21 in a normal state with no degraded insulation between the degraded cells in the short-side direction, the process proceeds to step S21. On the other hand, if there are multiple battery cells 21 determined to be degraded cells and there are no battery cells 21 in a normal state between the degraded cells in the short-side direction, the process proceeds to step S16.

[0054] In step S16, it is determined whether or not the multiple battery cells 21 determined as degraded cells are located at either end in the short side direction among the multiple battery cells 21 arranged side by side in the short side direction. If none of the multiple battery cells 21 determined as degraded cells are located at an end in the short side direction, the process proceeds to step S21. On the other hand, if any one of the multiple battery cells 21 determined as degraded cells is located at an end in the short side direction, the process proceeds to step S17.

[0055] In step S17, it is determined that the insulation deterioration of the degraded cell is due to a refrigerant-induced deterioration. In the following step S18, the use of the storage battery 20 is prohibited, and the determination process is terminated. When a refrigerant-induced deterioration occurs, the degraded cell may continue to exist depending on the vehicle's running conditions (inclination), and the vehicle may not be able to continue running. Therefore, in step S18, the driver is notified, for example via the notification unit 46, that use of the storage battery 20 will be prohibited after the current vehicle running ends.

[0056] In step S21, the number of degraded cells is determined. Specifically, it is determined whether or not the number of battery cells 21 determined as degraded cells is equal to or less than a predetermined number. The predetermined number varies depending on the temperature and SOC of the battery cells 21, and is smaller, for example, as the SOC decreases. If the number of battery cells 21 determined as degraded cells is equal to or less than the predetermined number and the storage battery 20 can be energized appropriately even if degraded cells exist, the determination process ends. On the other hand, if the number of battery cells 21 determined as degraded cells is greater than the predetermined number and there is a risk of interference with energization of the storage battery 20, the process proceeds to step S22.

[0057] In step S22, it is determined that the insulation deterioration of the degraded cell is due to a foreign object-induced deterioration. In the following step S23, the control device 43 transmits a message to the upper ECU to suppress the output voltage of the storage battery 20, and ends the determination process. When a foreign object-induced deterioration occurs, a conductive foreign object 50 attached to the degraded cell may peel off from the degraded cell depending on the running conditions of the vehicle, and the degraded cell may return to a normal battery cell 21 in which insulation has not been deteriorated. In addition, the peeled foreign object 50 may be removed by a filter provided in the circulation pump 32. Therefore, in step S23, the output voltage of the storage battery 20 is temporarily suppressed without prohibiting the use of the storage battery 20. In this embodiment, the processes of steps S18 and S23 correspond to a change unit.

[0058] Next, the criteria for determining whether a foreign object-induced deterioration or a refrigerant-induced deterioration has occurred, and the manner in which the storage battery 20 is used after a foreign object-induced deterioration or a refrigerant-induced deterioration has occurred will be described.

[0059] In this embodiment, it is determined whether the deterioration in insulation of a deteriorated cell is due to a foreign object or due to a refrigerant, based on the position of the deteriorated cell in the short-side direction. In the case of a deterioration due to a foreign object, the foreign object 50 moves irregularly due to the circulation of the liquid refrigerant 31, so that only the battery cell 21 located in the middle of the short-side direction may become a deteriorated cell. On the other hand, a deterioration due to a refrigerant occurs due to the inclination of the storage battery 20, so that a predetermined range of battery cells 21 continuing from one end in the short-side direction become deteriorated cells. Therefore, in this embodiment, when the positions of the deteriorated cells in the short-side direction are consecutive and located at the end in the short-side direction, it is determined that the deterioration is due to a refrigerant.

[0060] If it is determined that the deterioration is due to a foreign object, the driver is notified and the use of the storage battery 20 is not prohibited. If it is determined that the deterioration is due to a refrigerant, the use of the storage battery 20 is prohibited. In other words, the subsequent usage mode of the storage battery 20 is changed based on the determination result of whether the deterioration is due to a foreign object or a refrigerant. This makes it possible to appropriately determine the subsequent usage mode of the storage battery 20 depending on the state of the insulation deterioration that has occurred in the storage battery 20.

[0061] According to the present embodiment described above in detail, the following effects can be obtained.

[0062] In the present embodiment, in the determination process, the complex impedance Zm of each battery cell 21 is calculated, and a deterioration in insulation between the electrode terminals 22 of each battery cell 21 is determined based on the complex impedance Zm. This makes it possible to appropriately determine whether or not current is allowed to flow through the storage battery 20 based on the determination result of the deterioration in insulation of each battery cell 21.

[0063] Specifically, the deterioration of insulation caused by the liquid refrigerant 31 is determined based on the complex impedance Zm of each battery cell 21. This makes it possible to appropriately determine whether or not current is passed through the storage battery 20 in a configuration in which each battery cell 21 is immersed in the liquid refrigerant 31 and cooled.

[0064] In this embodiment, it is determined whether the cause of the insulation deterioration caused by the liquid refrigerant 31 is a foreign object-induced deterioration or a refrigerant-induced deterioration based on the position of the deteriorated cell in the short-side direction. This makes it possible to properly grasp the state of the insulation deterioration occurring in the storage battery 20.

[0065] In this embodiment, the subsequent usage mode of the storage battery 20 is changed based on the determination result of the cause of the insulation deterioration. This makes it possible to appropriately determine the subsequent usage mode of the storage battery 20 according to the state of the insulation deterioration that has occurred in the storage battery 20.

[0066] Second embodiment The second embodiment will be described below with reference to FIGS. 7 and 8, focusing on the differences from the first embodiment.

[0067] 7(A), in this embodiment, the amount of liquid refrigerant 31 in the battery casing 24 is adjusted so that the electrode terminals 22 of each battery cell 21 are immersed in the liquid refrigerant 31. In this embodiment, a liquid refrigerant having higher insulation properties than air is selected as the liquid refrigerant 31. Therefore, when the electrode terminals 22 of each battery cell 21 transition from a state in which they are immersed in the liquid refrigerant 31 to a state in which they are not immersed, the insulation between the electrode terminals 22 of the battery cells 21 decreases.

[0068] Specifically, as shown in Fig. 7(B), when the amount of liquid refrigerant 31 in the battery casing 24 decreases slightly and the storage battery 20 is tilted by angle θ, the electrode terminals 22 of two battery cells 21 at one end (the left end in Fig. 7(B)) of the multiple battery cells 21 arranged side by side in the short side direction become exposed from the liquid refrigerant 31. In this case, the insulation between the electrode terminals 22 of the battery cells 21 decreases.

[0069] 7(C), when the amount of liquid refrigerant 31 in the battery casing 24 is excessively reduced and the electrode terminals 22 of all the battery cells 21 are exposed from the liquid refrigerant 31, the insulation between the electrode terminals 22 of all the battery cells 21 is reduced. In this embodiment, the reduction in insulation between the electrode terminals 22 of the battery cells 21 due to the reduction in the liquid refrigerant 31 is referred to as a refrigerant-induced reduction.

[0070] A flowchart of the determination process of this embodiment is shown in Fig. 8. In Fig. 8, the same processes as those shown in Fig. 5 are denoted by the same step numbers for convenience, and the description thereof will be omitted.

[0071] In the determination process of this embodiment, the number of degraded cells is determined in step S31. Specifically, if a positive determination is made in step S14, it is determined in step S31 whether or not all battery cells 21 included in the storage battery 20 have been determined as degraded cells. As shown in Fig. 7(C), if all battery cells 21 have been determined as degraded cells, the process proceeds to step S17. On the other hand, as shown in Fig. 7(B), if only some battery cells 21 have been determined as degraded cells, the process proceeds to steps S15 and S16.

[0072] In this embodiment, it is determined whether the deterioration in insulation of the deteriorated cells is due to foreign matter or refrigerant. In the case of a deterioration due to foreign matter, since it is rare for foreign matter 50 to be mixed into the liquid refrigerant 31, only some of the battery cells 21 among the multiple battery cells 21 immersed in the liquid refrigerant 31 become deteriorated cells. On the other hand, since a deterioration due to refrigerant occurs due to a decrease in the liquid refrigerant 31, all of the battery cells 21 immersed in the liquid refrigerant 31 may become deteriorated cells. Therefore, in this embodiment, when all of the battery cells 21 become deteriorated cells, it is determined that the deterioration is due to refrigerant.

[0073] According to the present embodiment described above in detail, it is possible to determine the deterioration of insulation between the electrode terminals 22 of the battery cells 21 due to a decrease in the liquid refrigerant 31 according to the state of the deterioration of the insulation. Specifically, it is determined whether the cause of the deterioration of the insulation due to the liquid refrigerant 31 is a foreign matter-induced deterioration or a refrigerant-induced deterioration based on the number of deteriorated cells. This makes it possible to properly grasp the state of the deterioration of the insulation that has occurred in the storage battery 20, such as a decrease in the liquid refrigerant 31.

[0074] <Other embodiments> Each of the above embodiments may be modified as follows.

[0075] In the above embodiment, an example was shown in which a warning is given when the cause of the insulation deterioration of the deteriorated cell is a foreign object-induced deterioration, and the use of the storage battery 20 is prohibited when the cause is a refrigerant-induced deterioration, but this is not limited to the above. For example, when the cause of the insulation deterioration of the deteriorated cell is a foreign object-induced deterioration, the use of the storage battery 20 may be prohibited in order to prevent adjacent battery cells 21 from being short-circuited by the foreign object 50. Also, when it is determined in the second embodiment that the deterioration is due to a refrigerant-induced deterioration, the amount of liquid refrigerant 31 in the battery housing 24 may be increased and a warning may be given to the driver.

[0076] In the above embodiment, the determination process may be performed only when the insulation deterioration of the battery cell 21 can be properly calculated. For example, when the temperature of the battery cell 21 is low or when the SOC of the battery cell 21 is relatively small, the complex impedance Zm in the normal state where no insulation deterioration occurs is large, so that the insulation deterioration of the battery cell 21 may not be properly determined. Therefore, the determination process may be performed when the complex impedance Zm in the normal state becomes smaller than a reference value.

[0077] In the above embodiment, the liquid-cooled storage battery 20 in which the battery cells 21 are immersed in the liquid refrigerant 31 for cooling has been described, but the storage battery 20 may be an air-cooled storage battery. In this case, when a conductive foreign object 50 generated inside the battery casing 24 or the blower unit that blows air into the battery casing 24 adheres between the electrode terminals 22 of one battery cell 21 due to air circulation, the insulation between the electrode terminals 22 of the battery cells 21 decreases. In this case, the control device 43 can be used to determine the decrease in insulation of the battery cell 21 to which the foreign object 50 adheres, and it can be appropriately determined whether or not to energize the storage battery 20.

[0078] The battery monitoring device and the method described herein may be realized by a special-purpose computer provided by configuring a processor and a memory programmed to execute one or more functions embodied in a computer program. Alternatively, the battery monitoring device and the method described herein may be realized by a special-purpose computer provided by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, the battery monitoring device and the method described herein may be realized by one or more special-purpose computers configured by a combination of a processor and a memory programmed to execute one or more functions and a processor configured with one or more hardware logic circuits. Furthermore, the computer program may be stored in a computer-readable non-transitory tangible recording medium as instructions executed by the computer. [Explanation of symbols]

[0079] 20...storage battery, 21...battery cell, 43...control device.

Claims

1. A battery monitoring device (43) for monitoring a state of a storage battery (20) having a plurality of battery cells (21) connected to each other, comprising: Each of the battery cells is immersed in an insulating liquid coolant (31) to be cooled; an impedance calculation unit that acquires, for each of the battery cells, a response signal of the battery cell in response to the AC signal while applying a predetermined AC signal to the battery cell, and calculates an impedance of the battery cell based on the response signal; an insulation determination unit that determines a deterioration in insulation between the electrode terminals of each of the battery cells based on the impedance, The insulation determination unit of the battery monitoring device determines whether the insulation degradation is a foreign-matter-induced degradation due to the introduction of conductive foreign matter into the liquid refrigerant, or a refrigerant-induced degradation due to deterioration or reduction of the liquid refrigerant, based on the number of degraded cells, which are battery cells whose impedance has dropped below a predetermined threshold.

2. The plurality of battery cells are arranged in a predetermined arrangement direction, 2. The battery monitoring device of claim 1, wherein when a battery cell whose impedance has dropped below a predetermined threshold is determined to be a degraded cell, the insulation determination unit determines, based on a position of the degraded cell in the arrangement direction, whether the degradation in insulation is due to foreign matter caused by the introduction of a conductive foreign matter into the liquid refrigerant, or due to refrigerant deterioration or reduction in the liquid refrigerant.

3. A battery monitoring device (43) for monitoring a state of a storage battery (20) having a plurality of battery cells (21) connected to each other, comprising: Each of the battery cells is immersed in an insulating liquid coolant (31) to be cooled; The plurality of battery cells are arranged in a predetermined arrangement direction, an impedance calculation unit that acquires, for each of the battery cells, a response signal of the battery cell in response to the AC signal while applying a predetermined AC signal to the battery cell, and calculates an impedance of the battery cell based on the response signal; an insulation determination unit that determines a deterioration in insulation between the electrode terminals of each of the battery cells based on the impedance, When a battery cell whose impedance has dropped below a predetermined threshold is determined to be a degraded cell, the insulation determination unit determines, based on the position of the degraded cell in the arrangement direction, whether the degradation in insulation is due to foreign matter caused by the introduction of conductive foreign matter into the liquid refrigerant, or due to refrigerant-related degradation caused by deterioration or reduction of the liquid refrigerant.

4. The battery monitoring device according to any one of claims 1 to 3, further comprising a change unit that changes the manner in which the storage battery is subsequently used based on the determination result of whether the deterioration is due to a foreign object or due to the refrigerant.

5. A program for monitoring a state of a storage battery (20) having a plurality of battery cells (21) connected to each other, comprising: Each of the battery cells is immersed in an insulating liquid coolant (31) to be cooled; A computer (43) an impedance calculation process for applying a predetermined AC signal to each of the battery cells, acquiring a response signal of the battery cell in response to the AC signal, and calculating an impedance of the battery cell based on the response signal; an insulation determination process for determining a deterioration in insulation between the electrode terminals of each of the battery cells based on the impedance; In the insulation determination process, the program determines whether the insulation degradation is a foreign-matter-induced degradation due to the introduction of conductive foreign matter into the liquid refrigerant, or a refrigerant-induced degradation due to deterioration or reduction of the liquid refrigerant, based on the number of degraded cells, which are battery cells whose impedance has dropped below a predetermined threshold.

6. A program for monitoring a state of a storage battery (20) having a plurality of battery cells (21) connected to each other, comprising: Each of the battery cells is immersed in an insulating liquid coolant (31) to be cooled; The plurality of battery cells are arranged in a predetermined arrangement direction, A computer (43) an impedance calculation process for applying a predetermined AC signal to each of the battery cells, acquiring a response signal of the battery cell in response to the AC signal, and calculating an impedance of the battery cell based on the response signal; an insulation determination process for determining a deterioration in insulation between the electrode terminals of each of the battery cells based on the impedance; In the insulation determination process, when a battery cell whose impedance has dropped below a predetermined threshold is determined to be a degraded cell, the program determines, based on the position of the degraded cell in the arrangement direction, whether the degradation in insulation is due to foreign matter caused by the introduction of conductive foreign matter into the liquid refrigerant, or due to refrigerant-related degradation caused by deterioration or reduction of the liquid refrigerant.

7. A battery monitoring method for monitoring a state of a storage battery (20) having a plurality of battery cells (21) connected to each other, comprising: Each of the battery cells is immersed in an insulating liquid coolant (31) to be cooled; an impedance calculation step of acquiring, for each of the battery cells, a response signal of the battery cell in response to the AC signal while applying a predetermined AC signal to the battery cell, and calculating an impedance of the battery cell based on the response signal; an insulation determination step of determining a deterioration in insulation between the electrode terminals of each of the battery cells based on the impedance; A battery monitoring method in which, in the insulation determination step, it is determined whether the insulation degradation is a foreign-matter-induced degradation due to the introduction of conductive foreign matter into the liquid refrigerant, or a refrigerant-induced degradation due to deterioration or reduction of the liquid refrigerant, based on the number of degraded cells, which are battery cells whose impedance has dropped below a predetermined threshold.

8. A battery monitoring method for monitoring a state of a storage battery (20) having a plurality of battery cells (21) connected to each other, comprising: Each of the battery cells is immersed in an insulating liquid coolant (31) to be cooled; The plurality of battery cells are arranged in a predetermined arrangement direction, an impedance calculation step of acquiring, for each of the battery cells, a response signal of the battery cell in response to the AC signal while applying a predetermined AC signal to the battery cell, and calculating an impedance of the battery cell based on the response signal; an insulation determination step of determining a deterioration in insulation between the electrode terminals of each of the battery cells based on the impedance; In the insulation determination step, when a battery cell whose impedance has dropped below a predetermined threshold is determined to be a degraded cell, the battery monitoring method determines whether the degradation in insulation is due to foreign matter caused by the introduction of conductive foreign matter into the liquid refrigerant, or due to refrigerant-related degradation caused by deterioration or reduction of the liquid refrigerant, based on the position of the degraded cell in the arrangement direction.

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