Power control device

Abstract

To provide a power control device that is able to prevent a vehicle from becoming unable to start.SOLUTION: A power control device includes: a switching unit configured to switch connection between a plurality of battery modules and a traveling motor and an auxiliary device of a vehicle; a detection unit configured to detect a state of the battery module; and a processor configured to select the battery module that supplies electric power to the auxiliary device according to the state of the battery module and to switch the connection of the switching unit such that the selected battery module is connected to the auxiliary device.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a power control device. [Background technology]

[0002] Patent document 1 describes a vehicle that has multiple battery modules that supply power to a driving motor, and selects from among the multiple battery modules a battery module that supplies power to low-voltage equipment (auxiliary machinery) based on the calculation results of the health status. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-155131 Summary of the Invention [Problem to be solved by the invention]

[0004] The power required to start a vehicle is supplied from a battery module connected to the auxiliary equipment. When the vehicle is parked, a dark current flows from the battery module to the auxiliary equipment. As a result, if the dark current reduces the power of the battery module connected to the auxiliary equipment, the vehicle may not be able to start.

[0005] The present disclosure has been made in view of the above, and aims to provide an electric power control device that can prevent a vehicle from becoming unable to start. [Means for solving the problem]

[0006] The power control device of the present disclosure includes a switching unit that switches the connection between multiple battery modules and the vehicle's driving motor and auxiliary equipment, a detection unit that detects the state of the battery modules, and a processor configured to select the battery module that supplies power to the auxiliary equipment according to the state of the battery modules and switch the connection of the switching unit so that the selected battery module is connected to the auxiliary equipment. [Effects of the Invention]

[0007] According to the present disclosure, it is possible to realize a power control device that can prevent a vehicle from becoming unable to start. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating a schematic configuration of a vehicle including a power control device according to the first embodiment. [Figure 2] FIG. 2 is a diagram showing the change over time in the voltage of the battery module. [Figure 3] FIG. 3 is a diagram showing a state in which the battery module BM2 is connected to the auxiliary equipment. [Figure 4] FIG. 4 is a flowchart showing the processing in the power control device. [Figure 5] FIG. 5 is a diagram showing the change over time in the voltage of the battery module. [Figure 6] FIG. 6 is a flowchart showing the processing in the power control device. [Figure 7] FIG. 7 is a diagram illustrating a schematic configuration of a vehicle including a power control device according to the fourth embodiment. [Figure 8] FIG. 8 is a diagram showing the change over time in the voltage of the battery module. [Figure 9] FIG. 9 is a flowchart showing the processing in the power control device. [Figure 10] FIG. 10 is a diagram showing the change over time in the SOH of the battery module. [Figure 11]FIG. 11 is a diagram showing a schematic configuration of a vehicle including a power control device according to the sixth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] A power control device according to an embodiment of the present disclosure will be described with reference to the drawings. Note that the components in the following embodiments include those that are easily replaceable by those skilled in the art, or those that are substantially the same.

[0010] (Embodiment 1) [Vehicle configuration] 1 is a diagram showing a schematic configuration of a vehicle including a power control device according to embodiment 1. Vehicle 1 includes an electric circuit 2, a detection unit 3, a BCU (Battery Control Unit) 4, a traction motor 5, accessories 6, and battery modules BM1 to BM4. Electric circuit 2 includes a switching unit 7, a relay 8, and a DC-DC converter 9.

[0011] The power control device of the vehicle 1 includes a detection unit 3, a BCU 4, and a switching unit 7, and controls the supply of power from the battery modules BM1 to BM4 to the traction motor 5 and the accessories 6.

[0012] The detector 3 detects the states of the battery modules BM1 to BM4, such as the voltage, current, and temperature of the battery modules BM1 to BM4, and estimates the battery states such as the battery capacity, internal resistance, SOC (State Of Charge), and SOH (State Of Health).

[0013] The BCU4 controls the electric circuit 2. The BCU4 is configured using a memory and a processor having hardware such as a CPU (Central Processing Unit). The BCU4 selects a battery module that supplies power to the auxiliary device 6 according to the states of the battery modules BM1 to BM4, and switches the connection of the switching unit 7 so that the selected battery module is connected to the auxiliary device 6. Specifically, the BCU4 selects a battery module whose battery state is equal to or greater than the power requirement of the auxiliary device 6 as the battery module that supplies power to the auxiliary device 6. The power requirement of the auxiliary device 6 is, for example, starting power for the vehicle 1, but may also be starting power for the DC-DC converter 9, power for operating a sliding door, etc.

[0014] The traction motor 5 drives the wheels of the vehicle 1 to rotate, thereby causing the vehicle 1 to travel.

[0015] The accessories 6 include a minimum configuration for starting the engine and auxiliary devices such as a security system.

[0016] The switching unit 7 includes switches SW11 to SW34, and switches the connection between the battery modules BM1 to BM4 and the traction motor 5 and accessories 6 of the vehicle 1. The switches SW11 to SW34 include terminals t111 to t343, respectively.

[0017] According to the switching unit 7 shown in FIG. 1, the terminals t111 and t112 of the switch SW11 are connected, the terminals t211 and t212 of the switch SW21 are connected, the terminals t121 and t123 of the switch SW12 are connected, the terminals t221 and t223 of the switch SW22 are connected, the terminals t131 and t133 of the switch SW13 are connected, the terminals t231 and t233 of the switch SW23 are connected, and the terminals t131 and t133 of the switch SW14 are connected. Terminals t141 and t143 of switch SW4 are connected, terminals t241 and t243 of switch SW24 are connected, terminals t311 and t313 of switch SW31 are connected, terminals t321 and t322 of switch SW32 are connected, and terminals t341 and t342 of switch SW34 are connected, and power is supplied from battery module BM1 to auxiliary equipment 6, and power is supplied from battery modules BM2 to BM4 to traction motor 5.

[0018] The relay 8 supplies power from the battery modules BM1 to BM4 to the traction motor 5 in an IG (ignition)-ON state, and cuts off the connection between the battery modules BM1 to BM4 and the traction motor 5 in an IG-OFF state.

[0019] The DC-DC converter 9 has a function of stepping down the voltage of the battery module connected to the driving motor 5 and supplying the voltage to the auxiliary device 6 .

[0020] [Processing of power control device] Next, the processing of the power control device will be described. First, the BCU 4 determines whether the status of the vehicle 1 is parked. Then, if the BCU 4 determines that the status of the vehicle 1 is in the IG-ON state and not parked, the BCU 4 switches the connection of the switching unit 7 so that all battery modules BM1 to BM4 are connected to the traction motor 5, and the vehicle 1 becomes ready to run.

[0021] On the other hand, if BCU4 determines that the status of vehicle 1 is in the IG-OFF state and that the vehicle is parked, BCU4 selects the battery module whose voltage is at a value that allows vehicle 1 to start as the battery module to supply power to auxiliary equipment 6.

[0022] 1, the BCU4 may select, for example, battery module BM1 as the battery module that supplies power to the auxiliary device 6, and may connect battery module BM1 to the auxiliary device 6 while connecting battery modules BM2 to BM4 to the traction motor 5 or the electric circuit 2. As a result, in the IG-ON state, the vehicle can travel while power is supplied from battery module BM1 to the auxiliary device 6, and in the IG-OFF state, power can be supplied from battery module BM1 to the auxiliary device 6 while power can be supplied from battery modules BM2 to BM4 to the electric circuit 2.

[0023] 2 is a diagram showing the change in the voltage of the battery module over time. When the battery module BM1 is connected to the auxiliary machine 6, a dark current flows from the battery module BM1 to the auxiliary machine 6, and the voltage of the battery module BM1 decreases over time as shown in days 0 to D1 in FIG.

[0024] Then, when the BCU4 determines that the voltage of the battery module BM1 has fallen below the limit voltage at which the vehicle 1 can be started, the BCU4 selects, for example, the battery module BM2 as the battery module that supplies power to the auxiliary equipment 6, and connects the battery module BM2 to the auxiliary equipment 6. Furthermore, while changing the battery module connected to the auxiliary equipment 6, the battery module connected to the traction motor 5 may be switched from the battery modules BM2 to BM4 to the battery modules BM1, BM3, and BM4.

[0025] Fig. 3 is a diagram showing a state in which the battery module BM2 is connected to the auxiliaries. According to the switching unit 7 shown in Fig. 3, the terminals t111 and t113 of the switch SW11 are connected, the terminals t211 and t213 of the switch SW21 are connected, the terminals t121 and t122 ​​of the switch SW12 are connected, the terminals t221 and t222 of the switch SW22 are connected, and the terminals t321 and t323 of the switch SW32 are connected, so that power is supplied from the battery module BM2 to the auxiliaries 6 and from the battery modules BM1, BM3, and BM4 to the traction motor 5.

[0026] Thereafter, when the battery module BM2 is connected to the auxiliary device 6, a dark current flows from the battery module BM2 to the auxiliary device 6, and the voltage of the battery module BM2 decreases over time as shown in days D1 to D2 in FIG.

[0027] Then, when BCU4 determines that the voltage (or SOC) of battery module BM2 is below a threshold value (e.g., the limit voltage at which vehicle 1 can be started), BCU4 selects, for example, battery module BM3 as the battery module that supplies power to auxiliary equipment 6, connects battery module BM3 to auxiliary equipment 6, and connects battery modules BM1, BM2, and BM4 to the traction motor 5.

[0028] According to the first embodiment described above, the BCU 4 selects a battery module whose battery state is at a value that allows starting of the vehicle 1 as the battery module that supplies power to the auxiliary equipment 6, thereby preventing a voltage drop in the battery module connected to the auxiliary equipment 6 while the vehicle is parked, which would prevent the vehicle 1 from being unable to start. In particular, in vehicles such as HEVs (Hybrid Electric Vehicles), the battery capacity of the battery module is very small (for example, 5 Ah or less), but even in such vehicles, it is possible to prevent the vehicle 1 from being unable to start.

[0029] (Embodiment 2) Fig. 4 is a flowchart showing the processing in the power control device. As shown in Fig. 4, the BCU 4 determines whether the status of the vehicle 1 is parked or not (step S1).

[0030] If BCU4 determines that the status of vehicle 1 is not parked (step S1: No), BCU4 switches the connection of switching unit 7 so that all battery modules BM1 to BM4 are connected to the traction motor 5 (step S2), and ends the series of processes.

[0031] On the other hand, if the BCU4 determines that the status of the vehicle 1 is parked (step S1: Yes), the BCU4 selects a battery module to be used as the auxiliary equipment 6 based on the SOC detected by the detection unit 3, and switches the connection of the switching unit 7 so that the battery module is connected to the auxiliary equipment 6 (step S3).

[0032] 5 is a diagram showing the change in the voltage of the battery module over time. When the battery module BM1 is connected to the auxiliary machine 6, a dark current flows from the battery module BM1 to the auxiliary machine 6, and therefore the voltage (or SOC) of the battery module BM1 decreases over time as shown in days 0 to D11 in FIG.

[0033] Next, the BCU4 determines whether the difference in SOC among the battery modules BM1 to BM4 is equal to or greater than a threshold value (step S4).

[0034] If the BCU4 determines that the difference in SOC between the battery modules BM1 to BM4 is equal to or greater than the threshold value (step S4: Yes), the BCU4 changes the battery module used as the auxiliary device 6 and switches the connection of the switching unit 7 so that the changed battery module is connected to the auxiliary device 6 (step S5). In the example of FIG. 5, on the day D11, the difference in SOC between battery module BM1 and battery modules BM2 to BM4 is equal to or greater than the threshold value, so battery module BM2 is connected to the auxiliary device 6. Similarly, on the day D12, the difference in SOC between battery module BM2 and battery modules BM3 and BM4 is equal to or greater than the threshold value, so battery module BM3 is connected to the auxiliary device 6. Similarly, on the day D13, the difference in SOC between battery module BM3 and battery module BM4 is equal to or greater than the threshold value, so battery module BM4 is connected to the auxiliary device 6.

[0035] On the other hand, if BCU4 determines that the difference in SOC between each battery module BM1 to BM4 is smaller than the threshold value (step S4: No), BCU4 determines whether the vehicle 1 cannot be started using the battery module currently connected to the auxiliary equipment 6 (step S6).

[0036] If the BCU 4 determines that the vehicle 1 cannot be started using the battery module currently connected to the auxiliary device 6 (step S6: Yes), the BCU 4 changes the battery module to be used as the auxiliary device 6 and switches the connection of the switching unit 7 so that the new battery module is connected to the auxiliary device 6 (step S5). As a result, similar to the first embodiment, if the voltage of the battery module connected to the auxiliary device 6 falls below the limit voltage at which the vehicle 1 can be started, another battery module is connected to the auxiliary device 6.

[0037] On the other hand, if the BCU 4 determines that the vehicle 1 can be started by the battery module currently connected to the auxiliary device 6 (step S6: No), the process returns to step S1.

[0038] According to the above-described embodiment 2, the BCU4 selects the battery module whose battery state is at a value that allows the vehicle 1 to be started as the battery module that supplies power to the auxiliary equipment 6, thereby preventing the voltage of the battery module connected to the auxiliary equipment 6 from dropping while the vehicle is parked, which would prevent the vehicle 1 from being unable to start.

[0039] Furthermore, according to the second embodiment, the BCU4 uses the power of the battery modules BM1 to BM4 so that there is no difference in SOC between the battery modules BM1 to BM4 that is equal to or greater than a threshold value. As a result, it is possible to avoid a situation in which one of the battery modules BM1 to BM4 runs out of power first, making it impossible to travel, and thus making it impossible to fully utilize the battery performance.

[0040] (Embodiment 3) Fig. 6 is a flowchart showing the processing in the power control device. As shown in Fig. 6, the BCU 4 determines whether or not the battery module connected to the auxiliary device 6 satisfies the auxiliary device BM switching condition (step S11). If the BCU 4 determines that the battery module does not satisfy the auxiliary device BM switching condition (step S11: No), the processing of step S11 is repeatedly executed. The auxiliary device BM switching condition is determined, for example, by whether or not the SOH of the battery module is equal to or greater than a threshold value.

[0041] On the other hand, if the BCU4 determines that the battery module satisfies the auxiliary BM switching condition (step S11: Yes), the BCU4 determines whether the battery module connected to the auxiliary 6 can be switched to a battery module for driving (step S12).

[0042] If the BCU 4 determines that switching to a battery module for driving is possible (step S12: Yes), the BCU 4 determines a battery module as a candidate for switching from the battery modules that can be switched (step S13). For example, the BCU 4 determines that switching is possible if there is a battery module for driving whose SOH is equal to or greater than a threshold, and determines a battery module as a candidate for switching from the battery modules whose SOH is equal to or greater than the threshold.

[0043] Next, the BCU 4 determines whether the battery voltage of the battery module that is a candidate for switching is within the operating voltage range of the auxiliary system included in the auxiliary 6 (step S14). If the BCU 4 determines that the battery voltage of the battery module that is a candidate for switching is not within the operating voltage range of the auxiliary system (step S14: No), the process returns to step S13, and the battery module that is a candidate for switching is changed.

[0044] On the other hand, if BCU4 determines that the battery voltage of the battery module that is a candidate for switching is within the operating voltage range of the auxiliary system (step S14: Yes), BCU4 switches the battery module for the auxiliary to the battery module that is a candidate for switching (step S15) and terminates the series of processes.

[0045] Also, if the BCU 4 determines in step S12 that switching to the battery module for driving is not possible (step S12: No), the series of processes also ends.

[0046] According to the third embodiment described above, when the SOC of the battery module connected to the auxiliary equipment 6 drops, the battery module for driving, whose battery voltage is within the operating voltage range of the auxiliary equipment system, can be replaced with a battery module for the auxiliary equipment. The timing of this switching can be set arbitrarily, so when switching is performed while the vehicle 1 is traveling, it is preferable to switch when the voltage levels become the same in order to prevent the generation of an inrush current due to a pressure difference at the time of switching.

[0047] When a ternary battery module is used, the number of series-connected cells required to fall within the auxiliary operation voltage range varies depending on the SOC state. As a result, when attempting to switch battery modules in the IG-OFF state, a mechanism is required to determine whether the number of series-connected cells should be set to 3 or 4 depending on the SOC state after driving. In contrast, in the third embodiment, the battery module is switched according to the SOC range, not the number of series-connected cells, so no mechanism for switching the number of series-connected cells is required.

[0048] (Embodiment 4) Fig. 7 is a diagram showing a schematic configuration of a vehicle including a power control device according to embodiment 4. As shown in Fig. 7, a vehicle 1A includes a DC-DC converter 10A.

[0049] The DC-DC converter 10A steps down the power from the battery modules BM2 to BM4 and supplies the power to the battery module BM1.

[0050] 8 is a diagram showing the change in the voltage of the battery module over time. When the battery module BM1 is connected to the auxiliary machine 6, a dark current flows from the battery module BM1 to the auxiliary machine 6, and the voltage of the battery module BM1 decreases over time as shown in days 0 to D21 in FIG.

[0051] Then, the BCU4 determines whether the difference in voltage (or SOC) among the battery modules BM1-BM4 is equal to or greater than a threshold. If the BCU4 determines that the difference in voltage among the battery modules BM1-BM4 is equal to or greater than the threshold, the BCU4 steps down the power from the battery modules BM2-BM4 using the DC-DC converter 10A and supplies the power to the battery module BM1. As a result, the voltage of the battery module BM1 increases over time, as shown by days D21-D22 in FIG. 8.

[0052] Furthermore, the BCU4 determines whether the difference in voltage (or SOC) among the battery modules BM1 to BM4 has become approximately zero. If the BCU4 determines that the difference in voltage among the battery modules BM1 to BM4 has become approximately zero, the BCU4 stops the supply of power from the battery modules BM2 to BM4. As a result, the voltage of the battery module BM1 decreases over time, as shown by days D22 to D23 in FIG. 8.

[0053] According to the fourth embodiment described above, the BCU4 supplies power from the battery modules BM2 to BM4 to the battery module BM1 so that a voltage difference equal to or greater than a threshold value does not occur among the battery modules BM1 to BM4. As a result, it is possible to prevent a voltage drop in the battery module BM1 connected to the auxiliary equipment 6 while the vehicle 1 is parked, which would cause the vehicle 1 to be unable to start. Furthermore, it is possible to avoid a situation in which the battery module BM1 runs out of power first, preventing the vehicle from running, and the battery performance being underutilized.

[0054] When the voltage (or SOC) of the battery module BM1 connected to the auxiliary device 6 becomes equal to or lower than a threshold, the BCU4 may step down the power from the battery modules BM2 to BM4 using the DC-DC converter 10A and supply the power to the battery module BM1.

[0055] (Embodiment 5) Fig. 9 is a flowchart showing the processing in the power control device. As shown in Fig. 9, steps S1 and S2 are the same as those in the second embodiment, and therefore a description thereof will be omitted.

[0056] In step S1, if the BCU4 determines that the status of the vehicle 1 is parked (step S1: Yes), the BCU4 selects a battery module to be used as the auxiliary equipment 6 according to the SOH detected by the detection unit 3, and switches the connection of the switching unit 7 so that the battery module is connected to the auxiliary equipment 6 (step S21).

[0057] 10 is a diagram showing changes in the SOH of the battery module over time. When the battery module BM1 is connected to the auxiliary machine 6, the battery module BM1 deteriorates, and the SOH of the battery module BM1 decreases over time, as shown by years 0 to Y1 in FIG.

[0058] Next, the BCU4 determines whether the difference in SOH among the battery modules BM1 to BM4 is equal to or greater than a threshold value (step S22).

[0059] When the BCU4 determines that the difference in SOH among the battery modules BM1 to BM4 is equal to or greater than the threshold value (step S22: Yes), the BCU4 changes the battery module used as the auxiliary device 6 and switches the connection of the switching unit 7 so that the changed battery module is connected to the auxiliary device 6 (step S5). In the example of FIG. 10, when the number of years reaches Y1, the difference in SOH between battery module BM1 and battery modules BM2 to BM4 is equal to or greater than the threshold value, so battery module BM2 is connected to the auxiliary device 6. Similarly, when the number of years reaches Y2, the difference in SOH between battery module BM2 and battery modules BM3 and BM4 is equal to or greater than the threshold value, so battery module BM3 is connected to the auxiliary device 6. Similarly, when the number of years reaches Y3, the difference in SOH between battery module BM3 and battery module BM4 is equal to or greater than the threshold value, so battery module BM4 is connected to the auxiliary device 6.

[0060] On the other hand, if BCU4 determines that the difference in SOH between each battery module BM1 to BM4 is smaller than the threshold value (step S22: No), BCU4 determines whether the vehicle 1 cannot be started using the battery module currently connected to the auxiliary equipment 6 (step S6).The processing thereafter is the same as in embodiment 2, so explanation is omitted.

[0061] According to the above-described embodiment 5, the BCU4 selects the battery module whose battery state is at a value that allows the vehicle 1 to be started as the battery module that supplies power to the auxiliary equipment 6, thereby preventing the voltage of the battery module connected to the auxiliary equipment 6 from dropping while the vehicle is parked, which would prevent the vehicle 1 from being able to start.

[0062] Furthermore, according to the fifth embodiment, the BCU 4 uses the battery modules BM1 to BM4 so that there is no difference in SOH between the battery modules BM1 to BM4 that is equal to or greater than a threshold value. As a result, it is possible to avoid a situation in which one of the battery modules BM1 to BM4 deteriorates first and the battery performance is not fully utilized.

[0063] (Embodiment 6) Fig. 11 is a diagram showing a schematic configuration of a vehicle including a power control device according to embodiment 6. As shown in Fig. 11, a switching unit 7B of vehicle 1B includes switches SW11 to SW22, SW31, and SW33, and switches the connection between battery modules BM1 and BM2 and the traction motor 5 and accessories 6 of vehicle 1. On the other hand, battery modules BM3 and BM4 are connected to the traction motor 5 of vehicle 1.

[0064] According to the embodiment 6 described above, it is possible to minimize the number of switches in the switching unit 7B while preventing the voltage of the battery module connected to the auxiliary equipment 6 from dropping while parked, preventing the vehicle 1B from being unable to start.

[0065] Further advantages and modifications will readily occur to those skilled in the art. Thus, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described above. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents. [Explanation of symbols]

[0066] Cars 1, 1A, and 1B 2 Electrical Circuits 3. Detection unit 4 BCU 5. Traction motor 6 Auxiliary equipment 7, 7B switching section 8 Relay 9, 10A DC-DC converter BM1 to BM4 battery modules SW11 to SW34 switches t111~t343 terminal

Claims

1. a switching unit that switches connections between the plurality of battery modules and the vehicle's traction motor and auxiliary machines; a detection unit that detects a state of the battery module; a processor configured to select the battery module that supplies power to the auxiliary equipment according to a state of the battery module, and to switch the connection of the switching unit so that the selected battery module is connected to the auxiliary equipment; A power control device comprising:

2. The power control device according to claim 1 , wherein the processor selects the battery module whose battery state is equal to or greater than the power requirement of the auxiliary device as the battery module that supplies power to the auxiliary device.

3. The power control device according to claim 1 , wherein the processor selects the battery module whose voltage is within an operating voltage range of an auxiliary system included in the auxiliary as the battery module that supplies power to the auxiliary.

4. The processor: monitor a first voltage or a first SOC, which is the voltage or the SOC of the battery module that supplies power to the auxiliary equipment, and a second voltage or a second SOC, which is the voltage or the SOC of any one of the battery modules other than the battery module that supplies power to the auxiliary equipment; 4. The power control device according to claim 2, wherein the connection of the switching unit is switched when the difference between the first voltage and the second voltage or the difference between the first SOC and the second SOC becomes equal to or greater than a threshold, or when the first voltage or the first SOC becomes equal to or less than a threshold.

5. 3. The power control device according to claim 2, wherein the power requirement of the auxiliary device is a starting power for the vehicle.

6. The power control device according to claim 1 , wherein the processor selects the battery module with a high state of health as the battery module that supplies power to the auxiliary equipment.

7. a DC-DC converter that reduces the voltage of the power from the battery module; The processor: monitor a first voltage or a first SOC, which is the voltage or the SOC of the battery module that supplies power to the auxiliary equipment, and a second voltage or a second SOC, which is the voltage or the SOC of any one of the battery modules other than the battery module that supplies power to the auxiliary equipment; 2. The power control device according to claim 1, wherein when the difference between the first voltage and the second voltage or the difference between the first SOC and the second SOC becomes equal to or greater than a threshold, or when the first voltage or the first SOC becomes equal to or less than a threshold, power from the battery modules other than the battery module that supplies power to the auxiliary equipment is stepped down by the DC-DC converter and supplied to the battery module that supplies power to the auxiliary equipment.

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