Power supply system

Abstract

To provide a technique that can protect a secondary battery from overcharge and continuously supply power to a load.SOLUTION: A power supply system may comprise: a power supply; a load that is supplied with power from the power supply; a first secondary battery that is connected in parallel with the load and supplied with power from the power supply; a second secondary battery that is connected in parallel with the load and the first secondary battery and supplied with power from the power supply; and a control unit. The load may be connected with the power supply through a main switch, the first secondary battery may be connected with the power supply through the main switch and a first switch connected in series with the main switch, and the second secondary battery may be connected with the power supply through the main switch and a second switch connected in series with the main switch. The control unit may control the opening and closing operations of the main switch, first switch, and second switch.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The technology disclosed in this specification relates to a power supply system. [Background technology]

[0002] Patent Document 1 describes, for example, disconnecting a battery from a power supply line of a DC-DC converter in order to prevent overcharging of a fully charged battery. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7073865 Summary of the Invention [Problem to be solved by the invention]

[0004] Even if the technology described in Patent Document 1 prevents overcharging, it is possible that power cannot be supplied to important loads by disconnecting the battery from the power supply line. This specification provides a technology that can protect a secondary battery from overcharging and continue to supply power to a load. [Means for solving the problem]

[0005] In a first aspect of the present technology, a power supply system may include a power supply, a load to which power from the power supply is supplied, a first secondary battery connected in parallel with the load and to which power from the power supply is supplied, a second secondary battery connected in parallel with the load and the first secondary battery and to which power from the power supply is supplied, and a control device. The load may be connected to the power supply via a main switch, the first secondary battery may be connected to the power supply via the main switch and a first switch connected in series with the main switch, and the second secondary battery may be connected to the power supply via the main switch and a second switch connected in series with the main switch. The control device may control opening and closing operations of the main switch, the first switch, and the second switch.

[0006] According to this configuration, by controlling the opening and closing operations of the main switch, the first switch, and the second switch, it is possible to protect the second secondary battery from overcharging while continuing to supply power to the load. For example, if the second secondary battery is overcharged, the main switch is turned off to prohibit charging the second secondary battery from the power source. This makes it possible to protect the second secondary battery from overcharging. In this case, for example, the second switch is turned on to allow discharging from the second secondary battery. This makes it possible to supply power from the second secondary battery to the load even if power is not supplied from the power source to the load.

[0007] In a second aspect, in the first aspect above, the power supply system may further include a converter that converts the voltage of the power supply and supplies power to the load, the first secondary battery, and the second secondary battery, and a capacitor connected to the output side of the converter.

[0008] According to this configuration, it is possible to suppress abrupt changes in the voltages applied to the load, the first secondary battery, and the second secondary battery.

[0009] In a third aspect, in the first or second aspect above, the control device may prohibit charging of the second secondary battery from the power source by turning off the main switch when the second secondary battery is overcharged.

[0010] According to this configuration, the second secondary battery is not charged, so that the second secondary battery can be protected from overcharging.

[0011] In a fourth aspect, in the third aspect, the control device may allow discharging from the second secondary battery by turning on the second switch when the second secondary battery is overcharged.

[0012] According to this configuration, the amount of charge stored in the second secondary battery can be reduced, so that the second secondary battery can be protected from overcharging.

[0013] In a fifth aspect, in the fourth aspect above, the control device may allow charging from the second secondary battery to the first secondary battery by turning on the first switch when the second secondary battery is overcharged and the voltage of the second secondary battery is higher than the voltage of the first secondary battery.

[0014] According to this configuration, the amount of charge stored in the second secondary battery can be reduced, so that the second secondary battery can be protected from overcharging.

[0015] In a sixth aspect, in the fourth aspect above, the control device may prohibit charging from the first secondary battery to the second secondary battery by turning off the first switch when the second secondary battery is overcharged and the voltage of the first secondary battery is higher than the voltage of the second secondary battery.

[0016] According to this configuration, the second secondary battery is not charged, so that the second secondary battery can be protected from overcharging.

[0017] In a seventh aspect, in any one of the first to sixth aspects above, when the second secondary battery is not overcharged, the voltage of the second secondary battery is higher than a predetermined voltage threshold, and the current flowing through the main switch is lower than a predetermined current threshold, the control device may allow power supply from the power source to the load by turning on the main switch, allow charging of the first secondary battery from the power source by turning on the first switch, and prohibit charging of the second secondary battery from the power source by turning off the second switch.

[0018] According to this configuration, the second secondary battery is not charged when the second secondary battery is approaching overcharge even if it is not overcharged, so that the second secondary battery can be protected from overcharge. At the same time, charging of the first secondary battery by the power source can be promoted while supplying power from the power source to the load. The power of the power source can be appropriately distributed to the load, the first secondary battery, and the second secondary battery according to the charging state of the second secondary battery.

[0019] In an eighth aspect, in any one of the first to seventh aspects, the second secondary battery may be a battery for an auxiliary device of the electric vehicle.

[0020] According to this configuration, the second secondary battery for the accessories of the electric vehicle can be protected from overcharging, and power can be continuously supplied to the accessories. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is a diagram illustrating a power supply system according to an embodiment of the present invention. [Diagram 2] 11 is a flowchart of a switch process according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] A power supply system of the embodiment will be described with reference to the drawings. As shown in Fig. 1, the power supply system 2 of the embodiment includes a power supply 10, a converter 12, a capacitor 14, an auxiliary device 20, a first secondary battery 21, and a second secondary battery 22. The power supply system 2 also includes a power switch 34, a main switch 30, a first switch 31, and a second switch 32. The power supply system 2 is mounted on, for example, an electrically powered vehicle 60 (for example, an electric vehicle or a hybrid vehicle).

[0023] The power supply 10 is, for example, a lithium ion battery or a nickel-metal hydride battery. The power supply 10 stores power for propelling the electric vehicle 60 on which the power supply system 2 is mounted. The power supply 10 can supply power to a motor (not shown) for propelling the electric vehicle 60. The power supply 10 can also supply power to the auxiliary equipment 20, the first secondary battery 21, and the second secondary battery 22 of the power supply system 2. The voltage V0 of the power supply 10 is higher than the voltages of the first secondary battery 21 and the second secondary battery 22 described below, and is, for example, 200V-1000V.

[0024] The converter 12 is a device that converts voltage. The converter 12 includes, for example, a plurality of switching elements, and can convert voltage by periodically switching on and off the plurality of switching elements. The input side of the converter 12 is connected to the power source 10. The output side of the converter 12 is connected to the auxiliary device 20, the first secondary battery 21, and the second secondary battery 22. The converter 12 converts the voltage of the power source 10 and supplies power to the auxiliary device 20, the first secondary battery 21, and the second secondary battery 22. The converter 12 is, for example, an insulated or non-insulated DC / DC converter. The converter 12 of the embodiment is a step-down converter that steps down the voltage input from the power source 10 and outputs it.

[0025] The input side of the converter 12 is connected to the power source 10 via a power switch 34. The power switch 34 is disposed between the converter 12 and the power source 10. The power switch 34 opens and closes an electric path between the converter 12 and the power source 10. When the power switch 34 is turned on (closed), power is supplied from the power source 10 to the converter 12. When the power switch 34 is turned off (open), the power supply from the power source 10 to the converter 12 is cut off.

[0026] A capacitor 14 is connected to the output side of the converter 12. The capacitor 14 is disposed between the converter 12 and the main switch 30. The capacitor 14 is connected in parallel with the auxiliary device 20, the first secondary battery 21, and the second secondary battery 22. The capacitor 14 accumulates electric charge on the output side of the converter 12 and releases the accumulated electric charge.

[0027] The auxiliary device 20 (an example of a load) is connected to the power source 10 via the converter 12. The auxiliary device 20 is a device that operates on power supplied from the power source 10 via the converter 12. The auxiliary device 20 is also connected to a first secondary battery 21 and a second secondary battery 22. The auxiliary device 20 may operate on power supplied from the first secondary battery 21 or the second secondary battery 22. The auxiliary device 20 is, for example, a light, an air conditioner, a power window, a starter motor, a pump, a fan, etc. of the electric vehicle 60 on which the power supply system 2 is mounted. The type of the auxiliary device 20 is not particularly limited.

[0028] The auxiliary device 20 is connected to the converter 12 via a main switch 30. The main switch 30 is disposed between the converter 12 and the auxiliary device 20. The main switch 30 opens and closes an electric path between the converter 12 and the auxiliary device 20. When the main switch 30 is turned on (closed) while the converter 12 is operating, power is supplied from the power source 10 to the auxiliary device 20. When the main switch 30 is turned off (open), the power supply from the power source 10 to the auxiliary device 20 is cut off.

[0029] The first secondary battery 21 is, for example, a lead storage battery. The first secondary battery 21 is connected to the power source 10 via the converter 12. The first secondary battery 21 is charged with power supplied from the power source 10 via the converter 12. The first secondary battery 21 can store power to be supplied to the auxiliary device 20. The first secondary battery 21 functions as a backup power source for the power source 10.

[0030] The first secondary battery 21 is connected in parallel with the auxiliary device 20. The first secondary battery 21 can supply backup power to the auxiliary device 20 when power is not supplied from the power source 10 to the auxiliary device 20. The voltage V1 of the first secondary battery 21 is lower than the voltage V0 of the power source 10, and is, for example, 10V-50V.

[0031] The first secondary battery 21 is connected to the converter 12 via a first switch 31 and a main switch 30. The first switch 31 is disposed between the first secondary battery 21 and the main switch 30. The first switch 31 is connected in series with the main switch 30. The first switch 31 is connected in parallel with the auxiliary device 20. The first switch 31 opens and closes an electric path between the first secondary battery 21 and the main switch 30. When the first switch 31 is turned on (closed), the first secondary battery 21 is charged or discharged. When the first switch 31 is turned off (open), charging or discharging of the first secondary battery 21 is not performed.

[0032] The main switch 30 is disposed between the converter 12 and the first switch 31. The main switch 30 opens and closes the electrical path between the converter 12 and the first switch 31. When the main switch 30 and the first switch 31 are turned on (closed) while the converter 12 is operating, power is supplied from the power source 10 to the first secondary battery 21. When the main switch 30 or the first switch 31 is turned off (open), the power supply from the power source 10 to the first secondary battery 21 is cut off.

[0033] The second secondary battery 22 is, for example, a lithium ion battery. The second secondary battery 22 is connected to the power source 10 via the converter 12. The second secondary battery 22 is charged with power supplied from the power source 10 via the converter 12. The second secondary battery 22 can store power to be supplied to the auxiliary device 20. The second secondary battery 22 functions as a backup power source for the power source 10.

[0034] The second secondary battery 22 is connected in parallel with the auxiliary device 20. The second secondary battery 22 can supply backup power to the auxiliary device 20 when power is not supplied from the power source 10 to the auxiliary device 20. The voltage V2 of the second secondary battery 22 is lower than the voltage V0 of the power source 10, and is, for example, 10V-50V.

[0035] In addition, the second secondary battery 22 is connected in parallel with the first secondary battery 21. The second secondary battery 22 can also supply power to the first secondary battery 21. The power supplied from the second secondary battery 22 may also be charged into the first secondary battery 21.

[0036] The second secondary battery 22 is connected to the converter 12 via the second switch 32 and the main switch 30. The second switch 32 is disposed between the second secondary battery 22 and the main switch 30. The second switch 32 is connected in series with the main switch 30. The second switch 32 is connected in parallel with the auxiliary device 20. The second switch 32 is connected in parallel with the first switch 31. The second switch 32 opens and closes the electric path between the second secondary battery 22 and the main switch 30. When the second switch 32 is turned on (closed), the second secondary battery 22 is charged or discharged. When the second switch 32 is turned off (open), charging or discharging of the second secondary battery 22 is not performed.

[0037] The main switch 30 is disposed between the converter 12 and the second switch 32. The main switch 30 opens and closes the electrical path between the converter 12 and the second switch 32. When the main switch 30 and the second switch 32 are turned on (closed) while the converter 12 is operating, power is supplied from the power source 10 to the second secondary battery 22. When the main switch 30 or the second switch 32 is turned off (open), the power supply from the power source 10 to the second secondary battery 22 is cut off.

[0038] The control device 50 of the power supply system 2 includes, for example, a CPU, a ROM, and a RAM, and executes predetermined control and processing related to the power supply system 2 based on a program stored in a storage unit. For example, the control device 50 controls the opening and closing operations of the main switch 30, the first switch 31, and the second switch 32.

[0039] (Switch processing; Figure 2) Next, the switching process of the embodiment will be described. The switching process of the embodiment starts, for example, when the switching operation of the converter 12 starts. At the stage when the switching process starts, it is assumed that the main switch 30, the first switch 31, the second switch 32, and the power switch 34 are all on.

[0040] As shown in FIG. 2, in S12 of the switch process, the control device 50 judges whether the second secondary battery 22 is overcharged. Overcharge is a state in which a secondary battery (e.g., the second secondary battery 22) is fully charged or nearly fully charged and the secondary battery is further charged. Whether the second secondary battery 22 is overcharged is judged, for example, based on the voltage V2 of the second secondary battery 22. For example, if the voltage V2 of the second secondary battery 22 exceeds a predetermined overcharge threshold (e.g., 99% of the value at full charge), the second secondary battery 22 is judged to be overcharged, and if the voltage V2 of the second secondary battery 22 does not exceed the overcharge threshold, the second secondary battery 22 is judged not to be overcharged. The voltage V2 of the second secondary battery 22 is measured, for example, by a voltmeter (not shown). If the second secondary battery 22 is overcharged (YES in S12), the process proceeds to S14, and if not (NO in S12), the process proceeds to S32. The method for determining whether the second secondary battery 22 is overcharged is not particularly limited.

[0041] In S14 after YES in S12, the control device 50 stops the converter 12. When the converter 12 stops, power from the power source 10 is no longer supplied to the auxiliary equipment 20. Furthermore, power from the power source 10 is no longer supplied to the first secondary battery 21 and the second secondary battery 22. In the following S16, the control device 50 turns off the main switch 30. When the main switch 30 is turned off, the electrical connection between the power source 10 and the auxiliary equipment 20 is cut off. Furthermore, the electrical connection between the power source 10 and the first secondary battery 21 and the second secondary battery 22 is cut off.

[0042] In the next S18, the control device 50 judges whether the voltage V2 of the second secondary battery 22 is higher than the voltage V1 of the first secondary battery 21. The voltage V2 of the second secondary battery 22 and the voltage V1 of the first secondary battery 21 are measured, for example, by a voltmeter (not shown). The voltage V1 of the first secondary battery 21 is more likely to fluctuate than the voltage V2 of the second secondary battery 22. If the voltage V2 of the second secondary battery 22 is higher than the voltage V1 of the first secondary battery 21 (YES in S18), the process proceeds to S20. On the other hand, if the voltage V1 of the first secondary battery 21 is higher than the voltage V2 of the second secondary battery 22 (NO in S18), the process proceeds to S22. Note that if V1 and V2 are equal, the process may wait in S18.

[0043] In S20 after YES in S18, the control device 50 keeps the first switch 31 on and keeps the second switch 32 on. By keeping the second switch 32 on, the control device 50 allows discharging from the second secondary battery 22. Furthermore, by keeping the first switch 31 on, the control device 50 allows charging from the second secondary battery 22 to the first secondary battery 21. In a state in which the main switch 30 is off (S16), the voltage V2 of the second secondary battery 22 is higher than the voltage V1 of the first secondary battery 21 (YES in S18), and the first switch 31 and the second switch 32 are on (S20), the power stored in the second secondary battery 22 is supplied to the first secondary battery 21 and the auxiliary device 20. After S20, the process returns to S12.

[0044] On the other hand, in S22 after NO in S18, the control device 50 turns off the first switch 31 and keeps the second switch 32 on. By keeping the second switch 32 on, the control device 50 allows discharging from the second secondary battery 22 and allows power supply from the second secondary battery 22 to the auxiliary device 20. In addition, the control device 50 turns off the first switch 31 to prohibit charging from the first secondary battery 21 to the second secondary battery 22. In a state in which the main switch 30 is off (S16), the voltage V1 of the first secondary battery 21 is higher than the voltage V2 of the second secondary battery 22 (NO in S18), the first switch 31 is off, and the second switch 32 is on (S22), the power stored in the second secondary battery 22 is supplied to the auxiliary device 20. After S22, the process returns to S12.

[0045] If the switch process S12 is NO (i.e., the second secondary battery 22 is not overcharged), the process proceeds to S32. In S32, the control device 50 judges whether the voltage V2 of the second secondary battery 22 is higher than a predetermined voltage threshold Vth. The predetermined voltage threshold Vth can be set appropriately. The voltage threshold Vth is a value indicating that the second secondary battery 22 is sufficiently charged. If the voltage V2 of the second secondary battery 22 is higher than the voltage threshold Vth (YES in S32), the process proceeds to S34. If the voltage V2 of the second secondary battery 22 is lower than the voltage threshold Vth (NO in S32), the process returns to S12. Note that if V2 is equal to Vth, the process may wait in S32.

[0046] In S34 after YES in S32, the control device 50 determines whether or not the current I30 flowing through the main switch 30 in the ON state is lower than a predetermined current threshold Ith. The current I30 flowing through the main switch 30 is measured, for example, by an ammeter (not shown). The predetermined current threshold Ith can be set appropriately. The current threshold Ith is a value indicating that the power supplied from the power source 10 to the auxiliary device 20 is small. If the current I30 flowing through the main switch 30 is lower than the current threshold Ith (YES in S34), the process proceeds to S36. If the current I30 flowing through the main switch 30 is higher than the current threshold Ith (NO in S34), the process returns to S12. Note that if I30 is equal to Ith, the process may wait in S34.

[0047] In S36 after YES in S34, the control device 50 keeps the main switch 30 on, keeps the first switch 31 on, and turns the second switch 32 off. The control device 50 allows power supply from the power source 10 to the auxiliary device 20 by keeping the main switch 30 on. The control device 50 allows charging from the power source 10 to the first secondary battery 21 by keeping the first switch 31 on. The control device 50 also prohibits charging from the power source 10 to the second secondary battery 22 by turning off the second switch 32. In a state in which the main switch 30 is on, the first switch 31 is on, and the second switch 32 is off, power from the power source 10 is supplied to the first secondary battery 21 and the auxiliary device 20. After S36, the process returns to S12.

[0048] (effect) The power supply system 2 of the embodiment has been described above. As is clear from the above description, the power supply system 2 includes a power supply 10, an auxiliary device 20 to which the power of the power supply 10 is supplied, a first secondary battery 21 connected in parallel to the auxiliary device 20 and to which the power of the power supply 10 is supplied, and a second secondary battery 22 connected in parallel to the auxiliary device 20 and the first secondary battery 21 and to which the power of the power supply 10 is supplied. The auxiliary device 20 is connected to the power supply 10 via a main switch 30. The first secondary battery 21 is connected to the power supply 10 via the main switch 30 and a first switch 31 connected in series to the main switch 30. The second secondary battery 22 is connected to the power supply 10 via the main switch 30 and a second switch 32 connected in series to the main switch 30. The control device 50 controls the opening and closing operations of the main switch 30, the first switch 31, and the second switch 32.

[0049] According to this configuration, by controlling the opening and closing operations of the main switch 30, the first switch 31, and the second switch 32, it is possible to protect the second secondary battery 22 from overcharging and to continue supplying power to the auxiliary device 20. For example, when the second secondary battery 22 is overcharged, the main switch 30 is turned off to prohibit charging of the second secondary battery 22 from the power source 10. This makes it possible to protect the second secondary battery 22 from overcharging. In this case, for example, the second switch 32 is turned on to allow discharging from the second secondary battery 22. This makes it possible to supply power from the second secondary battery 22 to the auxiliary device 20 even if power is not supplied from the power source 10 to the auxiliary device 20.

[0050] The power supply system 2 includes a converter 12 that converts the voltage of a power supply 10 and supplies power to an auxiliary device 20, a first secondary battery 21, and a second secondary battery 22, and a capacitor 14 connected to the output side of the converter 12. With this configuration, it is possible to suppress abrupt changes in the voltage applied to the auxiliary device 20.

[0051] When the second secondary battery 22 is overcharged, the control device 50 prohibits charging of the second secondary battery 22 from the power source 10 by turning off the main switch 30 (see S12-S16 in FIG. 2). With this configuration, the second secondary battery 22 is not charged, so that the second secondary battery 22 can be protected from overcharging.

[0052] When the second secondary battery 22 is overcharged, the control device 50 allows discharging from the second secondary battery 22 by turning on the second switch 32 (see S20 in FIG. 2). With this configuration, the amount of charge stored in the second secondary battery 22 can be reduced, so that the second secondary battery 22 can be protected from overcharging.

[0053] When the second secondary battery 22 is overcharged and the voltage V2 of the second secondary battery 22 is higher than the voltage V1 of the first secondary battery 21, the control device 50 turns on the first switch 31 to allow charging from the second secondary battery 22 to the first secondary battery 21 (see YES in S18 and S20 in FIG. 2). With this configuration, the amount of charge stored in the second secondary battery 22 can be reduced, so the second secondary battery 22 can be protected from overcharging.

[0054] When the second secondary battery 22 is overcharged and the voltage V1 of the first secondary battery 21 is higher than the voltage V2 of the second secondary battery 22, the control device 50 turns off the first switch 31 to prohibit charging from the first secondary battery 21 to the second secondary battery 22 (see NO in S18 and S22 in FIG. 2). With this configuration, the second secondary battery 22 is not charged, so the second secondary battery 22 can be protected from overcharging.

[0055] When the second secondary battery 22 is not overcharged, the voltage V2 of the second secondary battery 22 is higher than a predetermined voltage threshold Vth, and the current I30 flowing through the main switch 30 is lower than a predetermined current threshold Ith, the control device 50 allows power supply from the power source 10 to the auxiliary equipment 20 by turning on the main switch 30, allows charging of the first secondary battery 21 from the power source 10 by turning on the first switch 31, and prohibits charging of the second secondary battery 22 from the power source 10 by turning off the second switch 32 (see NO at S12 in Figure 2, S32-S36).

[0056] According to this configuration, even if the second secondary battery 22 is not overcharged, the second secondary battery 22 is not charged when it is approaching overcharge, so that the second secondary battery 22 can be protected from overcharging. At the same time, charging of the first secondary battery 21 can be promoted while supplying power to the auxiliary device 20. The power of the power source 10 can be appropriately distributed to the auxiliary device 20, the first secondary battery 21, and the second secondary battery 22 according to the charging state of the second secondary battery 22.

[0057] The second secondary battery 22 is a battery for the auxiliary equipment 20 of the electric vehicle 60. With this configuration, the second secondary battery 22 for the auxiliary equipment 20 of the electric vehicle 60 can be protected from overcharging and can continue to supply power to the auxiliary equipment 20.

[0058] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. The technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of these objectives is itself technically useful. [Explanation of symbols]

[0059] 2: power supply system, 10: power supply, 12: converter, 14: capacitor, 20: auxiliary equipment, 21: first secondary battery, 22: second secondary battery, 30: main switch, 31: first switch, 32: second switch, 34: power switch, 50: control device

Claims

1. Power supply, a load to which the power of the power source is supplied; a first secondary battery connected in parallel with the load and supplied with power from the power source; a second secondary battery connected in parallel to the load and the first secondary battery and supplied with power from the power source; A control device, The load is connected to the power supply via a main switch; the first secondary battery is connected to the power source via the main switch and a first switch connected in series with the main switch; the second secondary battery is connected to the power source via the main switch and a second switch connected in series with the main switch; The control device controls opening and closing operations of the main switch, the first switch, and the second switch.

2. 2. The power supply system of claim 1, a converter that converts the voltage of the power source and supplies power to the load, the first secondary battery, and the second secondary battery; A capacitor connected to an output side of the converter.

3. 3. The power supply system according to claim 1, The control device, when the second secondary battery is overcharged, prohibits charging of the second secondary battery from the power source by turning off the main switch.

4. 4. The power supply system according to claim 3, The control device, when the second secondary battery is overcharged, allows discharging from the second secondary battery by turning on the second switch.

5. 5. The power supply system according to claim 4, The control device, when the second secondary battery is overcharged and the voltage of the second secondary battery is higher than the voltage of the first secondary battery, allows charging from the second secondary battery to the first secondary battery by turning on the first switch.

6. 5. The power supply system according to claim 4, The control device, when the second secondary battery is overcharged and the voltage of the first secondary battery is higher than the voltage of the second secondary battery, prohibits charging from the first secondary battery to the second secondary battery by turning off the first switch.

7. 3. The power supply system according to claim 1, The control device, when the second secondary battery is not overcharged, the voltage of the second secondary battery is higher than a predetermined voltage threshold, and the current flowing through the main switch is lower than a predetermined current threshold, turns on the main switch to allow power supply from the power source to the load, turns on the first switch to allow charging of the first secondary battery from the power source, and turns off the second switch to prohibit charging of the second secondary battery from the power source.

8. 3. The power supply system according to claim 1 or 2, which is mounted on an electric vehicle, The second secondary battery is a battery for an auxiliary device of the electric vehicle.

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