Power supply system
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- AISAN IND CO LTD
- Filing Date
- 2023-08-07
- Publication Date
- 2026-08-03
Smart Images
Figure 0007899137000001 
Figure 0007899137000002
Abstract
Description
Technical Field
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[0001] The technology disclosed in this specification relates to a power supply system.
Background Art
[0002] Patent Document 1 describes that, in order to prevent overcharging of a fully charged battery, for example, the battery is disconnected from the power supply line of a DCDC converter.
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0004] In the technology described in Patent Document 1, even if overcharging is prevented, it is conceivable that power cannot be supplied to an important load 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 Problems
[0005] In a first aspect of this technology, the power supply system may include a power supply, a load to which the power supply is supplied, a first secondary battery connected in parallel with the load and supplied with power from the power supply, a second secondary battery connected in parallel with the load and the first secondary battery and supplied with power from the power supply, 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 the opening and closing operations of the main switch, the first switch, and the second switch.
[0006] This configuration allows for the protection of the secondary battery from overcharging while simultaneously supplying power to the load by controlling the opening and closing operations of the main switch, the first switch, and the second switch. For example, if the secondary battery is overcharged, turning off the main switch prevents charging from the power source to the secondary battery. This protects the secondary battery from overcharging. In that case, for example, turning on the second switch allows discharge from the secondary battery. This ensures that power can be supplied to the load from the secondary battery even if power is not supplied from the power source.
[0007] In a second embodiment, the power supply system may further include, in the first embodiment, a converter that converts the voltage of the power supply to supply 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] This configuration makes it possible to suppress abrupt changes in the voltage applied to the load, the primary battery, and the secondary battery.
[0009] In a third embodiment, in the first or second embodiment, the control device may, if the second secondary battery is overcharged, prohibit charging of the second secondary battery from the power source by turning off the main switch.
[0010] With this configuration, the secondary battery is not charged, thus protecting it from overcharging.
[0011] In a fourth embodiment, in the third embodiment, the control device may allow discharge from the second secondary battery by turning on the second switch if the second secondary battery is overcharged.
[0012] This configuration allows for a reduction in the amount of charge stored in the secondary battery, thereby protecting the secondary battery from overcharging.
[0013] In a fifth embodiment, in the fourth embodiment, the control device may, 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, turn on the first switch to allow charging from the second secondary battery to the first secondary battery.
[0014] This configuration allows for a reduction in the amount of charge stored in the secondary battery, thereby protecting the secondary battery from overcharging.
[0015] In the sixth embodiment, in the fourth embodiment, the control device may, 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, prohibit charging from the first secondary battery to the second secondary battery by turning off the first switch.
[0016] With this configuration, the secondary battery is not charged, thus protecting it from overcharging.
[0017] In the seventh embodiment, in any one of the first to sixth embodiments, the control device may, 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, allow power supply from the power source to the load by turning on the main switch, allow charging from the power source to the first secondary battery by turning on the first switch, and prohibit charging from the power source to the second secondary battery by turning off the second switch.
[0018] This configuration protects the secondary battery from overcharging because it stops charging when it approaches overcharging, even if it is not currently overcharged. Simultaneously, it allows power to be supplied from the power source to the load while simultaneously promoting the charging of the primary battery by the power source. The power from the power source can be appropriately distributed to the load, the primary battery, and the secondary battery according to the charge state of the secondary battery.
[0019] In the eighth aspect, in any one of the first to seventh aspects described above, the second secondary battery may be a battery for the auxiliary equipment of the electric vehicle.
[0020] This configuration protects the secondary battery used for the auxiliary equipment of the electric vehicle from overcharging while continuously supplying power to the auxiliary equipment. [Brief explanation of the drawing]
[0021] [Figure 1] This diagram schematically shows the power supply system of the embodiment. [Figure 2] This is a flowchart of the switch operation in the example. [Modes for carrying out the invention]
[0022] The 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 machine 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. This power supply system 2 is mounted on, for example, an electric vehicle 60 (such as an electric car or a hybrid car).
[0023] The power supply 10 is, for example, a lithium-ion battery, a nickel-hydrogen battery, or the like. The power supply 10 stores the power for running 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 running the electric vehicle 60. The power supply 10 can also supply power to the auxiliary machine 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 later, 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 the voltage by periodically switching on and off the plurality of switching elements. The input side of the converter 12 is connected to the power supply 10. The output side of the converter 12 is connected to the auxiliary machine 20, the first secondary battery 21, and the second secondary battery 22. The converter 12 converts the voltage of the power supply 10 and supplies power to the auxiliary machine 20, the first secondary battery 21, and the second secondary battery 22. The converter 12 is, for example, an isolated or non-isolated DC / DC converter. The converter 12 of the embodiment is a step-down converter that steps down and outputs the voltage input from the power supply 10.
[0025] The input side of the converter 12 is connected to the power supply 10 via a power switch 34. The power switch 34 is located between the converter 12 and the power supply 10. The power switch 34 opens and closes the electrical circuit between the converter 12 and the power supply 10. When the power switch 34 is turned on (closed), power is supplied from the power supply 10 to the converter 12. When the power switch 34 is turned off (open), the power supply from the power supply 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 located between the converter 12 and the main switch 30. The capacitor 14 is connected in parallel with the auxiliary equipment 20, the first secondary battery 21, and the second secondary battery 22. The capacitor 14 stores charge on the output side of the converter 12 and releases the stored charge.
[0027] Auxiliary equipment 20 (an example of a load) is connected to the power supply 10 via a converter 12. Auxiliary equipment 20 is a device that operates using power supplied from the power supply 10 via the converter 12. Auxiliary equipment 20 is also connected to a first secondary battery 21 and a second secondary battery 22. Auxiliary equipment 20 may also operate using power supplied from the first secondary battery 21 or the second secondary battery 22. Examples of auxiliary equipment 20 include lights, air conditioners, power windows, starter motors, pumps, fans, etc., of the electric vehicle 60 on which the power supply system 2 is installed. The type of auxiliary equipment 20 is not particularly limited.
[0028] The auxiliary equipment 20 is connected to the converter 12 via the main switch 30. The main switch 30 is located between the converter 12 and the auxiliary equipment 20. The main switch 30 opens and closes the electrical circuit between the converter 12 and the auxiliary equipment 20. When the converter 12 is operating and the main switch 30 is turned on (closed), power is supplied from the power supply 10 to the auxiliary equipment 20. When the main switch 30 is turned off (open), the power supply from the power supply 10 to the auxiliary equipment 20 is cut off.
[0029] The first secondary battery 21 is, for example, a lead-acid battery. The first secondary battery 21 is connected to the power supply 10 via the converter 12. Power supplied from the power supply 10 via the converter 12 charges the first secondary battery 21. The first secondary battery 21 can store power to supply to the auxiliary equipment 20. The first secondary battery 21 functions as a backup power source for the power supply 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 to the auxiliary device 20 from the power supply 10. The voltage V1 of the first secondary battery 21 is lower than the voltage V0 of the power supply 10, 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 located 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 equipment 20. The first switch 31 opens and closes the circuit 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 and discharging of the first secondary battery 21 ceases.
[0032] The main switch 30 is located between the converter 12 and the first switch 31. The main switch 30 opens and closes the electrical circuit between the converter 12 and the first switch 31. When the converter 12 is operating and both the main switch 30 and the first switch 31 are turned on (closed), power is supplied from the power supply 10 to the first secondary battery 21. When either the main switch 30 or the first switch 31 is turned off (open), the power supply from the power supply 10 to the first secondary battery 21 is cut off.
[0033] The secondary battery 22 is, for example, a lithium-ion battery. The secondary battery 22 is connected to the power supply 10 via the converter 12. Power supplied from the power supply 10 via the converter 12 charges the secondary battery 22. The secondary battery 22 can store power to supply to the auxiliary equipment 20. The secondary battery 22 functions as a backup power source for the power supply 10.
[0034] The secondary battery 22 is connected in parallel with the auxiliary device 20. The secondary battery 22 can supply backup power to the auxiliary device 20 when power is not supplied to the auxiliary device 20 from the power supply 10. The voltage V2 of the secondary battery 22 is lower than the voltage V0 of the power supply 10, for example, 10V-50V.
[0035] Furthermore, 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. Power supplied from the second secondary battery 22 can also be used to charge the first secondary battery 21.
[0036] The secondary battery 22 is connected to the converter 12 via the second switch 32 and the main switch 30. The second switch 32 is located between the 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 equipment 20. The second switch 32 is connected in parallel with the first switch 31. The second switch 32 opens and closes the circuit between the secondary battery 22 and the main switch 30. When the second switch 32 is turned on (closed), the secondary battery 22 is charged or discharged. When the second switch 32 is turned off (open), charging and discharging of the secondary battery 22 stops.
[0037] The main switch 30 is located between the converter 12 and the second switch 32. The main switch 30 opens and closes the electrical circuit between the converter 12 and the second switch 32. When the converter 12 is operating and both the main switch 30 and the second switch 32 are turned on (closed), power is supplied from the power supply 10 to the second secondary battery 22. When either the main switch 30 or the second switch 32 is turned off (open), the power supply from the power supply 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, ROM, and RAM, and performs predetermined controls and processes related to the power supply system 2 based on a program stored in the memory 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] (Switching process; 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 begins. At the stage when the switching process starts, the main switch 30, the first switch 31, the second switch 32, and the power switch 34 are all on.
[0040] As shown in Figure 2, in the switch operation S12, the control device 50 determines whether or not the secondary battery 22 is overcharged. Overcharging is a state in which the secondary battery (e.g., the secondary battery 22) is fully charged or nearly fully charged and is further charged. Whether or not the secondary battery 22 is overcharged is determined, for example, based on the voltage V2 of the secondary battery 22. For example, if the voltage V2 of the secondary battery 22 exceeds a predetermined overcharge threshold (e.g., 99% of the value when fully charged), the secondary battery 22 is determined to be overcharged, and if the voltage V2 of the secondary battery 22 does not exceed the overcharge threshold, the secondary battery 22 is determined not to be overcharged. The voltage V2 of the secondary battery 22 is measured, for example, by a voltmeter (not shown). If the secondary battery 22 is overcharged (YES in S12), the process proceeds to S14; if it is not overcharged (NO in S12), the process proceeds to S32. Furthermore, the method for determining whether or not the second secondary battery 22 is overcharged is not particularly limited.
[0041] In S14, following the YES response in S12, the control device 50 stops the converter 12. When the converter 12 stops, power from the power supply 10 is no longer supplied to the auxiliary equipment 20. Also, power from the power supply 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 supply 10 and the auxiliary equipment 20 is interrupted. Also, the electrical connection between the power supply 10 and the first secondary battery 21 and the second secondary battery 22 is interrupted.
[0042] In the subsequent S18, the control device 50 determines whether the voltage V2 of the second secondary battery 22 is higher than the voltage V1 of the first secondary battery 21. The voltages V2 of the second secondary battery 22 and 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 prone to fluctuation 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 be paused in S18.
[0043] In S20, following a YES response in S18, the control device 50 maintains the first switch 31 in the ON position and the second switch 32 in the ON position. By maintaining the second switch 32 in the ON position, the control device 50 allows discharge from the second secondary battery 22. Also, by maintaining the first switch 31 in the ON position, the control device 50 allows charging from the second secondary battery 22 to the first secondary battery 21. When 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 both 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 equipment 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 discharge from the second secondary battery 22 and allows power supply from the second secondary battery 22 to the auxiliary equipment 20. Also, by turning off the first switch 31, the control device 50 prohibits charging from the first secondary battery 21 to the second secondary battery 22. When 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 equipment 20. After S22, the process returns to S12.
[0045] If the answer to the switch process in S12 is NO (i.e., the secondary battery 22 is not overcharged), the process proceeds to S32. In S32, the control device 50 determines whether the voltage V2 of the secondary battery 22 is higher than a predetermined voltage threshold Vth. The predetermined voltage threshold Vth can be set as appropriate. The voltage threshold Vth is a value that indicates that the secondary battery 22 is sufficiently charged. If the voltage V2 of the secondary battery 22 is higher than the voltage threshold Vth (YES in S32), the process proceeds to S34. If the voltage V2 of the 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, following a YES response in S32, the control device 50 determines whether the current I30 flowing through the ON main switch 30 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 as appropriate. The current threshold Ith is a value that indicates that the power supplied from the power supply 10 to the auxiliary equipment 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, following a YES in S34, the control device 50 keeps the main switch 30 ON, keeps the first switch 31 ON, and turns off the second switch 32. By keeping the main switch 30 ON, the control device 50 allows power to be supplied from the power supply 10 to the auxiliary equipment 20. By keeping the first switch 31 ON, the control device 50 allows charging of the first secondary battery 21 from the power supply 10. Also, by turning off the second switch 32, the control device 50 prohibits charging of the second secondary battery 22 from the power supply 10. When the main switch 30 is ON, the first switch 31 is ON, and the second switch 32 is OFF, power from the power supply 10 is supplied to the first secondary battery 21 and the auxiliary equipment 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 comprises a power supply 10, an auxiliary device 20 to which power from the power supply 10 is supplied, a first secondary battery 21 connected in parallel with the auxiliary device 20 and supplied with power from the power supply 10, and a second secondary battery 22 connected in parallel with the auxiliary device 20 and the first secondary battery 21 and supplied with power from the power supply 10. The auxiliary device 20 is connected to the power supply 10 via the 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 with 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 with 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] With this configuration, by controlling the opening and closing operations of the main switch 30, the first switch 31, and the second switch 32, the secondary battery 22 can be protected from overcharging while continuously supplying power to the auxiliary equipment 20. For example, if the secondary battery 22 is overcharged, the main switch 30 is turned off to prevent charging from the power supply 10 to the secondary battery 22. This protects the secondary battery 22 from overcharging. In that case, for example, the second switch 32 is turned on to allow discharge from the secondary battery 22. This allows power to be supplied from the secondary battery 22 to the auxiliary equipment 20 even if power is not supplied from the power supply 10.
[0050] The power supply system 2 includes a converter 12 that converts the voltage of the power supply 10 to supply power to the auxiliary equipment 20, the first secondary battery 21, and the 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 sudden changes in the voltage applied to the auxiliary equipment 20.
[0051] The control device 50 prevents charging of the secondary battery 22 from the power supply 10 by turning off the main switch 30 if the secondary battery 22 is overcharged (see S12-S16 in Figure 2). With this configuration, the secondary battery 22 is not charged, thus protecting it from overcharging.
[0052] The control device 50 allows discharge from the secondary battery 22 by turning on the second switch 32 if the secondary battery 22 is overcharged (see S20 in Figure 2). With this configuration, the amount of charge stored in the secondary battery 22 can be reduced, thereby protecting the secondary battery 22 from overcharging.
[0053] If 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 (YES in S18, see S20 in Figure 2). With this configuration, the amount of charge stored in the second secondary battery 22 can be reduced, thereby protecting the second secondary battery 22 from overcharging.
[0054] If 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 will turn off the first switch 31 to prevent charging from the first secondary battery 21 to the second secondary battery 22 (see NO in S18 and S22 in Figure 2). With this configuration, the second secondary battery 22 is not charged, thus protecting the second secondary battery 22 from overcharging.
[0055] When the second secondary battery 22 is not overcharged, and 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 supply 10 to the auxiliary equipment 20 by turning on the main switch 30, allows charging of the first secondary battery 21 from the power supply 10 by turning on the first switch 31, and prohibits charging of the second secondary battery 22 from the power supply 10 by turning off the second switch 32 (see NO in S12, S32-S36 in Figure 2).
[0056] With this configuration, the secondary battery 22 will not be charged when it approaches overcharging, even if it is not overcharged, thus protecting the secondary battery 22 from overcharging. At the same time, it is possible to supply power to the auxiliary equipment 20 while promoting the charging of the first secondary battery 21. The power from the power supply 10 can be appropriately distributed to the auxiliary equipment 20, the first secondary battery 21, and the secondary battery 22 according to the charge state of the 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 is protected from overcharging and power can be continuously supplied to the auxiliary equipment 20.
[0058] Although specific examples of the present invention have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples illustrated above. The technical elements described in this specification or drawings exhibit technical usefulness individually or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technologies illustrated in this specification or drawings can achieve multiple objectives simultaneously, and achieving even one of these objectives itself constitutes technical usefulness. [Explanation of symbols]
[0059] 2: Power system, 10: Power supply, 12: Converter, 14: Capacitor, 20: Auxiliary equipment, 21: Primary battery, 22: Secondary battery, 30: Main switch, 31: First switch, 32: Second switch, 34: Power switch, 50: Control unit
Claims
1. Power supply and The load to which the power supply is supplied, A first secondary battery connected in parallel with the aforementioned load and supplied with power from the aforementioned power supply, A second secondary battery is connected in parallel to the load and the first secondary battery, and is supplied with power from the power source, A control device is provided, The load is connected to the power supply via the main switch. The first secondary battery is connected to the power supply via the main switch and a first switch connected in series with the main switch. The second secondary battery is connected to the power supply via the main switch and a second switch connected in series with the main switch. The control device controls the opening and closing operations of the main switch, the first switch, and the second switch. The control device is a power supply system that, when the second secondary battery is overcharged, prohibits charging of the second secondary battery from the power supply by turning off the main switch.
2. A power supply system according to claim 1, 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, A power supply system further comprising a capacitor connected to the output side of the converter.
3. A power supply system according to claim 1 or 2, The control device is a power supply system that, when the second secondary battery is overcharged, allows discharge from the second secondary battery by turning on the second switch.
4. A power supply system according to claim 3, The control device is a power supply system that, 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.
5. A power supply system according to claim 3, The control device is a power supply system that, 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.
6. Power supply and The load to which the power supply is supplied, A first secondary battery connected in parallel with the aforementioned load and supplied with power from the aforementioned power supply, A second secondary battery is connected in parallel to the load and the first secondary battery, and is supplied with power from the power source, A control device is provided, The load is connected to the power supply via the main switch. The first secondary battery is connected to the power supply via the main switch and a first switch connected in series with the main switch. The second secondary battery is connected to the power supply via the main switch and a second switch connected in series with the main switch. The control device controls the opening and closing operations of the main switch, the first switch, and the second switch. The control device is a power supply system that, 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, allows power supply from the power source to the load by turning on the main switch, allows charging from the power source to the first secondary battery by turning on the first switch, and prohibits charging from the power source to the second secondary battery by turning off the second switch.
7. A power supply system to be installed in an electric vehicle, Power supply and The load to which the power supply is supplied, A first secondary battery connected in parallel with the aforementioned load and supplied with power from the aforementioned power supply, A second secondary battery is connected in parallel to the load and the first secondary battery, and is supplied with power from the power source, A control device is provided, The load is connected to the power supply via the main switch. The first secondary battery is connected to the power supply via the main switch and a first switch connected in series with the main switch. The second secondary battery is connected to the power supply via the main switch and a second switch connected in series with the main switch. The control device controls the opening and closing operations of the main switch, the first switch, and the second switch. The aforementioned second secondary battery is a power supply system, which is a battery for auxiliary equipment of the electric vehicle.