Power supply circuit and drive system

Abstract

This power supply circuit comprises a first terminal that is connected to a power supply, a second terminal that is connected to a load, a first switch that is connected between the first terminal and the second terminal, a power storage unit, a booster circuit, a second switch, and a control unit. The power storage unit has a first end and a second end. The control unit controls the booster circuit, the first switch, and the second switch. The first end is connected to a first path between the first terminal and the first switch. The booster circuit is connected between a second path and the second end of the power storage unit, the second path being located between the second terminal and the first switch. The second switch is connected between the second path and the second end of the power storage unit, in parallel with the booster circuit.

Description

Power supply circuit and drive system

[0001] The present disclosure relates to a power supply circuit and a drive system, and more particularly to a power supply circuit for supplying power from a power source to a load, and a drive system including the power supply circuit.

[0002] Patent Document 1 discloses an electric motorcycle having a rechargeable battery (power source) and a direct current (DC) motor (load). In the electric motorcycle of Patent Document 1, the DC motor is operated using power from the rechargeable battery.

[0003] Japanese Utility Model Application Laid-Open Publication No. 6-53389

[0004] Depending on the load, a large current may be temporarily required for the load to operate. For example, if the load is a DC motor that is a power source for a moving object, a large current is temporarily required when starting or accelerating. In the electric motorcycle of Patent Document 1, the voltage output from the power supply decreases due to a voltage drop caused by the internal resistance of the power supply, which may cause the power supply to the load to become unstable.

[0005] A power supply circuit according to one aspect of the present disclosure includes a first terminal connected to a power supply, a second terminal connected to a load, a first switch, a power storage unit, a boost circuit, a second switch, and a control unit. The first switch is connected between the first terminal and the second terminal. The power storage unit has a first end and a second end. The control unit controls the boost circuit, the first switch, and the second switch. The first end of the power storage unit is connected to a first path between the first terminal and the first switch. The boost circuit is connected between a second path between the second terminal and the first switch and a second end of the power storage unit. The second switch is connected in parallel with the boost circuit between the second path and the second end of the power storage unit.

[0006] A drive system according to one aspect of the present disclosure includes the power supply circuit, a power supply connected to the first terminal of the power supply circuit, and a load connected to the second terminal of the power supply circuit. The load includes an operation determination unit that determines an operating state of the load. The control unit controls the operation of the boost circuit based on the determination result of the operation determination unit.

[0007] According to a power supply circuit and a drive system according to an aspect of the present disclosure, it is possible to stabilize the power supply from a power supply to a load.

[0008] FIG. 1A is a block diagram of a power supply circuit according to a first embodiment. FIG. 1B is a circuit diagram showing the inside of a power storage unit in the power supply circuit according to the first embodiment. FIG. 1C is a schematic diagram of a moving body including the power supply circuit according to the first embodiment. FIG. 2 is a schematic diagram showing operation of the power supply circuit according to the first embodiment in a first power supply mode. FIG. 3 is a schematic diagram showing operation of the power supply circuit according to the second power supply mode. FIG. 4 is a schematic diagram showing operation of the power supply circuit according to the third power supply mode. FIG. 5 is a schematic diagram showing operation of the power supply circuit according to the first embodiment in a first charging mode. FIG. 6 is a schematic diagram showing operation of the power supply circuit according to the second charging mode. FIG. 7 is a schematic diagram showing operation of a power supply circuit according to a modified example of the first embodiment in a first charging mode. FIG. 8 is a block diagram of a power supply circuit according to a second embodiment. FIG. 9 is a block diagram of a drive system according to a third embodiment.

[0009] (Embodiment 1) (1) Configuration As shown in Fig. 1A, a power supply circuit 1 according to embodiment 1 is connected between a power supply 2 and a load 3. As shown in Fig. 1C, the power supply circuit 1 is used in a mobile object 101, which may be a vehicle such as an electric motorcycle or an automobile. The mobile object 101 includes the power supply circuit 1 and a mobile object main body 101a. The mobile object main body 101a is equipped with the power supply circuit 1, a power supply 2, and a load 3. When the mobile object 101 is a vehicle, the mobile object main body 101a is the vehicle main body.

[0010] The power source 2 is the main power source of the mobile object 101 and is, for example, a rechargeable secondary battery such as a lithium ion battery. The load 3 is, for example, an electric motor for driving the mobile object 101.

[0011] The power supply circuit 1 includes a first terminal Ta1 and a second terminal Ta2, a first switch SW1, a second switch SW2, a power storage unit 11, a boost circuit 12, and a control unit 13.

[0012] The first terminal Ta1 is connected to a power supply 2. More specifically, the positive electrode of the power supply 2 is connected to the first terminal Ta1, and the negative electrode of the power supply 2 is connected to the ground electrode 1z.

[0013] The second terminal Ta2 is connected to the load 3. More specifically, the positive side of the power receiving terminal of the load 3 is connected to the second terminal Ta2, and the negative side of the power receiving terminal of the load 3 is connected to the ground electrode 1z.

[0014] The first switch SW1 is connected between the first terminal Ta1 and the second terminal Ta2. More specifically, one terminal (first end S11) of the first switch SW1 is connected to the first terminal Ta1. A path between the first terminal Ta1 and the first switch SW1, i.e., the first end S11 of the first switch SW1, is a first path R1. The other terminal (second end S12) of the first switch SW1 is connected to the second terminal Ta2. A path between the second terminal Ta2 and the first switch SW1, i.e., the second end S12 of the first switch SW1, is a second path R2. In this embodiment, the first path R1 is made up of conductors such as conductors or printed wiring patterns connected between the first terminal Ta1 and the first end S11 of the first switch SW1, and the second path R2 is made up of conductors such as conductors or printed wiring patterns connected between the second terminal Ta2 and the first switch SW1.

[0015] The power storage unit 11 stores power supplied from the power source 2 and supplies the stored power to the load 3. For example, as shown in FIG. 1B , the power storage unit 11 includes a plurality of capacitors C1 (eight in FIG. 1B ). In this embodiment, the capacitors C1 are electric double layer capacitors (EDLCs). An electric double layer capacitor is a device capable of multiple rapid charging and discharging. More specifically, the power storage unit 11 includes a plurality of circuits (two in FIG. 1B ) in which a plurality of unit cells (four in FIG. 1B ) are connected in series, with each of the plurality of capacitors C1 serving as a unit cell.

[0016] As shown in FIGS. 1A and 1B , the power storage unit 11 has a first terminal Tb1 and a second terminal Tb2. The first terminal Tb1 is connected to a final-stage capacitor C12. Here, the “final-stage capacitor C12” refers to a capacitor C12 in a series circuit including multiple capacitors C1, whose negative pole is not connected to the positive pole of any other capacitor C1. The second terminal Tb2 is connected to a first-stage capacitor C11. Here, the “first-stage capacitor C11” refers to a capacitor C11 in a series circuit including multiple capacitors C1, whose positive pole is not connected to the negative pole of any other capacitor C1. That is, the first terminal Tb1 is connected to one end on the positive side of the circuit in which multiple capacitors C1 are connected in series, and the second terminal Tb2 is connected to one end on the negative side of the circuit in which multiple capacitors C1 are connected in series. The first terminal Tb1 of the power storage unit 11 is connected to a first path R1.

[0017] The boost circuit 12 is connected between the second path R2 and the second end Tb2 of the power storage unit 11. The boost circuit 12 is, for example, a DC-DC converter including a capacitor and a plurality of switch elements.

[0018] When the boost circuit 12 is in an operating state, it passes a current from the second path R2 toward the second end Tb2 of the power storage unit 11. At this time, the boost circuit 12 operates so that the voltage at the second end Tb2 of the power storage unit 11 is higher than the voltage on the second path R2. Furthermore, when the boost circuit 12 is in a stopped state, it blocks a current from the second end Tb2 of the power storage unit 11 toward the second path R2. The boost circuit 12 further includes, for example, a diode whose forward direction is from the second path R2 toward the second end Tb2 of the power storage unit 11.

[0019] The second switch SW2 is connected between the second path R2 and the second end Tb2 of the power storage unit 11. More specifically, the second switch SW2 is connected in parallel with the boost circuit 12 between the second path R2 and the second end Tb2 of the power storage unit 11. One terminal (first end S21) of the second switch SW2 is connected to the second path R2, and the other terminal (second end S22) is connected to the second end Tb2 of the power storage unit 11.

[0020] The control unit 13 includes, for example, a computer system having a processor and a memory. The processor executes a program stored in the memory, causing the computer system to function as the control unit 13. The program executed by the processor is pre-recorded in the memory of the computer system here, but may also be provided by being recorded on a non-transitory recording medium such as a memory card, or may be provided via a telecommunications line such as the Internet.

[0021] The control unit 13 controls the first switch SW1, the second switch SW2, and the boost circuit 12. More specifically, the control unit 13 determines, for example, the operation mode of the power supply circuit 1 and controls the first switch SW1, the second switch SW2, and the boost circuit 12 according to the operation mode. The control unit 13 determines the operation mode based on, for example, the voltage of the first terminal Ta1, the charging voltage of the power storage unit 11, and the voltage of the second terminal Ta2. The operation modes will be described later.

[0022] (2) Operation A number of operation modes of the power supply circuit 1 and detailed operations in each operation mode will now be described.

[0023] (2.1) Overview of Operation Modes The multiple operation modes of the power supply circuit 1 include a first power supply mode, a second power supply mode, and a third power supply mode as modes in which the load 3 is operated with power supplied from the power supply 2. The multiple operation modes of the power supply circuit 1 also include a first charging mode and a second charging mode as modes in which the power storage unit 11 or the power supply 2 is charged with power supplied from the load 3.

[0024] (2.2) Details of Operation Modes Each operation mode will be described in detail below.

[0025] 2, the power supply circuit 1 supplies the power supplied from the power supply 2 to the load 3 and also uses the power to charge the power storage unit 11. The control unit 13 selects the first power supply mode when, for example, the voltage Va1 of the first terminal Ta1 is equal to or greater than the first threshold value and the charging voltage of the power storage unit 11 is less than the second threshold value.

[0026] In the first power supply mode, the control unit 13 closes the first switch SW1 and opens the second switch SW2 to operate the boost circuit 12. In the first power supply mode, the power supplied from the power source 2 to the power supply circuit 1 passes through the first path R1, the first switch SW1, and the second path R2 and is supplied to the load 3. At this time, a portion of the power supplied from the power source 2 to the power supply circuit 1 is supplied to the load 3.

[0027] Furthermore, the boost circuit 12 passes a current from the second path R2 toward the second end Tb2 of the power storage unit 11. At this time, the boost circuit 12 makes the voltage Va2 at the second end Tb2 of the power storage unit 11 higher than the voltage on the second path R2. Because the voltage on the second path R2 is, for example, the same as the voltage Va1 at the first terminal Ta1, a voltage that depends on the output voltage of the boost circuit 12 is applied between the first end Tb1 and the second end Tb2 of the power storage unit 11. As a result, a portion of the power supplied from the power source 2 to the power supply circuit 1 is charged to the power storage unit 11 via the boost circuit 12.

[0028] (2.2.2) Second Power Supply Mode In the second power supply mode, as shown in Fig. 3 , the power supply circuit 1 supplies power to the load 3 from a series circuit including the power supply 2 and the power storage unit 11. The control unit 13 selects the second power supply mode, for example, when the voltage Va1 of the first terminal Ta1 is less than the first threshold. In the embodiment, the control unit 13 selects the second power supply mode regardless of the voltage of the power storage unit 11, for example, when the voltage Va1 of the first terminal Ta1 is less than the first threshold.

[0029] In the second power supply mode, the control unit 13 opens the first switch SW1 and closes the second switch SW2 to stop the boost circuit 12. In the second power supply mode, the power source 2 and the power storage unit 11 are connected in series, and power is supplied to the load 3 through the second switch SW2 and the second path R2.

[0030] At this time, the voltage Va3 applied by the power supply circuit 1 to the load 3 is the sum of the voltage Va1 at the first terminal Ta1 and the electromotive force of the power storage unit 11. Therefore, the power supply circuit 1 can apply a voltage Va3 higher than the voltage Va1 at the first terminal Ta1 to the load 3. This reduces the decrease in the voltage Va3 applied by the power supply circuit 1 to the load 3, making it possible to stabilize the voltage.

[0031] (2.2.3) Third Power Supply Mode In the third power supply mode, as shown in Fig. 4 , the power supply circuit 1 supplies power supplied from the power supply 2 to the load 3. In addition, in the third power supply mode, the power supply circuit 1 neither charges nor discharges the power storage unit 11. The control unit 13 selects the third power supply mode when, for example, the voltage Va1 of the first terminal Ta1 is equal to or greater than the first threshold value and the charging voltage of the power storage unit 11 is equal to or greater than the second threshold value.

[0032] In the third power supply mode, the control unit 13 closes the first switch SW1, opens the second switch SW2, and stops the boost circuit 12. In the third power supply mode, the power supplied from the power supply 2 passes through the first path R1, the first switch SW1, and the second path R2 and is supplied to the load 3. At this time, the voltage Va3 applied to the load 3 is equal to, for example, the voltage Va1 at the first terminal Ta1.

[0033] In the third power supply mode, the boost circuit 12 is in a stopped state and the second switch SW2 is open, so that the second terminal Tb2 of the power storage unit 11 is not connected to the path connected to the first terminal Ta1 or the second terminal Ta2. Therefore, in the third power supply mode, the power storage unit 11 is neither charged nor discharged.

[0034] (2.2.4) First Charging Mode In the first charging mode, as shown in Fig. 5 , the power supply circuit 1 charges the power storage unit 11 with power supplied from the load 3. The power supplied from the load 3 is, for example, regenerative power that can be extracted from the load 3 when the moving object 101 decelerates. For example, when the moving object 101 decelerates, the control unit 13 selects the first charging mode if the voltage Va1 of the first terminal Ta1 is equal to or greater than the third threshold and the charging voltage of the power storage unit 11 is less than the second threshold. In this embodiment, the third threshold is lower than the first threshold.

[0035] In the first charging mode, the control unit 13 opens the first switch SW1, closes the second switch SW2, and stops the boost circuit 12.

[0036] In the first charging mode, the power supplied from the load 3 passes through the second path R2 and the second switch SW2 and is supplied to the second terminal Tb2 of the power storage unit 11. Therefore, a voltage corresponding to the difference between the voltage Vc1 of the regenerative power from the load 3 and the voltage Va1 of the first terminal Ta1 is applied between the first terminal Tb1 and the second terminal Tb2 of the power storage unit 11. Therefore, the power storage unit 11 is charged by the power supplied from the load 3. Generally, when the upper limit of the allowable voltage of the load 3 is higher than the voltage of the power source 2, the voltage Vc1 of the regenerative power from the load 3 is also higher than the voltage of the power source 2. Therefore, in the first charging mode, the power supply circuit 1 can charge the power storage unit 11 without operating the boost circuit 12.

[0037] (2.2.5) Second Charging Mode In the second charging mode, as shown in Fig. 6 , the power supply circuit 1 charges the power supply 2 using power supplied from the load 3. For example, when decelerating the moving object 101, the control unit 13 selects the second charging mode if the voltage at the first terminal Ta1 is less than the third threshold value.

[0038] In the second charging mode, the control unit 13 closes the first switch SW1, opens the second switch SW2, and stops the voltage boosting circuit 12.

[0039] In the second charging mode, power supplied from the load 3 passes through the second path R2, the first switch SW1, and the first path R1 and is supplied to the power supply 2. Therefore, the power supply 2 is charged by the power supplied from the load 3. Furthermore, in the second charging mode, the boost circuit 12 is in a stopped state and the second switch SW2 is open, so the second end Tb2 of the power storage unit 11 is not connected to the path connected to the first terminal Ta1 or the second terminal Ta2. Therefore, in the second charging mode, the power storage unit 11 neither charges nor discharges.

[0040] (2.3) Selection of Operation Mode When supplying power from the power supply circuit 1 to the load 3, the control unit 13 selects one of the first power supply mode, the second power supply mode, and the third power supply mode shown in Figures 2, 3, and 4, respectively.

[0041] 3 when the voltage at the first terminal Ta1 is less than the first threshold. In this embodiment, when the voltage at the first terminal Ta1 is less than the first threshold, the control unit 13 selects the second power supply mode regardless of the charging voltage of the power storage unit 11. This connects the power supply 2 and the power storage unit 11 in series, making it possible to stabilize the power supply from the power supply circuit 1 to the load 3.

[0042] Furthermore, when the voltage Va1 at the first terminal Ta1 is equal to or greater than the first threshold, the control unit 13 selects either the first power supply mode or the third power supply mode based on the charging voltage of the power storage unit 11. For example, the control unit 13 selects the first power supply mode shown in FIG. 2 when the charging voltage of the power storage unit 11 is less than the second threshold, and selects the third power supply mode shown in FIG. 4 when the charging voltage of the power storage unit 11 is equal to or greater than the second threshold. As a result, when it is possible to stabilize the power supply from the power supply circuit 1 to the load 3 without connecting the power source 2 and the power storage unit 11 in series, the control unit 13 selects whether to charge the power storage unit 11 depending on the charging voltage of the power storage unit 11. Therefore, when it is possible to stably supply power from the power source 2 to the load 3, the control unit 13 charges the power storage unit 11 as necessary, thereby enabling the power supply circuit 1 to be switched to the second power supply mode.

[0043] When power is supplied from the load 3 to the power supply circuit 1, the control unit 13 selects one of the first charging mode and the second charging mode shown in FIGS. 5 and 6, respectively.

[0044] More specifically, when the voltage Va1 at the first terminal Ta1 is less than the third threshold, the control unit 13 selects the second charging mode shown in FIG. 6 . Furthermore, when the voltage Va1 at the first terminal Ta1 is equal to or greater than the third threshold and the charging voltage of the power storage unit 11 is equal to or less than the second threshold, the control unit 13 selects the first charging mode shown in FIG. 5 . This allows the power source 2 or the power storage unit 11 to be charged when power is supplied from the load 3 to the power supply circuit 1. Furthermore, in the first charging mode, the power source 2 and the power storage unit 11 are connected in series, and therefore the power source 2 may also be charged by the power from the load 3. Therefore, when the voltage of the power source 2 is low and the operating mode of the power supply circuit 1 is switched to the first charging mode, the voltage applied to the power storage unit 11 may become too high, resulting in an excessively high charging voltage for the power storage unit 11. Therefore, when the voltage Va1 of the first terminal Ta1 is less than the third threshold, it is preferable to select the second charging mode to restore the voltage of the power source 2 before the operating mode of the power supply circuit 1 changes to the first charging mode, thereby preventing the voltage applied to the storage unit 11 from becoming too high.

[0045] 2. Effects The power supply circuit 1 according to the first embodiment includes a first terminal Ta1 connected to the power supply 2, a second terminal Ta2 connected to the load 3, a first switch SW1, a power storage unit 11, a boost circuit 12, a second switch SW2, and a control unit 13. The first switch SW1 is connected between the first terminal Ta1 and the second terminal Ta2. The power storage unit 11 has a first end Tb1 and a second end Tb2. The control unit 13 controls the boost circuit 12, the first switch SW1, and the second switch SW2. The first end Tb1 of the power storage unit 11 is connected to a first path R1 between the first terminal Ta1 and the first switch SW1. The boost circuit 12 is connected between a second path R2 between the second terminal Ta2 and the first switch SW1 and the second end Tb2 of the power storage unit 11. The second switch SW2 is connected in parallel with the boost circuit 12 between the second path R2 and the second end Tb2 of the power storage unit 11. This makes it possible to connect the power storage unit 11 between the power supply 2 and the load 3, for example, when the load 3 temporarily requires a large current. This makes it possible to stabilize the voltage supplied from the power supply circuit 1 to the load 3.

[0046] In the power supply circuit 1 according to the first embodiment, the power storage unit 11 includes a plurality of capacitors C1 connected in series. Therefore, even if the power consumption of the load 3 changes suddenly, the voltage of the power supplied from the power supply circuit 1 to the load 3 is less likely to fluctuate.

[0047] Furthermore, in the power supply circuit 1 according to the first embodiment, when charging the power storage unit 11 using the power supply 2, the control unit 13 closes the first switch SW1, opens the second switch SW2, and operates the boost circuit 12. When supplying power from the power storage unit 11 to the load 3, the control unit 13 opens the first switch SW1 and closes the second switch SW2. As a result, when charging the power storage unit 11 using the power supply 2, the boost circuit 12 operates to apply a voltage between the first terminal Tb1 and the second terminal Tb2 of the power storage unit 11, thereby charging the power storage unit 11. When supplying power from the power storage unit 11 to the load 3, the voltage of the power supplied from the power supply circuit 1 to the load 3 is stabilized by connecting the power supply 2 and the power storage unit 11 in series.

[0048] Furthermore, in the power supply circuit 1 according to the first embodiment, the control unit 13 opens the first switch SW1 when charging the power storage unit 11 using the load 3. This allows the power storage unit 11 to be charged based on the difference between the voltage of the power supplied from the load 3 to the second end Tb2 of the power storage unit 11 and the voltage of the power source 2 when charging the power storage unit 11 using the load 3.

[0049] Furthermore, in the power supply circuit 1 according to the first embodiment, the control unit 13 closes the second switch SW2 when charging the power storage unit 11 using the load 3. As a result, in the power supply circuit 1 according to the first embodiment, the power storage unit 11 is charged by the power supplied from the load 3. Furthermore, since the power storage unit 11 can be charged without using the boost circuit 12, the control of the power supply circuit 1 can be simplified.

[0050] Furthermore, in the power supply circuit 1 according to the first embodiment, when the control unit 13 controls the boost circuit 12 not to operate, the boost circuit 12 at least cuts off the current in the direction from the second terminal Tb2 of the power storage unit 11 to the second path R2. As a result, when the control unit 13 stops the boost circuit 12 and opens the second switch SW2, the second terminal Tb2 of the power storage unit 11 is not connected to the path connected to the first terminal Ta1 or the second terminal Ta2. Therefore, when the control unit 13 stops the boost circuit 12 and opens the second switch SW2, charging and discharging of the power storage unit 11 is suppressed, and power can be stored in the power storage unit 11.

[0051] (Modification) 1. Configuration In the power supply circuit 1 according to the first embodiment, in the first charging mode, the control unit 13 closes the second switch SW2 and stops the voltage boost circuit 12. In contrast, in the power supply circuit 1 according to the modification, in the first charging mode, the control unit 13 opens the second switch SW2 and operates the voltage boost circuit 12.

[0052] FIG. 7 is a schematic diagram illustrating the operation of a power supply circuit 1 according to a modified example of the power supply circuit 1 shown in FIG. 5 in the first charging mode. In the modified power supply circuit 1, the control unit 13 opens the second switch SW2 and activates the boost circuit 12 in the first charging mode. Therefore, power supplied from the load 3 passes through the second path R2 and the boost circuit 12 and is supplied to the second terminal Tb2 of the power storage unit 11. Therefore, the output voltage Vc2 of the boost circuit 12 is applied to the second terminal Tb2 of the power storage unit 11. The output voltage Vc2 of the boost circuit 12 is higher than the voltage Vc1 of the regenerative power from the load 3. As a result, a voltage based on the difference between the output voltage Vc2 of the boost circuit 12 and the voltage Va1 at the first terminal Ta1 is applied between the first terminal Tb1 and the second terminal Tb2 of the power storage unit 11. Therefore, the power supplied from the load 3 charges the power storage unit 11. Furthermore, in the power supply circuit 1 according to the first modification, the voltage Vc1 of the regenerative power from the load 3 does not need to be higher than the voltage Va1 of the first terminal Ta1. That is, even if the voltage Vc1 of the regenerative power from the load 3 is low, it is possible to charge the power storage unit 11.

[0053] 2. Effects In the power supply circuit 1 according to the modification, when the load 3 is used to charge the power storage unit 11, the control unit 13 controls the operation of the boost circuit 12 so that a potential difference is generated between the second end Tb2 of the power storage unit 11 and the second path R2, and opens the second switch SW2. As a result, in the power supply circuit 1 according to the modification 1, the power storage unit 11 is charged by the power supplied from the load 3. Furthermore, even if the voltage Vc1 of the regenerative power from the load 3 is low, the power storage unit 11 can be charged.

[0054] Second Embodiment 1. Configuration As shown in FIG. 8, a power supply circuit 1a according to a second embodiment further includes a voltage monitoring unit 14 in addition to the configuration of the power supply circuit 1 of the first embodiment.

[0055] The voltage monitoring unit 14 monitors a charging voltage Vb1 between the first terminal Tb1 and the second terminal Tb2 of the power storage unit 11. The voltage monitoring unit 14 outputs the charging voltage Vb1 to the control unit 13.

[0056] The control unit 13 controls the operation of the boost circuit 12 based on the charging voltage Vb1 output by the voltage monitoring unit 14. More specifically, in the first charging mode, the control unit 13 determines, for example, whether to turn on the second switch SW2 to put the boost circuit 12 in a stopped state as shown in Fig. 5 or to turn off the second switch SW2 to put the boost circuit 12 in an operating state as shown in Fig. 7.

[0057] The control unit 13 controls the operation of the boost circuit 12 so that the sum of the voltage of the power source 2 and the charging voltage Vb1 is equal to or lower than the upper limit of the allowable voltage of the load 3, for example.

[0058] More specifically, when switching to the first charging mode, the control unit 13 first determines whether the sum of the voltage of the power source 2 and the charging voltage Vb1 is less than the upper limit of the allowable voltage of the load 3. Here, the voltage Va1 at the first terminal Ta1 can be used as the voltage of the power source 2. If the sum of the voltage of the power source 2 and the charging voltage Vb1 is equal to or greater than the upper limit of the allowable voltage of the load 3, the control unit 13 does not switch to the first charging mode. As a result, if there is a possibility that a voltage exceeding the upper limit of the allowable voltage will be applied to the load 3 when switching to the second power supply mode, it is possible to suppress charging of the power storage unit 11 and reduce the possibility of an overvoltage being applied to the load 3.

[0059] On the other hand, when the sum of the voltage of the power source 2 and the charging voltage Vb1 is less than the upper limit of the allowable voltage of the load 3, the control unit 13 opens the second switch SW2 to activate the boost circuit 12. The control unit 13 then monitors the charging voltage Vb1. When the sum of the voltage of the power source 2 and the charging voltage Vb1 is equal to or greater than the upper limit of the allowable voltage of the load 3, the control unit 13 turns on the second switch SW2 to stop the boost circuit 12. This causes the control unit 13 to reduce the voltage applied to the power storage unit 11 based on the power supplied from the load 3. The control unit 13 further monitors the charging voltage Vb1. When the sum of the voltage of the power source 2 and the charging voltage Vb1 is equal to or greater than the upper limit of the allowable voltage of the load 3, the control unit 13 switches to an operation mode other than the first charging mode. This makes it possible to prevent overcharging of the power storage unit 11.

[0060] 2. Effects The power supply circuit 1a according to the second embodiment includes a voltage monitoring unit 14. The voltage monitoring unit 14 monitors the charging voltage Vb1, which is the voltage between the first terminal Tb1 and the second terminal Tb2 of the power storage unit 11. The control unit 13 controls the operation of the boost circuit 12 based on the charging voltage Vb1 monitored by the voltage monitoring unit 14. This enables the power supply circuit 1a to appropriately charge the power storage unit 11.

[0061] Furthermore, in the power supply circuit 1a according to the second embodiment, the control unit 13 controls the operation of the boost circuit 12 so that the sum of the charging voltage Vb1 and the voltage of the power supply 2 is equal to or less than the upper limit of the allowable voltage of the load 3. This allows the power supply circuit 1a to supply a voltage equal to or less than the upper limit of the allowable voltage of the load 3 even when the power supply 2 and the power storage unit 11 are connected in series. Therefore, the power supply circuit 1a can stably output power to the load 3 without causing an overvoltage.

[0062] 9 , a drive system 4 according to the third embodiment includes a power supply circuit 1, a power supply 2, and a load 3. The power supply 2 is connected to a first terminal Ta1 of the power supply circuit 1. The load 3 is connected to a second terminal Ta2 of the power supply circuit 1.

[0063] The load 3 includes an operation determination unit 31. The operation determination unit 31 determines the operation state of the load 3. The operation determination unit 31 outputs an operation instruction SG1 indicating the determined operation state of the load 3 to the control unit 13 of the power supply circuit 1. The operation determination unit 31 and the control unit 13 are connected, for example, by wire, and the operation determination unit 31 outputs the operation instruction SG1 to the control unit 13. The operation determination unit 31 and the control unit 13 are capable of communicating, for example, wirelessly, and the operation determination unit 31 outputs the operation instruction SG1 to the control unit 13 via wireless communication.

[0064] The operation state of the load 3 includes information indicating the magnitude of the power consumption of the load 3. More specifically, the operation determination unit 31 determines whether the operation state of the load 3 is, for example, a first state in which the power consumption of the load 3 is large, a second state in which the power consumption of the load 3 is small or not consuming any power, or a third state in which the load 3 generates regenerative power. When the drive system 4 is used in the mobile object 101, the first state is, for example, a state in which the mobile object 101 starts moving, a state in which the mobile object 101 is accelerating, a state in which the mobile object 101 is climbing a slope, a state in which the mobile object 101 is traveling on a rough road, etc. Furthermore, the third state is, for example, a state in which the mobile object 101 is decelerating by regenerative braking, a state in which the mobile object 101 is descending a slope, etc. Furthermore, the second state is, for example, a state in which the mobile object 101 is stopped, a state in which the mobile object 101 is traveling at a constant speed on flat ground, etc.

[0065] When the control unit 13 receives the operation instruction SG1 from the operation determination unit 31, it changes the operation mode of the power supply circuit 1. That is, the control unit 13 controls the operation of the boost circuit 12 based on the determination result of the operation determination unit 31. For example, if the operation state of the load 3 indicated in the operation instruction SG1 is the first state, the control unit 13 switches the operation mode to the second power supply mode. This allows the power supply circuit 1 to supply power from the power storage unit 11 to the load 3 in the drive system 4 when the power consumption of the load 3 increases. Also, for example, if the operation state of the load 3 indicated in the operation instruction SG1 is the third state, the control unit 13 selects the first charging mode or the second charging mode as the operation mode. This makes it easier for the power supply circuit 1 to utilize regenerative power when regenerative power is generated from the load 3 in the drive system 4. Also, for example, if the operation state of the load 3 indicated in the operation instruction SG1 is the second operation and the operation mode of the power supply circuit 1 is the second power supply mode, the control unit 13 switches the operation mode of the power supply circuit 1 to the first power supply mode or the third power supply mode. This makes it possible to prevent unnecessary discharge from the power storage unit 11 of the power supply circuit 1 in the drive system 4 .

[0066] 2. Effects The drive system 4 according to the third embodiment includes a power supply circuit 1, a power supply 2 connected to a first terminal Ta1 of the power supply circuit 1, and a load 3 connected to a second terminal Ta2 of the power supply circuit 1. The load 3 includes an operation determination unit 31 that determines the operating state of the load 3. The control unit 13 controls the operation of the boost circuit 12 based on the determination result of the operation determination unit 31. As a result, the drive system 4 can control the operation of the boost circuit 12 based on, for example, whether the load 3 consumes or outputs power and the amount of power consumed by the load 3. Therefore, it is possible to appropriately operate the power supply circuit 1 in synchronization with changes in the operating state of the load 3.

[0067] (Other Modifications of the Embodiments) (1) In the power supply circuits 1 and 1a according to the first to third embodiments and the modifications, the power supply 2 is a secondary battery, but the power supply 2 may be any DC power supply, such as a primary battery, a solar cell, etc. Here, if the power supply 2 is a non-rechargeable power supply, the power supply circuits 1 and 1a do not operate in the second charging mode.

[0068] Similarly, the load 3 is not limited to a motor as long as it is a load that operates on DC power. If the load 3 is a load that does not generate regenerative power, the power supply circuits 1 and 1a do not operate in the first charging mode or the second charging mode.

[0069] (2) In the power supply circuits 1 and 1a according to the first to third embodiments and the modified example, the positive electrode of the power supply 2 is connected to the first terminal Ta1, the positive electrode of the load 3 is connected to the second terminal Ta2, and the negative electrode of the power supply 2 and the negative electrode of the load 3 are connected to the ground electrode 1z. However, for example, the negative electrode of the power supply 2 may be connected to the first terminal Ta1, the negative electrode of the load 3 may be connected to the second terminal Ta2, and the positive electrode of the power supply 2 and the positive electrode of the load 3 may be connected to the ground electrode 1z. In this case, the first end Tb1 of the power storage unit 11 becomes the negative electrode, and the second end Tb2 becomes the positive electrode. In this case, the voltage of a terminal that becomes negative when connected to the ground electrode 1z is evaluated by the absolute value of the potential difference from the ground potential, which is the potential of the ground electrode 1z. For example, the control unit 13 controls the boost circuit 12 so that the sum of the voltage of the power storage unit 11 and the electromotive force of the power supply 2 is equal to or less than the upper limit of the allowable voltage that can be applied to the load 3. Furthermore, when the boost circuit 12 is in an operating state, the absolute value of the potential difference between the potential of the second terminal Ta2 and the ground potential is higher than the absolute value of the potential difference between the potential of the second end Tb2 of the storage unit 11 and the ground potential.

[0070] (3) In the power supply circuit 1a according to the second embodiment, the voltage monitoring unit 14 monitors the charging voltage Vb1 of the power storage unit 11, but the voltage monitoring unit 14 may also monitor the voltage of each of the plurality of capacitors C1. This makes it possible to prevent overcharging of the other capacitors C1 when, for example, a particular capacitor C1 deteriorates and its capacity decreases, thereby enabling control to extend the life of the other capacitors C1.

[0071] (4) In the power supply circuit 1a according to the second embodiment, the control unit 13 determines whether to operate the boost circuit 12 based on the charging voltage Vb1 of the power storage unit 11, but the control unit 13 may also control the voltage between the second path R2 generated by the boost circuit 12 and the second end Tb2 of the power storage unit 11. For example, the control unit 13 may control the boost circuit 12 so that the voltage applied to the power storage unit 11 is equal to or higher than the charging voltage Vb1 and the sum of the voltage applied to the power storage unit 11 and the voltage of the power source 2 is less than the upper limit of the allowable voltage of the load 3.

[0072] (5) In the power supply circuits 1 and 1a according to the first and second embodiments and the modified examples, when power is supplied from the power supply circuit 1 and 1a to the load 3, the operation mode is selected based on the voltage Va1 at the first terminal Ta1 and the voltage of the power storage unit 11. However, the control unit 13 may detect the charge levels of the power supply 2 and the power storage unit 11 and select the operation mode based on the charge levels. For example, the control unit 13 may select the second power supply mode when the charge level of the power supply 2 is low. Furthermore, the control unit 13 may receive information about the power consumption of the load 3 from an external device (e.g., a control circuit of the mobile object 101, an acceleration sensor provided in the mobile object 101, etc.) and select the operation mode. For example, the control unit 13 may receive information about whether the mobile object 101 is accelerating from the control circuit of the mobile object 101, and select the second power supply mode when the mobile object 101 is accelerating.

[0073] (Aspect) A power supply circuit (1; 1a) according to a first aspect includes a first terminal (Ta1) connected to a power supply (2), a second terminal (Ta2) connected to a load (3), a first switch (SW1), a power storage unit (11), a boost circuit (12), a second switch (SW2), and a control unit (13). The first switch (SW1) is connected between the first terminal (Ta1) and the second terminal (Ta2). The power storage unit (11) has a first end (Tb1) and a second end (Tb2). The control unit (13) controls the boost circuit (12), the first switch (SW1), and the second switch (SW2). The first end (Tb1) of the power storage unit (11) is connected to a first path (R1) between the first terminal (Ta1) and the first switch (SW1). The boost circuit (12) is connected between a second path (R2) between the second terminal (Ta2) and the first switch (SW1) and a second end (Tb2) of the power storage unit (11). The second switch (SW2) is connected in parallel with the boost circuit (12) between the second path (R2) and the second end (Tb2) of the power storage unit (11).

[0074] According to the power supply circuit (1; 1a) of the above aspect, for example, when the load (3) temporarily requires a large current, it is possible to connect the power storage unit (11) between the power supply (2) and the load (3), thereby stabilizing the voltage supplied from the power supply circuit (1) to the load (3).

[0075] The power supply circuit (1a) according to the second aspect is the same as that of the first aspect, and further includes a voltage monitoring unit (14) that monitors a charging voltage (Vb1) that is a voltage between a first terminal (Tb1) and a second terminal (Tb2) of the storage unit (11). The control unit (13) controls the operation of the boost circuit (12) based on the charging voltage (Vb1) monitored by the voltage monitoring unit (14).

[0076] According to the power supply circuit (1a) of the above aspect, it is possible to appropriately charge the electricity storage unit (11).

[0077] In the power supply circuit (1a) according to the third aspect, in the second aspect, the control unit (13) controls the operation of the boost circuit (12) so that the sum of the charging voltage (Vb1) and the voltage of the power supply (2) does not exceed the upper limit of the allowable voltage of the load (3).

[0078] According to the power supply circuit (1a) of the above aspect, even when the power supply (2) and the power storage unit (11) are connected in series, a voltage equal to or lower than the upper limit of the allowable voltage of the load (3) can be supplied. Therefore, the power supply circuit (1a) can stably output power to the load (3) without causing an overvoltage.

[0079] In the power supply circuit (1; 1a) according to the fourth aspect, in any one of the first to third aspects, the power storage unit (11) includes a plurality of capacitors (C1) connected in series.

[0080] According to the power supply circuit (1a) of the above aspect, even when the power consumption of the load (3) changes suddenly, for example, fluctuations in the voltage of the power supplied from the power supply circuit (1) to the load (3) are less likely to occur.

[0081] In the power supply circuit (1; 1a) according to the fifth aspect, in any of the first to fourth aspects, the control unit (13) closes the first switch (SW1), opens the second switch (SW2), and operates the boost circuit (12) when charging the storage unit (11) using the power source (2). When supplying power from the storage unit (11) to the load (3), the control unit (13) opens the first switch (SW1) and closes the second switch (SW2).

[0082] According to the power supply circuit (1; 1a) of the above aspect, when the power supply (2) is used to charge the storage unit (11), the operation of the boost circuit (12) allows a voltage to be applied between the first terminal (Tb1) and the second terminal (Tb2) of the storage unit (11) to charge the storage unit (11). Furthermore, when power is supplied from the storage unit (11) to the load (3), the voltage of the power supplied from the power supply circuit (1) to the load (3) is stabilized by connecting the power supply (2) and the storage unit (11) in series.

[0083] In the power supply circuit (1; 1a) according to the sixth aspect, in the fifth aspect, the control unit (13) opens the first switch (SW1) when charging the storage unit (11) using the load (3).

[0084] According to the power supply circuit (1; 1a) of the above aspect, when the load (3) is used to charge the storage unit (11), the storage unit (11) can be charged based on the difference between the voltage of the power supplied from the load (3) to the second end (Tb2) of the storage unit (11) and the voltage of the power source (2).

[0085] In the power supply circuit (1; 1a) according to the seventh aspect, in the sixth aspect, the control unit (13) closes the second switch (SW2) when charging the storage unit (11) using the load (3).

[0086] According to the power supply circuit (1; 1a) of the above aspect, the power storage unit (11) is charged by the power supplied from the load (3). In addition, since the power storage unit (11) can be charged without using a boost circuit (12), it is possible to simplify the control of the power supply circuit (1; 1a).

[0087] In the power supply circuit (1; 1a) according to the eighth aspect, in the seventh aspect, when the storage unit (11) is charged using the load (3), the control unit (13) controls the operation of the boost circuit (12) so that a potential difference occurs between the second end (Tb2) of the storage unit (11) and the second path (R2), and opens the second switch (SW2).

[0088] According to the power supply circuit (1; 1a) of the above aspect, the power storage unit (11) is charged by the power supplied from the load (3). Furthermore, even if the voltage from the load (3) is low, the power storage unit (11) can be charged.

[0089] In the power supply circuit (1; 1a) according to the ninth aspect, in any of the first to eighth aspects, the boost circuit (12) cuts off at least the current in the direction from the second end (Tb2) of the storage unit (11) to the second path (R2) when the boost circuit (12) is controlled not to operate by the control unit (13).

[0090] According to the power supply circuit (1; 1a) of the above aspect, when the control unit (13) stops the boost circuit (12) and opens the second switch (SW2), it is possible to prevent charging and discharging of the power storage unit (11) and store power in the power storage unit (11).

[0091] A drive system (4) according to a tenth aspect includes a power supply circuit (1) according to any one of the first to ninth aspects, a power supply (2) connected to a first terminal (Ta1) of the power supply circuit (1), and a load (3) connected to a second terminal (Ta2) of the power supply circuit (1). The load (3) includes an operation determination unit (31) that determines the operating state of the load (3). A control unit (13) controls the operation of a boost circuit (12) based on the determination result of the operation determination unit (31).

[0092] According to the drive system (4) of the above aspect, for example, the operation of the boost circuit (12) can be controlled based on whether the load (3) consumes or outputs power and the magnitude of the power consumption of the load (3). Therefore, it is possible to operate the power supply circuit (1) appropriately in synchronization with changes in the operating state of the load (3).

[0093] REFERENCE SIGNS LIST 1, 1a Power supply circuit 2 Power supply 3 Load 31 Operation determination unit 4 Drive system 11 Power storage unit 12 Boost circuit 13 Control unit 14 Voltage monitoring unit Ta1 First terminal Ta2 Second terminal SW1 First switch SW2 Second switch R1 First path R2 Second path Tb1 First terminal Tb2 Second terminal C1 Capacitor Va1 Voltage Vb1 Charging voltage

Claims

1. A power supply circuit comprising: a first terminal connected to a power source; a second terminal connected to a load; a first switch connected between the first terminal and the second terminal; a power storage unit having a first end and a second end; a boost circuit; a second switch; and a control unit that controls the boost circuit, the first switch, and the second switch, wherein the first end of the power storage unit is connected to a first path between the first terminal and the first switch, the boost circuit is connected between a second path between the second terminal and the first switch and the second end of the power storage unit, and the second switch is connected in parallel with the boost circuit between the second path and the second end of the power storage unit.

2. The power supply circuit according to claim 1, further comprising a voltage monitoring unit that monitors a charging voltage, which is the voltage between the first end and the second end of the storage unit, and the control unit controls the operation of the boost circuit based on the charging voltage monitored by the voltage monitoring unit.

3. The power supply circuit according to claim 2, wherein the control unit controls the operation of the boost circuit so that the sum of the charging voltage and the voltage of the power supply is equal to or lower than an upper limit of an allowable voltage of the load.

4. The power supply circuit according to claim 1, wherein the power storage unit includes a plurality of capacitors connected in series.

5. The power supply circuit according to any one of claims 1 to 3, wherein the control unit, when charging the storage unit using the power supply, closes the first switch, opens the second switch, and operates the boost circuit, and when supplying power from the storage unit to the load, opens the first switch and closes the second switch.

6. The power supply circuit according to claim 5, wherein the control unit opens the first switch when the power storage unit is charged using the load.

7. The power supply circuit according to claim 6, wherein the control unit closes the second switch when the power storage unit is charged using the load.

8. The power supply circuit according to claim 6, wherein the control unit, when charging the storage unit using the load, controls the operation of the boost circuit so that a potential difference is generated between the second end of the storage unit and the second path, and opens the second switch.

9. A power supply circuit as claimed in any one of claims 1 to 3, wherein the boost circuit, when controlled not to operate by the control unit, at least cuts off current flowing from the second end of the storage unit to the second path.

10. A drive system comprising: a power supply circuit as claimed in claim 1; a power supply connected to the first terminal of the power supply circuit; and a load connected to the second terminal of the power supply circuit, wherein the load includes an operation determination unit that determines an operating state of the load, and the control unit controls the operation of the boost circuit based on a determination result of the operation determination unit.

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