Power supply system

Abstract

To provide a technique capable of appropriately charging two batteries having different voltages during full charging in a circuit in which the two batteries are connected in parallel.SOLUTION: A power supply system comprises: a first battery; a second battery having a voltage during full charging higher than a voltage during full charging of the first battery; a connection circuit configured to form a parallel circuit in which the first battery and the second battery are connected in parallel; a first relay provided in the connection circuit, and for conducting and cutting off energization from an external power supply to the first battery in the parallel circuit; a second relay provided in the connection circuit, and for conducting and cutting off energization from the external power supply to the second battery in the parallel circuit; and a controller capable of executing charging processing for charging the first battery and the second battery by the external power supply. The charging processing includes processing for cutting off the first relay to cut off the energization from the external power supply to the first battery while continuing charging the second battery when the first battery reaches full charge.SELECTED DRAWING: Figure 7

Description

Technical Field

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

Background Art

[0002] Patent Document 1 discloses a power supply device that charges a first battery and a second battery in a parallel circuit in which the first battery and the second battery are connected in parallel. In Patent Document 1, even when the charging rates of the first battery and the second battery are different, the first battery and the second battery can be appropriately charged while suppressing the circulating current flowing from one of the first battery and the second battery to the other is described.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 1, the first battery and the second battery have the same discharge capacity. That is, a situation where the voltages at full charge of the first battery and the second battery are equal and the voltages at full charge of the first battery and the second battery are different is not assumed. For this reason, in the technology of Patent Document 1, in such a situation, there are problems such that the battery with a higher voltage at full charge is not fully charged, or the battery with a lower voltage at full charge is overcharged. This specification provides a technology capable of appropriately charging two batteries in a circuit in which two batteries with different voltages at full charge are connected in parallel.

Means for Solving the Problems

[0005] In a first aspect disclosed in this specification, a power supply system may include a first battery rechargeable by an external power source, a second battery rechargeable by the external power source and having a voltage at full charge higher than that of the first battery at full charge, a connection circuit configured to form a parallel circuit in which the first battery and the second battery are connected in parallel, a first relay provided in the connection circuit and configured to conduct and cut off energization from the external power source to the first battery in the parallel circuit, a second relay provided in the connection circuit and configured to conduct and cut off energization from the external power source to the second battery in the parallel circuit, and a control device capable of executing a charging process for charging the first battery and the second battery by the external power source. The charging process may include a process of cutting off the first relay to cut off energization from the external power source to the first battery while continuing to charge the second battery when the first battery reaches full charge.

[0006] In the above configuration, when the first battery, whose voltage at full charge is lower than that of the second battery, reaches full charge, the charging of the first battery is stopped and the charging of the second battery is continued by cutting off the first relay. Thereby, both the first battery and the second battery can be appropriately charged to full charge.

[0007] In a second aspect disclosed in this specification, in the above first aspect, the first relay may include a non-contact relay. In a third aspect disclosed in this specification, in the above second aspect, the non-contact relay may include a semiconductor switching element. In a fourth aspect disclosed in this specification, in the above third aspect, the non-contact relay may include a first diode connected in anti-parallel with the semiconductor switching element. The first diode may be provided in a direction that allows discharge of the first battery and prohibits charging of the first battery.

[0008] In the above configuration, disconnection and welding of the first relay can be suppressed.

[0009] In the fifth aspect disclosed in this specification, in any one of the first to fourth aspects, the connection circuit in the parallel circuit may include a second diode connected in series with the second battery. The second diode may be provided in a direction that prohibits discharge of the second battery and allows charging of the second battery.

[0010] With the above configuration, in the parallel circuit, it is possible to suppress the flow of a circulating current from the second battery to the first battery.

[0011] In the sixth aspect disclosed in this specification, in any one of the first to fifth aspects, the charging process may include a process of charging the first battery by conducting the first relay before the process of interrupting the power supply to the first battery, and a process of starting the charging of the second battery by conducting the second relay when the voltage of the first battery reaches the voltage of the second battery.

[0012] With the above configuration, the charging of the first battery is started before the second battery. Generally, a battery with a lower full-charge voltage has a lower voltage before charging. Thus, by charging the first battery first, it is not necessary to measure the voltages of the first battery and the second battery, and the process can be simplified.

[0013] In the seventh aspect disclosed in this specification, in the sixth aspect, it may further include a charging relay that conducts and interrupts the power supply from the external power source to the connection circuit, and a first capacitor connected in parallel with the first battery and the second battery in the parallel circuit. The charging process may include a process of pre-charging the first capacitor with the first battery by conducting the first relay in a state where the charging relay is interrupted before the process of charging the first battery, and the charging relay may be conducted in the process of charging the first battery.

[0014] In the above configuration, by pre-charging the first capacitor using the first battery, the inrush current from the external power supply to the connection circuit can be suppressed, and the charging relay can be prevented from being loaded.

[0015] In an eighth aspect disclosed in this specification, in any one of the first to seventh aspects, the connection circuit in the parallel circuit may include a third diode connected in series with the first battery. The third diode may be provided in a direction that prohibits the discharge of the first battery and allows the charging of the first battery.

[0016] In the above configuration, in the parallel circuit, it is possible to suppress the flow of a circulating current from the first battery to the second battery.

[0017] In a ninth aspect disclosed in this specification, in any one of the first to eighth aspects, the control device may be capable of executing a power supply process of supplying power from the connection circuit to an external load by the first battery and the second battery. The power supply process may include a process of blocking the first relay and conducting the second relay to supply power from the second battery to the external load.

[0018] In the above configuration, by blocking the first relay, a circulating current from the second battery to the first battery can be suppressed, and by conducting the second relay, power can be supplied to the external load using only the second battery.

[0019] In a tenth aspect disclosed in this specification, in the ninth aspect described above, it may further include a power supply relay that conducts and interrupts power supply from the connection circuit to the external load, and a second capacitor connected in parallel with the first battery and the second battery in the parallel circuit. The power supply process may include a process of interrupting the first relay and conducting the second relay in a state where the power supply relay is interrupted before the process of supplying power from the second battery to the external load, and pre-charging the second capacitor with the second battery. The power supply relay may be conducted in the process of supplying power from the second battery to the external load.

[0020] In the above configuration, by pre-charging the second capacitor using the second battery, it is possible to suppress an excessive current from flowing from the back connection circuit to the external load, and suppress a load from being applied to the power supply relay.

[0021] In an eleventh aspect disclosed in this specification, in the tenth aspect described above, the first relay may include a semiconductor switching element and a first diode connected in anti-parallel with the semiconductor switching element. The first diode may be provided in a direction that allows discharge of the first battery and prohibits charging of the first battery.

[0022] In the above configuration, when power is being supplied to the external load by the second battery, when the voltages of the first battery and the second battery become substantially equal, it is possible to supply power to the external load from both the first battery and the second battery while suppressing a circulating current from flowing between the first battery and the second battery.

[0023] In a twelfth aspect disclosed in this specification, in any one of the first to eleventh aspects described above, the connection circuit may be configured to selectively form the parallel circuit and a series circuit in which the first battery and the second battery are connected in series.

[0024] In the above configuration, in the parallel circuit, the first battery and the second battery can be appropriately charged, and in the series circuit, a large amount of power can be supplied to the outside.

Brief Description of the Drawings

[0025]

Figure 1

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Figure 7

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Figure 13

Figure 14

Modes for Carrying Out the Invention

[0026] (Example 1) FIG. 1 shows the power supply system 1 of Example 1. The power supply system 1 is mounted on the vehicle 100 and supplies power to a load 3 (for example, a PCU (Power Control Unit), etc.) provided in the vehicle 100. The vehicle 100 is an electric vehicle such as, for example, a battery electric vehicle (BEV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), or a fuel cell electric vehicle (FCEV).

[0027] As shown in FIG. 1, the power supply system 1 includes a first battery 21, a second battery 22, a connection circuit 24, a control device 26, and a first capacitor 28.

[0028] The first battery 21 and the second battery 22 are storage batteries capable of charging and discharging DC power, and each has a plurality of battery cells arranged in a stacked manner. Each battery cell is composed of a secondary battery capable of repeatedly charging and discharging, and is composed of, for example, a lithium ion battery, a all-solid-state battery, a nickel metal hydride battery, etc. The number of battery cells of the first battery 21 and the second battery 22 is not particularly limited, but the voltage at full charge of the second battery 22 is higher than the voltage at full charge of the first battery 21. Specifically, in this embodiment, the number of battery cells of the second battery 22 is larger than the number of battery cells of the first battery 21. The voltage at full charge of the first battery 21 is about 390V, and the voltage at full charge of the second battery 22 is about 410V. However, the voltages at full charge of the first battery 21 and the second battery 22 may be appropriately changed according to the required output voltage. The first battery 21 and the second battery 22 are respectively provided between the high-potential wiring 12 (the wiring connected to the positive electrodes of the first battery 21 and the second battery 22) and the low-potential wiring 14 (the wiring connected to the negative electrodes of the first battery 21 and the second battery 22) of the power supply system 1.

[0029] The connection circuit 24 includes a first switching element 30, a second switching element 32, a third switching element 34, a fourth switching element 36, a first changeover relay 38, a second changeover relay 40, and a third changeover relay 42. The control device 26 controls the operations of the switching elements 30, 32, 34, 36 and the changeover relays 38 to 42. In this embodiment, the switching elements 30, 32, 34, 36 are n-channel type MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors).

[0030] The first switching element 30, the second switching element 32, and the first changeover relay 38 are connected in series between the high potential wiring 12 and the positive electrode of the first battery 21. The drain of the first switching element 30 is connected to the high potential wiring 12, the source of the first switching element 30 is connected to the source of the second switching element 32, and the drain of the second switching element 32 is connected to the positive electrode of the first battery 21 via the first changeover relay 38. That is, the first switching element 30 is provided in a direction to conduct and cut off the energization from the high potential wiring 12 to the first battery 21. The second switching element 32 is provided in a direction to conduct and cut off the energization from the first battery 21 to the high potential wiring 12. Further, the first switching element 30 and the second switching element 32 each have diodes 31, 33 connected in antiparallel thereto. The anode of the diode 31 is connected to the source of the first switching element 30, and the cathode is connected to the drain of the first switching element 30. That is, the diode 31 is provided in a direction to allow the discharge of the first battery 21 and prohibit the charging of the first battery 21. The anode of the diode 33 is connected to the source of the second switching element 32, and the cathode is connected to the drain of the second switching element 32. That is, the diode 33 is provided in a direction to allow the charging of the first battery 21 and prohibit the discharge of the first battery 21.

[0031] The third switching element 34, the fourth switching element 36, and the second changeover relay 40 are connected in series between the low-potential wiring 14 and the negative electrode of the second battery 22. The source of the third switching element 34 is connected to the low-potential wiring 14, the drain of the third switching element 34 is connected to the drain of the fourth switching element 36, and the source of the fourth switching element 36 is connected to the negative electrode of the second battery 22 via the second changeover relay 40. That is, the third switching element 34 is provided in a direction to conduct and cut off the energization from the second battery 22 to the low-potential wiring 14 (in other words, the energization from the high-potential wiring 12 to the second battery 22). The fourth switching element 36 is provided in a direction to conduct and cut off the energization from the low-potential wiring 14 to the second battery 22 (in other words, the energization from the second battery 22 to the high-potential wiring 12). Further, the third switching element 34 and the fourth switching element 36 each have diodes 35 and 37 connected in anti-parallel thereto. The anode of the diode 35 is connected to the source of the third switching element 34, and the cathode is connected to the drain of the third switching element 34. That is, the diode 35 is provided in a direction to allow the discharge of the second battery 22 and prohibit the charging of the second battery 22. The anode of the diode 37 is connected to the source of the fourth switching element 36, and the cathode is connected to the drain of the fourth switching element 36. That is, the diode 37 is provided in a direction to allow the charging of the second battery 22 and prohibit the discharge of the second battery 22.

[0032] The third switching relay 42 is provided between the wiring connecting the first battery 21 and the first switching relay 38 and the wiring connecting the second battery 22 and the second switching relay 40. The first switching relay 38, the second switching relay 40, and the third switching relay 42 are provided to switch the connection mode between the first battery 21 and the second battery 22. That is, the control device 26 is configured to selectively form the series circuit shown in FIG. 3 and the parallel circuit shown in FIG. 4 or the like by controlling the opening and closing of each switching relay 38 to 42. Specifically, when the control device 26 opens the first switching relay 38 and the second switching relay 40 and closes the third switching relay 42, the connection circuit 24 forms the series circuit shown in FIG. 3. In this series circuit, the first battery 21 and the second battery 22 are connected in series. On the other hand, when the control device 26 closes the first switching relay 38 and the second switching relay 40 and opens the third switching relay 42, the connection circuit 24 forms the parallel circuit shown in FIG. 4 or the like. In this parallel circuit, the first battery 21 and the second battery 22 are connected in parallel.

[0033] The first capacitor 28 is provided between the high-potential wiring 12 and the low-potential wiring 14. The first capacitor 28 is connected in parallel with the first battery 21 and the second battery 22.

[0034] The power supply system 1 further includes a charging relay 52 and a discharging relay 54. The charging relay 52 is provided between the connection circuit 24 and the charging inlet 50 of the vehicle 100. The charging relay 52 conducts and interrupts the energization between the connection circuit 24 and the charging inlet 50. The charging inlet 50 is configured to be detachable from an external power source 60 (see FIG. 4). The charging inlet 50 is electrically connected to the external power source 60 via a connector, for example, when charging the first battery 21 and the second battery 22. Thereby, power is input from the external power source 60 to the charging inlet 50. In this case, the control device 26 forms a parallel circuit in the connection circuit 24 and closes the charging relay 52. As a result, the first battery 21 and the second battery 22 are connected in parallel to the charging inlet 50. Thereby, the first battery 21 and the second battery 22 can be charged at a relatively low voltage. The external power source 60 is, for example, a household commercial power source, a power source that supplies power such as a charging stand.

[0035] The discharging relay 54 is provided between the connection circuit 24 and the load 3 of the vehicle 100. The discharging relay 54 conducts and interrupts the energization between the connection circuit 24 and the load 3. When the vehicle 100 is running, the control device 26 forms a series circuit in the connection circuit 24 and closes the discharging relay 54. Thereby, the first battery 21 and the second battery 22 are connected in series to the load 3, and power can be supplied to the load 3 at a relatively high voltage.

[0036] The control device 26 monitors the state of charge (SOC) of the first battery 21 and the state of charge of the second battery 22, respectively. The method for monitoring the state of charge is not particularly limited. For example, the control device 26 can calculate the state of charge of the first battery 21 by integrating the charging current and discharging current of the first battery 21 over time. The same applies to the second battery 22. The control device 26 can estimate the voltages of the first battery 21 and the second battery 22 based on the state of charge of the first battery 21 and the state of charge of the second battery 22, respectively. Note that the voltages of the first battery 21 and the second battery 22 may be directly detected by a voltage sensor.

[0037] Next, the operation of the power supply system 1 will be described. FIG. 2 is a flowchart showing a charging process for charging the first battery 21 and the second battery 22 by the external power supply 60. The process shown in FIG. 2 starts in a state where the connection circuit 24 forms a series circuit. Specifically, as shown in FIG. 3, the first switching relay 38, the second switching relay 40, and the charging relay 52 are open, and the third switching relay 42 and the discharge relay 54 are closed. Also, each of the switching elements 30, 32, 34, 36 is off. That is, in this state, power can be supplied from the first battery 21 and the second battery 22 to the load 3, and current flows as indicated by the dashed arrow. In the following drawings, similar to FIG. 3, the flow of current in the power supply system 1 is indicated by a dashed arrow. In this embodiment, it is assumed that at the start of the process in FIG. 2, the voltage of the first battery 21 is about 190V and the voltage of the second battery 22 is about 200V.

[0038] First, as shown in FIG. 2, in S10, it is determined whether or not the charging of the first battery 21 and the second battery 22 has started. For example, when the voltage on the charging inlet 50 side is higher than the voltage on the connection circuit 24 side, the control device 26 determines that the connector of the external power supply 60 is connected to the charging inlet 50 and charging has started.

[0039] When the control device 26 determines that the charging of the first battery 21 and the second battery 22 has started (YES in S10), in S12, a parallel circuit is formed in the connection circuit 24. Specifically, the control device 26 opens the discharge relay 54, opens the third switching relay 42, and closes the first switching relay 38 and the second switching relay 40. As a result, as shown in FIG. 4, the connection circuit 24 is switched from a series circuit to a parallel circuit.

[0040] Next, in S14, the control device 26 pre-charges the first capacitor 28. Specifically, the control device 26 turns on the second switching element 32 and also turns on the first switching element 30 and the third switching element 34. While the second switching element 32 is on, the fourth switching element 36 is off, so the discharge of the first battery 21 is permitted and the discharge of the second battery 22 is prohibited. For this reason, as shown in FIG. 4, the first capacitor 28 is pre-charged by the first battery 21 without a circulating current flowing from the second battery 22 to the first battery 21. Thereby, the first capacitor 28 is charged up to the voltage of the first battery 21 (i.e., approximately 190V).

[0041] When the pre-charge of the first capacitor 28 is completed, in S16, the control device 26 turns off the second switching element 32 and closes the charging relay 52. Thereby, the connection circuit 24 and the external power supply 60 are electrically connected. The voltage of the first battery 21 at the start of charging (approximately 190V) is lower than the voltage of the second battery 22 at the start of charging (approximately 200V). For this reason, when S16 is executed, power is supplied only to the first battery 21. That is, as shown in FIG. 5, only the charging of the first battery 21 is started without current flowing through the second battery 22. Note that in FIGS. 5 to 8, the illustration of the load 3 and the discharge relay 54 is omitted.

[0042] Thereafter, in S18, the control device 26 monitors whether current is flowing through the second battery 22. In other words, the control device 26 monitors whether the second battery 22 is being charged. As described above, in S16, current flows only through the first battery 21, and the charging of the second battery 22 is not started until the voltage of the first battery 21 reaches the voltage of the second battery 22. When the voltage of the first battery 21 is charged up to the voltage of the second battery 22, as shown in FIG. 6, current also starts to flow through the second battery 22. When the control device 26 determines that current is flowing through the second battery 22 (YES in S18), it proceeds to S20.

[0043] In S20, the control device 26 outputs a command to increase the current supplied to the connection circuit 24 to the external power supply 60. As a result, charging of the first battery 21 and the second battery 22 continues while maintaining the charging rates of the first battery 21 and the second battery 22.

[0044] Thereafter, in S22, the control device 26 determines whether the first battery 21 has reached full charge. For example, the control device 26 calculates the charge rate of the first battery 21 and estimates the voltage of the first battery 21 based on the calculated charge rate. When the control device 26 determines that the first battery 21 has reached full charge (YES in S22), it proceeds to S24.

[0045] In S24, the control device 26 cuts off the power supply from the external power supply 60 to the first battery 21. Specifically, after turning off the first switching element 30, the control device 26 opens the first switching relay 38. As a result, charging of the first battery 21 stops. On the other hand, since the third switching element 34 is on, as shown in FIG. 7, charging of the second battery 22 continues.

[0046] Thereafter, in S26, the control device 26 determines whether the second battery 22 has reached full charge. Whether the second battery 22 has reached full charge can be determined in the same manner as in S22.

[0047] When the control device 26 determines that the second battery 22 has reached full charge (YES in S26), in S28, the power supply from the external power supply 60 to the second battery 22 is cut off. Specifically, after turning off the third switching element 34, the control device 26 opens the second switching relay 40 and the charging relay 52. As a result, as shown in FIG. 8, the power supply from the external power supply 60 to the second battery 22 (connection circuit 24) is cut off. When the control device 26 executes S28, it ends a series of processes.

[0048] As described above, in the power supply system 1 of this embodiment, when the first battery 21, whose voltage at full charge is lower than that of the second battery 22, reaches full charge (YES in S24), by turning off the first switching element 30 (S26), the charging of the first battery 21 is stopped and the charging of the second battery 22 is continued. Thereby, both the first battery 21 and the second battery 22 can be appropriately charged up to full charge.

[0049] Also, in the power supply system 1 of this embodiment, the fourth switching element 36 connected in series with the second battery 22 includes a diode 37. Since the diode 37 prohibits the discharge of the second battery 22 and is provided in a direction that allows the charging of the second battery 22, when the connection circuit 24 forms a parallel circuit, the flow of a circulating current from the second battery 22 to the first battery 21 can be suppressed.

[0050] Also, in the power supply system 1 of this embodiment, before closing the charging relay 52, both the first switching element 30 and the third switching element 34 are turned on (S14). Thereby, when the charging relay 52 is closed, current starts to flow first to the battery with a lower voltage before charging (the first battery 21 in the embodiment). Thus, in this embodiment, without measuring the voltages of the first battery 21 and the second battery 22, the charging process is executed so as to charge the battery with a lower voltage first, so that the process can be simplified. Also, when the first battery 21 is charged up to the voltage of the second battery 22, current also starts to flow to the second battery 22, so that both the first battery 21 and the second battery 22 can be charged.

[0051] Also, in the power supply system 1 of this embodiment, after pre-charging the first capacitor 28 using the first battery 21 (S14), the charging relay 52 is closed (S16). Thereby, the inrush current from the external power supply 60 to the connection circuit 24 can be suppressed, and the charging relay 52 can be prevented from being loaded.

[0052] Also, in the power supply system 1 of this embodiment, the second switching element 32 connected in series with the first battery 21 includes a diode 33. Since the diode 33 is provided in a direction that prohibits the discharge of the first battery 21 and allows the charging of the first battery 21, when the connection circuit 24 forms a parallel circuit, it is possible to suppress the flow of a circulating current from the first battery 21 to the second battery 22.

[0053] (Embodiment 2) In Embodiment 2, in addition to the charging process of Embodiment 1, the power supply system 1 can execute a power supply process of supplying power to an external load 62 (for example, an electric device or the like) by the first battery 21 and the second battery 22. As shown in FIG. 9, the power supply system 1 of Embodiment 2 includes a second capacitor 29 and a power supply relay 56. In FIGS. 9 and 11 to 14, the illustration of the configuration other than the first battery 21, the second battery 22, each switching element 30, 32, 34, 36, and each switching relay 38 to 42 in FIG. 1 is omitted.

[0054] As shown in FIG. 9, the second capacitor 29 is provided between the high-potential wiring 12 and the low-potential wiring 14. The second capacitor 29 is connected in parallel with the first battery 21 and the second battery 22.

[0055] The power supply relay 56 is provided between the connection circuit 24 and the vehicle power supply outlet 58. The power supply relay 56 conducts and cuts off the energization between the connection circuit 24 and the power supply outlet 58. The power supply outlet 58 is configured to be detachable from the external load 62 (see FIG. 11). The power supply outlet 58 is electrically connected to the external load 62 via a connector, for example, when supplying power to the external load 62. Thereby, the power input from the first battery 21 and / or the second battery 22 to the power supply outlet 58 is supplied to the external load 62.

[0056] Next, the operation of the power supply system 1 will be described. FIG. 10 is a flowchart showing a power supply process in which the first battery 21 and the second battery 22 supply power to the external load 62. The process shown in FIG. 10 starts in a state where the connection circuit 24 forms a series circuit, similar to FIG. 2. At the start of the process in FIG. 10, it is assumed that both the first battery 21 and the second battery 22 are fully charged. That is, the voltage of the first battery 21 is about 390V, and the voltage of the second battery 22 is about 410V.

[0057] First, as shown in FIG. 10, in S40, the control device 26 determines whether power supply by the first battery 21 and the second battery 22 has started. For example, when the voltage on the power supply outlet 58 side is lower than the voltage on the connection circuit 24 side, the control device 26 determines that the connector of the external load 62 is connected to the power supply outlet 58 and power supply has started.

[0058] When the control device 26 determines that power supply by the first battery 21 and the second battery 22 has started (YES in S40), in S42, it causes a parallel circuit to be formed in the connection circuit 24. Specifically, the control device 26 opens the third switching relay 42 and closes the first switching relay 38 and the second switching relay 40. As a result, similar to FIG. 4, the connection circuit 24 is switched from a series circuit to a parallel circuit.

[0059] Next, in S44, the control device 26 pre-charges the second capacitor 29. Specifically, the control device 26 turns on the third switching element 34 and the fourth switching element 36. While the fourth switching element 36 is on and the second switching element 32 is off, discharge of the second battery 22 is permitted and discharge of the first battery 21 is prohibited. Also, since the first switching element 30 is off, charging of the first battery 21 is prohibited. Therefore, as shown in FIG. 11, the second capacitor 29 is pre-charged by the second battery 22 without a circulating current flowing from the second battery 22 to the first battery 21. As a result, the second capacitor 29 is charged up to the voltage of the second battery 22 (that is, about 410V).

[0060] When the pre-charge of the second capacitor 29 is completed, at S46, the control device 26 turns on the second switching element 32, turns off the third switching element 34, and closes the power supply relay 56. As a result, the connection circuit 24 and the external load 62 are electrically connected. At this time, since the fourth switching element 36 is on, the discharge of the second battery 22 is permitted. Since the voltage of the second battery 22 is higher than the voltage of the first battery, when S46 is executed, power is supplied to the external load 62 only from the second battery 22. That is, as shown in FIG. 12, power supply is started only by the second battery 22 without current flowing from the first battery 21.

[0061] Since the second switching element 32 is on, the discharge of the first battery 21 is permitted. Therefore, after S46 is executed, when power is being supplied by the second battery 22 and the voltage of the second battery 22 drops to the voltage of the first battery 21, as shown in FIG. 13, power also starts to be supplied to the external load 62 from the first battery 21. That is, power supply to the external load 62 is started from both the first battery 21 and the second battery 22.

[0062] At S48, the control device 26 determines whether or not the power supply has stopped. For example, when the control device 26 receives that the connection between the external load 62 and the power supply outlet 58 has been released, it determines that the power supply has stopped. When the control device 26 determines that the power supply has stopped (YES at S48), at S50, it disconnects the connection between the connection circuit 24 and the external load 62. Specifically, the control device 26 turns off the second switching element 32 and the fourth switching element 36, and then opens the first switching relay 38, the second switching relay 40, and the power supply relay 56. As a result, as shown in FIG. 14, the energization from the first battery 21 and the second battery 22 to the external load 62 is interrupted. When the control device 26 executes S50, it ends a series of processes.

[0063] As described above, in the power supply system 1 of the present embodiment, by turning off the first switching element 30, while suppressing the circulating current flowing from the second battery 22 to the first battery 21, the third switching element 34 and the fourth switching element 36 allow the second battery 22 to discharge, so that power can be supplied to the external load 62 using only the second battery 22 (S46).

[0064] Also, in the power supply system 1 of the present embodiment, after pre-charging the second capacitor 29 using the second battery 22 (S44), the power supply relay 56 is closed (S46). Thereby, it is possible to suppress an excessive current from flowing from the connection circuit 24 to the external load 62, and to suppress a load being applied to the power supply relay 56.

[0065] Also, in the power supply system 1 of the present embodiment, the first switching element 30 connected in series with the first battery 21 includes a diode 31. The diode 31 is provided in a direction that allows the first battery 21 to discharge. Therefore, when power is being supplied to the external load 62 by the second battery 22, if the voltage of the second battery 22 drops to the voltage of the first battery 21, it is possible to suppress a circulating current from flowing between the first battery 21 and the second battery 22, and to supply power to the external load 62 from both the first battery 21 and the second battery 22.

[0066] (Corresponding relationship) The first switching element 30 and the third switching element 34 are examples of the "first relay" and the "second relay", respectively. The diode 31, the diode 37, and the diode 33 are examples of the "first diode", the "second diode", and the "third diode", respectively.

[0067] Although the embodiments have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

[0068] (Modification example) In the above-described embodiment, as an example in which the voltage at full charge of the second battery 22 is higher than the voltage at full charge of the first battery 21, the case where the number of battery cells of the second battery 22 is larger than the number of battery cells of the first battery 21 has been described. However, for example, even in the case of two batteries having the same number of battery cells, the voltages at full charge may be different due to deterioration or the like. Even in such a case, the technology disclosed in this specification can be applied.

[0069] Further, each of the switching elements 30, 32, 34, 36 may be a non-contact relay different from a semiconductor switching element, or may be a contact relay. Also, in the charging process of the first embodiment, a diode may be used instead of the second switching element 32 and the fourth switching element 36.

[0070] Note that each of the switching elements 30, 32, 34, 36 may not be provided. In this modification, the first switching relay 38 is an example of the "first relay", and the second switching relay 40 is an example of the "second relay".

[0071] Also, the number of batteries included in the power supply system 1 may not be two, and may be three or more.

[0072] The technical elements described in this specification or the 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. Also, the technology illustrated in this specification or the drawings achieves a plurality of purposes simultaneously, and has technical utility by achieving one of those purposes itself.

Description of Reference Numerals

[0073] 1: Power supply system, 3: Load, 12: High-potential wiring, 14: Low-potential wiring, 21: First battery, 22: Second battery, 24: Connection circuit, 26: Control device, 28: First capacitor, 29: Second capacitor, 30: First switching element, 31: Diode, 32: Second switching element, 33: Diode, 34: Third switching element, 35: Diode, 36: Fourth switching element, 37: Diode, 38: First changeover relay, 40: Second changeover relay, 42: Third changeover relay, 50: Charging inlet, 52: Charging relay, 54: Discharging relay, 56: Power supply relay, 58: Power supply outlet, 60: External power source, 62: External load, 100: Vehicle

Claims

1. A first battery rechargeable by an external power source, A second battery rechargeable by the external power source and having a voltage at full charge higher than the voltage of the first battery at full charge, A connection circuit configured to form a parallel circuit in which the first battery and the second battery are connected in parallel, A first relay provided in the connection circuit and configured to conduct and cut off energization from the external power source to the first battery in the parallel circuit, A second relay provided in the connection circuit and configured to conduct and cut off energization from the external power source to the second battery in the parallel circuit, A control device capable of executing a charging process for charging the first battery and the second battery by the external power source, Comprising, The charging process is, When the first battery reaches full charge, including a process of cutting off the first relay to cut off energization from the external power source to the first battery while continuing to charge the second battery, A power supply system.

2. The first relay includes a non-contact relay, and the power supply system according to claim 1.

3. The non-contact relay includes a semiconductor switching element, and the power supply system according to claim 2.

4. The non-contact relay includes a first diode connected in anti-parallel with the semiconductor switching element, The first diode is provided in a direction that allows discharge of the first battery and prohibits charging of the first battery, and the power supply system according to claim 3.

5. The connection circuit includes a second diode connected in series with the second battery in the parallel circuit, The second diode is provided in a direction that prohibits discharge of the second battery and allows charging of the second battery, and the power supply system according to claim 1.

6. Before the process of cutting off energization to the first battery, the charging process includes, A process of turning on the first relay to charge the first battery, When the voltage of the first battery reaches the voltage of the second battery, a process of starting to charge the second battery with the second relay turned on, and the power supply system according to claim 1.

7. A charging relay for conducting and cutting off energization from the external power source to the connection circuit, A first capacitor connected in parallel with the first battery and the second battery in the parallel circuit, The charging process includes a process of pre-charging the first capacitor with the first battery by turning on the first relay while turning off the charging relay before the process of charging the first battery. Turning on the charging relay in the process of charging the first battery. The power supply system according to claim 6.

8. The connection circuit includes a third diode connected in series with the first battery in the parallel circuit. The third diode is provided in a direction that prohibits discharge of the first battery and allows charging of the first battery. The power supply system according to claim 1.

9. The control device is capable of executing a power supply process of supplying power from the connection circuit to an external load by the first battery and the second battery. The power supply process is as follows. The power supply process includes a process of turning off the first relay and turning on the second relay to supply power from the second battery to the external load. The power supply system according to claim 1.

10. A power supply relay for conducting and interrupting energization from the connection circuit to the external load, and a second capacitor connected in parallel with the first battery and the second battery in the parallel circuit. The power supply system according to claim 9. The power supply process is as follows. Before the process of supplying power from the second battery to the external load, the first relay is turned off and the second relay is turned on while the power supply relay is turned off to pre-charge the second capacitor with the second battery. Turning on the power supply relay in the process of supplying power from the second battery to the external load. The power supply system according to claim 9.

11. The first relay includes a semiconductor switching element and a first diode connected in anti-parallel with the semiconductor switching element. The first diode is provided in a direction that allows discharge of the first battery and prohibits charging of the first battery. The power supply system according to claim 10.

12. The connection circuit is configured to selectively form the parallel circuit and a series circuit in which the first battery and the second battery are connected in series. The power supply system according to any one of claims 1 to 11.

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