JP2017093226A - Power supply system for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a voltage conversion loss at the time of charging and discharging of an auxiliary machine battery.SOLUTION: A power supply system 100 includes a main battery 10, a DC/DC converter 21, and an auxiliary machine battery 23 having a voltage lower than a target output voltage of the DC/DC converter 21, and supplies electric power of the main battery 10 from the DC/DC converter 21 to an auxiliary machine load 22. The power supply system 100 has: a discharge circuit 40 turning a first switching element 91 ON and supplying the electric power from the auxiliary machine battery 23 to the auxiliary machine load 22 when an output voltage of the DC/DC converter 21 is lower than the voltage of the auxiliary machine battery 23; and a charging circuit 30 turning a second switching element 92 ON/OFF, stepping down the output voltage of the DC/DC converter 21, and performing charging to the auxiliary machine battery 23 when residual capacity of the auxiliary machine battery 23 is equal to a predetermined threshold value or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a structure of a vehicle power supply system.

  In recent years, electric vehicles such as hybrid vehicles that use an engine and a motor as driving sources and electric vehicles that are driven by a motor are often used. Such an electric vehicle is equipped with a main battery for supplying driving power to the motor. In addition, for example, a power steering device, a hydraulic device, a window opening / closing device, a main battery cooling device and the like, which are driven by a small motor, and many auxiliary equipment such as a lighting device are mounted on the electric vehicle. ing. The driving power of these auxiliary machines is supplied from an auxiliary battery having a lower voltage than the main battery. Conventionally, auxiliary battery is often charged by a power generator such as an alternator.

  In such an electric vehicle, when charging / discharging to the main battery is repeated as the vehicle travels, the main battery may deteriorate and input / output power of the main battery may be limited. When the input / output power of the main battery is limited, there is a problem in that required power cannot be output and drivability is lowered, or regenerative power cannot be sufficiently charged in the main battery and energy efficiency is lowered.

  Therefore, as shown in FIG. 16, a main battery 201 and an auxiliary battery 205 that supply electric power to a motor generator 203 for driving a vehicle via an inverter 202 are connected in parallel via a bidirectional DC / DC converter 204. A method has been proposed in which the auxiliary battery 205 compensates for the shortage of output power when the main battery 201 deteriorates, and energy efficiency is improved by allowing sufficient power regeneration (see, for example, Patent Document 1). ). The power supply system 200 shown in FIG. 16 continuously supplies power from the auxiliary battery 205 to the auxiliary load 206. When the remaining capacity (SOC) of the auxiliary battery 205 decreases, the bidirectional DC / DC converter 204 compensates. The battery 205 is charged.

Japanese Patent Laid-Open No. 2015-76958

  By the way, a lead storage battery is often used for the auxiliary battery. The lead-acid battery is a lithium-ion battery that is lighter and requires little maintenance because of its disadvantages such as being replaced in a few years and requiring maintenance such as checking the battery fluid and being heavy. There is an increasing demand for configuring auxiliary batteries.

  However, unlike a lead-acid battery having a substantially constant voltage, the voltage of the lithium ion battery changes depending on the remaining capacity (SOC). Therefore, as shown in FIG. 16, the auxiliary battery 205 continuously supplies power to the auxiliary load 206, and when the remaining capacity (SOC) of the auxiliary battery 205 decreases, the bi-directional DC / DC converter 204 supplies the auxiliary machine. In the power supply system 200 of the prior art that charges the battery 205, when the auxiliary battery 205 is composed of a lithium ion battery, a predetermined voltage is supplied from the auxiliary battery 205 to the auxiliary load 206, or the auxiliary battery 205 is A dedicated DC / DC converter 207 (shown by a broken line in FIG. 16) that always performs a step-up operation or a step-down operation in accordance with the remaining capacity (SOC) of the auxiliary battery 205 for charging is connected in series with the auxiliary battery 205 It is necessary to provide it. In this case, a large voltage conversion loss occurs when the auxiliary battery 205 is charged / discharged.

  In addition, when there is only one dedicated DC / DC converter 207, when the DC / DC converter 207 fails, power cannot be supplied from the auxiliary battery 205 to the auxiliary load 206, and the electric vehicle cannot be started. Or the auxiliary battery 205 may not be charged and the auxiliary battery 205 may be overdischarged.

  Then, an object of this invention is to reduce the voltage conversion loss at the time of charging / discharging of an auxiliary machine battery.

  The vehicle power supply system of the present invention includes a vehicle drive battery, a voltage converter for converting the voltage of the vehicle drive battery, and an auxiliary battery having a voltage lower than a target output voltage of the voltage converter, A power supply system for supplying electric power of the vehicle drive battery from the voltage converter to an auxiliary load, including a first switching element, connected between the auxiliary load and the auxiliary battery, and the voltage A discharge circuit for turning on the first switching element and supplying power from the auxiliary battery to the auxiliary load when an output voltage of the converter becomes lower than a voltage of the auxiliary battery; and a second switching element Is connected between the voltage converter and the auxiliary battery, and the second switching element is turned on when the remaining capacity of the auxiliary battery becomes a predetermined threshold value or less. - turn off and having a charging circuit for charging the auxiliary battery by stepping down the output voltage of the voltage converter.

  In this way, the voltage of the auxiliary battery is set to a voltage lower than the target output voltage of the voltage converter, continuous power supply to the auxiliary load is performed by the voltage converter, and the auxiliary battery is operated by the voltage converter. If the output voltage of the voltage converter becomes lower than the voltage of the auxiliary battery, such as when the auxiliary battery is not connected, the auxiliary battery will be intermittently supplied to the auxiliary load as in the prior art. Therefore, the discharge amount of the auxiliary battery is smaller than that in the case where electric power is continuously output, and the required charge amount of the auxiliary battery is also reduced. For this reason, the ON / OFF operation time of the first and second switching elements is shortened, and the voltage conversion loss can be reduced as compared with the prior art.

  The vehicle power supply system of the present invention includes a controller that adjusts the operation of the charging circuit and the discharging circuit, and an end portion of the discharging circuit connected to the auxiliary load is also connected to the voltage converter. And when the controller detects an open failure of the second switching element of the charging circuit and the remaining capacity of the auxiliary battery is equal to or lower than a predetermined threshold, the controller of the discharge circuit It is also preferable to turn on the first switching element and charge the auxiliary battery from the voltage converter.

  Thereby, even when the second switching element of the charging circuit has an open failure, the auxiliary battery can be charged, so that overdischarge of the auxiliary battery can be suppressed.

  The vehicle power supply system according to the present invention includes a controller that adjusts the operation of the charging circuit and the discharging circuit, and an end of the charging circuit connected to the voltage converter is also connected to the auxiliary load. And when the controller detects an open failure of the first switching element of the discharge circuit and when the voltage of the auxiliary battery is higher than the output voltage of the voltage converter, It is also preferable that power is supplied from the auxiliary battery to the auxiliary load by turning on the second switching element.

  As a result, even when the first switching element of the discharge circuit has an open failure, it is possible to supply power to the auxiliary load when the vehicle is started or during retreating.

  The vehicle power supply system according to the present invention includes: an auxiliary relay connected between the auxiliary battery, the charging circuit, and the discharging circuit; and a controller that adjusts the operation of the charging circuit and the discharging circuit. The end of the discharge circuit connected to the auxiliary load is also connected to the voltage converter, and the end of the charging circuit connected to the voltage converter is also connected to the auxiliary load. The controller is preferably connected to cut off the auxiliary relay when one or both of the first switching element and the second switching element are short-circuited.

  Thereby, when one or both of the first switching element and the second switching element are short-circuited, an excessive current is prevented from flowing from the voltage converter to the auxiliary battery through the charging circuit or the discharging circuit, The auxiliary battery can be suitably protected.

  The present invention can reduce voltage conversion loss during charging / discharging of an auxiliary battery.

It is a systematic diagram which shows the structure of the power supply system in embodiment of this invention. It is a graph which shows the change of the voltage Vb with respect to SOC of the auxiliary battery of the power supply system in embodiment of this invention, and the change of the output voltage Vdc of a DC / DC converter. It is a flowchart which shows the discharge operation of the power supply system in embodiment of this invention. It is explanatory drawing which shows the flow of the electric current to the auxiliary machine load at the time of vehicle starting. It is explanatory drawing which shows the flow of the electric current to the auxiliary machine load at the time of normal driving | running | working. It is a graph which shows the change of the output voltage Vdc of a DC / DC converter, and the voltage Vb of an auxiliary battery when the rush current to the auxiliary machine load generate | occur | produces during normal driving | running | working. It is a graph which shows the time change of the electric current Ib of an auxiliary machine battery, the output current Idc of a DC / DC converter, and the request | requirement electric current Ireq of an auxiliary machine load in case the rush current to an auxiliary machine load generate | occur | produces during normal driving | running | working. It is explanatory drawing which shows the flow of an electric current when the rush current to auxiliary machinery load generate | occur | produces during normal driving | running | working. It is a flowchart which shows the charging operation of the power supply system in this embodiment. It is explanatory drawing which shows the flow of the electric current at the time of charging an auxiliary machine battery during normal driving | running | working. 4 is a flowchart illustrating an operation when an open failure occurs in a charging circuit in the power supply system according to the present embodiment. In the power supply system in this embodiment, it is explanatory drawing which shows the flow of an electric current at the time of charging an auxiliary battery through a discharge circuit, when a charging circuit carries out an open failure during normal driving | running | working. 5 is a flowchart showing an operation when the discharge circuit has an open failure in the power supply system according to the present embodiment. In the power supply system in this embodiment, it is explanatory drawing which shows the flow of an electric current in the case of starting electric power by supplying electric power to an auxiliary machine load through a charging circuit when a discharge circuit has an open failure. In the power supply system in this embodiment, it is explanatory drawing which shows the flow of an electric current when the discharge circuit has an open failure and the rush current to the auxiliary machine load is generated during normal traveling. 5 is a flowchart illustrating an operation when a short circuit failure occurs in a charging circuit and a discharging circuit in the power supply system according to the present embodiment. It is a systematic diagram which shows the structure of the power supply system of a prior art.

  Hereinafter, a vehicle power supply system 100 according to the present embodiment will be described with reference to the drawings. As shown in FIG. 1, the power supply system 100 of this embodiment includes a main battery 10 that is a vehicle driving battery, a DC / DC converter 21 that is a voltage converter that steps down the voltage of the main battery 10, and an auxiliary battery. 23, a charging circuit 30 for stepping down the output voltage Vdc of the DC / DC converter 21 to charge the auxiliary battery 23 when the remaining capacity (SOC) of the auxiliary battery 23 is equal to or lower than a predetermined threshold, and DC A discharge circuit 40 that supplies power from the auxiliary battery 23 to the auxiliary load 22 when the output voltage Vdc of the DC converter 21 becomes lower than the voltage Vb of the auxiliary battery 23, and a controller 70 are provided. In FIG. 1, the alternate long and short dash line indicates a signal line.

  As shown in FIG. 1, the main battery 10 is connected to an inverter 12 by a high voltage line 61, and a motor generator 13 for driving a vehicle is connected to the inverter 12. The system main relay 11 is disposed in the high-voltage line 61. The high voltage line 61 on the inverter 12 side of the system main relay 11 and the DC / DC converter 21 are connected by a connection line 63. The DC / DC converter 21 and the auxiliary load 22 are connected by a low voltage line 64. Here, the auxiliary machine load 22 includes, for example, a power steering device, a hydraulic device, a window opening / closing device, a small motor for driving a cooling device for the main battery 10, a lighting device, and the like. The intermediate point 54 of the low voltage line 64 and the output terminal 56 of the discharge circuit 40 are connected by a first auxiliary battery line 65, and the input terminal 55 of the discharge circuit 40 and the auxiliary battery 23 are connected by a second auxiliary battery line 67. It is connected. The intermediate point 52 of the first auxiliary battery line 65 and the input terminal 57 of the charging circuit 30 are connected by a charging circuit input line 66a, and the intermediate point of the output terminal 58 of the charging circuit 30 and the second auxiliary battery line 67. 51 is connected by a charging circuit output line 66b. A current sensor 26, a fuse 27, and an auxiliary relay 28 are connected to the second auxiliary battery line 67 in this order from the auxiliary battery 23 side. A Zener diode 29 is connected between the auxiliary relay 28 and the intermediate point 51. The Zener diode 29 prevents an overvoltage from being applied to the auxiliary battery 23 when the auxiliary battery 23 is charged.

  Thus, the charging circuit 30 includes the DC / DC converter 21 and the auxiliary machine by the low voltage line 64, the first and second auxiliary battery lines 65 and 67, the charging circuit input line 66a, and the charging circuit output line 66b. It is connected between the battery 23. An input end 57 of the charging circuit 30 is an end connected to the DC / DC converter 21 of the charging circuit 30, and is also connected to the auxiliary load 22 via the low-voltage line 64. The discharge circuit 40 is connected between the auxiliary load 22 and the auxiliary battery 23 by the low voltage line 64 and the first and second auxiliary battery lines 65 and 67, and the output terminal of the discharge circuit 40 is connected to the discharge circuit 40. Reference numeral 56 denotes an end portion of the discharge circuit 40 connected to the auxiliary load 22 and is also connected to the DC / DC converter 21 via the low voltage line 64.

  The charging circuit 30 includes a second switching element 92 and a reactor 32 connected in series between the input end 57 and the output end 58, and a connection point 53 between the second switching element 92 and the reactor 32 and the ground. The on-off operation of the second switching element 92 and the third switching element 93 connected to the gates of the capacitor 34, the third switching element 93, the second switching element 92, and the third switching element 93 connected therebetween is controlled. And a charging control IC 35. The second switching element 92 and the third switching element 93 have parasitic diodes 92a and 93a, respectively. The charging circuit 30 has a function of alternately turning on / off the second switching element 92 and the third switching element 93 to step down the voltage input to the input terminal 57 and output the voltage from the output terminal 58. Regardless of the configuration described above, the charging circuit 30 may be configured with, for example, a step-down chopper circuit or a step-down switching regulator as long as it is a circuit that can step down and output an input voltage.

  The discharge circuit 40 includes a first switching element 91 connected between the input terminal 55 and the output terminal 56, and a discharge control IC 42 connected to the gate of the first switching element 91 to turn on / off the first switching element 91. Including. The first switching element 91 has a parasitic diode 91a. The discharge control IC 42 is connected to the intermediate point 52 of the first auxiliary battery line 65 and the intermediate point 51 of the second auxiliary battery line 67, and detects the voltage at each intermediate point 51, 52. Since the voltage at the intermediate point 52 is equal to the output voltage Vdc of the DC / DC converter 21, and when the auxiliary relay 28 is on, the voltage at the intermediate point 51 is equal to the voltage Vb of the auxiliary battery 23, the discharge control IC 42 When the auxiliary relay 28 is on, the voltage Vb of the auxiliary battery 23 and the output voltage Vdc of the DC / DC converter 21 are detected.

  A voltage sensor 24 that detects the voltage Vb and a temperature sensor 25 that detects the temperature Tb are attached to the auxiliary battery 23.

  As shown in FIG. 1, the DC / DC converter 21, the charge control IC 35, the discharge control IC 42, the auxiliary relay 28, the voltage sensor 24, the temperature sensor 25, and the current sensor 26 are connected to the controller 70. The DC / DC converter 21, the charge control IC 35, the discharge control IC 42, and the auxiliary relay 28 operate according to commands from the controller 70. However, the discharge control IC 42 can turn on / off the first switching element 91 independently of the controller 70. Each signal detected by the voltage sensor 24, the temperature sensor 25, and the current sensor 26 is input to the controller 70. Further, signals of voltages at the intermediate points 51 and 52 detected by the discharge control IC 42 are also input from the discharge control IC to the controller 70. The controller 70 is a computer that includes a CPU 71 that performs arithmetic processing therein and a memory 72 that stores control programs and control data. The controller 70 is connected to the auxiliary battery 23 through a connection line 68 and is connected to the DC / DC converter 21 through a connection line 69 and a low voltage line 64, and operating power is supplied from the auxiliary battery 23 or the DC / DC converter 21. The

  The auxiliary battery 23 of this embodiment is composed of a lithium ion battery, and the voltage Vb increases as the remaining capacity (SOC) increases as shown by the broken line in FIG. The remaining capacity (SOC) is the ratio (%) of the charge amount (A · h) of the battery to the full charge capacity (A · h), and is 100% at full charge. In the following description, the remaining capacity (SOC) is referred to as SOC. As shown in FIG. 2, in the auxiliary battery 23 of the present embodiment, the voltage Vb with 0% SOC is V0, the voltage Vb with 100% SOC (full charge) is V100 higher than V0, and the SOC As V becomes larger, the voltage Vb changes from V0 to V100. The voltage change range from V0 to V100 of the auxiliary battery 23 is a voltage range in which the auxiliary load 22 can be driven intermittently. 2 represents the output voltage Vdc when the target output voltage of the DC / DC converter 21 is Vd0. As shown in FIG. 2, the target output voltage Vd0 of the DC / DC converter 21 is higher than V100, which is the full charge voltage of the auxiliary battery 23 (Vdc> V100). Accordingly, the voltage Vb of the auxiliary battery 23 is lower than the target output voltage Vd0 of the DC / DC converter 21 (Vb <Vd0). The target output voltage Vd0 of the DC / DC converter 21 is a voltage that can drive the auxiliary load 22 continuously.

  The operation of the power supply system 100 configured as described above will be described. First, the discharge operation of the auxiliary battery 23 will be described with reference to FIGS. 3 to 7B.

<Discharge control>
The discharge control IC 42 of the discharge circuit 40 has a voltage at the intermediate point 51 equal to the voltage Vb of the auxiliary battery 23 and a voltage at the intermediate point 52 equal to the output voltage Vdc of the DC / DC converter 21 when the auxiliary relay 28 is on. Is detected. Then, as shown in step S101 of FIG. 3, the discharge control IC 42 determines that the voltage Vb of the auxiliary battery 23 is higher than the output voltage Vdc of the DC / DC converter 21 (when Vb> Vdc), FIG. In step S102, the first switching element 91 is turned on to discharge the auxiliary battery 23, and power is supplied from the auxiliary battery 23 to the auxiliary load 22. Further, when the discharge control IC 42 determines NO in step S101 of FIG. 3, that is, when the voltage Vb of the auxiliary battery 23 is equal to or lower than the output voltage Vdc of the DC / DC converter 21 (Vb ≦ Vdc), the first switching is performed. The element 91 is turned off and the discharge of the auxiliary battery 23 is stopped.

<Operation of discharge circuit at vehicle start-up>
As shown in FIG. 4, when the vehicle start switch is turned on and the vehicle is started, the auxiliary relay 28 is turned on by a command from the controller 70. Then, the voltage at the intermediate point 51 becomes equal to the voltage Vb of the auxiliary battery 23. Thereby, the discharge control IC 42 detects the voltage Vb of the auxiliary battery 23 and the output voltage Vdc of the DC / DC converter 21.

  At this time, since the system main relay 11 is still off and the DC / DC converter 21 is also stopped, the output voltage Vdc of the DC / DC converter 21 is zero. For this reason, the discharge control IC 42 determines that the voltage Vb of the auxiliary battery 23 is higher than the output voltage Vdc of the DC / DC converter 21 (Vb> Vdc) in step S101 of FIG. 3, and proceeds to step S102 of FIG. The first switching element 91 is turned on to discharge the auxiliary battery 23, and power is supplied from the auxiliary battery 23 to the auxiliary load 22.

  Then, current flows from the auxiliary battery 23 toward the auxiliary load 22 as indicated by an arrow R1 in FIG. In addition, since the current flows from the auxiliary battery 23 toward the auxiliary load 22 through the parasitic diode 91a of the discharge circuit 40 until the first switching element 91 is turned on from the OFF state, When voltage Vb is higher than output voltage Vdc of DC / DC converter 21, power can be supplied from auxiliary battery 23 to auxiliary load 22 without time delay. Even when the vehicle stops and the DC / DC converter 21 stops, power is supplied from the auxiliary battery 23 to the auxiliary load 22 in the same manner as described above.

<Operation of discharge circuit during normal driving>
As described above with reference to FIG. 4, when electric power is supplied from the auxiliary battery 23 to the auxiliary load 22, an ECU (not shown) is activated. The ECU turns on the system main relay 11 to connect the main battery 10 and the DC / DC converter 21. Further, the controller 70 activates the DC / DC converter 21. When the DC / DC converter 21 starts operation, as shown in FIG. 2, the output voltage Vdc of the DC / DC converter 21 becomes a target output voltage Vd0 higher than the voltage Vb of the auxiliary battery 23 (Vb ≦ Vdc = Vd0). Then, the discharge control IC 42 determines NO in step S <b> 101 of FIG. 3, turns off the first switching element 91, stops discharging the auxiliary battery 23, and supplies power from the auxiliary battery 23 to the auxiliary load 22. To stop.

  When the power supply from the auxiliary battery 23 to the auxiliary load 22 is stopped, the power of the main battery 10 is supplied from the DC / DC converter 21 to the auxiliary load 22 as indicated by arrows R2 and R4 in FIG. . Further, as indicated by an arrow R3 in FIG. 5, the electric power of the main battery 10 is supplied from the inverter 12 to the motor generator 13, and the vehicle travels normally. While the vehicle is running normally, the output voltage Vdc of the DC / DC converter 21 is maintained at the target output voltage Vd0 that is higher than the voltage Vb of the auxiliary battery 23. Therefore, the discharge control IC 42 performs the first switching. The element 91 is kept off.

  As described above, the power supply system 100 according to the present embodiment supplies power from the auxiliary battery 23 to the auxiliary load 22 when the vehicle in which the DC / DC converter 21 is not operating or when the vehicle is stopped. During normal traveling in which the / DC converter 21 is operating, power is continuously supplied from the DC / DC converter 21 to the auxiliary load 22.

<Operation of discharge circuit during rush current generation of auxiliary load during normal driving>
As shown in FIG. 6A from time zero to time t1, during the normal traveling of the vehicle, the output voltage Vdc of the DC / DC converter 21 (indicated by a one-dot chain line in FIG. 6A) is the voltage Vb of the auxiliary battery 23. Higher than the target output voltage Vd0. 6B, the output current Idc of the DC / DC converter 21 (indicated by a one-dot chain line in FIG. 6B) is the required current Ireq of the auxiliary load 22 (in FIG. 6B). (Shown by a solid line). The output current Id at this time is smaller than the upper limit output current Idmax when the output voltage Vdc of the DC / DC converter 21 is the target output voltage Vd0.

  The auxiliary machine load 22 includes a power steering device and a small motor that drives the hydraulic device. These small motors require a large current (rush current) in a short time in order to operate rapidly when the driver operates a sudden handle or a sudden brake. For this reason, when the sudden handle or the sudden brake operation is performed at time t1 in FIG. 6B, the required current Ireq of the auxiliary machine load 22 increases rapidly after time t1, as shown by the solid line in FIG. 6B. . Along with this, as indicated by a broken line in FIG. 6B, the output current Id of the DC / DC converter 21 also increases rapidly. When the output current Id of the DC / DC converter 21 reaches the upper limit output current Idmax at time t2 in FIG. 6B, the DC / DC converter 21 converts the output voltage Vdc to the target output voltage as shown by the one-dot chain line in FIG. 6A. Vd0 cannot be maintained, and the output voltage Vdc of the DC / DC converter 21 starts to decrease from the target output voltage Vd0.

  When the output voltage Vdc of the DC / DC converter 21 becomes lower than the voltage Vb of the auxiliary battery 23 at time t3 in FIG. 6A, that is, the voltage Vb of the auxiliary battery 23 is higher than the output voltage Vdc of the DC / DC converter 21. If the voltage becomes higher (Vb> Vdc), the discharge control IC 42 determines YES in step S101 of FIG. 3 and proceeds to step S102 to turn on the first switching element 91 and start discharging of the auxiliary battery 23. To do. Then, current Ib flows from auxiliary battery 23 to auxiliary load 22 as indicated by a broken line in FIG. 6B. At this time, the output current Id flows from the DC / DC converter 21 to the auxiliary load 22 as indicated by the arrow R4 in FIG. 7, and the current Ib flows from the auxiliary battery 23 as indicated by the arrow R1 in FIG. Accordingly, power is supplied to the auxiliary load 22 from the DC / DC converter 21 and the auxiliary battery 23. When power is supplied from the auxiliary battery 23 to the auxiliary load 22, the output voltage Vdc of the DC / DC converter 21 depends on the balance between the power supplied from the DC / DC converter 21 and the power supplied from the auxiliary battery 23. The voltage is kept slightly lower than the voltage Vb of the auxiliary battery 23.

  As shown in FIG. 6B, when the operation of the abrupt steering wheel or the abrupt brake is finished at time t3, the required current Ireq of the auxiliary machine load 22 rapidly decreases from the peak current Ipeak. Then, as shown in FIG. 6A, output voltage Vdc of DC / DC converter 21 begins to rise, and output voltage Vdc of DC / DC converter 21 becomes equal to or higher than voltage Vb of auxiliary battery 23 at time t4 in FIG. 6A. (Vb ≦ Vdc). Then, the discharge control IC 42 determines NO in step S101 of FIG. 3, and turns off the first switching element 91 as shown in step S103 of FIG. Thereby, after time t4 of FIG. 6B, the current Ib of the auxiliary battery 23 becomes zero. Further, after time t4 shown in FIG. 6B, the required current Ireq of the auxiliary load 22 rapidly decreases. Accordingly, as shown in FIG. 6A, the output voltage Vdc of the DC / DC converter 21 increases. come.

  When the required current Ireq of the auxiliary load 22 becomes smaller than the upper limit output current Idmax of the DC / DC converter 21 at time t5 in FIG. 6B, the output voltage Vdc of the DC / DC converter 21 returns to the target output voltage Vd0. When the vehicle returns to normal running at time t6, the output voltage Vdc of the DC / DC converter 21 is maintained at the target output voltage Vd0 that is higher than the voltage Vb of the auxiliary battery 23, and the discharge control IC 42 has the first switching element. Keep 91 off.

  As described above, the sudden handle or the sudden brake operation is performed during the normal traveling, the rush current of the auxiliary load 22 is generated, and the output voltage Vdc of the DC / DC converter 21 becomes the voltage Vb of the auxiliary battery 23. When the voltage becomes lower (Vb> Vdc), the discharge control IC 42 turns on the first switching element 91 to discharge the auxiliary battery 23 and back up the power supplied to the auxiliary load 22. Further, when the rush current of the auxiliary load 22 is not generated and the output voltage Vdc of the DC / DC converter 21 does not become lower than the voltage Vb of the auxiliary battery 23, the auxiliary load 22 has a DC / DC Electric power is continuously supplied from the converter 21.

  As described above, the power supply system 100 according to the present embodiment continuously supplies power from the DC / DC converter 21 to the auxiliary load 22 during normal running, and when the rush current of the auxiliary load 22 is generated. The power supply from the auxiliary battery 23 to the auxiliary load 22 is intermittently performed to back up the power supplied from the DC / DC converter 21.

<Charge control>
Next, the charging operation of the auxiliary battery 23 will be described with reference to FIGS. The controller 70 stores a map indicating the relationship between the voltage Vb, current Ib, temperature Tb, and SOC of the auxiliary battery 23 in the memory 72. As shown in step S201 in FIG. 8, the controller 70 performs auxiliary equipment based on the voltage Vb, current Ib, temperature Tb of the auxiliary battery 23 detected by the voltage sensor 24, current sensor 26, and temperature sensor 25, and this map. The SOC of the battery 23 is calculated and compared with a charging start threshold value Ca that is a predetermined threshold value. When the SOC of the auxiliary battery 23 becomes equal to or lower than the charging start threshold value Ca, the process proceeds to step S202 in FIG. 8, and the voltages at the intermediate points 51 and 52 detected by the discharge control IC 42 are set to the voltage Vb of the auxiliary battery 23, respectively. As the output voltage Vdc of the DC / DC converter 21, the output voltage Vdc of the DC / DC converter 21 and the voltage Vb of the auxiliary battery 23 are compared. If the output voltage Vdc of the DC / DC converter 21 is equal to or higher than the voltage Vb of the auxiliary battery 23 in step S202 of FIG. 8 (Vdc ≧ Vb), the process proceeds to step S203 of FIG. The start command 30 is output and the voltage Vb of the auxiliary battery 23 detected by the discharge control IC 42 is output to the charge control IC 35.

  When the charging circuit 30 is activated, the controller 70 proceeds to step S204 in FIG. 8, calculates the SOC of the auxiliary battery 23 in the same manner as in step S201, and charges until the SOC of the auxiliary battery 23 becomes equal to or higher than the charging stop threshold Cb. While maintaining the operation of the circuit 30, the voltage Vb of the auxiliary battery 23 detected by the discharge control IC 42 is output to the charge control IC 35 (step S203). Then, when the SOC of the auxiliary battery 23 becomes equal to or higher than the charging stop threshold Cb in step S204 of FIG. 8, the controller 70 proceeds to step S205 and outputs a command to stop the operation of the charging circuit 30 to the charging control IC 35.

  On the other hand, if the controller 70 determines NO in step S201 in FIG. 8 and NO in step S202 in FIG. 8, the controller 70 returns to the beginning without activating the charging circuit 30, and steps S201 to S205. repeat.

  When the activation command from the controller 70 is input, the charging control IC 35 alternately turns on and off the second switching element 92 and the third switching element 93 to change the output voltage Vdc of the DC / DC converter 21 to the auxiliary battery 23. The charging voltage is reduced to Vch. The charging voltage Vch is equal to or slightly higher than the voltage Vb of the auxiliary battery 23 input from the controller 70. Since the voltage Vb of the auxiliary battery 23 changes from V0 to V100 according to the SOC as shown in FIG. 2, the charge control IC 35 uses the second switching element based on the voltage Vb of the auxiliary battery 23 input from the controller 70. The charging voltage Vch is adjusted to be equal to or slightly higher than the voltage Vb of the auxiliary battery 23 by changing the duty ratio of the second switching element 92 and the third switching element 93. The charging voltage Vch of the auxiliary battery 23 may not be changed, and charging may be performed as V100 that is the full charging voltage of the auxiliary battery 23 described with reference to FIG.

<Charging operation of auxiliary battery during normal driving>
As described above with reference to FIG. 5, when the vehicle is traveling normally, the power of the main battery 10 is supplied from the DC / DC converter 21 to the auxiliary load as indicated by arrows R2 and R4 in FIG. 22 is supplied. Since the output voltage Vdc of the DC / DC converter 21 is maintained at the target output voltage Vd0 higher than the voltage Vb of the auxiliary battery 23, the discharge control IC 42 keeps the first switching element 91 off. When the activation command from the controller 70 is input to the charging control IC 35, the charging control IC 35 alternately turns on / off the second switching element 92 and the third switching element 93 to change the output voltage Vdc of the DC / DC converter 21. The voltage is reduced to the charging voltage Vch, and the auxiliary battery 23 is charged as indicated by an arrow R5 in FIG.

  In the charge control described above, the charge start threshold value Ca and the charge stop threshold value Cb can take various values. For example, the charge start threshold value Ca is set so that the voltage Vb of the auxiliary battery 23 does not become too low. As the charging stop threshold Cb is higher, the vehicle stop period can be lengthened. However, if the charging stop threshold Cb is too high, the auxiliary battery 23 may be overcharged, so that it may be about 80-90%. As described above, the power supply from the auxiliary battery 23 is performed when the DC / DC converter 21 is stopped when the vehicle is started or stopped, or when the rush current is applied to the auxiliary load 22. In this case, power is not supplied from the auxiliary battery 23 to the auxiliary load 22 during normal travel. For this reason, the discharge amount of the auxiliary battery 23 is small and the required charge amount is also small.

<Basic effects of the power supply system of this embodiment>
As described above, the power supply system 100 of this embodiment sets the voltage Vb of the auxiliary battery 23 to a voltage lower than the target output voltage Vd0 of the DC / DC converter 21, and continuously supplies power to the auxiliary load 22. Is performed by the DC / DC converter 21, and the auxiliary battery 23 generates DC / DC when a rush current is generated in the auxiliary load 22 when the vehicle in which the DC / DC converter 21 is not operating is started or stopped. When the output power of the DC converter 21 is insufficient and the output voltage Vdc decreases, power is intermittently supplied to the auxiliary load 22. For this reason, the amount of discharge from the auxiliary battery 23 to the auxiliary load 22 is reduced, and the first switching element 91 need not always be turned on / off. Further, since the discharge amount of the auxiliary battery 23 is small, the required charge amount of the auxiliary battery 23 is also reduced, and the second switching element 92 and the third switching element 93 need not always be turned on / off. As a result, as in the power supply system 200 of the prior art shown in FIG. 16, the power is supplied to the auxiliary load 206 by the auxiliary battery 205, and the dedicated DC / DC converter 207 is always stepped up or stepped down. Compared with the voltage conversion loss can be reduced.

<Operation at the time of open failure of charging circuit>
Next, the operation of the power supply system 100 when the second switching element 92 of the charging circuit 30 has an open failure will be described with reference to FIGS. The same reference numerals are given to the portions described above with reference to FIGS.

  When the auxiliary battery 23 is charged from the DC / DC converter 21 by starting the charging circuit 30, as shown in the graph of the voltage Vb with respect to the SOC of the auxiliary battery 23 shown in FIG. The voltage Vb of the auxiliary battery 23 is also increased. However, since the auxiliary battery 23 cannot be charged when the second switching element 92 of the charging circuit 30 has an open failure, even if the controller 70 outputs a start command to the charging control IC 35, the voltage of the auxiliary battery 23 The voltage at the intermediate point 51 that is the same voltage as Vb does not rise. Therefore, the controller 70 outputs an activation command for the charging circuit 30 to the charging control IC 35 in step S203 of FIG. 8, and if the voltage at the intermediate point 51 acquired from the discharging control IC 42 does not increase, the controller 70 of FIG. In step S301, it is determined that the second switching element 92 of the charging circuit 30 has an open failure, and the process proceeds to step S302 in FIG.

  In step S302 in FIG. 10, the controller 70 calculates the SOC of the auxiliary battery 23 by the same method as in step S201 in FIG. 8, and compares it with the charging start threshold value Ca that is a predetermined threshold value. If the SOC of the auxiliary battery 23 is equal to or lower than the charging start threshold Ca, the process proceeds to step S303 in FIG. 10 and the output voltage Vdc of the DC / DC converter 21 is adjusted to become the charging voltage Vch of the auxiliary battery 23. To do. The charge voltage Vch is the same as or slightly higher than the voltage Vb of the auxiliary battery 23 as described above in the charge control. Then, when the controller 70 confirms that the output voltage Vdc of the DC / DC converter 21 has become the charging voltage Vch, the controller 70 proceeds to step S304 in FIG. 10 to force the discharge control IC 42 to turn on the first switching element 91. Command to output. In response to this command, the discharge control IC 42 turns on the first switching element 91. When the first switching element 91 is turned on, a current flows from the DC / DC converter 21 through the discharge circuit 40 to the auxiliary battery 23 as shown by an arrow R6 in FIG. 11, and the auxiliary battery 23 is charged. .

  In step S305 of FIG. 10, the controller 70 calculates the SOC of the auxiliary battery 23 in the same manner as in step S201 of FIG. 8, and forces the first switching element 91 until the SOC of the auxiliary battery 23 becomes equal to or higher than the charge stop threshold Cb. Keep on. Further, when the SOC increases due to charging and the voltage Vb of the auxiliary battery 23 increases, the controller 70 increases the charging voltage Vch in accordance with this, and increases the output voltage Vdc of the DC / DC converter 21. Then, when the SOC of the auxiliary battery 23 becomes equal to or higher than the charge stop threshold Cb in step S305 in FIG. 10, the controller 70 proceeds to step S306 and outputs a signal for turning off the first switching element 91 to the discharge control IC 42. . In response to this command, the discharge control IC 42 turns off the first switching element 91. Then, the controller 70 proceeds to step S307 in FIG. 10, sets the output voltage Vdc of the DC / DC converter 21 as the target output voltage Vd0, and ends the routine.

<Auxiliary battery charging when the charging circuit fails during normal driving>
When the vehicle is traveling normally, as described with reference to FIG. 5, the system main relay 11 is on and the DC / DC converter 21 is operating, as indicated by arrows R2 and R4 in FIG. In addition, the power of the main battery 10 is supplied from the DC / DC converter 21 to the auxiliary load 22. In this case, the output voltage Vdc of the DC / DC converter 21 is higher than the voltage Vb of the auxiliary battery 23.

  At this time, as described in step S201 in FIG. 8, when the controller 70 determines that the SOC of the auxiliary battery 23 is equal to or less than the charging start threshold value Ca, the controller 70 proceeds to step S202 in FIG. move on. During normal traveling, the output voltage Vdc of the DC / DC converter 21 is higher than the voltage Vb of the auxiliary battery 23 (Vdc ≧ Vb), so the controller 70 determines YES in step S202 of FIG. Proceeding to step S <b> 203, an activation command is output to the charging control IC 35 of the charging circuit 30.

  When the voltage at the intermediate point 51 acquired from the discharge control IC 42 does not increase, the controller 70 determines that the second switching element 92 of the charging circuit 30 has an open failure in step S301 in FIG. Proceed to step S302 of FIG. Since the SOC of auxiliary battery 23 is equal to or lower than charging start threshold value Ca, controller 70 determines YES in step S302 of FIG. 10 and proceeds to step S303 of FIG. 10 to output voltage Vdc of DC / DC converter 21. Is adjusted to be the charging voltage Vch of the auxiliary battery 23.

  In this case, the supply voltage to the auxiliary load 22 is also the charging voltage Vch. As described above, the charging voltage Vch is equal to or slightly higher than the voltage Vb of the auxiliary battery 23, and as described with reference to FIG. 2, the voltage range of V0 to V100 of the auxiliary battery 23 Is a voltage that can drive the auxiliary load 22 intermittently. Therefore, even if the voltage of the DC / DC converter 21 is lowered to the charging voltage Vch, the auxiliary load 22 can operate intermittently, and the power of the main battery 10 is DC as shown by arrows R2 and R4 in FIG. / Supplied from the DC converter 21 to the auxiliary machine load 22, and the auxiliary machine load 22 continues to operate. Further, since the charging voltage Vch is equal to or slightly higher than the voltage Vb of the auxiliary battery 23 (Vb ≦ Vch), the discharge control IC 42 determines NO in step S101 of FIG. Is off.

  Next, the controller 70 proceeds to step S304 in FIG. 10 and outputs a command to forcibly turn on the first switching element 91 to the discharge control IC 42. In response to this command, the discharge control IC 42 turns on the first switching element 91 that has been turned off. As a result, as indicated by an arrow R6 in FIG. 11, a current flows from the DC / DC converter 21 through the first switching element 91 of the discharge circuit 40 to the auxiliary battery 23, and the auxiliary battery 23 is charged.

  Then, as shown in steps S304 and S305 of FIG. 10, the controller 70 continues to forcibly turn on the first switching element 91 until the SOC of the auxiliary battery 23 reaches the charge stop threshold Cb, and the SOC of the auxiliary battery 23 is increased. Is equal to or greater than the charge stop threshold Cb, the process proceeds to step S306 in FIG. 10, and the first switching element 91 is turned off. As a result, the discharge circuit 40 returns to the discharge control described with reference to FIG.

  When the charging of the auxiliary battery 23 is completed, the controller 70 changes the output voltage Vdc of the DC / DC converter 21 from the charging voltage Vch to the target output voltage Vd0 as shown in step S307 in FIG. As a result, the vehicle returns to the normal running state described with reference to FIG.

  When the controller 70 forcibly turns on the first switching element 91 and charges the auxiliary battery 23, the voltage of the intermediate point 51 acquired from the discharge control IC 42 and the current of the auxiliary battery 23 acquired by the current sensor 26 are charged. When the absolute value of Ib is equal to or greater than a predetermined value, it is determined that an overvoltage or overcurrent has been applied to the auxiliary battery 23, and the auxiliary relay 28 is turned off to protect the auxiliary battery 23. Further, as shown in step S201 of FIG. 8, when the SOC of the auxiliary battery 23 exceeds the charging start threshold value Ca during normal traveling of the vehicle, the controller 70 does not charge the auxiliary battery 23. The routine ends. In this case, the discharge circuit 40 performs the discharge control as described with reference to FIGS.

  As described above, the power supply system 100 according to the present embodiment discharges after the output voltage Vdc of the DC / DC converter 21 is lowered to the charging voltage Vch when the second switching element 92 of the charging circuit 30 has an open failure. Since the auxiliary battery 23 can be charged by forcibly turning on the first switching element 91 of the circuit 40, overdischarge of the auxiliary battery 23 can be suppressed. Further, even when the charging circuit 30 has an open failure, the vehicle can continue the normal travel and the retreat travel.

<Operation at open failure of discharge circuit>
Next, the operation when the first switching element 91 of the discharge circuit 40 has an open failure will be described with reference to FIGS. The same parts as those described above with reference to FIGS. 1 to 11 are denoted by the same reference numerals, and description thereof is omitted.

  When the voltage Vb of the auxiliary battery 23 is higher than the output voltage Vdc of the DC / DC converter 21 (Vb> Vdc), the parasitic battery 91a of the first switching element 91 is passed through even when the first switching element 91 is off (open). A current flows from the auxiliary battery 23 to the auxiliary load 22. However, since the parasitic diode 91a has a large resistance, the voltage drop is large, and a voltage difference is generated between the voltage at the intermediate point 51 and the intermediate point 52 detected by the discharge control IC. On the other hand, when the first switching element 91 is turned on, there is almost no resistance, so even if a current flows from the auxiliary battery 23 to the DC / DC converter 21, there is almost no voltage difference between the intermediate point 51 and the intermediate point 52. . Therefore, the controller 70 outputs the voltage of the intermediate point 51 and the intermediate point 52 acquired from the discharge control IC 42 when the discharge control IC 42 outputs a signal for turning on the first switching element 91 in step S401 of FIG. When the voltage difference between the first and second voltages continues for a predetermined period, it is determined that the first switching element 91 has caused an open failure. Then, the process proceeds to step S402, and if it is confirmed that the voltage Vb of the auxiliary battery 23 is higher than the output voltage Vdc of the DC / DC converter 21, the process proceeds to step S403 in FIG. A command to set the to discharge mode is output. The charge control IC 35 forcibly turns on the second switching element 92 and fixes the third switching element 93 to OFF in response to this command. Then, as indicated by an arrow R7 in FIG. 13, electric power is supplied from the auxiliary battery 23 to the auxiliary load 22 through the charging circuit 30.

<Vehicle activation at the time of discharge circuit open failure>
As shown in FIG. 13, when the vehicle start switch is turned on and the vehicle is started, the auxiliary relay 28 is turned on by a command from the controller 70. Then, the voltage at the intermediate point 51 becomes equal to the voltage Vb of the auxiliary battery 23. Thereby, the discharge control IC 42 detects the voltage Vb of the auxiliary battery 23 by detecting the voltage at the intermediate point 51, and detects the output voltage Vdc of the DC / DC converter 21 by detecting the voltage at the intermediate point 52. To do.

  At this time, as shown in FIG. 13, since the DC / DC converter 21 is stopped, the output voltage Vdc of the DC / DC converter 21 is zero, and the discharge control IC 42 proceeds to step S101 in FIG. As shown, it is determined that the voltage Vb of the auxiliary battery 23 is higher than the output voltage Vdc of the DC / DC converter 21 (Vb> Vdc), and the process proceeds to step S102 in FIG. 2 to turn on the first switching element 91. Output a signal.

  When the auxiliary relay 28 is turned on and the voltage at the intermediate point 51 becomes the voltage Vb of the auxiliary battery 23, the auxiliary battery 23 passes through the parasitic diode 91a of the first switching element 91 from the auxiliary battery 23 as shown by an arrow R8 in FIG. As a result, a current flows through the auxiliary load 22. Since the parasitic diode 91 a has a large resistance, a voltage difference is generated between the voltage at the intermediate point 51 and the voltage at the intermediate point 52.

  When the voltage difference between the voltage at the intermediate point 51 and the voltage at the intermediate point 52 acquired from the discharge control IC 42 continues for a predetermined period, the controller 70 causes the first switching element 91 to be activated as shown in step S401 in FIG. Judge that an open failure has occurred. At this time, the DC / DC converter 21 is stopped, and the voltage Vb of the auxiliary battery 23 is higher than the output voltage Vdc of the DC / DC converter 21, so the controller 70 determines YES in step S402 in FIG. The process proceeds to step S403 in FIG. 12, and a command for setting the charging circuit 30 to the discharging mode is output to the charging control IC 35. The charge control IC 35 forcibly turns on the second switching element 92 and fixes the third switching element 93 to OFF in response to this command. Then, as indicated by an arrow R7 in FIG. 13, electric power is supplied from the auxiliary battery 23 to the auxiliary load 22 through the charging circuit 30.

  When electric power is supplied from the auxiliary battery 23 to the auxiliary load 22, an ECU (not shown) is activated, and the system main relay 11 is turned on. When the controller 70 activates the DC / DC converter 21, electric power is supplied from the DC / DC converter 21 to the auxiliary load 22, and the activation of the vehicle is completed, so that the vehicle can run normally as shown in FIG. Become. Thus, even when the first switching element 91 of the discharge circuit 40 has an open failure, the vehicle can be started with the charging circuit 30 in the discharge mode.

<Operation at the time of rush current generation of auxiliary load during normal driving due to discharge circuit open failure>
When the rush current of the auxiliary load is generated during normal traveling, the discharge control IC 42 outputs an ON command to the first switching element 91, but the voltage between the intermediate point 51 and the intermediate point 52 is When the voltage difference continues for a predetermined time, the controller 70 determines that the first switching element 91 of the discharge circuit 40 has an open failure and turns on the second switching element 92 of the charging circuit 30. As a result, electric power is supplied from the auxiliary battery 23 to the auxiliary load 22 as indicated by an arrow R7 in FIG. As described above with reference to FIGS. 6A, 6 </ b> B, and 7, the auxiliary load 22 is supplied with power from the DC / DC converter 21 and the auxiliary battery 23. Thus, even when the first switching element 91 of the discharge circuit 40 has an open failure, the charging circuit 30 is set to the discharge mode, and the output power of the DC / DC converter 21 is backed up when a rush current is generated in the auxiliary load 22. To do. Thereby, the vehicle can continue the normal traveling or the retreat traveling.

  The controller 70 is obtained by discharging the auxiliary battery 23 with the charging circuit 30 in the discharge mode, when the SOC of the auxiliary battery 23 becomes equal to or lower than the charging start threshold value Ca, or by the current sensor 26. When the absolute value of the current Ib of the auxiliary battery 23 becomes equal to or greater than a predetermined value, it is determined that an overdischarge or overcurrent of the auxiliary battery 23 has occurred, and the auxiliary relay 28 is turned off to turn off the auxiliary battery. 23 is protected. When the output voltage Vdc of the DC / DC converter 21 is higher than the voltage Vb of the auxiliary battery 23, the controller 70 performs a charging operation as described with reference to FIGS.

  As described above, the power supply system 100 according to the present embodiment compensates for the start-up of the vehicle or during normal driving by setting the charging circuit 30 in the discharge mode even when the first switching element 91 of the discharge circuit 40 has an open failure. Electric power can be supplied to the auxiliary machine load 22 when a rush current of the machine load is generated.

<Operation at the time of short-circuit failure of charging circuit and discharging circuit>
When electric power is supplied to the auxiliary load 22 by the DC / DC converter 21, the output voltage Vdc of the DC / DC converter 21 is higher than the voltage Vb of the auxiliary battery 23. In this case, if one or both of the second switching element 92 of the charging circuit 30 and the first switching element 91 of the discharging circuit 40 are short-circuited, the voltage at the intermediate point 51 is higher than the voltage Vb of the auxiliary battery 23. The voltage increases to the output voltage Vdc of the DC / DC converter 21. Therefore, when the voltage at the intermediate point 51 acquired from the discharge control IC 42 is higher than the voltage of the auxiliary battery 23 acquired by the voltage sensor 24 in step S501 of FIG. Alternatively, it is determined that one or both of the first switching elements 91 have short-circuited, and the process proceeds to step S502 in FIG. When it is confirmed in step S502 in FIG. 15 that the output voltage Vdc of the DC / DC converter 21 is higher than the voltage Vb of the auxiliary battery 23, the process proceeds to step S503 in FIG. 15 and the auxiliary relay 28 is turned off.

  The controller 70 determines that no short-circuit failure has occurred in step S501 of FIG. 15, and the output voltage Vdc of the DC / DC converter 21 is not higher than the voltage of the auxiliary battery 23 in step S502 ( If it is determined that Vdc ≦ Vb), the auxiliary relay 28 is not turned off and the routine is terminated.

  As a result, when one or both of the second switching element 92 and the first switching element 91 are short-circuited, an excessive current is supplied from the DC / DC converter 21 to the auxiliary battery 23 through the charging circuit 30 or the discharging circuit 40. Inflow can be suppressed and the auxiliary battery 23 can be protected.

  10,201 Main battery, 11 System main relay, 12,202 Inverter, 13,203 Motor generator, 21,207 DC / DC converter, 22,206 Auxiliary load, 23,205 Auxiliary battery, 24 Voltage sensor, 25 Temperature Sensor, 26 Current sensor, 27 Fuse, 28 Auxiliary relay, 29 Zener diode, 30 Charging circuit, 32 Reactor, 34 Capacitor, 35 Charge control IC, 40 Discharge circuit, 42 Discharge control IC, 51, 52, 54 Midpoint, 53 connection point, 55, 57 input terminal, 56, 58 output terminal, 61 high voltage line, 63 connection line, 64 low voltage line, 65 first auxiliary battery line, 66a charging circuit input line, 66b charging circuit output line, 67th 2 Auxiliary battery lines, 68, 6 Connection line, 70 controller, 71 CPU, 72 memory, 91 first switching element, 91a, 92a, 93a parasitic diode, 92 second switching element, 93 third switching element, 100, 200 power supply system, 204 bidirectional DC / DC converter.

Claims (4)

A battery for driving the vehicle;
A voltage converter for converting the voltage of the vehicle driving battery;
An auxiliary battery having a voltage lower than a target output voltage of the voltage converter,
A power supply system for supplying electric power of the vehicle drive battery from the voltage converter to an auxiliary load,
A first switching element, connected between the auxiliary load and the auxiliary battery, and when the output voltage of the voltage converter becomes lower than the voltage of the auxiliary battery, the first switching element A discharge circuit that supplies power from the auxiliary battery to the auxiliary load,
Including a second switching element, connected between the voltage converter and the auxiliary battery, and turning on / off the second switching element when a remaining capacity of the auxiliary battery becomes a predetermined threshold value or less. A charging circuit that steps down the output voltage of the voltage converter and charges the auxiliary battery;
A vehicle power supply system. The vehicle power supply system according to claim 1,
A controller for adjusting the operation of the charging circuit and the discharging circuit;
The end of the discharge circuit connected to the auxiliary load is also connected to the voltage converter,
The controller is
When an open failure of the second switching element of the charging circuit is detected, and the remaining capacity of the auxiliary battery falls below a predetermined threshold value, the first switching element of the discharge circuit is turned on. And a power supply system for a vehicle that charges the auxiliary battery from the voltage converter. The vehicle power supply system according to claim 1,
A controller for adjusting the operation of the charging circuit and the discharging circuit;
The end of the charging circuit connected to the voltage converter is also connected to the auxiliary load,
The controller is
When the open failure of the first switching element of the discharge circuit is detected and the voltage of the auxiliary battery is higher than the output voltage of the voltage converter, the second switching element of the charging circuit is A vehicle power supply system that supplies power from the auxiliary battery to the auxiliary load when turned on. The vehicle power supply system according to claim 1,
An auxiliary relay connected between the auxiliary battery and the charging circuit and the discharging circuit;
A controller for adjusting the operation of the charging circuit and the discharging circuit,
The end of the discharge circuit connected to the auxiliary load is also connected to the voltage converter,
The end of the charging circuit connected to the voltage converter is also connected to the auxiliary load,
The controller is
A vehicle power supply system that cuts off the auxiliary relay when one or both of the first switching element and the second switching element are short-circuited.

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