Power supply, and diagnostic method for power supply

Abstract

This power supply comprises: a first switch configured to be connected at one end to a first DC power supply; a first capacitance connected between the other end of the first switch and a reference potential; a second switch configured to be connected at one end to a second DC power supply; a second capacitance connected between the other end of the second switch and the reference potential; first and second DC-DC converters connected in parallel with each other between the other end of the first switch and the other end of the second switch; and a control unit. The control unit has a step-down operation mode, a step-up operation mode, and a step-up / step-down operation mode. In the step-up / step-down operation mode, while the first switch and the second switch are shut off, the control unit causes the first DC-DC converter to step down the voltage of the first capacitance and output the stepped-down voltage to the second capacitance, and in parallel causes the second DC-DC converter to step up the voltage of the second capacitance and output the stepped-up voltage to the first capacitance.

Description

Power supply device and method for diagnosing the power supply device

[0001] The present disclosure relates to a power supply device and a method for diagnosing a power supply device, and more particularly to a power supply device that is connected between two DC power sources to convert voltage.

[0002] A power supply device including a DC-DC converter connected between two DC power sources to convert voltage has been disclosed (see, for example, Patent Document 1). In this power supply device, for protection purposes, a switch is inserted between each of the two DC power sources and the power supply device. To diagnose the interrupting capability of the switch, the switch is placed in an interrupting state and the potential difference across the switch is measured. If the potential difference is greater than a predetermined value, the interrupting capability of the switch is determined to be normal. If not, the interrupting capability of the switch is determined to be abnormal.

[0003] International Publication No. 2019 / 077958

[0004] In conventional diagnostic methods, if an electric charge (hereinafter, this electric charge will also be referred to as "internal charge") is stored inside the DCDC converter, the method is affected by the internal charge, and after turning the switch to the OFF state, it is necessary to wait for the internal charge to discharge, which requires a long waiting time.

[0005] According to one embodiment of the present disclosure, there is provided a power supply device connected to a first DC power supply that supplies and maintains a first voltage and a second DC power supply that supplies and maintains a second voltage lower than the first voltage. The power supply device includes: a first switch having one end connected to the first DC power supply; a first capacitance connected between the other end of the first switch and a reference potential; a second switch having one end connected to the second DC power supply; a second capacitance connected between the other end of the second switch and the reference potential; a first DC-DC converter connected between the other end of the first switch and the other end of the second switch; a second DC-DC converter connected in parallel with the first DC-DC converter between the other end of the first switch and the other end of the second switch; and a control unit configured to control the first switch, the second switch, the first DC-DC converter, and the second DC-DC converter. The control unit has a buck operation mode, a boost operation mode, and a buck-boost operation mode. In a step-down operation mode, with the first switch and the second switch connected, step-down control is performed for the first DC-DC converter and the second DC-DC converter in parallel to step-down the first voltage supplied from the first DC power supply to the second voltage and output it to the second DC power supply. In a step-up operation mode, with the first switch and the second switch connected, step-up control is performed for the first DC-DC converter and the second DC-DC converter in parallel to step-up the second voltage supplied from the second DC power supply to the first voltage and output it to the first DC power supply. In a step-up / step-down operation mode, with the first switch and the second switch disconnected, step-up / step-down control is performed for the first DC-DC converter to step-down the voltage of the first capacitance and output it to the second capacitance, and in parallel to step-up / step-down the voltage of the second capacitance and output it to the first capacitance.

[0006] In a power supply device diagnostic method according to one aspect of the present disclosure, a power supply device is provided including: a first switch having one end connected to the first DC power supply; a first capacitance connected between the other end of the first switch and a reference potential; a second switch having one end connected to the second DC power supply; a second capacitance connected between the other end of the second switch and the reference potential; a first DC-DC converter connected between the other end of the first switch and the other end of the second switch; and a second DC-DC converter connected between the other end of the first switch and the other end of the second switch. With the first switch and the second switch in a disconnected state, a step-up / step-down control is performed to cause the first DC-DC converter to step down the voltage of the first capacitance and output it to the second capacitance, and simultaneously cause the second DC-DC converter to step up the voltage of the second capacitance and output it to the first capacitance.

[0007] The present disclosure provides a power supply device and a power supply device diagnostic method that can diagnose the interruption capabilities of switches connected between each of two DC power sources and the power supply device in a shorter time than conventional methods.

[0008] FIG. 1 is a block diagram showing the configuration of a power supply device according to an embodiment. FIG. 2 is a diagram showing a specific circuit example of a DC-DC converter included in the power supply device shown in FIG. 1. FIG. 3A is a diagram showing current flow in a step-down operation mode of the power supply device shown in FIG. 2. FIG. 3B is a diagram explaining a failure of a switching element in the step-down operation mode of the power supply device shown in FIG. 3A. FIG. 3C is a timing chart showing operation of a first DC-DC converter for explaining an open failure of a second switching element. FIG. 4A is a diagram showing current flow in a step-up operation mode of the power supply device shown in FIG. 2. FIG. 4B is a diagram explaining a failure of a switching element in the step-up operation mode of the power supply device shown in FIG. 4A. FIG. 4C is a timing chart showing operation of the first DC-DC converter for explaining an open failure of a first switching element. FIG. 5A is a flowchart showing a method for diagnosing a switch in the power supply device shown in FIG. 2. FIG. 5B is a diagram showing current flow in the flowchart of FIG. 5A. FIG. 5C is a diagram showing a modified example of current flow in diagnosing a switch in the power supply device shown in FIG. 2. Fig. 6A is a flowchart showing a method for detecting a fault in a switching element in the buck-boost operation mode of the power supply device shown in Fig. 2. Fig. 6B is a diagram explaining the basis for determination in the flowchart of Fig. 6A. Fig. 6C is a flowchart showing a method for detecting a fault in a switching element in the buck-boost operation mode of the power supply device shown in Fig. 2, in which the buck operation and the boost operation of the first DC-DC converter and the second DC-DC converter in the buck-boost operation mode shown in Fig. 6A are interchanged. Fig. 6D is a diagram explaining the basis for determination in the flowchart of Fig. 6C. Fig. 7 is a block diagram showing the configuration of a power supply device according to a first modification of the embodiment. Fig. 8 is a block diagram showing the configuration of a power supply device according to a second modification of the embodiment. Fig. 9 is a block diagram showing the configuration of a power supply device according to a third modification of the embodiment.

[0009] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that each embodiment described below represents a specific example of the present disclosure. The numerical values, shapes, materials, components, the arrangement and connection of the components, steps, and the order of steps shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Furthermore, each figure is not necessarily an exact illustration. In each figure, substantially identical configurations are assigned the same reference numerals, and redundant explanations are omitted or simplified. Furthermore, "A and B are connected" means that A and B are electrically connected, and includes not only the case where A and B are directly connected, but also the case where A and B are indirectly connected with another circuit element sandwiched between A and B.

[0010] FIG. 1 is a block diagram showing the configuration of a power supply device 1 according to an embodiment.

[0011] The power supply device 1 is mounted on a vehicle 100 and connected to a first DC power supply 2 that supplies and maintains a first voltage and a second DC power supply 3 that supplies and maintains a second voltage lower than the first voltage, and includes: a first switch 5 having one end connected to the first DC power supply 2; a first capacitance 91 connected between the other end of the first switch 5 and a reference potential GND (ground); a second switch 6 having one end connected to the second DC power supply 3; a second capacitance 92 connected between the other end of the second switch 6 and the reference potential GND; a DCDC converter unit 4 having a first DCDC converter 41 and a second DCDC converter 42 connected in parallel between the other end of the first switch 5 and the other end of the second switch 6; and a control unit 7 having a diagnostic unit 8 that controls the first switch 5, the second switch 6, and the DCDC converter unit 4.

[0012] The power supply device 1 further includes a first potential detection unit 51 that detects the voltage at one end of the first switch 5, a second potential detection unit 52 that detects the voltage at the other end of the first switch 5, a third potential detection unit 61 that detects the voltage at one end of the second switch 6, and a fourth potential detection unit 62 that detects the voltage at the other end of the second switch 6.

[0013] The first DC power supply 2 is, for example, a chargeable and dischargeable battery, and the second DC power supply 3 is, for example, a chargeable and dischargeable electric double layer capacitor or battery.

[0014] The first switch 5 and the second switch 6 are switches that selectively take on a connected state or a disconnected state, and are, for example, semiconductor switches such as MOSFETs (metal oxide film field effect transistors), or contactors such as electromagnetic relays.

[0015] In accordance with instructions from the control unit 7, the first DC-DC converter 41 performs a step-down operation to step down the first voltage supplied from the first DC power source 2 side to a second voltage and output it to the second DC power source 3 side, and a step-up operation to step up the second voltage supplied from the second DC power source 3 side to the first voltage and output it to the first DC power source 2 side.

[0016] In accordance with instructions from the control unit 7, the second DC-DC converter 42 performs a step-down operation to step down the first voltage supplied from the first DC power source 2 side to a second voltage and output it to the second DC power source 3 side, and a step-up operation to step up the second voltage supplied from the second DC power source 3 side to the first voltage and output it to the first DC power source 2 side.

[0017] The first potential detection unit 51, the second potential detection unit 52, the third potential detection unit 61, and the fourth potential detection unit 62 are, for example, A / D converters. The first potential detection unit 51 and the second potential detection unit 52 constitute a first potential difference detection unit that detects a potential difference V5 across the first switch 5. The third potential detection unit 61 and the fourth potential detection unit 62 constitute a second potential difference detection unit that detects a potential difference V6 across the second switch 6.

[0018] The control unit 7 has the following three operation modes by controlling the first switch 5, the second switch 6, and the DCDC converter unit 4. The first operation mode is a step-down operation mode in which, with the first switch 5 and the second switch 6 connected, the first DCDC converter 41 and the second DCDC converter 42 perform step-down control in parallel, i.e., simultaneously, to step down a first voltage supplied from the first DC power supply 2 to a second voltage and output the voltage to the second DC power supply 3. The second operation mode is a step-up operation mode in which, with the first switch 5 and the second switch 6 connected, the first DCDC converter 41 and the second DCDC converter 42 perform step-up control in parallel, i.e., simultaneously, to step up a second voltage supplied from the second DC power supply 3 to the first voltage and output the voltage to the first DC power supply 2. The third operating mode is a step-up / step-down operating mode in which, with the first switch 5 and the second switch 6 turned off, the first DC-DC converter 41 is caused to step down the voltage of the first capacitance 91 and output it to the second capacitance 92, and in parallel, the second DC-DC converter 42 is caused to step up the voltage of the second capacitance 92 and output it to the first capacitance 91.

[0019] In the buck-boost operation mode, the buck operation and the boost operation of the first DC-DC converter 41 and the second DC-DC converter 42 may be interchanged. That is, with the first switch 5 and the second switch 6 cut off, buck-boost control may be performed to cause the first DC-DC converter 41 to boost the voltage of the second capacitance 92 and output it to the first capacitance 91, and in parallel, cause the second DC-DC converter 42 to lower the voltage of the first capacitance 91 and output it to the second capacitance 92.

[0020] Here, the step-down operation mode is one of voltage conversion operations in which a first voltage supplied from the first DC power supply 2 is stepped down and converted into a second voltage, and the first DC power supply 2 is charged with the stepped-up operation mode. The step-up operation mode is one of voltage conversion operations in which a second voltage supplied from the second DC power supply 3 is stepped up and converted into the first voltage, and the first DC power supply 2 is charged with the stepped-up operation mode. The step-up / step-down operation mode is an operation mode used for diagnosing the interruption capabilities of the first switch 5 and the second switch 6 and for diagnosing faults in the switching elements included in the DCDC converter unit 4, and is also called a diagnosis mode.

[0021] In the step-up / step-down operation mode, after step-up / step-down control, the diagnostic unit 8 calculates a first potential difference V5, which is the difference between the voltage detected by the first potential detection unit 51 and the voltage detected by the second potential detection unit 52, as the potential difference between the two ends of the first switch 5, and determines whether the calculated first potential difference V5 is larger than a predetermined first reference potential difference.If the first potential difference V5 is larger than the first reference potential difference, it determines that the breaking ability of the first switch 5 is normal, and if not, it determines that the breaking ability of the first switch 5 is abnormal.

[0022] Similarly, in the step-up / step-down operation mode, after step-up / step-down control, the diagnostic unit 8 calculates a second potential difference V6, which is the difference between the voltage detected by the third potential detection unit 61 and the voltage detected by the fourth potential detection unit 62, as the potential difference V6 across the second switch 6, and determines whether the calculated second potential difference V6 is larger than a predetermined second reference potential difference.If the second potential difference V6 is larger than the second reference potential difference, it determines that the breaking ability of the second switch 6 is normal, and if not, it determines that the breaking ability of the second switch 6 is abnormal.

[0023] The control unit 7 and the diagnosis unit 8 are realized by a memory that stores a program, a processor that executes the program, an A / D converter, a timer, and the like.

[0024] Note that, instead of the first potential detection unit 51 and the second potential detection unit 52, a first potential difference detection unit that directly detects the potential difference V5 across the first switch 5 may be provided. Similarly, instead of the third potential detection unit 61 and the fourth potential detection unit 62, a second potential difference detection unit that directly detects the potential difference V6 across the second switch 6 may be provided.

[0025] Fig. 2 is a diagram showing a specific example of the circuit of the DC-DC converter unit 4 included in the power supply device 1 shown in Fig. 1. Here, an overall circuit diagram of the power supply device 1 including a specific circuit of the DC-DC converter unit 4 is shown.

[0026] The first DC-DC converter 41 has a first current sensor 414, a first switching element 411, and a first reactor 413 connected in series between the first switch 5 and the second switch 6, and a second switching element 412 connected between a connection point J41 where the first switching element 411 and the first reactor 413 are connected in series and a reference potential GND.

[0027] The second DC-DC converter 42 has a second current sensor 424, a third switching element 421, and a second reactor 423 connected in series between the first switch 5 and the second switch 6, and a fourth switching element 422 connected between a connection point J42 where the third switching element 421 and the second reactor 423 are connected in series and a reference potential GND.

[0028] The first current sensor 414 and the second current sensor 424 are sensors that detect the current flowing through the first DC-DC converter 41 and the second DC-DC converter 42, respectively, and are composed of, for example, a resistive element and an A / D converter that converts the voltage across the resistive element into a digital value.

[0029] Each of the first switching element 411, the second switching element 412, the third switching element 421, and the fourth switching element 422 is, for example, an N-channel MOSFET, and has a body diode. The body diode has an anode on the source electrode side of the switching element and a cathode on the drain electrode side.

[0030] Next, the operation of the power supply device 1 according to this embodiment configured as above will be described.

[0031] FIG. 3A is a diagram showing the current flow in the step-down operation mode of the power supply device 1 shown in FIG.

[0032] In the step-down operation mode, under the control of the control unit 7, the first switch 5 and the second switch 6 maintain their connected states, and the first DC-DC converter 41 and the second DC-DC converter 42 perform the following operations in parallel.

[0033] In the first DC-DC converter 41, the first switching element 411 is turned on and the second switching element 412 is turned off, which causes a current supplied from the first DC power supply 2 to flow to the second DC power supply 3 via the first switch 5, the first current sensor 414, the first switching element 411, the first reactor 413, and the second switch 6, as shown in current path 21a, resulting in energy being stored in the first reactor 413. Furthermore, the first switching element 411 is turned off and the second switching element 412 is turned on, which causes the energy stored in the first reactor 413 to be released, as shown in current path 21b, and a current flows from the reference potential GND to the second DC power supply 3 via the second switching element 412, the first reactor 413, and the second switch 6, and further, depending on the output mode (high output / low output), a current may flow in the opposite direction. In the first DC-DC converter 41, the above-described state in which energy is stored in the first reactor 413 and the above-described state in which the energy stored in the first reactor 413 is released are alternately and repeatedly switched.

[0034] At this time, the control unit 7 monitors the current value detected by the first current sensor 414, and controls the switching operation of the first switching element 411 and the second switching element 412 by controlling the on-duty of the PWM (pulse width modulation) control signal output to the first switching element 411 and the second switching element 412 so that the current value is below a predetermined upper limit value or within a predetermined range.

[0035] In the second DC-DC converter 42, the third switching element 421 is turned on and the fourth switching element 422 is turned off, whereby, as shown in a current path 22a, a current supplied from the first DC power supply 2 flows to the second DC power supply 3 via the first switch 5, the second current sensor 424, the third switching element 421, the second reactor 423, and the second switch 6, and as a result, energy is accumulated in the second reactor 423. In addition, the third switching element 421 is turned off and the fourth switching element 422 is turned on, whereby, as shown in a current path 22b, the energy accumulated in the second reactor 423 is released and a current flows from the reference potential GND to the second DC power supply 3 via the fourth switching element 422, the second reactor 423, and the second switch 6, and further, depending on the output mode (high output / low output), a current may flow through the reverse path. In the second DC-DC converter 42, the above-described state in which energy is stored in the second reactor 423 and the above-described state in which the energy stored in the second reactor 423 is released are alternately and repeatedly switched.

[0036] At this time, the control unit 7 monitors the current value detected by the second current sensor 424, and controls the switching operation of the third switching element 421 and the fourth switching element 422 by controlling the on-duty of the PWM control signal output to the third switching element 421 and the fourth switching element 422 so that the current value is below a predetermined upper limit value or within a predetermined range.

[0037] In this way, in the step-down operation mode, the first DC-DC converter 41 and the second DC-DC converter 42 perform step-down operation in parallel to step down the first voltage supplied from the first DC power source 2 to the second voltage and output it to the second DC power source 3.

[0038] 3B is a diagram illustrating a switching element failure in the step-down operation mode of the power supply device 1 shown in FIG. 3A. This diagram illustrates the current flow when the second switching element 412 has an open fault. An open fault in a switching element refers to a failure in which the switching element remains disconnected and not connected. As shown in this diagram, when the second switching element 412 has an open fault, as shown in current path 21b, the current flowing from the reference potential GND through the second switching element 412 toward the first reactor 413 becomes a current flowing in the forward direction of the body diode of the second switching element 412, and no current flows in the reverse direction, resulting in asynchronous rectification.

[0039] 3C is a timing chart showing the operation of the first DC-DC converter 41 to explain an open fault of the second switching element 412. In FIG. 3C, "Hi-Side switch (411)" indicates the on / off of the first switching element 411, "Lo-Side switch (412)" indicates the on / off of the second switching element 412, "inductor (413) current: at high output" indicates the current flowing through the first reactor 413 at high output, "inductor (413) current: at low output (synchronous rectification: continuous mode)" indicates the current flowing through the first reactor 413 when the second switching element 412 is normal at low output, and "inductor (413) current: at low output (asynchronous rectification: discontinuous mode)" indicates the current flowing through the first reactor 413 when an open fault occurs in the second switching element 412 at low output.

[0040] As can be seen from the current waveform of "Inductor (413) Current: At Low Output (Asynchronous Rectification: Discontinuous Mode)" in FIG. 3C, even if the second switching element 412 has an open fault, at low output, the operation mode simply changes from synchronous rectification (continuous mode) to asynchronous rectification (discontinuous mode), and the step-down operation is performed.

[0041] This phenomenon also occurs when the fourth switching element 422 in the second DC-DC converter 42 has an open fault.

[0042] Therefore, in the step-down operation mode, even if the switching elements on the low side of each DCDC converter, that is, the second switching element 412 and the fourth switching element 422, have an open fault, it is difficult to detect the fault because the step-down operation is performed. In contrast, as will be described later, in the diagnosis mode, it is possible to detect an open fault in the switching elements.

[0043] FIG. 4A is a diagram showing the current flow in the boost operation mode of the power supply device 1 shown in FIG.

[0044] In the boost operation mode, under the control of the control unit 7, the first switch 5 and the second switch 6 maintain their connected state, and the first DC-DC converter 41 and the second DC-DC converter 42 perform the following operations in parallel, i.e., simultaneously.

[0045] In the first DC-DC converter 41, the first switching element 411 is turned off and the second switching element 412 is turned on, which causes current supplied from the second DC power supply 3 to flow to the reference potential GND via the first reactor 413 and the second switching element 412, as shown in current path 31a, resulting in energy being stored in the first reactor 413. Furthermore, the first switching element 411 is turned on and the second switching element 412 is turned off, which causes the energy stored in the first reactor 413 to be released, as shown in current path 31b, and current flows from the second DC power supply 3 to the first DC power supply 2 via the first reactor 413, the first switching element 411, the first current sensor 414, and the first switch 5. In the first DC-DC converter 41, the above-mentioned state in which energy is stored in the first reactor 413 and the state in which the energy stored in the first reactor 413 is released are repeatedly switched alternately.

[0046] At this time, the control unit 7 monitors the current value detected by the first current sensor 414, and controls the switching operation of the first switching element 411 and the second switching element 412 by controlling the on-duty of the PWM control signal output to the first switching element 411 and the second switching element 412 so that the current value is below a predetermined upper limit value or within a predetermined range.

[0047] In the second DC-DC converter 42, the third switching element 421 is turned off and the fourth switching element 422 is turned on, which causes current supplied from the second DC power supply 3 to flow to the reference potential GND via the second reactor 423 and the fourth switching element 422, as shown by current path 32a, resulting in energy being stored in the second reactor 423. Furthermore, the third switching element 421 is turned on and the fourth switching element 422 is turned off, which causes the energy stored in the second reactor 423 to be released, as shown by current path 32b, and current flows from the second DC power supply 3 to the first DC power supply 2 via the second reactor 423, the third switching element 421, the second current sensor 424, and the first switch 5. The second DC-DC converter 42 alternately and repeatedly switches between the state in which energy is stored in the second reactor 423 and the state in which the energy stored in the second reactor 423 is released.

[0048] At this time, the control unit 7 monitors the current value detected by the second current sensor 424, and controls the switching operation of the third switching element 421 and the fourth switching element 422 by controlling the on-duty of the PWM control signal output to the third switching element 421 and the fourth switching element 422 so that the current value is below a predetermined upper limit value or within a predetermined range.

[0049] In this way, in the boost operation mode, the first DC-DC converter 41 and the second DC-DC converter 42 perform a boost operation in parallel to boost the second voltage supplied from the second DC power source 3 to the first voltage and output it to the first DC power source 2.

[0050] 4B is a diagram illustrating a switching element failure in the boost operation mode of the power supply device 1 shown in FIG. 4A. This diagram shows the current flow when the first switching element 411 has an open fault. As shown in this diagram, when the first switching element 411 has an open fault, the current flowing from the first reactor 413 to the first current sensor 414 becomes a current flowing in the forward direction of the body diode of the first switching element 411, as shown by current path 31b.

[0051] 4C is a timing chart showing the operation of the first DC-DC converter 41 to explain an open fault of the first switching element 411. In FIG. 4C, "Lo-Side switch (412)" indicates the on / off of the second switching element 412, "Hi-Side switch (411)" indicates the on / off of the first switching element 411, "inductor (413) current: at high output" indicates the current flowing through the first reactor 413 at high output, "inductor (413) current: at low output (synchronous rectification: continuous mode)" indicates the current flowing through the first reactor 413 when the first switching element 411 is normal at low output, and "inductor (413) current: at low output (asynchronous rectification: discontinuous mode)" indicates the current flowing through the first reactor 413 when an open fault occurs in the first switching element 411 at low output.

[0052] As can be seen from the current waveform of “Inductor (413) Current: At Low Output (Asynchronous Rectification: Discontinuous Mode)” in FIG. 4C , even if the first switching element 411 has an open fault, at low output, the operation mode simply changes from synchronous rectification (continuous mode) to asynchronous rectification (discontinuous mode), and the boost operation is still performed.

[0053] This phenomenon also occurs when the third switching element 421 in the second DC-DC converter 42 has an open fault.

[0054] Therefore, in the boost operation mode, even if the switching elements on the high side of each DCDC converter, that is, the first switching element 411 and the third switching element 421, have an open fault, it is difficult to detect the fault because the boost operation is performed. In contrast, as will be described later, in the diagnosis mode, it is possible to detect an open fault in the switching elements.

[0055] FIG. 5A is a flowchart showing a method for diagnosing the switches 5 and 6 in the power supply device 1 shown in FIG.

[0056] First, the control unit 7 instructs the first switch 5 and the second switch 6 to turn off the first switch 5 and the second switch 6 (S10).

[0057] Next, the control unit 7 causes the DCDC converter unit 4 to perform a voltage step-up / step-down operation, thereby discharging the charge accumulated in the first capacitance 91 and the second capacitance 92 (S11). Specifically, the control unit 7 causes the first DCDC converter 41 to perform a voltage step-down operation for a certain period of time (e.g., one second), and in parallel, i.e., simultaneously, causes the second DCDC converter 42 to perform a voltage step-up operation, thereby discharging the charge accumulated in the first capacitance 91 and the second capacitance 92.

[0058] FIG. 5B is a diagram showing the current flow in step S11 of FIG. 5A.

[0059] In the first DC-DC converter 41, the first switching element 411 is turned on and the second switching element 412 is turned off, which causes the charge stored in the first capacitance 91 to be released and a current to flow to the second capacitance 92 via the first current sensor 414, the first switching element 411, and the first reactor 413, as shown in current path 21a, resulting in energy being stored in the first reactor 413. Furthermore, the first switching element 411 is turned off and the second switching element 412 is turned on, which causes the energy stored in the first reactor 413 to be released and a current to flow from the reference potential GND to the second capacitance 92 via the second switching element 412 and the first reactor 413, as shown in current path 21b, and furthermore, depending on the output mode (high output / low output), a current may flow in the opposite direction. In the first DC-DC converter 41, the above-described state in which energy is stored in the first reactor 413 and the above-described state in which the energy stored in the first reactor 413 is released are alternately and repeatedly switched.

[0060] By such a voltage step-down operation by the first DC-DC converter 41, the charge stored in the first capacitance 91 is released, and the voltage of the first capacitance 91 decreases.

[0061] In the second DC-DC converter 42, the third switching element 421 is turned off and the fourth switching element 422 is turned on, which causes the charge stored in the second capacitance 92 to be released as shown by current path 32a, and a current flows to the reference potential GND via the second reactor 423 and the fourth switching element 422, resulting in energy being stored in the second reactor 423. Furthermore, the third switching element 421 is turned on and the fourth switching element 422 is turned off, which causes the energy stored in the second reactor 423 to be released as shown by current path 32b, and a current flows from the second capacitance 92 to the first capacitance 91 via the second reactor 423, the third switching element 421, and the second current sensor 424. The second DC-DC converter 42 alternately and repeatedly switches between the state in which energy is stored in the second reactor 423 and the state in which the energy stored in the second reactor 423 is released.

[0062] Such a voltage boosting operation by the second DC-DC converter 42 causes the charge stored in the second capacitance 92 to be released, and the voltage of the second capacitance 92 drops.

[0063] At this time, the second capacitance 92 is charged by the first DC-DC converter 41, and the first capacitance 91 is charged by the second DC-DC converter 42. However, for example, due to losses caused by the on-resistance of the switches 5 and 6 and conduction losses in the inductors 413 and 423, the conversion efficiency of the first DC-DC converter 41 and the second DC-DC converter 42 does not reach 100% or more. Therefore, although the second capacitance 92 is charged by the first DC-DC converter 41 and the first capacitance 91 is charged by the second DC-DC converter 42, the sum of the energies of the first capacitance 91 and the second capacitance 92 decreases due to losses in the first DC-DC converter 41 and the second DC-DC converter 42, and therefore the voltages of both the first capacitance 91 and the second capacitance 92 drop.

[0064] Next, in order to detect the potential difference V5 across the first switch 5, the diagnostic unit 8 of the control unit 7 calculates a first potential difference V5, which is the difference between the voltage detected by the first potential detection unit 51 and the voltage detected by the second potential detection unit 52 (S12), and determines whether the calculated first potential difference V5 is greater than a predetermined first reference potential difference (S13).If the first potential difference V5 is greater than the first reference potential difference (Yes in S13), it determines that the breaking ability of the first switch 5 is normal (S14), and if the first potential difference V5 is not greater than the first reference potential difference (No in S13), it determines that the breaking ability of the first switch 5 is abnormal (S15).

[0065] Next, in order to detect the potential difference V6 across the second switch 6, the diagnostic unit 8 of the control unit 7 calculates a second potential difference V6, which is the difference between the voltage detected by the third potential detection unit 61 and the voltage detected by the fourth potential detection unit 62 (S16), and determines whether the calculated second potential difference V6 is greater than a predetermined second reference potential difference (S17).If the second potential difference V6 is greater than the second reference potential difference (Yes in S17), it determines that the breaking ability of the second switch 6 is normal (S18), and if the second potential difference V6 is not greater than the second reference potential difference (No in S17), it determines that the breaking ability of the second switch 6 is abnormal (S19).

[0066] In this way, in diagnosing the first switch 5 and the second switch 6, after the first switch 5 and the second switch 6 are instructed to be in a cut-off state, the charge stored in the first capacitance 91 is released by the step-down operation of the first DC-DC converter 41, causing the voltage of the first capacitance 91 to decrease, and at the same time, the charge stored in the second capacitance 92 is released by the step-up operation of the second DC-DC converter 42, causing the voltage of the second capacitance 92 to decrease.

[0067] Therefore, compared to a power supply device of the comparative example that does not have a step-down operation by the first DC-DC converter 41 and a step-up operation by the second DC-DC converter 42, if the breaking capability of the first switch 5 is normal, the potential difference V5 across the first switch 5 increases in a short time, and similarly, if the breaking capability of the second switch 6 is normal, the potential difference V6 across the second switch 6 increases in a short time. As a result, the breaking capabilities of the first switch 5 and the second switch 6 are diagnosed simultaneously and in a short time compared to the power supply device of the comparative example. Note that in FIG. 5A , the diagnosis of the second switch 6 in steps S16 to S19 may be performed before the diagnosis of the first switch 5 in steps S12 to S15.

[0068] After the switches 5 and 6 are disconnected and the diagnosis of the switches 5 and 6 is completed, the control unit 7 may monitor the voltage detected by the second potential detection unit 52 and cause the first DC-DC converter 41 and the second DC-DC converter 42 to perform a boost operation to charge the first capacitance 91 so as to bring the voltage of the first capacitance 91 closer to the original first voltage, and after the potential difference V5 across the first switch 5 falls within a predetermined range, the first switch 5 may be switched to a connected state. This suppresses the generation of a rush current caused by switching the first switch 5 from a disconnected state to a connected state when the potential difference V5 across the first switch 5 is large.

[0069] Similarly, after the switches 5 and 6 are disconnected and the diagnosis of the switches 5 and 6 is completed, the control unit 7 may monitor the voltage detected by the fourth potential detection unit 62 and cause the first DC-DC converter 41 and the second DC-DC converter 42 to perform a step-down operation to charge the second capacitance 92 so as to bring the voltage of the second capacitance 92 closer to the original second voltage, and after the potential difference V6 across the second switch 6 falls within a predetermined range, the second switch 6 may be switched to a connected state. This suppresses the generation of a rush current caused by switching the second switch 6 from a disconnected state to a connected state when the potential difference V6 across the second switch 6 is large.

[0070] Fig. 5C is a diagram showing a modified example of the current flow in the diagnosis of the switches in the power supply device 1 shown in Fig. 2. In this modified example, in the voltage step-up / step-down operation mode, the control unit 7 performs voltage step-up / step-down control in a state in which the second switching element 412 and the third switching element 421 are always turned off (hereinafter, this state is also referred to as "fixed open").

[0071] Specifically, in the first DC-DC converter 41, under the control of the control unit 7, the first switching element 411 is turned on while the second switching element 412 is maintained off, which causes the charge stored in the first capacitance 91 to be released and a current to flow to the second capacitance 92 via the first current sensor 414, the first switching element 411, and the first reactor 413, as shown in current path 21a, resulting in energy being stored in the first reactor 413. Also, in the first DC-DC converter 41, under the control of the control unit 7, the first switching element 411 is turned off while the second switching element 412 is maintained off, which causes the energy stored in the first reactor 413 to be released and a current to flow from the reference potential GND to the second capacitance 92 via the body diode of the second switching element 412 and the first reactor 413, as shown in current path 21b. In the first DC-DC converter 41, under the control of the control unit 7, the second switching element 412 is kept off, and the above-mentioned state in which energy is stored in the first reactor 413 and the above-mentioned state in which the energy stored in the first reactor 413 is released are alternately and repeatedly switched.

[0072] By such a voltage step-down operation by the first DC-DC converter 41, the charge stored in the first capacitance 91 is released, and the voltage of the first capacitance 91 decreases.

[0073] Moreover, in the second DC-DC converter 42, under the control of the control unit 7, the fourth switching element 422 is turned on while the third switching element 421 is maintained off, whereby, as shown by a current path 32a, the charge stored in the second capacitance 92 is released and a current flows to the reference potential GND via the second reactor 423 and the fourth switching element 422, resulting in energy being stored in the second reactor 423. Also, in the second DC-DC converter 42, under the control of the control unit 7, the fourth switching element 422 is turned off while the third switching element 421 is maintained off, whereby, as shown by a current path 32b, the energy stored in the second reactor 423 is released and a current flows from the second capacitance 92 to the first capacitance 91 via the second reactor 423, the body diode of the third switching element 421, and the second current sensor 424. In the second DC-DC converter 42, under the control of the control unit 7, the third switching element 421 is kept off, and the above-mentioned state in which energy is stored in the second reactor 423 and the above-mentioned state in which the energy stored in the second reactor 423 is released are alternately and repeatedly switched.

[0074] Such a voltage boosting operation by the second DC-DC converter 42 causes the charge stored in the second capacitance 92 to be released, and the voltage of the second capacitance 92 drops.

[0075] Even in the buck-boost operation mode according to this modified example, compared to the conventional technology in which there is no buck operation by the first DC-DC converter 41 or no boost operation by the second DC-DC converter 42, if the breaking capability of the first switch 5 is normal, the potential difference V5 across the first switch 5 increases in a short time, and if the breaking capability of the second switch 6 is normal, the potential difference V6 across the second switch 6 increases in a short time. As a result, the breaking capabilities of the first switch 5 and the second switch 6 are diagnosed simultaneously and in a shorter time than conventionally possible.

[0076] FIG. 6A is a flowchart showing a method for detecting a fault in a switching element in the step-up / step-down operation mode of the power supply device 1 shown in FIG.

[0077] First, the control unit 7 turns off the first switch 5 and the second switch 6 (S20).

[0078] Next, the control unit 7 causes the DCDC converter unit 4 to perform a voltage step-up / step-down operation, thereby discharging the charge accumulated in the first capacitance 91 and the second capacitance 92 (S21). Specifically, the control unit 7 causes the first DCDC converter 41 to perform a voltage step-down operation for a certain period of time (e.g., one second), and in parallel causes the second DCDC converter 42 to perform a voltage step-up operation, thereby discharging the charge accumulated in the first capacitance 91 and the second capacitance 92.

[0079] Then, the control unit 7 detects the first potential P15 using the second potential detection unit 52 (S22), and determines whether the first potential P15 detected by the second potential detection unit 52 is equal to or less than a predetermined first reference potential (S23).If the first potential P15 is equal to or less than the first reference potential (Yes in S23), the control unit 7 determines that the first switching element 411 is normal (S24).On the other hand, if the first potential P15 is not equal to or less than the first reference potential (No in S23), the control unit 7 determines that the first switching element 411 is abnormal (open failure) and is fixed off (S25).

[0080] Next, the control unit 7 detects the second potential P16 using the fourth potential detection unit 62 (S36), and determines whether the second potential P16 detected by the fourth potential detection unit 62 is equal to or less than a predetermined second reference potential (S27).If the second potential P16 is equal to or less than the second reference potential (Yes in S27), the control unit 7 determines that the fourth switching element 422 is normal (S28).On the other hand, if the second potential P16 is not equal to or less than the second reference potential (No in S27), the control unit 7 determines that the fourth switching element 422 is abnormal and fixed to off (open failure) (S29).

[0081] Fig. 6B is a diagram illustrating the basis for the determinations in steps S23 to S25 in Fig. 6A and the determinations in steps S27 to S29 in Fig. 6A. Here, based on Fig. 5C, the difference in current flow when the first switching element 411 and the fourth switching element 422 have an open fault is shown.

[0082] In the first DC-DC converter 41, when the first switching element 411 is normal, the first switching element 411 is turned on as shown in current path 21a, thereby discharging the charge stored in the first capacitance 91 and causing a current to flow to the second capacitance 92 via the first current sensor 414, the first switching element 411, and the first reactor 413, resulting in energy being stored in the first reactor 413. Furthermore, in the first DC-DC converter 41, when the first switching element 411 is normal, the first switching element 411 is turned off as shown in current path 21b, thereby discharging the energy stored in the first reactor 413 and causing a current to flow from the reference potential GND to the second capacitance 92 via the body diode of the second switching element 412 and the first reactor 413. In the first DC-DC converter 41, when the first switching element 411 is normal, the above-mentioned state in which energy is stored in the first reactor 413 and the above-mentioned state in which the energy stored in the first reactor 413 is released are alternately and repeatedly switched over.

[0083] Therefore, due to such a step-down operation by the first DC-DC converter 41, the charge accumulated in the first capacitance 91 is released, and the voltage of the first capacitance 91 decreases. However, if the first switching element 411 has an open fault, no current flows from the first capacitance 91 to the first reactor 413 via the first switching element 411. Therefore, the step-down operation by the first DC-DC converter 41 is not performed, the charge accumulated in the first capacitance 91 is not sufficiently released, and the voltage of the first capacitance 91, i.e., the first potential P15 detected by the second potential detection unit 52, does not decrease sufficiently, or it takes time for the voltage to decrease sufficiently.

[0084] Therefore, if the first potential P15 detected by the second potential detection unit 52 is not equal to or lower than the first reference potential (No in S23), the control unit 7 can determine that the first switching element 411 has an open failure (S25).

[0085] Similarly, in the second DC-DC converter 42, when the fourth switching element 422 is normal, the fourth switching element 422 is turned on as shown in current path 32a, thereby discharging the charge stored in the second capacitance 92 and causing a current to flow to the reference potential GND via the second reactor 423 and the fourth switching element 422, and as a result, energy is stored in the second reactor 423. Furthermore, in the second DC-DC converter 42, when the fourth switching element 422 is normal, the fourth switching element 422 is turned off as shown in current path 32b, thereby discharging the energy stored in the second reactor 423 and causing a current to flow from the second capacitance 92 to the first capacitance 91 via the second reactor 423, the body diode of the third switching element 421, and the second current sensor 424. In the second DC-DC converter 42, when the fourth switching element 422 is normal, the above-mentioned state in which energy is stored in the second reactor 423 and the above-mentioned state in which the energy stored in the second reactor 423 is released are alternately and repeatedly switched over.

[0086] Due to this voltage step-up operation by the second DC-DC converter 42, the charge stored in the second capacitance 92 is released, and the voltage of the second capacitance 92 decreases. However, if the fourth switching element 422 has an open fault, no current flows from the second capacitance 92 toward the reference potential GND via the second reactor 423 and the fourth switching element 422. As a result, the voltage step-up operation by the second DC-DC converter 42 is not performed, the charge stored in the second capacitance 92 is not sufficiently released, and the second capacitance 92, i.e., the second potential P16 detected by the fourth potential detection unit 62, does not decrease sufficiently, or it takes time for the second capacitance 92 to decrease sufficiently.

[0087] Therefore, if the second potential P16 detected by the fourth potential detection unit 62 is not equal to or lower than the second reference potential (No in S27), the control unit 7 can determine that the fourth switching element 422 has an open failure (S29).

[0088] Therefore, in the step-up / step-down operation mode (diagnosis mode), it is possible to not only diagnose the interruption capabilities of the first switch 5 and the second switch 6, but also simultaneously diagnose the first switching element 411 and the fourth switching element 422 for open failures.

[0089] 6A , the step-down operation and step-up operation of the first DC-DC converter 41 and the second DC-DC converter 42 may be interchanged. That is, with the first switch 5 and the second switch 6 cut off, step-up / step-down control may be performed to cause the first DC-DC converter 41 to step up the voltage of the second capacitance 92 and output it to the first capacitance 91, while simultaneously causing the second DC-DC converter 42 to step down the voltage of the first capacitance 91 and output it to the second capacitance 92.

[0090] 6C is a flowchart showing a method for detecting a fault in a switching element in the buck-boost operation mode of the power supply device 1 shown in FIG. 2, in which the buck operation and the boost operation of the first DC-DC converter 41 and the second DC-DC converter 42 are interchanged in the buck-boost operation mode shown in FIG. 6A.

[0091] First, the control unit 7 turns off the first switch 5 and the second switch 6 (S30).

[0092] Next, the control unit 7 causes the DCDC converter unit 4 to perform a voltage step-up / step-down operation, thereby discharging the charge accumulated in the first capacitance 91 and the second capacitance 92 (S31). Specifically, the control unit 7 causes the first DCDC converter 41 to perform a voltage step-up operation for a certain period of time (e.g., one second), and in parallel causes the second DCDC converter 42 to perform a voltage step-down operation, thereby discharging the charge accumulated in the first capacitance 91 and the second capacitance 92.

[0093] Then, the control unit 7 detects the first potential P15 using the second potential detection unit 52 (S32), and determines whether the first potential P15 detected by the second potential detection unit 52 is equal to or less than a predetermined first reference potential (S33).If the first potential P15 is equal to or less than the first reference potential (Yes in S33), the control unit 7 determines that the third switching element 421 is normal (S34).On the other hand, if the first potential P15 is not equal to or less than the first reference potential (No in S33), the control unit 7 determines that the third switching element 421 is abnormal (open failure) and is fixed off (S35).

[0094] Next, the control unit 7 detects the second potential P16 using the fourth potential detection unit 62 (S36), and determines whether the second potential P16 detected by the fourth potential detection unit 62 is equal to or less than a predetermined second reference potential (S37).If the second potential P16 is equal to or less than the second reference potential (Yes in S37), the control unit 7 determines that the second switching element 412 is normal (S38).On the other hand, if the second potential P16 is not equal to or less than the second reference potential (No in S37), the control unit 7 determines that the second switching element 412 is abnormal and fixed to the off position (Open failure) (S39).

[0095] Fig. 6D is a diagram illustrating the basis for the determinations in steps S33 to S35 in Fig. 6C and the determinations in steps S37 to S39 in Fig. 6C. Here, based on Fig. 5C, the difference in current flow when the second switching element 412 and the third switching element 421 have an open fault is shown.

[0096] In the second DC-DC converter 42, when the third switching element 421 is normal, the third switching element 421 is turned on as shown in current path 22a, causing the charge stored in the first capacitance 91 to be released and a current to flow to the second capacitance 92 via the second current sensor 424, the third switching element 421, and the second reactor 423, resulting in energy being stored in the second reactor 423. Furthermore, in the second DC-DC converter 42, when the third switching element 421 is normal, the third switching element 421 is turned off as shown in current path 22b, causing the energy stored in the second reactor 423 to be released and a current to flow from the reference potential GND to the second capacitance 92 via the body diode of the fourth switching element 422 and the second reactor 423. In the second DC-DC converter 42, when the third switching element 421 is normal, the above-mentioned state in which energy is stored in the second reactor 423 and the above-mentioned state in which the energy stored in the second reactor 423 is released are alternately and repeatedly switched over.

[0097] Therefore, due to the voltage step-down operation by the second DC-DC converter 42, the charge stored in the first capacitance 91 is released, and the voltage of the first capacitance 91 decreases. However, if the third switching element 421 has an open fault, no current flows from the first capacitance 91 to the second reactor 423 via the third switching element 421. Therefore, the voltage step-down operation by the second DC-DC converter 42 is not performed, the charge stored in the first capacitance 91 is not sufficiently released, and the voltage of the first capacitance 91, i.e., the first potential P15 detected by the second potential detection unit 52, does not decrease sufficiently, or it takes time for the voltage to decrease sufficiently.

[0098] Therefore, if the first potential P15 detected by the second potential detection unit 52 is not equal to or lower than the first reference potential (No in S33), the control unit 7 can determine that the third switching element 421 has an open failure (S35).

[0099] Similarly, in the first DC-DC converter 41, when the second switching element 412 is normal, the second switching element 412 is turned on as shown in current path 31a, thereby discharging the charge stored in the second capacitance 92 and causing a current to flow to the reference potential GND via the first reactor 413 and the second switching element 412, and as a result, energy is stored in the first reactor 413. Furthermore, in the first DC-DC converter 41, when the second switching element 412 is normal, the second switching element 412 is turned off as shown in current path 31b, thereby discharging the energy stored in the first reactor 413 and causing a current to flow from the second capacitance 92 to the first capacitance 91 via the first reactor 413, the body diode of the first switching element 411, and the first current sensor 414. In the first DC-DC converter 41, when the second switching element 412 is normal, the above-mentioned state in which energy is stored in the first reactor 413 and the above-mentioned state in which the energy stored in the first reactor 413 is released are alternately and repeatedly switched.

[0100] Due to this voltage step-up operation by the first DC-DC converter 41, the charge stored in the second capacitance 92 is released, and the voltage of the second capacitance 92 decreases. However, if the second switching element 412 has an open fault, no current flows from the second capacitance 92 toward the reference potential GND via the first reactor 413 and the second switching element 412. As a result, the voltage step-up operation by the first DC-DC converter 41 is not performed, the charge stored in the second capacitance 92 is not sufficiently released, and the second capacitance 92, i.e., the second potential P16 detected by the fourth potential detection unit 62, does not decrease sufficiently, or it takes time for the second capacitance 92 to decrease sufficiently.

[0101] Therefore, if the second potential P16 detected by the fourth potential detection unit 62 is not equal to or lower than the second reference potential (No in S37), the control unit 7 can determine that the second switching element 412 has an open failure (S39).

[0102] Therefore, in the step-up / step-down operation mode (diagnosis mode), it is possible to not only diagnose the interruption capabilities of the first switch 5 and the second switch 6, but also simultaneously diagnose the second switching element 412 and the third switching element 421 for open failures.

[0103] As described above, the power supply device 1 according to the embodiment is a power supply device connected to a first DC power supply 2 that supplies and maintains a first voltage and a second DC power supply 3 that supplies and maintains a second voltage lower than the first voltage, and includes: a first switch 5 having one end connected to the first DC power supply 2; a first capacitance 91 connected between the other end of the first switch 5 and the reference potential GND; a second switch 6 having one end connected to the second DC power supply 3; a second capacitance 92 connected between the other end of the second switch 6 and the reference potential GND; a DCDC converter unit 4 having a first DCDC converter 41 and a second DCDC converter 42 connected in parallel between the other end of the first switch 5 and the other end of the second switch 6; and a control unit 7 that controls the first switch 5, the second switch 6, and the DCDC converter unit 4. The control unit 7 controls the first DCDC converter 41 and the second DCDC converter 42 when the first switch 5 and the second switch 6 are connected. The control circuit has a step-down operation mode in which step-down control is performed on the CDC converter 41 and the second DC-DC converter 42 in parallel to step-down a first voltage supplied from the first DC power supply 2 to a second voltage and output the second voltage to the second DC power supply 3; a step-up operation mode in which step-up control is performed on the first DC-DC converter 41 and the second DC-DC converter 42 in parallel to step-up a second voltage supplied from the second DC power supply 3 to the first voltage and output the first DC power supply 2 with the first switch 5 and the second switch 6 connected; and a step-up / step-down operation mode (diagnosis mode) in which step-up / step-down control is performed on the first DC-DC converter 41 and the second DC-DC converter 42 in parallel to step-down a second voltage supplied from the second DC power supply 3 to the first voltage and output the first DC power supply 2 with the first switch 5 and the second switch 6 disconnected, to cause the first DC-DC converter 41 to step-down the voltage of the first capacitance 91 and output it to the second capacitance 92, and in parallel to step-up / step-down control is performed on the second DC-DC converter 42 to step-up the voltage of the second capacitance 92 and output it to the first capacitance 91 with the first switch 5 and the second switch 6 disconnected.

[0104] As a result, in the diagnosis mode, with the first switch 5 and the second switch 6 in an interrupted state, the first DC-DC converter 41 steps down the voltage of the first capacitance 91 and outputs it to the second capacitance 92, and in parallel, the second DC-DC converter 42 steps up the voltage of the second capacitance 92 and outputs it to the first capacitance 91. Therefore, if the interruption capability of the first switch 5 is normal, the potential difference V5 across both ends of the first switch 5 increases in a short time, and if the interruption capability of the second switch 6 is normal, the potential difference V6 across both ends of the second switch 6 increases in a short time. As a result, the interruption capabilities of the first switch 5 and the second switch 6 are diagnosed simultaneously and in a shorter time than before.

[0105] Specifically, the power supply device 1 includes a first potential difference detection unit that detects a potential difference V5 across the first switch 5 and a second potential difference detection unit that detects a potential difference V6 across the second switch 6, and in the step-up / step-down operation mode, the control unit 7 determines whether the first potential difference V5 detected by the first potential difference detection unit is greater than a first reference potential difference after step-up / step-down control, and determines that the first switch 5 is normal if the first potential difference V5 is greater than the first reference potential difference, and determines that the first switch 5 is abnormal and cannot be shut off if the first potential difference V5 is not greater than the first reference potential difference. Furthermore, in the step-up / step-down operation mode, after step-up / step-down control, the control unit 7 determines whether the second potential difference V6 detected by the second potential difference detection unit is greater than the second reference potential difference, and determines that the second switch 6 is normal if the second potential difference V6 is greater than the second reference potential difference, and determines that the second switch 6 is abnormal and cannot be turned off if the second potential difference V6 is not greater than the second reference potential difference.

[0106] Here, in the voltage step-up / step-down operation mode, the control unit 7 may, after turning off the first switch 5 and the second switch 6, perform voltage step-down by the first DC-DC converter 41 and voltage step-up by the second DC-DC converter 42 for a certain period of time. This makes it possible to set the potential difference V6 across the first switch 5 and the second switch 6 to an appropriate value.

[0107] Here, the first DC-DC converter 41 may include a first switching element 411 and a first reactor 413 connected in series between the first switch 5 and the second switch 6, and a second switching element 412 having a body diode connected between a junction J41 where the first switching element 411 and the first reactor 413 are connected in series and the reference potential GND, while the second DC-DC converter 42 may include a third switching element 421 and a second reactor 423 having a body diode connected in series between the first switch 5 and the second switch 6, and a fourth switching element 422 connected between a junction J42 where the third switching element 421 and the second reactor 423 are connected in series and the reference potential GND. This allows the first DC-DC converter 41 and the second DC-DC converter 42 to be realized with simple circuits.

[0108] Furthermore, in the step-up / step-down operation mode, the control unit 7 may perform step-up / step-down control while constantly keeping the second switching element 412 and the third switching element 421 off. As a result, in the step-up / step-down operation mode, current flows through the body diodes of the second switching element 412 and the third switching element 421, which increases the power consumption and enables the interruption capabilities of the first switch 5 and the second switch 6 to be diagnosed in a shorter time.

[0109] Furthermore, the first DC-DC converter 41 and the second DC-DC converter 42 have a first current sensor 414 and a second current sensor 424 that detect the current flowing through the first DC-DC converter 41 and the second DC-DC converter 42, and the control unit 7 may control the DC-DC converter unit 4 so that the currents detected by the first current sensor 414 and the second current sensor 424 are within a predetermined range in the step-down operation mode, the step-up operation mode, and the step-up / step-down operation mode. This limits the current flowing through the first DC-DC converter 41 and the second DC-DC converter 42 to a certain level or less, thereby suppressing the generation of rush current.

[0110] The power supply device 1 may also include a second potential detector 52 that detects a potential P15 at the other end of the first switch 5 and a fourth potential detector 62 that detects a potential P16 at the other end of the second switch 6. In the step-up / step-down operation mode, the control unit 7 may determine whether the first potential P15 detected by the second potential detector 52 is equal to or lower than a first reference potential, and if the first potential P15 is not equal to or lower than the first reference potential, determine that an abnormality has occurred in which the first switching element 411 is fixed to OFF. The control unit 7 may also determine whether the second potential P16 detected by the fourth potential detector 62 is equal to or lower than a second reference potential, and if the second potential P16 is not equal to or lower than the second reference potential, determine that an abnormality has occurred in which the fourth switching element 422 is fixed to OFF. In this way, open faults in the first switching element 411 and the fourth switching element 422 are also detected simultaneously with the diagnosis of the first switch 5 and the second switch 6.

[0111] Furthermore, a diagnostic method for a power supply device 1 according to an embodiment is a diagnostic method for a power supply device connected to a first DC power supply 2 that supplies and maintains a first voltage and a second DC power supply 3 that supplies and maintains a second voltage lower than the first voltage, the power supply device 1 including: a first switch 5 having one end connected to the first DC power supply 2; a first capacitance 91 connected between the other end of the first switch 5 and a reference potential GND; a second switch 6 having one end connected to the second DC power supply 3; a second capacitance 92 connected between the other end of the second switch 6 and the reference potential GND; and a DCDC converter unit 4 having a first DCDC converter 41 and a second DCDC converter 42 connected in parallel between the other end of the first switch 5 and the other end of the second switch 6, a step-down step of performing step-down control in which the first DC-DC converter 41 and the second DC-DC converter 42, in parallel, step down the first voltage supplied from the first DC power supply 2 to a second voltage and output it to the second DC power supply 3; a step-up step of performing step-up control in which, with the first switch 5 and the second switch 6 connected, the first DC-DC converter 41 and the second DC-DC converter 42, in parallel, step up the second voltage supplied from the second DC power supply 3 to the first voltage and output it to the first DC power supply 2; and a step-up / step-down step (diagnosis mode) of performing step-up / step-down control in which, with the first switch 5 and the second switch 6 disconnected, the first DC-DC converter 41 steps down the voltage of the first capacitance 91 and outputs it to the second capacitance 92, and, in parallel, the second DC-DC converter 42 steps up the voltage of the second capacitance 92 and output it to the first capacitance 91.

[0112] As a result, in the diagnosis mode, with the first switch 5 and the second switch 6 in an interrupted state, the first DC-DC converter 41 steps down the voltage of the first capacitance 91 and outputs it to the second capacitance 92, and in parallel, the second DC-DC converter 42 steps up the voltage of the second capacitance 92 and outputs it to the first capacitance 91. Therefore, if the interruption capability of the first switch 5 is normal, the potential difference V5 across both ends of the first switch 5 increases in a short time, and if the interruption capability of the second switch 6 is normal, the potential difference V6 across both ends of the second switch 6 increases in a short time. As a result, the interruption capabilities of the first switch 5 and the second switch 6 are diagnosed simultaneously and in a shorter time than before.

[0113] Specifically, in the voltage step, after the voltage step-up / down control, it is determined whether or not the first potential difference V5 detected by the first potential difference detection unit is larger than the first reference potential difference, and if the first potential difference V5 is larger than the first reference potential difference, it is determined that the first switch 5 is normal, and if the first potential difference V5 is not larger than the first reference potential difference, it is determined that the first switch 5 is abnormal and cannot be turned off. Furthermore, in the voltage step, after the voltage step-up / down control, it is determined whether or not the second potential difference V6 detected by the second potential difference detection unit is larger than the second reference potential difference, and if the second potential difference V6 is larger than the second reference potential difference, it is determined that the second switch 6 is normal, and if the second potential difference V6 is not larger than the second reference potential difference, it is determined that the second switch 6 is abnormal and cannot be turned off.

[0114] While the power supply device and power supply device diagnostic method according to the present disclosure have been described above based on the embodiments, the present disclosure is not limited to these embodiments. As long as they do not deviate from the gist of the present disclosure, various modifications that would occur to those skilled in the art to the present embodiments and other forms constructed by combining some of the components of the embodiments are also included within the scope of the present disclosure.

[0115] For example, the DC-DC converter included in the power supply device is not limited to the circuit shown in Fig. 2, and may be another circuit. Below, a power supply device according to a modified example that includes a different type of DC-DC converter will be described.

[0116] Fig. 7 is a block diagram showing the configuration of a power supply device 1a according to a first modification of the embodiment. The power supply device 1a according to this modification has a configuration in which the DC-DC converter unit 4 in the power supply device 1 according to the embodiment shown in Fig. 2 is replaced with a DC-DC converter unit 4a according to this modification. The following description will focus on the differences from the embodiment.

[0117] The DC-DC converter unit 4a has a first DC-DC converter 41a and a second DC-DC converter 42a connected in parallel.

[0118] The first DC-DC converter 41a has, in addition to the configuration of the first DC-DC converter 41 according to the embodiment, a fifth switching element 415 connected in series with the first reactor 413, and a sixth switching element 416 connected between a reference potential GND and a connection point J41a where the fifth switching element 415 and the first reactor 413 are connected in series. The second DC-DC converter 42a has, in addition to the configuration of the second DC-DC converter 42 according to the embodiment, a seventh switching element 425 connected in series with the second reactor 423, and an eighth switching element 426 connected between a connection point J42a where the seventh switching element 425 and the second reactor 423 are connected in series and the reference potential GND.

[0119] The fifth switching element 415, the sixth switching element 416, the seventh switching element 425, and the eighth switching element 426 are, for example, N-channel MOSFETs each having a body diode, which has an anode on the source electrode side of the switching element and a cathode on the drain electrode side.

[0120] The first DC-DC converter 41a can perform not only a step-down operation but also a step-up operation when charging the second DC power supply 3 from the first DC power supply 2 under the control of the control unit 7. When performing a step-down operation, the first DC-DC converter 41a operates in the same manner as the DC-DC converter unit 4 according to the embodiment, with the fifth switching element 415 kept on and the sixth switching element 416 kept off.

[0121] On the other hand, when a boost operation is performed, a state in which the first switching element 411 is kept on and the second switching element 412 is kept off, the fifth switching element 415 is kept off and the sixth switching element 416 is kept on, causing a current to flow from the first DC power supply 2 to the reference potential GND via the first current sensor 414, the first switching element 411, the first reactor 413, and the sixth switching element 416, thereby storing energy in the first reactor 413, and a state in which the fifth switching element 415 is kept on and the sixth switching element 416 is kept off, causing the energy stored in the first reactor 413 to be released, causing a current to flow from the first DC power supply 2 to the second DC power supply 3 via the first current sensor 414, the first switching element 411, the first reactor 413, and the fifth switching element 415 are alternately repeated.

[0122] Furthermore, under the control of the control unit 7, the first DC-DC converter 41a can perform not only a step-up operation but also a step-down operation when charging the first DC power source 2 from the second DC power source 3. When performing a step-up operation, the first DC-DC converter 41a operates in the same manner as the DC-DC converter unit 4 according to the embodiment, with the fifth switching element 415 kept on and the sixth switching element 416 kept off.

[0123] On the other hand, when a step-down operation is performed, a state in which the first switching element 411 is kept on and the second switching element 412 is kept off, the fifth switching element 415 is kept on and the sixth switching element 416 is kept off, causing a current to flow from the second DC power supply 3 to the first DC power supply 2 via the fifth switching element 415, the first reactor 413, the first switching element 411, and the first current sensor 414, thereby storing energy in the first reactor 413, and a state in which the fifth switching element 415 is kept off and the sixth switching element 416 is kept on, causing the energy stored in the first reactor 413 to be released, causing a current to flow from the reference potential GND to the first DC power supply 2 via the sixth switching element 416, the first reactor 413, the first switching element 411, and the first current sensor 414 are alternately repeated.

[0124] The second DC-DC converter 42a, like the first DC-DC converter 41a, can perform not only a step-down operation but also a step-up operation under control of the control unit 7 when charging from the first DC power supply 2 to the second DC power supply 3. Furthermore, the second DC-DC converter 42a, like the first DC-DC converter 41a, can perform not only a step-up operation but also a step-down operation under control of the control unit 7 when charging from the second DC power supply 3 to the first DC power supply 2.

[0125] In the power supply device 1a according to this modification, the control unit 7 operates as follows in the step-down operation mode, step-up operation mode, and step-up / step-down operation mode (diagnosis mode). That is, the control unit 7 can perform the following operation control in addition to the operation control in the embodiment.

[0126] When the second voltage supplied from the second DC power supply 3 is higher than the first voltage supplied from the first DC power supply 2, the control unit 7 performs the following control.

[0127] In the step-down operation mode, the control unit 7, with the first switch 5 and the second switch 6 connected, performs step-down control on the first DC-DC converter 41 and the second DC-DC converter 42 in parallel to step down the second voltage supplied from the second DC power source 3 to the first voltage and output it to the first DC power source 2.

[0128] In addition, in the boost operation mode, the control unit 7, with the first switch 5 and the second switch 6 connected, performs boost control on the first DC-DC converter 41 and the second DC-DC converter 42 in parallel to boost the first voltage supplied from the first DC power source 2 to a second voltage and output it to the second DC power source 3.

[0129] Furthermore, as the step-up / step-down operation (diagnosis mode), with the first switch 5 and the second switch 6 disconnected, the control unit 7 performs step-up / step-down control to cause the first DC-DC converter 41 to step down the voltage of the second capacitance 92 and output it to the first capacitance 91, and in parallel, cause the second DC-DC converter 42 to step up the voltage of the first capacitance 91 and output it to the second capacitance 92. Alternatively, with the first switch 5 and the second switch 6 disconnected, the control unit 7 performs step-up / step-down control to cause the first DC-DC converter 41 to step up the voltage of the first capacitance 91 and output it to the second capacitance 92, and in parallel, cause the second DC-DC converter 42 to step down the voltage of the second capacitance 92 and output it to the first capacitance 91.

[0130] According to the power supply device 1a of this modified example, as in the embodiment, in the step-up / step-down operation mode (diagnostic mode), after the first switch 5 and the second switch 6 are turned off, the charge stored in the first capacitance 91 is released by the step-down operation or step-up operation by the first DC-DC converter 41, causing the voltage of the first capacitance 91 to decrease, while the charge stored in the second capacitance 92 is released by the step-up operation or step-down operation by the second DC-DC converter 42, causing the voltage of the second capacitance 92 to decrease.

[0131] Therefore, compared to the conventional technology in which the first DC-DC converter 41 and the second DC-DC converter 42 do not perform step-up or step-down operations, if the breaking capability of the first switch 5 is normal, the potential difference V5 across the first switch 5 increases in a short time, and if the breaking capability of the second switch 6 is normal, the potential difference V6 across the second switch 6 increases in a short time. As a result, the breaking capabilities of the first switch 5 and the second switch 6 are diagnosed simultaneously and in a shorter time than before.

[0132] Fig. 8 is a block diagram showing the configuration of a power supply device 1b according to a second modification of the embodiment. The power supply device 1b according to this modification has a configuration in which the DC-DC converter unit 4 in the power supply device 1 according to the embodiment shown in Fig. 2 is replaced with a DC-DC converter unit 4b according to this modification. The following description will focus on the differences from the embodiment.

[0133] The DC-DC converter unit 4b has a first DC-DC converter 41b and a second DC-DC converter 42b connected in parallel.

[0134] The first DC-DC converter 41b has a first current sensor 414, a ninth switching element 417, a tenth switching element 418, and a first transformer 419. The first current sensor 414, a primary winding of the first transformer 419, and the ninth switching element 417 are connected in series. Furthermore, the secondary winding of the first transformer 419 and the tenth switching element 418 are connected in series.

[0135] The second DC-DC converter 42b has a second current sensor 424, an eleventh switching element 427, a twelfth switching element 428, and a second transformer 429. The second current sensor 424, the primary winding of the second transformer 429, and the eleventh switching element 427 are connected in series. Furthermore, the secondary winding of the second transformer 429 and the twelfth switching element 428 are connected in series.

[0136] The ninth switching element 417, the tenth switching element 418, the eleventh switching element 427, and the twelfth switching element 428 are each, for example, an N-channel MOSFET, and each have a body diode. The body diode has an anode on the source electrode side of the switching element and a cathode on the drain electrode side.

[0137] The first DC-DC converter 41b performs a step-up / step-down operation under the control of the control unit 7 when charging the second DC power supply 3 from the first DC power supply 2. At this time, whether the step-up operation or the step-down operation is performed is determined by the turns ratio of the first transformer 419, the on-duty of the control signal from the control unit 7 to the ninth switching element 417, etc.

[0138] Specifically, when charging the second DC power supply 3 from the first DC power supply 2, the ninth switching element 417 performs switching operation in accordance with control by the control unit 7, and the DC voltage of the first DC power supply 2 is increased or decreased to charge the second DC power supply 3. Specifically, as an example, a state in which a current flows from the first DC power supply 2 to the reference potential GND via the first current sensor 414, the primary winding of the first transformer 419, and the ninth switching element 417 when the ninth switching element 417 is turned on, thereby storing energy in the first transformer 419, and a state in which the ninth switching element 417 is turned off, and the energy stored in the first transformer 419 is released, causing a current to flow from the reference potential GND to the second DC power supply 3 via the secondary winding of the first transformer 419 and the body diode of the tenth switching element 418 are alternately repeated.

[0139] Furthermore, under the control of the control unit 7, the first DC-DC converter 41b performs a step-up / step-down operation when charging the first DC power supply 2 from the second DC power supply 3. At this time, whether the step-up operation or the step-down operation is performed is determined by the winding ratio of the first transformer 419, the on-duty of the control signal from the control unit 7 to the tenth switching element 418, etc.

[0140] Specifically, when charging the first DC power supply 2 from the second DC power supply 3, the tenth switching element 418 performs switching operation in accordance with control by the control unit 7, and the DC voltage of the second DC power supply 3 is increased or decreased to charge the first DC power supply 2. Specifically, as an example, a state in which a current flows from the second DC power supply 3 to the reference potential GND via the tenth switching element 418 and the secondary winding of the first transformer 419 when the tenth switching element 418 is turned on, thereby storing energy in the first transformer 419, and a state in which a current flows from the reference potential GND to the first DC power supply 2 via the body diode of the ninth switching element 417, the primary winding of the first transformer 419, and the first current sensor 414 when the tenth switching element 418 is turned off, due to the release of the energy stored in the first transformer 419, are alternately repeated.

[0141] The second DC-DC converter 42b performs a step-up / step-down operation under the control of the control unit 7 when charging the second DC power supply 3 from the first DC power supply 2. At this time, whether the operation is a step-up operation or a step-down operation is determined by the turns ratio of the second transformer 429, the on-duty of the control signal from the control unit 7 to the eleventh switching element 427, etc.

[0142] Specifically, when charging the second DC power supply 3 from the first DC power supply 2, the eleventh switching element 427 performs switching operation in accordance with control by the control unit 7, and the DC voltage of the first DC power supply 2 is increased or decreased to charge the second DC power supply 3. Specifically, as an example, a state in which a current flows from the first DC power supply 2 to the reference potential GND via the second current sensor 424, the primary winding of the second transformer 429, and the eleventh switching element 427 when the eleventh switching element 427 is turned on, thereby storing energy in the second transformer 429, and a state in which a current flows from the reference potential GND to the second DC power supply 3 via the secondary winding of the second transformer 429 and the body diode of the twelfth switching element 428 when the eleventh switching element 427 is turned off, due to the release of the energy stored in the second transformer 429.

[0143] Moreover, the second DC-DC converter 42b performs a step-up / step-down operation under the control of the control unit 7 when charging the first DC power supply 2 from the second DC power supply 3. At this time, whether the step-up operation or the step-down operation is performed is determined by the winding ratio of the second transformer 429, the on-duty of the control signal from the control unit 7 to the twelfth switching element 428, etc.

[0144] Specifically, when the second DC power supply 3 charges the first DC power supply 2, the twelfth switching element 428 performs switching operation in accordance with control by the control unit 7, and the DC voltage of the second DC power supply 3 is increased or decreased to charge the first DC power supply 2. Specifically, as an example, a state in which the twelfth switching element 428 is turned on, causing a current to flow from the second DC power supply 3 to the reference potential GND via the twelfth switching element 428 and the secondary winding of the second transformer 429, thereby storing energy in the second transformer 429, and a state in which the twelfth switching element 428 is turned off, causing the energy stored in the second transformer 429 to be released, causing a current to flow from the reference potential GND to the first DC power supply 2 via the body diode of the eleventh switching element 427, the primary winding of the second transformer 429, and the second current sensor 424 are alternately repeated.

[0145] According to the power supply device 1b of this modified example, the control unit 7 can perform the following operation control. That is, in the step-down operation mode or the step-up operation mode, the control unit 7, with the first switch 5 and the second switch 6 connected, performs step-up control or step-down control on the first DC-DC converter 41 and the second DC-DC converter 42 in parallel to step-up or step-down the first voltage supplied from the first DC power supply 2 to a second voltage and output it to the second DC power supply 3. Alternatively, with the first switch 5 and the second switch 6 connected, the control unit 7 performs step-up control or step-down control on the first DC-DC converter 41 and the second DC-DC converter 42 in parallel to step-up or step-down the second voltage supplied from the second DC power supply 3 to the first voltage and output it to the first DC power supply 2.

[0146] In the step-up / step-down operation mode (diagnosis mode), the control unit 7, with the first switch 5 and the second switch 6 cut off, causes the first DC-DC converter 41 to step up or step down the voltage of the first capacitance 91 and output it to the second capacitance 92, and in parallel performs step-up / step-down control to cause the second DC-DC converter 42 to step up or step down the voltage of the second capacitance 92 and output it to the first capacitance 91. Alternatively, with the first switch 5 and the second switch 6 cut off, the control unit 7 performs step-up / step-down control to cause the first DC-DC converter 41 to step up or step down the voltage of the second capacitance 92 and output it to the first capacitance 91, and in parallel performs step-up / step-down control to cause the second DC-DC converter 42 to step up or step down the voltage of the first capacitance 91 and output it to the second capacitance 92.

[0147] According to the power supply device 1b of this modified example, as in the embodiment, in the step-up / step-down operation mode (diagnostic mode), after the first switch 5 and the second switch 6 are turned off, the charge stored in the first capacitance 91 is released by the step-down operation or step-up operation by the first DC-DC converter 41, causing the voltage of the first capacitance 91 to decrease, while the charge stored in the second capacitance 92 is released by the step-up operation or step-down operation by the second DC-DC converter 42, causing the voltage of the second capacitance 92 to decrease.

[0148] Therefore, compared to the conventional technology in which the first DC-DC converter 41 and the second DC-DC converter 42 do not perform step-up or step-down operations, if the breaking capability of the first switch 5 is normal, the potential difference V5 across the first switch 5 increases in a short time, and if the breaking capability of the second switch 6 is normal, the potential difference V6 across the second switch 6 increases in a short time. As a result, the breaking capabilities of the first switch 5 and the second switch 6 are diagnosed simultaneously and in a shorter time than before.

[0149] Furthermore, the DC-DC converter provided in the power supply device according to the present disclosure is not limited to a configuration consisting of two DC-DC converters connected in parallel, but may be configured with three or more DC-DC converters as shown in FIG. 9 .

[0150] Fig. 9 is a block diagram showing the configuration of a power supply device 1c according to a third modification of the embodiment. The power supply device 1c according to this modification has a configuration in which the DC-DC converter unit 4 in the power supply device 1 according to the embodiment shown in Fig. 2 is replaced with a DC-DC converter unit 4c according to this modification. The following description will focus on the differences from the embodiment.

[0151] The DC-DC converter unit 4c has a first DC-DC converter 41, a second DC-DC converter 42, and a third DC-DC converter 43 connected in parallel. The detailed configuration of the third DC-DC converter 43 may be the configuration of the first DC-DC converter 41 according to the embodiment shown in Fig. 2, or the configuration of the first DC-DC converter 41a according to Modification 1 shown in Fig. 7, or may be configured with another type of circuit.

[0152] In the power supply device 1c according to this modification, in addition to the operational control in the embodiment, the following operational control can be performed.

[0153] In other words, when the first voltage supplied from the first DC power supply 2 is charged to the second DC power supply 3, the control unit 7 controls the first DC-DC converter 41, the second DC-DC converter 42, and the third DC-DC converter 43 in parallel, with the first switch 5 and the second switch 6 connected, to boost or lower the first voltage supplied from the first DC power supply 2 to a second voltage and output it to the second DC power supply 3.

[0154] Furthermore, when the second voltage supplied from the second DC power supply 3 is charged to the first DC power supply 2, the control unit 7 controls the first DC-DC converter 41, the second DC-DC converter 42, and the third DC-DC converter 43 in parallel, with the first switch 5 and the second switch 6 connected, to boost or lower the second voltage supplied from the second DC power supply 3 to the first voltage and output it to the first DC power supply 2.

[0155] In addition, as a voltage boost / buck operation (diagnostic mode), the control unit 7, with the first switch 5 and the second switch 6 turned off, controls one or two of the first DC-DC converter 41 to the third DC-DC converter 43 to boost or lower the voltage of the first capacitance 91 and output it to the second capacitance 92, and simultaneously controls the remaining two or one DC-DC converter to boost or lower the voltage of the second capacitance 92 and output it to the first capacitance 91.

[0156] As a result, after the first switch 5 and the second switch 6 are turned off, the charge stored in the first capacitance 91 is released by the operation of one or two DC-DC converters, causing the voltage of the first capacitance 91 to decrease, while the charge stored in the second capacitance 92 is released by the operation of two or one DC-DC converters, causing the voltage of the second capacitance 92 to decrease.

[0157] Therefore, compared to the prior art in which no operation is performed by a DCDC converter, if the breaking capability of the first switch 5 is normal, the potential difference V5 across the first switch 5 increases in a short time, and if the breaking capability of the second switch 6 is normal, the potential difference V6 across the second switch 6 increases in a short time. As a result, the breaking capabilities of the first switch 5 and the second switch 6 are diagnosed simultaneously and in a shorter time than in the past.

[0158] The power supply device according to the present disclosure can be used as a power supply device connected between two DC power sources to convert voltage, in particular as a power supply device that can diagnose the interruption capability of switches connected between each of the two DC power sources and the power supply device in a shorter time than conventional methods, for example, as a voltage conversion device that is mounted on a vehicle and connected between a battery and an electric double layer capacitor that serves as its backup.

[0159] 1, 1a to 1c Power supply device 2 First DC power supply 3 Second DC power supply 4, 4a to 4c DCDC converter section 41, 41a, 41b First DCDC converter 411 First switching element 412 Second switching element 413 First reactor 414 First current sensor 415 Fifth switching element 416 Sixth switching element 417 Ninth switching element 418 Tenth switching element 419 First transformer 42, 42a, 42b Second DCDC converter 421 Third switching element 422 Fourth switching element 423 Second reactor 424 Second current sensor 425 Seventh switching element 426 Eighth switching element 427 Eleventh switching element 428 Twelfth switching element 429 Second transformer 43 Third DCDC converter 5 First switch 51 First potential detection section 52 Second potential detection section 6 Second switch 61 Third potential detection unit 62 Fourth potential detection unit 7 Control unit 8 Diagnosis unit 91 First capacitance 92 Second capacitance 100 Vehicle

Claims

1. A power supply device configured to be connected to a first DC power supply that supplies and maintains a first voltage, and a second DC power supply that supplies and maintains a second voltage lower than the first voltage, A first switch having one end connected to the first DC power source; a first capacitance connected between the other end of the first switch and a reference potential; A second switch having one end connected to the second DC power source; a second capacitance connected between the other end of the second switch and the reference potential; a first DC-DC converter connected between the other end of the first switch and the other end of the second switch; a second DC-DC converter connected in parallel with the first DC-DC converter between the other end of the first switch and the other end of the second switch; a control unit configured to control the first switch, the second switch, and the first and second DC-DC converters; Equipped with The control unit is a step-down operation mode in which, in a state in which the first switch and the second switch are connected, step-down control is performed on the first DCDC converter and the second DCDC converter in parallel to step-down the first voltage supplied from the first DC power supply to the second voltage and output the second voltage to the second DC power supply; a boost operation mode in which, in a state in which the first switch and the second switch are connected, the first DCDC converter and the second DCDC converter perform boost control in parallel to boost the second voltage supplied from the second DC power supply to the first voltage and output the first voltage to the first DC power supply; a step-up / step-down operation mode in which a step-up / step-down control is performed in which, in a state in which the first switch and the second switch are cut off, the first DC-DC converter is caused to step down the voltage of the first capacitance and output the voltage to the second capacitance, and in parallel, the second DC-DC converter is caused to step up the voltage of the second capacitance and output the voltage to the first capacitance; having power supply.

2. a first potential difference detector configured to detect a first potential difference across the first switch; a second potential difference detector configured to detect a second potential difference across the second switch; Further equipped with The control unit, in the step-up / step-down operation mode, After the voltage increase / decrease control, it is determined whether or not the first potential difference detected by the first potential difference detection unit is larger than a first reference potential difference; determining that the first switch is normal when the first potential difference is greater than the first reference potential difference; determining whether the second potential difference detected by the second potential difference detection unit is greater than a second reference potential difference; determining that the second switch is normal when the second potential difference is greater than the second reference potential difference; It is configured as follows:

2. The power supply device of claim 1.

3. The control unit, in the step-up / step-down operation mode, determining that the first switch is abnormal when the first potential difference is not greater than the first reference potential difference; determining that the second switch is abnormal when the second potential difference is not greater than the second reference potential difference; It is configured as follows:

3. The power supply device of claim 2.

4. The control unit is configured to, in the step-up / step-down operation mode, perform step-down by the first DC-DC converter and step-up by the second DC-DC converter for a certain period of time after blocking the first switch and the second switch.

3. The power supply device of claim 2.

5. The first DC-DC converter is a first switching element and a first reactor connected in series to each other at a first connection point between the first switch and the second switch; a second switching element having a body diode connected between the first connection point and the reference potential; having The second DC-DC converter is a third switching element having a body diode and a second reactor, the third switching element and the second reactor being connected in series to each other at a second connection point between the first switch and the second switch; a fourth switching element connected between the second connection point and the reference potential; having 2. The power supply device of claim 1.

6. The control unit is configured to perform the step-up / step-down control in the step-up / step-down operation mode while keeping the second switching element and the third switching element always off.

6. The power supply device according to claim 5.

7. A current sensor is further provided to detect a current flowing through one of the first DC-DC converter and the second DC-DC converter. The control unit is configured to control one of the first DC-DC converter and the second DC-DC converter in the step-down operation mode, the step-up operation mode, and the step-up / step-down operation mode so that a current detected by the current sensor is within a predetermined range. The power supply device according to any one of claims 1 to 6.

8. a first potential detection unit that detects a potential of the other end of the first switch; a second potential detection unit that detects a potential of the other end of the second switch; Further equipped with The control unit, in the step-up / step-down operation mode, determining whether or not the first potential detected by the first potential detection unit is equal to or lower than a first reference potential; When the first potential is not equal to or less than the first reference potential, it is determined that an abnormality occurs in which the first switching element is fixed to an off state; determining whether the second potential detected by the second potential detection unit is equal to or lower than a second reference potential; When the second potential is not equal to or less than the second reference potential, it is determined that an abnormality occurs in which the fourth switching element is fixed to an off state. It is configured as follows:

6. The power supply device according to claim 5.

9. The control unit, in the step-up / step-down operation mode, determining that the first switching element is normal when the first potential is equal to or lower than the first reference potential; determining that the fourth switching element is normal when the second potential is equal to or lower than the second reference potential; It is configured as follows:

9. The power supply device of claim 8.

10. 1. A method for diagnosing a power supply device connected to a first DC power supply that supplies and maintains a first voltage and a second DC power supply that supplies and maintains a second voltage lower than the first voltage, comprising: A first switch having one end connected to the first DC power source; a first capacitance connected between the other end of the first switch and a reference potential; a second switch having one end connected to the second DC power source; a second capacitance connected between the other end of the second switch and the reference potential; a first DC-DC converter connected between the other end of the first switch and the other end of the second switch; a second DC-DC converter connected between the other end of the first switch and the other end of the second switch; Equipped with performing step-down control on the first DCDC converter and the second DCDC converter in parallel with each other while the first switch and the second switch are connected, stepping down the first voltage supplied from the first DC power supply to the second voltage and outputting the second voltage to the second DC power supply; performing a boost control for the first DC-DC converter and the second DC-DC converter in parallel with each other in a state in which the first switch and the second switch are connected, to boost the second voltage supplied from the second DC power source to the first voltage and output the boosted voltage to the first DC power source; providing a power supply device configured to: a step of performing step-up / step-down control in which, while the first switch and the second switch are cut off, the first DC-DC converter steps down the voltage of the first capacitance and outputs the voltage to the second capacitance, and in parallel, the second DC-DC converter steps up the voltage of the second capacitance and outputs the voltage to the first capacitance; Including, How to diagnose a power supply.

11. The power supply device is a first potential difference detector that detects a potential difference between both ends of the first switch; a second potential difference detector that detects a potential difference between both ends of the second switch; Further equipped with a step of determining whether or not the first potential difference detected by the first potential difference detection unit is larger than a first reference potential difference after the step of performing the step-up / step-down control; determining that the first switch is normal when the first potential difference is greater than the first reference potential difference; a step of determining whether or not the second potential difference detected by the second potential difference detection unit is larger than a second reference potential difference after the step of performing the step-up / step-down control; determining that the second switch is normal when the second potential difference is greater than the second reference potential difference; The method of diagnosing a power supply as recited in claim 10, further comprising:

12. determining that the first switch is abnormal when the first potential difference is not greater than the first reference potential difference; determining that the second switch is abnormal when the second potential difference is not greater than the second reference potential difference; The method of diagnosing a power supply as recited in claim 11, further comprising:

13. 1. A method for diagnosing a power supply device connected to a first DC power supply that supplies and maintains a first voltage and a second DC power supply that supplies and maintains a second voltage lower than the first voltage, comprising: A first switch having one end connected to the first DC power source; a first capacitance connected between the other end of the first switch and a reference potential; a second switch having one end connected to the second DC power source; a second capacitance connected between the other end of the second switch and the reference potential; a first DC-DC converter connected between the other end of the first switch and the other end of the second switch; a second DC-DC converter connected between the other end of the first switch and the other end of the second switch; providing a power supply device comprising: a step of performing step-up / step-down control in which, while the first switch and the second switch are cut off, the first DC-DC converter steps down the voltage of the first capacitance and outputs the voltage to the second capacitance, and in parallel, the second DC-DC converter steps up the voltage of the second capacitance and outputs the voltage to the first capacitance; Including, How to diagnose a power supply.

14. The power supply device is a first potential difference detector that detects a potential difference between both ends of the first switch; a second potential difference detector that detects a potential difference between both ends of the second switch; Further equipped with a step of determining whether or not the first potential difference detected by the first potential difference detection unit is larger than a first reference potential difference after the step of performing the step-up / step-down control; determining that the first switch is normal when the first potential difference is greater than the first reference potential difference; a step of determining whether or not the second potential difference detected by the second potential difference detection unit is larger than a second reference potential difference after the step of performing the step-up / step-down control; determining that the second switch is normal when the second potential difference is greater than the second reference potential difference; The method of diagnosing a power supply as recited in claim 13, further comprising:

15. determining that the first switch is abnormal when the first potential difference is not greater than the first reference potential difference; determining that the second switch is abnormal when the second potential difference is not greater than the second reference potential difference; The method of diagnosing a power supply as recited in claim 14, further comprising: