Vehicle power control device

Abstract

To solve the problem of a vehicular electric power control apparatus in which the occurrence of a layer short circuit in wiring is difficult to detect and may cause a vehicle fire.SOLUTION: In a vehicular electric power control apparatus 10, a layer short circuit determination section 11B compares first current detection values which are current values flowing through semiconductor fuses 22A-26A with second current detection values which are current values flowing through vehicular auxiliary devices 17-21, and determines whether or not a layer short circuit occurs in wiring between each of the semiconductor fuses 22A-26A and a corresponding one of the vehicular auxiliary devices 17-21. The occurrence of the layer short circuit in the wiring between any of the semiconductor fuses 22A-26A and the corresponding one of the vehicular auxiliary devices 17-21 is detected by such a structure, and a switch changeover section 11C cuts off a current flowing toward the corresponding one of the vehicular auxiliary devices 17-21. As a result, it is possible to prevent heat generation in the wiring where the layer short circuit occurs, and to prevent the occurrence of smoking or a vehicle fire afterward.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a vehicle power control device that compares the current value flowing through a semiconductor fuse as a switching element with the current value flowing through a vehicle auxiliary device to determine whether a layer short has occurred in the internal electrical circuit. [Background technology]

[0002] BACKGROUND ART A known example of a conventional vehicle power control device is the device described in Patent Document 1.

[0003] In a vehicle power control device, a fuse element and a PTC element are arranged in series along the wiring in a vehicle wiring system that supplies power to the vehicle's power loads. When an abnormal current flows through the wiring, the fuse element melts before the wiring is damaged. On the other hand, when an abnormal current flows and the resistance value suddenly increases, the PTC element throttles the current flowing through the wiring at the latest before the fuse element melts.

[0004] This structure reduces the number of fuse elements that will blow even if an abnormal current flows through the wiring in the vehicle power control device, and also reduces the work required to find and replace blown fuse elements, thereby reducing repair time and labor. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-327068 Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, in conventional vehicle power control devices, when an abnormal current that could damage the wiring occurs, the temperature of the PTC element rises and exceeds the resistance transformation point, increasing the electrical resistance of the PTC element. This increase in electrical resistance of the PTC element then restricts the current flowing through the wiring, reducing the number of fuse elements that melt.

[0007] However, in a vehicle power control device, if a layer short occurs in an internal circuit such as wiring, the PTC element may not generate heat until the temperature exceeds the resistance transformation point. In this case, power continues to be supplied to the vehicle's power load, and current continues to flow through the wiring including the area where the layer short occurred. As a result, the current continues to flow for a long period of time, causing heat to be generated at the area where the layer short occurred, which can lead to smoke or a vehicle fire.

[0008] In other words, while conventional vehicle power control devices are capable of responding to short circuits caused by abnormal current, they have the problem of being unable to respond to the above-mentioned smoke and other issues when abnormal current does not flow through the wiring, such as in the case of a rare short circuit.

[0009] The present invention has been made in consideration of the above circumstances, and relates to a vehicle power control device that compares the current value flowing through a semiconductor fuse as a switching element with the current value flowing through a vehicle auxiliary device to determine whether a layer short has occurred in the internal electrical circuit. [Means for solving the problem]

[0010] One embodiment of the present invention relates to a vehicle power control device, which controls the power supplied to a plurality of vehicle auxiliaries from a vehicle power source mounted on a vehicle, and includes a plurality of semiconductor fuses respectively arranged between the vehicle power source and the plurality of vehicle auxiliaries, a plurality of current sensors which detect the current values ​​flowing through the plurality of semiconductor fuses, a layer short judgment unit which judges a layer short between the semiconductor fuse and the plurality of vehicle auxiliaries using a first current detection value input from the current sensor and a second current detection value input from the vehicle auxiliaries, and a switch switching unit which switches the semiconductor fuse from an on operation to an off operation based on the judgment by the layer short judgment unit, wherein the layer short judgment unit judges the occurrence of the layer short when the second current detection value is different from the allowable value of the first current detection value, and the switch switching unit switches the semiconductor fuse in the path subject to the layer short occurrence judgment to the off operation. [Effects of the Invention]

[0011] In one embodiment of the present invention, a vehicle power control device includes a layer short circuit determination unit that compares a first current detection value, which is the value of the current flowing through the semiconductor fuse, with a second current detection value, which is the value of the current flowing through the vehicle auxiliary, to determine whether a layer short circuit has occurred in the wiring between the semiconductor fuse and the vehicle auxiliary. If a layer short circuit occurs in the wiring between the semiconductor fuse and the vehicle auxiliary, a switch changeover unit switches the semiconductor fuse connected to the wiring from an on operation to an off operation, thereby interrupting the current flowing to the vehicle auxiliary. As a result, the wiring at the location where the layer short circuit has occurred will heat up, and the subsequent generation of smoke or the occurrence of a vehicle fire will be prevented. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a block diagram illustrating a vehicle power control device according to an embodiment of the present invention; [Figure 2] 1 is a block diagram illustrating a vehicle power control device according to an embodiment of the present invention; [Figure 3] 4 is a graph illustrating a method for determining a layer short circuit in a vehicle power control device according to an embodiment of the present invention. [Figure 4] 1 is a block diagram illustrating a vehicle power control device according to an embodiment of the present invention; [Figure 5] 3 is a flowchart illustrating a power control method in a vehicle power control device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] A vehicle power control device 10 according to one embodiment of the present invention will be described in detail below with reference to the drawings. In the description of this embodiment, the same reference numerals are used for the same components, and repeated description will be omitted.

[0014] FIG. 1 is a block diagram illustrating a vehicle power control device 10 according to this embodiment. FIG. 2 is a block diagram illustrating a state in which the vehicle power control device 10 according to this embodiment operates normally. FIG. 3 is a graph illustrating a method for determining a layer short circuit in the vehicle power control device 10 according to this embodiment. FIG. 4 is a block diagram illustrating an operating state when a layer short circuit occurs in the vehicle power control device 10 according to this embodiment. FIG. 5 is a flowchart illustrating a power control method in the vehicle power control device 10 according to this embodiment.

[0015] 1, a vehicle power control device 10 mainly includes a power supply control unit 11, a vehicle power supply 12, a power supply sensor 13, a current sensor 14, an alternator 15, a relay unit 16, and a plurality of vehicle accessories 17, 18, 19, 20, and 21. Although not shown, the power supply control unit 11 is connected to the engine via a starter motor, supplies power to the engine, and controls its operation.

[0016] The power supply control unit 11 is configured to include a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), etc. The power supply control unit 11 is an electronic control unit (ECU) having one or more processors for controlling the relay unit 16 and executing various calculations for supplying the electric power output from the vehicle power supply 12 to the vehicle accessories 17-21.

[0017] The power supply control unit 11 includes a storage unit 11D, which is configured with a nonvolatile memory such as an EEPROM (Electrically Erasable Programmable Read-only Memory), etc. The storage unit 11D stores various data required for controlling the relay unit 16 and one or more programs executable by the one or more processors.

[0018] The power supply control unit 11 also includes, for example, an abnormal current determination unit 11A, a layer short determination unit 11B, a switch changeover unit 11C, and a storage unit 11D. The power supply control unit 11 is connected to and can communicate with the relay unit 16 and vehicle accessories 17 to 21 via an in-vehicle network 31 (see FIG. 2) such as a CAN or a LAN.

[0019] The abnormal current determination unit 11A determines whether or not an abnormal current has flowed through the vehicle power control device 10, using first current detection values ​​detected by the current sensors 22B, 23B, 24B, 25B, and 26B of the semiconductor modules 22, 23, 24, 25, and 26 of the relay unit 16. The abnormal current determination unit 11A acquires the first current detection values ​​via the in-vehicle network 31.

[0020] In this embodiment, abnormal current determination unit 11A determines that an abnormal current has flowed through vehicle power control device 10 when the value of the current flowing through semiconductor fuses 22A, 23A, 24A, 25A, and 26A is greater than a preset first threshold. Then, switch changeover unit 11C switches semiconductor fuses 22A-26A of the wiring for which the determination was made to be in an ON state to an OFF state. As a result, abnormal current is prevented from flowing to vehicle auxiliaries 17-21, and vehicle auxiliaries 17-21 and semiconductor fuses 22A-26A are less likely to be damaged.

[0021] The current value that flows varies depending on the type of vehicle auxiliary devices 17 to 21. Therefore, the first threshold value is set in advance for each of the semiconductor fuses 22A to 26A that correspond to the vehicle auxiliary devices 17 to 21, and is set to, for example, a value that is larger than the maximum current value that flows through the semiconductor fuses 22A to 26A under normal conditions.

[0022] The layer short-circuit determination unit 11B determines whether or not a layer short has occurred in the internal circuit of the vehicle power control device 10, using the first current detection value and the second current detection value detected by the current sensors 17A, 18A, 19A, 20A, and 21A (see FIG. 2) built into the vehicle accessories 17-21. The layer short-circuit determination unit 11B acquires the first and second current detection values ​​via the in-vehicle network 31. The method for determining a layer short in the layer short-circuit determination unit 11B will be described later with reference to FIG. 3.

[0023] The switch changeover unit 11C is configured with, for example, logic elements and transistors, and switches between on and off operations of the semiconductor fuses 22A to 26A of the semiconductor modules 22 to 26. Then, the switch changeover unit 11C switches the semiconductor fuses 22A to 26A from on operation to off operation based on the determination results from the abnormal current determination unit 11A and the layer short-circuit determination unit 11B.

[0024] Vehicle power supply 12 is, for example, a battery pack that houses a plurality of battery modules (not shown). Vehicle power supply 12 outputs, for example, 12.6 V as a power supply voltage. The power supply voltage from vehicle power supply 12 is supplied to vehicle accessories 17 to 21 and the like via current sensor 14 and the like. Current sensor 14 is formed of, for example, a shunt resistor, which is a resistor for detecting current.

[0025] Power supply sensor 13 measures the capacity, voltage, temperature, internal resistance, current characteristics, etc. of vehicle power supply 12. Power supply sensor 13 inputs the measured values ​​to power supply control unit 11, and stores the measured values ​​in memory section 11D.

[0026] The alternator 15 generates electricity in response to the rotation of an engine (not shown), and supplies the generated charging current to the vehicle power supply 12 under the control of the power supply control unit 11. The output voltage of the alternator 15 is, for example, about 14V.

[0027] Relay unit 16 is composed of a plurality of semiconductor modules 22-26 corresponding to vehicle auxiliaries 17-21, respectively. Semiconductor modules 22-26 have semiconductor fuses 22A-26A and current sensors 22B-26B, respectively. Relay unit 16 is controlled by power supply control unit 11, and semiconductor fuses 22A-26A are switched on or off to control the supply of current to vehicle auxiliaries 17-21.

[0028] The semiconductor fuses 22A to 26A are, for example, power MOSFETs. The power MOSFETs are controlled by the switch changeover unit 11C, and are turned on or off by controlling the voltage applied to the gate terminals. When the semiconductor fuses 22A to 26A are turned on, power is supplied from the vehicle power supply 12 to the vehicle accessories 17 to 21. Note that the semiconductor fuses 22A to 26A are not limited to being power MOSFETs, and IGBTs or bipolar transistors may also be used.

[0029] Current sensors 22B to 26B are arranged, for example, downstream of semiconductor fuses 22A to 26A and detect the value of a current flowing through semiconductor fuses 22A to 26A. Then, current sensors 22B to 26B input the detected current value as a first current detection value to power supply control unit 11 via in-vehicle network 31. Note that current sensors 22B to 26B may also be arranged upstream of semiconductor fuses 22A to 26A.

[0030] Vehicle auxiliaries 17-21 mounted on a vehicle can be broadly divided into loads for ensuring safe vehicle driving performance and other loads for ensuring the comfort of vehicle occupants. Vehicle auxiliaries 17-21 are connected to vehicle power supply 12 via semiconductor fuses 22A-26A, respectively. Vehicle auxiliaries 17-21 are turned on when supplied with power from vehicle power supply 12.

[0031] In this embodiment, for example, vehicle accessory 17 is an electric brake, vehicle accessory 18 is an electric power steering, vehicle accessory 19 is an anti-skid device, vehicle accessory 20 is an air conditioning device, and vehicle accessory 21 is a seat heater. Note that the vehicle is equipped with many other vehicle accessories, which are turned on by receiving power from vehicle power supply 12 in the same way as vehicle accessories 17 to 21.

[0032] 2 shows a state in which vehicle auxiliaries 17-20 are turned on, vehicle auxiliaries 21 are turned off, and vehicle power control device 10 is operating normally. As described above, switch selector 11C of power supply control unit 11 applies a drive voltage to semiconductor fuses 22A-25A of semiconductor modules 22-25, causing semiconductor fuses 22A-25A to turn on. Then, vehicle auxiliaries 17-20 are turned on when power is supplied from vehicle power supply 12.

[0033] Current sensors 22B to 26B of semiconductor fuses 22A to 26A detect current values ​​I1 to I5 flowing through each of semiconductor fuses 22A to 26A. Current sensors 22B to 26B then input the detected current values ​​I1 to I5 as first current detection values ​​to power supply control unit 11 via in-vehicle network 31 indicated by dotted lines, and the first current detection values ​​are stored in memory 11D. At this time, semiconductor fuse 26A is in an OFF state, so no current flows through current sensor 26B, and so the first current detection value is 0.

[0034] As described above, the abnormal current determination unit 11A compares the first current detection value stored in the memory unit 11D with the first threshold value previously stored in the memory unit 11D to determine whether or not an abnormal current has flowed through each of the semiconductor fuses 22A to 26A.

[0035] Current sensors 17A-21A built into vehicle auxiliaries 17-21 detect current values ​​i1-i5 flowing through each of vehicle auxiliaries 17-21. Current sensors 17A-21A then input the detected current values ​​i1-i5 as second current detection values ​​to power supply control unit 11 via in-vehicle network 31 indicated by dotted lines, and the second current detection values ​​are stored in memory 11D. At this time, semiconductor fuse 26A of current sensor 21A is in an OFF state, so no current flows to vehicle auxiliaries 21, and the second current detection value is zero.

[0036] In Fig. 3, the Y axis represents current values ​​I1 to I5 flowing through semiconductor fuses 22A to 26A, and the X axis represents current values ​​i1 to i5 flowing through vehicle auxiliaries 17 to 21. As mentioned above, current values ​​i1 to i5 flowing through vehicle auxiliaries 17 to 21 differ depending on the model of each vehicle auxiliaries, and therefore Fig. 3 shows the current value flowing through vehicle auxiliaries 17 as an example. The same applies to the other vehicle auxiliaries 18 to 21, and their description will be omitted.

[0037] As shown in the figure, tolerance lines 32 and 33, which take into consideration tolerances indicated by dashed dotted lines, are set above and below the line of the linear function of Y = X where current values ​​I1 to I5 are equal to current values ​​i1 to i5. The tolerances are set in advance taking into consideration measurement errors during detection by current sensors 22B and 17A and the wiring resistance between current sensors 22B and 17A.

[0038] The layer short-circuit determination unit 11B of this embodiment compares the first current detection value from the current sensor 22B with the second current detection value from the current sensor 17A. If the value obtained by subtracting the second current detection value from the first current detection value is greater than the allowable value, it determines that a layer short has occurred in the wiring between the current sensors 22B and 17A.

[0039] Specifically, if the plotted values ​​of the first and second current detection values ​​to be compared are located in the area indicated by sand-colored hatching 34, it is determined that a layer short has occurred in the wiring between current sensors 22B and 17A. On the other hand, if the plotted values ​​of the first and second current detection values ​​to be compared are located in the area indicated by diagonal hatching 35 between the linear function line of Y=X and the tolerance line 32, it is determined that a layer short has not occurred in the wiring between current sensors 22B and 17A.

[0040] Note that I1max is the maximum current value that flows through semiconductor fuse 22A during normal operation of vehicle power control device 10, and i1max is the maximum current value that flows through vehicle auxiliary device 17 during normal operation of vehicle power control device 10. As described above, the first threshold value used in abnormal current determination unit 11A can be set in advance to, for example, a value that is greater than maximum current value I1max that flows through current sensor 22B.

[0041] FIG. 4 shows the operating state of the vehicle power control device 10 when a layer short occurs in the wiring supplying power to the vehicle auxiliary device 20, while the vehicle power control device 10 shown in FIG. 2 is operating normally.

[0042] Here, a layer short circuit in this embodiment will be described. The vehicle power source 12 and the vehicle accessories 17 to 21 are electrically connected via a wire harness, and power is supplied to the vehicle accessories 17 to 21 from the vehicle power source 12. The wire harness is fixed along the vehicle body and is wired, so that repeated rubbing against the vehicle body due to vibrations while the vehicle is running can cause part of the insulating coating on the surface to peel off. As a result, the wire harness and the vehicle body become conductive, and a small leakage current can occur between them.

[0043] Conventionally, when a minute leakage current occurs in the middle of the wire harness, unlike when the wiring is completely shorted, power continues to be supplied from vehicle power source 12 to vehicle accessories 17 to 21. When a minute leakage current continues to occur in the wire harness for a long period of time, the leakage point generates heat, which can then cause smoke or a vehicle fire.

[0044] 4, in this embodiment, when the layer short determination unit 11B determines that a layer short has occurred in the wiring between the current sensors 25B and 20A in the wiring of the vehicle auxiliary device 20, the switch changeover unit 11C forcibly switches the semiconductor fuse 25A to the OFF operation. As a result, the supply of power from the vehicle power source 12 to the vehicle auxiliary device 20 is stopped, and the location of the wiring where the layer short has occurred generates heat, which can then be prevented from emitting smoke or causing a vehicle fire.

[0045] On the other hand, the wiring of vehicle accessories 17-19 is in a normal operating state without any layer short circuit, and therefore continues to receive power from vehicle power source 12. Then, memory section 11D of power supply control unit 11 stores the occurrence of a layer short circuit in the wiring of vehicle accessory 20.

[0046] 5, in step S11, when a passenger such as a driver gets into the vehicle and presses an ignition switch (not shown), the vehicle enters an ignition-on state. Then, in step S12, the power supply control unit 11 starts supplying power from the vehicle power source 12 to the vehicle accessories 17-21 according to the driving states of the vehicle accessories 17-21.

[0047] In step S13, current sensors 22B to 26B of relay unit 16 detect current values ​​I1 to I5 flowing through semiconductor fuses 22A to 26A, respectively. Then, current sensors 22B to 26B input the detected current values ​​I1 to I5 to power supply control unit 11 via in-vehicle network 31 as first current detection values.

[0048] Similarly, current sensors 17A to 21A built into vehicle auxiliaries 17 to 21 detect current values ​​i1 to i5 flowing through vehicle auxiliaries 17 to 21, respectively. Current sensors 17A to 21A input the detected current values ​​i1 to i5 to power supply control unit 11 via in-vehicle network 31 as second current detection values.

[0049] In step S14, the abnormal current determination unit 11A of the power supply control unit 11 compares the first current detection value stored in the memory unit 11D with the first threshold value. If the abnormal current determination unit 11A determines that the first current detection value is greater than the first threshold value (YES in step S14), the process proceeds to step S17. In step S17, the abnormal current determination unit 11A determines that an abnormal current has occurred inside the vehicle power control device 10, and the switch changeover unit 11C switches off the semiconductor fuses 22A to 26A of the wiring in which the abnormal current has occurred.

[0050] On the other hand, if the result of step S14 is NO and the abnormal current determination unit 11A determines that the first current detection value is smaller than the first threshold value, the process proceeds to step S15. Then, in step S15, the abnormal current determination unit 11A determines that no abnormal current is occurring inside the vehicle power control device 10.

[0051] Next, in step S15, the layer short-circuit determination unit 11B of the power supply control unit 11 determines the occurrence of a layer short-circuit using the first and second current detection values ​​stored in the memory unit 11D. If the result of step S15 is YES, and the layer short-circuit determination unit 11B determines that the value obtained by subtracting the second current detection value from the first current detection value is greater than the allowable value, the process proceeds to step S16.

[0052] In step S16, the layer short-circuit determination unit 11B determines that a layer short-circuit has occurred in the wiring that satisfies the above condition between the first and second current detection values, and proceeds to step S17. Then, in step S17, the switch changeover unit 11C switches off the semiconductor fuses 22A to 26A of the wiring in which the layer short-circuit has occurred.

[0053] On the other hand, if the result of step S15 is NO and the layer short determination unit 11B determines that the value obtained by subtracting the second current detection value from the first current detection value is equal to or less than the allowable value, the process returns to step S13. In this case, the vehicle power control device 10 is operating normally, and therefore the power supply control unit 11 continues to monitor for the occurrence of an abnormal current or a layer short circuit.

[0054] In step S18, the power supply control unit 11 notifies the vehicle occupants of the abnormality in the vehicle power control device 10 by displaying the occurrence of an abnormal current or a layer short on the multi-function display device, or by emitting a warning light or an alarm sound or voice.

[0055] In step S19, the vehicle occupant recognizes the abnormality in the vehicle power control device 10 from the above notification and stops the vehicle in a safe place such as the shoulder of the road, a nearby parking lot, etc. Then, when the vehicle occupant presses the ignition switch after stopping the vehicle, the vehicle enters the ignition-off state.

[0056] In this embodiment, the layer short determination unit 11B determines that a layer short has occurred in the target wiring when the plot values ​​of the first and second current detection values ​​to be compared are located in the area indicated by the shaggy hatching 34, as shown in FIG. 3 . However, this is not limited to this case. For example, a layer short may be determined to have occurred in the target wiring when the plot values ​​of the first and second current detection values ​​to be compared are located in the area indicated by the shaggy hatching 36. In a circuit configuration in which the current sensor 17A is located downstream of the current sensor 22B during normal operation of the vehicle power control device 10, the current values ​​i1 to i5 are never greater than the current values ​​I1 to I5. If such a phenomenon occurs, it is assumed that some kind of malfunction has occurred in the vehicle power control device 10. Therefore, by switching the semiconductor fuses 22A to 26A off in the target wiring, the semiconductor fuses 22A to 26A, the vehicle accessories 17 to 21, and the like can be protected.

[0057] In addition, although the current sensors 17A to 21A are described as being built into the vehicle auxiliaries 17 to 21, the present invention is not limited to this. For example, an external current sensor may be electrically connected to the upstream or downstream side of the vehicle auxiliaries 17 to 21 to detect the current values ​​i1 to i5 flowing through the vehicle auxiliaries 17 to 21. Various other modifications are possible without departing from the spirit of the present invention. [Explanation of symbols]

[0058] 10 Vehicle power control device 11 Power Control Unit 11A abnormal current determination section 11B Rare Short Judgment Section 11C Switching section 12 Vehicle power supply 13 Power Sensor 14 Current Sensor 15 Alternator 16 Relay Unit 17, 18, 19, 20, 21 Vehicle accessories 17A, 18A, 19A, 20A, 21A current sensor 22, 23, 24, 25, 26 Semiconductor modules 22A, 23A, 24A, 25A, 26A semiconductor fuses 22B, 23B, 24B, 25B, 26B Current Sensors 31 In-vehicle network 32,33 Tolerance lines

Claims

1. A vehicle power control device that controls power supplied to a plurality of vehicle accessories from a vehicle power source mounted on a vehicle, a plurality of semiconductor fuses respectively disposed between the vehicle power supply and the plurality of vehicle accessories; a plurality of current sensors that detect the values ​​of currents flowing through the plurality of semiconductor fuses; a layer short-circuit determination unit that determines a layer short between the semiconductor fuse and the plurality of vehicle auxiliaries using a first current detection value input from the current sensor and a second current detection value input from the vehicle auxiliaries; a switch changeover unit that changes the semiconductor fuse from an on operation to an off operation based on the determination by the layer short determination unit, the layer short-circuit determination unit determines whether the layer short has occurred when the second current detection value is different from an allowable value of the first current detection value, The vehicle power control device, wherein the switch changeover unit switches the semiconductor fuse of the path that is the target of the layer short occurrence determination to the off operation.

2. an abnormal current determination unit that determines an abnormal current flowing through the semiconductor fuse using the first current detection value, the abnormal current determination unit determines that the abnormal current has occurred when the first current detection value is greater than a first threshold value; 2. The vehicle power control device according to claim 1, wherein the switch changeover unit switches the semiconductor fuse of the path that is the target of the abnormal current occurrence determination to the off operation.

3. The vehicle power control device described in claim 2, characterized in that the switch switching unit switches the semiconductor fuse of the target path for the rare short occurrence determination to the off operation when the rare short occurrence determination unit determines that the rare short occurrence has occurred, even if the abnormal current determination unit determines that the abnormal current has not occurred.

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