Ground fault detection device, control method therefor, and control program

Abstract

To enable accurate detection of deterioration in insulation resistance.SOLUTION: An insulation resistance deterioration detection process for detecting deterioration in insulation resistance starts when a first time period T1 has elapsed after completion of a startup process for starting up a ground fault detection device 100.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to a ground fault detection device, a control method thereof, and a control program thereof. [Background technology]

[0002] Hybrid vehicles and electric vehicles are becoming more and more popular. Hybrid vehicles and electric vehicles are equipped with an electric motor and a battery that supplies power to the electric motor. The battery installed in hybrid vehicles and electric vehicles is a high-voltage battery of 200V or more, and in order to ensure safety, it needs to be electrically insulated from the vehicle body, which is the ground reference potential point. Therefore, vehicles such as hybrid vehicles and electric vehicles are also equipped with a ground fault detection device that detects a decrease in insulation resistance between the system including the battery, which is ungrounded, and the vehicle body.

[0003] One example of a ground fault detection device is a flying capacitor type ground fault detection device (for example, Patent Document 1). The flying capacitor type ground fault detection device has a capacitor that operates as a flying capacitor, and switches between a first charging path in which the capacitor is connected between the positive and negative electrodes of a battery without going through ground, a second charging path in which the capacitor is connected between the positive and negative electrodes of the battery and ground, a third charging path in which the capacitor is connected between the negative and negative electrodes of the battery and ground, and a measurement path for measuring the charging voltage of the first capacitor, to charge the capacitor and measure the charging voltage of the capacitor, and detect a decrease in insulation resistance based on the measured charging voltage of the capacitor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2004-170103 A Summary of the Invention [Problem to be solved by the invention]

[0005] Generally, a Y capacitor is connected to a system including a battery to reduce common-mode noise. In the second and third charging paths, the voltage of the Y capacitor is in an unbalanced state. In general, insulation resistance measurements are based on the assumption that the voltage of the Y capacitor is in a balanced state. For this reason, the insulation resistance value measured based on the charging voltage of a capacitor that is charged when the voltage of the Y capacitor is in an unbalanced state may have low measurement accuracy. For this reason, after measurements in the second and third charging paths, the voltage of the Y capacitor is waited to be in a balanced state, and then the charging path is switched to another one.

[0006] In general, before starting to detect the decrease in insulation resistance, a start-up process is performed to start up the earth fault detection device. During this start-up process, the voltage of the Y capacitor may become unbalanced. However, in the past, the unbalanced state of the Y capacitor after the start-up process has not been taken into consideration.

[0007] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to accurately detect a decrease in insulation resistance. [Means for solving the problem]

[0008] In order to solve the above problem, an earth fault detection device according to one embodiment of the present invention is a ground fault detection device that detects a decrease in insulation resistance of a system including an ungrounded battery and a Y capacitor, and includes a first capacitor, a first charging path in which the first capacitor is connected between the positive and negative electrodes of the battery without grounding, a second charging path in which the first capacitor is connected between the positive electrode of the battery and ground, a third charging path in which the first capacitor is connected between the negative electrode of the battery and ground, and a measurement path for measuring the charging voltage of the first capacitor, and a control unit that controls the switching unit, measures the charging voltage of the first capacitor, and detects the decrease in insulation resistance based on the measured charging voltage of the first capacitor, and the control unit starts detecting the decrease in insulation resistance after a first period has elapsed since the end of a startup process for starting up the earth fault detection device.

[0009] A control method according to one embodiment of the present invention is a control method for a ground fault detection device executed by a computer, the control method for the ground fault detection device being executed by a computer and detecting a decrease in insulation resistance of a system including an ungrounded battery and a Y capacitor, the ground fault detection device having a first capacitor, a first charging path in which the first capacitor is connected between the positive and negative electrodes of the battery without going through ground, a second charging path in which the first capacitor is connected between the positive electrode of the battery and ground, a third charging path in which the first capacitor is connected between the negative electrode of the battery and ground, and a measurement path for measuring a charging voltage of the first capacitor, the control method having an insulation resistance decrease detection process of controlling the switching unit to measure the charging voltage of the first capacitor and detecting a decrease in the insulation resistance based on the measured charging voltage of the first capacitor, the insulation resistance decrease detection process being started after a first period has elapsed since the end of a startup process for starting up the ground fault detection device.

[0010] A control program according to an embodiment of the present invention causes a computer to execute the above-described information processing method. Effect of the Invention

[0011] According to the present invention, a decrease in insulation resistance can be accurately detected. [Brief description of the drawings]

[0012] [Figure 1] 1 is a diagram showing a ground fault detection device 100 according to an embodiment of the present invention. [Diagram 2] 1 is a diagram illustrating an example of the configuration of a ground fault detection device 100. FIG. [Diagram 3] FIG. 4 is a diagram illustrating a first charging path. [Figure 4] FIG. 11 is a diagram illustrating a second charging path. [Diagram 5] FIG. 13 is a diagram illustrating a third charging path. [Figure 6]FIG. 2 is a diagram illustrating a measurement path. [Figure 7] FIG. 2 is a diagram illustrating a discharge path. [Figure 8] 4 is a diagram showing an example of a processing operation executed in the ground fault detection device 100 after the ground fault detection device 100 is started up. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] <Ground fault detection device 100> 1 is a diagram showing a ground fault detection device 100 according to one embodiment of the present invention. The ground fault detection device 100 is a flying capacitor type ground fault detection device that is connected to an ungrounded battery 200 and detects a decrease in insulation resistance of a system including the battery 200. Here, the insulation resistance between the positive electrode side of the battery 200 and the ground is taken as a positive electrode side insulation resistance RLp, and the insulation resistance between the negative electrode side of the battery 200 and the ground is taken as a negative electrode side insulation resistance RLn.

[0014] Battery 200 is, for example, a battery for supplying power to an electric motor of a vehicle, and is a high-voltage battery (for example, 200 V or higher). Battery 200 is, for example, composed of a plurality of rechargeable batteries (for example, lithium ion batteries). The positive electrode side of battery 200 is connected to positive electrode side power supply line 210, and the negative electrode side of battery 200 is connected to negative electrode side power supply line 220.

[0015] A Y capacitor is connected to the system including the battery 200 to reduce common mode noise. In the example shown in Fig. 1, a positive Y capacitor CYp is connected between the positive power supply line 210 and the ground, and a negative Y capacitor CYn is connected between the negative power supply line 220 and the ground. The positive Y capacitor CYp includes a stray capacitance between the positive power supply line 210 and the ground, and the negative Y capacitor CYn includes a stray capacitance between the negative power supply line 220 and the ground.

[0016] The ground fault detection device 100 is connected to the positive electrode of the battery 200 via a positive power supply line 210, and is connected to the positive electrode of the battery 200 via a negative power supply line 220. The ground fault detection device 100 has a first capacitor 110, a switching unit 120, and a control unit 130.

[0017] The first capacitor 110 is a capacitor having a first plate and a second plate, and operates as a flying capacitor.

[0018] The switching unit 120 switches between a first charging path in which the first capacitor 110 is connected between the positive electrode and the negative electrode of the battery 200 without grounding, a second charging path in which the first capacitor 110 is connected between the positive electrode of the battery 200 and ground, a third charging path in which the first capacitor 110 is connected between the negative electrode of the battery 200 and ground, and a measurement path for measuring the charging voltage of the first capacitor 110.

[0019] In the first charging path, the first capacitor 110 is charged by a current flowing through a closed circuit in which the positive electrode of the battery 200, the first capacitor 110, and the negative electrode of the battery 200 are connected in series in this order without being grounded. Therefore, in the first charging path, the first capacitor 110 is charged with a first charging voltage V0 corresponding to the charging voltage of the battery 200.

[0020] In the second charging path, the first capacitor 110 is charged by a current flowing through a closed circuit in which the positive electrode of the battery 200, the first capacitor 110, the negative electrode side insulation resistance RLn, and the negative electrode of the battery 200 are connected in series in this order. Therefore, in the second charging path, the first capacitor 110 is charged with a second charging voltage VC1n that reflects the influence of the negative electrode side insulation resistance RLn.

[0021] In the third charging path, the first capacitor 110 is charged by a current flowing through a closed circuit in which the positive electrode of the battery 200, the positive electrode side insulation resistance RLp, the first capacitor 110, and the negative electrode of the battery 200 are connected in series in this order. Therefore, in the third charging path, the first capacitor 110 is charged with a third charging voltage VC1p that reflects the influence of the positive electrode side insulation resistance RLp.

[0022] The control unit 130 measures the charging voltage of the first capacitor 110. The control unit 130, for example, controls the switching unit 120 to measure, in the measurement path, a first charging voltage V0 which is the charging voltage of the first capacitor 110 charged via the first charging path, a second charging voltage VC1n which is the charging voltage of the first capacitor 110 charged via the second charging path, and a third charging voltage VC1p which is the charging voltage of the first capacitor 110 charged via the third charging path.

[0023] Then, the control unit 130 detects the decrease in the insulation resistances RLp, RLn (detects a ground fault) based on this measured charging voltage of the first capacitor 110. The control unit 130 detects the decrease in the insulation resistances RLp, RLn, for example, based on the first charging voltage V0, the second charging voltage VC1n, and the third charging voltage VC1p. At this time, the control unit 130 measures the values ​​of the insulation resistances RLp, RLn, for example, based on the charging voltage of the first capacitor 110, and detects the decrease in the insulation resistances RLp, RLn, based on the measured values ​​of the insulation resistances RLp, RLn. The control unit 130 is, for example, configured by a computer.

[0024] The control unit 130 detects the decrease in the insulation resistances RLp, RLn for each measurement cycle. That is, the control unit 130 repeats the measurement cycle for detecting the decrease in the insulation resistances RLp, RLn. At this time, the control unit 130 detects the decrease in the insulation resistances RLp, RLn by, for example, measuring the values ​​of the insulation resistances RLp, RLn for each measurement cycle and comparing the values ​​of the insulation resistances RLp, RLn measured in the measurement cycle with the values ​​of the insulation resistances RLp, RLn measured in the measurement cycle before the measurement cycle (for example, the measurement cycle immediately before the measurement cycle).

[0025] The measurement cycle includes a first measurement period (V0 measurement period) in which the first capacitor 110 is charged via a first charging path, and a first charging voltage V0 is measured, which is the charging voltage of the first capacitor 110 charged via the first charging path, while discharging the first capacitor 110 via a measurement path; a second measurement period (VC1n measurement period) in which the first capacitor 110 is charged via a second charging path, and a second charging voltage VC1n is measured, which is the charging voltage of the first capacitor 110 charged via the second charging path, while discharging the first capacitor 110 via the measurement path; and a third measurement period (VC1p measurement period) in which the first capacitor 110 is charged via a third charging path, and a third charging voltage VC1p is measured, which is the charging voltage of the first capacitor 110 charged via the third charging path, while discharging the first capacitor 110 via the measurement path. That is, the control unit 130 measures the first charging voltage V0, the second charging voltage VC1n, and the third charging voltage VC1p for each measurement cycle, and detects the decrease in insulation resistance based on the measured first charging voltage V0, the second charging voltage VC1n, and the third charging voltage VC1p. In the measurement cycle, the measurement periods are performed in the order of, for example, the first measurement period, the second measurement period, the first measurement period, and the third measurement period.

[0026] When an abnormality occurs (for example, when a decrease in the insulation resistances RLp and RLn is detected), the control unit 130 notifies the occurrence of the abnormality (for example, a decrease in the insulation resistances RLp and RLn). At this time, the control unit 130 may notify the occurrence of the abnormality by displaying information indicating the occurrence of the abnormality using a display device (for example, a display or a lamp) that displays information, may notify the occurrence of the abnormality by outputting a sound indicating the occurrence of the abnormality using a display device (for example, a speaker) that outputs a sound indicating the occurrence of the abnormality, or may notify the occurrence of the abnormality by transmitting information indicating the occurrence of the abnormality to another device (for example, a higher-level ECU (Electronic Control Unit)) using a communication device that transmits information to another device.

[0027] The control unit 130 may be configured to notify the measured values ​​of the insulation resistances RLp, RLn. In this manner, a person who receives information from the notification or another device that receives information from the information can detect the decrease in the insulation resistances RLp, RLn, instead of the control unit 130.

[0028] <Configuration example of ground fault detection device 100> The switching unit 120 may have, for example, four switches (a first switch S1, a second switch S2, a third switch S3, and a fourth switch S4) as shown in Fig. 2. These four switches are, for example, insulating switching elements (for example, optical MOSFETs).

[0029] The first switch S1 is connected between the positive electrode of the battery 200 and the first plate of the first capacitor 110. At this time, the first switch S1 is connected to the first plate of the first capacitor 110 via a first resistor R1 as shown in FIG. 2. A first diode D1 may be connected between the first switch S1 and the first resistor R1 or between the first resistor R1 and the first capacitor 110. The forward direction of the first diode D1 is from the positive electrode of the battery 200 to the first plate of the first capacitor 110. In the configuration example shown in FIG. 2, the first diode D1 is connected between the first switch S1 and the first resistor R1.

[0030] The second switch S2 is connected between the negative electrode of the battery 200 and the second plate of the first capacitor 110. A second resistor R2 may be connected between the second switch S2 and the second plate of the first capacitor 110 or between the second switch S2 and the negative electrode of the battery 200. In the configuration example shown in FIG. 2, the second resistor R2 is connected between the second switch S2 and the second plate of the first capacitor 110.

[0031] The third switch S3 is connected between the first plate of the first capacitor 110 and the ground. At this time, the third switch S3 is connected to the ground via the third resistor R3 as shown in FIG. 2. In addition, the second diode D2 and the third diode D3 may be connected in parallel between the third switch S3 and the first plate of the first capacitor 110. The forward direction of the second diode D2 is from the first plate of the first capacitor 110 to the third switch S3. The forward direction of the third diode D3 is from the third switch S3 to the first plate of the first capacitor 110. Between the third switch S3 and the first plate of the first capacitor 110, the fifth resistor R5 may be connected in series with the second diode D2. In the configuration example shown in FIG. 2, the fifth resistor R5 is connected to the cathode side of the second diode D2.

[0032] The fourth switch S4 is connected between the second plate of the first capacitor 110 and ground. The fourth switch S4 is connected to ground through a fourth resistor R4 as shown in FIG.

[0033] Therefore, in the configuration example shown in Fig. 2, when the first switch S1 and the second switch S2 are on and the third switch S3 and the fourth switch S4 are off, as shown in Fig. 3, the first capacitor 110 is connected between the positive and negative electrodes of the battery 200 without being grounded, forming a first charging path. In the configuration example shown in Fig. 2, the first capacitor 110 is charged by a closed circuit connected in series in the following order: the positive electrode of the battery 200, the first switch S1, the first diode D1, the first resistor R1, the first capacitor 110, the second resistor R2, the second switch S2, and the negative electrode of the battery 200. Therefore, in the first charging path, the first charging voltage V0 corresponding to the charging voltage of the battery 200 is charged to the first capacitor 110.

[0034] In the configuration example shown in Fig. 2, when the first switch S1 and the fourth switch S4 are on and the second switch S2 and the third switch S3 are off, the first capacitor 110 becomes a second charging path connected between the positive electrode of the battery 200 and the ground as shown in Fig. 4. In the configuration example shown in Fig. 2, in the second charging path, the first capacitor 110 is charged by a closed circuit connected in series in the following order: the positive electrode of the battery 200, the first switch S1, the first diode D1, the first resistor R1, the first capacitor 110, the fourth switch S4, the fourth resistor R4, the negative electrode insulation resistor RLn, and the negative electrode of the battery 200. Therefore, in the second charging path, the second charging voltage VC1n reflecting the influence of the negative electrode insulation resistor RLn of the battery 200 is charged to the first capacitor 110.

[0035] In the configuration example shown in Fig. 2, when the second switch S2 and the third switch S3 are on and the first switch S1 and the fourth switch S4 are off, the first capacitor 110 is connected between the negative electrode of the battery 200 and the ground as a third charging path as shown in Fig. 5. In the configuration example shown in Fig. 2, in the third charging path, the first capacitor 110 is charged by a closed circuit connected in series in the following order: the positive electrode of the battery 200, the positive electrode side insulation resistance RLp, the third resistor R3, the third switch S3, the third diode D3, the first capacitor 110, the second resistor R2, the second switch S2, and the negative electrode of the battery 200. Therefore, in the third charging path, the third charging voltage VC1p reflecting the influence of the positive electrode side insulation resistance RLp of the battery 200 is charged to the first capacitor 110.

[0036] The control unit 130 is connected to the first plate of the first capacitor 110 via the third switch, as shown in FIG. 2. Therefore, when the third switch S3 and the fourth switch S4 are on and the first switch S1 and the second switch S2 are off, a current flows from the first plate of the first capacitor 110 to the control unit 130, as shown in FIG. 6. Therefore, the control unit 130 can measure the charging voltage of the detection capacitor C1. That is, when the third switch S3 and the fourth switch S4 are on and the first switch S1 and the second switch S2 are off, the measurement path is used to measure the charging voltage of the first capacitor 110. The line connecting the third switch S3 and the control unit 130 may be grounded via the second capacitor C2, as shown in FIG. 2.

[0037] 6, in the measurement path, a current flows from the first plate to the second plate of the first capacitor 110. Therefore, in the measurement path, the first capacitor 110 is discharged.

[0038] The switching unit 120 may further include a measurement switch Sa as shown in FIG. 2. In this way, when the third switch S3, the fourth switch S4, and the measurement switch Sa are on and the first switch S1 and the second switch S2 are off, the path becomes a measurement path for measuring the charging voltage of the first capacitor 110 as shown in FIG. 6. When the third switch S3 and the fourth switch S4 are on and the first switch S1, the second switch S2, and the measurement switch Sa are off, the control unit 130 is separated from the first capacitor 110 as shown in FIG. 7, and the path becomes a discharge path for discharging the first capacitor 110. In the first charging path, the second charging path, and the third charging path, the measurement switch Sa is turned off as shown in FIG. 3-5.

[0039] <Post-boot process> In the second charging path and the third charging path, the voltages of the Y capacitors CYp and CYn are in an unbalanced state. In general, the measurement of the insulation resistances RLp and RLn is premised on the premise that the charging of the first capacitor 110 is started when the voltages of the Y capacitors CYp and CYn are in an balanced state. Therefore, the value of the insulation resistances RLp and RLn measured based on the charging voltage of the first capacitor 110, which is started to be charged when the voltages of the Y capacitors CYp and CYn are in an unbalanced state, may have low measurement accuracy. Therefore, after the second charging voltage VC1n and the third charging voltage VC1p are measured, the voltages of the Y capacitors CYp and CYn are waited to be in an balanced state, and then the charging path is switched to another one.

[0040] In the ground fault detection device 100, a startup process is generally performed to start the ground fault detection device 100 before starting to detect the decrease in the insulation resistances RLp, RLn by repeating the measurement cycle. During this startup process, the voltages of the Y capacitors CYp, CYn may become unbalanced. However, in the past, the capacitance of the Y capacitors CYp, CYn was not so large, and it was not necessary to wait for the voltages of the Y capacitors CYp, CYn to become balanced after the startup process. However, in recent years, the capacitance of the Y capacitors CYp, CYn has increased, and the time it takes for the voltages of the Y capacitors CYp, CYn to become balanced after the voltages of the Y capacitors CYp, CYn become unbalanced has become longer.

[0041] Therefore, in this embodiment, the control unit 130 starts detecting the decrease in the insulation resistances RLp, RLn after the first period T1 has elapsed since the end of the startup process. At this time, the first period T1 is, for example, a time constant τ of a circuit consisting of the insulation resistances RLp, RLn and the Y capacitors CYp, CYn, and is calculated as follows based on the combined resistance value RL of the insulation resistances RLp, RLn and the combined capacitance CY of the Y capacitors CYp, CYn.

number

[0042] Therefore, in this embodiment, the values ​​of the insulation resistances RLn, RLp are measured when the Y capacitors CYp, CYn are in a balanced state. As a result, the measurement accuracy of the values ​​of the insulation resistances RLn, RLp is improved, and it is possible to accurately detect a decrease in the insulation resistance.

[0043] Moreover, the first period T1 may be calculated by multiplying the time constant τ by a predetermined constant A as follows:

number

[0044] The predetermined constant A is set, for example, so that the voltages of the Y capacitors CYp, CYn are balanced by the start of the measurement period which is executed first among the measurement periods other than the first measurement period (V0 measurement period) of the first measurement cycle (the second measurement period (VC1n measurement period) or the third measurement period (VC1p measurement period). For example, when the measurement periods in the measurement cycle are executed in the order of the first measurement period, the second measurement period, the first measurement period, and the third measurement period, the predetermined constant A is set, for example, so that the voltages of the Y capacitors CYp, CYn are balanced by the start of the second measurement period, which is the measurement period which is executed first among the measurement periods other than the first measurement period.

[0045] The startup process may include an insulation resistance measurement process (e.g., the above-mentioned measurement cycle) for measuring the insulation resistances RLp and RLn, and the combined resistance value of the insulation resistances RLp and RLn may be calculated based on the values ​​of the insulation resistances RLp and RLn measured by the insulation resistance measurement process.

[0046] 8 is a diagram showing an example of a processing operation executed in the ground fault detection device 100 after the ground fault detection device 100 is started. The ground fault detection device 100 performs a start-up process (step S801). After a first period T1 has elapsed since the end of the start-up process (step S802, YES), detection of a decrease in the insulation resistances RLp, RLn (measurement cycle) is started, and detection of a decrease in the insulation resistances RLp, RLn (measurement cycle) is repeated (step S803) until a decrease in the insulation resistances RLp, RLn is detected (step S804, YES) or an end trigger occurs (step S805, YES).

[0047] The present invention has been described above in terms of preferred embodiments thereof. Although the present invention has been described herein with reference to specific examples, various modifications and variations can be made to these examples without departing from the spirit and scope of the present invention as set forth in the claims. [Explanation of symbols]

[0048] 100 Earth fault detection device 110 First Capacitor 120 Switching section 130 Control section 200 Battery 210 Positive power line 220 Negative power line

Claims

1. A ground fault detection device for detecting a decrease in insulation resistance of a system including an ungrounded battery and a Y capacitor, A first capacitor; a switching unit that switches among a first charging path in which the first capacitor is connected between the positive electrode and the negative electrode of the battery without being connected to ground, a second charging path in which the first capacitor is connected between the positive electrode and the ground of the battery, a third charging path in which the first capacitor is connected between the negative electrode and the ground of the battery, and a measurement path for measuring a charging voltage of the first capacitor; a control unit that controls the switching unit, measures a charging voltage of the first capacitor, and detects a decrease in the insulation resistance based on the measured charging voltage of the first capacitor, A ground fault detection device, wherein the control unit starts detecting a decrease in the insulation resistance after a first period has elapsed since completion of a startup process for starting up the ground fault detection device.

2. The ground fault detection device according to claim 1 , wherein the first period is calculated based on a value of the insulation resistance and a capacitance of the Y capacitor.

3. 3. The ground fault detection device according to claim 2, wherein the first period is calculated by multiplying a combined resistance value of a positive insulation resistance and a negative insulation resistance of the insulation resistor by a combined capacitance of a positive Y capacitor and a negative Y capacitor of the Y capacitor.

4. 4. The ground fault detection device according to claim 3, wherein the first period is a value obtained by multiplying a combined resistance value of a positive insulation resistance and a negative insulation resistance of the insulation resistor, a combined capacitance of a positive Y capacitor and a negative Y capacitor of the Y capacitor, and a predetermined constant.

5. The ground fault detection device according to claim 4 , wherein the predetermined constant is a safety factor.

6. The control unit detects the decrease in the insulation resistance for each measurement cycle, The measurement cycle comprises: a first measurement period in which the first capacitor is charged in the first charging path and a first charging voltage, which is a charging voltage of the first capacitor charged through the first charging path, is measured in the measurement path; a second measurement period in which the first capacitor is charged in the second charging path and a second charging voltage, which is a charging voltage of the first capacitor charged through the second charging path, is measured in the measurement path; a third measurement period in which the first capacitor is charged in the third charging path and a third charging voltage, which is a charging voltage of the first capacitor charged through the third charging path, is measured in the measurement path; 6. The ground fault detection device according to claim 5, wherein the predetermined constant is set so that the voltage of the Y capacitor is in a balanced state by the time a measurement period other than the first measurement period of the first measurement cycle is started.

7. the startup process includes an insulation resistance measurement process for measuring a value of the insulation resistance, The ground fault detection device according to claim 2 , wherein the value of the insulation resistance used in calculating the first period is a value of the insulation resistance measured by the insulation resistance measurement process.

8. A method for controlling a ground fault detection device for detecting a decrease in insulation resistance of a system including an ungrounded battery and a Y capacitor, the method being executed by a computer, comprising the steps of: The ground fault detection device includes: A first capacitor; a switching unit that switches among a first charging path in which the first capacitor is connected between a positive electrode and a negative electrode of the battery without a ground, a second charging path in which the first capacitor is connected between a positive electrode of the battery and a ground, a third charging path in which the first capacitor is connected between a negative electrode of the battery and a ground, and a measurement path for measuring a charging voltage of the first capacitor, The control method includes an insulation resistance decrease detection step of controlling the switching unit, measuring a charging voltage of the first capacitor, and detecting a decrease in the insulation resistance based on the measured charging voltage of the first capacitor, A control method, wherein the insulation resistance decrease detection step is started after a first period has elapsed since completion of a startup process for starting up the ground fault detection device.

9. An information processing program that causes a computer to execute the control method according to claim 8.

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