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

Abstract

[Problem] The purpose of the present invention is to accurately detect a reduction in insulation resistance. [Solution] An insulation resistance reduction detection step starts when a first period (T1) has elapsed from the end of an activation process for activating a ground fault detection device (100).

Description

Technical Field

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

[0002] Recently, 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 for powering the electric motor. The battery installed in the hybrid vehicle and the electric vehicle is a high-voltage battery with a voltage equal to or greater than 200V, and in order to ensure its safety, it is necessary to electrically insulate the battery from the vehicle body which is a reference potential of ground. 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 a system including an ungrounded battery and the vehicle body.

[0003] As a ground fault detection device, there 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 operating as a flying capacitor, and the ground fault detection device switches among a first charging path, a second charging path, a third charging path, and a measurement path, wherein the capacitor is connected between the positive and negative electrodes of the battery without being grounded, the capacitor is connected between the positive electrode of the battery and the ground, the capacitor is connected between the negative electrode of the battery and the ground, and the measurement path is used to measure the charging voltage of the first capacitor, to charge the capacitor and measure the charging voltage of the capacitor, and to detect a decrease in insulation resistance based on the measured charging voltage of the capacitor.

[0004] [Citation List]

[0005] [Patent Document]

[0006] [Patent Document 1] JP 2004-170103A Summary of the invention

[0007] [Technical issues]

[0008] Typically, in order to reduce the common mode noise, the Y capacitor is connected to a system including a battery. With respect to the second charging path and the third charging path, the voltage of the Y capacitor enters an unbalanced state. Typically, the measurement of the insulation resistance is based on the premise that the voltage of the Y capacitor is in a balanced state. Therefore, when the voltage of the Y capacitor is in an unbalanced state, the measurement accuracy of the value of the insulation resistance measured based on the charging voltage of the charged capacitor may be reduced. Therefore, after the measurement in the second charging path and the third charging path, wait for the voltage of the Y capacitor to reach a balanced state, and then the process is performed to switch to other charging paths.

[0009] According to the ground fault detection device, generally, before detecting the decrease in insulation resistance, a startup process for starting the ground fault detection device is performed. In the startup process, there is a case where the voltage of the Y capacitor enters an unbalanced state, however, generally, the unbalanced state of the Y capacitor after the startup process is not taken into consideration.

[0010] SUMMARY OF THE INVENTION It is therefore an object of the present invention to accurately detect a decrease in insulation resistance.

[0011] [Solution to the problem]

[0012] In order to solve the above technical problems, a ground fault detection device according to an embodiment of the present application is a ground fault detection device for detecting a reduction in insulation resistance of a system including a Y capacitor and an ungrounded battery, wherein the ground fault detection device includes: a first capacitor; a switching unit configured to switch between a first charging path, a second charging path, a third charging path, and a measurement path, in which the first charging path, the first capacitor is connected between the positive electrode and the negative electrode of the battery but not connected to the ground, in the second charging path, the first capacitor is connected between the positive electrode and the ground of the battery, in the third charging path, the first capacitor is connected between the negative electrode and the ground of the battery, and the measurement path is used to measure the charging voltage of the first capacitor; and a control unit configured to control the switching unit to measure the charging voltage of the first capacitor, wherein the control unit is configured to start detecting the reduction in insulation resistance after a first period of time has passed since a start-up process for starting the ground fault detection device.

[0013] A control method according to an embodiment of the present invention is a control method of a ground fault detection device for detecting a decrease in insulation resistance of a system including a Y capacitor and an ungrounded battery, the control method being executed by a computer, wherein the ground fault detection device includes: a first capacitor; and a switching unit configured to switch between a first charging path, a second charging path, a third charging path, and a measurement path, wherein in the first charging path, the first capacitor is connected between a positive electrode and a negative electrode of the battery but not connected to the ground, in the second charging path, the first capacitor is connected between a positive electrode and the ground of the battery, in the third charging path, the first capacitor is connected between a negative electrode and the ground of the battery, and the measurement path is used to measure a charging voltage of the first capacitor; and the control method includes: an insulation resistance decrease detection step of controlling the switching unit to measure a charging voltage of the first capacitor and detecting a decrease in insulation resistance based on the measured charging voltage of the first capacitor, wherein the insulation resistance decrease detection step is started after a first period of time has passed since a start-up process for starting the ground fault detection device ends.

[0014] A control program according to an embodiment of the present invention causes a computer to execute the above-mentioned information processing method.

[0015] [Effects of the invention]

[0016] According to the present invention, it is possible to accurately detect a decrease in insulation resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a view showing a ground fault detection device 100 according to an embodiment of the present invention.

[0018] Figure 2 2 is a diagram showing a configuration example of the ground fault detection device 100 .

[0019] Figure 3 is a diagram describing a first charging path.

[0020] Figure 4 is a diagram describing a second charging path.

[0021] Figure 5 is a diagram describing a third charging path.

[0022] Figure 6 is a view that describes the measurement path.

[0023] Figure 7 is a view describing the discharge path.

[0024] Figure 8 is an example of a processing operation performed in the ground fault detection device 100 after the ground fault detection device 100 is started.

[0025] Reference Mark List

[0026] 100 Ground fault detection device

[0027] 110 First capacitor

[0028] 120 Switching Department

[0029] 130 Control Department

[0030] 200 Batteries

[0031] 210 Positive side power cable

[0032] 220 Negative power line DETAILED DESCRIPTION

[0033] <Ground Fault Detection Device 100>

[0034] Figure 1is a view showing a ground fault detection device 100 according to an embodiment of the present invention. The ground fault detection device 100 is a flying capacitor type ground fault detection device, which is connected to a non-grounded battery 200 to detect 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 referred to 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 referred to as a negative electrode side insulation resistance RLn.

[0035] The battery 200 is, for example, a battery for supplying power to the motor of the vehicle, and is a high voltage (for example, 200 V or more) battery. The battery 200 includes, for example, a plurality of rechargeable batteries (for example, lithium ion batteries). The positive side of the battery 200 is connected to the positive side power line 210, and the negative side of the battery 200 is connected to the negative side power line 220.

[0036] The system including the battery 200 is connected with a Y capacitor for reducing the noise caused by the common mode. Figure 1 In the example shown, the positive side Y capacitor CYp is connected between the positive side power line 210 and the ground, and the negative side Y capacitor CYn is connected between the negative side power line 220 and the ground. The positive side Y capacitor CYp includes stray capacitance between the positive side power line 210 and the ground, and the negative side Y capacitor CYn includes stray capacitance between the negative side power line 220 and the ground.

[0037] The ground fault detection device 100 is connected to the positive electrode of the battery 200 via the positive electrode side power line 210 and is connected to the negative electrode of the battery 200 via the negative electrode side power line 220. The ground fault detection device 100 includes a first capacitor 110, a switch 120, and a control unit 130.

[0038] The first capacitor 110 is a capacitor having a first electrode plate and a second electrode plate and configured to operate as a flying capacitor.

[0039] The switching unit 120 is configured to switch between a first charging path, a second charging path, a third charging path and a measurement path, in which in the first charging path, the first capacitor 110 is connected between the positive electrode and the negative electrode of the battery 200 without being grounded, in the second charging path, the first capacitor 110 is connected between the positive electrode of the battery 200 and the ground, in the third charging path, the first capacitor 110 is connected between the negative electrode of the battery 200 and the ground, and the measurement path is used to measure the charging voltage of the first capacitor 110.

[0040] Regarding 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 sequentially connected in series without being grounded. Thus, in the first charging path, a first charging voltage V0 corresponding to the charging voltage of the battery 200 is charged to the first capacitor 110.

[0041] Regarding the second charging path, the first capacitor 110 is charged by the current flowing through the closed circuit in which the positive electrode of the battery 200, the first capacitor 110, the negative electrode side insulation resistor RLn, and the negative electrode of the battery 200 are sequentially connected in series. Thus, in the second charging path, the second charging voltage VC1n reflecting the influence of the negative electrode side insulation resistor RLn is charged to the first capacitor 110.

[0042] Regarding the third charging path, the first capacitor 110 is charged by the current flowing through the closed circuit in which the positive electrode of the battery 200, the positive electrode side insulation resistor RLp, the first capacitor 110, and the negative electrode of the battery 200 are sequentially connected in series. Thus, in the third charging path, the third charging voltage VC1p reflecting the influence of the positive electrode side insulation resistor RLp is charged to the first capacitor 110.

[0043] The control section 130 is configured to measure the charging voltage of the first capacitor 110. For example, the control section 130 controls the switching section 120 to measure a first charging voltage V0 as the charging voltage of the first capacitor 110 charged through the first charging path, a second charging voltage VC1n as the charging voltage of the first capacitor 110 charged through the second charging path, and a third charging voltage VC1p as the charging voltage of the first capacitor 110 charged through the third charging path in the measurement path.

[0044] Then, the control unit 130 detects the decrease of the insulation resistance RLp, RLn (detects the ground fault) based on the measured charging voltage of the first capacitor 110. For example, the control unit 130 detects the decrease of the insulation resistance RLp, RLn 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 resistance RLp, RLn based on the charging voltage of the first capacitor 110, and then detects the decrease of the insulation resistance RLp, RLn based on the measured values ​​of the insulation resistance RLp, RLn. For example, the control unit 130 is composed of a computer.

[0045] The control unit 130 detects the reduction of the insulation resistance RLp, RLn in each measurement cycle. That is, the control unit 130 repeats the measurement cycle for detecting the reduction of the insulation resistance RLp, RLn. At this time, for example, the control unit 130 measures the value of the insulation resistance RLp, RLn in each measurement cycle, and then detects the reduction of the insulation resistance RLp, RLn by comparing the insulation resistance RLp, RLn measured in the current measurement cycle with the insulation resistance RLp, RLn measured in the measurement cycle before the current measurement cycle (for example, the measurement cycle immediately before the current measurement cycle).

[0046] The measurement cycle includes a first measurement period (V0 measurement period), a second measurement period (VC1n measurement period), and a third measurement period (VC1p measurement period). In the first measurement period, the first capacitor 110 is charged through the first charging path, and then the first charging voltage V0 as the charging voltage of the first capacitor 110 charged through the first charging path is measured while the first capacitor 110 is discharged through the measurement path. In the second measurement period, the first capacitor 110 is charged through the second charging path, and then the second charging voltage VC1n as the charging voltage of the first capacitor 110 charged through the second charging path is measured while the first capacitor 110 is discharged through the measurement path. In the third measurement period, the first capacitor 110 is charged through the third charging path, and then the third charging voltage VC1p as the charging voltage of the first capacitor 110 charged through the third charging path is measured while the first capacitor 110 is discharged through the measurement path. In other words, for each measurement cycle, the control unit 130 measures the first charging voltage V0, the second charging voltage VC1n, and the third charging voltage VC1p, and then detects the reduction of the insulation resistance based on the measured first charging voltage V0, the second charging voltage VC1n, and the third charging voltage VC1p. Within the measurement cycle, for example, the above measurement periods are implemented in the order of the first measurement period, the second measurement period, the first measurement period, and the third measurement period.

[0047] When an abnormality occurs (for example, the moment when the reduction of the insulation resistance RLp, RLn is detected), the control unit 130 notifies the occurrence of the abnormality (for example, the reduction of the insulation resistance RLp, RLn). At this time, the control unit 130 may be configured to notify the occurrence of the abnormality by displaying information indicating the occurrence of the abnormality using an indicating device for displaying information (for example, a display and a lamp), or configured to notify the occurrence of the abnormality by outputting a sound indicating the occurrence of the abnormality using an indicating device for outputting a sound for displaying information (for example, a speaker), or configured to notify the occurrence of the abnormality by sending information indicating the occurrence of the abnormality to another device (for example, a superior ECU (electronic control unit)) using a communication device for sending information to another device.

[0048] The control unit 130 may be configured to notify the measured insulation resistance RLp, RLn values. In this way, not the control unit 130, but a person or other device that obtains information through the notification can detect a decrease in the insulation resistance RLp, RLn.

[0049] <Configuration Example of Ground Fault Detection Device 100>

[0050] For example, Figure 2 As shown, the switching unit 120 may be configured to include four switches (a first switch S1, a second switch S2, a third switch S3, and a fourth switch S4). The four switches are insulating switch elements (eg, optical MOSFETs).

[0051] The first switch S1 is connected between the positive electrode of the battery 200 and the first electrode plate of the first capacitor 110. Figure 2 As shown, the first switch S1 is connected to the first electrode plate of the first capacitor 110 through the first resistor R1. In addition, the first diode D1 can 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 toward the first electrode plate of the first capacitor 110. Figure 2 In the configuration example shown, the first diode D1 is connected between the first switch S1 and the first resistor R1.

[0052] The second switch S2 is connected between the negative electrode of the battery 200 and the second electrode plate of the first capacitor 110. The second resistor R2 can be configured to be connected between the second switch S2 and the second electrode plate of the first capacitor 110, or between the second switch S2 and the negative electrode of the battery 200. Figure 2 In the configuration example shown, the second resistor R2 is connected between the second switch S2 and the second electrode plate of the first capacitor 110 .

[0053] The third switch S3 is connected between the first electrode plate of the first capacitor 110 and the ground. Figure 2 As shown, the third switch S3 is grounded through the third resistor R3. In addition, the second diode D2 and the third diode D3 can be connected in parallel between the third switch S3 and the first electrode plate of the first capacitor 110. The forward direction of the second diode D2 is the direction from the first electrode plate of the first capacitor 110 toward the third switch S3. The forward direction of the third diode D3 is the direction from the third switch S3 toward the first electrode plate of the first capacitor 110. Between the third switch S3 and the first electrode plate of the first capacitor 110, a fifth resistor R5 can be connected in series with the second diode D2. Figure 2In the illustrated configuration example, the fifth resistor R5 is connected to the cathode side of the second diode D2.

[0054] The fourth switch S4 is connected between the second electrode plate of the first capacitor 110 and the ground. Figure 2 As shown, the fourth switch S4 is grounded via a fourth resistor R4.

[0055] Therefore, in Figure 2 In the configuration example shown in FIG. 1 , when the first switch S1 and the second switch S2 are turned on, and the third switch S3 and the fourth switch S4 are turned off, as shown in FIG. Figure 3 As shown, a first charging path is formed, in which the first capacitor 110 is connected between the positive electrode and the negative electrode of the battery 200 without being grounded. Figure 2 In the configuration example shown, according to the first charging path, the first capacitor 110 is charged due to a closed circuit in which 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 are sequentially connected in series. Thus, with respect to 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.

[0056] In addition, Figure 2 In the configuration example shown in FIG. 1 , when the first switch S1 and the fourth switch S4 are turned on, and the second switch S2 and the third switch S3 are turned off, Figure 4 As shown, a second charging path is formed, in which the first capacitor 110 is connected between the positive electrode of the battery 200 and the ground. Figure 2 In the configuration example shown, according to the second charging path, the first capacitor 110 is charged due to a closed circuit in which 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 side insulation resistor RLn, and the negative electrode side of the battery 200 are sequentially connected in series. Thus, in the second charging path, the second charging voltage VC1n reflecting the influence of the negative electrode side insulation resistor RLn of the battery 200 is charged to the first capacitor 110.

[0057] exist Figure 2 In the configuration example shown in FIG. 1 , when the second switch S2 and the third switch S3 are turned on, and the first switch S1 and the fourth switch S4 are turned off, Figure 5 As shown, a third charging path is formed, in which the first capacitor 110 is connected between the negative electrode of the battery 200 and the ground. Figure 2In the illustrated configuration example, in the third charging path, the first capacitor 110 is charged due to a closed circuit in which 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 are sequentially connected in series. Thus, 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.

[0058] like Figure 2 As shown, the control unit 130 is connected to the first electrode plate of the first capacitor 110. Thus, when the third switch S3 and the fourth switch S4 are turned on, and the first switch S1 and the second switch S2 are turned off, as shown in FIG. Figure 6 As shown, the current flows from the first electrode plate of the first capacitor 110 to the control unit 130. Thus, 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 turned on and the first switch S1 and the second switch S2 are turned off, a measurement path for measuring the charging voltage of the first capacitor 110 is formed. Figure 2 As shown, the line connecting the third switch S3 and the control unit 130 may be grounded through the second capacitor C2.

[0059] In addition, if Figure 6 As shown, in the measurement path, current flows from the first electrode plate to the second electrode plate of the first capacitor 110. Thus, in the measurement path, the first capacitor 110 is discharged.

[0060] like Figure 2 As shown, the switching unit 120 can also be configured to include a measuring switch Sa. Figure 6 As shown in FIG. 1 , when the third switch S3, the fourth switch S4 and the measuring switch Sa are turned on, and the first switch S1 and the second switch S2 are turned off, a measuring path for measuring the charging voltage of the first capacitor 110 is formed. Figure 7 As shown, when the third switch S3 and the fourth switch S4 are turned on, and the first switch S1, the second switch S2, and the measuring switch Sa are turned off, a discharge path is formed in which the control unit 130 is disconnected from the first capacitor 110 to discharge the first capacitor 110. Figure 3-5 As shown, in the first charging path, the second charging path and the third charging path, the measuring switch Sa is set to be open.

[0061] <Processing after startup processing>

[0062] In the second charging path and the third charging path, the voltages of the Y capacitors CYp and CYn are in an unbalanced state. Generally, the measurement of the insulation resistances RLp and RLn is based on the assumption that the charging of the first capacitor 110 is started when the voltages of the Y capacitors CYp and CYn are in a balanced state. Therefore, the measurement accuracy of the values ​​of the insulation resistances RLp and RLn measured based on the charging voltage of the first capacitor 110 that starts charging when the voltages of the Y capacitors CYp and CYn are in an unbalanced state may be reduced. Therefore, after the second charging voltage VC1n and the third charging voltage VC1p have been measured, it is waited for the voltages of the Y capacitors CYp and CYn to reach a balanced state, and then the process is performed to switch to other charging paths.

[0063] According to the ground fault detection device 100, generally, before detecting the decrease of the insulation resistance RL, RLn by repeating the measurement cycle, a startup process for starting the ground fault detection device 100 is performed. In the startup process, there is a case where the voltage of the Y capacitors CYp, CYn enters an unbalanced state, however, generally, the capacity of the Y capacitors CYp, CYn is not so large, and a process of waiting for the voltage of the Y capacitors CYp, CYn to reach a balanced state after the startup process is not performed. However, in recent years, the capacity of the Y capacitors CYp, CYn has become larger, and the period of waiting for the voltage of the Y capacitors CYp, CYn to reach a balanced state after the voltage of the Y capacitors CYp, CYn has entered an unbalanced state has become longer.

[0064] Therefore, in the present embodiment, after the first period T1 has passed from the start-up process, the control section 130 starts the detection of the decrease of the insulation resistance RL, RLn. At this time, for example, the first period T1 is the time constant τ of the circuit formed by the insulation resistance RLp, RLn and the Y capacitor CYp, CYn, which is calculated by the following formula based on the combined resistance value RL of the insulation resistance RLp, RLn and the combined capacity CY of the Y capacitor CYp, CYn.

[0065] [Mathematical formula 1]

[0066] T1=τ=RL·CY

[0067] Thus, according to this embodiment, when the Y capacitors CYp and CYn enter a balanced state, the values ​​of the insulation resistances RLn and RLp are measured. As a result, the measurement accuracy of the values ​​of the insulation resistances RLn and RLp is improved, and a decrease in the insulation resistance can be accurately detected.

[0068] In addition, the first period T1 may be calculated by multiplying the time constant τ by a predetermined constant A, as shown in the following equation.

[0069] [Mathematical formula 2]

[0070] T1=A·T=A·RL·CY

[0071] Here, the predetermined constant A is, for example, a safety factor.

[0072] For example, the predetermined constant A is set so that the voltage of the Y capacitors CYp, CYn enters a balanced state before the start of the measurement period (the second measurement period (VC1n measurement period) or the third measurement period (VC1p measurement period)) performed first among the measurement periods other than the first measurement period (V0 measurement period) in the first measurement cycle. For example, in the case where each measurement period in the measurement cycle is performed in the order of the first measurement period, the second measurement period, the first measurement period, and the third measurement period, for example, the predetermined constant A is set so that the voltage of the Y capacitors CYp, CYn enters a balanced state before the start of the second measurement period, which is the measurement period performed first among the measurement periods other than the first measurement period.

[0073] Preferably, the startup process includes an insulation resistance measurement process (for example, the above-mentioned measurement cycle) for measuring the insulation resistances RLp and RLn. Also, preferably, the combined resistance value of the insulation resistances RLp and RLn is calculated based on the values ​​of the insulation resistances RLp and RLn measured by the insulation resistance measurement process.

[0074] Figure 8 1 is a view showing an example of processing operations performed in the ground fault detection device 100 after the ground fault detection device 100 is started. The ground fault detection device 100 performs a startup process (step S801). After a first period T1 has passed since the end of the startup process (step S802, yes), the detection of a decrease in the insulation resistance RLp, RLn (measurement cycle) is started to detect the decrease in the insulation resistance RLp, RLn (step S804, yes), or until the trigger is terminated (step S805, yes), the detection of a decrease in the insulation resistance RLp, RLn (measurement cycle) is repeated (step S803).

[0075] The present invention has been described above using the preferred embodiments of the present invention. Although the present invention has been described by referring to specific examples, various modifications and changes can be made to these examples without departing from the spirit and scope of the present invention as described in the claims.

Claims

1. A ground fault detection device (100) for detecting a decrease in insulation resistance (RLp, RLn) of a system including an ungrounded battery (200) and Y capacitors (CYp, CYn), the ground fault detection device (100) comprising: A first capacitor (110); a switching unit (120), the switching unit (120) being configured to switch between a first charging path, a second charging path, a third charging path and a measuring path, In the first charging path, the first capacitor (110) is connected between the positive electrode and the negative electrode of the battery (200) but not connected to the ground. In the second charging path, the first capacitor (110) is connected between the positive electrode of the battery (200) and the ground. In the third charging path, the first capacitor (110) is connected between the negative electrode of the battery (200) and the ground. The measurement path is used to measure the charging voltage of the first capacitor (110); and a control unit (130) configured to control the switch unit (120) to measure a charging voltage of the first capacitor (110), The control unit (130) is configured to start detecting a decrease in the insulation resistance (RLp, RLn) when a first period (T1) has passed since a start-up process (S801) for starting the ground fault detection device (100) is completed.

2. The ground fault detection device (100) according to claim 1, wherein: The first period (T1) is calculated based on the value of the insulation resistance (RLp, RLn) and the capacity of the Y capacitor (CYp, CYn).

3. The ground fault detection device (100) according to claim 2, wherein: The first time period (T1) is calculated by multiplying the combined resistance value (RL) of the positive side insulation resistance (RLp) and the negative side insulation resistance (RLn) of the insulation resistance (RLp, RLn) by the combined capacity (CY) of the positive side Y capacitor (CYp) and the negative side Y capacitor (CYn) of the Y capacitor (CYp, CYn).

4. The ground fault detection device (100) according to claim 3, wherein: The first time period (T1) is calculated by multiplying the combined resistance value (RL) of the positive side insulation resistance (RLp) and the negative side insulation resistance (RLn) of the insulation resistance (RLp, RLn) by the combined capacity (CY) of the positive side Y capacitor (CYp) and the negative side Y capacitor (CYn) of the Y capacitor (CYp, CYn) and a predetermined constant (A).

5. The ground fault detection device (100) according to claim 4, wherein: The predetermined constant (A) is a safety factor.

6. The ground fault detection device (100) according to claim 5, wherein: The control unit (130) is configured to perform detection for a decrease in the insulation resistance (RLp, RLn), and Wherein, the measurement cycle includes: a first measurement period, in which the first capacitor (110) is charged in the first charging path and a first charging voltage (V0) is measured in the measurement path, the first charging voltage (V0) being a charging voltage of the first capacitor (110) charged through the first charging path; a second measurement period, in which the first capacitor (110) is charged in the second charging path and a second charging voltage (VC1n) is measured in the measurement path, the second charging voltage (VC1n) being a charging voltage of the first capacitor (110) charged through the second charging path; and a third measurement period, in which the first capacitor (110) is charged in the third charging path and a third charging voltage (VC1p) is measured in the measurement path, the third charging voltage (VC1p) being the charging voltage of the first capacitor (110) charged through the third charging path, and The predetermined constant (A) is set so that the voltage of the Y capacitor (CYp, CYn) enters a balanced state before the start of a measurement period that is first performed among measurement periods other than the first measurement period.

7. The ground fault detection device (100) according to any one of claims 2 to 6, in, The startup process (S801) includes an insulation resistance measurement process for measuring the value of the insulation resistance (RLp, RLn), and The value of the insulation resistance (RLp, RLn) used in the calculation of the first period (T1) is the value of the insulation resistance (RLp, RLn) measured by the insulation resistance measurement process.

8. A control method for a ground fault detection device (100), the ground fault detection device (100) being used to detect a decrease in insulation resistance (RLp, RLn) of a system including an ungrounded battery (200) and a Y capacitor (CYp, CYn), the control method being executed by a computer, The ground fault detection device (100) comprises: A first capacitor (110); as well as A switching unit (120) configured to switch between a first charging path, a second charging path, a third charging path and a measurement path In the first charging path, the first capacitor (110) is connected between the positive electrode and the negative electrode of the battery (200) but not connected to the ground. In the second charging path, the first capacitor (110) is connected between the positive electrode of the battery (200) and the ground. In the third charging path, the first capacitor (110) is connected between the negative electrode of the battery (200) and the ground. The measurement path is used to measure the charging voltage of the first capacitor (110), The control method comprises: an insulation resistance reduction detection step of controlling the switching unit (120) to measure the charging voltage of the first capacitor (110), and detecting the reduction of the insulation resistance (RLp, RLn) based on the measured charging voltage of the first capacitor (110); The insulation resistance reduction detection step is started when a first period (T1) has passed since a start-up process (S801) for starting the ground fault detection device (100) is completed.

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

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