Ground fault detection device

Abstract

The object of this invention is to prevent the detection accuracy of insulation resistance from being reduced due to the influence of Y capacitors without increasing detection time and cost. This object is achieved by a ground fault detection device (100) comprising: a detection capacitor (C1); a switch group (S1-S4) for switching between a first charging path connecting a battery (300) and the detection capacitor, a second charging path connecting the battery, the negative side insulation resistance (RLn), and the detection capacitor, a third charging path connecting the battery, the positive side insulation resistance (RLp), and the detection capacitor, and a measurement path for measuring the charging voltage of the detection capacitor; and a controller (110) configured to calculate the insulation resistance based on the measured value of the charging voltage of the detection capacitor present after charging of each charging path, wherein, after measuring the charging voltage of the second charging path, the controller is configured to switch the switch group to the third charging path before switching to the first charging path.

Description

Technical Field

[0001] This invention relates to a ground fault detection device with a flying capacitor. Background Technology

[0002] In hybrid vehicles equipped with both an engine and an electric motor as drive sources, or in vehicles powered by an electric motor such as electric vehicles, a battery mounted on the vehicle body is charged, where driving force is generated by utilizing electrical energy supplied from the battery. Typically, the battery-related power circuitry is configured to operate at high voltages equal to or greater than 200V. For safety, such high-voltage circuitry, including the battery, is configured ungrounded, meaning the high-voltage circuitry is electrically insulated from the vehicle body, which serves as a reference potential point for grounding.

[0003] Vehicles equipped with ungrounded high-voltage batteries are fitted with ground fault detection devices to monitor the system in which the high-voltage battery is located. Specifically, they monitor the insulation status (ground fault) between the vehicle body and the main power supply system extending from the high-voltage battery to the electric motor. Such ground fault detection devices widely utilize a system employing capacitors called flying capacitors.

[0004] To determine the insulation resistance, a ground fault detection device based on a flying capacitor performs V0, Vc1n, and Vc1p measurements. These measurements are performed by switching the charging path of a detection capacitor, configured to function as a flying capacitor, using a switch. Here, the V0 measurement is a measurement of the charging voltage corresponding to the voltage of the high-voltage battery, the Vc1n measurement is a measurement of the charging voltage reflecting the effect of the negative-side insulation resistance, and the Vc1p measurement is a measurement of the charging voltage reflecting the effect of the positive-side insulation resistance.

[0005] It is known that the insulation resistance generated by the positive and negative insulation resistances can be calculated based on the voltages V0, Vc1n, and Vc1p obtained through the above measurements. Since the calculation is complex, a conversion mapping for calculating the insulation resistance is usually provided in advance, using Vc1 / V0 as a reference value (where Vc1 = Vc1p + Vc1n). To determine whether a ground fault has occurred, the insulation resistance is calculated using this reference conversion mapping based on the measured value of Vc1 / V0.

[0006] To eliminate high-frequency noise and / or stabilize operation, a capacitor known as a Y capacitor (bypass capacitor) is typically connected between ground and the positive and negative power supply lines of the high-voltage battery. In this specification, stray capacitances existing between ground and the positive and negative power supply lines should be treated as included in the Y capacitor. Especially in recent years, advancements in vehicle performance have led to a tendency for stray capacitances to increase.

[0007] Reference List

[0008] Patent documents

[0009] Patent Document 1: JP2013-205082A Summary of the Invention

[0010] Because charge exchange occurs between the Y capacitor and the sensing capacitor during the switching of the charging path, the charging voltage of the sensing capacitor may be affected by the Y capacitor, which may reduce the accuracy of the insulation resistance calculation.

[0011] The effect of the Y capacitors will be described. Since the positive and negative Y capacitors exist in parallel with the insulation resistances on the positive and negative sides, respectively, these Y capacitors are thus charged in equilibrium under conditions where no external changes are applied, determined by the voltage division ratio of the insulation resistances on the positive and negative sides, thereby stabilizing the Y capacitors. Here, this state should be referred to as the equilibrium state. Also assuming that the measured value obtained using V0, corresponding to the voltage of the high-voltage battery, is a value existing in the equilibrium state, the calculation of the insulation resistance using a ground fault detection device will be performed.

[0012] However, since each of the Vc1n and Vc1p measurements uses one of the insulation resistances as the charging path, this balance can be disrupted in the Vc1n and Vc1p measurements, which respectively reflect the effects of the negative and positive insulation resistances. If the V0 measurement is performed before the disrupted balance is restored, the aforementioned assumption that the Y capacitor is in equilibrium may not be satisfied. This leads to reduced accuracy in calculating the insulation resistance.

[0013] If V0 measurement is initiated after full restoration of equilibrium to minimize the impact of the Y capacitor, this could lead to an increase in the time required for ground fault detection. This is especially true when the Y capacitor has a large capacitance; in cases of high grounding resistance, the restoration of equilibrium may be substantially delayed. Increasing the size of the detection capacitor is also an option. However, the required charging time also increases by the amount corresponding to the size increase. Again, in this case, the time required for ground fault detection increases.

[0014] To address this problem, Patent Document 1 describes a balance-state forming circuit comprising a control resistor, one end of which is grounded, wherein the control resistor is connected to each of the positive and negative power supply lines via a control switch. According to the invention described in Patent Document 1, after the balance is disrupted due to Vc1n / Vc1p measurement, the restoration of the balance state can be facilitated by switching the control switch closed, thus rapidly changing the charging state of the Y capacitors on the positive / negative sides to the voltage division ratio of the control resistor.

[0015] This allows for the prevention of reduced insulation resistance detection accuracy due to the influence of the Y capacitor without increasing ground fault detection time. On the other hand, a dedicated circuit, namely a balance state forming circuit, is required, which increases costs.

[0016] Therefore, the purpose of this invention is to prevent the reduction in the detection accuracy of insulation resistance due to the influence of Y capacitors without increasing detection time and cost.

[0017] To achieve the above objectives, a ground fault detection device according to a first aspect of the present invention is configured to connect to an ungrounded battery and calculate the insulation resistance of a system in which the battery is located. The ground fault detection device includes: a detection capacitor configured to function as a flying capacitor; a switch group for switching between a first charging path, a second charging path, a third charging path, and a measurement path, wherein the first charging path connects the battery to the detection capacitor, the second charging path connects the battery, a negative-side insulation resistance (which is the insulation resistance from the negative side line of the battery to ground), the third charging path connects the battery, a positive-side insulation resistance (which is the insulation resistance from the positive side line of the battery to ground), and the measurement path for measuring the charging voltage of the detection capacitor; and a controller configured to control the switch group and calculate the insulation resistance based on a measured charging voltage of the detection capacitor present after charging in each charging path, wherein after measuring the charging voltage of the second charging path, the controller is configured to temporarily switch the switch group to the third charging path before switching to the first charging path.

[0018] In one or more embodiments, after measuring the charging voltage of the third charging path, the controller is also configured to temporarily switch the switch group to the second charging path before switching to the first charging path.

[0019] To achieve the above objectives, a ground fault detection device according to a second aspect of the present invention is configured to connect to an ungrounded battery and calculate the insulation resistance of a system in which the battery is located. The ground fault detection device includes: a detection capacitor configured to function as a flying capacitor; a switch group for switching between a first charging path, a second charging path, a third charging path, and a measurement path, wherein the first charging path connects the battery to the detection capacitor, the second charging path connects the battery, a negative-side insulation resistance (which is the insulation resistance from the negative side line of the battery to ground), the third charging path connects the battery, a positive-side insulation resistance (which is the insulation resistance from the positive side line of the battery to ground), and the measurement path for measuring the charging voltage of the detection capacitor; and a controller configured to control the switch group and calculate the insulation resistance based on a measured charging voltage of the detection capacitor present after charging in each charging path, wherein after measuring the charging voltage of the third charging path, the controller is configured to temporarily switch the switch group to the second charging path before switching to the first charging path. Attached Figure Description

[0020] Figure 1 This is a block diagram illustrating the configuration of a ground fault detection device according to an embodiment of the present invention;

[0021] Figure 2A It is a diagram used to illustrate the V0 charging path and measurement path;

[0022] Figure 2B It is a diagram used to illustrate the V0 charging path and measurement path;

[0023] Figure 2C It is a diagram used to illustrate the V0 charging path and measurement path;

[0024] Figure 3A This is a diagram used to illustrate the Vc1n charging path and the Vc1p charging path;

[0025] Figure 3B This is a diagram used to illustrate the Vc1n charging path and the Vc1p charging path;

[0026] Figure 4 It is a timing diagram used to illustrate the charging state of a Y capacitor during a typical measurement cycle according to the prior art; and

[0027] Figure 5 This is a timing diagram used to illustrate the charging state of the Y capacitor during the measurement according to the embodiment.

[0028] Reference tag list

[0029] 100 Ground Fault Detection Device

[0030] 110 Control Device

[0031] 300 high-voltage battery

[0032] 301 Positive side power cable

[0033] 302 Negative side power cable

[0034] C1 Sensing capacitor

[0035] CYp Y capacitor

[0036] CYn Y capacitor

[0037] RLp positive side insulation resistance

[0038] RLn Negative side insulation resistance

[0039] S1-S4 and Sa switches Detailed Implementation

[0040] Embodiments of the present invention will be described in detail with reference to the accompanying drawings. Figure 1 A block diagram illustrating the configuration of a ground fault detection device 100 according to an embodiment of the present invention is shown. As shown in the figure, the ground fault detection device 100 is a device based on a flying capacitor, wherein the device is configured to be connected to a high-voltage battery 300 and to detect ground faults in a system in which the high-voltage battery 300 is arranged. Here, RLp and RLn should represent the insulation resistance between ground and the positive terminal side of the high-voltage battery 300 and the insulation resistance between ground and the negative terminal side of the high-voltage battery 300, respectively.

[0041] The high-voltage battery 300 is a battery used to drive the vehicle. The high-voltage battery 300 is formed of a rechargeable battery such as a lithium-ion battery and drives a load such as an electric motor (not shown), which is connected to the positive side power line 301 and / or the negative side power line 302.

[0042] Capacitors CYp and CYn, referred to as Y capacitors, are connected between the positive power line 301 and ground, and between the negative power line 302 and ground, respectively. Here, stray capacitance between ground and each of the power lines 301 and 302 should also be included in the Y capacitors CYp and CYn.

[0043] As shown in the figure, the ground fault detection device 100 includes a detection capacitor C1 and a control device 110, wherein the detection capacitor C1 operates as a flying capacitor. The ground fault detection device 100 also includes four switches S1 to S4 around the detection capacitor C1 for switching the charging path of the detection capacitor C1 and for forming a charging voltage measurement path. These switches can be formed by insulated switching elements, such as optical MOSFETs. Furthermore, the ground fault detection device 100 includes a switch Sa for sampling the voltage measured corresponding to the charging voltage of the detection capacitor C1.

[0044] The first terminal of switch S1 is connected to the positive power supply line 301, and the second terminal of switch S1 is connected to the anode side of diode D1. The cathode side of diode D1 is connected to the first terminal of resistor R1, and the second terminal of resistor R1 is connected to the first terminal of sensing capacitor C1. The first terminal of switch S2 is connected to the negative power supply line 302, and the second terminal of switch S2 is connected to the first terminal of resistor R2. The second terminal of resistor R2 is connected to the second terminal of sensing capacitor C1.

[0045] The first terminal of switch S3 is connected to the first terminal of resistor R5 and the anode side of diode D3, and the second terminal of switch S3 is connected to the first terminal of resistor R3 and the first terminal of switch Sa. The second terminal of switch Sa is connected to the analog input terminal of control device 110 and the first terminal of capacitor C2, wherein capacitor C2 has a second ground terminal. The cathode side of diode D3 is connected to the first terminal of sensing capacitor C1, and the second terminal of resistor R5 is connected to the cathode side of diode D2. The anode side of diode D2 is connected to the first terminal of sensing capacitor C1. Resistor R3 has a second ground terminal. The first terminal of switch S4 is connected to the second terminal of sensing capacitor C1, and the second terminal of switch S4 is connected to the first terminal of resistor R4. Resistor R4 has a second ground terminal.

[0046] The control device 110 is formed, for example, by a microcomputer, and performs various controls required by the ground fault detection device 100 by executing programs pre-built into the control device 110. Specifically, the control device 110 switches the charging path by individually controlling switches S1 to S4 and switch Sa, and controls the measurement and discharge of the charging voltage of the detection capacitor C1.

[0047] Although the basic circuit configuration widely used in ground fault detection devices based on flying capacitors has been described above, various exemplary modifications of ground fault detection devices based on flying capacitors exist, and the configuration of ground fault detection device 100 is not limited to the example in this figure.

[0048] To determine the insulation resistances RLp and RLn, the ground fault detection device 100 repeats the measurement operation in the same manner as in the prior art, wherein one cycle of the measurement operation is defined as the sequence of V0 measurement cycle → Vc1n measurement cycle → V0 measurement cycle → Vc1p measurement cycle. However, in this embodiment, immediately after the Vc1n and Vc1p measurement cycles, which cause a loss of the state-of-charge balance of the Y capacitors CYp and CYn, the charge in these Y capacitors is forcibly discharged so that the Y capacitors quickly approach the equilibrium state. This operation will be described below.

[0049] In all V0, Vc1n, and Vc1p measurement cycles, the detection capacitor C1 is charged through its respective charging path before the measurement of its charging voltage. Subsequently, the detection capacitor C1 is discharged for the next measurement.

[0050] During the V0 measurement cycle, the voltage corresponding to the voltage of the high-voltage battery 300 is measured. For this purpose, switches S1 and S2 are closed and switches S3 and S4 are open to charge the sensing capacitor C1. This means that the high-voltage battery 300, resistor R1, sensing capacitor C1, and resistor R2 form a charging path, as follows: Figure 2A As shown. The charging path that connects the high-voltage battery 300 to the detection capacitor C1 should be referred to as the V0 charging path or the first charging path.

[0051] To measure the charging voltage of capacitor C1, switches S1 and S2 are open, switches S3 and S4 are closed, and switch Sa is closed. Figure 2B As shown, the control device 110 performs sampling. Then, as... Figure 2C As shown, by disconnecting switch Sa, the detection capacitor C1 is discharged to proceed with the next measurement. The measurement of the charging voltage of the detection capacitor C1 and the discharge of the detection capacitor C1 are performed in the same manner during the remaining measurement cycles.

[0052] The path formed by disconnecting switches S1 and S2 and connecting switches S3 and S4 should be called the measurement path. That is, the charging voltage measurement and discharging of the detection capacitor C1 are performed in the measurement path.

[0053] During the Vc1n measurement cycle, the voltage reflecting the effect of the insulation resistance RLn is measured. For this purpose, switches S1 and S4 are closed and switches S2 and S3 are open to charge the sensing capacitor C1. This means that the high-voltage battery 300, resistor R1, sensing capacitor C1, resistor R4, and insulation resistance RLn form a charging path, as shown below. Figure 3AAs shown in the diagram, the charging path connecting the high-voltage battery 300, the insulation resistor RLn, and the detection capacitor C1 should be referred to as the Vc1n charging path or the second charging path.

[0054] During the Vc1p measurement cycle, the voltage reflecting the effect of the insulation resistance RLp is measured. For this purpose, switches S2 and S3 are closed and switches S1 and S4 are open to charge the sensing capacitor C1. That is, as... Figure 3B As shown, the high-voltage battery 300, insulation resistor RLp, ground, resistor R3, resistor R1, and detection capacitor C1 form the charging path. This charging path connecting the high-voltage battery 300, insulation resistor RLp, and detection capacitor C1 should be referred to as the Vc1p charging path or the third charging path.

[0055] Based on the voltages V0, Vc1n, and Vc1p obtained during these measurement cycles, the control device 110 calculates the insulation resistance. If the calculated value is equal to or lower than a predetermined reference level, a ground fault is determined to have occurred, and an alarm is output.

[0056] The following operation will be described: where the charge in the Y capacitors CYp and CYn, which are in an unbalanced state due to the formation of the Vc1n charging path / Vc1p charging path, is forcibly discharged so that the Y capacitors quickly approach the equilibrium state.

[0057] First, refer to Figure 4 The timing diagrams in the figure depict the charging states of the Y capacitors CYp and CYn during a typical measurement cycle as a reference example for comparison with embodiments of the present invention.

[0058] As described above, the ground fault detection process involves repeated measurement operations, which follow a cycle defined as V0 measurement cycle → Vc1n measurement cycle → V0 measurement cycle → Vc1p measurement cycle. Initially, the Y capacitors CYp and CYn should be in a balanced state.

[0059] At point t1, switches S1 and S2 are turned on, and switches S3 and S4 are turned off to form a charging path for V0. In this way, the detection capacitor C1 is charged to V0.

[0060] At time t2 after a predetermined time, switches S1 and S2 are opened, switches S3 and S4 are closed, and switch Sa is closed to form a measurement path, and then V0 is measured. Once V0 has been measured, switch Sa is opened. The sensing capacitor C1 discharges through resistors R3 and R4.

[0061] At point t3, switches S1 and S4 are turned on, and switches S2 and S3 are turned off to form a charging path for Vc1n. In this way, the detection capacitor C1 is charged to Vc1n. In the Vc1n charging path, the insulation resistance RLn forms part of the charging path, which disrupts the balance between the Y capacitors CYp (dashed line) and CYn (solid line), thus amplifying the degree of imbalance.

[0062] At time t4 after a predetermined time, switches S1 and S2 are opened, switches S3 and S4 are closed, and switch Sa is closed to form a measurement path, and then Vc1n is measured. Once Vc1n has been measured, switch Sa is opened. The sensing capacitor C1 discharges through resistors R3 and R4. The Y capacitors CYp and CYn slowly transition to an equilibrium state according to their capacitance and the time constants of their positive and negative insulation resistances.

[0063] At t5, switches S1 and S2 are turned on, and switches S3 and S4 are turned off to form a V0 charging path. In this way, the sensing capacitor C1 is charged to V0. However, the Y capacitors CYp and CYn do not return from an unbalanced state to a balanced state, which affects the charging voltage of the sensing capacitor C1. Therefore, if the insulation resistance is calculated using the V0 measurement obtained at t6 after a predetermined time, the calculation accuracy is reduced. This also applies to the V0 measurement in the next cycle after the Vc1p charging path is formed at t7.

[0064] Next, we will refer to Figure 5 The timing diagram described in the figure illustrates the charging states of the Y capacitors CYp and CYn during the measurement cycle performed by the ground fault detection device 100 of the above embodiment as a reference example for comparison with embodiments of the present invention. Essentially, the ground fault detection process according to this embodiment also repeats the measurement operation, which has a cycle defined as the order of V0 measurement cycle → Vc1n measurement cycle → V0 measurement cycle → Vc1p measurement cycle. Initially, the Y capacitors CYp and CYn should be in a balanced state. Furthermore, the following processing is performed under the control of the control device 110.

[0065] At point t1, switches S1 and S2 are turned on, and switches S3 and S4 are turned off to form a charging path for V0. In this way, the detection capacitor C1 is charged to V0.

[0066] At time t2 after a predetermined time, switches S1 and S2 are opened, switches S3 and S4 are closed, and switch Sa is closed to form a measurement path, and then V0 is measured. Once V0 has been measured, switch Sa is opened. The sensing capacitor C1 discharges through resistors R3 and R4.

[0067] At point t3, switches S1 and S4 are turned on, and switches S2 and S3 are turned off to form a charging path for Vc1n. In this way, the detection capacitor C1 is charged to Vc1n. In the Vc1n charging path, the insulation resistance RLn forms part of the charging path, which disrupts the balance between the Y capacitors CYp (dashed line) and CYn (solid line), thus increasing the degree of imbalance.

[0068] At time t4 after a predetermined time, switches S1 and S2 are opened, switches S3 and S4 are closed, and switch Sa is closed to form a measurement path, and then Vc1n is measured. Once Vc1n has been measured, switch Sa is opened. Capacitor C1 is then detected to discharge.

[0069] Immediately following this, at t5 before switching to the V0 charging path, a temporary switch to the Vc1p charging path is performed. This means that switches S1 and S4 are open and switches S2 and S3 are closed. In this way, the detection capacitor C1 is charged toward Vc1p. Moreover, since the Y capacitors CYp and CYn are forced to discharge in the opposite direction to the Vc1n charging path, the Y capacitors quickly transition to an equilibrium state.

[0070] At the next time t6, switches S1 and S2 are opened, and switches S3 and S4 are closed to switch back to the measurement path so that the detection capacitor C1 can be discharged. Y capacitors CYp and CYn transition towards an equilibrium state according to their capacitance and the time constants of their positive and negative insulation resistances. However, due to the forced charging and discharging in opposite directions, Y capacitors CYp and CYn are already sufficiently close to equilibrium.

[0071] At t7, switches S1 and S2 are turned on, and switches S3 and S4 are turned off to form a charging path for V0. In this way, the sensing capacitor C1 is charged to V0. Since the Y capacitors CYp and CYn have almost returned to their equilibrium state, they do not affect the charging voltage of the sensing capacitor C1.

[0072] After measuring V0 at t8, switches S2 and S3 are turned on at t9, and switches S1 and S4 are turned off to switch to the Vc1p charging path. Thereafter, Y capacitors CYp and CYn are forced to charge / discharge in opposite directions in a similar manner to those described above.

[0073] This means that at time t10, a switch to the measurement path is performed and Vc1p is measured. Immediately after this, before switching to the V0 charging path, a temporary switch to the Vc1n charging path is performed at time t11. This means that switches S1 and S4 are turned on and switches S2 and S3 are turned off. Since the Y capacitors CYp and CYn are forced to discharge in the opposite direction to the Vc1n charging path as described above, the Y capacitors quickly transition to an equilibrium state. At the next time t12, switches S1 and S2 are turned off, and switches S3 and S4 are turned on to switch back to the measurement path so that the detection capacitor C1 can discharge. During the V0 charging path in the next cycle, since the Y capacitors CYp and CYn have almost returned to an equilibrium state, the Y capacitors CYp and CYn do not affect the charging voltage of the detection capacitor C1.

[0074] As described above, according to the ground fault detection device 100 of this embodiment, even when the Y capacitor enters an unbalanced state due to the influence of the charging path, the Y capacitor is forced to charge / discharge in the opposite direction immediately after the charging voltage is measured, thus quickly returning to a balanced state. In this way, the detection accuracy of insulation resistance can be prevented from decreasing due to the influence of the Y capacitor without increasing the detection time. In addition, since the Y capacitor is charged / discharged by temporarily switching the charging path without increasing costs, software-based control is sufficient to cause the Y capacitor to charge / discharge in the opposite direction without the need for dedicated equipment, such as a balance state forming circuit.

[0075] Although this embodiment has been described with reference to an example of a repetitive measurement operation having a cycle defined as the sequence V0 measurement cycle → Vc1n measurement cycle → V0 measurement cycle → Vc1p measurement cycle, it should be noted that the invention can also be applied to measurements having a cycle defined as the sequence V0 measurement cycle → Vc1n measurement cycle → Vc1p measurement cycle or the sequence V0 measurement cycle → Vc1p measurement cycle → V0 measurement period → Vc1n measurement cycle. In any case, after the charging state of the Y capacitor reaches an imbalance in the Vc1n charging path / Vc1p charging path, it is sufficient to force the Y capacitor to charge / discharge in the opposite direction before switching to the V0 charging path.

Claims

1. A ground fault detection device, the ground fault detection device being configured to connect to an ungrounded battery and to calculate the insulation resistance of a system in which the battery is located, the ground fault detection device comprising: A detection capacitor, configured to function as a flying capacitor; A switch group is used to switch between the following paths: A first charging path connects the battery to the detection capacitor; The second charging path connects the battery, the negative side insulation resistor, and the detection capacitor. The negative side insulation resistor is the insulation resistance from the negative side line of the battery to ground. A third charging path is provided, which connects the battery, the positive side insulation resistor, and the detection capacitor. The positive side insulation resistor is the insulation resistance from the positive side line of the battery to the ground. and A measurement path for measuring the charging voltage of the detection capacitor; as well as A controller configured to control the switch group and calculate the insulation resistance based on a measured charging voltage of the detection capacitor present after charging in each of the charging paths; Wherein, after measuring the charging voltage of the second charging path, the controller is configured to temporarily switch the switch group to the third charging path before switching to the first charging path, and not to measure the charging voltage of the detection capacitor when temporarily switching to the third charging path.

2. The grounding fault detection device according to claim 1, in, After measuring the charging voltage of the third charging path, the controller is also configured to temporarily switch the switch group to the second charging path before switching to the first charging path.

3. A ground fault detection device, the ground fault detection device being configured to connect to an ungrounded battery and to calculate the insulation resistance of a system in which the battery is located, the ground fault detection device comprising: A detection capacitor, configured to function as a flying capacitor; A switch group is used to switch between the following paths: A first charging path connects the battery to the detection capacitor; The second charging path connects the battery, the negative side insulation resistor, and the detection capacitor. The negative side insulation resistor is the insulation resistance from the negative side line of the battery to ground. A third charging path is provided, which connects the battery, the positive side insulation resistor, and the detection capacitor. The positive side insulation resistor is the insulation resistance from the positive side line of the battery to the ground. and A measurement path for measuring the charging voltage of the detection capacitor; as well as A controller configured to control the switch group and calculate the insulation resistance based on a measured charging voltage of the detection capacitor present after charging in each of the charging paths; Wherein, after measuring the charging voltage of the third charging path, the controller is configured to temporarily switch the switch group to the second charging path before switching to the first charging path, and not to measure the charging voltage of the detection capacitor when temporarily switching to the second charging path.

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