JP2020106517A - Electric leak detection circuit - Google Patents

Abstract

To limit a reduction in measurement accuracy of a capacitance value of a flowing capacitance connected in parallel to an insulation resistance in an electric leak detection circuit for detecting a drop in a resistance value of an insulation resistance between a ground line of a direct current power source installed on a vehicle and a vehicle body earth.SOLUTION: An electric leak detection circuit 1 comprises a floating capacitance measurement circuit 4 for acquiring without decay a voltage applied to a detection resistance Rd when a floating capacitance measurement oscillation signal Sc is output from an oscillation circuit 2, and a detection part 6 for measuring a capacitance value of a floating capacitance connected in parallel to an insulation resistance Rd based on a wave height value of the voltage V2 acquired by the floating capacitance measurement circuit 4 when the floating capacitance measurement oscillation signal Sc is output from the oscillation circuit 2.SELECTED DRAWING: Figure 1

Description

The present invention relates to a leakage detection circuit.

As an earth leakage detection circuit, an oscillation circuit that outputs an oscillation signal for earth leakage detection between the detection resistance connected to the ground line of the DC power supply mounted on the vehicle through a coupling capacitor and the ground line and the vehicle body ground. And an insulation resistance measurement circuit that acquires the voltage applied to the detection resistance via a low-pass filter, and the resistance value of the insulation resistance decreases when the peak value of the voltage acquired by the insulation resistance measurement circuit is less than or equal to the threshold value. That is, some of them include a detection unit that detects that an electric leakage has occurred.

By the way, when the capacitance value of the stray capacitance connected in parallel with the insulation resistance increases, the peak value of the voltage applied to the detection resistance decreases.

Therefore, the leakage detection circuit may erroneously detect that the resistance value of the insulation resistance has decreased, although the resistance value of the insulation resistance has not actually decreased.

Therefore, as another leakage detection circuit, the peak value of the voltage acquired by the insulation resistance measurement circuit is used when the floating capacitance measurement oscillation signal having a frequency higher than that of the leakage detection oscillation signal is output from the oscillation circuit. There is a method in which the capacitance value of stray capacitance is measured and the threshold value is lowered as the measured capacitance value of stray capacitance increases.

As a related technique, there is Patent Document 1, for example.

JP, 2014-155329, A

However, in other leakage detection circuits described above, the peak value of the voltage applied to the detection resistor is attenuated by the low-pass filter when the oscillation signal for measuring stray capacitance is being output from the oscillation circuit. The peak value of the generated voltage tends to fluctuate due to the influence of noise, and the measurement accuracy of the stray capacitance may decrease.

An object according to one aspect of the present invention is that in a leakage detection circuit that detects a decrease in resistance value of an insulation resistance between a ground line of a DC power supply mounted on a vehicle and a body ground of the vehicle, the circuit is connected in parallel to the insulation resistance. It is to suppress the deterioration of the measurement accuracy of the capacitance value of the stray capacitance.

A leakage detection circuit, which is one form according to the present invention, is a leakage detection circuit that detects a decrease in resistance value of an insulation resistance between a ground line of a DC power supply mounted on a vehicle and a body ground of the vehicle, Connected between the oscillator circuit that outputs the leakage detection oscillation signal or the oscillation signal for measuring stray capacitance of a frequency higher than that of the leakage detection oscillation signal, and the coupling capacitor connected to the ground line. Detection resistance, an insulation resistance measurement circuit that acquires the voltage applied to the detection resistance without attenuating when the leakage detection oscillation signal is output from the oscillation circuit, and an oscillation signal for floating capacitance measurement is output from the oscillation circuit. The stray capacitance measurement circuit that acquires the voltage applied to the detection resistor without attenuating it, and the peak value of the voltage that is acquired by the insulation resistance measurement circuit when the leakage detection oscillation signal is output from the oscillation circuit. When it is less than the threshold value, it detects that the resistance value of the insulation resistance has dropped, and the peak value of the voltage acquired by the stray capacitance measurement circuit when the oscillation signal for stray capacitance measurement is output from the oscillation circuit. And a detection unit for measuring the capacitance value of the stray capacitance connected in parallel with the insulation resistance.

The insulation resistance measuring circuit acquires the voltage applied to the detection resistor through the first low-pass filter having a cutoff frequency higher than the frequency of the leakage detection oscillation signal, and the stray capacitance measuring circuit determines the stray capacitance measuring oscillation. A voltage applied to the detection resistor is acquired via a second low-pass filter having a cutoff frequency higher than the frequency of the signal and higher than the cutoff frequency of the first lowpass filter.

In this way, since the cutoff frequency of the second low-pass filter is higher than the frequency of the stray capacitance measuring oscillation signal, the peak value of the voltage applied to the detection resistor when the stray capacitance measuring oscillation signal is output from the oscillation circuit. Can be prevented from being attenuated by the second low pass filter. As a result, changes in the peak value of the voltage acquired by the detector while the oscillation signal for measuring stray capacitance is being output from the oscillation circuit are more likely to appear without being damped, which reduces the accuracy of the stray capacitance measurement. Can be suppressed.

Further, the leakage detection circuit may be configured to include capacitors provided between the coupling capacitor and the first low-pass filter and between the coupling capacitor and the second low-pass filter, respectively.

As a result, from the inside of the first low-pass filter to the outside of the first low-pass filter, from the inside of the second low-pass filter to the outside of the second low-pass filter, and from the ground line to the first low-pass filter or the second low-pass filter. Since it is possible to prevent the direct current from flowing into the low-pass filter of, the direct current flows into the insulation resistance, the resistance of the first low-pass filter, the resistance of the second low-pass filter, etc. to cause a voltage drop. It is possible to prevent the voltage output from the insulation resistance measuring circuit or the stray capacitance measuring circuit from fluctuating, and it is possible to suppress deterioration of the leakage detection accuracy.

In addition, the detection unit waits until the DC power supply and the load are disconnected by turning on and off the switch connected between the DC power supply and the load after the current flowing in the DC power supply becomes less than or equal to the current threshold value. You may comprise so that the capacitance value of a stray capacitance may be measured between them.

In addition, the detection unit operates from when the switch connected between the DC power supply and the load is turned on to when the DC power supply is electrically connected to the load until the current flowing through the DC power supply becomes greater than the current threshold value. In, the capacitance value of the stray capacitance may be measured.

In this way, since the capacitance value of the stray capacitance is measured when the current flowing in the DC power supply is less than or equal to the current threshold, the traveling motor is stopped when the current flowing in the DC power supply is less than or equal to the current threshold. When the traveling motor is driven, noise generated from the inverter circuit or the like when the traveling motor is driven can be prevented from being included in the voltage output from the stray capacitance measuring circuit. Further, since the capacitance value of the stray capacitance is measured when the switch is turned on, the capacitance value of the stray capacitance can be measured with the same circuit configuration as that at the time of detecting the leakage. As a result, the correspondence relationship between the peak value of the voltage and the capacitance value of the stray capacitance acquired during the measurement of the stray capacitance is different from the correspondence relationship between the peak value of the voltage and the capacitance value of the stray capacitance stored in the storage unit in advance. Since this can be suppressed, the capacitance value of the stray capacitance can be accurately obtained.

An earth leakage detection circuit according to another aspect of the present invention has a first frequency for detecting a decrease in a resistance value of an insulation resistance between a ground line of a DC power supply mounted on a vehicle and a body ground of the vehicle. An oscillation circuit for superimposing and outputting the leakage detection oscillation signal and an oscillation signal for measuring stray capacitance having a second frequency higher than the first frequency, and a coupling capacitor connected to the oscillation circuit and the ground line. A detection resistor connected between the detection resistor and the oscillation circuit for detecting the leakage current and the oscillation signal for measuring the stray capacitance from the oscillation circuit, the voltage signal of the second frequency applied to the detection resistor. An insulation resistance measuring circuit that obtains the voltage signal of the first frequency while removing it, and the detection resistance when the leakage detecting oscillation signal and the floating capacitance measuring oscillation signal are output from the oscillation circuit. A stray capacitance measuring circuit that obtains the voltage signal of the second frequency while removing the voltage signal of the first frequency, and a parallel circuit to the insulation resistance based on the peak value of the voltage obtained by the stray capacitance measuring circuit. A detector that measures the capacitance value of the connected stray capacitance and that detects a decrease in the resistance value of the insulation resistance based on a comparison between the peak value of the voltage acquired by the insulation resistance measurement circuit and a threshold value is provided. ..

According to this configuration, the detection unit can measure the stray capacitance and determine the leakage at substantially the same time. Therefore, the time required for the leakage determination is shortened.

A leakage detection circuit according to still another aspect of the present invention includes a first switch that switches between a state in which the insulation resistance and the detection resistance are connected and a state in which the insulation resistance and the detection resistance are cut off, A simulated resistance having a known resistance value and a simulated capacitance having a known capacitance value, which are provided between the detection resistor and the body ground and are connected in parallel with each other, the simulated resistance and the simulated capacitance, and the detection. It further comprises a second switch for switching between a state in which a resistor is connected and a state in which the simulated resistor and the simulated capacitor and the detection resistor are cut off. Then, the detection unit obtains the leakage detection oscillation obtained by the insulation resistance measurement circuit when the first switch is controlled to be in an off state and the second switch is controlled to be in an on state. A first correction value is calculated based on a crest value of a voltage corresponding to a signal and a resistance value of the simulated resistor, the first switch is controlled to an on state, and the second switch is turned to an off state. When controlled, the peak value of the voltage corresponding to the leakage detection oscillation signal acquired by the insulation resistance measuring circuit may be corrected using the first correction value. Further, the detection unit is for measuring the stray capacitance, which is obtained by the stray capacitance measuring circuit when the first switch is controlled to be in an off state and the second switch is controlled to be in an on state. A second correction value is calculated based on the peak value of the voltage corresponding to the oscillation signal and the capacitance value of the simulated capacitance, the first switch is controlled to be in the ON state, and the second switch is in the OFF state. When controlled to, the peak value of the voltage corresponding to the stray capacitance measuring oscillation signal acquired by the stray capacitance measuring circuit may be corrected using the second correction value.

With this configuration, it is possible to correct an error that occurs in the insulation resistance measuring circuit and/or the stray capacitance measuring circuit. Therefore, the detection error of the resistance value of the insulation resistance and/or the capacitance value of the stray capacitance is reduced, and the accuracy of leakage detection is improved.

According to the present invention, in a leakage detection circuit that detects a decrease in resistance value of an insulation resistance between a ground line of a DC power supply mounted on a vehicle and a body ground of the vehicle, a stray capacitance connected in parallel to the insulation resistance It is possible to suppress a decrease in the measurement accuracy of the capacitance value.

It is a figure which shows an example of the earth leakage detection circuit of embodiment. It is a figure which shows an example of the frequency characteristic of a low-pass filter. It is a figure which shows an example of an insulation resistance measuring circuit and a floating capacitance measuring circuit. It is a flow chart which shows an example of operation of a primary detecting element. It is a figure which shows an example of the earth leakage detection circuit concerning other embodiment of this invention. It is a figure which shows an example of the earth leakage detection circuit concerning other embodiment of this invention.

Embodiments will be described below in detail with reference to the drawings.
FIG. 1 is a diagram illustrating an example of a leakage detection circuit according to the embodiment.

The DC power supply P is a high-voltage battery composed of a plurality of batteries (for example, a lithium-ion battery or a nickel-hydrogen battery) connected in series, and is installed in a vehicle such as a hybrid vehicle or an electric vehicle and has a running motor. Electric power is supplied to a load Lo such as an inverter circuit to be driven or a monitoring circuit to monitor the state of the DC power supply P.

The leakage detection circuit 1 detects a decrease in the resistance value of the insulation resistance Ri between the ground line GL of the DC power source P and the body ground BE of the vehicle, and includes the oscillation circuit 2, the detection resistance Rd, and the insulation resistance Rd. A resistance measuring circuit 3, a stray capacitance measuring circuit 4, a storage unit 5, and a detection unit 6 are provided.

The oscillation circuit 2 is connected to the body ground BE and outputs an oscillation signal S such as a rectangular wave between the ground line GL and the body ground BE. The oscillation signal S is the leakage detection oscillation signal Sd or the stray capacitance measurement oscillation signal Sc. As an example, the oscillation circuit 2 can select and output the leakage detection oscillation signal Sd or the stray capacitance measurement oscillation signal Sc in accordance with an instruction given from the detection unit 6. It is assumed that the frequency f2 of the floating capacitance measuring oscillation signal Sc is higher than the frequency f1 of the leakage detecting oscillation signal Sd.

The detection resistor Rd is connected between the coupling capacitor Cc connected to the ground line GL and the oscillation circuit 2.

The insulation resistance measuring circuit 3 includes a first low-pass filter LPF1 and is connected between the detection capacitor Rc and the coupling capacitor Cc side of the detection resistor Rd. Further, the insulation resistance measurement circuit 3 acquires the voltage Vd applied to the detection resistance Rd via the first low-pass filter LPF1 and outputs the acquired voltage Vd to the detection unit 6 as the voltage V1. The first low pass filter LPF1 attenuates the high frequency component (the voltage Vd having a frequency higher than the cutoff frequency fc1 of the first low pass filter LPF1) included in the voltage Vd.

The stray capacitance measuring circuit 4 includes a second low-pass filter LPF2 and is connected between the detection capacitor Rc and the coupling capacitor Cc side of the detection resistor Rd. Further, the stray capacitance measuring circuit 4 acquires the voltage Vd applied to the detection resistor Rd via the second low-pass filter LPF2, and outputs the acquired voltage Vd to the detection unit 6 as the voltage V2. The second low pass filter LPF2 attenuates the high frequency component (the voltage Vd having a frequency higher than the cutoff frequency fc2 of the second low pass filter LPF2) included in the voltage Vd.

The storage unit 5 includes, for example, a RAM (Random Access Memory) or a ROM (Read Only Memory), and has a peak value of the voltage V2 and a capacitance value of the stray capacitance Cf virtually connected in parallel to the insulation resistance Ri. It stores the correspondence relationship of the.

The detection unit 6 includes, for example, a CPU (Central Processing Unit), a multi-core CPU, or a programmable device (FPGA (Field Programmable Gate Array) or PLD (Programmable Logic Device)).

Further, when the detection unit 6 outputs the leakage detection oscillation signal Sd from the oscillation circuit 2, if the peak value of the voltage V1 output from the insulation resistance measurement circuit 3 is equal to or less than the threshold value Vth, the detection unit 6 detects the insulation resistance Ri. It is detected that the resistance value is decreasing, that is, the occurrence of electric leakage. Note that the threshold value Vth is obtained by experiments, simulations, or the like and is stored in the storage unit 5, and is, for example, the peak value of the voltage V1 immediately before the electric leakage occurs.

Further, when the detection unit 6 is outputting the stray capacitance measurement oscillation signal Sc from the oscillation circuit 2, the correspondence between the peak value of the voltage V2 and the capacitance value of the stray capacitance Cf stored in the storage unit 5 in advance. With reference to the relationship, the capacitance value of the stray capacitance Cf corresponding to the peak value of the voltage V2 output from the stray capacitance measuring circuit 4 is set as the current capacitance value of the stray capacitance Cf. That is, the detection unit 6 estimates the current capacitance value of the stray capacitance Cf based on the peak value of the voltage V2 obtained when the oscillation circuit 2 outputs the stray capacitance measurement oscillation signal Sc.

Further, the detection unit 6 corrects the threshold value Vth according to the estimated capacitance value of the stray capacitance Cf. Here, when the capacitance value of the stray capacitance Cf increases, the impedance between the ground line GL and the vehicle body earth BE decreases. Therefore, the detection unit 6 corrects the threshold value Vth so that the threshold value Vth decreases as the capacitance value of the stray capacitance Cf increases. As an example, the detection unit 6 may correct the threshold value Vth so as to be inversely proportional to the capacitance value of the stray capacitance Cf. As a result, the threshold value Vth can be lowered in accordance with the drop of the peak value of the voltage V1 accompanying the increase of the capacitance value of the stray capacitance Cf. Therefore, although the peak value of the voltage V1 is lower than that of the insulation resistance Ri due to the increase of the capacitance value of the stray capacitance Cf, it is erroneous that the insulation resistance Ri is small. It is possible to suppress the detection. That is, erroneous detection of electric leakage due to variation in the capacitance value of the stray capacitance Cf is suppressed.

FIG. 2A is a diagram showing a frequency characteristic (solid line) of the low-pass filter LPF including the insulation resistance Ri, the stray capacitance Cf, the coupling capacitor Cc, and the detection resistance Rd. The horizontal axis of the two-dimensional orthogonal coordinates shown in FIG. 2A represents the frequency [Hz] of the oscillation signal S, and the vertical axis represents the gain [dB] of the low-pass filter LPF. The broken line shown in FIG. 2A shows the frequency characteristic of the low-pass filter LPF after the capacitance value of the stray capacitance Cf has increased.

As shown in FIG. 2A, the cutoff frequency fc of the low-pass filter LPF is higher than the frequency f1 of the leakage detection oscillation signal Sd and lower than the frequency f2 of the stray capacitance measurement oscillation signal Sc.

FIG. 2B is a diagram showing the frequency characteristic of the first low pass filter LPF1 (dashed line) and the frequency characteristic of the second low pass filter LPF2 (dashed line). The horizontal axis of the two-dimensional orthogonal coordinates shown in FIG. 2B represents the frequency [Hz] of the oscillation signal S, and the vertical axis represents the gain [dB] of the first low-pass filter LPF1 or the second low-pass filter LPF2. Show. The cutoff frequency fc2 of the second lowpass filter LPF2 is set to be higher than the cutoff frequency fc1 of the first lowpass filter LPF1.

As shown in FIG. 2B, the cutoff frequency fc1 of the first low-pass filter LPF1 is higher than the frequency f1 of the leakage detection oscillation signal Sd, and the cut-off frequency fc2 of the second low-pass filter LPF2 is It is assumed that the frequency is higher than the frequency f2 of the floating capacitance measuring oscillation signal Sc. The cutoff frequency fc1 of the first low pass filter LPF1 is lower than the frequency f2 of the stray capacitance measurement oscillation signal Sc.

As shown in FIG. 2A, since the cutoff frequency fc of the low pass filter LPF is higher than the frequency f1 of the leakage detection oscillation signal Sd, the leakage detection oscillation signal Sd is not attenuated by the low pass filter LPF. Therefore, when the leakage detection oscillation signal Sd is output from the oscillation circuit 2 and the resistance value of the insulation resistance Ri is not lowered, the peak value of the voltage Vd applied to the detection resistor Rd is the leakage detection voltage. It becomes the same or substantially the same as the peak value of the oscillation signal Sd. Further, as shown in FIG. 2B, since the cutoff frequency fc1 of the first low-pass filter LPF1 is higher than the frequency f1 of the leakage detection oscillation signal Sd, the oscillation circuit 2 outputs the leakage detection oscillation signal Sd. During this time, the peak value of the voltage Vd applied to the detection resistor Rd is not attenuated by the first low pass filter LPF1. Therefore, the peak value of the voltage V1 output from the insulation resistance measuring circuit 3 is the same or substantially the same as the peak value of the voltage Vd applied to the detection resistor Rd. Further, as the resistance value of the insulation resistance Ri decreases, the peak value of the voltage Vd applied to the detection resistance Rd decreases. That is, as the resistance value of the insulation resistance Ri decreases, the crest value of the voltage V1 decreases. As a result, when the detecting unit 6 outputs the leakage detection oscillation signal Sd from the oscillation circuit 2, if the peak value of the voltage V1 is equal to or less than the threshold value Vth, the resistance value of the insulation resistance Ri is lowered. That is, it is possible to detect that the leakage has occurred.

Further, as shown in FIG. 2A, since the frequency f2 of the stray capacitance measuring oscillation signal Sc is higher than the cutoff frequency fc of the low pass filter LPF, the stray capacitance measuring oscillation signal Sc is attenuated by the low pass filter LPF. .. Therefore, as the capacitance value of the stray capacitance Cf increases and the cutoff frequency fc of the low-pass filter LPF decreases, the gain of the low-pass filter LPF corresponding to the frequency f2 of the stray capacitance measurement oscillation signal Sc decreases and the stray capacitance measurement The oscillation signal Sc is further attenuated. That is, as the capacitance value of the stray capacitance Cf increases, the peak value of the voltage Vd applied to the detection resistor Rd when the stray capacitance measurement oscillation signal Sc is output from the oscillation circuit 2 decreases. Further, as shown in FIG. 2B, since the cutoff frequency fc2 of the second low pass filter LPF2 is higher than the frequency f2 of the stray capacitance measuring oscillation signal Sc, the oscillation circuit 2 outputs the stray capacitance measuring oscillation signal Sc. The peak value of the voltage Vd applied to the detection resistor Rd when being output is not attenuated by the second low pass filter LPF2. Therefore, the peak value of the voltage V2 output from the stray capacitance measuring circuit 4 becomes the same or substantially the same as the peak value of the voltage Vd applied to the detection resistor Rd. That is, as the capacitance value of the stray capacitance Cf increases, the peak value of the voltage V2 decreases. As a result, when the detection circuit 6 outputs the stray capacitance measuring oscillation signal Sc from the oscillation circuit 2, the peak value of the voltage V2 and the capacitance value of the stray capacitance Cf stored in the storage unit 5 in advance are stored. The capacitance value of the stray capacitance Cf corresponding to the peak value of the voltage V2 output from the stray capacitance measuring circuit 4 can be measured as the current capacitance value of the stray capacitance Cf by referring to the correspondence.

As described above, in the leakage detection circuit 1 of the embodiment, the cutoff frequency fc2 of the second low-pass filter LPF2 is higher than the frequency f2 of the stray capacitance measuring oscillation signal Sc, so that the stray capacitance measuring oscillation signal Sc is output from the oscillation circuit 2. It is possible to prevent the peak value of the voltage Vd applied to the detection resistor Rd from being attenuated by the second low-pass filter LPF2 when is output. As a result, the change in the peak value of the voltage V2 acquired by the detection unit 6 while the stray capacitance measuring oscillation signal Sc is being output from the oscillation circuit 2 is likely to occur without being attenuated, so that the capacitance value of the stray capacitance Cf is increased. It is possible to suppress a decrease in the measurement accuracy of.

The leakage detection circuit according to the embodiment of the present invention is not limited to the configuration shown in FIG. For example, the insulation resistance measurement circuit 3 may include a bandpass filter that passes the leakage detection oscillation signal Sd and blocks the stray capacitance measurement oscillation signal Sc instead of the first low-pass filter LPF1. In addition, the stray capacitance measuring circuit 4 may include a bandpass filter that passes the stray capacitance measuring oscillation signal Sc and blocks the leakage detection oscillation signal Sd, instead of the second low pass filter LPF2.

<Example of insulation resistance measuring circuit 3 and stray capacitance measuring circuit 4>
FIG. 3 is a diagram showing an example of the insulation resistance measuring circuit 3 and the stray capacitance measuring circuit 4.

The insulation resistance measuring circuit 3 shown in FIG. 3 includes a capacitor C1 in addition to the first low pass filter LPF1, and the stray capacitance measuring circuit 4 includes a capacitor C2 in addition to the second low pass filter LPF2.

The first low-pass filter LPF1 is a so-called second-order active low-pass filter, and includes a comparator Cmp1, resistors R1 to R5, capacitors C3 to C4, and diodes D1 to D2. The negative input terminal of the comparator Cmp1 is connected to one terminal of the resistor R1, the anode terminal of the diode D1, the cathode terminal of the diode D2, and one terminal of the capacitor C3. The plus input terminal of the comparator Cmp1 is connected to one terminal of the resistor R2. The output terminal of the comparator Cmp1 is connected to the other terminal of the capacitor C3, one terminal of the resistor R3, one terminal of the resistor R4, and one input terminal of the detection unit 6. The other terminal of the resistor R3 is connected to the other terminal of the resistor R1, one terminal of the resistor R5, and one terminal of the capacitor C4. The cathode terminal of the diode D1 is connected to the power supply, and the anode terminal of the diode D2, the other terminal of the resistor R2, the other terminal of the resistor R4, and the other terminal of the capacitor C4 are connected to the body ground BE, respectively. The other terminal of the resistor R5 is connected to one terminal of the capacitor C1, and the other terminal of the capacitor C1 is connected to a connection point between the coupling capacitor Cc and the detection resistor Rd. The first low-pass filter LPF1 does not attenuate the peak value of the voltage Vd applied to the detection resistor Rd when the oscillation detection oscillation signal Sd is being output from the oscillation circuit 2, and the oscillation detection oscillation from the oscillation circuit 2 is not performed. As long as the high frequency component of the voltage Vd applied to the detection resistor Rd when the signal Sd is output (noise generated from the inverter circuit or the like when the traveling motor is driven) is attenuated, FIG. The configuration is not limited to that shown.

The second low-pass filter LPF2 is a so-called first-order active low-pass filter, and includes a comparator Cmp2, resistors R6 to R9, a capacitor C5, and diodes D3 to D4. The negative input terminal of the comparator Cmp2 is connected to one terminal of the resistor R6, the anode terminal of the diode D3, the cathode terminal of the diode D4, one terminal of the resistor R7, and one terminal of the capacitor C5. The plus input terminal of the comparator Cmp2 is connected to one terminal of the resistor R8. The output terminal of the comparator Cmp2 is connected to the other terminal of the resistor R7, the other terminal of the capacitor C5, one terminal of the resistor R9, and the other input terminal of the detection unit 6. The cathode terminal of the diode D3 is connected to the power source, and the anode terminal of the diode D4, the other terminal of the resistor R8, and the other terminal of the resistor R9 are connected to the body ground BE. The other terminal of the resistor R6 is connected to one terminal of the capacitor C2, and the other terminal of the capacitor C2 is connected to the connection point between the coupling capacitor Cc and the detection resistor Rd. The second low-pass filter LPF2 does not attenuate the peak value of the voltage Vd applied to the detection resistor Rd when the oscillating circuit 2 outputs the stray capacitance measuring oscillation signal Sc, and measures the stray capacitance from the oscillating circuit 2. The configuration is not limited to that shown in FIG. 3 as long as it attenuates the high frequency component of the voltage Vd applied to the detection resistor Rd when the oscillation signal for use Sc is output.

The diodes D1 and D2 limit the voltage input to the negative input terminal of the comparator Cmp1 within the voltage range from the voltage of the body earth BE connected to the diode D2 to the voltage of the power supply connected to the diode D1.

The diodes D3 and D4 limit the voltage input to the negative input terminal of the comparator Cmp2 within the voltage range from the voltage of the body earth BE connected to the diode D4 to the voltage of the power supply connected to the diode D3.

The capacitor C1 prevents the direct current flowing from the body earth BE to the resistors R1 and R5 via the diode D2 from flowing to the outside of the first low pass filter LPF1 (on the side of the capacitor C1) and from the ground line GL to the cup. The direct current leaked through the ring capacitor Cc is prevented from flowing into the inside of the first low pass filter LPF1.

The capacitor C2 prevents the direct current flowing from the body earth BE to the resistor R6 via the diode D4 from flowing to the outside of the second low pass filter LPF2 (on the side of the capacitor C2), and from the ground line GL to the coupling capacitor. The direct current leaked through Cc is prevented from flowing into the second low pass filter LPF2.

As a result, from the inside of the first low-pass filter LPF1 to the outside of the first low-pass filter LPF1, from the inside of the second low-pass filter LPF2 to the outside of the second low-pass filter LPF2, and from the ground line GL to the first Since it is possible to prevent a direct current from flowing into the low-pass filter LPF1 or the second low-pass filter LPF2, the direct-current can be prevented by the insulation resistance Ri, the resistors R1 and R5 of the first low-pass filter LPF1, and the second low-pass filter. It is possible to prevent the voltage V1 and V2 from fluctuating due to the voltage drop caused by the current flowing through the resistor R6 of the filter LPF2 and the like, and it is possible to prevent the leakage detection accuracy from decreasing.

<Current detection unit Si, switch SW, and traveling control unit Cd shown in FIG. 1>
The current detector Si is composed of an ammeter or the like, and is connected to the DC power source P in series. Further, the current detection unit Si detects the current flowing through the DC power supply P and sends the detection result to the travel control unit Cd that controls the travel of the vehicle.

The switch SW is composed of an electromagnetic relay, a semiconductor switch, or the like, and is connected in series between the DC power supply P and the load Lo. Further, the switch SW is controlled to be turned on and off by the traveling control unit Cd. When the switch SW is turned on, the DC power supply P and the load Lo are brought into conduction, and a current flows in the DC power supply P. When the switch SW is off, the DC power supply P and the load Lo are disconnected, and no current flows in the DC power supply P. When the switch SW is turned on and the traveling motor and the monitoring circuit are driven, a discharge current flows from the DC power source P to the traveling motor and the monitoring circuit, or the traveling motor and the DC power source are driven. Charge current flows to P. Further, when the switch SW is on and only the monitoring circuit is driven, a discharge current flows from the DC power source P to the monitoring circuit. The switch SW may be connected between the DC power source P and the ground line GL.

The traveling control unit Cd is configured such that when a driver or a mechanic pushes a stop button mounted on the vehicle after the traveling vehicle stops, or after the traveling vehicle stops, the driver or the mechanic. When the ignition key mounted on the vehicle is turned off or the idling stop starts, the operation of the inverter circuit is controlled so that the drive motor stops. State). Note that the monitoring circuit is always driven even after the traveling motor is stopped. Further, when the switch SW is on and only the monitoring circuit is driven, the current flowing through the DC power supply P is when the switch SW is on, the traveling motor and the monitoring circuit. Is smaller than the current flowing through the DC power supply P when the is driven.

Further, when the current detected by the current detection unit Si becomes less than or equal to the current threshold value Ith after the traveling motor is stopped, the traveling control unit Cd informs that the current flowing through the DC power supply P becomes less than or equal to the current threshold value. It is sent to the detection unit 6. The current threshold value Ith is the maximum value of the current flowing through the DC power supply P when the increase in the fluctuation amount of the crest value of the voltage Vd due to the increase in the current flowing through the DC power supply P is suppressed.

Alternatively, the traveling control unit Cd may be configured to send the fact that the traveling motor has been stopped to the detection unit 6 when the traveling motor is stopped. In such a configuration, when the traveling motor is stopped, the traveling control unit Cd drives only the monitoring circuit so that the current flowing through the DC power supply P becomes the current threshold value Ith or less. That is, when the current flowing through the DC power source P is less than or equal to the current threshold value Ith, the traveling motor is in a stopped state.

Further, the traveling control unit Cd switches the switch SW from ON to OFF after sending the fact that the current flowing through the DC power source P has become equal to or less than the current threshold value Ith or the traveling motor has been stopped to the detection unit 6. .. Note that the traveling control unit Cd sends the fact that the current flowing through the DC power source P is equal to or lower than the current threshold value Ith or the traveling motor is stopped to the detection unit 6, and then the switch SW is not welded. The switch SW may be switched from on to off after the determination.

Further, after the detection unit 6 receives the fact that the current flowing through the DC power source P has become equal to or less than the current threshold value Ith, the period from when the switch SW is turned off to when the DC power source P is disconnected from the load Lo. Alternatively, the period from when the detection unit 6 receives the fact that the traveling motor is stopped to when the DC power source P and the load Lo are disconnected by turning the switch SW from ON to OFF is a constant time T1. To do.

In addition, when the driver or mechanic or the like presses the start button while the vehicle is parked, or when the driver or mechanic or the like turns on the ignition key while the vehicle is parked, the traveling control unit Cd Alternatively, when the idling stop is completed, the switch SW is switched from off to on.

Further, when the traveling control unit Cd switches the switch SW from OFF to ON, the traveling control unit Cd sends the fact that the switch SW has been switched from OFF to ON to the detection unit 6.

In addition, the traveling control unit Cd controls the operation of the inverter circuit so that the traveling motor is driven after sending the fact that the switch SW has been turned from OFF to ON to the detection unit 6, thereby driving the traveling motor. (Ready ON state). It is assumed that when the traveling motor is in a driving state, the current flowing through the DC power source P becomes larger than the current threshold value Ith.

Further, the period from when the detection unit 6 receives the fact that the switch SW is turned on to when the switch SW is turned on until the current flowing through the DC power source P becomes larger than the current threshold value Ith is a fixed time T2.

<Example of operation of the detection unit 6>
FIG. 4 is a flowchart showing an example of the operation of the detection unit 6.

First, when the detection unit 6 does not receive a notification that the current flowing through the DC power supply P is less than or equal to the current threshold value Ith or that the traveling motor is stopped, and the switch SW is turned on. If not received (step S1: No, step S2: No), whether or not it has been received that the current flowing through the DC power source P has become equal to or less than the current threshold value Ith or that the traveling motor has been stopped, and , It is repeatedly determined whether or not it is received that the switch SW is turned on from off.

Next, when the detection unit 6 receives the fact that the current flowing through the DC power supply P has become equal to or less than the current threshold value Ith or the traveling motor has been stopped (step S1: Yes), the current flowing through the DC power supply P changes. The oscillation circuit 2 outputs the floating capacitance measuring oscillation signal Sc from the oscillation circuit 2 until the fixed time T1 elapses after the fact that the current threshold value Ith or less is received or the traveling motor is stopped is received (step S3). ), the voltage V2 output from the stray capacitance measuring circuit 4 is acquired (step S4), and the capacitance value of the stray capacitance Cf is measured using the correspondence relationship between the peak value and the capacitance value stored in the storage unit 5. (Step S5). That is, the detection unit 6 detects the stray capacitance Cf from when the current flowing through the DC power source P becomes equal to or less than the current threshold value Ith until the switch SW is turned on and off to disconnect the DC power source P and the load Lo. Measure the capacitance value of. It should be noted that the detection unit 6 strays capacitance only during the period when the current flowing in the DC power source P becomes equal to or less than the current threshold value Ith and the switch SW is turned on and off to disconnect the DC power source P and the load Lo. It may be configured to measure the capacitance value of Cf. That is, while omitting step S2, if step S1 is No, the detection unit 6 repeatedly executes step S1, and if step S1 is Yes, the detection unit 6 executes step S3 and subsequent steps.

On the other hand, when the detection unit 6 receives the fact that the switch SW is turned on from the off state (step S2: Yes), the detection unit 6 receives the fact that the switch SW is turned on from the off state until a predetermined time T2 elapses. In step S1, steps S1 to S5 are executed. That is, the detection unit 6 detects the stray capacitance Cf from the time when the switch SW is turned on to the time when the direct current power supply P and the load Lo are conducted until the current flowing through the direct current power supply P becomes larger than the current threshold value Ith. Measure the capacitance value. Note that the detection unit 6 sets the threshold value Vth only after the switch SW is turned on to turn on the DC power supply P and the load Lo until the current flowing through the DC power supply P becomes larger than the current threshold value Ith. May be configured to be corrected. That is, while omitting step S1, when the step S2 is No, the detecting section 6 repeatedly executes the step S2, and when the step S2 is Yes, the detecting section 6 executes the step S3 and thereafter.

Next, the detection unit 6 corrects the threshold value Vth using the capacitance value obtained in step S5 (step S6). Here, the threshold value Vth is corrected based on the capacitance value of the stray capacitance Cf obtained in step S5 using, for example, a previously created calculation formula. As an example, the threshold value Vth may be corrected so as to be inversely proportional to the capacitance value. After the threshold value Vth is corrected, if the switch SW is off, the detection unit 6 switches the switch SW from off to on and then performs the leakage detection after step S7.

Next, the detection unit 6 causes the oscillation circuit 2 to output the leakage detection oscillation signal Sd (step S7), and acquires the voltage V1 output from the insulation resistance measurement circuit 3 (step S8). Then, when the crest value of the voltage V1 is larger than the threshold value Vth (step S9: No), the detection unit 6 determines that no leakage has occurred (step S10), and the crest value of the voltage V1 is equal to or less than the threshold value Vth. If there is (step S9: Yes), it is determined that a leakage has occurred (step S11).

As described above, since the capacitance value of the stray capacitance Cf is measured when the current flowing through the DC power source P is less than or equal to the current threshold value Ith, that is, when the traveling motor is stopped, the traveling motor It is possible to prevent noise generated from an inverter circuit or the like during driving from being included in the voltage V2 output from the stray capacitance measuring circuit 4. Further, since the capacitance value of the stray capacitance Cf is measured when the switch SW is turned on, the capacitance value of the stray capacitance Cf can be measured with the same circuit configuration as that at the time of detecting the leakage. As a result, the correspondence relationship between the peak value of the voltage V2 and the capacitance value of the stray capacitance Cf acquired at the time of measuring the stray capacitance is the peak value of the voltage V2 and the capacitance value of the stray capacitance Cf stored in the storage unit 5 in advance. Since it is possible to suppress the deviation from the correspondence relationship of, it is possible to accurately obtain the capacitance value of the stray capacitance Cf.

<Other Embodiments>
FIG. 5 shows an example of a leakage detection circuit according to another embodiment of the present invention. The DC power supply P, the load Lo, the current detection unit Si, the switch SW, the coupling capacitor Cc, the insulation resistance Ri (and the stray capacitance Cf), and the traveling control unit Cd are substantially the same in FIGS. 1 and 5. Shall be

The leakage detection circuit 1x includes an oscillation circuit 2x, an insulation resistance measurement circuit 3x, a stray capacitance measurement circuit 4x, a storage unit 5, and a detection unit 6x. The storage unit 5 is assumed to be substantially the same in FIGS. 1 and 5. That is, the storage unit 5 stores information indicating the correspondence relationship between the peak value of the voltage V2 and the capacitance value of the stray capacitance Cf obtained at the time of measuring the stray capacitance.

When the oscillation circuit 2x receives the signal instructing to execute the leakage detection from the detection unit 6x, the oscillation circuit 2x superimposes the leakage detection oscillation signal Sd and the stray capacitance measurement oscillation signal Sc and outputs the superimposed signal. The frequency f1 of the leakage detection oscillation signal Sd and the frequency f2 of the stray capacitance measurement oscillation signal Sc are different from each other. In this embodiment, the frequency f2 of the stray capacitance measurement oscillation signal Sc is higher than the frequency f1 of the leakage detection oscillation signal Sd.

The insulation resistance measuring circuit 3x and the stray capacitance measuring circuit 4x are each supplied with a signal representing the voltage applied to the detection resistor Rd. Therefore, when the oscillation circuit 2x superimposes and outputs the leakage detection oscillation signal Sd and the stray capacitance measurement oscillation signal Sc, the input signals of the insulation resistance measurement circuit 3x and the stray capacitance measurement circuit 4x are the leakage detection oscillation signal. The frequency component of Sd (that is, f1) and the frequency component of the oscillation signal for floating capacitance measurement Sc (that is, f2) are included.

The insulation resistance measuring circuit 3x includes a bandpass filter BPF1. The bandpass filter BPF1 passes the frequency f1 and the frequency components near the frequency f1 and blocks other frequency components. That is, when the oscillation circuit 2x superimposes and outputs the leakage detection oscillation signal Sd and the stray capacitance measurement oscillation signal Sc, the band pass filter BPF1 removes the frequency component of the stray capacitance measurement oscillation signal Sc while detecting the leakage. The frequency component of the oscillation signal Sd for use is passed. Then, the insulation resistance measuring circuit 3x outputs the voltage V1 representing the leakage detection oscillation signal Sd passing through the band pass filter BPF1.

The stray capacitance measuring circuit 4x includes a bandpass filter BPF2. The band pass filter BPF2 passes the frequency f2 and the frequency components near the frequency f2, and blocks the other frequency components. That is, when the oscillation circuit 2x superimposes and outputs the leakage detection oscillation signal Sd and the stray capacitance measurement oscillation signal Sc, the bandpass filter BPF2 removes the frequency component of the leakage detection oscillation signal Sd while measuring the stray capacitance. The frequency component of the oscillation signal Sc for use is passed. Then, the stray capacitance measuring circuit 4x outputs a voltage V2 representing the stray capacitance measuring oscillation signal Sc passing through the band pass filter BPF2.

The detection unit 6x measures the capacitance value of the stray capacitance Cf based on the peak value of the voltage signal V2 output from the stray capacitance measurement circuit 4x. At this time, the detection unit 6x measures the capacitance value of the stray capacitance Cf with reference to the information stored in the storage unit 5. Further, the detection unit 6x determines whether or not the resistance value of the insulation resistance Ri has decreased based on the comparison between the peak value of the voltage signal V1 output from the insulation resistance measurement circuit 3x and the threshold value Vth.

The threshold value Vth is determined by the detection unit 6x based on the measured value of the stray capacitance Cf in this example. Then, the detection unit 6x determines that the resistance value of the insulation resistance Ri is based on the comparison between the peak value of the voltage signal V1 output from the insulation resistance measurement circuit 3x and the threshold value Vth determined based on the measurement value of the stray capacitance Cf. It is determined whether or not it has decreased. If the peak value of the voltage signal V1 is less than or equal to the threshold value, the detection unit 6x determines that the resistance value of the insulation resistance Ri has decreased (that is, leakage has occurred).

Note that the detection unit 6x, for example, similar to the detection unit 6 shown in FIG. 1, when the current detected by the current detection unit Si is smaller than the threshold value Ith and the switch SW is controlled to be in the ON state, The leak detection described above is executed. In this case, the influence of noise generated from the inverter or the like when the traveling motor is driven is suppressed. Moreover, since the capacitance value of the stray capacitance Cf is measured with high accuracy, the accuracy of determination as to whether or not a leakage has occurred is also improved.

As described above, in the embodiment shown in FIG. 5, the leakage detection oscillation signal Sd and the stray capacitance measurement oscillation signal Sc are superimposed and output, and the detection unit 6x measures the stray capacitance and the threshold value substantially at the same time. Correction and leakage determination can be performed. Therefore, according to the configuration shown in FIG. 5, the time required for the leakage determination can be shortened as compared with the configuration shown in FIG.

The leakage detection circuit according to another embodiment is not limited to the configuration shown in FIG. For example, the insulation resistance measuring circuit 3x may include a low pass filter instead of the band pass filter BPF1. In this case, the low-pass filter passes the frequency component of the leakage detection oscillation signal Sd while removing the frequency component of the stray capacitance measurement oscillation signal Sc.

<Still another embodiment>
The leakage detection circuit shown in FIG. 1 or FIG. 5 estimates the capacitance of the stray capacitance Cf appearing in parallel with the insulation resistance Ri by detecting the voltage applied to the detection resistor Rd, and further uses the estimated value to detect the leakage current. Determine whether it has occurred. Here, the capacitance of the stray capacitance Cf is estimated based on the voltage V2 detected by the stray capacitance measuring circuit. Further, whether or not the leakage has occurred is determined based on the voltage V1 detected by the insulation resistance measuring circuit. Therefore, an error that occurs in the insulation resistance measuring circuit and/or the stray capacitance measuring circuit may reduce the accuracy of leak detection. Therefore, in still another embodiment, a function of correcting the error of the circuit (mainly the insulation resistance measuring circuit and the stray capacitance measuring circuit) that detects the voltage applied to the detection resistor Rd is provided.

FIG. 6 shows an example of a leakage detection circuit according to still another embodiment of the present invention. In this embodiment, the leakage detection circuit 1y includes an oscillator circuit 2x, an insulation resistance measurement circuit 3x, a stray capacitance measurement circuit 4x, a storage unit 5, a detection unit 6x, a switch SWa, a simulated resistance Rv, a simulated capacitance Cv, and The switch SWb is provided. The oscillator circuit 2x, the insulation resistance measuring circuit 3x, the floating capacitance measuring circuit 4x, the storage unit 5, and the detecting unit 6x are substantially the same as each other in FIGS. 5 and 6.

One terminal of the switch SWa is connected to the ground line GL via the coupling capacitor Cc. The other terminal of the switch SWa is connected to the detection resistor Rd. Therefore, the switch SWa can switch between a state in which the insulation resistance Ri and the detection resistance Rd are connected and a state in which the insulation resistance Ri and the detection resistance Rd are cut off. The state of the switch SWa is controlled by the detection unit 6x.

The simulated resistance Rv and the simulated capacitance Cv are connected in parallel with each other. Then, one terminal of the simulated resistance Rv and one terminal of the simulated capacitance Cv connected to each other are grounded to the body ground BE. The other terminal of the simulated resistance Rv and the other terminal of the simulated capacitance Cv connected to each other are connected to one terminal of the switch SWb. The other terminal of the switch SWb is connected to the detection resistor Rd. That is, the simulated resistance Rv and the simulated capacitance Cv connected in parallel with each other are provided between the detection resistance Rd and the body ground BE via the switch SWb. Therefore, the switch SWb can switch between a state where the simulated resistance Rv and the simulated capacitance Cv are connected to the detection resistance Rd, and a state where the simulated resistance Rv and the simulated capacitance Cv and the detection resistance Rd are cut off. The state of the switch SWb is controlled by the detection unit 6x.

The resistance value of the simulated resistance Rv is known. The resistance value of the simulated resistance Rv is, for example, a value equivalent to the resistance value of the insulation resistance Ri when the electric leakage occurs. As an example, the resistance value of the simulated resistance Rv is the same resistance value as the threshold value for determining whether or not the leakage has occurred, or a predetermined resistance value smaller than the threshold value. The capacitance value of the simulated capacitance Cv is also known. The capacitance value of the simulated capacitance Cv is set to the same value as the assumed capacitance value of the stray capacitance Cf, for example.

In the leakage detection circuit 1y having the above-described configuration, the detection unit 6x provides a correction value for correcting an error in a circuit (mainly the insulation resistance measurement circuit 3x and the stray capacitance measurement circuit 4x) that detects the voltage applied to the detection resistance Rd. calculate. The correction process of calculating the correction value is performed, for example, when the leakage detection circuit 1y is manufactured. Alternatively, in the case where the electric leakage detection circuit 1y is mounted on the vehicle, the correction process may be performed when the ignition switch is in the off state.

When performing the correction process, the detection unit 6x controls the switch SWa to be in the off state and the switch SWb to be in the on state. That is, the leakage detection circuit 1y is separated from the insulation resistance Ri and the stray capacitance Cf. A line from the oscillation circuit 2x to the insulation resistance measuring circuit 3x and the stray capacitance measuring circuit 4x via the detection resistor Rd is connected to the body ground BE via the simulated resistance Rv and the simulated capacitance Cv.

In this state, the oscillation circuit 2x superimposes the leakage detection oscillation signal Sd and the stray capacitance measurement oscillation signal Sc, as described with reference to FIG. Then, the detection unit 6x measures the resistance value of the simulated resistance Rv based on the peak value of the voltage signal V1 output from the insulation resistance measurement circuit 3x. Here, the resistance value of the simulated resistance Rv is known. Therefore, the peak value of the voltage signal V1 output from the insulation resistance measuring circuit 3x when the leakage detection oscillation signal Sd having a predetermined amplitude is output is also known. In the following description, this known peak value may be referred to as "true value V1".

The detection unit 6x calculates a first correction value for correcting the circuit error based on the peak value and the true value V1 of the voltage signal V1 obtained by the measurement. As an example, it is assumed that the circuit error is caused by the gain error of the insulation resistance measuring circuit 3x. The peak value of the voltage signal V1 obtained by the measurement is "4.00" and the true value V1 is "3.96". In this case, the true value V1 can be obtained by multiplying the peak value of the voltage signal V1 obtained by the measurement by "0.99". Therefore, “first correction value=0.99” is obtained.

Further, the detection unit 6x measures the capacitance value of the simulated capacitance Cv based on the peak value of the voltage signal V2 output from the stray capacitance measurement circuit 4x. Here, the capacitance value of the simulated capacitance Cv is known. Therefore, the peak value of the voltage signal V2 output from the stray capacitance measuring circuit 4x when the stray capacitance measuring oscillation signal Sc having a predetermined amplitude is output is also known. In the following description, this known peak value may be referred to as "true value V2".

The detection unit 6x calculates a second correction value for correcting the circuit error based on the peak value and the true value V2 of the voltage signal V2 obtained by the measurement. As an example, the circuit error is caused by the gain error of the stray capacitance measuring circuit 4x. Then, it is assumed that the peak value of the voltage signal V2 obtained by the measurement is “4.00” and the true value V2 is “3.92”. In this case, the true value V2 is obtained by multiplying the peak value of the voltage signal V2 obtained by the measurement by "0.98". Therefore, “second correction value=0.98” is obtained.

After that, the detection unit 6x performs leakage detection using the first correction value and the second correction value. When executing the electric leakage detection, the detection unit 6x controls the switch SWa to be in the ON state and the switch SWb to be in the OFF state. That is, the simulated resistance Rv and the simulated capacitance Cv are separated from the line from the oscillation circuit 2x to the insulation resistance measurement circuit 3x and the stray capacitance measurement circuit 4x via the detection resistance Rd, and the insulation resistance Ri and the stray capacitance Cf are connected to the line. To be done.

The oscillation circuit 2x superimposes the leakage detection oscillation signal Sd and the stray capacitance measurement oscillation signal Sc and outputs them. Then, the detection unit 6x measures the capacitance value of the stray capacitance Cf by correcting the peak value of the voltage signal V2 output from the stray capacitance measurement circuit 4x with the second correction value. As an example, the capacitance value of the stray capacitance Cf is measured by referring to the storage unit 5 based on the result of multiplying the measured value of the peak value of the voltage signal V2 by the second correction value. Further, the detection unit 6x determines the threshold value Vth based on the capacitance value of the stray capacitance Cf thus obtained.

Further, the detection unit 6x measures the resistance value of the insulation resistance Ri by correcting the peak value of the voltage signal V1 output from the insulation resistance measurement circuit 3x with the first correction value. As an example, the resistance value of the insulation resistance Ri is measured based on the result of multiplying the measured value of the peak value of the voltage signal V1 by the first correction value. Then, the detection unit 6x determines whether or not leakage has occurred by comparing the resistance value of the insulation resistance Ri thus obtained with the threshold value Vth.

In the case of determining the first correction value or the second correction value as described above, if the leakage detection oscillation signal Sd or the stray capacitance measurement oscillation signal Sc is clipped, an accurate correction value is obtained. I can't. Therefore, when the switch SWa is controlled to the OFF state and the switch SWb is controlled to the ON state, the oscillation circuit 2x and the detection unit 6x are prevented from clipping the leakage detection oscillation signal Sd or the stray capacitance measurement oscillation signal Sc. It is preferable to set the impedance of the line leading to.

Further, in the embodiment shown in FIG. 6, the leakage detection oscillation signal Sd and the stray capacitance measurement oscillation signal Sc are superimposed and output, but the present invention is not limited to this configuration. That is, the embodiment shown in FIG. 6 can be applied to the configuration shown in FIG.

Further, the present invention is not limited to the configuration shown in FIG. 1, FIG. 5, or FIG. 6, and various improvements and changes can be made without departing from the gist of the present invention.

1, 1x, 1y Leakage detection circuit 2, 2x Oscillation circuit 3, 3x Insulation resistance measurement circuit 4, 4x Stray capacitance measurement circuit 5 Storage section 6, 6x Detection section P DC power supply Lo load GL Ground line BE Body earth Ri Insulation resistance Cf Floating capacitance Cc Coupling capacitor Rd Detecting resistance Cd Travel controller SW, SWa, SWb Switch Rv Simulated resistance Cv Simulated capacity

Claims (9)

A leakage detection circuit for detecting a decrease in resistance value of an insulation resistance between a ground line of a DC power supply mounted on a vehicle and a body ground of the vehicle,
An oscillation circuit for outputting an oscillation signal for detecting leakage, or an oscillation signal for measuring stray capacitance having a frequency higher than the frequency of the oscillation signal for detecting leakage,
A detection resistor connected between the oscillation circuit and the coupling capacitor connected to the ground line,
An insulation resistance measuring circuit that acquires the voltage applied to the detection resistor without attenuating when the leakage detection oscillation signal is output from the oscillation circuit,
A stray capacitance measuring circuit that acquires the voltage applied to the detection resistor without attenuating when the stray capacitance measuring oscillation signal is output from the oscillation circuit,
When the crest value of the voltage acquired by the insulation resistance measuring circuit when the leakage detection oscillation signal is output from the oscillation circuit is equal to or less than the threshold value, it is possible that the resistance value of the insulation resistance is decreased. The capacitance value of the stray capacitance connected in parallel with the insulation resistance is detected by the peak value of the voltage detected by the stray capacitance measuring circuit while the stray capacitance measuring oscillation signal is being output from the oscillation circuit. A detector to measure,
Earth leakage detection circuit. The leakage detection circuit according to claim 1,
The insulation resistance measurement circuit acquires a voltage applied to the detection resistance via a first low-pass filter having a cutoff frequency higher than the frequency of the leakage detection oscillation signal,
The stray capacitance measuring circuit applies a voltage to the detection resistor via a second low pass filter having a cutoff frequency higher than the frequency of the stray capacitance measuring oscillation signal and higher than the cutoff frequency of the first low pass filter. Leakage detection circuit characterized by acquiring. The leakage detection circuit according to claim 1 or 2, wherein
A leakage detection circuit comprising capacitors provided between the coupling capacitor and the first low-pass filter and between the coupling capacitor and the second low-pass filter, respectively. The leakage detection circuit according to claim 1 or 2, wherein
The detection unit disconnects the DC power supply and the load by turning a switch connected between the DC power supply and the load from ON to OFF after the current flowing through the DC power supply becomes a current threshold value or less. The leak detection circuit is characterized in that the capacitance value of the stray capacitance is measured during the period. The leakage detection circuit according to claim 1 or 2, wherein
In the detection unit, a switch connected between the DC power supply and the load is switched from OFF to ON so that a current flowing through the DC power supply after the DC power supply and the load are electrically connected to each other becomes larger than a current threshold value. The leak detection circuit is characterized in that the capacitance value of the stray capacitance is measured during the period. A leakage detection circuit for detecting a decrease in resistance value of an insulation resistance between a ground line of a DC power supply mounted on a vehicle and a body ground of the vehicle,
An oscillation circuit that outputs a leakage detection oscillation signal of a first frequency and a floating capacitance measurement oscillation signal of a second frequency higher than the first frequency in a superimposed manner,
A detection resistor connected between the oscillation circuit and the coupling capacitor connected to the ground line,
When the leakage detection oscillation signal and the stray capacitance measurement oscillation signal are output from the oscillation circuit, the voltage of the first frequency is removed while removing the voltage signal of the second frequency applied to the detection resistor. Insulation resistance measurement circuit that acquires the signal,
While the leakage detection oscillation signal and the stray capacitance measurement oscillation signal are being output from the oscillation circuit, the voltage of the second frequency is removed while removing the voltage signal of the first frequency applied to the detection resistor. A stray capacitance measurement circuit that acquires a signal,
While measuring the capacitance value of the stray capacitance that is connected in parallel to the insulation resistance based on the peak value of the voltage that the stray capacitance measurement circuit acquired, between the crest value and the threshold value of the voltage that the insulation resistance measurement circuit acquired. A detection unit that detects a decrease in the resistance value of the insulation resistance based on comparison,
Earth leakage detection circuit. The detection unit,
Determining the threshold value based on the measured value of the stray capacitance,
The decrease in the resistance value of the insulation resistance is detected based on the comparison between the peak value of the voltage acquired by the stray capacitance measuring circuit and the determined threshold value. Earth leakage detection circuit. A first switch for switching between a state where the insulation resistance and the detection resistance are connected and a state where the insulation resistance and the detection resistance are cut off;
Provided between the detection resistor and the body ground, connected in parallel with each other, a simulated resistance with a known resistance value and a simulated capacitance with a known capacitance value,
A second switch that switches between a state in which the simulated resistance and the simulated capacitance are connected to the detection resistance and a state in which the simulated resistance and the simulated capacitance are cut off from the detection resistance;
The detection unit,
When the first switch is controlled to the off state and the second switch is controlled to the on state, a wave of a voltage corresponding to the leakage detection oscillation signal acquired by the insulation resistance measuring circuit. Calculating a first correction value based on the high value and the resistance value of the simulated resistance,
When the first switch is controlled to be on and the second switch is controlled to be off, a wave of voltage corresponding to the leakage detection oscillation signal acquired by the insulation resistance measuring circuit. A high value is corrected using the said 1st correction value. The earth leakage detection circuit as described in any one of Claims 1-7 characterized by the above-mentioned. The detection unit,
When the first switch is controlled to the off state and the second switch is controlled to the on state, a voltage corresponding to the floating capacitance measuring oscillation signal acquired by the floating capacitance measuring circuit is detected. Calculating a second correction value based on the peak value and the capacitance value of the simulated capacitance,
When the first switch is controlled to the ON state and the second switch is controlled to the OFF state, a voltage corresponding to the floating capacitance measuring oscillation signal acquired by the floating capacitance measuring circuit is obtained. The leak detection circuit according to any one of claims 1 to 8, wherein the peak value is corrected using the second correction value.

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