JP2020159922A - Electric leakage detection circuit - Google Patents

Abstract

To provide an electric leakage detection circuit for detecting a decrease in resistance value of an insulating resistor between the ground line of a DC power supply mounted in a vehicle and the body earth of the vehicle, with which a fault of the electric leakage detection circuit is determined by itself.SOLUTION: A electric leakage detection circuit 1 refers to information D1 when an insulating resistor Ri and a dummy insulating resistor Ri' are not connected in parallel to each other and defines a resistance value that corresponds to the peak value Vd of the voltage acting on a detection resistor Rd as a fault determining resistance value, refers to information D1 and defines a peak value that corresponds to the synthesized resistance value of the fault determining resistance value and the dummy insulating resistor Ri' as a fault determining peak value, and determines that the electric leakage detection circuit 1 is faulty when the peak value Vd of the voltage acting on the detection resistor Rd differs from the fault determining peak value while the insulating resistor Ri and the dummy insulating resistor Ri' are connected in parallel to each other.SELECTED DRAWING: Figure 1

Description

The present invention relates to an earth leakage detection circuit.

As an earth leakage detection circuit, a detection resistor is connected to the ground line of the DC power supply mounted on the vehicle via a coupling capacitor, and an oscillation signal is output between the ground line and the body ground of the vehicle, and the detection resistor is applied. When the peak value of the voltage is equal to or less than the threshold value, there is a device that detects that the resistance value of the insulation resistance has decreased, that is, that an electric leakage has occurred.

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

Japanese Unexamined Patent Publication No. 2014-155329

However, in the above-mentioned leakage detection circuit, when the leakage detection circuit fails due to a decrease in the impedance of the detection resistance and the peak value of the voltage applied to the detection resistance becomes higher than when the leakage detection circuit does not fail, it actually becomes higher. There is a risk of erroneous detection that no electric leakage has occurred even though there is an electric leakage. Therefore, it is necessary to determine that the earth leakage detection circuit is out of order and urge the user to repair the earth leakage detection circuit.

An object according to one aspect of the present invention is to cause a failure of the earth leakage detection circuit for detecting a decrease in the resistance value of the insulation resistance between the ground line of the DC power supply mounted on the vehicle and the body ground of the vehicle by the earth leakage detection circuit itself. It is to judge.

The leakage detection circuit according to the present invention is a leakage detection circuit that detects a decrease in the resistance value of the insulation resistance between the ground line of the DC power supply mounted on the vehicle and the body ground of the vehicle. The oscillation circuit that outputs the oscillation signal, the detection resistance connected between the oscillation circuit and the coupling capacitor connected to the ground line, the simulated insulation resistance, and the insulation resistance and the simulated insulation resistance are connected in parallel with each other. The operation of the switch is controlled so that the switch switches to one of the first state, which is not present, and the second state, in which the insulation resistance and the simulated insulation resistance are connected in parallel to each other, and the first state. When the peak value of the voltage applied to the detection resistance is below the threshold value, the detection unit that detects that the resistance value of the insulation resistance has dropped and the insulation resistance when the leakage detection circuit is not faulty. It is provided with a storage unit that stores information indicating the correspondence between the resistance value of the above and the peak value of the voltage applied to the detection resistance.

Further, when the detection unit controls the operation of the switch so as to be in the first state, the resistance value corresponding to the peak value of the voltage applied to the detection resistance is set as the resistance value for failure determination by referring to the above information. Then, referring to the above information, the peak value corresponding to the combined resistance value of the resistance value for failure determination and the resistance value of the simulated insulation resistance is set as the peak value for failure determination, and the switch is operated so as to be in the second state. If the peak value of the voltage applied to the detection resistor is different from the peak value for failure determination, it is determined that the leakage detection circuit has failed.

If the earth leakage detection circuit is not faulty, it is assumed that the peak value of the voltage applied to the detection resistance when the insulation resistance and the simulated insulation resistance are connected in parallel to each other will be the same as the peak value for fault determination. Therefore, when the leakage detection circuit is out of order, such as when the impedance of the detection resistor drops, the peak value of the voltage applied to the detection resistor when the insulation resistance and the simulated insulation resistance are connected in parallel is the peak value for failure determination. Is expected to be different.

Therefore, in the leakage detection circuit, which is one embodiment of the present invention, the peak value of the voltage applied to the detection resistor is measured when the operation of the switch is controlled so that the insulation resistor and the simulated insulation resistor are connected in parallel with each other. If it is different from the fault determination peak value, it is determined that the leakage detection circuit has failed. As a result, the leakage detection circuit can determine that it is out of order.

Further, the detection unit may be configured to obtain the capacitance value of the stray capacitance connected in parallel to the insulation resistor and correct the above information based on the obtained capacitance value.

As the capacitance value of stray capacitance increases, the peak value of the voltage applied to the detection resistor decreases.
Therefore, in the leakage detection circuit, which is one embodiment of the present invention, the above information is corrected by the capacitance value of the stray capacitance. As a result, even if the crest value decreases as the capacitance value of the stray capacitance increases, the resistance value for failure determination and the crest value for failure determination can be appropriately obtained, so that the leakage detection circuit fails. The determination accuracy can be improved.

According to the present invention, the leakage detection circuit itself can determine the failure of the leakage detection circuit that detects a decrease in the resistance value of the insulation resistance between the ground line of the DC power supply mounted on the vehicle and the body ground of the vehicle. it can.

It is a figure which shows an example of the leakage detection circuit of an embodiment. It is a figure which shows an example of the frequency characteristic of a low-pass filter and the information which is stored in the storage part. It is a flowchart which shows an example of the operation of the detection part at the time of execution of failure detection processing. It is a figure which shows an example of the correction of information and an example of failure determination.

Hereinafter, embodiments will be described in detail based on the drawings.
FIG. 1 is a diagram showing an example of an earth leakage detection circuit of the embodiment.

The DC power supply P is a high-pressure battery composed of a plurality of batteries (for example, a lithium ion battery or a nickel hydrogen battery) connected in series, and is mounted on a vehicle such as a hybrid vehicle or an electric vehicle to drive a traveling motor. Power is supplied to the load Lo such as the inverter circuit.

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 supply P and the body ground BE of the vehicle. Further, the leakage detection circuit 1 includes an oscillation circuit 2, a detection resistor Rd, a simulated insulation resistor Ri', a switch SW, a storage unit 3, and a detection unit 4.

The oscillation circuit 2 is connected to the body ground BE and outputs an oscillation signal S such as a square wave between the ground line GL and the body ground BE. The oscillation signal S is an oscillation signal S1 for leakage detection or an oscillation signal S2 for stray capacitance detection. Further, the frequency of the oscillation signal S1 for leak detection is a cut of the low-pass filter LPF composed of the insulation resistor Ri, the stray capacitance Cf virtually connected in parallel to the insulation resistor Ri, the coupling capacitor Cc, the detection resistor Rd, and the like. The frequency is lower than the off frequency fc. Further, the frequency of the stray capacitance detection oscillation signal S2 is set to be higher than the cutoff frequency fc of the low-pass filter LPF.

Here, FIG. 2A is a diagram showing the frequency characteristics of the low-pass filter LPF. The horizontal axis of the two-dimensional coordinates shown in FIG. 2A indicates the frequency [Hz] of the oscillation signal S, and the vertical axis represents the ratio (detection) of the peak value Vd of the voltage applied to the detection resistance Rd to the peak value of the oscillation signal S. The peak value Vd of the voltage applied to the resistor Rd / the peak value of the oscillation signal S), that is, the gain [dB] of the low-pass filter LPF is shown.

When the operation of the oscillation circuit 2 is controlled so that the frequency of the oscillation signal S1 for leak detection becomes lower than the cutoff frequency fc of the low-pass filter LPF, when the resistance value ri of the insulation resistor Ri decreases, the detection resistor Rd The peak value Vd of the voltage applied to is lowered.

That is, when the leakage detection circuit 1 has not failed and the resistance value of the detection resistor Rd and the capacitance value of the coupling capacitor Cc do not fluctuate, the frequency of the leakage detection oscillation signal S1 becomes the frequency f1. By controlling the operation of the oscillation circuit 2 so as to be, the resistance value ri and the peak value Vd can be associated one-to-one.

In the embodiment, the information D1 indicating the correspondence relationship between the resistance value ri and the peak value Vd when the leakage detection circuit 1 is not broken is obtained by an experiment or a simulation and stored in the storage unit 3.

FIG. 2B is a diagram showing an example of information D1. The horizontal axis of the two-dimensional coordinates shown in FIG. 2A indicates the resistance value ri [kΩ] of the insulation resistance Ri when the leakage detection circuit 1 is not faulty, and the vertical axis relates to the detection resistance Rd. The peak value Vd [V] of the voltage is shown. Further, the solid line shown in FIG. 2B shows information D1 indicating the correspondence relationship between the resistance value ri and the peak value Vd when the leakage detection circuit 1 is not out of order.

In the information D1 shown in FIG. 2B, the smaller the resistance value ri, the smaller the peak value Vd. In other words, when the resistance value ri is equal to or more than the threshold value rit, the peak value Vd becomes the threshold value Vds1 or more, and when the resistance value ri is smaller than the threshold value rit, the peak value Vd becomes smaller than the threshold value Vds1.

Further, as shown in FIG. 2A, when the operation of the oscillation circuit 2 is controlled so that the frequency of the oscillation signal S2 for detecting floating capacitance is higher than the cutoff frequency fc of the low-pass filter LPF, the low-pass filter 2 is operated. The gain of the low-pass filter LPF drops to "G", which is smaller than "zero", due to the influence of the insulation resistance Ri, the floating capacitance Cf, the detection resistor Rd, and the coupling capacitor Cc that make up the filter LPF. The peak value Vd is lower than when the operation of the oscillation circuit 2 is controlled so that the frequency of the oscillation signal S2 becomes a frequency f1 higher than the cutoff frequency fc of the low-pass filter LPF.

Further, as the capacitance value cf of the floating capacitance Cf increases, the cutoff frequency fc decreases. That is, as shown in FIG. 2A, when the capacitance value cf of the floating capacitance Cf increases, the low-pass filter LPF Since the frequency characteristic changes from the frequency characteristic shown by the solid line to the frequency characteristic shown by the broken line, when the operation of the oscillation circuit 2 is controlled so that the frequency of the oscillation signal S2 for floating capacitance detection becomes the frequency f2, the low-pass filter The gain of the LPF further decreases from "G" to "G'", and the peak value Vd further decreases. It should be noted that "G'" <"G".

That is, when the resistance value ri of the insulation resistor Ri, the resistance value of the detection resistor Rd, and the capacitance value of the coupling capacitor Cc do not fluctuate, the oscillation circuit is such that the frequency of the stray capacitance detection oscillation signal S2 becomes the frequency f2. By controlling the operation of 2, the capacitance value cf and the peak value Vd can be associated one-to-one.

In the embodiment, the resistance value ri of the insulation resistor Ri, the resistance value of the detection resistor Rd, and the capacitance value of the coupling capacitor Cc do not fluctuate, and the frequency of the stray capacitance oscillation signal S2 becomes the frequency f2. When the operation of the oscillation circuit 2 is controlled, the information D2 indicating the correspondence between the peak value Vd and the capacitance value cf is obtained by an experiment or a simulation and stored in the storage unit 3.

FIG. 2C is a diagram showing an example of information D2.
In the information D2 shown in FIG. 2C, "cf1" as the capacitance value cf and "Vd3" as the peak value Vd are associated with each other, and "cf2" as the capacitance value cf and "cf2" as the peak value Vd are ". "Vd2" is associated with each other, and "cf3" as a capacitance value cf and "Vd1" as a peak value Vd are associated with each other. It should be noted that "cf1"<"cf2"<"cf3","Vd1"<"Vd2"<"Vd3". That is, in the information D2, as the capacitance value cf increases, the peak value Vd decreases. In other words, when the capacitance value cf is equal to or less than the threshold value cfth, the peak value Vd becomes equal to or greater than the threshold value Vdts2, and when the capacitance value cf is larger than the threshold value cfth, the peak value Vd becomes smaller than the threshold value Vds2.

Further, the detection resistor Rd shown in FIG. 1 is connected between the coupling capacitor Cc connected to the ground line GL and the oscillation circuit 2 connected to the body ground BE.

One end of the simulated insulation resistor Ri'is connected to the body ground BE, the other end of the simulated insulation resistor Ri'is connected to one end of the switch SW, and the other end of the switch SW is the coupling capacitor Cc and the detection resistor Rd. It is connected to the connection point.

The switch SW is composed of a semiconductor switch, an electromagnetic relay, or the like, and its operation is controlled by the detection unit 4. Further, in the switch SW, the connection point between the coupling capacitor Cc and the detection resistor Rd and the simulated insulation resistor Ri'are not connected to each other, that is, the insulation resistor Ri and the simulated insulation resistor Ri'are connected in parallel to each other. In the first state, the connection point between the coupling capacitor Cc and the detection resistor Rd and the simulated insulation resistor Ri'are connected to each other, that is, the insulation resistor Ri and the simulated insulation resistor Ri'are parallel to each other. Switch to either of the connected second states.

As for the resistance value of the simulated insulation resistor Ri', for example, the peak value Vd of the voltage applied to the detection resistor Rd when the switch SW is switched to the second state is switched to the first state by the switch SW. It is the resistance value of the simulated insulation resistor Ri when the voltage is equal to the peak value Vd of the voltage applied to the detection resistor Rd when the voltage is leaking.

The storage unit 3 is composed of, for example, a RAM (Random Access Memory) or a ROM (Read Only Memory), and stores the above-mentioned information D1 and D2.

The detection unit 4 is composed of, 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)), and includes a coupling capacitor Cc and a detection resistor Rd. Is connected to. A low-pass filter, a band-pass filter, or the like may be connected between the detection resistor Rd and the detection unit 4.

Further, when the detection unit 4 controls the operation of the switch SW so as to be in the first state and when the oscillation signal S1 for leakage detection is output from the oscillation circuit 2, the detection resistor Rd is set. When the peak value Vd of such a voltage is equal to or less than the threshold value Vds3, it is detected that the resistance value ri of the insulation resistor Ri is lowered, that is, that an electric leakage has occurred. It is assumed that the threshold value Vds3 is obtained by an experiment, a simulation, or the like and is stored in the storage unit 3, and is, for example, a peak value Vd immediately before an electric leakage occurs.

Further, the detection unit 4 determines whether or not the leakage detection circuit 1 has failed by executing the failure determination process. The failure of the leakage detection circuit 1 means that the impedance of the wiring from the coupling capacitor Cc to the detection unit 4 or the detection resistor Rd is higher than usual, or the wiring from the coupling capacitor Cc to the detection unit 4 or the detection resistor. The impedance of Rd is assumed to be lower than usual. The state in which the impedance of the wiring from the coupling capacitor Cc to the detection unit 4 or the detection resistor Rd is higher than usual is, for example, a state in which the wiring from the coupling capacitor Cc to the detection unit 4 or the detection resistor Rd is disconnected. .. When the impedance of the wiring from the coupling capacitor Cc to the detection unit 4 or the detection resistor Rd is lower than usual, for example, the wiring from the coupling capacitor Cc to the detection unit 4 or both ends of the detection resistor Rd are short-circuited. Make it a state.

FIG. 3 is a flowchart showing an example of the operation of the detection unit 4 when the failure detection process is executed.
First, the detection unit 4 controls the operation of the switch SW so as to be in the first state (step S1).

Next, the detection unit 4 obtains the capacitance value cf of the current stray capacitance Cf (step S2). For example, the detection unit 4 refers to the information D2 stored in the storage unit 3 and sets the peak value Vd of the voltage applied to the detection resistor Rd when the oscillation signal S2 for stray capacitance detection is output from the oscillation circuit 2. Let the corresponding capacitance value cf be the capacitance value cf of the current stray capacitance Cf.

Next, the detection unit 4 corrects the information D1 by using the capacitance value cf of the current stray capacitance Cf (step S3). For example, as shown in FIG. 4A, the detection unit 4 executes the previous failure determination process from the capacitance value cf of the current stray capacitance Cf (the capacitance value cf obtained at the time of executing the failure determination process this time). Information D1 is corrected to information D1'by reducing each peak value Vd shown in information D1 according to the difference obtained by subtracting the capacitance value cf obtained at the time.

Next, in the flowchart shown in FIG. 3, the detection unit 4 obtains a failure determination resistance value (step S4). For example, when the detection unit 4 controls the operation of the switch SW so as to be in the first state, the detection unit 4 acquires the peak value Vd3 as the peak value Vd of the voltage applied to the detection resistor Rd. Next, as shown in FIG. 4B, the detection unit 4 refers to the corrected information D1'and sets the resistance value ri3 corresponding to the peak value Vd3 as the failure determination resistance value.

Next, in the flowchart shown in FIG. 3, the detection unit 4 obtains the peak value for failure determination (step S5). For example, as shown in FIG. 4B, the detection unit 4 obtains the combined resistance value ri1 of the failure determination resistance value ri3 and the resistance value of the simulated insulation resistance Ri ′, and refers to the corrected information D1 ′. Therefore, the peak value Vd1 corresponding to the combined resistance value ri1 is set as the failure determination peak value. The detection unit 4 obtains the combined resistance value by calculating the combined resistance value = 1 / ((1 / resistance value for failure determination) + (1 / resistance value of the simulated insulation resistance Ri')). It is assumed that the resistance value of the simulated insulation resistor Ri'is stored in the storage unit 3.

Next, the detection unit 4 controls the operation of the switch SW so as to be in the second state (step S6).

Next, the detection unit 4 obtains the peak value Vd of the voltage applied to the detection resistor Rd (step S7).

Next, the detection unit 4 determines whether or not the peak value Vd obtained in step S7 is different from the failure determination peak value obtained in step S5 (step S8). For example, as shown in FIG. 4B, the detection unit 4 obtains the threshold value Vdsα which is the result of adding the constant value Vdα to the failure determination peak value Vd1, and obtains the constant value Vdβ from the failure determination peak value Vd1. The threshold value Vdsβ, which is the result of the subtraction, is obtained. Next, when the peak value Vd obtained in step S7 is larger than the threshold value Vdsα, or the peak value Vd obtained in step S7 is smaller than the threshold value Vdsβ, the detection unit 4 finds the peak value Vd in step S7 in step S5. It is determined that the peak value Vd1 for failure determination obtained in On the other hand, when the peak value Vd obtained in step S7 is equal to or less than the threshold value Vdsα and the peak value Vd obtained in step S7 is equal to or greater than the threshold value Vdsβ, the detection unit 4 finds the peak value Vd in step S7. Is not different from the failure determination crest value Vd1 obtained in step S5. The constant value Vdα and the constant value Vdβ may be the same value or different values from each other. Further, the constant value Vdα and the constant value Vdβ are obtained by a measurement error of the peak value Vd or the like by an experiment or a simulation, and are stored in the storage unit 3.

Next, in the flowchart shown in FIG. 3, when the peak value Vd obtained in step S7 is different from the failure determination peak value obtained in step S5 (step S8: Yes), the earth leakage detection circuit 1 (Step S9), and if the peak value Vd obtained in step S7 is not different from the failure determination peak value obtained in step S5 (step S8: No), the earth leakage detection circuit 1 has failed. It is determined that this has not been done (step S10).

Note that steps S2 and S3 may be omitted. In this configuration, the detection unit 4 obtains the failure determination resistance value and the failure determination peak value with reference to the uncorrected information D1.

When the leakage detection circuit 1 is not faulty, the peak value Vd of the voltage applied to the detection resistor Rd when the insulation resistance Ri and the simulated insulation resistance Ri'are connected in parallel to each other is the insulation resistance Ri and the simulated insulation resistance Ri'. Corresponds to the combined resistance value of the fault determination resistance value and the resistance value of the simulated insulation resistance Ri', which is the resistance value corresponding to the peak value Vd of the voltage applied to the detection resistor Rd when ´ and ′ are not connected in parallel with each other. It is assumed that the crest value will be the same as the crest value for fault determination. Therefore, when the leakage detection circuit 1 is out of order, such as when the impedance of the detection resistor Rd drops, the peak value Vd of the voltage applied to the detection resistor Rd when the insulation resistor Ri and the simulated insulation resistor Ri'are connected in parallel to each other. Is assumed to be different from the fault determination peak value.

Therefore, in the leakage detection circuit 1 of the embodiment, the peak value Vd of the voltage applied to the detection resistor Rd when the operation of the switch SW is controlled so that the insulation resistor Ri and the simulated insulation resistor Ri'are connected to each other in parallel. If is different from the fault determination peak value, it is determined that the leakage detection circuit 1 has failed. As a result, the leakage detection circuit 1 of the embodiment can determine that it is out of order.

Further, as the capacitance value cf of the stray capacitance Cf increases, the peak value Vd of the voltage applied to the detection resistor Rd decreases.

Therefore, in the leakage detection circuit 1 of the embodiment, the information D1 is corrected by the capacitance value cf of the stray capacitance Cf. As a result, even if the peak value Vd decreases as the capacitance value cf of the stray capacitance Cf increases, the resistance value for failure determination and the peak value for failure determination can be appropriately obtained, so that leakage detection can be performed. The failure determination accuracy of the circuit 1 can be improved.

Further, the present invention is not limited to the above embodiments, and various improvements and changes can be made without departing from the gist of the present invention.

1 Leakage detection circuit 2 Oscillation circuit 3 Storage unit 4 Detection unit P DC power supply Lo Load GL Ground line BE Body ground Ri Insulation resistance Cf Stray capacitance Cc Coupling capacitor Rd Detection resistance Ri'Simulated insulation resistance SW switch

Claims (2)

An earth leakage detection circuit that detects a decrease in the resistance value of the insulation resistance between the ground line of the DC power supply mounted on the vehicle and the body ground of the vehicle.
An oscillator circuit that outputs an oscillation signal and
A detection resistor connected between the oscillator circuit and the coupling capacitor connected to the ground line,
Simulated insulation resistance and
In either the first state in which the insulation resistance and the simulated insulation resistance are not connected in parallel to each other, or the second state in which the insulation resistance and the simulated insulation resistance are connected in parallel to each other. Toggle switch and
When the operation of the switch is controlled so as to be in the first state, if the peak value of the voltage applied to the detection resistor is equal to or less than the threshold value, it is detected that the resistance value of the insulation resistor is lowered. Detection unit and
A storage unit that stores information indicating the correspondence between the resistance value of the insulation resistor and the peak value of the voltage applied to the detection resistor when the leakage detection circuit is not broken.
With
The detector is
When the operation of the switch is controlled so as to be in the first state, the resistance value corresponding to the peak value of the voltage applied to the detection resistor is set as the failure determination resistance value with reference to the information.
With reference to the above information, the crest value corresponding to the combined resistance value of the failure determination resistance value and the resistance value of the simulated insulation resistance is defined as the failure determination crest value.
When the operation of the switch is controlled so as to be in the second state, if the peak value of the voltage applied to the detection resistor is different from the peak value for failure determination, it means that the leakage detection circuit has failed. An earth leakage detection circuit characterized by making a judgment. The leakage detection circuit according to claim 1.
The earth leakage detection circuit is characterized in that the detection unit obtains a capacitance value of a stray capacitance connected in parallel to the insulation resistor and corrects the information based on the obtained capacitance value.

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