JP6195547B2 - Earth leakage detector - Google Patents

Description

  The present invention relates to a leakage detection device using a coupling capacitor.

  For example, in a vehicle such as an electric vehicle or a hybrid vehicle, a large amount of power is consumed as driving energy, and therefore a power supply that handles high voltage is often mounted from the viewpoint of energy efficiency. That is, an in-vehicle battery (such as a lithium ion battery) capable of charging / discharging at high voltage, a high voltage charging circuit, and the like are provided.

  In a vehicle equipped with such a high voltage power source, it is necessary to consider that the driver, other passengers, and the like do not get an electric shock from the high voltage. In a typical vehicle, a vehicle body made of metal is connected to a power source as a ground. However, in a vehicle equipped with a high voltage power source, each electrode of the high voltage circuit is connected to the vehicle body to prevent electric shock. Electrically separated from earth. However, even in an electrically insulated state, there is a possibility that electric leakage may occur in the vehicle body from each electrode of the high voltage circuit due to deterioration of the insulator or some factor.

  Therefore, in order to confirm that a safe situation in which no electric shock occurs is maintained, it is necessary to detect the presence or absence of electric leakage between the electrode of the high voltage circuit and the vehicle body ground. Leakage detection devices used in such applications can be roughly classified into two types: a device using a flying capacitor and a device using a coupling capacitor.

  For example, Patent Literature 1, Patent Literature 2, and Patent Literature 3 are known as conventional techniques of a leakage detection device using a coupling capacitor.

  The leakage detection device shown in FIG. 1 of Patent Document 1 includes components such as a resistor, a coupling capacitor, a first changeover switch, a reference impedance circuit, a second changeover switch, a leakage determination circuit, and a high-voltage battery. . When the charging signal is on, the other end of the resistor is disconnected from the high voltage battery B1 and connected to the reference impedance circuit through the coupling capacitor to detect the peak value of the AC signal at the other end of the resistor. To the reference wave height value. Further, when the charging signal is turned off, the other end of the resistor is disconnected from the reference impedance circuit, and connected to the high voltage battery B1 via the coupling capacitor, and the peak value of the AC signal at the other end of the resistor is detected. . And the presence or absence of an electric leakage is determined based on the comparison result of a crest value and a reference crest value.

  In the ground fault detection circuit of Patent Document 2, an AC voltage is applied to one point of a high voltage battery through an output impedance element and a coupling capacitor, and a voltage at a connection point between the output impedance element and the coupling capacitor is amplified through a bandpass filter. Applied to the circuit section. This prevents erroneous ground fault determination due to voltage fluctuations of the high-voltage battery.

  The leakage detection device of Patent Document 3 includes a booster circuit for applying a boosted pulse voltage to the coupling capacitor C. Further, based on the output voltage of the booster circuit, a reference voltage is generated by the reference voltage generation circuit, and this reference voltage is switched by the switching element Q to be converted into a pulse voltage. The arithmetic circuit outputs a voltage obtained by subtracting the offset voltage from the voltage of the coupling capacitor C. The CPU determines whether or not the load power supply has a leakage based on the comparison result between the output voltage of the arithmetic circuit and the threshold value.

JP 2013-142658 A JP 2003-274504 A JP 2013-61163 A

  By the way, in the leakage detection device using the coupling capacitor as described above, the difference in the capacitance of the coupling capacitor has a great influence on the detection of the ground fault resistance. That is, the time constant of the circuit including the grounding resistance and stray capacitance potentially formed between the electrode of the high voltage circuit and the vehicle body and the coupling capacitor depends on the capacitance of the coupling capacitor. Therefore, the detected voltage waveform and peak value also vary as the capacitance of the coupling capacitor changes.

  In reality, there is a high possibility that the capacitance of the coupling capacitor will fluctuate due to the deterioration of the individual parts due to aging. Even if the coupling capacitor is not deteriorated, the capacitance of the coupling capacitor varies depending on the temperature difference when the ambient temperature changes greatly.

  Therefore, when the magnitude of the voltage at the connection point between the coupling capacitor and the impedance is detected and the voltage is compared with a predetermined threshold value, the magnitude of the ground fault resistance is identified. A large error occurs in the identification result due to the influence of the fluctuation of the capacitance of the capacitor. In other words, it may happen that the ground fault resistance value is within the allowable range, and that “earth leakage” is identified, or that the ground fault resistance value is smaller than the tolerance range, and “no ground leakage” is identified. .

  The present invention has been made in view of the above-described situation, and it is possible to suppress the occurrence of detection errors due to fluctuations in the capacitance of the coupling capacitor and to suppress erroneous determinations regarding leakage. An object is to provide a leakage detection device.

The above object of the present invention is achieved by the following configuration.
(1) A coupling capacitor having one end connected to a DC power source, a pulse generating unit connected to the other end of the coupling capacitor via an impedance to supply a pulse signal, and a connection between the impedance and the coupling capacitor A leakage detection device comprising: a voltage detection unit that detects a voltage at a point; and a leakage detection unit that detects a leakage of the DC power supply based on a comparison between a voltage detected by the voltage detection unit and a threshold value,
A pulse signal output from the pulse generator so as to detect a change in the capacitance of the coupling capacitor and suppress a change in the peak value of the voltage when the change in the capacitance is detected. Capacity fluctuation correction control unit for correcting
It is provided with.

  According to this leakage detection device, when the capacitance of the coupling capacitor varies due to deterioration or the like, the capacitance variation correction control unit automatically corrects the pulse signal so that the variation is compensated. Therefore, it is possible to prevent the influence of the variation in capacitance from appearing in the peak voltage detected by the voltage detector, and the detection error is reduced.

(2) The leakage detection device according to (1),
The capacitance variation correction control unit corrects at least one of a frequency, an amplitude, and a duty ratio of a pulse signal output from the pulse generation unit with respect to a variation in capacitance in the coupling capacitor.
It is characterized by that.

  According to this leakage detection device, even when the capacitance of the coupling capacitor fluctuates, the peak voltage detected by the voltage detector can be maintained substantially constant. That is, the peak voltage can be returned to the reference value by correcting at least one of the frequency, amplitude, and duty ratio of the pulse signal for the fluctuation of the voltage waveform corresponding to the fluctuation of the capacitance. Become.

(3) The leakage detection device according to (1) or (2),
Prior to the leakage detection process by the leakage detection unit, a high-accuracy mode in which the capacitance variation correction control unit detects the capacitance variation and corrects the pulse signal, and the capacitance variation correction control unit A mode selection unit that selectively switches between at least two modes: a high-speed measurement mode that omits detection of fluctuations in capacitance and correction of the pulse signal;
It is characterized by that.

  According to this leakage detection device, two types of modes can be properly used as necessary. That is, when the high-accuracy mode is selected, capacitance fluctuation is detected and the pulse signal is corrected to improve detection accuracy. When the high-speed measurement mode is selected, capacitance fluctuation Since the detection and correction of the pulse signal are omitted, it is possible to shorten the detection time and output the detection result quickly.

(4) The leakage detection device according to (3),
The mode selection unit automatically selects the high-speed measurement mode when a condition that requires high-speed operation is satisfied.
It is characterized by that.

  According to this leakage detection device, for example, immediately after the ignition is turned on, it is possible to automatically select the high-speed measurement mode in a situation where it is desired to quickly know whether or not the vehicle can be operated in a safe state. The time required for detection can be shortened.

  According to the leakage detection device of the present invention, it is possible to suppress erroneous detection of leakage due to fluctuations in the capacitance of the coupling capacitor.

  The present invention has been briefly described above. Furthermore, the details of the present invention will be further clarified by reading through the best mode for carrying out the invention described below with reference to the accompanying drawings.

FIG. 1 is a block diagram illustrating a configuration example (1) of a leakage detection device according to an embodiment of the present invention. FIG. 2 is a time chart showing signal waveforms at various parts in the basic operation of the leakage detecting apparatus shown in FIG. FIG. 3 is a flowchart showing a main operation procedure of the leakage detection apparatus shown in FIG. FIG. 4A is a time chart showing waveforms of respective parts when special control is not performed for Cc capacity change, and FIG. 4B is a case where pulse frequency is corrected for Cc capacity change. It is a time chart which shows the signal waveform of each part. FIG. 5A is a time chart showing the waveforms of the respective parts when correcting the duty ratio of the pulse with respect to the Cc capacity change, and FIG. 5B is a case of correcting the pulse amplitude with respect to the Cc capacity change. It is a time chart which shows the waveform of each part. FIG. 6 is a block diagram showing a configuration example (2) of the leakage detection device in the embodiment of the present invention. FIG. 7: is a block diagram which shows the structural example (3) of the leak detection apparatus in embodiment of this invention.

  Specific embodiments relating to the leakage detection apparatus of the present invention will be described below with reference to the drawings.

<Outline of in-vehicle system>
FIG. 1 shows a configuration example (1) of an in-vehicle system including a leakage detection device 10 according to an embodiment of the present invention. The in-vehicle system shown in FIG. 1 is mounted on a vehicle that consumes large electric power as driving energy for propulsion like an electric vehicle or a hybrid vehicle.

  The high-voltage power supply circuit 21 has a capability of supplying a high-voltage power supply power of, for example, about 300 [V] to the outside. Although not shown, the high-voltage power supply circuit 21 includes a battery that can store a large amount of power, such as a lithium ion battery, a charging circuit, and the like. The plus-side electrode 22 and the minus-side electrode 23 of the high-voltage power supply circuit 21 are connected to an electric motor or the like that drives the vehicle via a relay or a fuse (not shown).

  Further, an electronic control unit (ECU) 100 provided on the vehicle is connected to the high-voltage power supply circuit 21, and charging control of the leakage detection device 10 and the high-voltage power supply circuit 21 is performed.

  In order to ensure safety, the electrodes 22 and 23 of the high-voltage power supply circuit 21 and the vehicle body ground 30 are electrically insulated. However, equivalently, the ground fault resistance Rg and the stray capacitance Cg exist between the electrodes 22 and 23 and the vehicle body ground 30. Usually, since the ground fault resistance Rg is very large (for example, several hundred [MΩ] or more), safety is ensured.

  However, for example, when the insulation coating included in the wiring of each part deteriorates or is damaged due to some cause, there is a possibility that the ground fault resistance Rg becomes small and leakage occurs. For this reason, it is possible to identify whether or not the current state is safe by estimating the actual resistance value of the ground fault resistance Rg and identifying the presence or absence of electric leakage.

  The leakage detection device 10 shown in FIG. 1 has a function for identifying the magnitude of the resistance value of the ground fault resistance Rg between each electrode of the high-voltage power supply circuit 21 and the vehicle body ground 30, that is, the presence or absence of leakage. ing. The leakage detection device 10 is connected so as to be able to communicate with the host electronic control unit 100, and can transmit information indicating the presence or absence of leakage to the electronic control unit 100.

<Configuration of Earth Leakage Detector 10>
1 includes a microcomputer (CPU) 11, a pulse generation circuit 12, a voltage detection circuit 13, a nonvolatile memory 14, a low-voltage power supply circuit 15, a reference impedance circuit 16, a resistor Rc, and a coupling. A capacitor Cc and switching elements SW1 and SW2 are provided.

  The low-voltage power supply circuit 15 generates a power supply voltage Vcc (for example, +5 [V]) required by each circuit in the leakage detection device 10 based on the low-voltage power supply power (for example, +12 [V]) on the vehicle. .

  The microcomputer 11 controls each part by executing a program incorporated in advance, and realizes a function required for the leakage detection device 10.

  The pulse generation circuit 12 includes a switching element (not shown), and generates a signal SG2 based on the power supply voltage Vcc supplied from the low-voltage power supply circuit 15 and the signal SG1 output from the microcomputer 11. The signal SG1 is a pulse signal (rectangular wave), and the signal SG2 is a pulse signal that appears on the wiring 31 having the same waveform as the signal SG1. In the present embodiment, the pulse waveform of the signal SG2 is generated based on the low-voltage power supply voltage Vcc. However, the voltage of the signal SG2 can be increased by providing a booster circuit inside the pulse generation circuit 12. It is.

  As shown in FIG. 1, the output terminal of the pulse generation circuit 12 is connected to the electrode 23 of the high-voltage power supply circuit 21 via a resistor Rc, a coupling capacitor Cc, and a switching element SW1. Therefore, when the switching element SW1 is on, a pulse signal having a waveform similar to that of the signal SG2 output from the pulse generation circuit 12 can be applied to the electrode 23.

  The voltage detection circuit 13 incorporates an electric circuit such as an amplifier, and performs processing necessary to detect the voltage of the signal SG3 appearing on the wiring 32 at the connection point between the resistor Rc and the coupling capacitor Cc. Further, voltage conversion is performed to generate a signal SG4 having a voltage suitable for processing of the microcomputer 11 from the signal SG3. The signal SG4 is applied to the analog signal input port of the microcomputer 11.

  The nonvolatile memory 14 holds in advance various constant data such as a threshold value for the microcomputer 11 to identify the presence or absence of electric leakage. The microcomputer 11 can refer to each data on the nonvolatile memory 14 as necessary.

  The wiring 33 on the output side of the coupling capacitor Cc is connected to the vehicle body ground 30 via the switching element SW2 and the reference impedance circuit 16. The reference impedance circuit 16 is a circuit configured by connecting a reference resistor Rr and a reference capacitor Cr in parallel.

  As the reference resistor Rr, a device having a resistance value (for example, 100 [MΩ]) suitable for the measurement of the ground fault resistance Rg and having a relatively small resistance value error and stable characteristics is selected. For the reference capacitor Cr, a stable device having a capacitance equivalent to the stray capacitance Cg (for example, 0.1 [μF]) is selected.

  The switching elements SW1 and SW2 can control ON / OFF of the switches by control signals CON1 and CON2 output from the microcomputer 11, respectively. For the switching elements SW1 and SW2, for example, by adopting a device incorporating a photocoupler such as a photo MOS relay, electrical insulation between a high voltage system circuit and a low voltage system circuit is facilitated.

<Basic operation of leakage detection device 10>
FIG. 2 shows signal waveforms at various parts in the basic operation of the leakage detection device 10 shown in FIG. That is, when the switching element SW1 shown in FIG. 1 is turned on and the switching element SW2 is turned off, the pulse generation circuit 12 outputs a pulse signal as the signal SG2 based on an instruction from the microcomputer 11, so that it is shown in FIG. Such a waveform appears in the signals SG2 to SG4.

  That is, the voltage of the signal SG2 rises from the vicinity of 0 [V] to V1 (for example, a voltage similar to Vcc), then falls from V1 to 0 [V], and this operation is repeated at a constant cycle.

  In the circuit shown in FIG. 1, when the pulse of the signal SG2 rises, a current is supplied to the circuit composed of the resistor Rc, the coupling capacitor Cc, the switching element SW1, the ground fault resistor Rg, the stray capacitance Cg, and the vehicle body ground 30. Flows, and the coupling capacitor Cc and the stray capacitance Cg are charged. Therefore, the voltage of the signal SG3 at this time rises exponentially with time. The waveform and peak voltage of the voltage of the signal SG3 are determined by the time constant of the circuit and other constants.

  Further, when the pulse of the signal SG2 falls, the charge accumulated in the coupling capacitor Cc and the stray capacitance Cg is gradually discharged, so that the voltage of the signal SG3 falls exponentially with time. The waveform of the signal SG4 input to the microcomputer 11 is the same as that of the signal SG3.

  The rising speed of the waveform and the peak voltage V2 in the signal SG3 change under the influence of the ground fault resistance Rg and the stray capacitance Cg. Therefore, by comparing the peak voltage of the signal SG3 with a threshold value, it is possible to identify whether or not the ground fault resistance Rg is equal to or less than an allowable value (that is, whether or not there is a leakage).

  Various conventional techniques such as those disclosed in Patent Documents 1 to 3 can be applied to the basic measurement principle of the ground fault resistance Rg as described above.

<Explanation of incorrect leak detection>
FIG. 4A shows the waveforms of the respective parts when the leakage detection device 10 of FIG. 1 does not perform special control with respect to the capacitance change of the coupling capacitor Cc.

  In the leakage detection device 10 of FIG. 1, when the capacitance of the coupling capacitor Cc changes, the time constant of the circuit composed of the resistor Rc, the coupling capacitor Cc, the ground fault resistor Rg, and the stray capacitance Cg changes. Then, as shown in FIG. 4A, the rising and falling characteristics and peak voltage of the signal SG3 change. Therefore, when the ground fault resistance Rg is identified from the peak voltage of the signal SG3, an error is generated by the difference between the peak voltages Vp1 and Vp2 shown in FIG.

  Actually, when the capacitance of Cc decreases due to the deterioration or breakage of the coupling capacitor Cc, (Vp1 <Vp2) as shown in FIG. When it increases, it becomes (Vp1> Vp2).

  The microcomputer 11 stores the peak voltage Vp1 when the capacitance of the coupling capacitor Cc is not changed as a reference value. When the detection value Vp2 of the signal SG3 falls below the reference value, it is determined that a leakage has occurred, but when the capacitance of the coupling capacitor Cc becomes smaller than the normal state. However, since the detection value Vp2 of the signal SG3 increases, there is a possibility that the microcomputer 11 may be determined to be in a safe state even though the ground fault resistance Rg is actually outside the allowable range. Conversely, when the capacitance increases, there is a possibility that the ground fault resistance Rg may actually be erroneously determined to be dangerous although it is within the allowable range.

<Description of Characteristic Operation of Electric Leakage Detecting Device 10>
FIG. 3 shows a main operation procedure of the leakage detecting apparatus 10 shown in FIG. That is, the microcomputer 11 in the leakage detection device 10 executes the process according to the procedure of FIG. 3 to realize a characteristic function. FIG. 4B shows signal waveforms at various parts when the leakage detection device 10 corrects the pulse frequency with respect to the capacitance change of the coupling capacitor Cc.

  In step S11, the microcomputer 11 identifies whether or not the ignition (IG) of the vehicle has just been switched from off to on. If it is immediately after IG ON, it will progress to S12 next, and if it is not immediately after IG ON, it will progress to S13. Note that the information on IG on / off can be obtained from the electronic control unit 100.

  In step S <b> 12, the microcomputer 11 performs a leakage check in the “high speed mode”. Specifically, in the “high speed mode”, the occurrence of some measurement errors is ignored, and the measurement of the ground fault resistance is performed without correcting the pulse signal in a state where the measurement of the capacitance fluctuation in the coupling capacitor Cc is omitted. Determine leakage current. For example, by comparing the peak voltage V2 of the signal SG4 with the threshold voltage in the state shown in FIG. 2, it is identified whether or not the resistance value of the ground fault resistance Rg is within an allowable range.

  It is desirable that at the timing immediately after IG is turned on, it is possible to quickly determine whether or not the vehicle can start traveling safely rather than the detection accuracy of the ground fault resistance. Therefore, at this timing, the microcomputer 11 automatically selects the “high-speed mode” in which priority is given to reducing the detection time over the detection accuracy.

  In step S13, the microcomputer 11 identifies whether it is time to measure the ground fault resistance. For example, the microcomputer 11 recognizes that it is time to measure the ground fault resistance periodically or every time the electronic control unit 100 or the like gives an instruction to start measurement, and proceeds to the next S14. .

  In step S <b> 14, the microcomputer 11 performs measurement related to the variation in capacitance in the coupling capacitor Cc. That is, the Cc capacitance fluctuation that may be caused by factors such as component deterioration is measured. The process for measuring the capacitance variation will be described in detail later.

  In step S15, the microcomputer 11 automatically corrects the control parameter for measuring the ground fault resistance by using the result of the process in S14. Specifically, the repetition frequency of the pulse signals of the signals SG1 and SG2 is corrected as a control parameter.

  For example, as shown in FIG. 4B, when the capacitance of the coupling capacitor Cc decreases, the peak voltage of the signal SG3 is changed by correcting the frequency of the signal SG1 to be increased. Can be suppressed. Conversely, when the capacitance of the coupling capacitor Cc increases, the peak voltage of the signal SG3 can be prevented from fluctuating by correcting the frequency of the signal SG1 to decrease.

  In step S16, the microcomputer 11 performs ground fault resistance measurement in the same manner as in S12, and performs a leakage check. However, in this case, since the control parameter is corrected in the previous S15, the fluctuation of the peak voltage or the like in the signal SG3 is suppressed even when the fluctuation of the capacitance of the coupling capacitor Cc occurs. And high-precision measurement is possible. That is, the “high accuracy mode” is executed in S14 to S16. In the “high accuracy mode”, the time required for measurement is slightly longer in order to execute S14, but it is desirable that the detection accuracy be higher than the required time at normal timing.

<Description of Processing for Measuring Cc Capacitance Variation (1)>
In the leakage detection device 10 shown in FIG. 1, the variation in the capacitance of Cc can be measured using the reference impedance circuit 16. Specifically, processing is performed as described below.

  S01: The switching element SW1 is turned off, and the ground fault resistance Rg, the stray capacitance Cg and the like are disconnected from the output side of the coupling capacitor Cc. Further, the switching element SW2 is turned on, and the output terminal of the coupling capacitor Cc is connected to the reference impedance circuit 16 via the wiring 33 and the switching element SW2.

  S02: In the above state, the pulse of the signal SG2 is output, and the peak voltage Vpx (not shown) of the waveform of the signal SG3 is measured by the microcomputer 11.

  S03: The capacitance variation of Cc is calculated based on the difference or ratio between the peak voltage Vpx measured in S02 and the peak voltage reference value Vpr. The peak voltage reference value Vpr corresponds to the peak voltage that appears in the signal SG3 when the capacitance of Cc is not changed from the reference value at the time of design and the reference impedance circuit 16 is connected. Constants registered in the nonvolatile memory 14 can be used.

  That is, in the time constant circuit constituted by the resistor Rc, the coupling capacitor Cc, and the reference impedance circuit 16, the only factor that greatly fluctuates is the capacitance of Cc, and the signal SG2 input to this circuit The voltage is also known. Therefore, the fluctuation component of the capacitance of the coupling capacitor Cc is dominant for the cause of the deviation of (Vpx−Vpr) in the peak voltage of the signal SG3. Note that the reference impedance circuit 16 is energized with the SW2 turned on only when detection is performed, so that deterioration hardly occurs and impedance variation hardly occurs.

<Modification of Pulse Signal Correction Control>
<Pulse duty ratio control>
FIG. 5A shows the waveforms of the respective parts when correcting the duty ratio of the pulse with respect to the capacitance change of the coupling capacitor Cc. That is, the duty ratio of the pulse can be applied as the “control parameter” in step S15 in FIG. 3, and in the case of duty ratio control, the signal waveform is as shown in FIG.

  For example, as shown in FIG. 5A, when the capacitance of the coupling capacitor Cc decreases, the frequency is increased by adjusting the duty ratio of the signal SG2 and reducing the ratio of the ON section. Similarly to the case, it is possible to suppress the fluctuation of the peak voltage of the signal SG3. On the contrary, when the capacitance of the coupling capacitor Cc increases, the duty ratio of the signal SG1 is adjusted to increase the ratio of the on period, thereby suppressing the fluctuation of the peak voltage of the signal SG3.

<Pulse amplitude control>
FIG. 5B shows the waveforms of the respective parts when correcting the amplitude of the pulse with respect to the capacitance change of the coupling capacitor Cc. That is, the amplitude of the pulse can be applied as the “control parameter” in step S15 in FIG. 3. In the case of amplitude control, the signal waveform is as shown in FIG.

  For example, as shown in FIG. 5B, when the capacitance of the coupling capacitor Cc decreases, the frequency is switched from the amplitude voltage V11 to the amplitude voltage V12 so that the amplitude of the signal SG2 increases. As in the case of increasing the value, it is possible to suppress the fluctuation of the peak voltage of the signal SG3. On the contrary, when the capacitance of the coupling capacitor Cc increases, it is possible to suppress the peak voltage of the signal SG3 from changing by increasing the amplitude of the signal SG2.

  5B, it is necessary to add a function for changing the amplitude of the pulse in the pulse generation circuit 12 shown in FIG.

<Modification of the configuration of the leakage detection device 10>
<Configuration example (2)>
FIG. 6 shows a configuration example (2) of the leakage detection device in the embodiment of the present invention. In earth leakage detection device 10B shown in FIG. 6, ground wire 16B is connected instead of reference impedance circuit 16 in FIG. The rest of the configuration is the same as in FIG.

  In the leakage detection device 10B of FIG. 6, when the switching element SW2 is turned on, the output side of the coupling capacitor Cc is connected to the vehicle body ground 30 via the wiring 33, the switching element SW1, and the ground line 16B. Therefore, in this case, the pulse signal of the signal SG2 is applied to both ends of a serial CR time constant circuit composed of the resistor Rc and the coupling capacitor Cc. Then, the voltage across the coupling capacitor Cc is applied to the input of the voltage detection circuit 13 as the signal SG3.

  In this case, the amplitude voltage of the signal SG2 is known (constant), and the resistance value of the resistor Rc hardly changes. Therefore, it is assumed that the capacitance of the coupling capacitor Cc has not changed from the reference value at the time of design. Then, the voltage (theoretical value) at each time point generated in the signal SG3 can be obtained by calculating an exponential function including a time constant. However, since the capacitance of Cc actually fluctuates, the voltage at each time point generated in the signals SG3 and SG4 (transient voltage before reaching the saturation level) deviates from the voltage obtained by calculation. .

  Conversely, the reference value at the time of design is applied as the capacitance of Cc, and the voltage (theoretical value) at each time point of the signal SG3 calculated from the exponential function including this time constant is detected by the microcomputer 11 actually. The deviation of the signal SG4 from the voltage at each point in time becomes a value corresponding to the fluctuation of the capacitance of Cc.

  Therefore, the leakage detection device 10B shown in FIG. 6 is slightly different from the leakage detection device 10 of FIG. 1 in the content of the process of measuring the Cc capacity fluctuation in step S14 of FIG. However, by detecting the voltage of the signal SG4 at a certain point in time by the microcomputer 11 and calculating the deviation between this voltage and the theoretical value, the leakage detection device 10B of FIG. be able to. It is also possible to measure the required rise time instead of the voltage, and to detect the change in capacitance based on this time difference.

<Configuration example (3)>
FIG. 7 shows a configuration example (3) of the leakage detection device in the embodiment of the present invention. In the leakage detection device 10C shown in FIG. 7, the function for measuring the deviation of the capacitance of the coupling capacitor Cc is omitted, and instead, the function of detecting the temperature in the vicinity of the coupling capacitor Cc. Is installed.

  That is, the thermistor 29 and the resistor R01 are added in the leakage detection device 10C shown in FIG. The thermistor 29 is disposed in the vicinity of the coupling capacitor Cc. The signal SGth output from the thermistor 29 is applied to the analog signal input port of the microcomputer 11.

  Therefore, the microcomputer 11 shown in FIG. 7 can grasp the ambient temperature of the coupling capacitor Cc by acquiring the level of the signal SGth. Further, the microcomputer 11 shown in FIG. 7 executes the same process as step S15 in FIG. 3 in response to the change in the ambient temperature of Cc.

  That is, the capacitance of the coupling capacitor Cc tends to fluctuate with changes in ambient temperature, and the tendency of this fluctuation can be grasped in advance. Therefore, in the leakage detection device 10C of FIG. 7, the microcomputer 11 estimates the variation in the capacitance of Cc based on the change in the ambient temperature of the coupling capacitor Cc (corresponding to S14), and the estimation result is a step. In S15, it is reflected in the control parameter of the pulse signal.

  The correspondence relationship between the temperature change of the coupling capacitor Cc and the change in capacitance may be specified by a calculation formula, or may be specified using a constant table that can be arranged on the nonvolatile memory 14. May be.

  As described above, in any of the leakage detection device 10 of FIG. 1, the leakage detection device 10B of FIG. 6, and the leakage detection device 10C of FIG. Since the control parameter of the pulse signal is automatically corrected, fluctuations in the peak voltage of the signal SG3 can be suppressed and the measurement error can be reduced when measuring the ground fault resistance Rg.

10, 10B, 10C Leakage detection device 11 Microcomputer 12 Pulse generation circuit 13 Voltage detection circuit 14 Non-volatile memory 15 Low voltage system power supply circuit 16 Reference impedance circuit 16B Ground wire 21 High voltage system power supply circuit 22, 23 Electrode 29 Thermistor 30 Car body ground 31 , 32, 33 Wiring 100 Electronic control unit Cc Coupling capacitor Rc, R01 Resistor Rg Ground fault resistance Cg Floating capacitance Rr Reference resistor Cr Reference capacitor SW1, SW2 Switching element SG1, SG2, SG3, SG4, SGth signal CON1, CON2 Control signal Vcc Power supply voltage Vp1, Vp2 Peak voltage V11, V12 Amplitude voltage

Claims (4)

A coupling capacitor having one end connected to a DC power source, a pulse generating unit connected to the other end of the coupling capacitor via an impedance to supply a pulse signal, and a voltage at a connection point between the impedance and the coupling capacitor A leakage detection device including: a voltage detection unit that detects a leakage current of the DC power supply based on a comparison between a voltage detected by the voltage detection unit and a threshold value;
A pulse signal output from the pulse generator so as to detect a change in the capacitance of the coupling capacitor and suppress a change in the peak value of the voltage when the change in the capacitance is detected. Capacity fluctuation correction control unit for correcting
A leakage detection device comprising: The capacitance variation correction control unit corrects at least one of a frequency, an amplitude, and a duty ratio of a pulse signal output from the pulse generation unit with respect to a variation in capacitance in the coupling capacitor.
The leakage detection device according to claim 1. Prior to the leakage detection process by the leakage detection unit, a high-accuracy mode in which the capacitance variation correction control unit detects the capacitance variation and corrects the pulse signal, and the capacitance variation correction control unit A mode selection unit that selectively switches between at least two modes: a high-speed measurement mode that omits detection of fluctuations in capacitance and correction of the pulse signal;
The leakage detecting apparatus according to claim 1 or 2, wherein The mode selection unit automatically selects the high-speed measurement mode when a condition that requires high-speed operation is satisfied.
The leakage detection device according to claim 3.

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