JP2007187454A - Insulation resistance drop detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an insulation resistance drop detector capable of highly accurate self-diagnosis. <P>SOLUTION: The insulation resistance drop detector 50 can perform self-diagnosis only by making different(i.e., by altering control of) the duty ratio of pulse signals 65 output from an oscillator circuit 60 at normal times (while insulation resistance is being monitored) and during self-diagnosis. It is therefore possible to perform self-diagnosis without having to add new circuits nor parts to a conventional insulation resistance drop detector. Since the frequency of pulse signals 65 is not altered while insulation resistance is being monitored and at self-diagnosis, it is possible to exclude the effects of variations in attenuation factor due to a band pass filter 90. It is therefore possible to highly accurately perform self-diagnosis. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an insulation resistance decrease detector, and more particularly to an insulation resistance decrease detector having a self-abnormality diagnosis function for detecting an abnormality of the insulation resistance decrease detector itself.

  A circuit that detects a decrease in insulation resistance between the power supply and the ground (insulation resistance drop detection) for a power supply that is insulated from the ground (vehicle body), such as a battery (DC power supply) mounted on a vehicle such as an automobile. It is necessary to provide a container.

For example, Japanese Patent Application Laid-Open No. 2004-53367 (Patent Document 1) discloses a circuit for performing a failure diagnosis of an insulation resistance lowering detector. The fault diagnosis apparatus disclosed in Japanese Patent Application Laid-Open No. 2004-53367 (Patent Document 1) has a voltage amplitude when a rectangular wave pulse having a first frequency is supplied to a ground fault detection circuit (insulation resistance reduction detector). The occurrence of a ground fault is detected based on the voltage amplitude value detected by the detecting means. This fault diagnosis apparatus is configured to detect a ground fault based on a voltage amplitude value detected by a voltage amplitude detection means when a rectangular wave pulse having a second frequency higher than the first frequency is supplied to the ground fault detection circuit. Diagnose the detection circuit.
JP 2004-53367 A JP-A-2005-114496 JP 2005-127721 A JP-A-10-221395

  The insulation resistance reduction detector disclosed in Japanese Patent Application Laid-Open No. 2004-53367 (Patent Document 1) includes a band-pass filter. The bandpass filter is designed to pass a signal having a first frequency and attenuate a signal having a second frequency.

  However, the attenuation rate of the signal of the second frequency varies depending on the characteristics of each filter. For this reason, the voltage amplitude value detected by the voltage amplitude detecting means may be different for each insulation resistance drop detector. Therefore, it is not easy to perform a highly accurate diagnosis with this insulation resistance lowering detector.

  An object of the present invention is to provide an insulation resistance lowering detector capable of performing self-diagnosis with high accuracy.

  In summary, the present invention is an insulation resistance reduction detector that detects a reduction in insulation resistance of an isolated power supply. The insulation resistance lowering detector includes a coupling capacitor, a detection resistor, a bandpass filter, a signal generation unit, and a control circuit. One end of the coupling capacitor is connected to the insulation resistance. The detection resistor has one end connected to the other end of the coupling capacitor. The bandpass filter has an input terminal connected to a connection point between the coupling capacitor and the detection resistor. The signal generator applies a periodically changing signal to the other end of the detection resistor. The control circuit controls the signal generator and detects the voltage output from the bandpass filter. The control circuit detects a decrease in insulation resistance based on the detection voltage. The control circuit instructs the signal generator to generate the first signal during normal operation to detect a decrease in insulation resistance, and sets the same frequency as the first signal during self-diagnosis of the insulation resistance decrease detector. And instructing the signal generator to generate a second signal having a different waveform.

  Preferably, during the normal operation, the control circuit detects a decrease in insulation resistance by comparing a detection voltage corresponding to the first signal with a threshold voltage. During the self-diagnosis, the control circuit compares the detection voltage corresponding to the second signal with the threshold voltage to detect an abnormality in the insulation resistance lowering detector.

More preferably, the first and second signals are signals having different duty ratios.
More preferably, the passband frequency of the bandpass filter is set so that the bandpass filter passes the main component of the frequency components of the first signal.

More preferably, the first and second signals are rectangular wave signals.
More preferably, the duty ratio of the first signal is 50%.

  According to the present invention, failure diagnosis of an insulation resistance drop detector can be performed with high accuracy.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same reference numerals indicate the same or corresponding parts.

FIG. 1 is a block diagram illustrating the configuration of the insulation resistance lowering detector of the present embodiment.
Referring to FIG. 1, insulation resistance reduction detector 50 detects a reduction in insulation resistance Ri with respect to ground 30 of DC power supply 10. Connected to the DC power supply 10 is a circuit system 20 that operates when supplied with a power supply voltage from the DC power supply 10. The DC power supply 10 is a power storage device such as a secondary battery, a fuel cell, or a capacitor used as a vehicle drive motor power supply mounted on an electric vehicle, a hybrid vehicle, or the like.

  In such a vehicle, the ground 30 corresponds to the vehicle body. If the insulation resistance Ri decreases, a person who touches the vehicle body may receive an electric shock. Therefore, detection of the decrease in the insulation resistance Ri is important for safety. Therefore, it is desirable to determine not only the detection of the decrease in the insulation resistance Ri by the insulation resistance decrease detector 50 but also whether or not the insulation resistance decrease detector 50 itself is normal. In consideration of mounting on a vehicle, it is preferable to reduce the insulation resistance drop detector 50 to improve the on-vehicle performance.

  The insulation resistance drop detector 50 includes an oscillation circuit 60 that is a signal generation unit, a detection resistor 70, a coupling capacitor 80, a band pass filter (BPF) 90, a circuit block 91 including an offset circuit and an amplifier circuit, An overvoltage protection diode 92, a resistor 93, a capacitor 94, and a control circuit 110 are provided.

  The oscillation circuit 60 applies a pulse signal 65 that changes at a predetermined frequency (predetermined period Tp) to the node NA. The detection resistor 70 is connected between the node NA and the node N1. The coupling capacitor 80 is connected between the DC power supply 10 that is a leakage detection target and the node N1. The bandpass filter 90 has an input terminal connected to the node N1 and an output terminal connected to the node N2. The passband frequency of the bandpass filter 90 is designed according to the frequency of the pulse signal 65.

  The circuit block 91 is connected between the node N2 and the node N3. The circuit block 91 amplifies a voltage change in the vicinity of a threshold voltage set at the time of insulation resistance detection or self-diagnosis among the pulse signals that have passed through the band pass filter 90. The overvoltage protection diode 92 has a cathode connected to the constant voltage node and an anode connected to the node NB to remove the surge voltage (high voltage, negative voltage). Resistor 93 is connected between nodes N3 and NB. Capacitor 94 is connected between node NB and ground 30. The resistor 93 and the capacitor 94 function as a filter that removes noise from the signal output from the circuit block 91.

  The control circuit 110 controls the oscillation circuit 60. In addition, the control circuit 110 detects the voltage of the node NB and detects a decrease in the insulation resistance Ri based on the detected voltage. Control circuit 110 includes an oscillation command unit 111, an A / D conversion unit 112, and a determination unit 113.

  The oscillation command unit 111 instructs the oscillation circuit 60 to generate the pulse signal 65 and instructs to change the duty ratio of the pulse signal 65. The A / D converter 112 A / D converts the voltage (detected voltage) of the node NB detected at a predetermined sampling period Ts. Since the sampling period Ts is sufficiently shorter than the period Tp of the pulse signal 65, the maximum voltage (peak voltage Vp) and the minimum voltage of the node NB can be detected. The determination unit 113 compares the value of the peak voltage Vp acquired from the A / D conversion unit 112 with a threshold value. Thereby, the control circuit 110 detects the presence or absence of the fall of the insulation resistance Ri, and the circuit abnormality of the insulation resistance fall detector 50 itself.

Next, an operation (insulation monitoring operation) for detecting a decrease in the insulation resistance Ri will be described.
The pulse signal 65 generated by the oscillation circuit 60 is applied to a series circuit including a detection resistor 70, a coupling capacitor 80, an insulation resistor Ri, and a bandpass filter 90. As a result, the node N1 corresponding to the connection point of the detection resistor 70 and the coupling capacitor 80 has a voltage dividing ratio of the insulation resistance Ri and the detection resistor 70 (resistance value Rd): Ri / (Rd + Ri) and the amplitude of the pulse signal 65 ( A pulse voltage having a peak value as a product of the voltage + B) which is a power supply voltage is generated.

  In the pulse voltage generated at the node N1, components other than the frequency of the pulse signal 65 are attenuated by the band-pass filter 90. Of the pulse signal 65 that has passed through the bandpass filter 90, only the voltage change near the threshold voltage is amplified by the circuit block 91. A signal output from circuit block 91 is transmitted to node NB. When a signal is transmitted from the node N3 to the node NB, the surge voltage is removed by the overvoltage protection diode 92, and noise is removed by the resistor 93 and the capacitor 94.

  When the insulation resistance Ri is normal, Ri >> Rd. As Ri increases, the peak voltage Vp becomes substantially equal to the voltage + B. On the other hand, when the insulation resistance Ri is lowered, the voltage division ratio: Ri / (Rd + Ri) is lowered, so that the peak voltage Vp is lowered.

  FIG. 2 is a diagram illustrating the relationship between the insulation resistance Ri and the maximum voltage (peak voltage Vp) at the node NB.

  Referring to FIG. 2, as Ri increases, peak voltage Vp increases and becomes substantially equal to voltage + B. Therefore, if threshold voltage Vt is determined according to the voltage division ratio between the allowable lower limit value of insulation resistance Ri and resistance value Rd of detection resistor 70, control circuit 110 causes maximum value (peak voltage Vp) to change at node NB. ) And the value of the threshold voltage Vt, a decrease in the insulation resistance Ri can be detected.

  FIG. 3 is a diagram for explaining voltage waveforms detected by the control circuit 110 of FIG. 1 when a decrease in the insulation resistance Ri is detected.

  Referring to FIG. 3, when insulation is normal, peak voltage Vp exceeds threshold voltage Vt and reaches maximum voltage Vmax (this voltage is approximately equal to voltage + B). On the other hand, when insulation is abnormal, the peak voltage Vp is smaller than the threshold voltage Vt.

Next, the self-diagnosis operation of the insulation resistance lowering detector 50 will be described.
FIG. 4 is a diagram showing the waveform of the pulse signal 65 during normal times and during self-diagnosis. The “normal time” means “during normal operation for detecting a decrease in insulation resistance”.

  Referring to FIG. 4, pulse signal 65 (first signal) during normal time and pulse signal 65 (second signal) during self-diagnosis are rectangular wave signals. The pulse signal 65 at the time of self-diagnosis has the same frequency as the pulse signal 65 at the normal time and has a different waveform. More specifically, the normal pulse signal 65 has an amplitude + B and a period Tp. Further, the duty ratio of the pulse signal 65 at the normal time is 50%, and the period T1 in which the voltage is + B and the period T2 in which the voltage is 0 are equal.

  On the other hand, the pulse signal 65 at the time of self-diagnosis has the same amplitude (+ B) and the same period (Tp) as the normal time, but the duty ratio is X% (0 <X <100, where X is a value other than 50). Become. FIG. 4 shows an example in which the periods T1 and T2 of the pulse signal 65 at the time of self-diagnosis satisfy T1> T2 (an example in which the duty ratio X satisfies 50 <X <100). Thus, the duty ratio of the pulse signal 65 is changed from 50% during the self-diagnosis. The passband frequency of the bandpass filter 90 is set so that the bandpass filter 90 passes the main component of the frequency components of the pulse signal 65 during normal operation. Thereby, at the time of self-diagnosis, the spectrum of the oscillation frequency component (the so-called fundamental wave component) in the signal after passing through the band-pass filter 90 becomes small.

  Elements that can be changed by the control from the control circuit 110 in the pulse signal 65 include a frequency (period), a duty ratio, and a type of pulse signal (rectangular wave, sine wave, etc.). In the present embodiment, the pulse signal can be easily controlled by changing the duty ratio of the pulse signal 65 between the insulation monitoring and the self-diagnosis.

  FIG. 5 is a diagram for explaining the relationship between the insulation resistance Ri and the peak voltage Vp when the insulation resistance lowering detector 50 is normal and abnormal.

FIG. 6 is a diagram for explaining voltage waveforms detected by the control circuit 110 of FIG. 1 during self-diagnosis.
Referring to FIGS. 5 and 6, when insulation resistance drop detector 50 is normal, peak voltage Vp is lower than threshold voltage Vt even at the maximum value of insulation resistance Ri. By adjusting the duty ratio of the pulse signal 65, the peak voltage Vp at the time of self-diagnosis can be set in this way.

  On the other hand, the insulation resistance decrease detector 50 may become abnormal due to, for example, a decrease in the resistance value of the detection resistor 70, a change in the characteristics of the bandpass filter 90, or a decrease in the capacitance of the capacitor (coupling capacitor 80 or capacitor 94). . When abnormal, the peak voltage Vp is higher than when normal. Therefore, the control circuit 110 can detect the abnormality of the insulation resistance lowering detector 50 itself by comparing the value of the peak voltage Vp at the node NB and the value of the threshold voltage Vt as in the normal case.

  As shown in FIG. 6, when the insulation resistance lowering detector 50 is normal, the peak voltage Vp is smaller than the threshold voltage Vt. On the other hand, when the insulation resistance drop detector 50 is abnormal, the peak voltage Vp exceeds the threshold voltage Vt.

FIG. 7 is a flowchart for explaining processing of the insulation resistance lowering detector of the present embodiment.
Referring to FIGS. 7 and 1, when the process is started, the ignition switch is set to the on position (IG terminal is turned on) in step S1. As a result, power is supplied to the detector. Next, in step S2, the insulation resistance lowering detector 50 is activated.

  After a predetermined period (for example, several seconds) after activation of the insulation resistance lowering detector 50, the control circuit 110 starts a self-diagnosis process in step S3. In step S4, the control circuit 110 instructs the oscillation circuit 60 to change the duty ratio from 50% to X%.

  Subsequently, in step S5, the control circuit 110 determines whether or not the peak value (the value of the peak voltage Vp) is lower than the value of the threshold voltage Vt. If the crest value <Vt in step S5 (YES in step S5), in step S6, the control circuit 110 determines that the insulation resistance decrease detector is normal (the circuit is normal).

  On the other hand, if the crest value ≧ Vt in step S5 (NO in step S5), in step S12, the control circuit 110 performs a process of displaying that the insulation resistance decrease detector is abnormal (circuit abnormal). In this case, for example, the control circuit 110 turns on a warning lamp. When the process of step S12 ends, the entire process ends.

  In step S7 following step S6, the control circuit 110 instructs the oscillation circuit 60 to return the duty ratio of the pulse signal 65 from X% to 50%. Subsequently, in step S8, the control circuit 110 starts monitoring the insulation resistance Ri.

  In step S9, the control circuit 110 determines whether or not the peak value is higher than the threshold voltage Vt. If the crest value> Vt in step S9 (YES in step S9), in step S10, the control circuit 110 determines that the insulation resistance Ri is normal. When the process of step S10 ends, the entire process ends.

  On the other hand, if the peak value ≦ Vt in step S9 (NO in step S9), control circuit 110 determines that insulation resistance Ri has decreased. In this case, in step S11, the control circuit 110 performs a process of displaying that the insulation resistance has decreased. The control circuit 110 turns on a warning lamp, for example. When the process of step S11 ends, the entire process ends.

  Note that the threshold voltage at the time of self-detection may be different from the threshold voltage Vt at the time of detecting a decrease in insulation resistance Ri. This is because the peak voltage Vp can be set to be lower than the threshold voltage during self-detection by appropriately setting the duty ratio of the pulse signal 65.

  As described above, according to the present embodiment, the control circuit simply changes the duty ratio of the pulse signal output from the oscillation circuit (ie, changes the control) between the normal time (insulation resistance monitoring) and the self-diagnosis. Self-diagnosis can be performed. Therefore, according to the present embodiment, self-diagnosis can be performed without adding a new circuit or component to the conventional insulation resistance lowering detector.

  Further, according to the present embodiment, since the frequency of the pulse signal is not changed between the monitoring of the insulation resistance and the self-diagnosis, it is possible to eliminate the influence of the variation in the attenuation factor due to the band pass filter. Therefore, according to the present embodiment, highly accurate self-diagnosis can be performed.

  In the present embodiment, it has been described that the waveform of a signal generated from the oscillation circuit is a rectangular wave. However, the waveform of the signal emitted from the oscillation circuit 60 is not limited to a rectangular wave as long as the duty ratio of the signal can be changed in the oscillation circuit 60 of FIG.

FIG. 8 is a diagram illustrating another waveform example of a signal generated from the oscillation circuit 60 of FIG.
Referring to FIG. 8, the waveform of signal 65A is a triangular wave. As shown in FIG. 8, in the signal 65A, the period T1 in which the voltage V rises with time in the period Tp is different from the period T2 in which the voltage V falls.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a block diagram explaining the structure of the insulation resistance fall detector of this Embodiment. It is a figure explaining the relationship between the insulation resistance Ri and the maximum voltage (peak voltage Vp) in the node NB. It is a figure explaining the voltage waveform detected by the control circuit 110 of FIG. 1 at the time of the fall detection of the insulation resistance Ri. It is a figure which shows the waveform of the pulse signal 65 in the normal time and the time of self-diagnosis. It is a figure explaining the relationship between the insulation resistance Ri and the peak voltage Vp when the insulation resistance fall detector 50 is normal and abnormal. It is a figure explaining the voltage waveform which the control circuit 110 of FIG. 1 detects at the time of a self-diagnosis. It is a flowchart explaining the process of the insulation resistance fall detector of this Embodiment. It is a figure which shows the example of another waveform of the pulse signal 65 of FIG.

Explanation of symbols

  10 DC power supply, 20 circuit system, 30 ground, 50 insulation resistance drop detector, 60 oscillation circuit, 70 detection resistor, 80 coupling capacitor, 90 band pass filter, 91 circuit block, 92 diode for overvoltage protection, 93 resistor, 94 Capacitor, 110 control circuit, 111 oscillation command section, 112 A / D conversion section, 113 determination section, N1-N3, NA, NB node, Ri insulation resistance, S1-S12, S5A steps.

Claims (6)

An insulation resistance decrease detector for detecting a decrease in insulation resistance of an insulated power source,
A coupling capacitor having one end connected to the insulation resistance;
A detection resistor having one end connected to the other end of the coupling capacitor;
A bandpass filter having an input terminal connected to a connection point between the coupling capacitor and the detection resistor;
A signal generator for applying a periodically changing signal to the other end of the detection resistor;
A control circuit that controls the signal generation unit, detects a voltage output from the band-pass filter, and detects a decrease in the insulation resistance based on a detection voltage;
The control circuit instructs the signal generation unit to generate a first signal during a normal operation for detecting a decrease in the insulation resistance, and the first signal during a self-diagnosis of the insulation resistance decrease detector. An insulation resistance lowering detector that instructs the signal generator to generate a second signal having the same frequency as that of the second waveform but having a different waveform.   The control circuit detects a decrease in the insulation resistance by comparing the detection voltage corresponding to the first signal with a threshold voltage during the normal operation, and the second signal during the self-diagnosis. The insulation resistance lowering detector according to claim 1, wherein an abnormality of the insulation resistance lowering detector is detected by comparing the detection voltage corresponding to the threshold voltage with the threshold voltage.   The insulation resistance lowering detector according to claim 1 or 2, wherein the first and second signals are signals having different duty ratios.   The insulation resistance lowering detector according to claim 3, wherein a passband frequency of the bandpass filter is set so that the bandpass filter passes a main component of the frequency components of the first signal.   The insulation resistance lowering detector according to any one of claims 1 to 4, wherein the first and second signals are rectangular wave signals.   The insulation resistance lowering detector according to any one of claims 1 to 5, wherein a duty ratio of the first signal is 50%.

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