JP4331006B2 - GAIN ADJUSTMENT METHOD FOR BANDPASS FILTER AND SYNCHRONOUS RECTIFICATION CIRCUIT built in DC circuit ground fault detection device and DC circuit ground fault detection device - Google Patents

Description

In substations, power plants and large-scale plants, DC circuits are used to control equipment. A normal DC circuit is connected to a DC ground fault overvoltage relay 64D (referred to as a DC ground fault relay 64D) defined by JEM1090 (Japan Electrical Manufacturers Association Standard 1090). The adjustment method of the bandpass filter / synchronous rectifier circuit of the present invention is connected to a DC circuit instead of the DC ground fault relay 64D when a DC ground fault occurs, and an AC signal is connected between the N pole of the DC circuit and the ground. The present invention relates to a gain adjustment technique for a band-pass filter / synchronous rectifier circuit built in a DC circuit ground fault detection device that generates and detects a leakage current flowing from the AC signal to a ground fault resistance by a current transformer ZCT.

Resistors and capacitors are used in the bandpass filter unit and the synchronous rectifier circuit unit, but these components include an error range. Due to the balance between cost and characteristics, the parts actually used have an error of about ± 1% for the resistance and ± 10% for the capacitor. Since errors of these components constituting the circuit are accumulated, adjustment of the degree of amplification (referred to as gain) is always required for measurement (see Non-Patent Document 1).

Conventionally, a semi-fixed resistor is provided for each of the bandpass filter unit and the synchronous rectifier circuit unit, and the semi-fixed resistor is manually adjusted so that the output when the reference value is input to the measurement input becomes the adjustment value when measured with a measuring instrument. There was a need to adjust.
FIG. 3 shows an example of a gain adjustment circuit conventionally provided in a band-pass filter unit or a synchronous rectification circuit unit. With a predetermined calibration signal input, the output for the input signal is measured by a measuring instrument, and a semi-fixed resistor VR1 is set so that the output becomes an expected value corresponding to the predetermined calibration signal input. The gain was adjusted while turning manually.

Okamura Ikuo, “Design of Optoelectronic Circuits”, CQ Publishing, September 30, 1990, p. 178-180

However, in the conventional method, since the semi-fixed circuit is manually adjusted, there is a problem in that the adjustment varies due to the poorness of the work, the adjustment takes time, and the production cost increases. The breakdown of time includes test condition setting time, measuring instrument preparation and connection time, and adjustment time by turning a semi-fixed resistor. It took half a day to a day to adjust the process manually. Further, since the semi-fixed resistor in the adjustment circuit is expensive, there is a problem that the cost of the apparatus is increased. In addition, since the capacitance and resistance values of components such as capacitors and resistors change over time, they gradually deviate from the gain adjustment values adjusted at the time of factory shipment. As a result, maintenance work is required for a long period of time, and it is necessary for the engineer to go to the installation site and perform gain adjustment as described above. It was.

Therefore, the object of the present invention is to perform gain adjustment automatically, thereby eliminating the need for manual gain adjustment time, reducing the cost of gain adjustment during the manufacturing process and maintenance, and adding expensive semi-fixed resistors. An object of the present invention is to provide a method for adjusting a band-pass filter / synchronous rectifier circuit that can be eliminated to suppress an increase in cost.

In order to achieve the above object, in the present invention, when a DC ground fault occurs, the DC circuit is connected to the DC circuit instead of the DC ground fault relay 64D, and an AC signal is generated between the N pole and the ground of the DC circuit. , The leakage current that flows from the AC signal to the grounding resistance,
In a DC circuit ground fault detection device that detects by a zero-phase current transformer ZCT connected to the DC circuit, a mode switch that switches the band-pass filter / synchronous rectifier circuit built in the DC circuit ground fault detection device between a calibration mode and a measurement mode. With means,
In the calibration mode, the calibration rectangular wave a is input from the calibration rectangular wave generation circuit to the bandpass filter without passing through the ZCT inside the DC circuit ground fault detection device , and is obtained by passing through the bandpass filter. The wave a1 is input to the synchronous rectification circuit and the waveform shaping circuit, and the synchronous rectification circuit performs synchronous rectification by the rectangular wave a2 obtained by passing through the waveform shaping circuit. Convert to get value X, which
And a constant W / X representing the amplification degree (gain) of the bandpass filter from the expected value W of the output with respect to the calibration rectangular wave a, and
In the measurement mode, the measurement input b is input from the measurement input terminal to the bandpass filter, the sine wave b1 obtained by passing through the bandpass filter is input to the synchronous rectifier circuit, Synchronous rectification is performed by the reference rectangular wave c generated from the synchronous rectification reference rectangular wave generation circuit, and the value Y is obtained by performing AD conversion on the synchronously rectified output by the AD conversion unit,
Using the value Y and the constant W / X,
A gain adjustment method for a band-pass filter / synchronous rectifier circuit built in a DC circuit ground fault detector , characterized in that a measurement result value is obtained by calculating a measurement result value A = Y × W / X by a calculation unit. Is provided.

Further, in the direct current alley fault detector,
When the activation signal receiving unit receives the activation signal from the DC ground fault overvoltage relay 64D connected to the electric circuit, the operation mode is switched to the measurement mode by the mode switching means. The present invention provides a DC circuit ground fault detection device using the gain adjustment method according to claim 1.

  As described above, according to the present invention, the gain adjustment is automatically performed, thereby eliminating the need for manual gain adjustment time, reducing the cost of gain adjustment during the manufacturing process and maintenance, and providing an expensive semi-fixed resistor. It is possible to provide a bandpass filter / synchronous rectifier circuit gain adjustment method that can be eliminated to suppress an increase in cost, and a DC circuit ground fault detection device using the gain adjustment method.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of an automatic gain adjustment circuit of a band-pass filter / synchronous rectifier circuit according to the present invention.

Reference numeral 1 is a calibration rectangular wave generating circuit for generating a calibration rectangular wave, 2 is a measurement input terminal for inputting a measurement input during measurement, 3 is a band-pass filter, and 4 is a synchronous rectifier circuit. 3 and 4 constitute a band-pass filter / synchronous rectifier circuit.

The synchronous rectifier circuit is based on the logic of the rectangular wave for synchronous rectification (see Japanese Patent Laid-Open No. 8-182179) and is used to separate the leakage current of the resistance component (R component) from the total leakage current in the DC circuit. It is A low-frequency voltage is generated in the electric circuit, and the ground fault current is synchronized by utilizing the fact that the phase of the ground capacitance component (referred to as C component) and the resistance component (referred as R component) are shifted by 90 degrees. Based on the change point of the rectifying rectangular wave, the leakage current for C is canceled and the current for R is separated.

Reference numeral 5 denotes a waveform shaping circuit, which outputs a rectangular wave whose High-Low state is sequentially switched at the zero cross point of the sine wave when the sine wave output from the band pass filter passes.

6 is a circuit for generating a synchronous rectification reference rectangular wave, and the current transformer provided in a place not passing through the measurement circuit so that the low-frequency voltage generated in the circuit can be used as a reference for synchronous rectification. The reference rectangular wave used when performing synchronous rectification is generated using the signal detected and output by.

Reference numeral 70 denotes an AD converter (referred to as ADC) that converts analog data into digital data. Reference numeral 71 denotes a calculation unit that performs a calculation based on a signal output from the ADC 70. These 70 and 71 are provided inside the microcomputer 7 connected to the synchronous rectifier circuit.

The automatic gain adjustment circuit of the band-pass filter / synchronous rectifier circuit is provided with three mode switching means for switching between the calibration mode and the measurement mode. First, there is provided first mode switching means 8 for connecting the calibration rectangular wave generating circuit 1 in the calibration mode and the measurement input terminal 2 in the measurement mode to the bandpass filter. It consists of a mechanical changeover switch. Moreover, you may comprise with a semiconductor switch.

Second, the second mode switching means 72 provided as a software branching process inside the microcomputer 7 leads to a calibration mode processing routine in the calibration mode, and a measurement mode processing routine in the measurement mode. Is programmed to lead to

Thirdly, the waveform shaping circuit 5 is connected to the synchronous rectification circuit 4 in the calibration mode and the synchronous rectification reference rectangular wave generation circuit 6 is connected to the synchronous rectification circuit 4 in the measurement mode. A mechanical or semiconductor switch may be used, or it may be realized inside the microcomputer.

In this way, a band-pass filter / synchronous rectifier circuit is configured.

Next, the operation in the calibration mode will be described. In the calibration mode, the three switching means 8, 72, 9 are switched to the calibration mode. First, the calibration rectangular wave a is input from the calibration rectangular wave generating circuit 1 to the bandpass filter 3. The calibration rectangular wave is used when the apparatus is calibrated, and is used to determine an output value (expected value) after calculation for a predetermined input. In the present invention, calibration is performed using an output value (expected value) W after calculation expected for a predetermined calibration rectangular wave a.

The bandpass filter 3 amplifies only the fundamental wave of the calibration rectangular wave a and outputs a sine wave a1. Therefore, the desired value, that is, the expected value W can be calculated in advance from the voltage level (for example, 5 V) of the calibration rectangular wave a. That is, the voltage of the sine wave a1 serving as the fundamental wave can be calculated from the voltage level of the calibration rectangular wave a, and the expected value W when the voltage of the sine wave a1 serving as the fundamental wave is input is determined in advance. This expected value W is an ideal value that is desired to be output even though there is an error in the parts used in the circuit. The input sine wave a1 that has passed through the bandpass filter 3 is input to the synchronous rectification circuit 4 and the waveform shaping circuit 5. A rectangular wave a2 is obtained from the sine wave a1 that has passed through the waveform shaping circuit 5, and the synchronous rectification circuit 4 performs synchronous rectification by the input sine wave a1 and the rectangular wave a2.

By calibrating, it is possible to prevent measurement errors caused by changes in the capacitance value and resistance value of the component over time and changes in the capacitance value and resistance value of the component due to temperature changes.

The output of the synchronous rectifier circuit 4 is an integrated value of a full-wave rectified waveform obtained by folding the output waveform of the bandpass filter 3 at the zero cross point. This output value is AD converted by the ADC 70 of the microcomputer 7 to obtain a converted value (referred to as an ADC value) X. This value X is a measured value including an error of a component used in the circuit. After that, through the second mode switching means 72 switched to the calibration mode by software, the arithmetic unit 71 calculates a constant W / X representing the amplification degree (gain) from the ADC value X and the expected value W. The In the measurement mode, measurement is performed using this constant W / X.

Next, the operation in the measurement mode will be described. In the measurement mode, the three switching means 8, 72, 9 are switched to the measurement mode. First, the measurement input b is input from the measurement input terminal 2 to the bandpass filter 3. A sine wave b <b> 1 obtained by passing through the band pass filter 3 is input to the synchronous rectifier circuit 4. In addition, the synchronous rectification reference rectangular wave generation circuit 6 is connected to the synchronous rectification circuit 4 when the third mode switching means 9 is switched to the measurement mode. The reference rectangular wave input to the synchronous rectification circuit 4 by the synchronous rectification reference rectangular wave generation circuit 6 is phase-adjusted in advance so that an output of resistance (R) is output. Since synchronous rectification is performed based on the change point of the reference rectangular wave, measurement can be performed while absorbing the phase shift in the circuit conditions.

When the input b from the measurement input terminal 1 is a leakage current of a resistance component (R), the output of the synchronous rectifier circuit 4 is the integrated value of the full-wave rectified waveform obtained by folding the output waveform of the bandpass filter 3 at the zero cross point. It becomes. This output value is AD converted by the ADC 70 of the microcomputer 7 to obtain a converted value (referred to as an ADC value) Y. This value Y is a measurement value in the measurement circuit. Thereafter, the calculation unit 71 performs calculation using the ADC value Y and the constant W / X representing the gain obtained in the calibration mode through the second mode switching means 72 switched to the measurement mode by software. .

Assuming that the constant representing the gain obtained from the calibration mode is G, if G = W / X and the true measured value is A, then A = Y × G, that is, A = Y × (W / X) Can be calculated. By using the gain G = W / X obtained by calibration in this way, the measured value can always obtain a leakage current of R that is correct regardless of the circuit conditions.

As described above, according to the method of the present invention, it is not necessary to adjust the semi-fixed resistance, which has been conventionally required, and gain adjustment is automatically performed. Therefore, the time required for the adjustment and the cost associated with it become unnecessary, and the gain adjustment circuit as shown in FIG. 3 becomes unnecessary, so that an increase in cost can be suppressed. In addition, maintenance work associated with deviations in the capacitance values and resistance values of components due to secular changes is no longer necessary, and an increase in cost can be suppressed.

As a requirement to completely eliminate the adjustment, it is necessary not to saturate the waveform of the bandpass filter / synchronous rectifier circuit. For this purpose, for example, the maximum value of the input voltage may be halved when it is manually adjusted with a semi-fixed resistor. Although the magnitude of the measurement signal is halved, if the accuracy of ADC is increased or the number of ADC readings is increased so that the apparent accuracy is the same, a measurement value can be obtained with almost the same measurement accuracy. The ADC accuracy can be improved by using a dedicated ADC element, integrating with a microcomputer counter, switching the range, or using a microcomputer with a high precision ADC. .

Next, the calibration rectangular wave generating circuit 1 will be described. FIG. 4 shows an example of a calibration rectangular wave generating circuit. The output of the microcomputer is enhanced by a CMOS IC 42 and output. Since the switching power supply used for the power supply of the microcomputer is ± 5%, this circuit can be adjusted with an accuracy of almost ± 5%.

FIG. 5 shows another example of the calibration rectangular wave generating circuit 1. A stable voltage can be supplied by the reference voltage IC53. A reference voltage IC53 having an accuracy of ± 0.5% can be easily obtained. Therefore, an adjustment with an accuracy of about ± 0.5% can be easily realized.

FIG. 6 shows a circuit example when the input of the bandpass filter unit is a current input as another example of the calibration rectangular wave generating circuit 1. Since the output voltage of the CMOS inverter IC 65 is 0V or 5V, if the resistor R62 is set to twice R61, that is, R62 = 2 × R61, the DC component of the current of the calibration rectangular wave can be reduced to 0, and the bandpass filter section Waveform disturbance when the input is switched by mode switching can be reduced. The accuracy drops to ± 10% compared to the above example, but the switching speed can be increased.

FIG. 2 shows an example of a DC circuit ground fault detection apparatus to which the method of the present invention is applied. A case where a ground fault RE occurs in the electric circuit 1 among the plurality of electric circuits is shown. ZCT (1) to ZCT (n), which are zero-phase current transformers, are provided in the electric circuit, and the ZCT is connected to a DC electric circuit ground fault detector. The DC circuit ground fault detection device is provided with the bandpass filter / synchronous rectifier circuit described above.

In normal times without a ground fault RE, the P pole, ground pole, and N pole of the DC circuit are connected to a DC ground fault relay 64D (not shown). At normal time, the DC circuit ground fault detector 12 is set to operate in the calibration mode by a program stored in the microcomputer. Reference numeral 11 denotes a DC power supply, which supplies power to the electric circuit.

When the ground fault RE occurs, the DC ground fault relay 64D connected to the electric circuit outputs a start signal. The DC circuit ground fault detection device 12 that has received the startup signal at a startup signal receiving unit (not shown) is connected to the P pole, ground electrode, and N pole of the circuit instead of the DC ground fault relay 64D. 12 switches to the measurement mode. The AC signal generation circuit generates a low-frequency sine wave voltage in the electric circuit, and the generated sine wave voltage flows from the ground through the ground fault RE through the ZCT 1, so the output from the ZCT 1 is a band-pass filter / synchronous rectification. It is possible to detect the leakage current of the resistance component received by the circuit.

The time of occurrence of a ground fault is difficult to predict, and there are cases where a considerable period has passed since the installation of the equipment. However, since the DC circuit ground fault detection device normally operates in the calibration mode, the circuit is always calibrated until just before the start signal is received from the DC relay 64D, and the latest gain G is obtained at that time. . For this reason, when a ground fault occurs, the true measured value can be calculated from the measured value using the latest gain G, regardless of the secular change of the capacitance value and resistance value of the component. The value of the ground fault current of the component can be accurately detected.

Since the present invention is a method applicable to a bandpass filter / synchronous rectifier circuit, it can be applied to the field of current and voltage vector measurement using a bandpass filter / synchronous rectifier circuit. In addition, automatic gain adjustment can be applied to a portable ground fault detection device that is easy to operate by downsizing the circuit. Further, it can be applied to a C measuring device by matching a rectangular wave for synchronous rectification with a C component. In addition, in order to obtain the output of the resistance component leakage current in the present invention, the output of the synchronous rectification is used. As the output of the synchronous rectification, a value obtained by integrating the folded waveform with an integral multiple of the period of the generated signal is used. There is a possibility that more accurate measurement can be performed by measuring and increasing the output value.

It is a figure of the Example of the automatic gain adjustment circuit of the band pass filter and synchronous rectification circuit of this invention. It is the figure which showed the example of the DC electric circuit ground fault detection apparatus to which this invention is applied. It is the figure which showed the example of the conventional gain adjustment. It is the figure which showed the example of the generator circuit of the calibration rectangular wave. It is the figure which showed the example of the generator circuit of the calibration rectangular wave. It is the figure which showed the example of the generator circuit of the calibration rectangular wave.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Calibration rectangular wave generation circuit 2 Measurement input terminal 3 Band pass filter 4 Synchronous rectification circuit 5 Waveform shaping circuit 6 Synchronous rectification reference rectangular wave generation circuit 7 Microcomputer 70 AD conversion part 71 Calculation part 11 DC power supply 12 DC electric circuit ground fault detection apparatus 31 Operational amplifier 42 CMOS inverter 53 Reference voltage IC
54 operational amplifier 65 CMOS inverter

Claims (2)

When a DC ground fault occurs, it is connected to a DC circuit in place of the DC ground fault relay 64D, an AC signal is generated between the N pole and the ground of the DC circuit, and a leakage current flowing from the AC signal to the ground fault resistance is generated. ,
In a DC circuit ground fault detection device that detects by a zero-phase current transformer ZCT connected to the DC circuit, a mode switch that switches the band-pass filter / synchronous rectifier circuit built in the DC circuit ground fault detection device between a calibration mode and a measurement mode. With means,
In the calibration mode, the calibration rectangular wave a is input from the calibration rectangular wave generation circuit to the bandpass filter without passing through the ZCT inside the DC circuit ground fault detection device , and is obtained by passing through the bandpass filter. The wave a1 is input to the synchronous rectification circuit and the waveform shaping circuit, and the synchronous rectification circuit performs synchronous rectification by the rectangular wave a2 obtained by passing through the waveform shaping circuit. A value X is obtained by conversion, and the expected value W of the output for the value X and the calibration rectangular wave a
To calculate a constant W / X representing the amplification factor (gain) of the bandpass filter by the calculation unit,
In the measurement mode, the measurement input b is input from the measurement input terminal to the bandpass filter, the sine wave b1 obtained by passing through the bandpass filter is input to the synchronous rectifier circuit, Synchronous rectification is performed by the reference rectangular wave c generated from the synchronous rectification reference rectangular wave generation circuit, and the value Y is obtained by performing AD conversion on the synchronously rectified output by the AD conversion unit,
Using the value Y and the constant W / X,
Measurement result value A = Y × W / X
A gain adjustment method for a band-pass filter / synchronous rectifier circuit built in the DC circuit ground fault detection device, wherein the value of the measurement result is obtained by calculating the value of the signal by a calculation unit. In the DC circuit ground fault detection device,
When the activation signal receiving unit receives the activation signal from the DC ground fault overvoltage relay 64D connected to the electric circuit, the operation mode is switched to the measurement mode by the mode switching means. The DC circuit ground fault detection device using the gain adjustment method according to claim 1, wherein