TWI734430B - AC/DC leakage detection circuit - Google Patents

Abstract

An AC/DC leakage detection circuit includes a zero comparator. The primary side is coupled to a power input terminal, and the secondary side is connected to an oscillator. The oscillator provides a fixed frequency voltage to the zero comparator. , To make the zero comparator produce a positive and negative half-cycle symmetrical oscillating pulse current; and a leakage analysis circuit is connected to the secondary side of the zero comparator, when there is no leakage at the power input terminal, the oscillating pulse current analysis is received After processing, a zero-potential voltage value is output; when the power input terminal leaks, the oscillating pulse current output by the zero comparator will advance or delay according to the phase direction of the leakage current, resulting in a positive and negative half-cycle asymmetrical leakage oscillation The pulse current is analyzed and processed to generate a DC output voltage, and it is judged whether the DC output voltage reaches a preset value, that is, it only needs a zero comparator to detect 50Hz~3KHz leakage current and pulsating DC leakage. The purpose of current or pure DC leakage current.

Description

AC/DC leakage detection circuit

The present invention relates to an AC/DC leakage detection circuit, in particular to a leakage detection circuit capable of detecting 50Hz~3KHz AC, pulsating DC or pure DC.

With the development of science and technology, the load becomes more and more diversified, and the leakage current generated is no longer limited to the leakage of pure alternating current. Therefore, the leakage current including pure alternating current, pulsating direct current, and alternating current superimposed direct current is derived, as shown in Figure 1. Knowing that the circuit structure diagram of the AC leakage detection circuit is mainly composed of a leakage circuit (RCD) and a zero current transformer (ZCT). When the RCD detects that the leakage current control relay (Relay) trips the power line.

Traditional leakage detection technology is used in 50/60Hz AC or pulsating DC leakage. It cannot accurately detect high-frequency leakage current and pure DC leakage, and still cannot meet today's needs. Because of the "charging pile" or direct/AC used in electric vehicles The converted "frequency converter" and other products may produce "high frequency" or "pure DC" leakage current.

The above-mentioned pure AC or pulsating DC leakage detection, its core technology is mainly to generate a current with a time-varying amplitude through the primary side of the coil, the principle that the current can be induced on the secondary side of the coil and cooperate with the detection circuit for leakage detection However, the loop's performance in high-frequency detection is extremely poor and cannot meet the demand. The biggest difficulty of the pure DC leakage detection technology is that the DC current does not change with time, so any current cannot be induced by the secondary side of the coil.

In other words, it is impossible to directly use the existing AC detection technology to perform pure DC leakage. Current detection requires two sets of zero current transformers (ZCT) and two sets of detection circuits to detect leakage current with AC components and pure DC respectively. As shown in Figure 2, the conventional AC/DC leakage detection circuit circuit structure diagram is a combination of two sets of leakage circuits (RCD1, RCD2) and two sets of zero comparators (ZCT1, ZCT2). When any group of the leakage current is detected, the relay will be controlled to trip the power line. The AC/DC leakage detection circuit will make the volume too large, difficult to miniaturize, and expensive. Therefore, how to miniaturize the AC/DC leakage detection circuit, reduce manufacturing costs and increase the frequency detection range, will be A major issue that needs to be resolved at present.

In order to solve the lack of miniaturization of the conventional AC/DC leakage detection circuit and increase the frequency detection range, the purpose of the present invention is to provide an AC/DC leakage detection circuit, which only needs to use a zero comparator (ZCT). ) It can detect 50Hz~3KHz leakage current, pulsating DC leakage current, and pure DC leakage current, which not only reduces the cost, but also makes it easier to miniaturize the leakage detection loop, and the frequency detection range is also increased to 3KHz.

In order to achieve the above objective, the main technical feature of the present invention is to provide an AC/DC leakage detection circuit, including a zero phase current transformer, the primary side is coupled to a power input terminal, the secondary side is connected to an oscillator, oscillating The device provides a voltage with a fixed frequency to the zero comparator, so that the zero comparator works in a positive and negative saturation state, and generates a positive and negative half-cycle symmetrical oscillating pulse current; and a leakage analysis circuit is connected to the zero comparator. On the secondary side, when there is no leakage at the power input terminal, it receives the oscillating pulse current and outputs a zero-potential voltage value after rectification, filtering and amplification; when the power input terminal leaks, the zero phase current converter will output The oscillating pulse current will advance or delay according to the phase direction of the leakage current to produce a positive and negative half-cycle asymmetric leakage oscillating pulse current. After rectification, filtering and amplification, a DC output voltage is generated, and it is judged that the DC output voltage reaches a predetermined value. When setting the value, it means that AC/DC leakage is detected.

In order to achieve the above objective, the secondary technical feature of the present invention is to provide the above-mentioned AC/DC leakage detection circuit, wherein the leakage analysis circuit further includes a sampling resistor to compare the oscillating pulse current or leakage current output by the zero phase comparator. The oscillating pulse current is converted into an oscillating voltage; a first low-pass filter is used to filter the oscillating voltage out of a signal above the first cut-off frequency (fc1); a precision rectifier is used to convert the output signal of the first low-pass filter Full-wave rectification into a DC pulsating voltage; a second low-pass filter is used to filter the DC voltage out of noise above a second cut-off frequency (fc2) to generate a DC output voltage; an amplifier is used to amplify the DC output voltage ; And a comparator used to determine whether the amplified DC output voltage reaches a preset value, if it is to output a control signal to a brake fluid drive unit.

To achieve the above object, the secondary technical feature of the present invention is to provide the above AC/DC leakage detection circuit, wherein the thyristor driving unit includes a thyristor connected to the circuit breaker; and a driving circuit connected to the comparator and the thyristor, When the driving circuit receives the control signal output by the comparator, the brake fluid is turned on to control the tripping of the circuit breaker.

10: Power supply unit

11: Bridge rectifier

12: π filter

13: Buck power supply

20: Leakage detection unit

21: Oscillator

22: Zero comparator

30: Leakage analysis circuit

31: sampling resistor

32: The first low-pass filter

33: precision rectifier

34: second low-pass filter

35: Amplifier

36: Comparator

40: Brake fluid drive unit

41: brake fluid

42: drive circuit

Fig. 1 is a circuit structure diagram of a conventional AC leakage detection circuit.

Figure 2 is a circuit structure diagram of a conventional AC/DC leakage detection loop.

Fig. 3 is a block diagram of the AC/DC leakage detection circuit of the present invention.

Fig. 4 is a Bode plot of the frequency response of the first and second low-pass filters of the present invention.

Fig. 5 is a waveform diagram of the sampling resistor signal when there is no leakage in the present invention.

Fig. 6 is a waveform diagram of the sampling resistor signal when the current is leaked according to the present invention.

Fig. 7 is a diagram of the output waveform of the first low-pass filter when the current is leaked according to the present invention.

Fig. 8 is an output waveform diagram of the second low-pass filter of the present invention after being amplified.

Please refer to FIG. 3, which is a block diagram of the AC/DC leakage detection circuit of the present invention. The AC/DC leakage detection circuit of the embodiment of the present invention includes a power supply unit 10, a leakage detection unit 20, and a leakage detection circuit. Analysis circuit 30 and a brake fluid drive unit 40. The power supply unit 10 is connected to a power input terminal and the thyristor drive unit 40. The power supply unit 10 uses a bridge rectifier 11 to convert the AC power at a power input terminal into a pulsating DC power through full-wave rectification and send it to a π-type filter.器12.

The π-type filter 12 is composed of two capacitors (C1, C2) and an inductor (Coil) to form a low-pass filter to filter out unnecessary noise on the power line, and then pass it to a step-down power supply (Power Supply). ) 13. If the power on the power input end is direct current, it passes through the bridge rectifier 11 and the π-type filter 12 and is directly transmitted to the step-down power supply 13. The step-down power supply 13 can step down the pulsating direct current or pure direct current into a stable positive voltage (+V), a negative voltage (-V) and a working voltage (Vs) for sampling and analysis to provide overall leakage The detection loop is used.

The leakage detection unit 20 is composed of an oscillator (OSC) 21 and the zero comparator (ZCT) 22. The primary side of the zero comparator 22 is coupled to the power input terminal, and the secondary side It is connected to the oscillator 21 and the leakage analysis circuit 30 respectively. The zero comparator 22 can sense a phase shift due to leakage current in a two-phase or three-phase AC power system and output a leakage voltage to control a circuit breaker (not shown) to trip. However, the zero-phase current transformer 22 can only sense AC leakage current, but not DC leakage current. Therefore, the present invention is designed to use the oscillator 21 to provide a fixed-frequency voltage to the zero-phase current transformer 22, so that the zero phase The current comparator 22 is either in AC power system or DC The power system can work in the AC environment corresponding to the positive and negative half cycles. When there is a leakage current at the power input terminal, it will output a potential because the positive and negative half cycles do not correspond to the phase change. Therefore, the present invention can detect the potential of this potential. High and low are used as leakage detection of alternating current or direct current.

As shown in FIG. 3, the leakage analysis circuit 30 is further connected to the thyristor drive unit 40. The leakage analysis circuit 30 consists of a sampling resistor 31, a first low-pass filter (LP filter1) 32, and a precision rectifier (Rectifier). ) 33, a second low-pass filter (LP filter2) 34, an amplifier (Amplifier) 35 and a comparator (comparator) 36, wherein the sampling resistor 31 is connected to the second of the zero comparator 22 The secondary side and the first low-pass filter 32 are used to convert the output current of the zero comparator 22 into a voltage and transmit it to the first low-pass filter 32, and the first low-pass filter 32 in turn It is connected to the precision rectifier 33 for filtering the voltage from the sampling resistor 31 to a signal above the first cut-off frequency (fc1), and transmits it to the precision rectifier 33 for full-wave rectification into a DC pulsating voltage.

The precision rectifier 33 is connected to the second low-pass filter 34 for the DC pulsating voltage to be transmitted to the second low-pass filter 34 for a second time to filter out noise above a second cut-off frequency (fc2) A DC output voltage is generated, the second low-pass filter 34 is then connected to the amplifier 35 to amplify the DC output voltage, and the output of the amplifier 35 is connected to the comparator 36 to determine the amplified DC output voltage Whether it reaches a preset value, the preset value is a standard value for judging whether a circuit breaker has tripped, and if so, a control signal is output to the thyristor drive unit 40, and the thyristor drive unit 40 is made of a thyristor ( SCR) 41 and a driver circuit (Driver) 42, the thyristor 41 is connected to the circuit breaker, the driver circuit 42 is connected to the comparator 36 and the thyristor 41, the driver circuit 42 receives the output of the comparator 36 After the control signal is issued, the thyristor 41 is driven to conduct, so as to control the tripping of the circuit breaker.

Please refer to FIG. 3, FIG. 4, and FIG. 5. FIG. 4 is a Bode diagram of the frequency response of the first and second low-pass filters, and FIG. 5 is a waveform diagram of the sampling resistor signal when there is no leakage. The working principle of the present invention is that the leakage detection unit 20 provides a fixed frequency voltage from the oscillator 21 to the zero comparator 22, so that the zero comparator 22 works in a positive and negative saturation state, generating a positive and negative half cycle. A symmetrical oscillating current waveform, and the oscillating current generated by the zero comparator 22 is transmitted to the sampling resistor 31 of the leakage analysis circuit 30 and converted into an oscillating voltage, as shown in FIG.

The leakage analysis circuit 30 then filters the oscillating voltage through the first low-pass filter 32 to remove a signal above the first cutoff frequency (fc1), and then performs full-wave rectification on the filtered signal by the precision rectifier 33, but The rectified signal is the DC pulsating voltage, and the signal is extremely small and cannot be directly processed. Therefore, it is necessary to extract the DC component and amplify the signal. Therefore, the second low-pass filter 34 filters the components above the second cutoff frequency (fc2) In addition, the DC output voltage is generated, as shown in FIG. 4, which is the Bode plot of the frequency response of the first and second low-pass filters.

Please also refer to Figure 3, Figure 6, Figure 7 and Figure 8. Figure 6 is the waveform of the sampling resistance during leakage, and Figure 7 is the output waveform of the first low-pass filter during leakage. Figure 8 It is the output waveform after the amplification of the second low-pass filter at the time of leakage. When the zero comparator 22 detects the leakage current, according to the phase direction of the leakage current, the zero comparator 22 will saturate earlier or later. At this time, the positive and negative half cycles of the current waveform will no longer be symmetrical. The sampling resistor 31 converts the current signal into a voltage signal, as shown in FIG. 6 is a waveform diagram on the sampling resistor 31 when a high-frequency leakage current is generated.

The waveform of the voltage signal of the sampling resistor 31 after being filtered by the first low-pass filter 32 is as shown in FIG. 7. And then through the precision rectifier 33 full-wave rectification into the DC pulsating voltage, but Because the signal is very small, the DC output voltage is generated by filtering the second low-pass filter 34 and amplifying the signal by the amplifier 35, the waveform of which is shown in FIG. 8. At this time, the potential of the DC output voltage will be significantly increased. Finally, the comparator 36 is used to determine whether the preset value, that is, the trip standard of the circuit breaker, has been reached. If the trip standard has been reached, the signal is output to the thyristor. The drive unit 40 makes the drive circuit 42 output to drive the thyristor 41 to conduct, so that the circuit breaker coil driving mechanism is tripped.

To sum up, the AC/DC leakage detection circuit of the present invention can detect the leakage current of various power systems only by using a zero comparator. In addition to solving the problem that the AC/DC leakage detection circuit is difficult to miniaturize and bandwidth The lack of limitation can be achieved by appropriately designing a filter to expand the frequency detection range. It is not limited to the 3KHz described in this article. Therefore, it is sufficient to cope with various types of leakage currents. It is not only innovative in technical ideas, but also capable of To enhance the above-mentioned multiple functions compared with conventional articles, you should fully meet the statutory patent requirements for novelty and advancement, and file an application in accordance with the law. I implore your office to approve this invention patent case to encourage creativity and to feel good.

10: Power supply unit

11: Bridge rectifier

12: π filter

13: Buck power supply

20: Leakage detection unit

21: Oscillator

22: Zero comparator

30: Leakage analysis circuit

31: sampling resistor

32: The first low-pass filter

33: precision rectifier

34: second low-pass filter

35: Amplifier

36: Comparator

40: Brake fluid drive unit

41: brake fluid

42: drive circuit

Claims (7)

An AC/DC leakage detection circuit includes: a zero comparator, the primary side is coupled to a power input terminal; an oscillator, connected to the secondary side of the zero comparator, to provide a A voltage of a fixed frequency is applied to the zero comparator to make the zero comparator work in a positive and negative saturation state, generating a positive and negative half-cycle symmetrical oscillating pulse current; and a leakage analysis circuit connected to the zero comparator On the secondary side, when there is no leakage at the power input terminal, the oscillating pulse current is received, and a zero-potential voltage value is generated after rectification, filtering, and amplification; when the power input terminal leaks, the oscillating pulse current will be According to the phase direction of the leakage current advance or delay, a positive and negative half-cycle asymmetric leakage oscillating pulse current is generated. After rectification, filtering and amplification, a DC output voltage is generated to determine whether the DC output voltage reaches a preset value for detection AC/DC leakage. The AC/DC leakage detection circuit according to claim 1, which further includes a power supply unit connected to the power input terminal for converting the power system of the power input terminal into a stable positive voltage and a negative voltage. The voltage and a working voltage for sampling and analysis are used to provide the overall leakage detection circuit. The AC/DC leakage detection circuit according to claim 2, wherein the power supply unit includes: a bridge rectifier connected to the power input terminal for full-wave rectification of the AC power at the power input terminal into a pulsating DC power; A π-type filter is connected to the bridge rectifier to filter out unnecessary noise on the pulsating direct current; and a step-down power supply is connected to the π-type filter to convert the positive voltage and the negative The voltage and the working voltage. The AC/DC leakage detection circuit according to claim 1, wherein the zero phase current device and the oscillator Form a leakage detection unit. The AC/DC leakage detection circuit according to claim 1, wherein the leakage analysis circuit further includes: a sampling resistor connected to the secondary side of the zero comparator for the zero comparator The output oscillating pulse current or the leakage oscillating pulse current is converted into an oscillating voltage; a first low-pass filter is connected to the sampling resistor to filter the oscillating voltage above a first cut-off frequency Signal; a precision rectifier is connected to the first low-pass filter to full-wave rectify the output signal of the first low-pass filter into a DC pulsating voltage; a second low-pass filter is connected to the A precision rectifier is used to filter the direct current voltage above a second cut-off frequency to generate a direct current output voltage; an amplifier is connected to the second low-pass filter to amplify the direct current output voltage ; And a comparator, connected to the amplifier, used to determine whether the amplified DC output voltage reaches the preset value, and if it is to output a control signal. The AC/DC leakage detection circuit described in claim 1, wherein the preset value is a standard value for judging whether a circuit breaker has tripped. The AC/DC leakage detection circuit according to claim 6, wherein the leakage analysis circuit is connected to a thyristor drive unit, and the thyristor drive unit includes: a thyristor connected to the circuit breaker; and a drive circuit connected to In the comparator and the thyristor, the driving circuit drives the thyristor to conduct after receiving the control signal output by the comparator to control the circuit breaker to trip.

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