CN110794191A - Magnetic modulation type direct current leakage protection device for inhibiting zero drift influence - Google Patents
Magnetic modulation type direct current leakage protection device for inhibiting zero drift influence Download PDFInfo
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- CN110794191A CN110794191A CN201910987791.4A CN201910987791A CN110794191A CN 110794191 A CN110794191 A CN 110794191A CN 201910987791 A CN201910987791 A CN 201910987791A CN 110794191 A CN110794191 A CN 110794191A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
- G01R15/18—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using inductive devices, e.g. transformers
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/26—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents
- H02H3/32—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents involving comparison of the voltage or current values at corresponding points in different conductors of a single system, e.g. of currents in go and return conductors
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Abstract
The invention discloses a magnetic modulation type direct current leakage protection device for inhibiting the influence of zero drift, which comprises two magnetic modulation type residual current transformers, wherein the output end of each magnetic modulation type residual current transformer is respectively connected with the input end of a low-pass filter circuit, the output end of the low-pass filter circuit is connected with the input end of a difference circuit, the output end of the difference circuit is connected with the input end of an absolute value circuit, and the output end of the absolute value circuit is connected with a controller for controlling the action of a tripping device. The magnetic modulation type direct current leakage protection device for inhibiting the influence of the zero drift can effectively inhibit the influence of the zero drift on the leakage protection device, thereby avoiding the generation of false operation and improving the detection precision of the device.
Description
Technical Field
The invention relates to the technical field of direct current leakage protection, in particular to a magnetic modulation type direct current leakage protection device for inhibiting zero drift influence.
Background
With the continuous development of technologies such as photovoltaic power generation, new energy vehicles, electric vehicle charging stations, intelligent direct-current power distribution and utilization systems, micro-grids and the like, various direct-current systems are rapidly developed and widely popularized and applied. To ensure safe and reliable operation of the dc system, a large number of dc monitoring and protection devices are required. Therefore, a high-precision direct current sensor is developed and designed and is combined with a circuit breaker and the like to form a direct current system leakage protection device, so that accidents such as personal electric shock and the like can be greatly reduced in a direct current system, and the safety and reliability of the system are improved.
The magnetic modulation type current transformer has the advantages of long working stability time, no input, low null shift, small influence of environmental temperature, isolated design, high sensitivity, high linearity and the like, and is more suitable for direct current leakage protection.
When direct current leakage current exists, under the action of detected direct current, a direct current component and an even harmonic component appear in an excitation current waveform frequency spectrum. On the basis, two magnetic modulation type direct current detection methods are generally available, one method is formed by taking a frequency multiplication magnetic modulator as a core, the frequency multiplication magnetic modulator usually has a double-magnetic core structure, the current magnitude is measured by detecting a second harmonic component in a magnetic core secondary winding output signal, a signal processing circuit is complex, the steps of signal amplification, band-pass filtering, phase-sensitive detection, low-pass filtering and the like are generally needed, and the measurement process is complicated; in addition, the mutual inductor with the double-magnetic-core structure can cause a false balance point due to the inconsistency of the structures, sizes and magnetic characteristics of the two magnetic cores, so that the detection error is increased. The other method is to measure the magnitude and direction of the direct current leakage current by detecting the direct current component of the voltage spectrum of the sampling resistor, which is also called a direct current component method.
Although the direct current component method is low in zero drift and small in temperature influence in practical application, the influence cannot be completely ignored in practical engineering application, and when no input (no leakage current) is caused by the zero drift phenomenon, the phenomenon that the output is not zero brings great influence on the subsequent detection of direct current leakage, so that the misoperation of a leakage protector can be caused, and the detection precision of the device is reduced.
Disclosure of Invention
The invention aims to provide a magnetic modulation type direct current leakage protection device for inhibiting the influence of zero drift aiming at the technical defects in the prior art.
The technical scheme adopted for realizing the purpose of the invention is as follows:
a magnetic modulation type direct current leakage protection device for suppressing the influence of zero drift comprises:
the output end of each magnetic modulation type residual current transformer is connected with the input end of a low-pass filter circuit, the output end of the low-pass filter circuit is connected with the input end of a difference circuit, the output end of the difference circuit is connected with the input end of an absolute value circuit, and the output end of the absolute value circuit is connected with a controller for controlling the action of a tripping device.
The magnetic modulation type residual current transformer adopts square wave voltage output by an operational amplifier as an excitation voltage source of the transformer and comprises an annular magnetic core, the operational amplifier and a sampling resistor RsThreshold voltage setting resistor R1And R2The annular magnetic core is wound with a secondary winding which is used as an excitation winding and a detection winding; threshold voltage setting resistor R1One end of the resistor is connected with the non-inverting input end of the operational amplifier, the other end is grounded, and a threshold voltage setting resistor R2One end of the sampling resistor is connected with the non-inverting input end of the operational amplifier, the other end of the sampling resistor is connected with the secondary winding, and the inverting input end of the operational amplifier is connected with the sampling resistor RsThe other end of the non-grounded end is connected with the other end of the secondary winding and is also connected with the input end of the low-pass filter circuit.
When no leakage occurs, the output signal of the absolute value circuit is basically zero, and the influence that the direct current component is not zero due to the zero drift phenomenon is eliminated;
when positive/negative leakage occurs, the output value of the absolute value circuit is a positive integer multiple of the direct current component value corresponding to the leakage current signal.
The magnetic modulation type direct current leakage protection device for inhibiting the influence of the zero drift is based on a direct current component method of a single magnetic core magnetic modulation type as a theoretical basis, two magnetic cores with the same magnetic core material, size, winding turns, winding mode and the like (hereinafter, the magnetic cores are simply summarized as the magnetic core with the same characteristics) are selected and respectively connected into respective excitation circuits and filter circuits, then the direct current component difference value is processed and amplified, and the influence of the zero drift on the leakage protection device can be effectively inhibited by combining the control of a single chip microcomputer, so that the generation of misoperation is avoided, and the detection precision of the device is improved.
Drawings
FIG. 1 is a working principle of a magnetic modulation type residual current transformer;
FIG. 2 is an equivalent circuit of an excitation loop of a magnetic modulation type residual current transformer;
FIG. 3 is a simplified model of the piecewise linearization of a magnetization curve;
FIG. 4 is a schematic diagram of an output waveform without leakage current;
fig. 5 is a functional block diagram of a magnetic modulation type dc leakage protection device that suppresses the influence of zero drift.
Detailed Description
The invention is described in further detail below with reference to the figures and specific examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Although the direct current component method based on the magnetic modulation system has low null shift and small influence by temperature, the influence cannot be completely ignored in practical engineering application, and when no input (no leakage current) is caused by the null shift phenomenon, the phenomenon that the output is not zero brings great influence on the detection of subsequent direct current leakage. Because the zero drift phenomenon is mainly influenced by temperature, when no leakage occurs at the same temperature, the direct current component values of two magnetic cores with the same magnetic core characteristics and a peripheral circuit caused by the zero drift phenomenon are relatively close, so that two magnetic cores with the same magnetic core characteristics are selected and respectively connected to respective excitation circuits and filter circuits on the basis of a magnetic modulation type direct current component method, then the direct current component difference value is processed and amplified, and the influence of the zero drift on the leakage protection device can be effectively inhibited by combining a single chip microcomputer and a tripping device.
Therefore, the invention is based on a magnetic modulation type direct current component method, two magnetic cores with the same magnetic core characteristics are selected, and a line to be measured passes through one magnetic core in the forward direction and then passes through the other magnetic core in the reverse direction, as shown in fig. 5. The purpose of passing through one of the magnetic cores in the reverse direction is that for the same line to be tested, when electric leakage occurs, if one of the magnetic cores is a positive leakage signal, the other magnetic core is a negative leakage signal, and new direct current components processed by the respective filter circuits are shifted by the same numerical value in the opposite direction on the basis of the same initial direct current component value (caused by null shift phenomenon). Meanwhile, the difference circuit and the absolute value circuit perform difference processing and amplification on the direct current components of the circuits corresponding to the two magnetic cores so as to eliminate the influence of the null shift phenomenon, and the direct current leakage current protection function is realized by combining the singlechip and the tripping device.
As shown in fig. 5, the magnetic modulation dc leakage protection device for suppressing the influence of the zero drift according to the present invention includes: the output end of each magnetic modulation type residual current transformer is connected with the input end of a low-pass filter circuit, the output end of the low-pass filter circuit is connected with the input end of a difference circuit, the output end of the difference circuit is connected with the input end of an absolute value circuit, and the output end of the absolute value circuit is connected with a controller for controlling the action of a tripping device.
Under the above scheme, when no leakage occurs, the output signal of the absolute value circuit is basically zero, and the influence that the direct current component is not zero due to the zero drift phenomenon is eliminated;
when positive/negative leakage occurs, the output value of the absolute value circuit is a positive integer multiple of the direct current component value corresponding to the leakage current signal.
Wherein, the magnetic modulation type residual current transformer based on the magnetic modulation principle is composed of an annular magnetic core, an operational amplifier, a sampling resistor R as shown in figure 1sThreshold voltage setting resistor R1And R2And (4) forming. A secondary winding is wound on the magnetic core of the mutual inductor, which is used as an excitation winding and a detection winding, and the number of turns of the secondary winding is N2(ii) a The square wave voltage output by the operational amplifier is used as an excitation voltage source of the mutual inductor.
For the convenience of analysis, on the premise that the excitation current does not exceed the maximum output current of the operational amplifier, the maximum value of the output voltage of the operational amplifier is assumed to be UHMinimum value of ULAnd U isL＝-UH. When the circuit is in operation, the sampling resistor RsVoltage on to the threshold voltage + -UrWhen the voltage is applied, the polarity of the output voltage of the operational amplifier is reversed, so that the circuit automatically generates a square wave excitation voltage. Let the period of the exciting voltage be T and the frequency be f. Threshold voltage is formed by resistor R1、R2Partial pressure is obtained, which satisfies
An equivalent circuit of an excitation loop of a magnetic modulation type residual current transformer is shown in fig. 2, wherein direct current leakage current in the circuit refers to difference current in positive and negative wires, i.e. ip＝iL+iNUnder normal conditions, the current i to be measuredp0. i (t) represents the current in the secondary winding of the transformer, i.e. the excitation current; psi is the total flux linkage of the secondary winding of the transformer; d ψ/dt represents an induced electromotive force of the secondary winding of the transformer.
For the sake of simplicity of analysis, it is assumed that the magnetization curve of the magnetic modulation core is shown in fig. 3, the magnetic induction intensity is not changed in the saturation stage, the magnetic induction intensity is changed from the minimum negative value to the maximum positive value in the linear stage, and the critical point H between the saturation region and the linear region issCorresponding excitation current of Is. Under this assumption, the saturation phase winding inductance is approximately zero, while the linear phase inductance is a constant value L.
Because the excitation voltage is a square wave signal with a certain frequency, the working process of the magnetic core under the action of the periodic positive voltage and the periodic negative voltage can be analyzed as a transition process when positive direct current voltage and negative direct current voltage respectively act on a circuit, the stable state under the action of the periodic square wave voltage is regarded as a transition process one by one, and a mathematical model of the working process of the magnetic modulation type residual current transformer is established.
The following is the analysis process of the direct component method, and the excitation current expression can be written as follows:
a0is a DC component in the frequency spectrum of the exciting current, w is the angular frequency of the exciting current, an、bnIs harmonicThe wave coefficient is, among them,substituting i (t) into the formula to obtain
Due to ip＜＜IH,is＜＜IHTo obtain
Magnetic saturation current isWhen the measured current is zero, the magnetic core just reaches the corresponding excitation current when the positive magnetic saturation and the negative magnetic saturation are achieved,
Ipis the measured current ipReduced to a value on the secondary side, i.e.
Therefore, when the measured current is DC current, the DC component amplitude a of the exciting current i (t)0Exactly equal to the measured direct current ipValue I reduced to secondary sidepAnd they are opposite in sign. Therefore, the direct current component of the exciting current can reflect the magnitude and direction of the direct current to be measured.
The invention can realize that when no leakage occurs, the output signal of the absolute value circuit is basically zero, and the influence of non-zero direct current component caused by zero drift phenomenon is eliminated.
When the leakage current occurs in the positive (negative) direction, the output value of the absolute value circuit is the positive integer multiple of the direct current component value corresponding to the leakage current signal due to the action of the difference circuit and the absolute value circuit.
The invention takes the principle of a single-magnetic-core magnetic modulation type current sensor as a theoretical basis, realizes the detection of direct current residual current by detecting the direct current component of exciting current in an exciting winding, combines two magnetic cores with the same magnetic core characteristics, and accesses two new direct current components into a difference circuit and an absolute value circuit through respective exciting circuits and filter circuits, and combines a single chip microcomputer and a tripping device simultaneously, thereby eliminating the influence of zero drift on the detection precision and improving the reliability, flexibility and accuracy of a protection device.
When there is positive leakage current, the new DC component is shifted downwards by a certain value on the basis of the DC component caused by null shift, and when there is negative leakage current with the same current value, the new DC component is shifted upwards by the same value on the basis of the previous DC component. Therefore, based on the method, two magnetic cores with the same magnetic core characteristics are selected, effective suppression of the zero drift phenomenon can be achieved through the difference value amplification and absolute value circuit and the combination of the single chip microcomputer and the tripping device, the precision of the mutual inductor can be greatly improved, and therefore the leakage protection device can accurately act.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (3)
1. The magnetic modulation type direct current leakage protection device is characterized by comprising two magnetic modulation type residual current transformers, wherein the output end of each magnetic modulation type residual current transformer is connected with the input end of a low-pass filter circuit, the output end of the low-pass filter circuit is connected with the input end of a difference circuit, the output end of the difference circuit is connected with the input end of an absolute value circuit, and the output end of the absolute value circuit is connected with a controller for controlling the action of a tripping device.
2. The magnetically modulated dc leakage protection device of claim 1, wherein the magnetically modulated residual current transformer uses a square wave voltage outputted from an operational amplifier as the output voltageThe excitation voltage source of the mutual inductor comprises an annular magnetic core, an operational amplifier and a sampling resistor RsThreshold voltage setting resistor R1And R2The annular magnetic core is wound with a secondary winding which is used as an excitation winding and a detection winding; threshold voltage setting resistor R1One end of the resistor is connected with the non-inverting input end of the operational amplifier, the other end is grounded, and a threshold voltage setting resistor R2One end of the sampling resistor is connected with the non-inverting input end of the operational amplifier, the other end of the sampling resistor is connected with the secondary winding, and the inverting input end of the operational amplifier is connected with the sampling resistor RsAnd the other end of the non-grounded end is connected with the other end of the secondary winding and is also connected with the input end of the low-pass filter circuit.
3. The magnetically modulated dc leakage protection device of claim 1, wherein when no leakage occurs, the output signal of the absolute value circuit is substantially zero, eliminating the effect of non-zero dc component due to the zero-shift phenomenon;
when positive/negative leakage occurs, the output value of the absolute value circuit is a positive integer multiple of the direct current component value corresponding to the leakage current signal.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN111817258A (en) * | 2020-06-29 | 2020-10-23 | 天津相和电气科技有限公司 | Magnetic modulation type direct current leakage protection device based on improved direct current component method |
| CN114089013A (en) * | 2022-01-21 | 2022-02-25 | 华中科技大学 | Zero offset suppression method based on magnetization micro-asymmetric magnetic core group mirror image matching |
| CN114755487A (en) * | 2022-06-15 | 2022-07-15 | 深圳市航智精密电子有限公司 | Fluxgate current sensor and current measuring method |
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