阅读说明：本技术 基于磁芯工作状态切换下的复杂剩余电流检测方法 (Complex residual current detection method based on magnetic core working state switching ) 是由 江泽安 王建华 刘振 于 2019-10-09 设计创作，主要内容包括：本发明涉及一种利用磁芯工作状态切换的剩余电流检测方法。由于直流漏电信号并没有波动,线圈无法感应出信号,故需要将信号叠加到交变信号上,本发明使用芯片实现H桥电路输出正负方波两种状态来实现外加磁场,双向饱和激励方波信号进入磁芯双向饱和区,利用直流在磁化曲线不同区域产生的不同特性,通过算法提取、区分,完成直流漏电检测以及保护。交流漏电本身具有波动性,工作在磁芯线性区,因此线圈可直接感应出信号,包括50Hz,高频交流的400Hz,1kHz,20kHz,150kHz等,此时线圈为无激励信号,数据同样通过算法提取计算,完成交流漏电检测以及保护；利用正向激励、反向激励、无激励三种状态切换,完成对复杂剩余电流检测。(The invention relates to a residual current detection method by switching the working state of a magnetic core. Because the direct current leakage signal does not fluctuate, the coil cannot induce a signal, and the signal needs to be superposed on the alternating signal, the invention uses the chip to realize that the H-bridge circuit outputs positive and negative square waves to realize an external magnetic field, the bidirectional saturated excitation square wave signal enters the bidirectional saturated area of the magnetic core, and the direct current leakage detection and protection are finished by extracting and distinguishing through an algorithm by utilizing different characteristics generated by direct current in different areas of a magnetization curve. The alternating current leakage has volatility and works in a magnetic core linear region, so that a coil can directly induce signals including 50Hz, 400Hz, 1kHz, 20kHz, 150kHz and the like of high-frequency alternating current, the coil is a non-excitation signal at the moment, and data are extracted and calculated through an algorithm to finish alternating current leakage detection and protection; and the complex residual current detection is completed by switching the three states of forward excitation, reverse excitation and no excitation.)

1. The invention relates to a residual current detection method based on magnetic core working state switching, which is characterized by comprising the following steps:

step one, configuring a control chip into a pure induction mode without voltage, wherein the mode lasts for t1 ms;

step two, configuring the control chip into a mode of saturated excitation positive and negative square waves, wherein the mode lasts for t2 ms;

step three, finishing corresponding duration, outputting the characteristic quantity by the sampled data through an algorithm module, and processing the characteristic quantity by software to finish state judgment at the moment;

and step four, when the condition of suddenly increasing the current occurs, the current is timely adjusted to be a new detection mode through the state control module so as to timely respond to the current signal, the processing of the algorithm module is completed after the acquisition is completed, and the software immediately processes the current signal.

2. The method for detecting the residual current based on the switching of the working state of the magnetic core according to claim 1, wherein the method comprises the following steps:

the DC residual current is constant current and generates a constant magnetic field, and the detection winding cannot generate an induction signal at the moment, so that the DC signal is required to be superposed on an alternating signal; the alternating residual current is an alternating magnetic field, so that the alternating residual current can be sensed by the detection winding, a square wave excitation signal is not needed at the moment, the circuit is adjusted to be a pure sensing mode, and the sampling resistor is directly connected with the coil; the method for detecting the alternating current and direct current residual current is completed by switching three states of positive voltage, negative voltage and no voltage.

3. The method for detecting the residual current based on the switching of the working state of the magnetic core according to claim 1, wherein the method comprises the following steps:

the magnetic core for measuring the residual current is usually made of permalloy or amorphous soft magnetic materials with high magnetic permeability, low residual magnetism and low coercive force. Ferrite, which is relatively inexpensive, is not used because of its relatively low magnetic permeability, relatively wide magnetization curve, and insensitivity to small dc signals in the linear region. The induction signal output by the material with lower magnetic conductivity has small amplitude, the defect can be solved by using the high-sampling-rate and high-precision ADC (analog to digital converter), the conventional analog circuit is difficult to realize, the cost is high, but the problem can be solved by using the integrated IC (integrated circuit).

4. The method for detecting the residual current based on the switching of the working state of the magnetic core according to claim 1, wherein the method comprises the following steps: the second step is based on the principle that:

the direct current residual current is constant current and generates a constant magnetic field, at the moment, the detection winding cannot generate an induction signal, an H-bridge driving circuit is adopted to generate positive and negative saturated excitation voltages which are approximately regarded as square waves with positive and negative polarities, the switching frequency is adjusted, the signals can enter a saturation area of a hysteresis loop in a two-way mode, different induction signals can be generated in different areas of the hysteresis loop due to the direct current residual current, different direct current residual currents can be detected by utilizing the difference of the signals, and the actual direct current residual current value is obtained through algorithm extraction, so that corresponding operation is executed.

5. The method for detecting the residual current based on the switching of the working state of the magnetic core according to claim 1, wherein the method comprises the following steps:

the positive voltage and the negative voltage are used for generating a group of excitation response signals, data processing is carried out on the positive response signals and the negative response signals in one period through data processing at each time, a plurality of excitation periods are combined, and the residual current is judged, so that the residual current judging precision can be greatly improved.

6. The method for detecting the residual current based on the switching of the working state of the magnetic core according to claim 1, wherein the method comprises the following steps:

the detectable residual current waveform of the invention covers power frequency alternating current, smooth direct current, pulsating direct current and high frequency alternating current, the three modes of the detection state are switched by the chip control, thus completing the detection of the residual current with full waveform, the corresponding signal value is calculated by algorithm processing, and the corresponding operation is executed by multi-data signal processing.

7. The method for detecting the residual current based on the switching of the working state of the magnetic core according to claim 1, wherein the method comprises the following steps: according to the sudden addition condition of the large current in the step four:

the invention can respond to different waveform residual currents with larger amplitude of the sudden-adding condition in time, identify the sudden-adding characteristic through the algorithm module, and then switch the test state through the state control module, so that the signal can be acquired and processed in time, and the data processing is ensured to be timely and effective.

Technical Field

The invention belongs to the field of electric leakage detection, and mainly relates to a method for detecting complex residual current by switching working states by utilizing different responses of a magnetic core to alternating current and direct current residual currents in different areas of a magnetization curve

Background

Along with economic development, the power industry develops rapidly, and the scales of various household appliances are gradually enriched, so that how to ensure the electricity utilization safety of residents becomes more important, and various complex wave signals including alternating current, direct current, high-frequency signals and the like need to be detected; the AC residual current is extremely harmful to human bodies, namely 50mA/s (namely ventricular trembling), and with the increase of power consumption types, the problem of DC residual current detection also becomes important, the current DC is widely applied, including DC charging piles, variable frequency motors and the like, and is used for household purposes such as certain types of notebooks, microwave ovens, washing machines and the like; therefore, the high-precision detection of the alternating current and direct current residual current and the complex waveform is urgently needed.

At present, the market aims at the residual current detection products with B type and higher specification, and the electromagnetic current transformer, the Hall current sensor, the magnetic modulation type current transformer and the like are mostly used for detecting the residual current, so that the defects that the detection precision is low, all residual current waveforms cannot be covered and the like exist, and therefore, a method capable of effectively solving two problems needs to be developed.

Disclosure of Invention

Aiming at the problems, the invention overcomes the defects of the prior art, provides a method for combining a voltage excitation mode and a pure induction mode by using ferrite as a magnetic core material, and effectively solves two difficulties of residual current coverage of all types and high-precision distinguishing and judging through full electronic processing of data.

The invention relates to a detection technology for complex residual current by switching working states by utilizing different responses of a magnetic core to alternating current and direct current residual currents in different areas of a magnetization curve. The residual current in the detection circuit is used for electric leakage test, the values of different types of residual current are calculated through secondary algorithm analysis, and software discrimination is carried out, so that the protection on electric leakage is achieved.

The invention uses the residual current transformer of the two-phase coil as the detection device, as shown in the figure I, the working state of the detection winding is controlled by the chip, thereby realizing the detection of different types of residual currents. The alternating residual current is an alternating signal, so that an induction signal can be generated through a coil, at the moment, an undistorted alternating signal can be induced by utilizing a linear region of a magnetic core, the range of a detectable signal of the linear region meets the national standard requirement through calculation, and a signal exceeding the range can be directly judged as an over-threshold signal; the direct current residual current is considered to be constant current when the direct current residual current exists, so a constant magnetic field is generated, the direct current cannot be directly induced by using a coil, but the direct current has an induction signal in a nonlinear region of a hysteresis loop, so that a positive and negative excitation square wave mode is used when the direct current is measured, the signal alternately acts on two saturation regions of the hysteresis loop, different direct current quantities can generate different responses in different regions, and the direct current detection is completed by analyzing and processing through an algorithm.

The linear region of a hysteresis loop of the ferrite is utilized, when an alternating signal exists, a secondary side can induce a corresponding signal, the amplitude is inversely proportional to the number of turns of a coil, and the linear region of the ferrite is relatively wide, so that the ferrite has a better characteristic of measuring alternating residual current;

by utilizing the characteristics of a hysteresis loop of ferrite, a direct current signal is insensitive to a linear region, the same principle is adopted in a saturation region, but an induction value of a direct current quantity exists in the nonlinear region, and the detection of the direct current residual current can be completed just through the change value of the region; the magnetic core is excited by bipolar square waves, the magnetic core can enter a saturation region bidirectionally, the unipolar square waves are converted into the bipolar square waves through an H bridge, when the half waves enter saturation, reverse square wave excitation is immediately applied, namely a reverse magnetic field with the same size is generated, at the moment, a winding changes from the magnetic saturation region on one side to the magnetic saturation region on the other side, the time for reaching the saturation ampere-turn number is different due to different direct current leakage values, the corresponding currents are different, the difference of different direct current residual currents can be extracted from sampling resistor sampling, and the corresponding direct current leakage value is obtained through algorithm analysis.

Drawings

Fig. 1 is a schematic diagram of the operating principle of a residual current transformer.

Fig. 2 is a simplified model schematic of a detection device.

Fig. 3 is a schematic diagram of tri-state switching operating in different regions of the hysteresis loop.

Fig. 4 is a simplified model schematic of the hysteresis loop of a ferrite.

Fig. 5 is a graph of the effect of dc leakage using an excitation square wave.

Fig. 6 is a graph of dc residual current data.

Fig. 7 is an ac residual current data diagram.

Detailed Description

The following describes the complex residual current detection technology by using the tri-state switching manner of different working states of the magnetic core proposed in the present invention with reference to fig. 1 to 7, so as to specifically describe the technical scheme of the present invention

The invention uses ferrite residual current transformer as detection device, and completes the detection of complex residual current through three-state switching control. As shown in fig. two, when detecting alternating current, the state control module enables the loop to work in a pure induction mode without voltage, and alternating residual current can induce a current signal through the coil and be collected through the sampling resistor by utilizing the linear region characteristic of the magnetic core;

detecting that the magnetic core works in a linear region during alternating current, wherein the magnetic field intensity H is according to the ampere loop theorem;

when the magnetic core works in a linear region, the magnetic permeability u is almost constant, and the magnetic induction intensity B:

the induced electromotive force E is:

from the above formula, it can be inferred that: when the magnetic core works in a linear area, the signal is sensitive to an alternating current signal and is insensitive to a direct current signal, so that the induced signal is considered to be an alternating current signal value.

The permeability is changed when the signal passes through the nonlinear region, and can be considered as a time-varying parameter μ (t) when the excitation amplitude is varied with time. The induction signal of the coil can be represented as follows:

it can be analyzed by the formula: because the magnetic permeability mu (t) is changed when the magnetic sensor works in a nonlinear region, the direct current quantity can induce signals in the nonlinear region, and the direct current signals can be detected and distinguished by utilizing the change of the direct current quantity and extracting and analyzing through an algorithm.

When the magnetic core is in a saturation region by an excitation signal, the excitation signal enters deep saturation, the signal can completely reflect all characteristics of a hysteresis loop, when the signal enters the deep saturation region, because the magnetic permeability is approximately equal to 0 at the moment, no induction signal exists, but because of the existence of the excitation square wave, the inductance in the loop has no barrier action at the moment, which is equivalent to the voltage division of a small resistor, and therefore the signal acquired by the sampling resistor is a constant voltage value approximate to the amplitude of the excitation square wave.

If the alternating current residual current is large enough, a pure induction mode is used, the magnetic core works to enter a saturation area, alternating current signals can cover all areas of a magnetic hysteresis loop, induction waveforms of signals in different areas have different responses, alternating current signals can be still induced by the signals in a linear area, even harmonic waves can be superposed on the signals in a nonlinear area, and no induction signals exist in a deep saturation area, so that the signals can be attenuated.

When detecting direct current, outputting positive and negative saturation excitation signals through a state control module, wherein the frequency of a square wave signal is adjustable, calculating the charging time required for reaching saturation according to the number of saturated ampere-turns, controlling the period of the square wave signal to be more than or equal to the sum of two-way charging time, and enabling the signal to reach a two-way deep saturation region of a magnetic core in the period, wherein as shown in a simplified model of a magnetization curve in the figure IV, the magnetic conductivity is small in a time period of 0-t 1, the coil blocking effect is small at the moment, and the response of the excitation signals changes rapidly; in the time from t1 to t2, the magnetic permeability is considered to be the maximum, and a process of hindering the change is provided; in the time period from t2 to t3, as the magnetic permeability is reduced from large to small, the inductive reactance at the moment is restored to a small value, the blocking effect is reduced, and the response signal is changed rapidly; after t3, the coil enters a deep saturation region, and the signal on the resistor tends to be stable; when direct current residual current occurs, a waveform with a transversely stable upper waveform and a transversely stable lower waveform appears, and actual circuit sampling data are shown in a sixth graph.

The excitation square wave form of two states is used, not only the direct current residual current can be detected, but also the alternating current residual current with partial frequency can be analyzed and processed by an algorithm, because the frequency of the injected square wave is high, even for an alternating current signal, it can be considered that the magnitude of the leakage current is not changed in one excitation half-wave time, according to the different responses of the hysteresis loop to the different direct currents, different leakage signal values are superposed on the excitation square wave of the detection winding, the induction principle at the moment is the same as the direct current residual current detection principle, the signals are collected on the sampling resistor, the reproduction of complex waveforms can be completed by feature extraction, the excitation square wave is a modulation signal relative to the signal to be detected, according to the sampling theorem, the maximum frequency of the induction signal which can be analyzed is 1/5 of the frequency of the excitation square wave;

sensing the induced current i of the winding_sThe sampling resistor passes through the PGA amplifying circuit, is read by the ADC sampling module and then is input into the algorithm DSP unit for analysis;

the method comprises the following steps: controlling an internal circuit of the chip to enable the coil and the resistor to form a pure induction measurement alternating current mode, wherein the excitation voltage is 0 and is approximately directly connected for a duration time of t2ms, data passes through the operational amplifier circuit and then is sampled by the ADC to be sent to the hardware algorithm DSP module, and the data is operated and analyzed through the algorithm to be further distinguished;

step two: when the alternating current residual current detection is finished, the internal circuit of the control chip switches the working state, outputs a positive voltage state and a negative voltage state, alternately generates square wave excitation signals which are similar to positive and negative polarities, at the moment, the coil and the sampling resistor are superposed with excitation square waves, the magnetic core works back and forth in a positive saturation area and a negative saturation area through the square waves, the excitation time is t1ms, data passes through the operational amplifier circuit and then is sent into a hardware algorithm DSP module through ADC sampling, and the data is subjected to operation analysis through an algorithm and then is judged;

step three: in the algorithm DSP module, a special switching control algorithm is provided for preventing the detection time from failing to meet the national standard action requirement when the sudden large current is added, when the complex residual current detection is carried out in a certain state, if the sudden large current is found, the algorithm module controls to generate interruption, the type (large direct current, large alternating current and the like) of the sudden added signal is analyzed according to the sampled signal specificity, the detection state is controlled to continuously maintain t2/t1ms by combining the detection state working in alternating current/direct current at the moment, or the detection state is immediately switched to the direct current/alternating current detection state for the same duration time t2/t1ms, data is sent to the hardware algorithm DSP module after passing through an operational amplifier circuit and is subjected to ADC sampling, and the data is subjected to operational analysis through the algorithm, and then is judged.

And the sixth graph and the seventh graph respectively correspond to actual sampling signals of direct current and alternating current residual currents, and final results can be obtained through algorithm characteristic extraction and analysis.

The foregoing is only a preferred embodiment of this invention and modifications and variations such as will be apparent to those skilled in the art may be made without departing from the principles of the invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection of the present invention.