Technical Research On Residual Current Detection System Under Complex Waveform Conditions

At present,the AC type residual current protector is widely used in our country.It can only act correctly when the power frequency sinusoidal AC residual current is generated in the line.If the generated residual current contains pulsating DC component or smooth DC component,the protector will not be able to disconnect the line in time,leading to accidents of electric shock or equipment damage.Now,some scholars have studied the detection theory of complex waveform residual current,but the development of related equipment is still in the initial stage.The disadvantages of the existing residual current detection methods are: the stability of zero point is poor,large temperature drift,complex circuit structure and high power consumption.The disadvantages of the common residual current waveform recognition methods are: the selected waveform features are not typical enough,and the recognition accuracy of complex waveform is low.In order to realize the accurate detection and recognition of complex waveform residual current,this paper studies and analyzes the detection of residual current and the waveform recognition of residual current.Based on this theory,the fluxgate current sensor and related circuits are designed,and the residual current recognition algorithm program is written.1.The measurement principle of open-loop fluxgate current sensor is studied.According to the ampere loop theorem,when the magnetic core works in the linear region of the hysteresis loop,the output voltage of the current sensor is proportional to the magnetic induction generated by the current to be measured in space.Because the fluxgate magnetic field sensor has the characteristics of low offset and low drift,the measurement principle has the advantages of the zero point is stable and small temperature drift.2.The method of waveform recognition based on spectrum analysis is studied.In order to solve the problem that the current waveform characteristics are not typical enough,the spectrum of residual current waveform is analyzed.By comparison,the number and amplitude of spectrum peaks are proposed as waveform features,which makes the features more representative and significantly improves the accuracy of the algorithm.3.According to the theoretical research,the hardware and software of complex waveform residual current detection system are designed.In order to determine the parameters of the magnetic core of the sensor,the simulation model of the sensor is established,and the parameters of the magnetic core are designed by simulation.The circuit and software of the detection system are designed by modular design.4.The designed fluxgate current sensor is calibrated,the range of the sensor is 10? 500 m A,the sensitivity is 1.54mv/m A,the return error is 4.9m V,resolution is 0.6m A,the frequency band of the sensor is 6.7k Hz.The waveform recognition algorithm is tested,and the recognition accuracy is more than 95%.The prototype of complex waveform residual current detection system is tested.When there is no noise in the line,the measurement error is less than 5%,and the recognition accuracy is more than 98%.When the noise in the line is 20%,the detection error is less than 10%,and the recognition accuracy is more than 90%.It meets the requirements of national standard for complex waveform residual current detection.