Research On Power Quality Disturbance Detection Method Based On Improved HHT

With the continuous development of power system,the structure of power network becomes more and more complex,and the power quality requirements of electrical equipment become higher and higher.Therefore,the detection and analysis of power quality disturbance signal is of great significance for the treatment of power quality problems in the later stage and the adoption of appropriate protective measures,so as to improve the operation of power system and improve the quality of power quality.HHT method is a new non-linear non-stationary signal analysis method.Because of its good adaptability,completeness and time-frequency dispersion,it is suitable for power quality disturbance signal analysis.However,there are some limitations in the detection of power quality disturbances due to the terminal effect and modal aliasing.The main work of this paper is as follows:Firstly,the basic theory of HHT is introduced,including the concept of intrinsic mode function,the specific process of empirical mode decomposition and the realization method of Hilbert transform.This paper analyzes the advantages of HHT in power quality disturbance detection,including that it can detect the intermittent signal,transient signal and other abnormal signals,and the results are more accurate,which is suitable for signal detection.In view of the two most obvious problems in HHT,the endpoint effect and the mode mixing phenomenon are analyzed in detail.Because the existence of the problem has a great influence on the detection results of power quality disturbance signal,it needs to be improved in order to detect power quality disturbance signal more effectively.This paper analyzes the causes of each problem and its influence in the decomposition process,summarizes the existing targeted improvement methods,and makes a comparative simulation analysis of each method,and evaluates the improvement effect of each method from the perspective of correlation coefficient,root mean square error,calculation time,etc.,and draws the following conclusion: the EMD is improved by using the boundary local feature scale method,and the IMF component obtained is The fitting effect at the end point is better,and the performance of the end effect suppression is better than other methods;the IMF component obtained by the meemd method decomposition signal is closer to the real component contained in the signal,and the effect of suppressing modal aliasing is more obvious.Considering that the traditional HHT can not solve the two problems mentioned above,an improved HHT method is proposed,that is,the boundary local characteristic scale method is used to suppress the end effect,and the meemd method is used to improve the modal aliasing.In this paper,simulation analysis of typical power quality problems is carried out to verify the effectiveness of the improved method in power quality detection.Mathematical modeling of six common power quality disturbance signals in power systems: voltage sag,voltage swell,voltage interruption,harmonic signal,transient oscillation and transient pulse,and HHT analysis of the results shows that HHT The method accurately detects the start and end time,amplitude,frequency and other information of various disturbance signals.Considering the complexity of the power system,two complex power quality disturbance signals are established: harmonic signal + voltage swell signal,harmonic signal + voltage sag + transient pulse signal mathematical model,using traditional HHT method and improved HHT respectively Analyzing it,the results show that the traditional HHT method can not well identify the transient characteristics of the signal components,and the improved HHT results more accurately detect the transient characteristics of the signal.Finally,by analyzing the measured data,the improved HHT method is verified.The improved method can detect the start and end time,amplitude,frequency and other characteristics of the disturbance signal more accurately,and the error is small.