Study On Iterative Smoothing Filtering Methods And Applications In Power Harmonic Detection

Harmonic detection,as the vital part to study the harmonic problem in power system,is the scientific evidence for harmonic flow calculation,insulation equipment detection,harmonic energy measurement,harmonic compensation and suppression.A variety of harmonic detection methods such as frequency domain,time domain and time-frequency analysis are proposed with the development of electronic technology and digital signal processing technology.However,it is still a problem for the large number of scholars all around the world that how to accurately and timely detects the transient changes when current or voltage distorts in the power grid.Therefore,it is of great significance to detect harmonics in the electric power with a real-time and efficient method.This dissertation studies the iterative filtering method and its application in the harmonic detection,which includes:Firstly,the research background and significance of the harmonic detection,the definition and classification of the harmonics in power grid are summarized.And the research status of the harmonic detection at home and abroad is briefly concluded,which includes the advantages and disadvantages of each harmonic detection method Furthermore,it introduces the innovation of the proposed method,research objectives and content of this dissertation.Secondly,the principle of iterative smoothing filter method and the calculation formula of harmonic parameters are deduced,which includes the detection of the frequency,amplitude and phase angle of the harmonic signal based on the angle difference between the sampling points when the frequency deviates in the case of non-synchronous sampling after the frequency shift and filtering.Moreover,it provides the theoretical basis for practical application when gives the computational complexity of iterative smoothing filtering method.Thirdly,the measurement error modeling and analysis of the iterative smoothing filtering method is completed,which analyzes the systematic error of the proposed method and deduces the relationship between the system error and the frequency deviation,filter number and angle difference calculation.And the mathematical model of the error caused by the harmonics of the iterative smoothing method is established in the same way.Thus,the expression of the error caused by the harmonics is obtained.Finally,the simulation in Matlab and the experiment has been conducted to illustrate the correctness of the harmonic detection method proposed in this dissertation.It conducts under the fundamental frequency fluctuation with or without the harmonic to obtain the absolute error results of frequency,amplitude and phase angle.And the system error and the errors caused by the harmonics are simulated respectively,which verifies the correctness of the algorithm.Besides,the feasibility of the algorithm in practical application is proved by the detection of the actual harmonic parameters.Thus,the measurement uncertainty of the experimental results shows that the iterative smoothing method can meet the harmonic detection requirements of the GB/T 15945-2008 and GB/T 14549-1993.The iterative smoothing filtering method has the advantages in dealing with the time domain signal,which does not require the sampling period to be strictly synchronized with the signal period,and the circuit is simplified due to the remove of the hardware part to ensure the synchronization frequency.Therefore,it improves the reliability,efficiency and has the good practicality.