Research On The Algorithm Of Respective Harmonic Detection Of Active Power Filter

In recent years,the technology equipments such as sophisticated load have more requirements on the grid, what is more, various nonlinear loads have came into use, which make the harmonic distortion of the public grid more and more serious. How to detect and compensate harmonics generated by nonlinear load and improve the quality of grid become a problem which must to be solved.Therefore, the algorithm of the respective harmonic detection of active power filter is researched and compared:1. Making an analysis on two kinds of algorithms of the respective harmonic detection in frequency domain——the Recursive Discrete Fourier Transform(RDFT) and the Goertzel Recursive Discrete Fourier Transform(Goertzel RDFT). In order to solve the frequency leakage of RDFT under the condition of asynchronous sampling, an improved method based on RDFT is proposed in the second chapter, the sampling frequency is adjusted based on the frequency which detected by the phase locked loop in the new method. It proves effective by the Matlab simulation.2. Making an analysis on the principle of harmonic detection algorithm which based on synchronization rotational coordinate and putting forward the mathematical model of the single / multiple frequency detection algorithm. Based on the mathematical module of the single frequency detection algorithm, the principle and parameters of butterworth low-pass filter are analyzed and designed. Based on the mathematical module and the simulation of the multiple frequency detection algorithm, it shows that single detection module will influence another when they get together by parallel. In order to solve this problem, an improved harmonic detection algorithm is proposed after changing the structure of algorithm, it proves that the improved algorithm has better effect of harmonic detection.3.Making an analysis on the principle and mathematical model of harmonic detection algorithm which is based on the adaptive notch filter, the speed of frequency convergence of traditional harmonic detection based on the adaptive notch filter depends on the frequency and amplitude of the tested signal. An improved harmonic detection algorithm is proposed when the part used to detect frequency of traditional algorithm is instead of phase-locked loop. The simulation shows that the dynamic response speed of the new method is not affected by the frequency and amplitude of signal.4. Harmonic detection algorithms of multiple modules in parallel for three-phase system are simulated under the condition of the stable load current, the mutation of load current’s amplitude,the mutation of load current’s frequency and the load current with other harmonics which are not detected, the results of the simulation show that the effectiveness of the method for harmonic detection. At last the results of the simulation of each method are analyzed and comparised.