Fast Algorithm And Error Analysis Of The Method Of Harmonic Measurement Based On The Multiple Frequency Rotated Transform

In recent years, the electrical harmonic pollution is getting more and more serious with the wide use of power electronics technology. It has been a kind of general harm which affects the quality of the energy. Harmonic measurement is an important embranchment of harmonic problem. It is not only the main basis of studying the harmonic problem, but also the starting point of analyzing the problem. Harmonic measure method is the key of the measurement. In this paper, the harmonic measure method which based on the multiple frequency rotate transform theory is researched and analyzed.Based on the theory of instantaneous reactive power, the multiple frequency rotate transform theory is put forward. It overcomes the defect of that the theory of instantaneous reactive power can only measure the harmonic total amount. The positive sequence and negative sequence k-multiple frequency rotate coordinate is respectively put forward in detail. By the k-multiple frequency rotate coordinate, k time harmonic can be separated. The signal length commanded by the theory is shortest in the all measurement methods.The key sector of the multiple frequency rotate transform theory is detection of direct current component. In this paper, the alternating current component's lowest filter frequency of two-phase coordinate is brought forward. On the basis of the lowest filter frequency, to the three-phase symmetrical signal, 1/3 cycle is needed by adopting the method of the average filter to detect the direct current component. The average error is calculated. The Simulink results indicate that the average error can reach the national standard when Tc is suitable. But compare with FFT, the calculation time needed by the multiple frequency rotate transform is very long, which has influenced its wide application to a certain extent. The fast algorithm on the basis of the average filter is proposed. The strict calculation formula is derived. It has been proved that the fast form with FFT of algorithm formula can make operation with FFT, which accelerates the speed of operation greatly and makes it possible to develop the harmonic measuring apparatus based on this algorithm. The validity of this method is proved through emulation finally.The situation under which adopts several kinds of typical low pass filters to measure the weight of direct current is also analyzed in depth in the paper. The error calculate formulates is provided, MATLAB Simulink is utilized to compare good or bad,the reason is explained in term of theory. The transmission function of Butterworth type low pass filter is provided whose ranks and cut-off frequency match and emulation has carried on. It can play a guiding role to the choice of the parameter to the low pass filter.