Study On The Detection Of Harmonic And Inter-harmonics In Power System

The high power quality is the goal in the field of electric power.With the development of science and technology,more and more new complex power electronic devices are applied to the power system.At the same time,a large number of nonlinear loads are connected to the power system,which makes the harmonic and inter harmonic pollution in the power system become more serious.Real-time and accurate detection of harmonic and inter harmonic content is the prerequisite for analyzing power system and effective management of power system.Accordingly,the following research is carried out in this paper.This paper first introduces the instantaneous reactive power theory,and the harmonic detection model of p-q and i_p-i_q is built in MATLAB.The traditional i_p-i_q harmonic current detection algorithm,due to the existence of low pass filtering link,has a certain detection delay,so the low pass filter link is changed into high pass filter link.Comparing the final results of the two model systems,the improved i_p-i_q harmonic current detection algorithm is verified,and the total harmonic current in the simulation system can be detected accurately,and it has good real-time performance.The paper deeply studies the Hilbert-Huang transform theory(HHT),and applies HHT to the active power filter.In the HHT algorithm for harmonic and inter harmonic current detection,the measured current signal through empirical mode decomposition(EMD)into a series of intrinsic mode function components(IMFs).IMF represents the fundamental component or a harmonic component of a frequency.Through Hilbert transform to get the frequency and amplitude of each IMF,and then achieve the detection of each harmonic and inter harmonic.In the EMD process,in order to solve the problem of undershoot and overshoot of the envelope curve,the envelope of the signal to be measured is obtained by using the piece-wise Cubic Hermite Interpolating Polynomial.In view of the endpoint effect of EMD and the periodicity of the current signal to be measured,this paper replaces the mirror extension algorithm with the adaptive waveform continuation algorithm to weaken the impact of the endpoint effect on the decomposition effect.To further verify the effectiveness of the improved algorithm,the improved EMD is applied to the harmonic and inter harmonic current detection of active power filter,Compared with the improved i_p-i_q algorithm,it is proved that the improved EMD has good performance.