Research On RPWN Selective Harmonic Elimination Method Of Voltage-Type Inverter

With the development of science and technology,voltage-type inverters have become more and more widely used.In the Power Spectral Density（PSD）analysis of the Sinusoidal Pulse Width Modulation（SPWM）strategy with a fixed switching frequency,it can be observed that harmonic noise and electromagnetic interference are generated at the switching frequency and its multiples,which affects the quality of power.In Random Pulse Width Modulation（RPWM）strategy,the harmonic noise can be distributed uniformly at the fixed switching frequency and its multiples within a certain frequency range,but it cannot selectively eliminate or reduce specific harmonics.Hence,a RPWM method with selective harmonic elimination is proposed,which has great theoretical significance and important practical value.Firstly,the present situation of RPWM technology is summarized in this paper,and the harmonic is analyzed theoretically.Then,the method of RPWM selective harmonic elimination is proposed and the PWM pulse is expanded by Fourier transformation.The specific harmonic is eliminated by canceling each other before and after the expanded series.2 ideas of selective harmonic elimination are proposed in this paper.Taking the PWM pulse with leading distribution as an example,the two ideas are derived in detail.The general formula of switching period T,the random number k and and the switching frequency range corresponding to each k are calculated.In the same way,the formula of switching period,random number and corresponding frequency range of each idea for pulse position of center distribution and lag distribution are directly given.Secondly,taking the PWM leading distribution as an example,a simulation analysis of different modulations M and different frequencies f₀to be eliminated are carried out to verify the correctness of the proposed method.Based on the realization of selective harmonic elimination,the influence of different k on switching frequency is deeply studied and the frequency hysteresis control method is proposed.By selecting different k,the increase and decrease of the average switching frequency can be flexibly controlled and the frequency in the range of multiple frequency bands can be avoided and the switching frequency can be avoided from multiple frequency bands.Finally,the single-phase inverter experimental prototype platform was built.The idea 1 for the leading distribution of PWM was experimentally verified.The PSD waveforms of the output voltage and current corresponding to the different frequencies f₀to be eliminated were given.The idea 2 for lag distribution of PWM was also used verify different f₀and the PSD waveforms of the output voltage and current were also analyzed.It is verified that the harmonic power at the specific frequency and its multiples with different pulse positions,different selective harmonic elimination ideas and different frequencies to be eliminated can be eliminated by using the proposed method in this paper.Therefore,the algorithm is simple and practical.There are 42 pictures,8 tables and 70 references in this paper.