Harmonic Evaluation of Seven-phase VSI with PWM Switching Teqnique

In the past two decades, multiphase electrical motor drives (with more than three phases) have attracted a lot of attention due to their superior advantages. Obviously, multiphase voltage source inverters (VSIs) play an important role in supplying the multiphase motor drives. Moreover, in the field of multiphase VSIs based Pulse Width Modulation (PWM) switching strategy and their harmonic evaluation, adequate research has not been reported yet. Therefore, this paper concentrates on analytical analysis of seven-phase VSIs with Pulse Width Modulation (PWM) switching strategy. Consequently, new equations have been calculated to determine exactly the harmonic contents of the phase to midpoint and line-to-line voltages in seven-phase VSIs using the double Fourier integral (DFI) analysis. Correspondingly, the related frequency spectrum and the dominant harmonic components with respect to the amplitude modulation index have been represented in this work for the first time. In order to investigate the accuracy of the proposed analytical solutions, the results obtained from double Fourier integral calculation method are compared with the results achieved by directly applying Fast Fourier Transform (FFT) to a simulated waveform. Furthermore, to achieve a more valuable verification of the theoretical and simulation results, experimental results of a seven-phase VSI have been also provided. The simulation and experimental results validate the accuracy of extracted equations.