Harmonic Injection Scenarios for Enhanced DC-Link Utilization in Seven-Phase VSI-Fed Motor Drives

Abstract

Multiphase motor drives have enjoyed a lot of attention because they have a higher credibility of reliability, less torque ripple, and flexible fault tolerance as opposed to the conventional three-phase systems. Specifically, the seven-phase voltage source inverter (VSI) fed motor drives give extra modulation design and harmonic control degrees of freedom. But conventional sinusoidal pulse width modulation (SPWM) will restrict the fundamental voltage actually available in the linear modulation area and can result in poor harmonic performance at high modulation. The paper includes a comparative systematic investigation of harmonic injection pulse width modulation strategies of a two-level seven-phase VSI to serve a seven-phase motor drive. A number of injection cases are studied such as single harmonic injection (3rd , 5th and 7th ), combined harmonic injections and triple harmonic injected. Effects of each configuration are considered with regard to the maximum possible fundamental modulation index, total harmonic distortion (THD) of the phase voltage, and a voltage based torque ripple index (TRI). Generalized reference waveform formulation that involves the ability to choose harmonic amplitude and phase shifts is created and provided in MATLAB to assess performance comprehensively. The outcomes of the simulation prove that low-order harmonic injection, the third and the fifth harmonics in particular, can effectively enhance the utilization of the DC-link voltages by flatting the peaks of the reference waveform and expanding the linear modulation range. There is however, an increase in harmonic distortion and torque ripple. Conversely, seventh harmonic injection displays insignificant effect on fundamental voltage enhancement and has lowest THD and TRI since it is basically a common-mode phenomenon in seven-phase systems. The results obtained indicate a definite trade-off between DC-link utilization and quality of the waveforms positioned at the significance of choosing a suitable harmonic injection strategy based on the requirement of the application.