Modified Selective Harmonic Elimination PWM with Reduced Common Mode Voltages

Existing conventional common-mode voltage (CMV) suppression methods are based on selective harmonic elimination (SHE), which suffer from unacceptable harmonic distortion and limited modulation range for CMV reduction at low switching frequency or low carrier ratios. Hence, two enhanced strategies are proposed. On the one hand, a new closed-form representation derived, which can be added to the conventional SHE to accurately represent the CMV as an objective function. On the other hand, a discrete SHE formulation with CMV suppression ability in two-level inverters is proposed, which can suppress the CMV in a whole linear modulation range and reduce the switching frequency at certain modulation ratios simultaneously. In this formulation, minimized switching frequency is the optimization objective, while the CMV suppression and low-order harmonic elimination are used as constrains. Simulation results verify the effectiveness of the improved formulations, and comparison results that between proposed formulations and conventional methods are also provided.