A combined PWM algorithm to eliminate spikes of common mode voltages

Various pulse width modulation strategies have been proposed to reduce the common mode voltage (CMV) in the variable speed motor drive system. However, unexpected voltage spikes appear as a result of the dead time effect. This paper investigates the principles of those reduced CMV PWM (RCMV PWM) methods mathematically and analyzes the reasons for those voltage spikes theoretically and experimentally. Results suggest that three-dimension active zero state PWM and near state PWM can effectively eliminate the spikes even with the dead time effect taken into consideration. Then a combined algorithm using those two methods is proposed, and it covers the linearity modulation region as large as the conventional space vector PWM. The switchover between those two methods is smooth along with the variation of the modulation index. Experimental results show that no distortion is brought to the modulation wave and verify the validity and feasibility of the proposed combined algorithm.