Carrier overlapped PWM switching schemes for a cascaded three level voltage source inverter

Carrier based PWMs are easy to implement for the multilevel inverters compared to space vector based implementation. This paper proposes two carrier based PWMs called Carrier Overlapped Sinusoidal PWM (CO-SPWM) and Carrier Overlapped Switching Frequency Optimal PWM (CO-SFO-PWM) methods for the three-level cascaded inverter. The basic idea uses adding a simple offset to the carriers that create an overlap between the carrier signals. The THD performance achieved for the output voltage of the inverter and the motor phase voltage of the inverter drive is far superior especially at lower modulation indices. The proposed CO-PWMs are first simulated using Matlab/SIMULINK and are verified experimentally on a laboratory prototype by following the V/f control.