Harmonic Elimination of Cascaded Multilevel Inverter for Medium-voltage Application

In this paper, a low-frequency squarewave inverter with a series-connected pulse width modulation (PWM) inverter is investigated for highpower applications. The series compensators produce only the desired harmonic voltages to make the net output voltage sinusoidal with small PWM switching harmonics only. An open-loop control strategy for the series compensator is proposed in this paper. This strategy indirectly sets the compensator dc bus voltage to the desired level. No external dc source or active power at fundamental frequency is required to control this dc bus voltage. Different variations of this basic strategy are presented in this paper for mediumvoltage applications. Theoretical analysis of this strategy is presented in this paper with simulation and experimental results.