Harmonic Elimination in Multilevel Inverters Under Unbalanced Voltages and Switching Deviation Using a New Stochastic Strategy

Abstract

A new approach for minimization of total harmonic distortion (THD) of a multilevel flying capacitor inverter (MFCI) based on the selective harmonic elimination named stochastic THD (STHD) strategy is proposed. In the STHD strategy, the step voltage levels of multilevel inverter are considered to be varying due to unbalanced capacitor voltages. Moreover, this paper improves modeling of harmonic elimination by considering the effects of dissipative snubbers, blanking time, gate-drive circuits, and computation time in microcontrollers on the THD calculation. Switching instants are deviated from the desired moments by regarding the mentioned effects. In the proposed strategy, the switching angle variations and unbalancing of flying capacitor voltages are evaluated by 2 m + 1 point estimate strategy. Then, the formulation is combined with new modified cuckoo search algorithm and a self-adaptive mutation tactic for the establishment of new robust algorithm for minimization of the THD. The proposed STHD strategy is capable of determining the best switching angles pattern in low switching frequency without measuring current and capacitor voltages, as well as not using any controller. The proposed strategy is applied on three MFCIs and the results show that the proposed method effectively minimizes specific harmonics with low THD.