Modified selective harmonic elimination employed in four-leg NPC inverters

Abstract

Three-phase four-leg neutral point clamped (NPC) inverter is more suitable in dealing with all sort of the loads especially unbalanced/nonlinear due to harmonics issues. Most control strategies applied on four-leg NPC are classified as high switching frequency lead to high power losses and low efficiency. In this paper, selective harmonic elimination pulse width amplitude modulation (SHE-PWAM) technique has been implemented on a four-leg NPC inverter to reduce the switching frequency properly. In SHE-PWAM technique, the amplitude of input voltage is considered flexible in order to eliminate one more harmonic order without increasing switching frequency. The obtained switching angles of phase legs and amplitude of input voltage are used to eliminate the non-triplen harmonics (5th,…,23th) from the output voltage. On the other hand, switching angles calculated for the fourth leg are considered to eliminate the triplen harmonics (3th,…,21th) from phase voltage. The performance of proposed technique is verified by Matlab/SPS simulations.