A Modified Nearest Level Modulation Scheme for a Symmetric Cascaded HBridge Inverter

Abstract

An efficient pulse width modulation scheme for Cascaded H-Bridge inverter (CHBI) is proposedin this paper. The proposed modulation scheme is a low switching frequency modulation schemetermed as modified Nearest Level Modulation (mNLM) scheme. Compared to the conventionalnearest level modulation (NLM) scheme, the proposed modulation scheme reduces the totalharmonic distortion (THD) at the ac output of the inverter. The mNLM follows an algorithmpresented in the paper in order to arrive at a set of switching angles for MLI which offers reducedTHD. Simulation is carried out using MATLAB/Simulink 2015b software and hardware ispresented which validates the simulation results. Results show that there is a notable reduction inthe THD content with the use of proposed modulation scheme. Because of the improved THDcontent, improvement in the other inverter parameters such as rms voltage, rms current andincreased output power is also observed.