Comparative Analysis of NR and TBLO Algorithms in Control of Cascaded MLI at Low Switching Frequency

Abstract

To control multilevel inverters in medium voltage drives applications which operate at a power level of mega watts, modulation control strategies at high switching frequency are not preferable due to high thermal losses and poor converter efficiency. Instead, fundamental switching frequency technique such as selective harmonic elimination technique is one of the widely used methods. The non linear transcendental trigonometric SHE equations set which are formed in control of multilevel inverter are highly non linear in nature, hence it has been a challenging task for researchers to obtain feasible solution at desired value of modulation index. So far, in literature several techniques have been proposed to obtain the feasible switching angles in control of MLI with less %THD. All the proposed stochastic optimization techniques need the declaration of algorithmic specific parameters. This paper presents, comparative analysis of NR method with random initial guess and novel algorithm such as teaching learning based optimization technique to solve SHE equation set at different values of modulation index. To validate the proposed technique, a three phase CHB seven level inverter has been considered and the developed algorithms are tested at different modulation indices and comparative analysis have been carried out. MATLAB programming and SIMULINK environment has been considered to validate proposed method. The %THD produced at different values of modulation indices are complies with IEEE 519-1992 harmonic guidelines too.