Research Article Open Access

Optimization of Harmonics for Cascaded Multilevel Inverter with Variable DC Source Voltages Using Mutative Methods

Abstract

A new approach of Harmonic Optimization of a single phase 5-level Cascaded Inverter using Selective Harmonic Elimination (SHE) is proposed in this paper. Here the DC Source voltages are considered as time varying and hence a term DC link voltage ratio is taken into account in this regard. The switching angles and DC link voltage ratio are computed using Genetic Algorithm and Particle Swarm Optimization through solving the non-linear transcendental equations describing the SHE problem that would result in minimized Total Harmonic Distortion (THD) of the output voltage waveform. Two distinct approaches: firstly, elimination of lower order Harmonic (3rd) with maintaining a desired fundamental output voltage and secondly, reducing a number of lower order harmonics (3rd, 5th, 7th, 9th, & 11th) with maintaining the fundamental output voltage are considered in this paper to minimize the Total Harmonic Distortion (THD) with giving consideration to the switching angles and the DC link voltage ratio as the optimization variables. The %THD (considering all harmonics up to 49th) of the output voltage waveform is calculated using the switching angles and DC link voltage ratio for different modulation indices. The whole procedure is repeated for equal DC source voltages and the corresponding results are compared. The switching angles, DC link Voltage ratios, and %THD obtained from the offline computation are stored in a direct look up table which can be easily applied to the online control for real time application. Simulation is being done to demonstrate the analytical results.

Ananya Pal, P.K.Saha, G.K.Panda