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Selective harmonic elimination pulse width modulation (SHEPWM) is a well-known switching technique applied directly to the output voltage waveform of multilevel inverters which aims to omit low-order harmonics. Related equations for this technique are transcendental, so an objective function should be defined in order to cover all constraints. Evolutionary computation is demonstrated to be a promising tool meeting requirements of such problems. In this paper, the standard colonial competitive algorithm (CCA) is improved to be employed for the mentioned technique in two cases of equal and unequal dc sources. The results are compared with two other successful algorithms namely genetic algorithm (GA) and particle swarm optimization (PSO). Results indicate that this method outperforms other methods in terms of convergence rate and tackling local optima. Experimental results verify the simulation results. [ABSTRACT FROM PUBLISHER]

Multilevel inverters introduce harmonics to the network besides their remarkable advantages. Total harmonic distortion (THD) is one of the most important indexes to evaluate the harmonic contents of waveforms. The conventional method of line-voltage THD calculation gives approximate answers, because high-order harmonics are ignored. In this paper, an analytical algebraic method based on formulating the line-voltage THD of multilevel inverters with unequal dc sources is presented. This method, which is general and applicable to each number of switching angles, is implemented to a five-level inverter with staircase waveform as a case study. The implementing process of this method can be easily repeated for each number of levels. The accuracy of the proposed method is illustrated in comparison with the approximate method. Some advantages of the extracted formulas of line-voltage THD are simplicity and rapidity in calculations, considering all harmonics and the possibility of finding optimal switching angles analytically. Experimental results are presented to validate the theory. [ABSTRACT FROM PUBLISHER]