Deciding switching angles and voltage levels for a multilevel inverter using grey relational approach

Inverter is an integral part of any renewable energy conversion system. For a multilevel inverter, attempt is to obtain an output voltage which is near sinusoidal in shape. The switching angles and the voltage levels are decided in such a way so as to maximize the fundamental component with minimum THD. In this paper, it is shown how a simple method like Grey Analysis method can be used to decide the switching angles and voltage levels of a multilevel inverter so as to get an output with maximum fundamental component and reduced total harmonic distortion (THD). For a seven level inverter, six output waveforms are assumed and then the best suitable one from amongst these six waveforms is found out using this method. It is the magnitude of fundamental component and presence of harmonics, especially the lower order harmonics, which affects the output of any inverter. Thus a Multivariable Grey Relational Function is generated by quantifying the effects of multiple factors, i.e. magnitude of fundamental component and also the weighted (WTHD) effect of its harmonics, into a single index. The result thus obtained was authenticated using simulations in Matlab Simulink platform.