A novel problem formulation for selection of switching angles for minimization of total harmonic distortion in cascaded multilevel inverters

Among different topologies of multilevel inverters, cascaded multilevel inverters (CMLIs) are better suited for systems having multiple DC power sources such as solar and fuel cell based systems. In CMLIs, output is controlled through switching angles of cascaded stages resulting in the fundamental component and total harmonic distortion (THD) being functions of the switching angles. So, control of CMLIs requires optimal selection of the switching angles to set the fundamental harmonic to a specific value (or equivalently for specific modulation index `m') while minimizing THD. This paper proposes a novel formulation of the problem as a multidimensional optimization problem and then solves it using Genetic Algorithm. The results show that the proposed novel objective function successfully finds unique solutions for the whole range of m while minimizing THD well below than that was achieved previously by selective harmonic elimination (SHE). It is also shown that even a 3-stage CMLI meets IEEE-519 standards for 0.74<;m<;0.83 and 0.85<;m<;0.96 for low voltage application (<;1kV) which was not reported previously because of poor problem formulation as SHE.