Investigation about numerical methods for Selective Harmonics Elimination in cascaded multilevel inverters

Selective Harmonic Elimination (SHE) is a technique allowing the elimination of well defined harmonics by a complex signal, thus improving the quality of inverter output waveforms. SHE algorithms are very complex from a computational point as they consist of the solution of a set of nonlinear equations. This paper proposes two new approaches: (i) an analytical approach consisting of a graphical analysis allowing, in a 5-level inverter, the identification of all valid solutions; (ii) an iterative fixed point method applicable to 7-level inverters. Both the approaches, which can be easily implemented in real-time using digital controllers have been successfully verified through numerical simulations.