Optimal switching angles for minimization of total harmonic distortion in single phase cascaded multilevel inverters

In cascaded multilevel inverters (CMLIs), output is controlled through switching angles of cascaded stages. The fundamental component in the output and total harmonic distortion (THD) are functions of the switching angles. So, optimal selection of the switching angles is crucial to minimize THD for a certain value of modulation indexm. Selective harmonic elimination (SHE) is the most commonly used approach for THD minimization. For a k stage CMLI, SHE considers k-1 selected harmonics (generally of lower order) and focuses on their elimination. However, IEEE-519 standards dictate to consider first fifty harmonics in this regard. So, SHE is a poor problem formulation with many issues. The issues were investigated and previously we proposed a novel problem formulation as a constrained optimization problem in this regard and applied to balanced three phase systems. This paper argues that THD minimization for single phase CMLIs would result in a solution different than three phase system because of inclusion of triple-n harmonics that are ignored in balanced three phase systems. So, this paper extends the previously proposed novel problem formulation for minimization of THD in CMLIs to single phase systems. The computational results show that THD minimization for single phase systems result in different solution (switching angles) and higher value of THD as compared to three phase systems. The computational results are verified in circuit simulations.