Third Harmonic Elimination by SPWM for Filter Reduction in a Over-modulated Single-Phase Inverter

In the single-phase grid-connected inverter systems the high quality Total Harmonic Distortion (THD) factor must always be considered. In cases, when the supplying voltage is reduced, the output voltage can still be assured constant in the limited range by using the over-modulation strategy that also enables better utilization of dc bus. Unfortunately, this operation incurs high order harmonics' force into the inverter output voltage, which is a huge drawback in almost all industrial applications. This paper provides a comprehensive spectrum analysis of three-level output voltage in a single-phase inverter in an over-modulation working regime. The output voltage is generated by triangular Sinusoidal Pulse-Width Modulation (SPWM) and, based on the analytical results of a frequency spectrum evaluation the dominant 3rd harmonic could be eliminated while the rest higher harmonics can be easier attenuated by using smaller output filter and the THD is lower in the wide range.