Simple model for understanding harmonics propagation in single-phase microgrids

This paper presents an analytical method developed to explain the mechanism of harmonic transfer between the ac and dc sides of a single-phase inverter in a PV microgrid. The model explains how the feed-forward of the current from the ac side of the PV-inverter into the control system, causes even harmonics on the dc voltage. It further shows how the controller's feedback of the dc bus voltage carrying even harmonics results in odd harmonics on the ac side of the PV-inverter. This harmonic propagation model is verified with a simulation of the PV microgrid system. The results of this simulation study provides consistency by proving that odd harmonics on the ac voltage causes even harmonics on the dc bus, and that even harmonics on the dc bus again causes more odd harmonics on ac voltage.