Current distortion around grid zero-volt crossing and open-loop power factor in flyback AC module with a pseudo-DC link

AC modules or micro-inverters (MIC) have increasing importance in photovoltaic (PV) systems. This paper examines two issues with the flyback micro-inverter having a current-unfolding module or pseudo-dc link (FMICpseudo-dc). In one part, a theoretical analysis is proposed to explain the distortion of the grid-injected current around the grid voltage zero-crossings. It is argued that some distortion is inevitable. It is also shown that using a synchronous rectifier does not eliminate the zero-crossing distortion. However, it allows for reactive power injection. In another part an equivalent circuit and mathematical analysis are developed to predict the open loop displacement power factor of the FMICpseudo-dc operating in discontinuous conduction mode (DCM). It is shown that the power factor depends essentially on capacitor filter design while the inductor filter has little effect. To support the theoretical analysis, simulation and experimental results are provided for a digitally-controlled prototype.