An Approach to Mitigate Line Frequency Harmonics in a Single-Phase PV-Microinverter System

Single-phase microinverters used in household applications draw pulsating power from its input dc source while delivering ac power output to loads. While this introduces double line frequency harmonics into the dc bus of the microinverters, which lead to poor operational efficiencies of input energy sources (like solar arrays and fuel-cells etc.), it also deteriorates the quality of power fed to ac loads. Traditionally, large electrolytic capacitors or auxiliary decoupling circuits are used to mitigate the above-mentioned problems, making the converter system heavy, bulky, and thus increases the cost. In this letter, a new approach based on a simple pulsewidth modulation is proposed for single-phase microinverter system, aimed at mitigating the ill effects of double line frequency harmonics on both the dc side and ac side of the inverter. It is shown that by allowing a voltage swing of about 20% on the dc bus can significantly bring down the capacitance requirement by a factor of 3 to 5. Thus enabling, smaller and more durable film capacitors to be deployed instead of the bulky electrolytic capacitors. The envisaged approach is simulated and experimentally validated to support the claims on a laboratory setup.