Analysis and Implementation of an Improved Flyback Inverter for Photovoltaic AC Module Applications

Flyback inverter has the advantages such as compact conformation, simple control loop, electric isolation, high step-up ratio, high efficiency, etc., therefore is an attractive solution for photovoltaic ac module applications. In this topology, BCM is more preferred compared to DCM and CCM, because of its higher power level, higher efficiency and wider switching frequency bandwidth. However, the control of BCM is more complicated due to its variable switching frequency. This also leads to the difficulty to get the accurate mathematical model between the output current iout and the reference current iref, which has a great influence on the THD of iout. This paper analyzes and proposes a mathematical model between iout and iref in BCM through theoretical derivation, and proposes a novel control strategy to generate the reference current that can decrease THD of output current. Meanwhile the realization of MPPT based on the mathematical model is also investigated. Finally, simulation and experiment results based on an improved flyback-inverter prototype are presented, which validates the proposed mathematical model and the control strategy.