Modeling and control of a push-pull converter for photovoltaic microinverters operating in island mode

This paper presents the modeling and control of a push-pull converter integrated into a two-stage photovoltaic microinverter operating in island mode without backup energy storage components (batteries). A push-pull small signal model is presented, from which they are derived all transfer functions needed to implement the controllers that regulate the output current, input voltage and output voltage interacting with the MPPT algorithm. A significant contribution of the paper is the proposal of an innovative control structure that simultaneously regulates in island mode both the ac voltage and the dc voltage of the panels, in order to place it in the best operation point. Such operation point is calculated by a specific control loop that interacts with the MPPT algorithm. To validate the proposed concept, simulations in PSIM(TM) were carried out.