A Coupled Inductor Based Ćuk Microinverter for Single Phase Grid Connected PV Applications

A single phase, single stage, non-isolated microinverter scheme is proposed in this paper which can address the issues that are commonly associated with flyback derived microinverters, such as i) the appearance of high voltage turn OFF spikes across the high frequency switch, ii) the requirement of lossy snubbers to control these voltage spikes, iii) the necessity for high turns ratio of the transformer and iv) poor efficiency due to the involvement of a higher number of components. The proposed topology involves only one high frequency switch. A resonance capacitor is employed which not only controls the turn OFF voltage spikes across this power switch but also ensures zero voltage turn ON (ZVS) for this switch. A coupled inductor based Ćuk configuration is incorporated in this topology wherein the energy trapped in the transformer leakage inductance is fed back to the grid, thereby improving the overall efficiency. Implementation of a dedicated boundary conduction control (BCM) strategy effectively limits the value of overall system ohmic losses and thereby ensures performance with enhanced efficiency. The inverter operating principle, the process for deriving the reference current expression, and the optimum design strategy for the inverter parameters are discussed in detail. A 220 W laboratory prototype is fabricated to validate the efficacy of the proposed scheme.