An Isolated High-Frequency Link Microinverter Operated with Secondary-Side Modulation for Efficiency Improvement

This paper discusses the operation of a single-stage, isolated, high-frequency ac-link-based single-phase dc-ac converter, suitable for photovoltaic microinverter applications, controlled using phase modulation of the secondary-side cyclo-converter devices. A detailed analysis is presented explaining the impact of prominent circuit nonidealities such as device capacitance and transformer leakage inductance on circuit behavior. The proposed extended-dead-time based modulation scheme helps in achieving zero-voltage-switching of the primary devices over the entire line cycle of the ac output and also offers the benefit of reduced transformer rms current due to absence of circulating current in the zero state. A flyback-based regenerative clamp circuit is used for mitigating voltage spikes on the secondary devices arising due to leakage inductance induced oscillations. A generic commutation strategy is also discussed, which makes operation with nonunity power factor loads also possible. Experimental results on a 260-W laboratory prototype under different load conditions are presented to illustrate the discussed principles and highlight the performance improvements.