High-gain isolated DC-DC converter topologies for renewable energy microinverter applications

This thesis addresses this limitation by proposing and validating a new family of isolated high-gain DC/DC converters: QBFB, CFFB, and CFQFB. The novelty of this work lies in the development of a unified converter family in which a boost-cell stage is integrated on the input side, a voltage-multiplier cell is incorporated on the output side, and an active snubber is employed to clamp switch-voltage spikes and recycle leakage-inductance energy.

Through this architecture, very high voltage gain is achieved without extreme duty cycles or large transformer turns ratio, thereby advancing the state of the art toward more practical isolated high-step-up conversion. To validate the analytical findings, comprehensive theoretical, simulation, and experimental investigations were conducted. Closed-form analysis was developed for voltage gain, semiconductor stress, and key operating characteristics, and these results were verified using MATLAB/Simulink and hardware prototypes.

Experimental tests were carried out over a range of input voltages, duty cycles, and switching frequencies, including laboratory evaluation at 22 V, 32 V, and 42 V, to characterise efficiency, waveform behaviour, soft-switching performance, and dynamic response. <br><br><i>Thesis is embargoed until 31 July 2028.</i>