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A Dual-Active-Clamp Quasi-Resonant Isolated Boost Converter for PV Integration to Medium-Voltage DC Grids

With the development of renewable energy generation, medium-voltage dc collection in large-scale photovoltaic (PV) plants has become a research focus with less losses and less system complexity. Maximum power point tracking control of PV panels requires converters with a large input voltage range and a stable output, among which active-clamp isolated boost converters qualify for PV applications, due to their high and variable step-up ratio. In this paper, an improved dual-active-clamp quasi-resonant isolated boost converter is proposed to increase the efficiency and decrease the voltage pressure across switches. The proposed topology has an additional resonant branch with a small resonant capacitor on top of the conventional active-clamp isolated boost converters, where the capacitor resonates with the leakage inductor of the transformer to improve the voltage and current waveforms during switching transients. The proposed converter achieves soft switching of all the switches at both turn-on and turn-off transients, while retaining good voltage regulation ability. Additionally, the induced voltage spikes due to the parasitic inductors in the conventional topology are suppressed well. Discussions on detailed steady-state operation, zero-voltage switching (ZVS) regions, and design considerations are given to show the advantages of the proposed converter. Simulation and experimental results are presented to verify the expected performances.