This paper proposes an inductor current sensorless control strategy based on modified virtual synchronous generator (VSG) method for single-phase inverter-interfaced microgrid application. Firstly, the outer power loop with Q-U integral term is presented for output reactive power enhancement, and an inner voltage regulation loop based on luenberger state observer is proposed to reduce the inductor current sensor. Meanwhile, in order to improve the response speed of the observer, the luenberger observer is designed based on the optimal pole assignment method. Secondly, a seamless switching strategy based on the modified VSG method is proposed, which can realize the seamless transition between the island mode and grid-connected mode. Finally, a single-phase 3kW VSG prototype is built, and the effectiveness and correctness of the proposed control strategy is verified by the simulation and experimental results.

This paper presents a resonant step-up DC-DC converter for the photovoltaic microinverter system and describes the converter's operation principle in detail. In the proposed converter, the active-clamp technique is used to reduce the high voltage spike of the main power switch during its turns-off. Meanwhile, the output rectifier diodes can operate in the zero-current-switching (ZCS) operation and the clamping power switch can operate in zero-voltage-switching (ZVS) condition with the series LC resonant circuit. Then, the design procedure for the key components of the proposed DC-DC converter is derived. Finally, experimental prototype with 300 W is established to verify the validity of the proposed topology, and the experimental results shows that the proposed topology processes the merits of few components, simple control, galvanic isolation and high conversion efficiency in a wide photovoltaic voltage input and power range.

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