Research And Implementation On Soft-switching Based Micro-Inverter Under DCM

Abstract:Solar energy is a kind of clean, environmentally friendly, widely distributed, and boundless reserved renewable energy resources. Developing and utilizing is one of the ways to solve the energy crisis and environmental crisis. Solar energy distributed generation makes full use of its features of widely distributed and boundless reserved, which is the main trend of future development and utilization of solar energy. Micro-Inverter power generation system is an important method of solar energy distributed generation for its advantages of high solar energy utilization, modularization and intelligence.Interleaved Flyback-type Micro-Inverter is considered as the research object in this paper with choosing DCM (Discontinous Conduction Mode, the discontinuous Conduction Mode) as its working Mode.Firstly, the woking principle and the working conditions for DCM mode of Interleaved Flyback Micro-Inverter were analyzed, revealing that in conventional flyback topology, the flyback transformer excitation inductance will be resonant with the output capacitance of the flyback-type switch tube, resulting in that the excitation inductance current can’t be resetted at the start of switch cycle, and then leading to the problem of distortion of the output currtent.Secondly, the active clamp and soft switching circuit was designed, and a sectional control method was proposed. The section which current changes quickly when excitation inductance and clamping capacitance being resonant is replaced by the section that changes slowly in the new method, leading excitation inductance current stably near zero at the start of switching cycle and reaching the goal of resetting, and the problem of distortion for the output waveform of conventional flyback topology was well solved. Meanwhile, according to the control of the resonance time from the resonant between the excitation inductance current and the flyback-type switch tube output capacitance, a kind of soft switch for the flyback type swicth tube was achieved.Thirdly, based on the proposed sectional control method, a design scheme for200w Interleaved flyback Micro-Inverter has been proposed. The flyback transformer of the Micro-Inverter has been designed. And the selection of main components of the Micro-Inverter such as the flyback-type switch tube, auxiliary switch tube, the reversing switch tube bridge, the output diode, the input capacitance and the output filter have also been considered. Meanwhile, both a MPPT control method resulted from a short circuit current method combined with variable step disturbance observation method and an Anti-islanding detection algorithm from a combination of voltage and frequency have been proposed.Finally, the proposed sectional control method, the MPPT control method, and the effectiveness of islanding detection algorithm were verified through the simulation, proving the feasibility of the proposed design scheme for the micro inverter. And according to the design scheme, a prototype was made, and testing experiments were made. The reasonability and feasibility of the design scheme were well indicated according to the experimental results.