Two-stage Miniature Photovoltaic Grid-connected Inverter Based On LLC

Under the background of photovoltaic module production costs continue to reduce the household(rooftop) of small grid-connected PV system gradually into life, and access to millions of households. And with its matching miniature photovoltaic grid-connected inverter demand also will continue to increase. How to further improve the circuit topology optimization, improve the overall efficiency of the micro PV grid inverter and extend its working life already is an important research focus in the direction of power electronics. In this paper, veneer PV modules(power 260 W / each) developed a miniature photovoltaic grid inverters, main contents are as follows:(1) Introducing the photovoltaic grid development status and research status of the MI, and to determine the two-stage main circuit: preamp LLC resonance circuit stage full-bridge inverter circuit. At the same time, between the front and rear stages of the circuit increases the decoupling circuit, to extend the overall micro-inverter service life.(2) Designing the DC / DC circuit in the first stage. By analyzing and comparing different topologies, selected to achieve soft switching, and high power density of the LLC resonant converter as a front-end circuit; the use of simulation software to its stability is analyzed, and the design parameters; analyzing several common maximum power point tracking(MPPT), select a variable step perturbation and observation method.(3) Designing the second stage inverter circuit. This paper select the full-bridge inverter circuit bipolar control of the pre-reverse into a DC power frequency alternating current into the grid by LCL filter; using dual-loop control method for tracking the grid voltage and current functions.(4) Designing the decoupling circuit. This paper select the DC bus link increased decoupling design; decoupling circuit design to solve the micro inverter power imbalance at the same time, so that the circuit structure of the electrolytic capacitor capacitance values decrease, and can use a thin film capacitor replaced, thus extending the life of the micro-inverter.(5) Simulation and experiment of the studied MI. Using Saber software and Matlab software for circuit simulation; build hardware circuit and write a program.The simulation and experimental results show that this miniature photovoltaic grid inverters basically reached the design requirements, the program has effectively improved the micro-inverter efficiency and prolong the life of the micro-inverter.