Modular High-frequency PV Grid-connected Inverter

As a new type of green renewable energy, solar energy has many advantages such as large reserves, clean and environmental protection. With the energy crisis and the worsening environmental pollution, more and more attention has been paid on the use of solar energy, the most important technology to the use of solar energy is solar photovoltaic technology, development of recent two to three decades shows that the gird-connected photovoltaic energy generation is the mainstream of solar photovoltaic technology, in which grid-connected inverter of the grid-connected PV system becomes the core energy conversion device. Whether the market would accept the photovoltaic grid-connected inverter depends on its power generation efficiency and cost, which relates to whether photovoltaic power generation system could be used on a large scale, in which the maximum power point tracking (Maximum Power Point Tracking, MPPT) technology and the choice of circuit topology are closely related to these two factors, so at present, the development of high efficiency and high Cost-effective of photovoltaic energy generation system is a world goal.This paper analyzes some common circuit topologies in current grid-connected PV system, on the basis of summarizing the advantages and disadvantages of these topologies, Choose a high-frequency isolation circuit topology as the main circuit of grid-connected PV system in this thesis. Except for achieving higher voltage, the main function of the first stage phase-shifted full-bridge circuit is designed to implement maximum power point tracking. In this thesis, the mathematical model has been made and the output characteristic curves in different light intense and temperature of photovoltaic cells has been studied as well. Based on the conventional MPPT method, the sliding mode variable structure control (Sliding Mode Variable Structure Control,SMC) has been discussed, and then the fast dynamic response and the steady MPPT control have been achieved. Full-bridge inverter circuit is served as the second stage, and the conventional direct current control strategy was applied to implement the grid-connected power generation.In this thesis, the experimental prototype were developed to verfy the control algorithm and the modeling. Here, the DSP TMS320F2808from Texas Instrument is choosed as the main CPU so as to implement the fully digital control. The experiment results indicate that the system has good dynamic and steady state performance. MPPT SMC controller studied in this thesis can exactly track the step-change of the solar power...