Research On Single-stage Grid-connected Photovotaic Inverter System And MPPT Algorithms

Nowadays, the energy shortage problem is very serious in the world. Efforts are always being tried to develop new energy sources including wind, biomass, hydro and solar. Much attention has been paid in developing these new energy sources. Among them, one of the most significant developing orientation is solar energy for its energy potential, low environmental pollution, flexible installation and strong complementary with other energy. In recent years, the rankings of solar photovoltaic power generation in global average annual growth rate of total renewable energy is the first, as an impottant development of future energy sources.This paper has researched on single-phase single-stage grid-connected PV system and MPPT technology. Starting from the basic inverter structure, it has designed parameter of the circuit, built simulation model in simulink in Matlab software. At the same time, maximum power point tracking technology has been studied, and the validation of new MPPT algorithms is carried on in simulation model. Finall it is applied in practical system.First of all, the paper analizes the inverter structure. It designs fore-stage circuit including storage filter capacitor, post-stage filter inductor and SPWM prediction algorithm. According to the designed circuit structure and parameters, simulation model is created in the block of Simulink of Matlab. By the way, DC-AC inverter function has been realized. THD of inverter current is less than 5%. In the second, the thesis researches maximum power point technology. Classical MPPT algorithms are discussed, including constant voltage method, disturbance and observe method, three center of gravity method and incremental conductance method. According to the environmental transfering characteristics of PV cell operating point, two new MPPT methods have been designed which are called the improved disturbance and observe method and voltage loop, dp/dv compensation method. By programming in Embeded Function which is in the model of simulink, new MPPT methods are realized in the simulation model system. Meanwhile, the scope in simulation watches the efficiency of maximum power point tracking and THD of inverting current. Compared with the result of classical MPPT algorithms, obviously the new MPPT method is much advanced than other methods before. In the end, the system is actually designed including hardware system and software programming, making the inverter system work well. The MPPT algorithm is also loaded into DSP2812. The final acutual system is generating well with inverter current THD less than 5%, PV energy using efficiency more than 99%.The paper presents a detailed experimental simulation model and algorithms. The reliability of built software and hareware experimental platform is high. The waveform and data in this paper is correct and the inverter power is up to 3000W, successfully connected to the grid.