The Research And Design Of Two-stage Grid-connected PV System

The solar energy as a new energy, has the advantage of clean and non-pollution, whichwill gradually replace fossil energy and become the main way of human use of energy in the21st century. Therefore, the paper studies and designs a small power station photovoltaicprototype, which is very suitable for the field of distributed photovoltaic power generationand will be used widely in China.Firstly, the thesis builds an engineering model of photovoltaic cells on the simulationsoftware platform, and analyzes its output characteristics. Meanwhile, the thesis also analyzeslight and temperature changes to the effects of its output characteristics. Based on BOOSTcircuit, the thesis conducts the simulation with different MPPT control algorithms, the resultdemonstrates the superiority of improved incremental conductance method.Secondly, the photovoltaic system consists of pre-stage BOOST circuit and post-stageinverter circuit. Among them, the BOOST circuit is used to achieve MPPT, the inverter circuitis to keep grid current with the same frequency and phase of the grid voltage through doubleclosed-loop control. Designing the inner current loop and outer voltage loop, the thesisanalyzes and calculates their control parameters.Thirdly,according to the requirements of system parameters and indicators, the thesiscarries out the selection of device parameters, and sets up the hardware circuit which includesBOOST circuit,inverter bridge circuit,signal sampling and conditioning circuit,the voltagezero crossing detection circuit,isolation circuit and drive circuit. Using DSP controller, thethesis writes software programs of MPPT control module, pll module, double closed-loopcontrol module and SPWM wave generation module.Finally, in the software simulation platform, the entire PV system model is built,simulation results show that the system implements MPPT and grid current unity power factorcontrol. On the basis of the simulation model, the photovoltaic prototype is designed, andexperimental debugging results of the prototype further validate the feasibility of the design.