The Research On Three Phase Single Stage Photovoltaic Grid Connected System

Environmental pollution and energy shortage is becoming more and more serious in today's society. In order to solve this problem, we need develop and utilize more new energy. At present solar energy is internationally recognized as one of the ideal new energy sources. The two ways of photovoltaic power generation are independent and grid-connected generation system, including independent and grid-connected generation. Photovoltaic industry is on the rise as an emerging industry, and the proportion is bigger and bigger in the electric power industry.The current situation of domestic and international resources are briefly introduced in this thesis. The status of the core control technology of photovoltaic power generation grid connected system are summarized. For the three phase single stage grid connected photovoltaic system, theoretical analysis and simulation research are finished including the output characteristics of PV array, maximum power point tracking control method, LCL filter design, the inverter control strategy and so on. The details of this thesis is as follows:First of all,in this thesis, the working principle of solar photovoltaic cells is introduced. The simulation model of photovoltaic array in the Matlab/Simulink platform is established using mathematical methods for photovoltaic cell engineering based on the characteristics of a photovoltaic array. And the output characteristic curves under different working conditions are simulated and analyzed. In the case of partial shadow occlusion of photovoltaic array, a multi peak photovoltaic array model is simulated.Secondly, the principle of maximum power point tracking and the maximum power point tracking control methods commonly used are introduced. Based on the traditional perturbation method, an improved perturbation observation method based on Ant Colony Optimization (ACO) algorithm is proposed, which can be applied to local occlusion. The simulation results are compared with the traditional perturbation observation (P&O) method. Simulation results show that the traditional perturbation method is easy to fall into local optimum under the local shadow, but the improved perturbation method can track the global maximum power point tracking quickly and accurately.Thirdly, in the design of the filter, the LCL filter structure with damping resistor Rd is selected, and the filtering performance of L, LC and LCL filters are compared and analyzed.Finally, according to the three phase single stage grid-connected photovoltaic system, this thesis adopts double loop control strategy composed of voltage loop and current loop. The simulation model of the whole photovoltaic grid connected generation system is built on the Matlab/Simulink platform, and through the simulation results, we can see that the photovoltaic system has reached the requirements of grid connection.