Study On Theoretical Methods And Key Technologies Of Improving Photovoltaic Generation System Efficiency

Governments around the world have the full development and utilization of solar energy as a strategic decision for sustainable development, photovoltaic (PV) generation obtains the most attention.The solar PV market has been growing spectacularly over the resent years and is forecast confirm this trend in the coming years. However, a major drawback of PV source is the low output power density. Therefore how to maximize the use of PV array's output power is of the paramount importance which is beconing an emphasis research in this area.Combined the subject'Optimization of PV source flexibly connecting to micro-grid and the study of mechanism and effect on the micro-grid'(No.50977029)which is supported by National Natural Science Foundation of China, this thesis'Study on Technologies of Improving Efficiency of Photovoltaic Generation System' is carried on profoundly. The main contributions are as follows:1. A set of solar tracking method under all-weather was proposed. The amount of PV array's received light was raised; therefore PV array's output power was increased.The performance of solar traker under different control methods and different tracking modes was analysed, accurate calculation of the sun's position in celestial coordinates was described systematically. Based on this,2. A thorough analysis of PV module and PV array output characteristics in partial shading conditions was given,it was pointed out that ac modules system will be the mainstream of high efficient photovoltaic power generation systems.The reduction of output power in PV array can be mainly attributed to partial shadows. Comprehensive study of PV array's output power in partial shading conditions is of the most importace. Through the simulation, PV module output characteristics were carried on with one cell affected by shadowing, two cells affected by shadowing and whole module in the same shadow. Comparative analysis of the centralized system output power and ac modules system output power was obtained, with specific data confirms ac modules system can improve power output efficiency.3. A control algorithm based on Particle Swarm Optimization (PSO) algorithm for solving multiple MPPT was studied. A novel way of disperse locating the initial position of agents to all the possible local maximum voltage points is proposed in this paper, which can guarantee all the agents not converge at a local maximum and no maximum be missed. Objective function of PSO algorithm was the real-time PV array output power. The parameters of PSO algorithm were set, and efficient iteration stop strategy was proposed which can reduce the power oscillation and loss when trending to steady state. Simulation results indicate that the proposed global MPPT algorithm can fast and accurately track the global maximum under uniform solar irradiance and partially shaded conditions, and can improve the array output efficiency. This mothod is provided with good practical values.4. In the view of the judgment of islanding being easy to interfered by grid disturbance, a novel approach to detect and classify islanding or grid disturbance is presented based on Multi-resolution Singular Spectrum Entropy and Support Vector Machines (SVM). Simulation results indicate that the method can classify islanding or grid disturbance with good performance of accuracy and stability. This strategy can guarantee photovoltaic generation system take grid disturbance as islanding which can avoid system's unecessary exit, therefore efficiency of photovoltaic generation system is improved.