Study On Key Technologies Of Photovoltaic Array And Grid-connected Inverter

Photovoltaic (PV) power generation technology is one of the most important research topics in the field of renewable energy, which is significant in theory and practice to mitigate the world-wide energy crisis and environmental problem, as well as achieve the sustainable development of society. PV array and grid-connected inverter in PV system are researched in this thesis, in which focuses on output characteristics, optimization, simulation model, maximum power point tracking (MPPT) of PV array, and current control strategies of grid-connected inverter.The theoretical derivation of central PV array’s output characteristics under complicated illumination environment is firstly studied in the thesis. According to the different structures of PV array, the output characteristic equations of serial PV array and parallel PV array under complicated illumination environment is derived which is based on the output current and output voltage respectively; then the distribution and voltage expression of peak power points is summarized; Finally, the output characteristics of central PV array under complicated illumination environment is analyzed and related conclusions of peak power points are proposed.Simulation modeling is the key approach to research the output characteristics of PV array. The simulation model of PV module using MATLAB M file is established and it is based on the characteristic equation and equivalent circuit of PV cell; and then the model of serial PV array is given. According to the equivalent circuit of central PV array, a modularized programming model of central PV array is proposed. Simulation result demonstrates that the proposed model is suitable for different PV array structures and illumination distributions.Aiming at the complicated application environment of PV systems, local shadow becomes one of the main problems which restrict the generating efficiency of PV arrays. The output power of PV arrays with identical rated power and structure under different illumination distribution is analyzed by both theoretical derivation and simulation. Optimization rules of PV array’s prototype and installation in engineering applications are proposed, which can improve the output power of PV array under complicated illumination environment.A new maximum power point tracking algorithm based on improved optimum gradient method is proposed for the unimodal characteristic of PV module in the case of considering both control accuracy and response speed, the feasibility of the proposed algorithm is verified by simulation. In light of the multimodal characteristic of PV array under complicated illumination environment, a multi-interval MPPT algorithm is proposed, simulation result demonstrates that the proposed MPPT algorithm can improve the response speed of maximum power point tracking, and can be used in arbitrary illumination environment.Current control strategy of inverter is one of the key technologies for grid-connected photovoltaic power generation. The principle to design the predictive current control algorithm is summarized, and by means of improving the expressions for target current error and target output voltage, this thesis proposes a predictive current control model of single-phase grid-connected inverter. The key factors which influence the stability of control model are analyzed, and the interaction between model parameters and the tolerance of inductance mismatching is concluded. Finally, the proposed predictive current control model is verified by both MATLAB simulation and experimental platform, which provides theoretical basis for the selection of device parameters in engineering application.