Research On The Optimal Control Of Single-Phase Photovoltaic Systems

Energy is the basic material for survival and development of human and society, and it is also the blood of the world economy. In expected future, more than 60% of the worldwide energy will be indirectly consumed by converting into electrical energy. Along with the environmental problems caused by fossil fuels and the growing demand for electricity, the demand for using the new clean energy generation is increasingly urgent. As one of the most clean and huge renewable energy resources, solar energy has become focus of the world. Therefore, the study of photovoltaic grid-connected control methods is a hot topic for the current domestic and international industry and academia. Combing with the current research and development of control strategies in photovoltaic grid-connected systems, the control methods of the single-phase photovoltaic grid-connected system are in-depth research in this thesis. The research on the application of optimal control in the single-phase photovoltaic systems is the main line, and the main contents are:(1) The control methods of the two-stage photovoltaic generation system are discussed in detail. For the application of optimal control in the single-phase photovoltaic grid-connected system, the basic principle of optimal control is presented, and the application of the traditional shift operator and Delta operator in discrete systems is analyzed and compared. Moreover, the optimization method to the performance matrix of the optimal control law is proposed.(2) For the inherent nonlinear characteristics of the boost chopper converter, the discrete-time nonlinear average model of the boost chopper converter is constructed which overcomes the limitations of the traditional linear control strategy used in this non-linear system, and the optimal control method in the form of the inverse optimal is proposed in this thesis. The control law overcomes the difficulty of solving the Hamilton-Jacobi-Bellman equation and improves the robustness and the static and dynamic performance of the system. Simulation verifies the effectiveness and good characteristics of the proposed method for the boost chopper converter.(3) For the optimal control of the single-phase photovoltaic grid-connected system, the discrete-time mathematical model of the single-phase photovoltaic grid-connected system based on the synchronous rotating coordinate system is constructed, and the optimal controller for the model is proposed. More importantly, the performance matrix of the controller is also be optimized via the particle swarm optimization. Finally, simulations are provided to illustrate the effectiveness and the robustness for the changing parameters and external disturbances of the proposed method.