Research On Grid-Connected Photovoltaic System

In the future, one of the main utilization of solar energy will be the photovoltaic grid-connected system. With the appearance of high-performance Digital Signal Processor (DSP) chip, it is possible that some most advanced control strategies can be used to the PV grid-connected system. The main research contents of this thesis include:I. A dynamic model of the single phase grid-connected PV system is developed using POWER SYSTEM BLOCKSETS tool of the MATLAB. Some resultants of two simulations for open loop and close loop conditions are given in this dissertation. All those works provided considerable significance and concrete helps for designing the circuit hardware of the system. A mathematical model for small signal analysis of the inverter used in PV grid connected systems is established .and two simulations based on this model for open loop and close loop conditions are also given in this thesis by help of Simulink tool of the MATLAB software.II. MPPT(Maximum Power Point Tracking) is one of the most important and well-known problem for all PV systems. Some usually used MPPT designing are analyzed and compared in the thesis. Besides, the author provides some new concepts of MPPT with his own opinion.III. For keeping the frequency and phase synchronous to the grid, a PLL (Phase Locked Loop) is necessary . A new concept of a SPLL (soft PLL) principle including author's point of view is particularly analyzed.IV. In the future, PV grid-tied systems could be one of the most important means for improving the power factor of main grid. The author analyzed its performance and advantages and has been studied it's topological construction for using as an APF (Active Power Filter).V. Islanding effect must be prevented in the application of the grid-connected PV system. An active disturbing method developed by author for anti-islanding is also given with some simulation resultants.VI. A control unit based on DSP (TMS320F240) microchip for single phase grid-connected PV system has been developed by author. The experiments in laboratory and in Beijing Gulou Station are considerable encouraging.VII. For large scale utilization of grid-connected PV system the remote data acquisition will be very important. A modern concept of remote inspecting and corresponding software for grid-connected PV system is provided in this thesis.VIII. Some non-technical obstacles of large-scale application of PV grid-tied system areanalyzed. Corresponding suggestion of strategy for development with author's point of view are mentioned. The security of installation and operation, an economic, social and environment analysis with some examples are also given in this thesis.