Research On Three-Phase Grid-Connected Photovoltaic Power System

With the situation of global energy crisis and environment pollution becoming more and more severe, it is imperative to exploit and utilize the clean and regeneration energy resource. Solar energy is one of the most clean, large scale regeneration energy resource. The whole world focuses on the use of solar energy. Grid-connected Photovoltaic(PV) system will be the main utilization of solar energy. Therefore, Grid-connected PV generating technology becomes an important research field. Furthermore, with the development of high performance Digital Signal Processor(DSP), it is possible that some most advanced control strategies can be used to PV grid-connected system.This thesis focuses on single-stage three-phase grid-connected PV systems, which includes modeling of three-phase grid-connected PV systems, maximum power point tracking(MPPT) methods for PV arrays, grid-connected control of PV system.Firstly, the electrical characteristic and output characteristic of solar cell act a vital role in PV system research, especially in MPPT research. This thesis presents theoretical analysis. Avoiding the collapse of the DC bus voltage for the single-stage three-phase system when the irradiation changes greatly, an improved method based on the traditional perturb and observer (P&O) method is proposed. In the rotating frame synchronous with the grid vector voltage, SVPWM-based synchronous current vector PI controllers with feed forward compensation are used to control the grid-current of the common point in Three-phase Grid-connected PV system. The whole control system uses double loop control, the outer loop PI controller aims at controlling the output voltage of the PV array to track the voltage reference provided by the MPPT controller, and the inner loop controller has two synchronous vector PI controller to make the output current of the inverter consistent with the d-q reference currents separately.Then, this thesis makes a sufficient study in the solar energy applications and achievements in recent years, and then designs a lOkW Photovoltaic grid-connected system. The thesis carries out the details in the hardware topology, the DSP control board design, the main power items calculation. According to the design project, the thesis establishes an experiment platform. Now the built experiment platform provides a flexible and reliable foundation to realize the control algorithms.Finally, the thesis has done a lot of experiments and gathers many results on the built platform. The experiment results are shown and analyzed. Finally, the thesis gets the conclusions. The presented algorithm by the thesis reaches its synthetic control targets.