Research On Three-Phase Photovoltaic Grid-Connected Inverter

The progress of human comes from the supply of energy. Along with the conventional energy exhausting, new energy has become the competition focus in the world. The solar energy, as the ideal and clean energy, has the broad prospects of development. Solar photovoltaic grid-connected power generation has been an important development trend in solar energy utilization, in which the photovoltaic grid-connected inverter, as a key part, determines the performances. Photovoltaic grid-connected inverters have been studied a great deal, but up to now, many problems have not been solved, especially such as the control strategy, efficiency and practicality of big-capacity three-phase photovoltaic grid-connected inverters, which remain to be investigated further.A deep research of the three-phase photovoltaic grid-connected inverter and development of its prototype are performed. In this thesis, a detail description of its hardware architecture such as its main circuit, control system, the control strategy utilized, the flow chart of the control program, modeling, simulation, experiment and the results obtained is made. In the system, the main circuit is voltage-type three-phase full bridge topology, DSP is the core of the control system, and the SPWM modulation technology with double closed-loop PI control is adopted in the control strategy.First of all, MATLAB is used to establish the physical model of the system in which the main circuit module, detection module and a control module are mainly included, and the simulation is made. The simulation results show the system mathematical model and control strategy are correct, and the system power parameters are obtained by simulation. Then, the design of the hardware circuit of the three-phase photovoltaic grid-connected inverter is made, in which the driving circuit, detecting circuit, phase-locked circuit and protection circuit, etc. are included, and their circuit topology structure and parameter setting are determined. And then, the design of the software system of the three-phase photovoltaic grid-connected inverter is made and the execution of the control strategy program is performed by DSP, in which the main subroutine, AD conversion, SPWM signal generation, phase-locked control, PI control and protection control subprogram and etc, are included.The bus voltage in DC side, three-phase grid-connected current and voltage are obtained by AD conversion, and the reference sinusoidal signal is got by double closed-loop PI feedback control. The signal is sent to the program of SPWM generation to make SPWM signal in the given logical order.Finally, a practical experiment of the prototype is made, and the results show that the grid-connected current can follow the voltage synchronistically, and its harmonics is very small, thus satisfying the requirement of the grid-connection.