The Control Strategies For Grid-connected Inverter In Distributed Power System

With the growing consumption of the electric power, paying more attentions to environmental protection and renewable energy, distributed generation is to be the most important researches in the field of power system. But the useful technology needs high power factor, low harmonics pollution rectifiers and inverters to be its energy converters. In addition, traditional inverter could cause output voltage and current distortion and significant harmonics pollution, as well as low power factor because of its nonlinear characteristic. So, a focused research effort on the topic of grid-connected inverters is intrigued. This thesis focuses on three-phase grid-connected generation system. The main contents are as follows:Firstly, the new energy in distributed power system is summarized. The standards of grid-connected inverter are also introduced. Then the mathematic models in ABC,αβand dq frame for three-phase voltage source inverter (VSI) are established. Dead-time effect and nonlinear load disturbing are pointed as the reasons which causing the waveform distortion including.The main controllers of three-phase VSI are analyzed and the SVPWM modulation is introduced in detail. The transfer functions and closed loop design of voltage controlled and current controlled inverter paralleled with grid are described immediately. The system parameters and PI parameters are initiatively designed; meanwhile some simulation results are presented.Then, under analyzing on the reasons of output waveform distortion, repetitive control technology was adopted. A new control algorithm, PI + repetitive control, is proposed as the most effective function to eliminate the distortion of waveform. The simulation model and the proposed control algorithm are built by MATLAB, and the simulation results with linear load, nonlinear load and dead-time respectively, have shown that the inverter under PI + repetitive control can effectively reduce harmonic pollution, enhance power quality and improve dynamic characteristic of power system.The summary and further research directions would be given at last.