Analysis On Research On Three-phase Grid-connected Photovoltaic System

The solar energy is used as a kind of efficiently renewable energy, the important source of the normal regulations energy of future. Currently, the technique of photovoltaic(PV) grid-connected generates electricity among them have become the most prospected, turn to the main form of the solar application.This paper adopted the three-phase PV grid system, is based on the main grid circuit, in which a PV generation is with reactive power compensation and harmonic restrain. In this way, PV grid-connected systems can provided not only active power, but also reactive power, which improving the quality of power supplying and capacity.Under the control of PV grid-connected systems the topology of PV power generation, solar maximum power point tracking(MPPT), harmonic and active current detection, the instantaneous reactive power compensation and harmonic restrain technique are proposed. And those operation principles and math models are further analyzed of the unified control of the PV grid-connected and reactive power compensation.According to the V-I characteristics of various temperature and various irradiance, the output of solar cell has a strong non-linear. In PV grid-connected system, do further researching of MPPT methods, analyze advantages and disadvantages of various methods, choose incremental conductance as this MPPT algorithm.Based on the active power filter(APF) theory, the control strategy is proposed for a PV grid-connected system, in which a PV generation with reactive power and uniform grid-connected control. The compensation current tracking and controlling algorithm based on SVPWM are derived from the synchronous rotating dq reference frame and discrete state space equation. PV grid-connected system can be used to provide active power to the grid, but also for reactive power compensation, harmonic restrain for APF.Islanding of PV grid-connected system and the reason for the existence of dead zone are analyzed, and the active frequency drift method is proposed. The paper introduces a kind of island detection method which combining dq transformation and positive feedback principle. The island is judged by the change of the load voltage and inverter output current waveforms.The simulink model of PV grid-connected and APF system are built with SimPowerSystem Blockset and simulink in MATLAB/SIMULINK. The simulation results show the feasibility and precision of the proposed approach.