Research On The Technology Of Islanding Detection Of The Grid-connected Inverter

In recent years, as the energy and environmental problems become seriousincreasingly, the exploiting and utilizing of new energy attract much attention in thecurrent. Distributed generation system has brought a great change to the structure andoperation of power system. Islanding and islanding detection methods become the key ofthe safe and stable operation of power system.Grid-connected inverter is the core of distributed generation system connecting topower grid. Firstly, the paper presents an overview of the topologies and control methodsof grid-connected inverter, the single-phase and three-phase grid-connected inverter aremodeled and designed of closed loop control system, and the simulation verifies theeffectiveness of grid-connection.Secondly, the paper analyzes the principle of active frequency drift method, activefrequency drift method with positive feedback, active frequency drift method withperiodic disturbance and positive feedback in single-phase islanding detection methods. Inthree-phase active frequency drift method, the offset of frequency at the point of commoncoupling is resulted from the reactive current disturbance. And each method of the aboveis analyzed by simulation.Then, the paper analyzes the disadvantages of voltage positive feedback method, andthe single-phase adaptive voltage positive feedback method is proposed to increase thespeed of anti-islanding detection through adaptive transformation of the feedbackcoefficient. The per unit of voltage positive feedback method based on park’s transforma-tion is alse proposed. Meanwhile, for the unbalance of power grid voltage amplitude,negative-sequence voltage positive feedback method is analyzed. And the feedbackcoefficient is changed, following the change of rated current value and constantlychanging, increasing the speed of anti-islanding detection.At last, the hardware of the whole system is designed with the three-phasehalf-bridge inverter as the main circuit and with TMS320F2812as the main chip ofcontrol circuit. By C language programming and prototype debugging, the paper verifies the double closed-loop of three-phase stand-alone mode inverter, the soft phase lock loop,the current control of three-phase grid-connected inverter, the over voltage/under voltageprotection, the per unit of voltage positive feedback method and negative-sequencevoltage positive feedback method by experiments.