Research On Micro-grid Inverter Based On Droop Control Strategy

With the increasing depletion of fossil energy and serious environmental problems,distributed energy has been attached attention of more and more countries all over the worldfor its characteristic of clean and sustainable, Micro-grid technology has become a hot topicas a form of effectively utilize distributed energy. The system circulating current and phaselock are urgent to solve in micro-grid system. So as to inhibit system circulating current, thevirtual impedance method is used to improve the output impedance of the micro-grid system.The enhanced phase-locked loop is used to solve the problem of phase lock, and theself-adaptive control is used to improve the shortcomings of Enhanced PLL (EPLL) caused bymutated phase. The main contents of this article are as followings:Firstly the main circuit topology of micro-grid system is described. Photovoltaic cells areused as the energy source of the system. The single-phase full-bridge inverter structure is usedin the main circuit. The principle of selecting the filter inductor and capacitor is analyzed. Thedouble-loop control system which including inductor current feedback and output voltagefeedback is designed to reach the requirements of accuracy and stability.Secondly, according to the characteristics and requirements of micro-grid system,drooping parallel control project is researched as a key point. The reasons of the circulationsystem are studied, and the virtual impedance method is used to suppress the resistivecomponent of the output impedance so as to achieve the purpose of suppress circulationsystem.And the shortcomings of EPLL are analyzed in this paper, for which the self-adaptivecontrol is adopted to control the key parameter of EPLL. When phase is mutating, the systemcan response transiently and inhibit the influence of the phase parameter on frequency. As aresult, the quality of micro-grid system is improved.Finally the simulation based on droop control strategy is used to test the proposedmicro-grid’s inverter. And the results prove the output characteristic of the micro-grid systemcan be improved with proposed theory.