Research On Control Strategy Of Micro-grid Technology In Distributed Power System

The Distributed Generation System (DGS), which is based on microgrid technology, is the one of way to dramatically develop renewable energy resource, improve the reliability and expand the capacity of power supply system. The power supply of Distributed Energy System can be made up of various energy sources which are converted to electric power to form microgrid. Its units disperse separately, and connect to AC mains in parallel. To microgrid system of DG, its power supply units are parallel inverter commonly. Many parallel connection solutions, especially the wireless parallel control technique, fit to the DGS with many dispersed inverters. A perfect Distributed Micro-grid System includes parallel inverter module, output line impedance, AC mains, and the load connected to AC mains. Among the parts above, the inverter is the key component, which is in charge of converting the distributed energy to electric power and forming microgrid with proper techniques such as inverting and current sharing.The defects of conventional droop control strategy are analyzed that applied in microgrid system, and the synthetic control strategy composed of droop control and inverse droop control strategy is proposed. This control strategy perfects well in improving of stability, restricting the occurrence of over-current, achieving seamless switching during state transferring.In addition, the inverse droop control strategy provides possibility of setting different response time by various energy storage device.The system control strategy's idea and stability are demonstrated comprehensively, and the main circuit topology, the output characteristics and control stability of voltage control type inverter and voltage control type inverter are also researched as well. The parameter of output filter and the double closed-loop voltage adjuster of inverter are designed in detail, the same is the closed-loop current adjuster for power regulation. Moreover the math model of droop parallel control and synthetic control are build, based on the model, references for system design have been analyzed and discussed. At the same time, it expounded the effects on system performance of each control variable in power control loop with bode diagrams. With establishing and analyzing the simulation model of microgrid system based on single inverter by MATLAB, both dynamic and steady performances of the system, which controlled by the synthetic control strategy, have been proved well.