Research On Control Techniques Of Grid-connected Inverters Applying In Microgrid

Distributed generation (DG) is considered as power generation form that is more environmentally friendly and economical renewable energy. Distribution of generation units within an electric power system operating in parallel as microgrid, they support each other, and can perform most effectively in distributed generation energy supply system. Distributed Energy Resources in microgrid was connected to the traditional electric power system by three phase voltage sources inverter, therefore the studies on control problem of the microgrid will be simplified to the research of control techniques of grid-connected inverter applying in microgrid, which is the main point of this paper.The distributed generation system, the concept, structures and classification of microgrid were introduced in this paper successively. The paper presents state-of-the-art master/slave control method and decentralized control strategy applied currently to parallel inverter in microgrid. The control strategies Based on the principle of synchronous generator will be motivated and developed mainly. Meanwhile, after analysing the three-phase inverter control characteristic and droop control algorithm, the PQ and V/f control strategy will be described. Then the inverter outlet line resistance R and the ratio of the circuit reactance X's influence on droop control will be discussed. We describe the difference of mathematical model between VSI and synchronous generator, the synchronous generator governor and excitation system can still be used in virtual synchronous generator control system of microgrid inverter. Later, the control concept of virtual speed regulation system and virtual excitation system were established. The control strategies given can be easily operated in both island mode and connected grid mode, which can keep voltage and frequency balance. It also can effectively control the active power and reactive power. The simulation model has been established, the results verify the feasibility and effectiveness of control strategies given.