Research On The Improved Power Control Strategies Of The Distributed Generation In Microgrid

Microgrid is an effective solution to the intergration of various kinds of distributed generations(DG),and it is a helpful way for renewable energy comsuption in customer side.Control strategy of DGs is the key point to the stable operation of mictorid.In this dissertation,some power control strategies for DG units in microgrid are systematically and thoroughly studied,and the major work is illustrated as follows:(1)The sub-modules of microgrid,consisting of DG,line impedance and load are modeled in state-space form and all are combined together on a common reference frame.The mechanism of the microgird dynamic performance influenced by the change of control parameters and line impedance is analyzed in detail through the eigenvalue analysis and time-domain simulation.Further,the output power characteristics of DGs in parallel are studied,and it illustrates the relation between the circle current generation and mismatched line impedance.(2)An improved droop control is proposed to solve the reactive power sharing problem caused by the mismatched line impedance.The active and passive line impedance observers are designed,and an improved droop control strategy based on voltage compensator is given.The simulatrion results show the proposed line impedance observers can identificate the line impedance in different conditions,and the improved droop control can improve the reactive power sharing accuracy without need of the real-time communication system.(3)With consideration of network topology impact,an improved droop control strategy is proposed based on the consensus theory.It can improve the dynamic performance and reduce the communication demand.The virtual droop control scheme is proposed with combination of constant voltage,constant frequency control and constant power control,which can eliminate the frequency deviation in steady condition.(4)The dynamice performance of the conventional droop control is improved in structure and parameters aspects.In structure aspect,the angle of line impedance and a derivation term are added;in the parameter aspect,the optimization algorithm is introduced to obtain the optimal control parameter.The results show the improved control can obviously improve the dynamic performance,and don't pose any negative impact to steady performance.(5)On the basis of the line impedance observer,an adaptive virtual synchronous generator control scheme is proposed.It can tune the control parameter of virtual synchronous generator scheme according to the change of operation condition.The theory analysis and the experimental results show that the proposed control scheme is superior to the conventional virtual synchronous generator control scheme.