The Research Of Dynamic Power Sharing Technology Based On Virtual Synchronous Generator

With the increasingly prominent energy crisis and environmental problems,the proportion of distributed generators connect to the grid by inverters in power system is gradually increasing.The total inertia of system is reduced with a large number of distributed generators,and thus system stability is reduced.In order to achieve stable operation of parallel system of distributed generation units and traditional generators,the Virtual Synchronous Generator(VSG)concept was proposed.The paper studies dynamic power sharing technology based on Virtual Synchronous Generator.First,the overall structure and control block diagram of distributed generation based on VSG control are presented.The mathematical model of LCL fi lter is established and the selection method of LCL filter parameter is discussed.Meanwhile,active power and reactive power regulation scheme based on virtual rotor excitation characteristic and stator impedance characteristic is investigated.And various control strategies of voltage tracker is detailedly explained in this paper.Then,the paper discusses inertia matching of parallel generation units,and gets the conclusion that inertia matching is optimal when the inertia time constant is proportional to the active capacity of the generating unit.And power sharing of parallel inverters based on VSG control is studied.Reactive power of distributed generators based on VSG control can not realizes accurate distribution according to the capacity of micro-sources,when line impedance is out of proportion with the reactive power difference coefficient of micro-sources.Thus a improved VSG control method is proposed in the paper.And the two-inverters parallel system model adopted VSG control is built on PSCAD/EMTDC to verify superiority of the proposed improved control strategy.At last,the paper explores the inner connection of VSG control and droop control based on the principle of two control methods,and get the conclusion that droop control is a special case of VSG control that the inertia time constant and the virtual damping coefficient are all zero.Meanwhile,parallel system of distributed generators based on improved VSG control and Synchronous Generators(SG)is studied.Small signal models of improved VSG control and droop control are established in order to research transient response of rotor frequency and power distribution of parallel system.And simulation results on PSCAD/EMTDC verify the validity of established small signal models.