Research On Modeling And Control Strategy Of Virtual Synchronous Generator With Excitation Characteristics

The distributed generation(DG) based on renewable resources is undergoing a rapid development because of the serious problem caused by environmental deterioration and energy shortages.In order to fully absorb the output of the DG and ensure the stable operation of the power system,microgrid has been continuously developed.Unlike synchronous generator(SG)which have rotating parts to suppress the fluctuation of frequency and power flow,most of microsources in microgrid is connected to the maingrid through power electronic inverter,which has no inertia under disturbance or fault and response very fast to it.When this kind of microsources runs in island mode,it can't support the necessary voltage and frequency which load needs.Meanwhile,the parallel operation of inverters exists circulation problems which affect the efficiency and reliability of the inverter parallel operation,it is necessary to take measures to curb its circulation.Therefore,the main research contents are as follows:First of all,the main circuit topology of virtual synchronous generator is described.Then the third-order stator voltage equation and rotor motion equation of synchronous generator are introduced into the control of power electronic inverter.Virtual synchronous generator based on the third-order model is modeled.The key parameters of virtual synchronous generator control are simulated and analyzed,then the impacts of inertia and damping for the frequency of micro-grid system are obtained.Secondly,the voltage controller and power frequency controller of virtual synchronous generator are designed based on the operation characteristics of synchronous generator.In regard to voltage controller,two control strategies have been given,one is based on droop characteristic and the other is based on voltage feedback control.At last,the causes and physical meaning of circulating-current which occurs in parallel system has been discussed.Circulating-current restraint strategy has been given based on voltage control strategies.A simulation mode is built in PSCAD for proving the feasibility and effectiveness of the proposed strategies.