Droop Control Strategy Of Synchronous Fixed Frequency Microgrid

Microgrid promotes the large-scale development and application of distributed renewable energy,and effectively improves the reliability of power supply to users.Droop control is a hot topic in the research of island microgrid operation control because of its characteristics of high reliability,flexible configuration and plug and play.Due to the direct simulation of the power-frequency regulation characteristics of synchronous generators,the traditional droop control has the problem of frequency control is inaccurate and unstable.The synchronous fixed frequency microgrid uses the satellite timing signal to make the system frequency fixed in50 Hz,which avoids the frequency control deviation and frequency stability problems existing in the traditional droop control.At present,the droop control in the synchronous fixed frequency microgrid still continues the idea of active and reactive power decoupling,which makes the droop control complex in design and easy to generate circulation.To solve the above problems,a synchronous fixed frequency current control method based on I-U droop is proposed in this paper.In this method,the phase of the output current of the inverter is fixed directly by the satellite timing signal as the phase reference;The amplitude instruction value of the current is calculated by the I-U droop control to make the voltage run in a reasonable range.The synchronous fixed-frequency current control method based on I-U droop has the advantages of simple control strategy design,good power distribution effect and high stability,However,it only considers the control of power frequency current signal,and there is a serious problem of voltage distortion in the microgrid system with nonlinear load.Therefor,U-I droop based synchronous fixed frequency current method is proposed.This method adopts the droop-voltage-current three-loop control structure,which realizes the phase consistency of the output current of each inverter by the phase control loop in the droop controller,and gives the control instruction of the voltage amplitude by the U-I droop according to the output current,so as to ensure the voltage running in a reasonable range.Combined with the principles of the two control methods,the design principles of the inverter control strategy are given respectively.Through the state space model of simple microgrid,the influence of control parameters on system stability is analyzed,which provides a basis for parameter optimization.Finally,simulation and experiment prove the feasibility of the proposed method and the validity of the analysis results of the state space model.