Research On Distributed Secondary Control Strategy Of Island Microgrid

As a reliable means of incorporating distributed power sources into large power grids,microgrids can effectively develop and use renewable energy resources that were originally relatively decentralized.Due to the lack of support from large grids,isolated island microgrids generally adopt a hierarchical control strategy to ensure stable operation.Droop control is mostly used for primary control.However,due to the uneven distribution of the line impedance,it is difficult to meet the control requirements simply by droop control.The secondary control is divided into centralized and distributed.The centralized accuracy is high,but the reliability is poor,the distribution is more reliable,and the communication link is more flexible.Therefore,this paper studies the distributed secondary control strategy of the island microgrid.Firstly,mathematical modeling of commonly used distributed power sources is performed,and then the control strategy and operation mode of the microgrid inverter are studied.This article focuses on droop control and hierarchical control.On the premise of simulating the external characteristic curve of a traditional generator,the P-f and Q-v droop characteristic curves are established for the approximate linear relationship between active power and frequency,reactive power and voltage.The output frequency and voltage of the microgrid are stable and the power is sharing.Secondly,based on the droop control and hierarchical control,combining the finite-time theory and the consensus protocol,a finite-time distributed secondary control strategy is proposed.The proposed control strategy is completely distributed,each distributed power source communicates through a peer-to-peer sparse network without a central node.Therefore,under the premise of realizing the output to the reference value,the reliability and scalability of the system are guaranteed.In addition,considering the situation of network communication interruption,an improved extreme learning machine that increases the structural form error is proposed to predict the communication interruption data in order to solve communication packet loss and interruption issue,and validate the effectiveness of the proposed method through MATLAB.Then,accurate data transmission is the basis of the secondary control adjustment,especially considering the possible packet loss,delay,and interruption problems in communication.So properly reducing the communication pressure is very helpful to reduce the possibility of communication failure and can greatly improve the accuracy and real-time nature of communication data.Therefore,under the premise of finite-time distributed secondary control,an event-trigger mechanism is added and a trigger function is set.It is guaranteed that only when the trigger conditions are met,data is exchanged,and Lyapunov theory proves that the system can maintain stability during the entire event-trigger process,and use simulation experiments to verify the proposed theoretical methods.