Secondary Control Of Island Microgrid Based On Distributed Consistency Algorithm

Microgrid,as a new energy utilization method,is a system that integrates distributed generation units,energy storage units,energy conversion,control,and protection monitoring devices.There are two main operating modes of the microgrid: grid-connected operating mode.In this mode,the voltage and frequency of the microgrid are mainly controlled by the large grid connected to it.The off-grid operating mode is also called island operation mode.The microgrid is in this mode when the microgrid is disconnected or when the microgrid needs to operate independently due to certain conditions in the large grid.In this mode,the voltage and frequency of the microgrid are controlled by itself,so it is necessary to adopt certain control strategies to ensure the safe and stable operation of the system.For the isolated microgrid system,this paper uses a hierarchical control strategy to divide the microgrid control into two layers: primary control(local control)and secondary control.Among them,the local control mainly uses the droop control method to adjust the voltage and frequency to make it stable near the reference value.Compared with the original centralized control method,the distributed control method greatly reduces the dependence on the communication system,and at the same time,it can achieve the effect of "plug and play" and improve the reliability of the system.In the droop control,in order to realize the decoupling of the active power and the reactive power,the impedance characteristic of the line needs to be highly inductive.For this reason,a virtual impedance link is added to the traditional droop control to reduce the line.The effect of the resistive load will increase the sensitivity of the system to meet the droop control conditions.The primary droop control mainly stabilizes the voltage and frequency,but this adjustment is not perfect.It will generate a certain voltage and frequency deviation.The purpose of the secondary control is to solve this problem caused by droop control and eliminate the voltage.And frequency deviation to improve the power quality of the microgrid.In this paper,the theory of multi-agent distributed coordinated control is used.In the secondary control,a distributed consistency algorithm is used to adjust the voltage and frequency.Finally,the voltage and frequency of the distributed unit can track the reference value simultaneously.In the case of time delay,a delay consistency algorithm is used for simulation.For systems with time delay within the maximum allowable range,the effectiveness of the selected method is proved.Through the establishment of a microgrid model,this paper proves the synchronizati on of the distributed consensus algorithm,and finally performs a simulation analysis on MATLAB to verify the feasibility and effectiveness of the method used in this paper.