Research On Hybrid Event-Triggered Secondary Control Of Islanded Microgrids

Microgrids are typical small-scale power system that usually operates in grid-connected or islanded mode.In order to control an islanded microgrid,a hierarchical control structure is usually adopted.The primary control generally uses droop control to balance the generation and load demand,achieving voltage and frequency stability.The secondary control is used to restore the deviation in frequency and voltage caused by droop control.Traditionally,distributed secondary control is implemented using a periodic sampling mechanism.However,under fixed sampling intervals,communication resources may be wasted,and in practice,the communication resources of microgrid communication networks are limited.Therefore,in order to more efficiently use limited communication resources,distributed event-triggered secondary control has received widespread attention in recent years.In this paper,the focus is on the problem of distributed event-triggered secondary control in islanded microgrids.The main work of this paper is as follows:(1)The secondary control problem of islanded microgrids with external disturbances is studied.Distributed secondary control law is proposed to compensate for frequency and voltage deviation caused by primary control and to realize accurate active power sharing.In order to save communication resources,a hybrid event-triggering mechanism is proposed to schedule the information transmission for each distributed generator.A hybrid system model is constructed to describe the closed-loop dynamics of the system.Based on this model,Lyapunov stability analysis and event-triggering mechanism design are developed.Compared with the existing results,the proposed hybrid event-triggered secondary control strategy not only has the potential to reduce the triggering number but also guarantees a strictly positive minimum event-triggering interval even in the presence of external disturbances.(2)The secondary control problem of islanded microgrids with communication delays is studied under the hybrid system framework.A hybrid dynamic event-triggering mechanism is proposed to reduce the use of communication resources,with a strictly positive lower bound on the event-triggering interval.A hybrid closed-loop system model is constructed that incorporates communication delays and event-triggering mechanisms,which helps to analyze the stability and performance of the system.A stability analysis method based on Lyapunov theory is proposed,which can also determine the upper bound of the system’s delay tolerance,i.e.,the maximum allowable delay.In addition,even in the presence of external disturbances,the proposed hybrid dynamic event-triggering mechanism can still ensure that the minimum event-triggering interval can be designed and specified in advance.(3)A distributed adaptive control law that does not rely on global information is proposed to compensate for the frequency and voltage deviations caused by primary control,solving the problem of fully distributed event-triggered secondary control in islanded microgrids under external interference.The proposed distributed adaptive dynamic event-triggered mechanism introduces adaptive parameters into the design of the event-triggering mechanism,which can ensure the design of the event-triggering mechanism does not depend on global information such as the Laplacian matrix while ensuring a strictly positive minimum event-triggering interval even in the presence of interference.By utilizing auxiliary functions,a new Lyapunov function is constructed for stability analysis and event-triggering mechanism design.Compared with existing results,the proposed event-triggered secondary control strategy achieves a strictly positive minimum event-triggering interval without relying on any global information.In addition,the proposed adaptive dynamic event-triggered secondary control strategy has a certain robustness to external interference.