Distributed Secondary Control of AC Microgrid and its Frequency Domain Analysis Considering Time Delay

In this paper, distributed secondary control of AC microgrid (MG) is studied and the influence of communication delay on its control performance is analyzed and verified. Firstly, a secondary control strategy for the MG is designed to achieve frequency recovery and proportional active power dispatch. Secondly, the stability of the MG system is analyzed in the frequency domain and a rigorous formula is derived to calculate the delay margin for the stability of the distributed secondary control with communication delays. The theoretical calculation results of the stability margin are approximately consistent with the simulation results, with an error of only 1.27%. The effects of the algorithm gains, communication topology, and connection weights on the delay margin are discussed based on the derived formula. The results demonstrate that the algorithm gain is inversely proportional to the delay margin. Changes in the communication topology and connection weights lead to changes in the maximum eigenvalue of the adjacency matrix L, which in turn affects the delay margin. Moreover, the influence of time-varying delays is considered. The system can tolerate greater time-varying delays than fixed delays. Simulation and experimental results validate the effectiveness and feasibility of the proposed method.