Which Generation Unit Should be Selected as Control Leader in Secondary Frequency Control of Microgrids?

In this paper, we propose a novel metric to choose control leaders in secondary frequency control of microgrids. The microgrid, as the building block of distributed generation systems, is assumed to be composed of both synchronous and inverter-connected generation units, e.g., renewable sources. Here, we formulate the stability analysis of secondary cooperative control in microgrids. To control the frequency of the microgrid, the secondary control should set one (or more) of generation units as master and the others as follower. A novel metric is proposed to measure the impact of different generation sources on the rate of frequency recovery of the distributed generation power system. The proposed metric is based on the eigenvalue perturbation analysis of the state matrix of the microgrid, which includes information on the topology of both physical power and data communication networks. Using this metric, one can rank all generation units and choose the one with the largest influence as the master node. The metric is simple to compute and can be easily used in microgrids with large number of small size generation units. Numerical simulations show the effectiveness of the proposed metric over heuristic methods such as choosing the master nodes based on their degrees, betweenness centrality, or closeness centrality values in the data communication network.