Distributed Optimal Control for Stability Enhancement of Microgrids With Multiple Distributed Generators

The distributed secondary control in a microgrid can be used for complementing the function of the primary droop-based control. However, its dynamic performance may be undesirable and furthermore it may introduce new less-damped modes to the system leading to oscillatory responses. Unfortunately, mechanism analysis of the undesirable dynamic performance and the possible oscillations, and more importantly, stabilization of the microgrid with the distributed secondary control have not been reported. To fill this gap, this paper first develops a unified small-signal dynamic model of the microgrid. Based on the developed model, a small-signal stability analysis is utilized to perform the aforementioned mechanism analysis. A distributed optimal controller is thereafter proposed to enhance the system stability and improve the system dynamic performance. The distributed optimal controller can coordinate multiple distributed generation units in the microgrid and exhibits robust performance under a wide range of operating conditions. Finally, theoretical analysis and time-domain simulation results on a benchmark microgrid system are provided to verify the effectiveness of the proposed methods.