A frequency restoration control scheme of series-parallel-type microgrids with local low bandwidth communication

Series-parallel-type microgrids include several distributed generators (DGs) connected in series to form a string, with multiple such strings then connected in parallel. The existing centralized frequency restoration control needs global communications. To reduce the communication requirements of frequency restoration control for series-parallel-type microgrids, this paper proposes a frequency restoration control scheme that relies solely on local low bandwidth communication (LBC). Specifically, the first DG in each string utilizes the local LBC network to achieve consensus control, while the remaining DGs operate without any communications. In a series-connected system, the line current serves as a common information. Global frequency restoration can be achieved by enabling only the first DG’s line current in each string to perform frequency recovery control. Compared to existing global communication-based methods, the proposed method ensures frequency restoration using only the local LBC for the first DG in each string, significantly reducing the need for communication. Meanwhile, the system’s computational complexity is reduced. Further, the stability of the proposed controller is validated based on the root locus method. Finally, simulation results with the proposed method validated the frequency restoration performance, applicability to RL and RC loads, robustness under certain communication failures, and proportional active power allocations.