Two-Stage Coordinated Voltage and Frequency Control of Islanded Microgrids with Droop Controlled Inverters

Inverters can provide active and reactive power support for frequency and voltage. However, the deterministic droop control parameters are not applicable for microgrids operation under different load level. To address the frequency or voltage violation caused by the load fluctuation, this paper proposes a two-stage optimization model for islanded microgrids considering droop control of inverters. In this framework, the droop control parameters are set every 15 minutes in first-stage. And resources of inverters are allocated under the parameters in first-stage. The modification of droop control parameters is performed in second-stage when the unexpected frequency and voltage violation happens. After modifying the droop control parameters, the optimization returns to first-stage which reallocates resources of inverters. Accordingly, the second-stage is event-triggered when the load level is heavy. Moreover, the bilinear terms are relaxed using McCormick method. The proposed optimization model is tested on an islanded microgrid which is modified IEEE33-Bus system. The results show feasibility of frequency and voltage recovery.