Dynamics and control of microgrids as a resiliency source

Microgrids can be operated in a utility-connected mode or an islanded mode in separation with the transmission or distribution system. As major disasters occur, intentional islanding of a microgrid is a possible solution to serve critical loads, within or outside the microgrids, until the utility service is restored. Through a field test, the technical feasibility to utilize microgrids as a resiliency resource is evaluated. Waveforms of the system dynamics are recorded, and the acquired data and measurements are analyzed and compared with simulation results. Technical issues arising from the starting of an islanded microgrid have been identified. The parallel operation of distributed generators is a major issue in the field test. With different droop characteristics, the dispatch rule of real and reactive power between the DGs is established. Based on the field test experience, a control scheme integrating droop control and feedback control is designed for proper power dispatch among DGs and frequency/voltage control in a microgrid. During the parallel operation, regulation of the frequency and voltage within an acceptable range is provided by the proposed control method. The proposed dispatch and control capabilities would significantly improve the dynamic performance of the microgrid. Simulation results based on a modified IEEE 13-node test feeder validate the performance of the control strategy.