A Droop Frequency Control for Maintaining Different Frequency Qualities in a Stand-Alone Multimicrogrid System

Multiple microgrid (MG) systems can exist in a wide geographical area. They can interconnect and operate on different frequency qualities to enhance the penetration of renewable energy resources. To operate multiple MGs on different frequency qualities, a framework of the stand-alone multimicrogrid (MMG) system is proposed in this study. In the proposed MMG system, each MG connects to the common dc line through an ac/dc interlinking converter. A droop frequency control is proposed for the interlinking converter to improve frequency control performance and achieve autonomous power sharing. The sensitivity analysis with respect to the proposed control is performed to evaluate the stability of the converter system. The proposed droop frequency controller is evaluated in the MMG system with three MGs. The feasibility of the proposed controller is verified by the hardware-in-the-loop simulation using OPAL-RT technologies. The droop frequency controller is executed in digital signal processor TMS-320F-28335 while the proposed MMG system is modeled in a real-time simulator (OP5600). A comparison study on the proposed droop frequency control and conventional P/f control is presented. By using the proposed frequency control, the energy reserves in the adjacent microgrids can be shared effectively to achieve better performance of frequency regulation in the stand-alone MMG system.