Designing of control and adaptive protection architecture for microgrid clustering in a ring-connected distribution feeder

Abstract

A ring-connected microgrid cluster can increase the reliability in operation and effectively reduce the problems in the distribution network such as voltage rise, harmonics, and poor power factor. This research is focused on addressing the inherent challenges associated with ring-connected microgrid clusters with several grid in- feeders. Challenges include, the complex protection design requirements and energy management with possible system topology changes under contingencies, and synchronization with several grid in-feeders. In this thesis, a ring-connected microgrid cluster with four microgrids is derived based on a real distribution feeder model in Sri Lanka to improve resilience and reliability. A two-level energy management system (EMS) is designed to harness maximum renewable energy generation, maintenance of the state of charge (SOC) levels at effective levels, and minimize the usage of diesel engines. A coordinated control algorithm is used to maintain the stable operation of the system. A local synchronization algorithm is proposed for each microgrid to transit from islanded operation to grid-connected operation. The behavior of the proposed system under different contingencies are analyzed. Thesis contributes by designing a reliable protection scheme integrating an intelligent fault detection and localizing scheme based on pattern classification of transient characteristics of current and voltage signals. Simulation-based case studies assert that ring operation increases the utilization of renewable power generation while reducing the operation of diesel generators. Analysis confirms ring networked operation maintains the voltage and frequency profile of microgrids within limits specified in IEEE 1547-2018 as designed, while improving the resilience and reliability level compared to the radial operation. The proposed protection technique has accurate, fast, and intelligent fault detection capability compared to the existing protection schemes applied in microgrid clusters. Possible improvements to the current control and protection technologies and future directions for research, which could enhance the protection of ring-connected microgrid clusters, are also outlined in this thesis.