Title: Decentralized power flow controlling device with enhanced dynamic grid-support functionality
Committee:
Dr. Divan, Advisor
Dr. Grijalva, Chair
Dr. Saeedifard
Abstract: The objective of the proposed research is to further extend an existing hybrid transformer concept that is capable of providing steady-state power flow control to an enhanced version that is able to offer extra grid services and provide damping to small and large power and voltage disturbances and transients in the grid. With the promotion of environmentally friendly policies and advanced power electronics technology, the adoption of inverter-based resources (IBR) into the grid has exponentially increased. However, growth of IBR on the grid causes power flow congestion on critical nodes due to the volatile nature of the renewable energy sources (RES). A hybrid transformer concept has been developed to provide steady-state power flow control in the meshed grid. Besides the power congestion issues, the increased number of IBR on the grid also causes loss of inertia, loss of passivity, and potential conflicts in control objectives that result in power oscillations, power circulation and system instability. These challenges cannot be addressed with the state-of-the-art hybrid transformer concept. Using a multi-bus case study, the proposed work shows that grid-connected converters under grid-forming mode outperform converters under grid-following mode with respect to the grid-synchronization capability and dynamic voltage-forming capability. Hence, in the proposed work, the state-of-the-art hybrid transformer is extended with a storage element and a hybrid form of grid-following and grid-forming control. By applying this concept to certain weak nodes in the power system, a micro-grid can be formed to damp power and voltage oscillation and disturbances. This thesis will also explore the possibility of scalable transmission devices that can improve grid utilization of existing transmission assets, and can help to increase utility scale IBR penetration.