RESILIENT DISTRIBUTION SYSTEM USING GRID FORMING INVERTERS

Abstract

Increasing levels of inverter-based resources (IBRs) such as solar PV and battery storage has created several challenges and opportunities for reliable and resilient operation of power systems. Challenges have arisen because of variability and uncertainty of variable renewable generation resources, lack of natural inertia in IBRs, and limited short-circuit current capability of IBRs. However, opportunities for improving grid reliability and resilience also exist owing to distributed IBRs such as rooftop solar PV and distributed battery storage and the ability to program desired response in IBRs. In this thesis, the ability of distribution system connected IBRs to improve resilience is explored. Specifically, the thesis focuses on control approaches found in literature for controlling and sharing power between multiple IBRs with grid-forming inverters (GFMs) that are connected in the same distribution network. Various control strategies such as droop, virtual impedance and virtual synchronous generator control are reviewed and the performance of droop control to share both real and reactive powers without any communication under different ratios of network resistance (R) and reactance (X) is evaluated. Further, the power-sharing dynamics and the performance of droop-control in supplying a critical load in the IEEE 13-bus test feeder system is also evaluated. Simulation results show that the R/X ratio of the network alone is not a sufficient parameter to assess the power-sharing performance of GFMs. Instead, the R/X ratio of the entire system (including the IBR filter and transformer, if any) must be considered. Simulation results obtained when supplying a critical load in the IEEE 13-bus test feeder during grid outage show that IBRs with GFMs can play a significant role in improving the resilience of distribution systems in a high renewable energy future.