Flexible Control and Stability Paradigms for the Inverter-Dominated Power System

Abstract

The addition of inverter-based resources (IBR), distributed energy resources (DER), and retirement of synchronous generation has resulted in significant changes to the transient characteristics of the bulk power system (BPS). This dissertation proposes new control and stability paradigms that leverage the flexibility offered IBRs and DERs in shaping the power system transient response and creating a stable power system. This dissertation leverages the controllable nature of IBRs to propose a flexible control paradigm where the primary control performance of existing inverters is modified to meet the transient performance needs of an evolving power system. A model-free and black-box control strategy is proposed to shape the transient response of existing IBRs without access to their internal parameters. A reinforcement learning (RL)--based algorithm is proposed to utilize local measurements to enable black-box control of IBRs in transient timeframes. Further, Lyapunov functions are learned from measurements and integrated to the RL-based strategy for stable control. Additionally, the dissertation proposes a flexible stability paradigm that explores the stabilizing aspects of a distribution system with high DER penetration, rather than considering the distribution system in the traditional context as a simple unidirectional power delivery system. The characteristic aspects of transient stability in a distribution system with high penetration of DERs are analyzed along with the role of fast DERs in impacting BPS stability. The dissertation further proposes a new voltage sensitivity-based screening metric to evaluate relative stability of distribution systems with high DER penetration.