Unlock the Flexibility of HVDC Interconnected Systems: An Enhanced Emergency Frequency Response-Enforced Unit Commitment Model

In the High Voltage Direct Current (HVDC) interconnected synchronous areas (SAs), mutual frequency support has received increasing attention. However, with the growing magnitude power imbalance boosted by extreme weather and volatility of renewable energy, the adaptability challenges on conventional frequency regulation schemes are further intensified due to the intractability in parameter tuning or scheme design. To strengthen the system resilience against small-probability extreme events, we propose an enhanced emergency frequency response (EEFR) scheme in the framework of robust frequency-constrained unit commitment (FCUC). In the proposed EEFR scheme, the instant electromagnetic power is provided by HVDC and directly compensates for the power imbalance following extreme events. Thereby the intra-area frequency disturbance is actively apportioned among SAs leveraging the inter-area flexibility. Our study, for the first time, explores the methodology of embedding the EEFR scheme into robust FCUC model, by demonstrating the model convexity and then deriving its dual form. When solving the two-stage model, the convergence acceleration techniques are developed for Benders Decomposition algorithm based on duality theorem. Through the results on test systems, the EEFR-based FCUC model is validated to be more cost-efficient when ensuring frequency stability, and provides guidelines for operators to enhance the system's resilience against extreme circumstances.

I. Introduction

With the significant advantages in long-distance power transmission capability, High Voltage Direct Current (HVDC) systems make considerable contributions to spatially relieve the contradictions between renewable energy sources (RES) generation centers and load centers [1]. In the United States, HVDC lines transfer the energy between Eastern Interconnection (EI), Western Interconnection (WI), Texas, and Quebec [2], enabling reserve sharing, especially during contingency conditions, also improving the grid reliability as well as resilience.