Risk-Averse Unit Commitment for Hybrid AC/DC Systems Considering RoCoF-Based Inertia and Multi-Infeed Short-Circuit Ratio Constraints

To address the low-inertia frequency-security risk and insufficient voltage support at converter buses in receiving-end AC/DC hybrid systems with high wind power delivered through voltage source converter-based multi-terminal direct current (VSC-MTDC) transmission, this paper proposes a risk-averse unit commitment method that simultaneously considers rate-of-change-of-frequency (RoCoF)-based inertia constraints and multi-infeed short-circuit ratio (MSCR) constraints. The proposed method converts the post-contingency initial RoCoF limit into a minimum system inertia requirement and incorporates an operating-state MSCR constraint to jointly characterize the requirements for frequency security and converter-bus system strength. Meanwhile, an improved information-gap decision theory (IGDT) method is used to describe the upper and lower boundary deviations of wind power, and a risk-averse dispatch model is established with the objective of maximizing the allowable wind-power deviation range. Case studies on modified IEEE 30-bus and PEGASE 89-bus systems show that considering either constraint alone is insufficient to simultaneously maintain the post-contingency initial RoCoF within its prescribed limit and ensure adequate converter-bus system strength. Coordinating the two types of constraints can improve operating security, but it reduces the allowable wind-power deviation range and increases operating cost.