A Criterion and Stochastic Unit Commitment towards Frequency Resilience of Power Systems

High-capacity long-distance transmission lines, such as high-voltage direct-current (HVDC) lines, are vulnerable to extreme weather. Their failures may cause significant power loss and frequency drop in the receiving-end power systems, which should be considered in the power system scheduling. In this paper, the failure rates of transmission lines subject to extreme weather conditions are firstly modeled to obtain the probability of failure events. Then, a novel criterion defined by the integration of abnormal frequency during the primary and secondary frequency regulation process is proposed to measure frequency security. This criterion is capable to reflect the cumulative frequency deviation effect and distinguish the contributions of different frequency regulation reserve providers, e.g., generators and flexible loads. Moreover, the linearity of the criterion makes it easy to be incorporated into optimization problems. Finally, a two-stage stochastic frequency constrained unit commitment (FCUC) model is developed to optimally schedule generators and flexible loads while satisfying the frequency security constraints under transmission line failure events. The proposed FCUC model is efficiently solved by a regularized L-shape algorithm. The proposed model and techniques are validated based on the modified IEEE 118 and 300 bus systems with realistic meteorological data.