Unit Commitment With Frequency Stability Enhancement for an Isolated Power System

Abstract

This paper presents an efficient mixed-integer linear programming approach to unit commitment (UC) in isolated power systems while maintaining frequency stability under loss of generation contingencies. The dynamic frequency constraints considered are formulated using the center of inertia (COI) concept to determine the dominant parameters affecting system frequency response, specifically addressing the rate of change of frequency and the frequency nadir. Another significant contribution of this work is to propose a simple and computationally efficient method to obtain the lower bounds for the frequency constraints through the random sampling of generation unit combinations. Additionally, this paper introduces a load frequency sensitivity index-based method for determining the procured volume of dynamic regulation reserve from the ancillary service market. By incorporating these methods into the UC framework, the system can better adapt to system frequency dynamics. The proposed approach is validated using the benchmark system of Taiwan Power Company. Simulation results demonstrate the efficacy of the proposed methods in enhancing frequency stability during both low and high load demand days. Comparative analyses also highlight the benefits of Taipower’s internally provided dynamic regulation reserves. These reserves are enforced through frequency constraints in the proposed UC model, resulting in increased online units and enhanced frequency nadir compared to the conventional UC method. External procurement of dynamic regulation reserves is more cost-effective and recommended during low load demand days.

Keywords

• Dynamic regulation reserve
• load frequency sensitivity index
• mixed integer linear programming
• unit commitment