Lagrangian Relaxation-Based Unit Commitment Considering Fast Response Reserve Constraints

Abstract

Unit commitment (UC) is to determine the optimal unit status and generation level during each time interval of the scheduled period. The purpose of UC is to minimize the total generation cost while satisfying system demand, reserve requirements, and unit constraints. Among the UC constraints, an adequate provision of reserve is important to ensure the security of power system and the fast-response reserve is essential to bring system frequency back to acceptable level following the loss of an online unit within a few seconds. In this paper, the authors present and solve a UC problem including the frequency-based reserve constraints to determine the optimal FRR requirements and unit MW schedules. The UC problem is solved by using Lagrangian Relaxation-based approach and compared with the actual system schedules. It is observed that favorable reserve and unit MW schedules are obtained by the proposed method while the system security is maintained.

Improved real-coded genetic algorithm solution for unit commitment problem considering energy saving and emission reduction demands

“…Previous efforts, however, only concentrated on efficient algorithms for UC problem, which can be applied to realistic power systems and have a reasonable execution time [1] , without considering the energy saving and emission reduction demands. Among these algorithms, Lagrangian relaxation (LR) methodology uses Lagrange multiplier for the system constraints and adds the associated penalty terms in the objective function to form the Lagrangian function [2][3] . LR is considered as the most realistic and efficient method for large-scale systems, however, only a near optimal feasible solution can be expected, for the dual optimal solution seldom satisfies the once relaxed coupling constraints.…”