A New Algorithm for Hydrothermal Power System Scheduling

This paper presents a new algorithm for scheduling hydrothermal systems based on the Lagrangian relaxation technique. After system-wide constraints are relaxed by Lagrange multipliers, the problem is converted into the scheduling of individual units. This paper concentrates on the solution methodology for pumped-storage units. To over-come the difficulties caused by discontinuous operating regions of pumped-storage units, pond level constraints are relaxed. The problem can then be decomposed into the scheduling of individual hours, and the optimal generation or pumping at each hour is obtained by optimizing a single variable function without discretizing pond levels. A subgradient algorithm is used to update the Lagrangian multiliers. Testing results based on Northeast Utilities power system show that this algorithm is efficient, and near optimal solution are obtained.