Scheduling hydrothermal power systems with cascaded and head-dependent reservoirs

An optimization-based algorithm is presented for scheduling hydrothermal power systems with cascaded and head-dependent reservoirs. Within the Lagrangian relaxation framework, the hydro river catchment subproblems are difficult to solve because of the continuous reservoir dynamics and constraints, discontinuous operating regions, discrete operating states and hydraulic coupling of cascaded reservoirs. The head-dependent water-power conversion adds another dimension of difficulty since the objective functions of hydro subproblems are no longer stage-wise additive with respect to water discharge. It is difficult to solve the subproblems by relaxing the reservoir limits or the hydraulic coupling among units as in previous work. A new algorithm with a novel relaxation structure is presented in this paper to solve hydro river catchment subproblems. Numerical testing based on the data sets of a practical system shows that this method is efficient and effective to deal with hydrothermal systems with cascaded and head-dependent reservoirs, and discrete hydro constraints. The results indicate that near-optimal schedules are obtained.