Security-constrained generation scheduling with feasible energy delivery

Security-constrained generation scheduling (SCGS) is an indispensable tool for independent system operators (ISOs) to plan a secure and economical hourly generation schedule in the daily/weekly ahead markets. Power outputs of thermal units are usually formulated as step functions in almost all literature on SCGS, i.e., the generation level schedule is taken as an energy delivery schedule. The ramp-rate constraints are also simplified as limits on the differences of generation levels in consecutive time periods. However, it has been found in our previous work that the energy delivery schedule obtained from this formulation may not be realizable. The schedule obtained is generally different from what is implemented. In this paper, feasible energy delivery is embedded in SCGS model and power outputs of thermal units are formulated as piece-wise linear functions rather than step functions. The schedule obtained from the new formulation is deliverable in terms of energy and precise ramping process for implementing the energy schedule is also obtainable. A mixed-integer linear programming (MILP) method is applied to solve the problem with the new formulation and numerical testing is performed for a six-bus system and an IEEE 118-bus system. The testing results and primary analysis show that the new formulation is valid.