Unit maintenance scheduling with fuel constraints

In the unit maintenance scheduling (UMS) problem, fuel usage limitations at a unit affect the loading of the unit and hence the maintenance schedule of units. Accounting for this interaction of fuel limits at a unit with unit maintenance and system constraints greatly increases the complexity of the problem. Using duality theory, the UMS problem with fuel constraints (UMS-FCs) is decomposed into a master problem and subproblems. The definition and the coordination of master and subproblems give rise to alternate algorithms to solve the original problem. Results of one such decomposition are presented. In this approach, the master problem solves for a trial maintenance schedule to satisfy unit maintenance constraints and unit fuel limits over all time intervals of the study. Given the maintenance schedule from the master problem, a subproblem calculates the minimum operating cost subject to system constraints for each interval of the study period. If one or more subproblems are infeasible, additional constraints are generated and then added to the master problem so that an improved maintenance schedule that satisfies the fuel and system constraints is obtained. The iteration between master and subproblems is continued until an optimal or near-optimal solution is found