Makhdoumi - Tehran University
Ranjbar - Electric Power Research Center
Mostaghimi - Electric Power Research Center
Brahmandpour - Electric Power Research Center

Unit Commitment (UC) is the problem of determining the schedule of generation units within a power system subject to device, and operating constraints . The decision process selects units to be on or off and the power generation for each unit. Lagrangian Relaxation (LR) is one of the best optimization techniques for solution of the thermal unit commitment problem. In this paper Lagrangian Relaxation method is explained and its UC software is tested with a network which contains ten thermal units. The generic UC problem can be formulated as minimize operational cost subject to minimum Up-time and Down-time constraints Generation constraints Unit status Load satisfy constraints Reserve constraints Crew constraints The objective function is operational costs grouped into the following categories - Fuel costs -Start up cost This method decomposes the UC problem into master problem and more manageable subproblems that are solved iteratively until near optimal solution is obtained. The subproblems are solved independently Each subproblem determines the commitment of single unit. The subproblems links with lagrangian multipliers. The lagrange multipliers are computed at master problem. Once computed lagrange multipliers are passed to the subproblems . The solution of the subproblems by forward dynamic programming is fed back to the master problem and updated multipliers are obtained and used by the subproblems again. This process is repeated until solution converges.