Lecture onUnit commitment

Lecture on Unit commitment

AU sponsored FDTPDr R MeenakumariProfessorDepartment of EEE Kongu Engineering collegePaavai College of Engineering1What is Unit commitment?Scheduling of a set of generating units to be on, off, or in standby/banking mode for a given period of time to meet a certain objective.

For a power system operated by a vertically integrated monopoly, committing units is performed centrally by the utility, and the objective is to minimize costs subject to supplying all demand (and reserve margins)Paavai College of Engineering2What is Unit commitment?In a competitive environment, each GENCO must decide which units to commit, such that profit is maximized, based on the number of contracted MW

The additional MWhr it forecasts that it can profitably wrest from its competitors in the spot market; and the prices at which it will be compensated.Paavai College of Engineering3What is Unit commitment?A UC schedule is developed for N units and T periods. A typical UC schedule might look like

Paavai College of Engineering4

What is Unit commitment?Since uncertainty in the inputs becomes large beyond one week into the future, the UC schedule is typically developed for the following week.

It is common to consider schedules that allow unit-status change from hour to hour, so that a weekly schedule is made up of 168 periods.

UC decision involves committing the generating units during each hour of the planning period, by considering system capacity requirements, reserve, and the constraints on the start-up and shut-down of units.

Paavai College of Engineering5Factors to consider in solving UC problemObjective of the unit commitmentQuantity to be suppliedCompensating the electricity supplierSource of electrical energy

Regulated environment Cost minimization (or)De-regulated environment Profit maximization

Paavai College of Engineering6Constraints in the UC problemSpinning reserve Thermal unit constraintsMinimum up timeMinimum down timeCrew constraintsStart up cost

Other constraintsHydro constraintsMust runFuel constraints

Paavai College of Engineering7Solution methods for the UC problemFinding an optimal solution is very difficultsolving the UC problem requires that many economic dispatch calculations need to be performedOne possible way - do an exhaustive searchfor a small system this can be done, but for a reasonably sized system this would take too long

Paavai College of Engineering8Solution methods for the UC problem Optimisation techniques

Priority list methodInteger ProgrammingMixed Integer programmingBranch and bound methodLagrangian relaxation method

Paavai College of Engineering9Solution methods for the UC problem Stochastic Evolutionary search algorithms

Artificial Neural networksSimulated annealingGenetic algorithmsEvolutionary programmingAnt Colony optimisatonParticle swarm optimisation

Paavai College of Engineering10How Do We Solve the Problem?If a unit is on, designate this with 1 and respectively, the off unit is 0decide for the next hour. For eg., we will have 0 1 1 0 1" if we have five unitsBased on that, solve the economic dispatch problem for unit 2, 3 and 5start turning on U2, U3, U5When the next hour comes, committ them up and run 11Paavai College of EngineeringHow do we come up with this unit commitment "0 1 1 0 1" ?One very simplistic way: if we have very few units, go over all combinations from hour to hourFor each combination at a given hour, solve the economic dispatchFor each hour, pick the combination giving the lowest cost12Paavai College of EngineeringHow Do We Solve the Problem?