Unit Commitment Considering Regional Synchronous Reactive Power Requirements : Costs and Effects

Highly renewable power systems may have to
impose regional minima on the number of online synchronous units to ensure
appropriate availability of controllable reactive power. Given the declining
net loads associated with increasing wind penetration levels, these regional
constraints are anticipated to come into effect with greater frequency. Such
constraints have a tangible effect on the total cost of unit commitment
schedules, with out-of-merit units being committed solely to preserve secure
voltage regimes. The use of novel reactive power resources may make regional
constraints less necessary, and the voltage-control capabilities of
distribution-connected wind farms will be examined in this role. Harnessing
these resources may not require any roll-out of new technology, but would be an
operational change to utilise the pre-existing voltage-control capabilities
implicit in the power electronic topology of modern wind turbine generators.
Given the capital costs of new dedicated VAr sources, and the generating costs
associated with using synchronous plant for voltage control, it appears vital to
derive the greatest possible value from existing assets.