28-08-2012, 03:18 PM
A Simple Unit Commitment Problem
A Simple Unit Commitment.ppt (Size: 73 KB / Downloads: 170)
Economic Dispatch (Covered last time)
With a given set of units running, how of the load much should be generated at each to cover the load and losses? This is the question of Economic dispatch.
The solution is for the current state of the network and does not typically consider future time periods.
Deciding which units to “commit”
When should the generating units (G) controlled by the GENCO be run for most economic operation?
Concern must be given to environmental effects
How does one define “economic operation”? Profit maximizing? Cost minimizing? Depends on the market you’re in.
Problem Setup
Last meeting we discussed the economic dispatch problem
Now we will see how the unit commitment fits into the general picture
Unit commitment is bound to the economic dispatch
Use similar optimization methods
What is Unit Commitment (1)
We have a few generators (units)
Also we have some forecasted load
Besides the cost of running the units we have additional costs and constraints
start-up cost
shut-down cost
spinning reserve
ramp-up time... and more
What is Unit Commitment (2)
It turns out that we cannot just flip the switch of certain units on and use them!
We need to think ahead, and based on the forecasted load and unit constraints, determine which units to turn on (commit) and which ones to keep down
Minimize cost, cheap units play first
Expensive ones run only when demand is high
How Do We Solve the Problem
If a unit is on, we designate this with 1 and respectively, the off unit is 0
So, somehow we decide that for the next hour we will have "0 1 1 0 1" if we have five units
Based on that, we solve the economic dispatch problem for unit 2, 3 and 5
We start turning on U2, U3, U5
When the next hour comes, we have them up and running