LP Dispatch Logic
The zonal dispatch logic in Aurora uses a linear program (LP) to find the optimal generation pattern and flows between zones. The LP is solved to get the solution for each hour/sub-hour period using an embedded third party solver. The model is formulated to minimize the total production cost on the system, where this cost is based upon resource dispatch costs and link wheeling charges. The solution takes into account the transmission flow limits, loss values, resource generating limits, and other user input constraints. These may include Hourly Fuel Limits, Multi-link Transfer Limits, Operating Rules, and Operating Reserve Constraints.
When using the Traditional Commitment Logic, all commitment decisions are done prior to the LP dispatch. Each resource which is committed or is a must run unit will have the cost of the minimum segment adjusted by the min gen backdown penalty value. The cost seen by the LP for each minimum segment will be equal to the original dispatch cost minus the min gen backdown penalty. This penalty value should be relatively large so that the model will only need to back down minimum generation when the problem would be otherwise infeasible. This reduced cost can be input at the system and/or resource level and is applied only to the min gen amount, not to any discretionary generation in the first dispatch segment. See Min Gen Back Down Penalty for more information on inputting this on a resource level.
If zonal demand requirements cannot be met with the available resources in the system, the model will relax the demand constraints until the problem becomes feasible. A warning message will be sent to the status screen when this happens and the details will be written to the Study Log.
The solution to the LP from the solver gives the generation pattern and flows between the zones. The zonal prices are determined using the shadow prices (i.e., dual variable values) from the solution. If Calculate System-wide Marginal Resource is selected, for each zone marginal resource the model will report the resource in the entire system which would be the first to respond to an increase in load for that zone. If this setting is not selected, the model will report the most expensive dispatchable resource operating in the zone for the hour. Note that it will not always be possible to derive the zonal price directly from the dispatch cost of the marginal resource.
NOTE: Inputs for Min gen back down penalty can be specified for any time period (annual, monthly, weekly, hourly, or sub-hourly). For information on how to specify a time series for a variable, see Entering a Time Series. The resolved hourly value is adjusted for inflation.
See also LP Dispatch Logic Details for mathematical details in this method.
LP Dispatch Logic
