| Units: | - |
| Default Value: | 0 |
| Validation Rule: | In (0,1,2,3) |
| Description: | Unit commitment integerization scheme. |
Production Unit Commitment Optimality decides how the integer unit commitment decision variables are treated in the optimization. The options are:
- Linear Relaxation (value = 0)
- The integer restriction on unit commitment is relaxed so unit commitment can occur in non-integer increments. Unit start up variables are still included in the formulation but can take non-integer values in the optimal solution. This option is the fastest to solve but can distort the pricing outcome as well as the dispatch because semi-fixed costs (start cost and unit no-load cost) can be marginal and involved in price setting.
- Rounded Linear Relaxation (value = 1)
- The RR algorithm integerizes the unit commitment decisions in a multi-pass optimization. The result is an integer solution. The RR can be faster than a full integer optimal solution because it uses a finite number of passes of linear programming rather than integer programming. The extent to which the method 'explores' the solution space is controlled by the Rounded Relaxation Tuning setting. This setting decides if a constant rule is used to decide if non-integers meet the Rounding Up Threshold, or if the threshold is varied to find the best outcome.
- Integer Optimal (value = 2)
- The unit commitment problem is solved as a mixed-integer program (MIP). The unit on/off decisions are optimized within the criteria set by the Performance MIP Relative Gap and Performance MIP Max Time settings.
Note that this option affects integerization of the unit commitment variables only. There are often other integer variables in the formulation e.g. market block sales/purchase variables, generator AGC range constraints, and unit rough running ranges. These integer decisions are never relaxed.