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Multi Interval Optimization

Multi Interval Optimization. Issues To Be Discussed. Constraining units on/off during demand pick up and ramp down Thermal units reversing direction Thermal units operating below minimum Hydraulic units dispatched below safe operating range Reduction of number of dispatches

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Multi Interval Optimization

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  1. Multi Interval Optimization

  2. Issues To Be Discussed Constraining units on/off during demand pick up and ramp down Thermal units reversing direction Thermal units operating below minimum Hydraulic units dispatched below safe operating range Reduction of number of dispatches Any other issue

  3. Constraining Units • The dispatch problem: • Demand • 0 30 60 140 240 240 180 120 60 0 • OFFERS: • GEN A 120MW, 12 MW/MIN,$40 first 5 intervals,$50 after • GEN B 120MW,9 MW/MIN, $50 first 5 intervals,$40 after • GEN C 120MW,100MW/MIN, $200 all intervals

  4. Solution using Current Algorithm • Interval 1 2 3 4 5 6 7 8 9 • GEN A 30 60 120 120 120 60 0 0 0 • GEN B 0 0 20 65 110 120 120 75 30 • GEN C 0 0 0 55 10 0 0 0 0 • Over generation in intervals 8 and 9 • High cost in intervals 4 and 5 • GEN C is on for two intervals

  5. Pre-Dispatch, Real Time and Real Time Look Ahead Real Time - 5 min Dispatch Real Time Look Ahead - Looks 11 intervals out. Determines Max/Min requirements and passes to R/T Interchange Schedules Pre-Dispatch - Schedules IS Transactions and makes unit Committments

  6. Proposed Dispatch Algorithm • Dispatch for the peak demand interval will be used to set the minimum unit outputs for all the other intervals • Dispatch for all intervals will start with the last interval and move toward the first interval • unit outputs limited by their ramp capability from current time and the dispatches of next and peak demand intervals • These dispatches can be issued as advisories • They can be used to set the minimum and maximum output of units (constrained on/off) in the intervals before the critical times to ensure that this dispatch is achievable

  7. Possible Solution • interval 8 interval 9 interval 10 interval 11 • min dispatch min dispatch min dispatch min dispatch • GEN A 30 30 60 65 120 • GEN B 0 30 30 75 75 120 • interval 12 interval 1 interval 2 interval 3 • max dispatch max dispatch max dispatch max dispatch • GEN A 120 60 30 15 • GEN B 120 120 90 90 45 45

  8. General comments • If power system conditions don’t change, we should be able to produce dispatches consistent with the advisories • Only slow units are constrained on/off • The overall solution may not be optimal (in this case it is) • The only modification to the existing algorithm is the calculation of the minimum and maximum output of the units • Multiple critical points can be used. The highest minimum and lowest maximum will be used in the interval dispatches.

  9. Thermal Units Reversing Direction • Thermal units can not reverse direction without a period of time of steady operation • Proposed solution:If the unit was not in steady operation for pre specified period of time, set unit minimum to last dispatch instruction if it was ramping up or set its maximum to last dispatch instruction if ramping down. • Only change to current algorithm is to check unit previous dispatch instructions and set its minimum or maximum if required.

  10. Thermal Units Operating Below minimum • Once a unit starts, it must ramp up to its minimum • Proposed solution: If the unit is ramping up and is below its minimum, set its minimum output equal to the lesser of its minimum or its previous dispatch plus five times its ramp rate • Only change to current algorithm is to check previous unit dispatch instructions and set minimum unit output if required.

  11. Hydraulic Units Operating in an Unsafe Operating Range • Hydraulic units should not operate in a range that will cause damage to the unit. • Proposed solution: Perform post dispatch sanity check of the dispatch. Move hydraulic units up/down depending on where they are within the exclusion range. • Aggregated units may need special treatment • The point below which the dispatch goes to zero could be moved up/down to bring net change in dispatch within acceptable limit • The net change in dispatch to be handled by AGC • Need to decide if security assessment should be done after dispatch adjustment.

  12. Reduce number Of Dispatches • Three possible solutions: • Add a term to the cost function to reduce the number of dispatches - All are nonlinear can not be handled by LP • Change the LP engine to pick only the solutions that meet the number of dispatches criteria - ABB uses off the shelf LP package- cannot change it • Perform post dispatch sanity check to eliminate small dispatches - could be combined with safe operating range issue for hydraulic units issue to reduce the impact on AGC.

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