4aSCEDBasePointDispatchWhitePaperw-ERCOT.com.docVIP

SCED Base Point Dispatch Introduction: The Nodal Protocol requires that Resource Base Points be communicated to each QSE on each execution of SCED. On receipt of the Base Points, should QSEs control their Resources to those Base Points on their own using ramp rates selected by the QSE or should these Base Points be ramped from ERCOT, coordinated across all QSEs from one SCED execution to the next in order to minimize overall cost to manage power system frequency? NRG: Resources that are controlled by “Setpoint” vs. “Pulse” will produce different results. Pulse units need the “full time ramp” to move the Resource to the target output. Setpoint control can send the entire “step” change to the resource in one single output from the “GMS” and the local controls at the resource controls the ramp. When Resource controls are implemented at QSEs selected ramp rates, additional ACE or frequency deviation is produced from all the various Resources responding at different ramp rates and with different response delays on each Resource. For example, if two Resources with different ramp rates had both been asked to move 20 MW, one up and one down, the faster ramping Resource will complete its control first resulting in a frequency error until the other Resource completes its control. This effect can be reduced when the Resource controls are ramped in a coordinated manner and can reduce the total amount of Regulation Ancillary Service that ERCOT needs to manage the power grid. NRG: Permissive ACE is a great tool, but the permissive range needs to be outside “normal” frequency oscillation. (outside typical steel mill frequency swing). If Permissive operation blocks “Pulsed” resources from moving, they will lag farther behind “Setpoint” Resources since pulse units need the full ramp period to move the unit at maximum ramp rate. Pulsing while opposing frequency is necessary in order to get the Resource to the target. The Permissive limits should be set +/- 0.075 Hz, (firs