RUC Details

A Reliability Unit Commitment plan, or RUC, determines which dispatchable generators will be active during a portion of the simulation. RUCs work in conjunction with SCEDs (Security Constraint Economic Dispatch plans) to simulate operation of the power network.

Each RUC covers a specific period within the simulation. For each hour within its applicable period, a RUC dictates whether each dispatchable generator is on or off. The unit commitment decisions in a RUC are made by building a model which reflects the current state of the power network and forecasts for future loads and future renewable power generation. The model is solved to find the most cost-efficient way to satisfy forecasted loads while honoring system constraints such as reserve requirements and line limits.

RUCs may also include pricing schedules. This option is enabled when the compute-market-settlements option is set to true. The pricing schedule sets the contract price for expected power delivery and for reserves (ancillary service products).

A new RUC is generated at regular intervals. The number of hours between RUCs is called the RUC interval. The RUC interval also dictates how many hours each RUC is active. The RUC interval must be between 1 and 24 hours and must divide evenly into 24 hours.

The number of hours of forecast data to include in the RUC model is determined by the RUC horizon. The RUC horizon must be at least equal to the RUC interval, but typically extends further into the future to avoid poor choices at the end of the plan (“end effects”). A commonly used RUC horizon is 48 hours.

Each RUC may be generated just as its applicable period is about to begin, or it may be generated in advance. For this reason, Prescient splits RUC management into two phases: RUC generation and RUC activation. In the RUC generation phase, a RUC model is created and optimized, resulting in a RUC plan. In the RUC activation phase, the commitment decisions identified in the RUC plan begin to take effect.

A new RUC is always activated at the beginning of each day, and at each time that is a multiple of the RUC interval. For example, if the RUC interval is 8 hours, then a new RUC is activated each day at midnight, 8:00 a.m., and 4:00 p.m.

To generate RUCs in advance of their activation time, set the RUC execution hour to indicate the time of day that one of the day’s RUC should be generated. If the specified time falls on a scheduled RUC activation time, then RUCs will not be generated in advance. Otherwise, the specified time is interpreted as the time to generate the next scheduled RUC. For example, if the RUC interval is 8 hours and the RUC execution hour is 14 (2:00 p.m.), then each RUC will be generated 2 hours before its activation time (because the next RUC activation time ater 2:00 p.m. is 4:00 p.m.). The gap between RUC generation and RUC activation is called the RUC delay.

When there is a non-zero RUC delay, generating a RUC model includes an additional step at the beginning of the RUC generation process. In this first step, a SCED model is created and solved for the period starting with the current simulation time and ending after the RUC activation time. Next, a RUC model is created using the future system state predicted by the SCED as its initial conditions.

The very first RUC of the simulation is always generated with zero RUC delay, even if Prescient has been configured to generate other RUCs in advance.

Prescient provides several plugin points to allow the RUC generation and activation process to be observed or modified. These are documented in the Detailed Prescient Simulation Lifecycle.