Based on the allowable latency of the tasks, the cycles can be categorized into slower and faster ones. Communications technology imposes this dichotomy at about 1–2 s. As such, all sub- second cycles must reside closest to the physical system. Generally, the slower cycles acquire data from larger portions of the system and perform the more extensive computations required for system wide coordination of performance and control strategies. The faster cycles use data from a substation and vicinity to address local analytical needs to respond to rapid events, subject to the control strategies developed by the slower cycles. The execution cycles interact with each other through exchange of event triggers, control parameters, performance indicators, etc. A representative set of execution cycles for covering time scales ranging from 10 ms to 1 h is depicted in Fig. 6. The specific data and algorithms required to perform a given task (e.g., demand forecast) can vary for different cycles and hierarchical levels.
Depending on the hierarchical position of a cycle, the specific tasks assigned to it may address any or all of its objectives. For example, the objectives at the slower cycles may include various contingency analyses and resource dispatching/scheduling activities. In the 1-s cycle, the objectives may include mitigation of slow extended oscillations. The 100-ms cycle may be focused on detecting and containing instability, while the 10-ms cycle is dedicated to executing intelligent RAS designed in slower cycles and deployed subject to the defined guidelines.