Parallel-in-Time Solution of Power Systems with Unscheduled Events

Transient simulation of power systems can be challenging. As models become more complex, applications require acceleration or faster than real time operations to assist system operators, and new methods of solving the problem are required. One potential approach includes time-parallel multigrid reduction methods that distribute the simulation time domain onto multiple compute units and solve the system equations with a parallel, iterative nonlinear multigrid scheme. Achieving significant speedup via these methods for real world power system problems requires examination of how the different features and characteristics of power system simulations interact with the parallel-in-time calculations and how they can be handled by such tools. One such characteristic is the use of unscheduled events that change the system at solution-dependent times. Examples of such events include equipment limits, governor deadbands, voltage regulator adjustments, or protection system actions. In sequential simulations, such events are detected by using root-finding methods or directly in control system models. In time-parallel methods these roots must be handled in parallel. In this paper we propose a method for addressing unscheduled events in time-parallel calculations for power system transient simulation.