An implicitly-coupled solution approach for combined electromechanical and electromagnetic transients simulation

This paper presents a novel implicitly-coupled solution approach for the combined electromechanical and electromagnetic transients simulation. Unlike the existing hybrid simulators that use an explicit approach to interface separate transient stability (TS) and electromagnetic transients (EMT) programs, the authors propose combining the equations of the two simulators and solving them simultaneously by an implicit approach. To combine the two sets of equations with their different time steps, and ensure that the TS and EMT solutions are consistent, the equations for TS and coupled-in-time EMT equations are solved simultaneously, referred to as TSEMT simulation. The simulation results for the proposed implicitly-coupled solution approach on the WECC 9-bus system are discussed. Along with the implicitly-coupled solution approach, a novel strategy, referred to as TS3ph-TSEMT, based on difference between the phasor boundary bus voltages of the detailed and external systems is also proposed to terminate the implicitly-coupled TSEMT simulation and continue with only the TS simulation. The computational efficiency of the proposed TS3ph-TSEMT approach is presented for the 9-bus and 118-bus systems.