  Conventional electromagnetic transient (EMT) and phasor-domain hybrid
simulation approaches presently exist for trans-mission system level studies.
Their simulation efficiency is generally constrained by the EMT simulation.
With an increasing number of distributed energy resources and non-conventional
loads being installed in distribution systems, it is imperative to extend the
hybrid simulation application to include distribution systems and integrated
transmission and distribution systems. Meanwhile, it is equally important to
improve the simulation efficiency as the modeling scope and complexity of the
detailed system in the EMT simulation increases. To meet both requirements,
this paper introduces an advanced EMT and phasor-domain hybrid simulation
approach. This approach has two main features: 1) a comprehensive phasor-domain
modeling framework which supports positive-sequence, three-sequence,
three-phase and mixed three-sequence/three-phase representations and 2) a
robust and flexible simulation mode switching scheme. The developed scheme
enables simulation switching from hybrid simulation mode back to pure
phasor-domain dynamic simulation mode to achieve significantly improved
simulation efficiency. The proposed method has been tested on integrated
transmission and distribution systems. The results show that with the developed
simulation switching feature, the total computational time is significantly
reduced compared to running the hybrid simulation for the whole simulation
period, while maintaining good simulation accuracy.
