  The power system is expected to evolve rapidly with the increasing deployment
of power electronic interface and conditioning systems, microgrids, and hybrid
AC/DC grids. Among power electronic systems, back-to-back (BTB) converters can
be a powerful interface to integrate microgrids and networked microgrids. To
study the integration of such devices into large power systems, a balance
between power electronics model fidelity and system-level computational
efficiency is critical. In system-level simulations of bulk power systems
dominated by synchronous generators, detailed electromagnetic models of
back-to-back converters may be unnecessary and also computationally
inefficient. This paper focuses on developing a simple phasor model for
back-to-back converters that can be easily integrated into powerflow solvers to
facilitate large-scale power system simulations. The model is implemented using
C$^{++}$ language and integrated into GridLAB-D, an open source software for
distribution systems studies, as a potential new capability. The GridLAB-D
phasor domain model is validated against the electromagnetic transient (EMT)
simulation of the detailed switching model. Simulation results show that the
phasor model successfully captures the dominant dynamics of the converter with
significantly shorter simulation elapsed time.
