  The rapid deployment of distributed energy resources (DERs) in distribution
networks has brought challenges to balance the system and stabilize frequency.
DERs have the ability to provide frequency regulation; however, existing
dynamic frequency simulation tools-which were developed mainly for the
transmission system-lack the capability to simulate distribution network
dynamics with high penetrations of DERs. Although electromagnetic transient
(EMT) simulation tools can simulate distribution network dynamics, the
computation efficiency limits their use for large-scale
transmission-and-distribution (T&D) simulations. This paper presents an
efficient T&D dynamic frequency co-simulation framework for DER frequency
response based on the HELICS platform and existing off-the-shelf simulators.
The challenge of synchronizing frequency between the transmission network and
DERs hosted in the distribution network is approached by detailed modeling of
DERs in frequency dynamic models while DER phasor models are also preserved in
the distribution networks. Thereby, local voltage constraints can be respected
when dispatching the DER power for frequency response. The DER frequency
responses (primary and secondary)-are simulated in case studies to validate the
proposed framework. Lastly, fault-induced delayed voltage recovery (FIDVR)
event of a large system is presented to demonstrate the efficiency and
effectiveness of the overall framework.
