  This article develops a distributed framework for coordinating distributed
energy resources (DERs) in a power network to provide secondary frequency
response (SFR) as an ancillary service to the bulk power system. A distributed
finite-time protocol-based solution is adopted that allows each DER in the
network to determine power reference commands. The distributed protocol
respects information exchange constraints posed by a communication network
layer while being robust to delays in the communications channels. The proposed
framework enables coordinated response and control of the aggregated DERs by
apportioning the share of generation that each DER needs to provide towards
meeting any specified global SFR command while allowing for adjustments due to
variability in generation and demand in order to prioritize renewable energy
sources in the network. A novel early dispatch mechanism with brown start is
synthesized to achieve initial DER response to changing SFR commands that is
faster than state-of-the-art distributed approaches. The proposed power
apportioning protocol is validated using an end-to-end power
hardware-in-the-loop configuration at a distribution system scale with 40+
physical hardware DERs, underlying 7-MW power system model, a 250-DER
communication topology with physical and simulated distributed controller
nodes, varied communication protocols, and an underlying real-world power
system model. Experimental results demonstrate the efficacy of the proposed
method toward distributed coordination of hundreds of DERs for providing fast
response at SFR timescales.
