  This paper presents a two-layer distributed energy resource (DER)
coordination architecture that allows for separate ownership of data, operates
with data subjected to a large buffering delay, and employs a new measure of
power quality. The two-layer architecture comprises a centralized model
predictive controller (MPC) and several decentralized MPCs each operating
independently with no direct communication between them and with infrequent
communication with the centralized controller. The goal is to minimize a
combination of total energy cost and a measure of power quality while obeying
cyber-physical constraints. The global controller utilizes a fast AC optimal
power flow (OPF) solver and extensive parallelization to scale the solution to
large networks. Each local controller attempts to maximize arbitrage profit
while following the load profile and constraints dictated by the global
controller. Extensive simulations are performed for two distribution networks
under a wide variety of possible storage and solar penetrations enabled by the
controller speed. The simulations show that (i) the two-layer architecture can
achieve tenfold improvement in power quality relative to no coordination, while
capturing nearly all of the available arbitrage profit for a moderate amount of
storage penetration, and (ii) both power quality and arbitrage profits are
optimized when the solar and storage are distributed more widely over the
network, hence it is more effective to install storage closer to the consumer.
