  Volt-VAR and Volt-Watt functionality in photovoltaic (PV) smart inverters
provide mechanisms to ensure system voltage magnitudes and power factors remain
within acceptable limits. However, these control functions can become unstable,
introducing oscillations in system voltages when not appropriately configured
or maliciously altered during a cyberattack. In the event that Volt-VAR and
Volt-Watt control functions in a portion of PV smart inverters in a
distribution grid are unstable, the proposed adaptation scheme utilizes the
remaining and stably-behaving PV smart inverters and other Distributed Energy
Resources to mitigate the effect of the instability. The adaptation mechanism
is entirely decentralized, model-free, communication-free, and requires
virtually no external configuration. We provide a derivation of the adaptive
control approach and validate the algorithm in experiments on the IEEE 37 and
8500 node test feeders.
