  Packetized energy management (PEM) is a demand dispatch scheme that can be
used to provide ancillary services such as frequency regulation. In PEM,
distributed energy resources (DERs) are granted uninterruptible access to the
grid for a pre-specified time interval called the packet length. This results
in a down ramp-limited response in PEM for DERs that can only consume power
from the grid. In this work, a linearized virtual battery model of PEM is
provided that is capable of predicting the down-ramp limited output of PEM and
is used in a model predictive control (MPC) framework to improve the
performance of PEM in tracking an automatic generation control (AGC) signal. By
performing statistical analysis on the AGC regulation signal, PJM Reg-D, an
ARMA model is derived as a predictor for the MPC-based precompensator. Finally,
as an alternative to MPC, it is shown that by varying the packet length as a
function of time, for example through packet randomization, frequency
regulation can be improved under PEM.
