  With the increasing interest in converter-fed islanded microgrids,
particularly for resilience, it is becoming more critical to understand the
dynamical behavior of these systems. This paper takes a holistic view of
grid-forming converters and considers control approaches for both modeling and
regulating the DC-link voltage when the DC-source is a battery energy storage
system. We are specifically interested in understanding the performance of
these controllers, subject to large load changes, for decreasing values of the
DC-side capacitance. We consider a fourth, second, and zero-order model of the
battery; and establish that the zero-order model captures the dynamics of
interest for the timescales considered for disturbances examined. Additionally,
we adapt a grid search for optimizing the controller parameters of the DC/DC
controller and show how the inclusion of AC side measurements into the DC/DC
controller can improve its dynamic performance. This improvement in performance
offers the opportunity to reduce the DC-side capacitance given an admissible DC
voltage transient deviation, thereby, potentially allowing for more reliable
capacitor technology to be deployed.
