  In this work, we present new secondary regulators for current sharing and
voltage balancing in DC microgrids, composed of distributed generation units,
dynamic RLC lines, and nonlinear ZIP (constant impedance, constant current, and
constant power) loads. The proposed controllers sit atop a primary voltage
control layer, and exchange information over a communication network to perform
secondary control actions. We deduce sufficient conditions for the existence
and uniqueness of an equilibrium point, and show that the desired objectives
are attained in steady state. Our control design requires only the knowledge of
local parameters of the generation units, facilitating plug-and-play
operations. We provide a voltage stability analysis, and illustrate the
performance and robustness of our designs via simulations. All results hold for
arbitrary, albeit connected, microgrid and communication network topologies.
