  Considering the structure of dc Microgrids (MGs) composed of
grid-forming/feeding converters, a hierarchical Plug-and-Play (PnP)
voltage/current control architecture for MG clusters is proposed. In the
primary level, a PnP voltage/current controller is proposed to achieve
simultaneous voltage support and current feeding function according to local
references. In addition, stabilizing controller is characterized by explicit
inequalities which are only related to local parameters of a MG.
  In the secondary level, for the system with interconnection of MGs, a
leader-based voltage/current distributed controller is proposed to achieve both
voltage and current regulation without specifying the individual setpoints for
each MG. The proposed controller requires a communication network and each
controller exchanges information with its communication neighbors only.
  With the proposed controller, each MG can plug-in/out of the system
seamlessly, irrespectively of the power line parameters and models of other MGs .
  The proof of the MG cluster closed-loop stability exploits structured
Lyapunov functions, the LaSalle invariance theorem and properties of graph
Laplacians. Theoretical results are validated by hardware-in-loop (HiL) tests.
