  This paper proposes a decentralized and coordinated voltage and frequency
(Vf) control framework for islanded microgrids, with full consideration of the
limited capacity of distributed energy resources (DERs) and Vf dependent load.
First, the concept of DER inadequacy is illustrated with the challenges it
poses. Then, a decentralized and coordinated control framework is proposed to
regulate the output of inverter based generations and reallocate limited DER
capacity for Vf control. The control framework is composed of a power regulator
and a Vf regulator, which generates the supplementary signals for the primary
controller. The power regulator regulates the output of grid forming inverters
according to the real time capacity constraints of DERs, while the Vf regulator
improves the Vf deviation by leveraging the load sensitivity to Vf. Next, the
static feasibility and small signal stability of the proposed method are
rigorously proven through mathematical formulation and eigenvalue analysis.
Finally, a MATLAB Simulink simulation demonstrates the functionalities of the
control framework. A few goals are fulfilled within the decentralized and
coordinated framework, such as making the best use of limited DERs capacity,
enhancing the DC side stability of inverter based generations, and reducing
involuntary load shedding.
