  This paper presents a novel control structure and control synthesis method
for regulating the output voltage/frequency and power injection of DC-AC
inverters. The traditional droop method offers attractive solution to achieve
compromise between clashing power and voltage/frequency regulation objectives.
However, it relies on use of nonlinear power variables through slow outer
control loop. In this paper we formulate the traditional droop method as a
feedback control problem based on static power-flow equations and show how
neglecting the dynamics of inverter and transmission line restricts the
attainable closed-loop bandwidth and stability and robustness margin. Then we
introduce a mapping between power variables and current in $dq$ frame under
given PLL condition, allowing for replacing the fast acting current variables
as a proxy for power. Consequently, we present a novel control structure and
control synthesis method based on disturbance rejection framework, and
demonstrate inherent droop like characteristics in underlying dynamics for
special cases of resistive and inductive line. Moreover, we generalize the
proposed control synthesis procedure to include a generalized complex line
dynamical model and introduce concept of hybrid-sourced-intverter. Finally, we
validate higher bandwidth and better transient performance of our proposed
design through experimental validation.
