  The popular single-input single-output control structures and classic design
methods (e.g., root locus analysis) for the power control of grid-forming
converters have limitations in applying to different line characteristics and
providing favorable performance. This paper studies the grid-forming converter
power loops from the perspective of multi-input multi-output systems. First,
the error dynamics associated with power control loops (error-based state-space
model) are derived while taking into account the natural dynamical coupling
terms of the power converter models. Thereafter, the controllability Gramian of
the grid-forming converter power loops is studied. Last, a full-state feedback
control design using only the local measurements is applied. By this way, the
eigenvalues of the system can be arbitrarily placed in the timescale of power
loops based on predefined time-domain specifications. A step-by-step
construction and design procedure of the power control of grid-forming
converters is also given. The analysis and proposed method are verified by
experimental results.
