  The classic design of grid-forming control strategies for power converters
rely on the stringent assumption of the timescale separation between DC and AC
states and their corresponding control loops, e.g., AC and DC loops, power and
cascaded voltage and current loops, etc. This paper proposes a multi-input
multi-output based grid-forming (MIMO-GFM) control for the power converters
using a multivariable feedback structure. First, the MIMO-GFM control couples
the AC and DC loops by a general multivariable control transfer matrix. Then,
the parameters design is transformed into a standard fixed-structure H-infinity
synthesis. By this way, all the loops can be tuned simultaneously and optimally
without relying on the assumptions of loop decoupling. Therefore, a superior
and robust performance can be achieved. Experimental results verify the
proposed method.
