  As power systems transit to a state of high renewable penetration, little or
no presence of synchronous generators makes the prerequisite of well-regulated
frequency for grid-following inverters unrealistic. Thus, there is a trend to
resort to grid-forming inverters which set frequency directly. We propose a
novel grid-forming frequency shaping control that is able to shape the
aggregate system frequency dynamics into a first-order one with the desired
steady-state frequency deviation and Rate of Change of Frequency (RoCoF) after
a sudden power imbalance. The no overshoot property resulting from the
first-order dynamics allows the system frequency to monotonically move towards
its new steady-state without experiencing frequency Nadir, which largely
improves frequency security. We prove that our grid-forming frequency-shaping
control renders the system internally stable under mild assumptions. The
performance of the proposed control is verified via numerical simulations on a
modified Icelandic Power Network test case.
