  The grid-following and grid-forming controls in voltage-source converters are
considered as different operation modes and the synchronization mechanism of
them are studied separately. In this article, the intrinsic relationships
between gridfollowing and grid-forming controlled converters are established as
follows: 1) the proportional gain of PLL is in inverse proportion to damping;
2) the integral gain of PLL is similar to integral droop; 3) PLL has no
practical inertia but acts like grid-forming control in zero inertia cases.
Further, a general stability-enhanced method combining damping and inertia is
proposed, and the modified energy function is obtained to estimate the region
of attraction for the system. Finally, these findings are corroborated by
simulation tests with an intuitive conclusion.
