The class implements a model of a Power System Stabilizer according
to the IEEE Std
421.5TM-2005.
The type implemented is the
PSS2B, described in the chapter 8.2 of the
same IEEE Std
421.5TM-2005.
Since the PSS has zeros in the origin applied to both inputs,
its output at steady-state is always zero. Hence, its
initialization at steady state is trivial and corresponds to zero
output.