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.