Why the bode plot of the power system stabilizer model PSS2A between input vt and output Efd has phase starting at 180 degree?

I has just studied how to develop power system stabilizer model PSS2A but I'm not clear Why the bode plot of this model PSS2A between input dw and output has phase starting at 180 degree? Is there a way to adjust parameter of the synchronous generator or exciter for phase staring at 0 degree? or it depend on the system behavior? Anyone please help. Thanks.

Answer 1

[CHENG LIM]

The positive phase swift between the PSS input and output in this case around 172 degree is normal as this is required to compensate the lagging effect introduce by generator and exiter (GEP Transfer function). GEP transfer fucntion lagging effect is a normal system behaviour and depend on type of PSS deployed ( single input , dual input, etc) diffferent compensation need to be design to intorduce the right damping in phase with rotor angular speed.