In this forced oscillation case, the source of oscillations is at the governor of generator 77.
System model:
All the generators are in GENCLS model.
Parameter D for all generators equals 4.
All loads are in constant MVA model.
Small signal analysis:
All natural modes have reasonably good damping.
The system has a natural mode at 0.37Hz.
External force:
Forced oscillation is injected into the governor of generator 77 as a sinusoidal signal at frequency 0.37Hz to cause resonance.
The gain of the external force is 0.03 p.u.
Figure 1. Block diagram of the external force
Figure 2. WECC 179-bus power system