In this forced oscillation case, the sources of oscillations are at generators 70 and 118.
System model:
Generators 70 and 118 are in GENROU model.
All other generators are in GENCLS model.
Parameter D for all generators equals 4, except for generators 70 and 118 whose D equals 0.
All loads are in constant MVA model.
Small signal analysis:
All natural modes have reasonably good damping.
External force:
Forced oscillations are injected into excitation systems as sinusoidal signals at generators 70 and 118 respectively to cause resonance with the system mode with frequency 0.43Hz.
Figure 1. Block diagram of the external force at generator 70
Figure 2. Block diagram of the external force at generator 118
Figure 3. WECC 179-bus power system