Problem with Matlab example model in SimPowerSys - Performance of Three PSS for Interarea Oscillations

I have some problems with this model. Even without 3-phase fault and switching off the line and without any pulses on voltage reference of M2 system lost its synchronism due to low frequency oscillations in 50-80 seconds. What is the reason of rising of this oscillations in this system?

Thank you for the answer.

Answer 1

[Joel Van Sickel]

I ran this model with changes and saw no oscillations. Please include example files of problems when you want help debugging.