The method performs active power perturbation analysis respectively on the stable equilibrium point of pre-fault system, the trajectory of fault-on system and transient stability of post-fault system.

Using singular perturbation model, by the example of a simple power system losing stability in big disturbance, this paper analyses the mid-long term instability mechanisms affected by slow dynamics.

The results of simulation show that stability of power system and the controllers possess very high property of robustness for the perturbation in the system parameters.