Nonlinear Analysis of an Improved Swing Equation
  In this paper, we investigate the properties of an improved swing equation model for synchronous generators. This model is derived by omitting the main simplifying assumption of the conventional swing equation, and requires a novel analysis for the stability and frequency regulation. We consider two scenarios. First we study the case that a synchronous generator is connected to a constant load. Second, we inspect the case of the single machine connected to an infinite bus. Simulations verify the results. 
Pooya Monshizadeh, Claudio De Persis, Nima Monshizadeh, Arjan van der   Schaft
cs.SY