A methodology for long term dynamic analysis in power systems

The asymptotic expansion technique for systematically obtaining the fast and slow components of system variables to any degree of accuracy is clarified. Two related techniques are pointed out. In addition to analysis, decoupling into slow and fast subsystems is used as a basis for reduced-order energy function analysis. In the limit the equal-area criterion is equivalent to the decoupling of the system into two slow subsystems. Application to direct methods of stability analysis is made