This paper proposed an engineering approach to examine the stability margin of cascade circuits.

The stability margin could be obtained through the frequency model without fall into conservatism.

By introducing a concept of Fictitious Zero-Moment Point, the area of stable region and stability margin in single-support phase and double-support phase are deduced.

Quadratic stability and stability margin analysisof discrete interval systems;

The characteristics of mine power system,voltage stability and system stability margin were analyzed and the measures of preventing vlotage stability from destruction were set forth.

And the testing criteria are discussed,for example,stable margins, performance index,and controller fragility.

Based on the time domain simulation, the calculation method for single machine acceleration area and deceleration area, stable margin and unstable margin, critical machine equal area criterion (SMEAC) are proposed.

The stable margin is defined.

Besides the steady margin for the variation in process and equipment,the dynamic margin for control must be considered and its size is related to the control system.

For the catalyst inventory and air flow rate of FCCU regenerator,besides their steady margins for process change and equipment change,the dynamic margins for control and operation must be considered and their sizes are related to process control system.