Type Number Based Steady-State Error Analysis on Fractional Order Control Systems

In this paper, steady-state error of fractional order control systems (FOCSs) is analyzed based on the concept of type number. Some practical definitions of the reference and the error for FOCSs with non-unity feedback are first given. Based on these definitions, the type number concept is first introduced to FOCSs with non-unity feedback. Then steady-state error of various types of FOCSs are analyzed respectively via type number concept. It is also shown that FOCSs with type number more than 1 are not able to track particular reference without changing the sign of the tracking error.