The simplified STR applied to an asymmetric hydraulic servo system

A single–rod cylinder servo system driving a single–side load is typically a 4th–order non–linear and discontinuous system. However, its asymmetric nature will cause steady state error in position control. At the low frequency of interest, this system can be simplified as a 1st–order ARMA model and the PEDF algorithm is used for parameter adaptation. In addition to tracing the time–varying and discontinuous parameters, the PEDF is to ensure the covariance matrix is bounded so as to guard against peak in the parameter adaptation process. To eliminate steady state error, an integrator is included in the structure of implicit STR and it only estimates two controller parameters by applying the final value theorem of the z–transform. The proposed implicit STR not only avoids unstable pole–zero cancellation, but also prevents the redundant zero of the high order model from being hidden. Finally, various experiments prove its effectiveness and adaptation numerically.