Abstract: To investigate the dynamic and static performance of electro-hydraulic servo control system in theory, the accurate mathematic model of twin flapper-nozzle servo valve needs to be established. Firstly, for the non-linear effect of flow in twin flapper-nozzle servo valve, the nonlinear characters of valve’s electrical signal input to spool displacement output are analyzed, then a nonlinear model is set up to represent the actual system. Secondly, according to the character of actual system model, the localized linear model is achieved by nonlinear state feedback transforming, which is based on the input-output linearization method. then this model’s validity is proved theoretically by stability analysis of the system’s zero dynamic state. Finally, the linearization model of Taylor series expansion is chosen as the comparative object, the simulation and experiment results are provied to analysis the accuracy of the linear model.Results show that the local linear model achieved by nonlinear state feedback transforming more appropriate for the actual systems and has strong robustness.

Key words: Input-output linearization, Nonlinear model, Nozzle-flapper servo valve, Zero dynamics