Abstract
Valve-controlled servosystems are widely used in dynamic tracking, but, not properly studied, nonlinearity, perturbation of internal parameters, and external disturbance have significant impacts on the control performance and challenge in the controller design. This study, with consideration of the finite pressure gain of actual servovalves, proposes a new unified nonlinear model of the valve-controlled servosystem. Based on a U-control platform, this study makes the control strategy design independent from the nonlinear plant, and a virtual nominal plant is presented to eliminate the unmodeled high-frequency characteristics, acquire the desired control performance, and enable the control variable to be explicitly expressed. Then, there follows, designing the U-model-based finite-time control in the valve-controlled systems. Simulation demonstrations show the consistency with theoretical development that the valve-controlled system can smoothly track the command signal within the specified time, and the phase lag is eliminated. Moreover, U-model’s application effectively copes with the system chattering, and with the maximum of 1 m/s the dynamic position error caused by discretization of the controller is reduced to less than 0.15%, which can satisfy the demand of general valve-controlled servosystems.
Highlights
With the advantages of fast response and high stiffness, valve-controlled servosystems have been widely applied in machinery manufacturing, ship maneuvering, and industrial control. e traditional valve-controlled system often adopts output feedback and the PID control method to achieve dynamic tracking
For improving control performance, new research and development should expand those developed from linear model-based approaches that treat the valve-controlled systems as a linear system and simplify it into a second-order oscillating element
U-model’s application effectively copes with the system chattering, and with the maximum of 1 m/s the dynamic position error caused by discretization of the controller is reduced to less than 0.15%, which can satisfy the demand of general valve-controlled servosystems
Summary
With the advantages of fast response and high stiffness, valve-controlled servosystems have been widely applied in machinery manufacturing, ship maneuvering, and industrial control. e traditional valve-controlled system often adopts output feedback and the PID control method to achieve dynamic tracking. To reduce the complexity of the model-based control system design, for those nonlinear dynamic plants, Zhu [14,15,16] proposed a systematical universal transform to convert classical nonlinear polynomial models into U-models with time-varying parameters and controller output u(t − 1). E major contributions of the study include (1) Deriving a proper principle model to accommodate dynamic and nonlinearities for a typical valve-controlled servosystem (2) Using U-control to separate control system design and controller output determination (3) Developing a global robust sliding mode control scheme for valve-controlled systems (4) Providing computational experiments to validate the control scheme and to guide the potential users in their potential ad hoc applications e rest of the study is organised into five sections.
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