Active flutter suppression of nonlinear fin-actuator system via inverse system and immersion and invariance method

Structural nonlinearities such as freeplay will affect the stability and even flight safety of the fin-actuator system.There is a lack of a practical method for designing Active Flutter Suppression (AFS) control laws for nonlinear fin-actuator systems.A design method for the AFS controller of the nonlinear all-movable fin-electromechanical actuator system is established by combining the inverse system and the Immersion and Invariance (I&I) theory.First,the composite control law combining the inverse system principle and internal model control is used to offset the nonlinearity and dynamics of the actuator,so that its driving torque can follow the ideal signal.Then,the ideal torque of the actuator is designed employing the I&I theory.The unfavorable oscillation of the fin is suppressed by making the output torque of the actuator track the ideal signal.The simulation results reveal that the proposed AFS method can increase the flutter speed of the nonlinear finactuator system with freeplay,and a set of controller parameters is also applicable for wider freeplay within a certain range.The power required for the actuator does not exceed the power that can be provided by the commonly used aviation actuator.This method can also resist a certain level of noise and external disturbance.

Robust immersion and invariance adaptive coordinated control for a class of biaxial gantry systems

This paper proposes a robust Immersion and Invariance(I&I)adaptive coordinated controller for a class of uncertain linear-motor-driven biaxial gantry system subject to external disturbances for high-accuracy contour tracking.Firstly,the dynamic model of the gantry system is transformed into task coordinate frame,through which the contour tracking can be regarded as a regulation problem.Based on the transformed system dynamics,an I&I-based adaptation law with smooth projection is proposed to estimate the unknown parameters.Different from traditional adaptive control,the proposed robust I&I adaptive control introduces a new term called tuning function in adaptation law to shape the dynamic behaviour of the estimation vector.Then the stability of the closed-loop system is proved by Lyapunov theory.Finally,comparative experiments are executed on an industrial biaxial gantry system with two different cases to verify the effectiveness of the proposed control law.

A novel three-inflection-point sliding mode control framework for forward-tilting morphing aerospace vehicle with performance constraints and actuator faults

A prescribed performance control scheme based on the three-inflection-point hyperbolic function and predefined time performance function is proposed to solve the trajectory tracking problem of the forward-tilting morphing aerospace vehicle with time-varying actuator faults.To accurately estimate the loss degree of actuator faults,an immersion and invariance observer based on the predefined time dynamic scale factor is designed to estimate and compensate it.A composite dynamic sliding mode surface is designed using a three-inflection-point hyperbolic function,and a novel three-inflection-point sliding mode control framework is proposed.The convergent domain of the sliding manifold is adjusted by parameters,and the system error convergence is controllable.A transfer function is designed to eliminate the sensitivity of the three-inflection-point hyperbolic sliding mode to the unknown initial state,and combined with the barrier Lyapunov function,and the performance constraint of the system is realized.The global asymptotic stability of the system is demonstrated using a strict mathematical proof.The effectiveness and superiority of the proposed control scheme are proven by simulation experiments.

Nonlinear excitation controller design for power systems:an I&I approach

The Immersion and Invariance （I＆I） methodology provides a novel approach for nonlinear system control, which is distinct from the traditional feedback linearization and backstepping method. In this paper, a new excitation controller is designed for single machine infinite bus system （SMIBS） based on the I＆I approach. Firstly the dynamic model of SMIBS is homeomorphously transformed to a specific form for which a stable lower-order target system is selected. Then the I＆I excitation controller is designed by immersing the transformed system into the target system. Simulation results from PSCAD/EMTDC demonstrate that the proposed controller guarantees transient stability of the system after large disturbances.