Flexible-Fixed-Time-Performance-Based Adaptive Asymptotic Tracking Control of Switched Nonlinear Systems With Input Saturation

This work proposes an adaptive neural network asymptotic tracking control strategy, capable of ensuring flexible fixed-time prescribed transient behavior for switched nonlinear systems with external disturbances and input saturation. Unlike most existing prescribed performance controls with input constraints that ignore the contradiction in fulfilling the input constraint and the output constraint, the proposed strategy realizes a trade-off between them by constructing a modified fixed-time prescribed performance function. The performance function boundary will increase with the error between the actual input and the desired control input, which can sacrifice the user-specified performance while saturation exists and fix it while no saturation exists, lowering the risk of singularity. Together with the designed performance function, a Zeno-free event-triggered controller is built to enforce that the output error converges asymptotically and satisfies the performance function boundaries within a fixed time. Besides, the complexity explosion problem is circumvented through the command-filtered technique. Finally, two case studies are provided to validate the established control strategy. Note to Practitioners—Due to physical restrictions, there are various system input and output constraints in practical engineering, which severely hampers the application of both traditional and cutting-edge control algorithms, particularly in the chemical, boiler, robot, and other sectors. Regrettably, the existing approaches only consider input and output constraints separately and assume that they can be implemented simultaneously, which is unrealistic in many practical systems. Hence, this work focuses on developing a novel adaptive fixed-time prescribed performance control strategy by introducing a modification signal, which can not only comprehensively balance input and output constraints but also achieve the asymptotic tracking of the system output. Meanwhile, an event-triggered mechanism is introduced to deal with the problem of limited communication bandwidth.

I. Introduction

It is well-established that the majority of systems in service will run into various constraints to maintain the security and stability of the system performance for achieving regular operation [1], [2]. These constraints may often be divided into two groups: capability-related and performance-related constraints, such as input saturation and user-specified convergence rates. Since these two constraints are contradictory, it is possible that some constraints cannot be satisfied at the same time [3]. Therefore, it makes sense to explore an appropriate control method to accomplish the trade-off between these two constraints in both practice and theory.