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An adaptive robust approach to actuator fault-tolerant control in presence of uncertainties and input constraints.

机译:在存在不确定性和输入约束的情况下,用于执行器容错控制的自适应鲁棒方法。

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摘要

In this work, we develop adaptive robust schemes for actuator fault-tolerant control in presence of uncertainties and input saturation. The type of faults considered in the present work encompass hardover-failure, loss in efficiency and stuck actuators. The two chief ways in which the system performance can degrade following an actuator-fault are undesirable transients and unacceptably large steady-state tracking errors. Adaptive control based schemes are ideal for handling the jump in parameter values following an actuator fault, and can guarantee good final tracking accuracy. However, such schemes may not be able to suppress the transients due to sudden change in system parameters. Furthermore, the performance of adaptive control based schemes deteriorate significantly in presence of unknown modeling errors and disturbances. Robust control based schemes, on the other hand, can guarantee desired transient response due to the sudden jump in system parameters and attenuate the effect of modeling uncertainties on the tracking error. But, in face of large parametric uncertainties due to actuator faults, the final tracking accuracy of robust control based schemes may degrade as they cannot reduce the extent of parametric uncertainties. In the present work, we claim that an adaptive robust fault-tolerant control scheme can solve both the problems, as it seamlessly integrates adaptive and robust control design techniques. Comparative simulation studies are performed using linear and nonlinear aircraft models to illustrate the superior performance of the proposed scheme over robust MRAC and robust backstepping based adaptive control designs respectively.;One of the standard assumptions made in the design of adaptive fault-tolerant control is that the healthy actuators have sufficient control authority despite faults to recover desired closed-loop performance. In reality, however, the controller could generate large control commands to suppress the undesired transients, leading to actuator saturation. Furthermore, in direct adaptive schemes, the estimator may fail to generate reliable parameter estimates due to saturation. This could further degrade the performance of a actuator fault-tolerant control. As a first step towards developing an approach which can deal with input constraints, we propose a conceptually different technique for global stabilization of a chain of integrators. A novel and elegant approach to solve this problem was proposed by Teel [1] using saturation functions and coordinate transformation. With Teel's work as foundation, many results have been proposed to improve the performance of tracking/stabilizing controllers for chain of integrators. Naturally, all such approaches also inherited the limitations of Teel's approach. Most importantly, in presence of uncertainties, such a transformation would considerably shrink the region where the controller is unsaturated, and in some cases, may even render the task of designing a stabilizing controller impossible. We combine the backstepping based design with saturation functions to develop a simple controller which does not rely on coordinate transformation and meets all the desired objectives. Furthermore, necessary and sufficient conditions for the existence of the proposed control law, as well as a systematic way of choosing the controller parameters is also presented. Comparative simulation studies are performed on a third order integrator chain which shows the effectiveness of the proposed scheme.;Finally, an actuator fault-tolerant controller is designed which combines the proposed backstepping based saturation functions approach with a least-square estimator. The indirect scheme ensures that the adaptation mechanism is not affected adversely due to actuator saturation. Simulation studies performed on a hypersonic aircraft model demonstrate the effectiveness of the proposed scheme in addressing actuator faults in presence of input constraints.
机译:在这项工作中,我们针对存在不确定性和输入饱和度的执行器容错控制开发了自适应鲁棒方案。当前工作中考虑的故障类型包括故障转移故障,效率损失和执行器卡住。在执行器故障后,系统性能可能下降的两种主要方式是不希望的瞬变和不可接受的大稳态跟踪误差。基于自适应控制的方案非常适合处理执行器故障后参数值的跳跃,并且可以保证良好的最终跟踪精度。但是,由于系统参数的突然变化,此类方案可能无法抑制瞬变。此外,在存在未知的建模误差和干扰的情况下,基于自适应控制的方案的性能会大大降低。另一方面,基于鲁棒控制的方案可以保证由于系统参数的突然跳变而产生所需的瞬态响应,并减弱建模不确定性对跟踪误差的影响。但是,面对由于执行器故障而导致的大量参数不确定性,基于鲁棒控制的方案的最终跟踪精度可能会降低,因为它们无法减少参数不确定性的程度。在当前的工作中,我们声称自适应鲁棒容错控制方案可以解决这两个问题,因为它无缝地集成了自适应和鲁棒控制设计技术。使用线性和非线性飞机模型进行了比较仿真研究,以说明所提出的方案分别优于基于鲁棒MRAC和基于鲁棒Backstepping的自适应控制设计的优越性能。;自适应容错控制设计中的标准假设之一是:健康的执行器具有足够的控制权,即使有故障也能恢复所需的闭环性能。但是,实际上,控制器可能会生成大型控制命令以抑制不希望的瞬变,从而导致执行器饱和。此外,在直接自适应方案中,由于饱和度,估计器可能无法生成可靠的参数估计值。这可能会进一步降低执行器容错控制的性能。作为开发一种可以处理输入约束的方法的第一步,我们提出了一种概念上不同的技术,用于对集成商链进行全局稳定。 Teel [1]使用饱和函数和坐标变换提出了一种新颖而优雅的方法来解决该问题。以Teel的工作为基础,已提出了许多结果,以改善集成商链的跟踪/稳定控制器的性能。当然,所有这些方法都继承了Teel方法的局限性。最重要的是,在存在不确定性的情况下,这样的变换将大大缩小控制器不饱和的区域,在某些情况下,甚至可能使设计稳定控制器的任务变得不可能。我们将基于Backstepping的设计与饱和功能相结合,以开发出一种简单的控制器,该控制器不依赖于坐标变换并且可以满足所有期望的目标。此外,还提出了提出的控制律的必要条件和充分条件,以及选择控制器参数的系统方法。在三阶积分器链上进行了比较仿真研究,证明了所提出方案的有效性。最后,设计了一种执行器容错控制器,该控制器将所提出的基于反推的饱和函数方法与最小二乘估计器相结合。间接方案确保适配机构不会因执行器饱和而受到不利影响。在高超音速飞机模型上进行的仿真研究证明了该方案在存在输入约束的情况下解决执行器故障的有效性。

著录项

  • 作者

    Gayaka, Shreekant.;

  • 作者单位

    Purdue University.;

  • 授予单位 Purdue University.;
  • 学科 Engineering Mechanical.
  • 学位 Ph.D.
  • 年度 2010
  • 页码 150 p.
  • 总页数 150
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

  • 入库时间 2022-08-17 11:36:46

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