Backstepping and control allocation with applications to flight control
Backstepping and control allocation with applications to flight control
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发表时间：
2003
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通讯作者：
Ola Härkegård
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作者：
Ola Härkegård
本文研究了飞行控制中出现的非线性控制问题。结果是在一个一般框架中提出的，也可以应用于其他领域。两个主要的主题是回溯和控制分配。反演是一种非线性控制设计方法，提供了一种替代反馈线性化的方法。本文采用反推法推导了两个非线性系统的鲁棒线性控制律，分别涉及攻角控制和航迹角控制。所得到的控制律比基于反馈线性化的相应设计需要更少的建模信息，并且在反馈线性化只能在局部执行的情况下实现全局稳定。此外，基于动力学的矢量描述，开发了一种刚体反步控制方法。我们还讨论了如何增强现有的非线性控制器来抑制恒定输入干扰。提出了基于自适应反演和非线性观测器设计的两种方法。控制分配处理过致动系统的致动器利用率。在本文中，我们将控制分配问题作为一个约束最小二乘问题来考虑执行器的位置和速率约束。基于活动集方法的高效求解器与现有的近似伪逆方法具有相似的复杂度。提出了一种动态控制分配方法，实现了执行器间频率相关的控制分配。进一步研究了控制分配与线性二次控制的关系。结果表明，在一定条件下，这两种控制方法在执行器之间分配控制力时具有相同的自由度。然而，控制分配的一个优点是，由于考虑了执行器约束，因此可以充分利用执行器套件的控制能力。
In this thesis we study a number of nonlinear control problems motivated by their appearance in flight control. The results are presented in a general framework and can also be applied to other areas. The two main topics are backstepping and control allocation.Backstepping is a nonlinear control design method that provides an alternative to feedback linearization. Here, backstepping is used to derive robust linear control laws for two nonlinear systems, related to angle of attack control and flight path angle control, respectively. The resulting control laws require less modeling information than corresponding designs based on feedback linearization, and achieve global stability in cases where feedback linearization can only be performed locally. Further, a method for backstepping control of a rigid body is developed, based on a vector description of the dynamics. We also discuss how to augment an existing nonlinear controller to suppress constant input disturbances. Two methods, based on adaptive backstepping and nonlinear observer design, are proposed.Control allocation deals with actuator utilization for overactuated systems. In this thesis we pose the control allocation problem as a constrained least squares problem to account for actuator position and rate constraints. Efficient solvers based on active set methods are developed with similar complexity to existing, approximate, pseudoinverse methods. A method for dynamic control allocation is also proposed which enables a frequency dependent control distribution among the actuators to be designed. Further, the relationship between control allocation and linear quadratic control is investigated. It is shown that under certain circumstances, the two techniques give the same freedom in distributing the control effort among the actuators. An advantage of control allocation, however, is that since the actuator constraints are considered, the control capabilities of the actuator suite can be fully exploited.