四旋翼无人机预设性能非线性PI串级姿态控制

Nonlinear PI Cascade Attitude Control with Prescribed Performance for a Quadrotor UAV

仅在系统初始条件已知的前提下,针对具有未知外界扰动和未知非线性特性的四旋翼无人机系统,提出了一种预设性能非线性PI串级姿态控制方法.将四旋翼无人机姿态系统分解为欧拉角和角速率两个动态子系统,并充分考虑系统的内部动态因果关系;采用串级控制消除系统欠驱动对控制器设计带来的不利影响,以改善控制效果.针对系统的不确定性、未知外界扰动及预设性能可能引起的控制器奇异问题,基于预设性能的误差转换函数和泰勒多项式构造简单的非线性函数,分别为欧拉角和角速率动态子系统设计非线性PI控制器,并从理论上证明其可行性.所设计的控制器继承了传统PID的优点,其参数调整更加灵活,且具有很强的鲁棒性和自适应性.仿真试验结果验证了该方法的有效性和优越性.

In this paper,a prescribed performance nonlinear PI cascade(PPN-CPI)attitude tracking control scheme is proposed for a quadrotor unmanned aerial vehicle(QUAV)with unknown external disturbances and unknown nonlinearities based on known initial conditions.By dividing the quadrotor attitude system into two subsystems,i.e.,attitude angles and angular velocities,a cascade controller designed with consideration of the system internal causality is adopted to tackle underactuated constraints effectively.Next,a simple nonlinear function is established by using the error transformation theory and Taylor polynomials,and two nonlinear PI controllers are developed to handle the unknown nonlinearities,unknown external disturbances,and the singular value problem for attitude angles and angular velocities subsystems with the feasibility proved by theoretical analysis,respectively.The proposed controller inherits the advantages of traditional PID with better adaptability and robustness,and flexibility in parameter adjustment as well.Simulation studies results demonstrate the effectiveness and superiority of the proposed attitude tracking control scheme.