Output tracking of a non-linear non-minimum phase PVTOL aircraft based on non-linear state feedback control

In this paper, a special class of square multi-input multi-output (MIMO) non-linear non-minimum phase systems is considered whereby the internal dynamics does not depend explicitly on the inputs. For such systems, a new output tracking control aproach is proposed and applied to a planar vertical takeoff and landing (PVTOL) aircraft. This control approach first generates input-output linearization of the original non-linear system. Then the internal dynamics is rewritten by separating its linear part from its non-linear part. Finally, a non-linear auxiliary input is introduced to stabilize the overall closed-loop system by a Lyapunov-based technique and a minimum-norm strategy. The effectiveness and excellent performance of the resulting non-linear state feedback controller are demonstrated by using the simulation results.     

On global tracking control of a VTOL aircraft without velocity measurements

This note develops a nonlinear output-feedback controller to force a nonminimum phase, underactuated vertical take-off and landing aircraft to globally asymptotically track a reference trajectory generated by a reference model. The control development is based on a global exponential observer, some global coordinate transformations, Lyapunov's direct method and an extension of the backstepping technique. Interestingly, the proposed methodology also yields new results for the previously studied problems of stabilization and output tracking or regulation. Numerical simulations illustrate the effectiveness of the proposed controller.     

考虑侧倾的无人车NMPC轨迹跟踪控制

针对高速行驶工况下,无人车转弯时的侧倾易导致车辆模型非线性程度增加,引起轨迹跟踪精度下降和状态失稳的问题,设计一种考虑车辆侧倾因素,基于非线性模型预测控制(NMPC)的无人车轨迹跟踪控制器.根据拉格朗日分析力学和车辆运动学,考虑车辆侧倾几何学和载荷转移效应,建立考虑侧倾因素的非线性车辆模型,包括车体动力学模型和修正的“Magic Formula”轮胎模型;基于此车辆模型,构建非线性模型预测控制器(NMPC)的预测模型,并设定控制器的线性、非线性约束,以保证车辆的运动状态处于稳定区域内.在Carsim和Simulink联合仿真平台上,验证车辆高速蛇形工况和双移线工况下的轨迹跟踪控制效果,仿真结果显示,所设计的控制器可有效改善高速弯道工况下的跟踪精度和车辆状态稳定性.     

Minimum energy oriented global stabilizing control of the PVTOL aircraft

A global stabilizing control law is proposed for a non-minimum phase under-actuated planar vertical take-off and landing (PVTOL) aircraft. The proposed approach is based on receding horizon control and takes into account the positiveness of the thrust and its saturation to any arbitrary level. Moreover, the angular acceleration can also be bounded. Contrary to non-linear optimal control, the proposed approach, based on quadratic programming, improves significantly the computational cost of the algorithm and the convergence to a solution can be insured. The chosen cost function has a direct link with the energy needed to reach a desired point which is one of the main worries in the design of embedded control systems such as micro unmanned aerial vehicles (UAV).     

考虑状态约束与执行器饱和的水下机器人轨迹跟踪控制

针对执行器饱和、模型参数不确定以及海流干扰等因素影响下的水下机器人,提出一种考虑状态约束以及执行器饱和的轨迹跟踪控制器.首先,构建水下机器人水平面轨迹跟踪误差方程;然后,对载体模型参数不确定性产生的模型误差以及海流干扰,设计一个非线性观测器进行估计并用于对控制器进行扰动补偿;接着,引入执行器饱和补偿系统、二阶滤波器以及滤波器误差补偿系统,设计命令滤波反步滑模控制器来控制水下机器人的水平面轨迹跟踪;最后,严格验证命令滤波反步滑模控制器的稳定性并进行数值仿真,验证所提出控制器的有效性.     

CBA-neural network control of a non-linear full vehicle model

In this paper, the dynamic behavior of a non-linear eight degrees of freedom vehicle model having active suspensions and passenger seat controlled by a neural network (NN) controller is examined. A robust NN structure is established by using principle design data from the Matlab diagrams of system functions. In the NN structure, Classic Back-Propagation Algorithm (CBA) is employed. The user inputs a set of x₁ − x₁₆ while the output from the NN consists of f₁ − f₁₆ non-linear functions. Further, the Permanent Magnet Synchronous Motor (PMSM) controller is also determined using the same NN structure. According to various tests of the NN structure it is demonstrated that the model is able to give highly sensitive outputs for vibration condition, even using a more restricted input data set. The non-linearity occurs due to dry friction on the dampers. The vehicle body and the passenger seat using PMSM are fully controlled at the same time. The time responses of the non-linear vehicle model due to road disturbance and the frequency responses are obtained. Finally, uncontrolled and controlled cases are compared. It is seen that seat vibrations of a non-linear full vehicle model are controlled by NN based system exactly.     

非线性图像网格校正技术在车辆跟踪上的应用

在基于数字图像处理技术的交通监测系统中,由于摄像装置所处的角度和高度原因,使得拍摄到的图像存在非线性几何形变,致使不能精确地对车辆进行跟踪分析.为此提出了一种基于网格的图像非线性形变的校正算法,建立一个与实际路面相关的虚拟环境.在虚拟环境中,可以使车辆信息为线性变化.通过Kalman滤波器对车辆信息进行分析、预测,达到车辆跟踪的目的.     

Robust variable structure control of a PVTOL aircraft

This paper considers the development of tracking controllers for a multi-input nonlinear non-minimum phase Planar Vertical Take-off and Landing (PVTOL)aircraft. The system is considered to be subject to bounded/sector additive external uncertainties. A dynamic sliding mode control philosophy is employed. The stability and robustness of the resulting closed-loop system is analysed. It is demonstrated that ultimate bounded tracking may be achieved with bounded inputs despite the presence of uncertainty.     

Adaptive neural network tracking control for a class of non-linear systems

This article extends the application of the adaptive neural network control to a new class of uncertain MIMO non-linear systems, which are composed of interconnected subsystems where each interconnected subsystem is in the non-affine pure-feedback form. Because both the variables which are used as virtual controllers and the actual controllers appear non-linearly in unknown functions of the MIMO systems, thus, this class of systems is difficult to control. The radial basis function neural networks are utilised to approximate the desired virtual controllers and the desired actual controllers which are obtained by using implicit function theorem. The salient property of the proposed approach is that the number of the adjustable parameters is less than the numerous alternative approaches existing in the literature. It is proven that, under appropriate assumptions, all the signals in the closed-loop system are uniformly bounded and the tracking errors converge to a small neighbourhood of the origin by appropriately choosing design parameters. The feasibility of the developed approach is verified by two simulation examples.     

Dynamic path tracking control of a vehicle on slippery terrain

This paper deals with accuracy and reliability for the path tracking control of a four wheel mobile robot with a double-steering system when moving at high dynamics on a slippery surface. An extended kinematic model of the robot is developed considering the effects of wheel–ground skidding. This bicycle type model is augmented to form a dynamic model that considers an actuation of the four wheels. Based on the extended kinematic model, an adaptive and predictive controller for the path tracking is developed to drive the wheels front and rear steering angles. The resulting control law is combined with a stabilization algorithm of the yaw motion which modulates the actuation torque of each four wheels, on the basis of the robot dynamic model. The global control architecture is experimentally evaluated on a wet grass slippery terrain, with speeds up to 7 m/s. Experimental results demonstrate enhancement of tracking performances in terms of stability and accuracy relative to the kinematic control.     

Position feedback global tracking control of EL systems: a statetransformation approach

The contribution of this paper is a dynamic position feedback global tracking controller for fully actuated Euler-Lagrange (EL) systems. The properties we show for the closed loop system are uniform stability and exponential convergence, global in the initial tracking errors and semiglobal in the initial estimation errors. The novelty of our approach is that our observer and control design are based on a new model for EL systems which is linear in the immeasurable velocities. This model is shown to fit robot manipulators. We also provide some simulation results     

高超声速飞行器考虑数据丢失的预测控制研究

以高超声速飞行器纵向通道为研究对象,考虑飞行器控制系统中传感器–控制器以及控制器–执行器通道均存在数据丢失的问题,提出一种能有效处理丢包的预测控制方法。首先,对高超声速飞行器纵向通道非线性模型进行局部小扰动线性化,得到平衡点处线性化模型;接着,建立有数据丢失的系统动态模型,使用终端状态约束集和终端代价函数方法设计预测控制器并设计相关补偿策略,以实现高超声速飞行器输入指令的跟踪;最后,基于MATLAB和Truetime平台进行数值仿真。结果表明,所设计的预测控制器能保证系统在出现数据丢失时具有良好的跟踪性能和鲁棒性。     

Distributed estimation-based tracking control of multiple uncertain non-linear systems

This paper considers the tracking control of multiple uncertain non-linear systems with a desired signal which is not available to each system. An estimation-based controller design approach is proposed. Distributed estimation-based adaptive controllers are proposed with the aid of Lyapunov techniques and results from graph theory. Simulation results show the effectiveness of the proposed controllers.     

Optimal feedback control for route tracking with a bounded-curvature vehicle

The problem of driving a vehicle along a given path is considered. The vehicle is supposed to move forward only, with a given velocity profile, and to have a bounded turning radius. Such a model, also known as 'Dubins' vehicle', is relevant to the kinematics of road vehicles as well as aircraft cruising at constant altitude, or sea vessels. We consider the optimal control problem consisting of minimizing the length travelled by the vehicle starting from a generic configuration to connect to a specified route. A feedback law is proposed, such that straight routes can be approached optimally, while the system is asymptotically stabilized. Experimental results are reported showing real-time feasibility of the proposed approach.     

Trajectory tracking control for a miniature fixed-wing unmanned air vehicle

This article considers the problem of trajectory tracking control for a miniature fixed-wing unmanned air vehicle (UAV). With the UAV equipped with longitudinal and lateral autopilots, we adopt a kinematic model that takes into account the fact that the heading of the UAV is controlled by its roll motion and the autopilot responses to air speed and roll control commands are first order in nature. Backstepping techniques are applied to derive air speed and roll control commands from known air speed and heading control laws that explicitly account for air speed and heading rate constraints of the UAV. Regarding inaccurately known autopilot constants, a parameter adaptation technique is used to estimate autopilot constants. High-fidelity simulation results on a six degree-of-freedom (DOF) 12-state fixed-wing UAV model are presented to show the effectiveness of our approach.     

Finite-time observer-based output-feedback control for the global stabilisation of the PVTOL aircraft with bounded inputs

In this work, an output-feedback scheme for the global stabilisation of the planar vertical take-off and landing aircraft with bounded inputs is developed taking into account the positive nature of the thrust. The global stabilisation objective is proven to be achieved avoiding input saturation and by exclusively considering the system positions in the feedback. To cope with the lack of velocity measurements, the proposed algorithm involves a finite-time observer. The generalised versions of the involved finite-time stabilisers have not only permitted to solve the output-feedback stabilisation problem avoiding input saturation, but also provide additional flexibility in the control design that may be used in aid of performance improvements. With respect to previous approaches, the developed finite-time observer-based scheme guarantees the global stabilisation objective disregarding velocity measurements in a bounded input context. Simulation tests corroborate the analytical developments. The study includes further experimental results on an actual flying device.     

Nonlinear feedback control and trajectory tracking of vehicle

This paper mainly studies nonlinear feedback control applied to the nonlinear vehicle dynamics with varying velocity. The main objective of this study is the stabilisation of longitudinal, lateral and yaw angular vehicle velocities. To this end, a nonlinear vehicle model is developed which takes both the lateral and longitudinal vehicle dynamics into account. Based on this model, a method to build a nonlinear state feedback control is first designed by which the complexity of system structure can be simplified. The obtained system is then synthesised by the combined Lyapunov–LaSalle method. The simulation results show that the proposed control can improve stability and comfort of vehicle driving. Moreover, this paper presents a lemma which ensures the trajectory tracking and path-following problem for vehicle. It can also be exploited simultaneously to solve both the tracking and path-following control problems of the vehicle ride and driving stability. We also show how the results of the lemma can be applied to solve the path-following problem, in which the vehicle converges and follows a designed path. The effectiveness of the proposed lemma for trajectory tracking is clearly demonstrated by simulation results.     

Adaptive tracking control of an autonomous underwater vehicle

This paper presents the trajectory tracking control of an autonomous underwater vehicle(AUV). To cope with parametric uncertainties owing to the hydrodynamic effect, an adaptive control law is developed for the AUV to track the desired trajectory. This desired state-dependent regressor matrix-based controller provides consistent results under hydrodynamic parametric uncertainties.Stability of the developed controller is verified using the Lyapunov s direct method. Numerical simulations are carried out to study the efficacy of the proposed adaptive controller.     

Attitude tracking control of a flexible spacecraft under angular velocity constraints

In this paper, a new technique is proposed for trajectory tracking of a flexible spacecraft subject to angular velocity constraints. The problem is addressed using an output to input saturation transformation (OIST) which converts the prescribed bounds into state-dependent saturations on the control input signals. It is shown that an interval observer can be used in combination with the OIST technique to ensure that the constraints remain satisfied despite unmeasured flexible modes and torque disturbances. Some realistic simulations conclude the paper and validate our approach.     

考虑执行器性能约束的刚体航天器鲁棒姿态跟踪控制

针对存在模型不确定性、外界干扰力矩和执行器性能受限等约束条件下的刚体航天器姿态跟踪控制问题进行研究,并基于滑模控制、反步控制、自适应控制、辅助系统和动态面控制等方法设计相应的鲁棒姿态跟踪控制算法.利用自适应控制实现了对具有多项式形式上界函数的系统未知不确定性进行在线估计和补偿;通过建立描述执行器动态特性的低通滤波模型,并结合辅助系统方法,以确保执行器输出控制力矩的幅值及其变化率均满足一定的饱和约束;通过引入动态面控制法,避免期望虚拟控制信号的一阶导数项直接出现在控制器中,简化了闭环姿态跟踪控制器的设计形式.最后,通过数值仿真验证了所提出控制算法的有效性和可行性.