Airship horizontal trajectory tracking control based on Active Disturbance Rejection Control (ADRC)

Aiming at flight property of airship, a trajectory tracking controller of airship horizontal model is designed based on active disturbance rejection control (ADRC). The six Degree of Freedom (DOF) dynamic model of airship is simplified at a horizontal plane. ADRC is used to realize the decoupling control for the multivariable system. The uncertain items of the model and external disturbances are estimated by the extended state observer (ESO) and dynamic feedback compensation is carried on at real time. The disturbance of wind is added to the simulation environment. The simulation results show that the designed tracking controller can overcome the influences of uncertain items of the model and external disturbances, and track the desired trajectory rapidly and steadily, and possess good robustness and control performances.     

Robust predictive scheme for input delay systems subject to nonlinear disturbances

The predictor-based control is known as an effective method to compensate input delays. Yet the traditional predictors, like Smith predictor, have poor robustness with respect to system disturbances. In this paper, with the consideration of future disturbances, a novel robust predictive scheme is developed for input delay systems subject to nonlinear disturbances. The Artstein reduction method is used to provide performance analysis of different predictor-based controllers, which shows that the proposed predictor-based controller can provide better disturbance attenuation than previous approaches in the literature for a wide range of disturbances.     

Trajectory tracking control using velocity observer and disturbances observer for uncertain robot manipulators without tachometers

This paper deals with trajectory tracking control for rigid robot manipulators with model uncertainty and subject to external disturbances. The approach suggested herein does not require velocity measurement, because these robots are not equipped by tachometers for velocity measurement. For this purpose, two observers are proposed. The first is a velocity observer to estimate the missing velocity, and the second one is a disturbance observer to estimate the disturbance. Thereafter, these observers are integrated with the controller. Furthermore, semi-global asymptotic stability conditions of the composite controller consisting of a nonlinear controller, the velocity observer and the disturbance observer are established, and an estimate region of attraction is also given. This proof is based on Lyapunov theory. Finally, simulation results on two-links manipulator are provided to illustrate the effectiveness of the velocity observer based control using disturbance estimation (namely VOBCDE), when the Coulomb and viscous friction is considered as an external disturbance.     

Finite time integral sliding mode control of hypersonic vehicles

This study investigates the tracking control problem for the longitudinal model of an airbreathing hypersonic vehicle (AHV) with external disturbances. By introducing finite time integral sliding mode manifolds, a novel finite time control method is designed for the longitudinal model of an AHV. This control method makes the velocity and altitude track the reference signals in finite time. Meanwhile, considering the large chattering phenomenon caused by high switching gains, an improved sliding mode control method based on nonlinear disturbance observer is proposed to reduce chattering. Through disturbance estimation for feedforward compensation, the improved sliding mode controller may take a smaller value for the switching gain without sacrificing disturbance rejection performance. Simulation results are provided to confirm the effectiveness of the proposed approach.     

Robust trajectory tracking control for a laboratory helicopter

This paper presents a robust nonlinear control strategy to deal with the trajectory tracking control problem for a laboratory helicopter. The helicopter model is considered as a nominal one with uncertainties such as unmodeled nonlinear dynamics, parametric uncertainties, and external disturbances. The proposed control approach incorporates the feedback linearization technique (FLT) and the signal compensation technique. The FLT is first applied to achieve the linearization of the nominal nonlinear model for reducing the conservation of the robust compensator design. A nominal controller based on the linear quadratic regulation method is designed for the linearized nominal system, whereas a robust compensator is introduced to restrain the influences of the uncertainties. It is shown that the trajectory tracking errors of the closed-loop system are ultimately bounded, and the boundaries can be specified by choosing the controller parameters. Simulation and experimental results on the lab helicopter verify the effectiveness of the proposed method.     

Backstepping control for the optoelectronic stabilized platform based on adaptive fuzzy logic system and nonlinear disturbance observer

A composite controller based on a backstepping controller with an adaptive fuzzy logic system and a nonlinear disturbance observer is proposed in this paper to address the disturbance and uncertainty issues in the control of the optoelectronic stabilized platform. The matched and unmatched disturbances and system uncertainty are included in the stabilized platform model. The system's uncertainty and disturbance are approximated and estimated using an adaptive fuzzy logic system and a nonlinear disturbance observer. Moreover, the backstepping control algorithm is utilized to control the system. The simulations are performed in four states to confirm the viability of the proposed control technique. The proportional integral controller, proportional integral-disturbance observer controller, and fuzzy backstepping controller are contrasted with the proposed controller. It has been noted that the proposed controller's instantaneous disturbance's highest value is 5.1°/s. The maximal value of the coupling output for the two gimbals utilizing the proposed controller, however, is 0.0008°/s and 0.0018°/s, respectively. The findings presented here demonstrate that the backstepping controller, which is based on an adaptive fuzzy logic system and a nonlinear disturbance observer, is capable of precise tracking and dynamic tracking of a stabilized platform under disturbance and uncertainty.

     

惯性稳定平台扩张状态观测器/PD复合控制

为提高惯性稳定平台控制系统的稳定精度,在常规PID控制的基础上提出了一种扩张状态观测器与PID相结合的复合控制算法。利用扩张状态观测器将惯性稳定平台的各种内部扰动和外部扰动都视为总和扰动并观测出来,然后通过PID控制器进行误差反馈控制,从而提高控制系统的扰动抑制能力与稳定精度。以Lu Gre摩擦模型加入控制模型进行仿真分析,并通过北航自研的惯性稳定平台进行实验验证。结果表明:扩张状态观测器/PD复合控制方法具有高的扰动抑制能力,可显著提高稳定平台稳定精度。相比常规PID方法,扩张状态观测器/PD复合控制使横滚框和俯仰框的稳定精度分别提高了33.23%和55.01%。     

AIRSHIP ATTITUDE TRACKING SYSTEM

The attitude tracking control problem for an airship with parameter uncertainties and external disturbances was considered in this paper. The mathematical model of the airship attitude is a multi-input/multi-output uncertain nonlinear system. Based on the characteristics of this system, a design method of robust output tracking controllers was adopted based on the upper-bounds of the uncertainties. Using the input/output feedback linearization approach and Liapunov method, a control law was designed, which guarantees that the system output exponentially tracks the given desired output. The controller is easy to compute and complement. Simulation results show that, in the closed-loop system, precise attitude control is accomplished in spite of the uncertainties and external disturbances in the system.     

UDE-based decoupled full-order sliding mode control for a class of uncertain nonlinear MIMO systems

In this paper, a generalized control scheme for the class of nonlinear multiple-input multiple-output (MIMO) uncertain system with cross-coupling and nonlinearity in their input channels under the influence of external disturbances is presented. This is accomplished using full-order model following sliding mode control based on uncertainty and disturbance estimator (UDE) technique. The fourth-order uncertain nonlinear MIMO system is separated into multiple single-input single-output double integrator subsystems by considering the effect of input coupling and nonlinearity as a disturbance. The UDE is designed to estimate the plant uncertainties as well as external disturbances without the knowledge of the bounds on the uncertainties. The proposed method decouples the system and overcomes the problem of high initial control which ultimately eliminates the reaching phase and the chattering phenomenon which is generally occurred in sliding mode control. The effectiveness of the proposed control scheme is demonstrated through numerical simulation of two-link manipulator.     

折叠翼飞行器的动力学建模与稳定控制

折叠翼飞行器在变形过程中,其动力学模型呈现多刚体、多自由度和强非线性特点,同时气动力/力矩、压心、质心和转动惯量等参数也会大幅度变化,严重影响飞行稳定性. 由此,本论文将对飞行器的多刚体动力学建模与变形稳定控制进行研究.基于凯恩方法建立了折叠翼飞行器的多刚体动力学模型,并从中得到了变形所产生的附加力和力矩表达式.通过气动计算拟合出气动参数与折叠角之间的函数关系,由此分析了不同折叠角速度下飞行器的纵向动态特性, 结果表明,折叠翼飞行器变形过程中速度、高度和俯仰角均会发生变化,飞行器无法保持稳定飞行.为此提出了一种基于自抗扰理论的飞行器变形过程中的稳定控制方法.将折叠翼飞行器纵向非线性动力学模型中存在的非线性项、耦合项以及参数时变项都视为系统内外总扰动,利用扩张状态观测器对总扰动进行实时估计和补偿, 针对补偿后的系统设计PD控制器,实现了速度通道和高度通道的解耦控制.通过Lyapunov稳定性原理证明了系统的稳定性, 并进行数学仿真验证. 仿真结果表明,基于自抗扰理论设计的稳定控制器能够解决飞行器变形所带来的强非线性和参数时变等问题,保证飞行器的高精度稳定控制.      

Velocity-sensorless proportional–derivative trajectory tracking control with active damping for quadcopters

The proposed observer-based control mechanism solves the trajectory tracking problem in the presence of external disturbances with the reduction in sensor numbers. This systematically considers the quadcopter nonlinear dynamics and parameter and load variations by adopting the standard controller design approach based on a disturbance observer (DOB). The first feature is designing first-order observers for estimating the velocity and angular velocity error, with their parameter independence obtained from the DOB design technique. As the second feature, the resultant velocity observer-based control action including active damping and DOBs secures first-order tracking behavior for the position and attitude (angle) loops through pole zero cancellation, thereby forming a proportional–derivative control structure. Closed-loop analysis results reveal the performance recovery and steady-state error removal properties in the absence of tracking error integrators. The numerical verification confirms the effectiveness of the proposed mechanism using MATLAB/Simulink.

     

DYNAMIC MODELING AND STABILITY CONTROL OF FOLDING WING AIRCRAFT 1)

折叠翼飞行器在变形过程中,其动力学模型呈现多刚体、多自由度和强非线性特点,同时气动力/力矩、压心、质心和转动惯量等参数也会大幅度变化,严重影响飞行稳定性. 由此,本论文将对飞行器的多刚体动力学建模与变形稳定控制进行研究.基于凯恩方法建立了折叠翼飞行器的多刚体动力学模型,并从中得到了变形所产生的附加力和力矩表达式.通过气动计算拟合出气动参数与折叠角之间的函数关系,由此分析了不同折叠角速度下飞行器的纵向动态特性, 结果表明,折叠翼飞行器变形过程中速度、高度和俯仰角均会发生变化,飞行器无法保持稳定飞行.为此提出了一种基于自抗扰理论的飞行器变形过程中的稳定控制方法.将折叠翼飞行器纵向非线性动力学模型中存在的非线性项、耦合项以及参数时变项都视为系统内外总扰动,利用扩张状态观测器对总扰动进行实时估计和补偿, 针对补偿后的系统设计PD控制器,实现了速度通道和高度通道的解耦控制.通过Lyapunov稳定性原理证明了系统的稳定性, 并进行数学仿真验证. 仿真结果表明,基于自抗扰理论设计的稳定控制器能够解决飞行器变形所带来的强非线性和参数时变等问题,保证飞行器的高精度稳定控制.     

Second-order sliding-mode controller for autonomous underwater vehicle in the presence of unknown disturbances

We propose the use of a second-order sliding-mode controller (2-SMC) to stabilize an autonomous underwater vehicle (AUV) which is subject to modeling errors and often suffers from unknown environmental disturbances. The 2-SMC is effective in compensating for the uncertainties in the hydrodynamic and hydrostatic parameters of the vehicle and rejecting the unpredictable disturbance effects due to ocean waves, tides, and currents. The 2-SMC is comprised of an equivalent controller and a switching controller to suppress the parameter uncertainties and external disturbances, and its closed-loop system is exponentially stable in the presence of parameter uncertainties and unknown disturbances. We performed numerical simulations to validate the proposed control approach, and experimental tests using Cyclops AUV were conducted to demonstrate its practical feasibility. The proposed controller increased the accuracy of trajectory tracking for an AUV in the presence of uncertain hydrodynamics and unknown disturbances.     

基于浸入与不变原理的四旋翼姿态系统反步滑模控制

针对较大幅度外部不确定扰动下的四旋翼姿态稳定问题,设计了一种基于浸入与不变原理(ⅠⅠ)的自适应反步滑模控制器(ABSMC)。首先建立了未知大扰动下四旋翼姿态系统动力学模型,然后以横滚角子系统搭建为例,设计并应用了反步法和基于趋进率的滑模控制策略。在扰动估计误差流型设计中,融合了ⅠⅠ原理,即自适应率的选取实现了误差流型的不变和吸引,确保估计误差收敛到0。最后,对系统进行了稳定性分析和数字仿真。结果表明,在较大未知扰动情况下,融合ⅠⅠ原理方法后,经10 s所测跟踪误差平方的累加和仅为传统ABSMC方法的11.2%,控制精度大幅提高。     

猎雷声纳基阵姿态稳定系统自适应反步法控制

针对带非线性摩擦力矩和负载扰动的高精度猎雷声纳基阵姿态稳定系统,提出了一种基于神经网络的自适应反步法控制方法。其中神经网络用于估计未知非线性摩擦力矩,进而设计反步法控制器和参数自适应律来对神经网络估计误差和负载扰动进行补偿。最后应用Lyapunov方法证明了所提出的自适应控制器能保证闭环系统的稳定性,并且可以通过选择适当的控制器参数来调整收敛率。仿真结果表明,基于神经网络的自适应反步法控制方法与PID控制相比,系统的动、静态性能指标及鲁棒性得到了全面的改善,与双闭环PID控制相比,跟踪精度提高了3倍多。     

Adaptive neural tracking control for a class of perturbed pure-feedback nonlinear systems

This paper focuses on the problem of the adaptive neural control for a class of a perturbed pure-feedback nonlinear system. Based on radial basis function (RBF) neural networks’ universal approximation capability, an adaptive neural controller is developed via the backstepping technique. The proposed controller guarantees that all the signals in the closed-loop system are bounded and the tracking error eventually converges to a small neighborhood around the origin. The main advantage of this note lies in that a control strategy is presented for a class of pure-feedback nonlinear systems with external disturbances being bounded by functions of all state variables. A numerical example is provided to illustrate the effectiveness of the suggested approach.     

Adaptive trajectory tracking of magnetostrictive actuator based on preliminary hysteresis compensation and further adaptive filter controller

An adaptive dynamic surface control (DSC) scheme is proposed for the multi-input multi-output attitude control of near-space hypersonic vehicles (NHV). The proposed control strategy can improve the control performance of NHV despite uncertainties and external disturbances. The proposed controller combines dynamic surface control and radial basis function neural network (RBFNN) and is designed to control the longitudinal dynamics of NHV. The DSC technique is used to handle the problem of “explosion of complexity” inherent to the conventional backstepping method. RBFNN is used to approximate the unknown nonlinear function, and a robustness component is introduced in the controller to cancel the influence of compound disturbance and improve robustness and adaptation of the system. Simulation results show that the proposed strategy possesses good robustness and fast response.     

Robust adaptive sliding mode attitude maneuvering and vibration damping of three-axis-stabilized flexible spacecraft with actuator saturation limits

This paper presents a dual-stage control system design method for flexible spacecraft attitude maneuvering control by use of on-off thrusters and active vibration suppression by embedded smart material as actuator. As a stepping stone, an adaptive sliding mode controller with the assumption of knowing the upper bounds of the lumped perturbation is designed that ensures exponential convergence or uniform ultimate boundedness (UUB) of the attitude control system in the presence of bounded parameter variation/disturbances and control input saturation as well. Then this adaptive controller is redesigned such that the need for knowing the upper bound in advance is eliminated. Lyapunov analysis shows that this modified adaptive controller can also guarantee the exponential convergence or UUB of the system. For actively suppressing the induced vibration, linear quadratic regulator (LQR) based positive position feedback control method is presented. Numerical simulations are performed to show that rotational maneuver and vibration suppression are accomplished in spite of the presence of disturbance torque/parameter uncertainty and saturation input.     

Observer-based adaptive robust control of nonlinear nonaffine systems with unknown gain sign

In this paper, a direct adaptive robust controller for a class of SISO nonaffine nonlinear systems is presented. The existence of an ideal controller is proved based on the Implicit Function Theorem. Since the Implicit Function Theorem only guarantees the existence of the controller and does not provide a way to construct it, a neural network is employed to approximate the unknown ideal controller. In addition, an observer is designed to estimate the system states because all the states may not be available for measurements. In this method, a priori knowledge about the sign of control gain is not required and, in order to cope with unknown control direction, the Nussbaum-type technique is used. Moreover, only one adaptive parameter is needed to be updated and also a robust term is used in the control signal to reduce the effect of external disturbances and approximation errors. Furthermore, the stability analysis for the closed-loop system is presented based on the Lyapunov stability method. Theoretical results are illustrated through a simulation example. These simulations show the effectiveness of the proposed method.     

基于最优参数控制方法的齿轮系统混沌控制

基于最优参数控制方法,实现了齿轮传动系统中的混沌控制．以经典的间隙单齿轮副非线性动力学模型为研究对象,以啮合静载荷为控制参数,通过混沌吸引子中轨线的观测近似得到目标周期不动点、系统在目标不动点处的雅克比矩阵以及在控制原始参量处的梯度矩阵．最后运用最优参数控制策略计算得到啮合静载荷的小扰动量,实现了把齿轮系统的混沌运动镇定周期一轨道上的目的．研究结果表明,基于最优参数控制方法的控制过程,只是在控制的前几个周期内需要控制参数产生相对较大的扰动量,随着控制的继续进行,扰动量几乎稳定到了某一固定值,不再需要较大的变动．而且控制参数计算所需要的中间参量可以直接由混沌吸引子中轨线的观测近似得到,因而控制容易实现．