A solution to leader following of underactuated surface vessels with actuator magnitude and rate limits

This article investigates the leader following of underactuated surface vessels that operate in the presence of environmental disturbances, model uncertainties, and actuator saturation. What makes the design of controller challenging is that the sway cannot be directly controlled. Furthermore, the actuator is formulated with magnitude saturation and rate saturation. To express the effect of magnitude saturation and rate saturation, a continuous function is employed to model actuator. An auxiliary dynamic system is used to solve the problem of magnitude saturation and rate saturation. A disturbance observer is designed to provide estimation of the environmental disturbances and model uncertainties, and achieve finite time convergence of estimation error. A control law is designed based on disturbance observer, backstepping technique, and auxiliary dynamic system. The uniform ultimate boundedness of all signals in the closed-loop control system is proved. Simulations demonstrate the performance of the proposed controller.     

Saturated observer-based adaptive neural network leader-following control of N tractors with n-trailers with a guaranteed performance

This article addresses the leader-following neural network adaptive observer-based control of N tractors connected to n trailers with the prescribed performance specifications. To propose the controller, a change of coordinates and a nonlinear error transformation are used to transform the constrained error dynamics to a new second-order Euler-Lagrange unconstrained error dynamics which inherits all structural properties of ith vehicle dynamic model. By combining a projection-type neural network and an adaptive robust technique, a novel leader-following saturated output-feedback controller is proposed to force that ith vehicle tracks a virtual leader trajectory with the prescribed transient and steady-state characteristics while reducing the actuator saturation risk and compensating all unknown dynamic model parameters, external disturbances, unmolded dynamics, and NN approximation errors. A saturated velocity observer is heuristically proposed to obviate the requirement for the velocity measurements of ith vehicle without any unwanted peaking. A Lyapunov-based stability analysis is utilized to prove that all the tracking and state observation errors are semi-globally uniformly ultimately bounded (SGUUB) and they converge to small bounds including the origin with a prescribed performance. At the end, computer simulations will be shown to validate the efficacy of the proposed controller in practice.     

Time-varying formation control with attitude synchronization of multiple rigid body systems

In this article, we study the leader-following formation control problem for a group of rigid body systems whose followers' motions are described by dual quaternion equations. A few features are as follows. First, we introduce an exosystem to generate the leader's trajectory as well as the formation configuration, which can produce a large class of time-varying signals so that we can achieve a variety of time-varying formations. Second, to overcome the communication constraint described by a digraph, we extend the distributed observer to estimate not only the desired attitude and angular velocity but also the leader's position and linear velocity. Third, a novel distributed control law is synthesized to furnish a rigorous performance analysis of the closed-loop system. The effectiveness of our design is illustrated by a numerical example.     

Switched sampled output adaptive observer design for a class of switched nonlinearly parameterized systems under asynchronous switching

In this article, a switched sampled output adaptive observer for a class of switched nonlinearly parameterized systems is designed. Since the switching may occur during the sampling intervals while the sampled output only updates at sampling instants, the asynchronous switching phenomenon arises. Then, a collection of matched and mismatched corrective terms are introduced to deal with the asynchronous switching phenomenon based on sampled outputs and the designed observer. Moreover, some sufficient conditions are derived to achieve the boundedness of observation and parameter estimation errors based on an improved average dwell time method. Finally, the effectiveness of the theoretical result in this article is demonstrated through a simulation example.     

Adaptive prescribed performance control for hydraulic system with disturbance compensation

In this article, an adaptive prescribed performance controller is developed for hydraulic system with uncertainties. An extraordinary feature is that better prescribed performance control can be achieved by compensating the uncertainties including parameter uncertainties and disturbances. For this reason, the transformation of system output error is realized by a prescribed performance function, which is employed to constrain the boundary of tracking error and convergence rate, then the tracking error of the original system with a priori prescribed performance can be realized by stabilizing the transformed system. Adaptive control is employed to solve the system parametric uncertainties; extended state observers are built to estimate the multiple disturbances. Based on the backstepping method, they are integrated into the design of the novel controller to guarantee prescribed tracking error performance. The stability analysis of the proposed controller is carried out via the Lyapunov theory. Finally, experimental results indicate good performance of the proposed algorithm.     

A Robust Control Scheme Based on Sliding Mode Observer to Drive a Knee‐Exoskeleton

In this paper, a robust control scheme to drive a knee‐exoskeleton has been designed to assist people with limited knee movement. Dynamic modeling and parameter identification of the “subject's lower limb‐exoskeleton” has been performed and a sliding mode observer (SMO) developed and integrated in the system's closed loop to provide velocity. Lyapunov's theory allows demonstration of the stability of the system. Experimental tests have been performed with the aid of five voluntary subjects, in sitting position, and during flexion/extension of the knee joint. The performance of the proposed control scheme is compared with those obtained using the classical proportional integrator derivative (PID) controller. These tests track the desired position and velocity trajectories with small tracking errors and evaluate the system's stability and system's robustness against the subject's parameters, variations, and external disturbances.     

Extended state observer based control for generic hypersonic vehicles with nonaffine-in-control character

This paper investigates the flight control problem of generic hypersonic vehicles subject to nonaffine-in-control character. Considering the large uncertainties and external disturbance, the disturbance observer based control strategy is incorporated in the control scheme. Firstly, an extended state observer is used to estimate the system states and the total disturbance. Then, based on the output of the extended state observer, we follow the backstepping design procedure. The dynamic inversion method is involved in the last step of backstepping to solve the nonaffine-in-control problem. The proposed control scheme ensures that the hypersonic vehicle tracks the command signal with almost no aerodynamic knowledge. Rigorous stability proof is given based on the separated time-scale structure of the extended state observer and the dynamic inversion method. At last, numerical simulations are presented in different conditions to demonstrate the effectiveness and good tracking performance of the proposed control scheme.     

新型32挡自动变速器建模及加速性能仿真分析

为了提高车辆燃油经济性和发动机功率利用率,创新性设计了一种具有32挡位的双态逻辑自动变速器。基于MATLAB/Simulink仿真平台,搭建了新型双内啮合行星排和高效多锥形摩擦片通用仿真模块,并在此基础上建立双态逻辑自动变速器的动态模型,通过整车动力性仿真分析验证了模型的正确性。针对双态逻辑自动变速器挡位数量多的特点,为了得到最优加速特性,在所建立仿真模型基础上,研究以不同挡位起步以及跳跃不同挡位对车辆加速性能的影响。结果表明:以起步时刻车辆获得最大加速度来确定起步挡位,以当前挡位与目标挡位阶比不大于发动机转速自适应系数来确定跳挡策略。     

大功率永磁变频技术在矿井提升机上的应用研究

针对矿井提升机重载启动、快速加减速的应用工况,结合永磁电动机效率高、低速性能好,过载能力强等优点,采用转矩输出能力强的最大转矩电流比控制,开发出一款永磁提升机专用高压变频器。为提高系统转矩响应速度,加入了负载观测器功能。经过现场应用,该变频传动系统具有高功率因数、高效率、动态性能好、启动转矩大、机械冲击小等优点。