Mixed H2/H∞ distributed robust model predictive control for polytopic uncertain systems subject to actuator saturation and missing measurements

In this paper, we discuss the mixed H₂/H_∞ distributed robust model predictive control problem for polytopic uncertain systems subject to randomly occurring actuator saturation and packet loss. The global system is decomposed into several subsystems, and all the subsystems are connected by a fixed topology network, which is the definition for the packet loss among the subsystems. To better use the successfully transmitted information via Internet, both the phenomena of actuator saturation and packet loss resulting from the limitation of the communication bandwidth are taken into consideration. A novel distributed controller model is established to account for the actuator saturation and packet loss in a unified representation by using two sets of Bernoulli distributed white sequences with known conditional probabilities. With the nonlinear feedback control law represented by the convex hull of a group of linear feedback laws, the distributed controllers for subsystems are obtained by solving an linear matrix inequality (LMI) optimisation problem. Finally, numerical studies demonstrate the effectiveness of the proposed techniques.     

A new OFRMPC formulation with on‐line synthesis of the dynamic output feedback controller

This paper proposes a new approach for the design of output feedback robust model predictive control (OFRMPC) with a dynamic output feedback controller (DOFC) for linear uncertain systems subject to input and output constraints. The main contribution of this work is the full on‐line synthesis of the DOFC as part of a convex optimization problem, with constraint satisfaction and asymptotic stability guarantees. A numerical example is employed to illustrate the advantage of the proposed control law, as compared with another OFRMPC strategy with partial DOFC synthesis. The present paper also points out an inconsistency in the mathematical development of a previous related OFRMPC formulation (‘improved dynamic output feedback RMPC for linear uncertain systems with input constraints’). Copyright © 2017 John Wiley & Sons, Ltd.     

Energy-to-peak performance controller design for building via static output feedback under consideration of actuator saturation

The paper presents a static output feedback controller design approach for seismic-excited structures. An energy-to-peak control performance is used and actuator saturation is taken into consideration. By combining the linear matrix inequality (LMI) technique and the random search results of genetic algorithm (GA), a desirable static output feedback controller can be computed. Two building structures under seismic loads are used to validate the effectiveness of the proposed method in reducing the structural vibration. Simulation results also show that the energy-to-peak performance based controller can well realize the peak response suppression requirement and the static output feedback controller can achieve the same level of control performance as that of a full-state feedback controller.     

Non-fragile observer-based output feedback control for polytopic uncertain system under distributed model predictive control approach

In this paper, a non-fragile observer-based output feedback control problem for the polytopic uncertain system under distributed model predictive control (MPC) approach is discussed. By decomposing the global system into some subsystems, the computation complexity is reduced, so it follows that the online designing time can be saved.Moreover, an observer-based output feedback control algorithm is proposed in the framework of distributed MPC to deal with the difficulties in obtaining the states measurements. In this way, the presented observer-based output-feedback MPC strategy is more flexible and applicable in practice than the traditional state-feedback one. What is more, the non-fragility of the controller has been taken into consideration in favour of increasing the robustness of the polytopic uncertain system. After that, a sufficient stability criterion is presented by using Lyapunov-like functional approach, meanwhile, the corresponding control law and the upper bound of the quadratic cost function are derived by solving an optimisation subject to convex constraints. Finally, some simulation examples are employed to show the effectiveness of the method.     

Novel Optimal Design Approach for Output‐Feedback H∞ Control of Vehicle Active Seat‐Suspension System

In this paper, the output‐feedback control problem of a vehicle active seat‐suspension system is investigated. A novel optimal design approach for an output‐feedback H_∞ controller is proposed. The main objective of the controller is to minimize the seat vertical acceleration to improve vehicle ride comfort. First, the human body and the seat are considered in the modeling of a vehicle active suspension system, which makes the model more precise. Other constraints, such as tire deflection, suspension deflection and actuator saturation, are also considered. Then the output‐feedback control strategy is adopted since some state variables, such as body acceleration and body deflection, are unavailable. A concise and effective approach for an output‐feedback H_∞ optimal control is presented. The desired controller is obtained by solving the corresponding linear matrix inequalities (LMIs) and by the calculation of equations proposed in this paper. Finally, a numerical example is presented to show the effectiveness and advantages of the proposed controller design approach.     

基于输出反馈的欠驱动TORA系统的有界输入控制

针对欠驱动TORA(Translational oscillations with a rotational actuator)系统,设计了一种具有执行器饱和约束的输出反馈等[7]特别地,由Rand学者提出的TORA系统,最初控制器.与其他现有方法相比,本文方法不仅考虑了执行器饱和约束和作为双自旋航天器的简化模型用于研究自振现象.后来由于速度信号不可测情形,而且考虑了旋转小球可能存在的循环行为.具体而TORA系统具有强耦合、高度非线性、欠驱动等特性,而被言,首先根据TORA系统模型分析了TORA系统的控制目标;随后,作为一种非线性基准系统主要用于非线性控制器设计、验证构造了一种新颖的能量函数,在此基础上设计了一种考虑执行器饱和约非线性控制算法的控制性能或教学研究.目前国内外已有多束的输出反馈控制器,并通过严格的数学分析证明了闭环系统关于平衡点的稳定性;最后,借助数值仿真测试检验了所提控制器的控制性能,并所高校和研究机构针对TORA系统的控制问题展开研究.对与已有方法进行了对比.仿真测试结果表明本文所提方法具有更好的控法制性能.     

Dynamic Output Feedback Control for Systems Subject to Actuator Saturation via Event‐Triggered Scheme

In this paper, the event‐triggered dynamic output feedback control problem for linear systems with actuator saturation is investigated. Event‐triggered scheme only transmits the corresponding signal when the event‐triggered condition is violated. Due to its advantage of saving communication resources, it is utilized to design the dynamic output feedback controller. A criterion is established to guarantee the stability of the closed‐loop system by introducing an exponential term for the Lyapunov function, which corresponds to the exponential term in the event‐triggered condition. The explicit design of the coefficient matrices of the controller is presented. Furthermore, a lower bound of the inter‐event time is calculated to avoid Zeno behavior. An optimization algorithm is then formulated to maximize the estimation of the domain of attraction. Finally, a numerical example is given to illustrate the effectiveness of our methods and to show the trade‐off between the size of the domain of attraction and communication resources saving.     

Stabilization of linear systems over networks with bounded packet loss and its use in model predictive control

This paper considers stabilization of discrete-time linear systems, where network exists for transmitting the sensor and controller information, and arbitrary bounded packet loss occurs in the sensor–controller link and the controller–actuator link. The stabilization of this system is transformed into the robust stabilization of a set of systems. The stability result for this system is specially applied on model predictive control (MPC) that explicitly considers the satisfaction of input and state constraints. Two synthesis approaches of MPC are presented, one parameterizing the infinite horizon control moves into a single state feedback law, the other into a free control move followed by the single state feedback law. Two simulation examples are given to illustrate the effectiveness of the proposed techniques.     

Semi-global output regulation for linear systems with input saturation by composite nonlinear feedback control

To improve transient performance of output response, this paper applies composite nonlinear feedback (CNF) control technique to investigate semi-global output regulation problems for linear systems with input saturation. Based on a linear state feedback control law for a semi-global output regulation problem, a state feedback CNF control law is constructed by adding a nonlinear feedback part. The extra nonlinear feedback part can be applied to improve the transient performance of the closed-loop system. Moreover, an observer is designed to construct an output feedback CNF control law that also solves the semi-global output regulation problem. The sufficient solvability condition of the semi-global output regulation problem by CNF control is the same as that by linear control, but the CNF control technique can improve the transient performance. The effectiveness of the proposed method is illustrated by a disturbance rejection problem of a translational oscillator with rotational actuator system.     

一类网络控制系统的H2方法

由于网络传输带宽的限制, 在网络传输中可能造成数据的丢失. 对于同时具有测量数据和控制数据丢失的一类网络控制系统, 研究 H2 输出反馈控制问题. 数据的丢失采用满足 Bernoulli 分布的二进制随机变量进行表述. 利用矩阵不等式方法给出了 H2 动态输出反馈控制器存在的充分条件, 所设计的控制器使得闭环系统是均方意义下指数稳定并具有给定的 H2 性能. 采用 SLPMM (Sequentially linear programming matrix method) 给出相应的控制器求解算法. 最后用数值仿真验证了所提出算法的可行性.     

Two-step output feedback predictive control for Hammerstein systems with networked-induced time delays

This paper is mainly concerned with the design problem of two-step model predictive control (MPC) for nonlinear systems represented by Hammerstein model, where the network-induced time delays exist between sensor to controller (S2C) and controller to actuator (C2A) links. We assume that the system state is not measurable, so the state observer is employed to estimate the state. The intermediate variable for the linear part of the system is calculated by minimising the quadratic performance function. The time-delay compensation algorithm of two-step output feedback predictive control (TSOFPC) for Hammerstein systems is presented and validated by a numerical example.     

Stabilisation and control synthesis of switching systems subject to actuator saturation

This article presents sufficient conditions for the stabilisation of switching discrete-time linear systems subject to actuator saturations. These conditions are obtained by using successively state and output feedback control laws. The obtained results are formulated in terms of linear matrix inequalities (LMIs). The saturating and non-saturating controllers are synthesised for both cases in this work. Three sets of LMIs are presented for output feedback case. Numerical examples are used to illustrate these techniques by using a linear optimisation problem subject to LMI constraints.     

A Saturating Extension of an Output Feedback Controller for Internally Damped Euler‐Lagrange Systems

In this research, a novel extension of the passivity‐based output feedback trajectory tracking controller is developed for internally damped Euler‐Lagrange systems with input saturation. Compared with the previous output feedback controllers, this new design of a combined adaptive controller‐observer system will reduce the risk of actuator saturation effectively via generalized saturation functions. Semi‐global uniform ultimate boundedness stability of the tracking errors and state estimation errors is guaranteed by Lyapunov stability analysis. An application of the proposed saturated output feedback controller is the stabilization of a nonholonomic wheeled mobile robot with saturated actuators towards desired trajectories. Simulation results are provided to illustrate the efficiency of the proposed controller in dealing with the actuator saturation.     

基于约束H∞输出反馈的四轮转向模型跟踪控制

以跟踪参考模型为控制策略,提出一种基于约束H_∞输出反馈控制的四轮转向（4WS）控制新方法．将前馈控制和反馈控制相结合,同时控制前、后轮转角,以实现实际车辆模型对参考模型的期望性能跟踪．兼顾抗干扰能力与执行机构输出饱和,将约束H_∞输出反馈控制应用于反馈控制器的设计．仿真实验表明所设计的4WS车辆系统可以很好地跟踪参考车辆模型,提高了车辆的操纵稳定性．     

带执行器饱和的N 连杆机械臂输出反馈动态面控制

针对带执行器饱和的多关节刚性机械臂系统,提出一种基于RBF神经网络补偿的输出反馈动态面控制.通过观测器实现角速度的观测,采用RBF网络实现执行器饱和的补偿;通过Lyapunov方法证明闭环系统的稳定性,实现高精度的角度和角速度跟踪.仿真结果表明,所提出的方法能够有效补偿系统存在的执行器饱和,显著减小跟踪误差,并且对于外界干扰具有一定的鲁棒性.     

多自由度机械臂的饱和输出反馈有限时间同步位置控制EI北大核心CSCD

针对输入受限的多自由度机械臂高精度位置控制问题,本文充分考虑驱动器饱和非线性的影响,提出了多自由度机械臂输出反馈饱和有限时间比例–微分(PD)+同步位置控制策略,应用Lyapunov稳定性理论和几何齐次性技术证明了闭环系统的全局有限时间稳定性.非线性饱和函数的恰当引入,使得所提出的控制器具有清晰明确的上界,可以通过预先选择满足特定条件的控制器参数有效避免驱动器饱和问题;同步控制项的恰当引入,使得所提出的控制器兼顾了多自由度机械臂各轴间的同步协调性,从而获得更快的收敛速度和更好的系统整体性能,满足工程实际对机械臂的高精度要求.本文的数值仿真结果验证了所提出的控制方法的有效性和可行性.     

鲁棒输出反馈控制系统设计

本文利用文献[10]中提出的线性系统特征结构配置结果和Hellman-Feynman定理,导 出了输出反馈系统闭环极点关于开环矩阵中受扰元素灵敏度的参数表达式,并在此基础上给 出了具有最小闭环极点灵敏度的输出反馈控制系统设计的一个算法.该算法简单、有效,且具 有较好的"最优性".     

Distributed Self-triggered Control for Consensus of Multi-agent Systems

This paper studies the consensus problem of general linear multi-agent systems via self-triggered control. Two distributed self-triggered control schemes based on state feedback and output feedback are developed respectively. It is shown that under the proposed control protocols, consensus can be reached if the communication graph of the multi-agent system is connected. An example is presented to illustrate the effectiveness of the proposed control methods.      

An adaptive control scheme for systems with unknown actuator failures

A state feedback output tracking adaptive control scheme is developed for plants with actuator failures characterized by the failure pattern that some inputs are stuck at some unknown fixed values at unknown time instants. New controller parametrization and adaptive law are developed under some relaxed system conditions. All closed-loop signals are bounded and the plant output tracks a given reference output asymptotically, despite the uncertainties in actuator failures and plant parameters. Simulation results verify the desired adaptive control system performance in the presence of actuator failures.     

Output feedback guaranteed cost control of networked linear systems with random packet losses

This article is concerned with the output feedback guaranteed cost control problem for a class of networked control systems (NCSs) with both packet losses and network-induced delays. The packet-loss processes in the forward channel and the backward channel are modelled as two Markov chains. The dynamic output feedback controllers are considered, and the closed-loop NCS is modelled as a discrete-time Markovian system with two modes and unit time delay. By using a properly constructed Lyapunov function and the state transformation technique, a sufficient condition is derived for the closed-loop NCS to be mean-square exponentially stable and ensure a decay rate that can be tuned according to the packet loss situations in the networks. Moreover, design procedures for the guaranteed cost controllers are also presented based on the obtained stability condition and guaranteed cost performance result. Finally, an illustrative example is given to demonstrate the effectiveness of the proposed results.