Subspace Identification for Closed-Loop Systems With Unknown Deterministic Disturbances

This paper presents a subspace identification method for closed-loop systems with unknown deterministic disturbances.To deal with the unknown deterministic disturbances,two strategies are implemented to construct the row space that can be used to approximately represent the unknown deterministic disturbances using the trigonometric functions or Bernstein polynomials depending on whether the disturbance frequencies are known.For closed-loop identification,CCF-N4SID is extended to the case with unknown deterministic disturbances using the oblique projection.In addition,a proper Bernstein polynomial order can be determined using the Akaike information criterion(AIC)or the Bayesian information criterion(BIC).Numerical simulation results demonstrate the effectiveness of the proposed identification method for both periodic and aperiodic deterministic disturbances.

Disturbance observer based time-varying sliding mode control for uncertain mechanical system

It is now well known that the time-varying sliding mode control （TVSMC） is characterized by its global robustness against matched model uncertainties and disturbances. The accurate tracking problem of the mechanical system in the presence of the parametric uncertainty and external disturbance is addressed in the TVSMC framework. Firstly, an exponential TVSMC algorithm is designed and the main features are analyzed. Especially, the control parameter is obtained by solving an optimal problem. Subsequently, the global chattering problem in TVSMC is considered. To reduce the static error resulting from the continuous TVSMC algorithm, a disturbance observer based time-varying sliding mode control （DOTVSMC） algorithm is presented. The detailed design principle and the stability of the closed-loop system under the composite controller are provided. Simulation results verify the effectiveness of the proposed algorithm.

A novel stabilization approach for small signal disturbance of power system with time-varying delay

Small signal instability may cause severe accidents for power system if it can not be dear correctly and timely. How to maintain power system stable under small signal disturbance is a big challenge for power system operators and dispatchers. Time delay existing in signal transmission process makes the problem more complex. Conventional eigenvalue analysis method neglects time delay influence and can not precisely describe power system dynamic behaviors. In this work, a modified small signal stability model considering time varying delay influence was constructed and a new time delay controller was proposed to stabilize power system under disturbance. By Lyapunov-Krasovskii function, the control law in the form of nonlinear matrix inequality （NLMI） was derived. Considering synthesis method limitation for time delay controller at present, both parameter adjustment method by using linear matrix inequality （LMI） solver and iteration searching method by solving nonlinear minimization problem were suggested to design the controller. Simulation tests were carried out on synchronous-machine infinite-bus power system. Satisfactory test results verify the correctness of the proposed model and the feasibility of the stabilization approach.

Multi-agent Coordinated Control and Collision Avoidance with Unknown Disturbances

The formation problem of multi-agent systems via coordinated control is investigated,where the multiple agents can achieve the common velocity with leader and avoid collision during the evolution.In the real-world situation,the communication is often disturbed and inaccurate.Hence,the unknown disturbances are considered in the velocity measurements,which is assumed to be bounded and does not need to be modelled.Moreover,a complicated nonlinear interaction among agents is presented in the design of control.Based on the existing work of multi-agent systems,a flocking control protocol is proposed to address the formation problem in the dynamic topology.The stability analysis is given to prove that the velocities of all agents can converge to the velocity of leader and the stable motion with collision avoidance can be achieved eventually.Finally,some simulations are presented to verify the effectiveness of the proposed algorithm.

Feedforward and feedback optimal control for linear time-varying systems with persistent disturbances

The optimal control problem for linear time-varying systems affected by external persistent disturbances with known dynamic characteristics but unknown initial conditions is consider and a design procedure of a feedforward and feedbaek optimal controller is presented. The condition of existence and uniqueness of the control law is given. The disturbanee observer is proposed to make the feedforward control law realizable physically. Simulation results demonstrate that the feedforward and feedbaek optimal control law is more effective and robust than the elassical state feedbaek control law with respect to external disturbanees.

Precision motion control for electro-hydraulic axis systems under unknown time-variant parameters and disturbances

This article focuses on asymptotic precision motion control for electro-hydraulic axis systems under unknown time-variant parameters,mismatched and matched disturbances.Different from the traditional adaptive results that are applied to dispose of unknown constant parameters only,the unique feature is that an adaptive-gain nonlinear term is introduced into the control design to handle unknown time-variant parameters.Concurrently both mismatched and matched disturbances existing in electro-hydraulic axis systems can also be addressed in this way.With skillful integration of the backstepping technique and the adaptive control,a synthesized controller framework is successfully developed for electro-hydraulic axis systems,in which the coupled interaction between parameter estimation and disturbance estimation is avoided.Accordingly,this designed controller has the capacity of low-computation costs and simpler parameter tuning when compared to the other ones that integrate the adaptive control and observer/estimator-based technique to dividually handle parameter uncertainties and disturbances.Also,a nonlinear filter is designed to eliminate the“explosion of complexity”issue existing in the classical back-stepping technique.The stability analysis uncovers that all the closed-loop signals are bounded and the asymptotic tracking performance is also assured.Finally,contrastive experiment results validate the superiority of the developed method as well.

Set-Membership Filtering Approach to Dynamic Event-Triggered Fault Estimation for a Class of Nonlinear Time-Varying Complex Networks

The present study addresses the problem of fault estimation for a specific class of nonlinear time-varying complex networks,utilizing an unknown-input-observer approach within the framework of dynamic event-triggered mechanism(DETM).In order to optimize communication resource utilization,the DETM is employed to determine whether the current measurement data should be transmitted to the estimator or not.To guarantee a satisfactory estimation performance for the fault signal,an unknown-input-observer-based estimator is constructed to decouple the estimation error dynamics from the influence of fault signals.The aim of this paper is to find the suitable estimator parameters under the effects of DETM such that both the state estimates and fault estimates are confined within two sets of closed ellipsoid domains.The techniques of recursive matrix inequality are applied to derive sufficient conditions for the existence of the desired estimator,ensuring that the specified performance requirements are met under certain conditions.Then,the estimator gains are derived by minimizing the ellipsoid domain in the sense of trace and a recursive estimator parameter design algorithm is then provided.Finally,a numerical example is conducted to demonstrate the effectiveness of the designed estimator.

Dynamic Positioning System Design for A Marine Vessel with Unknown Dynamics Subject to External Disturbances Including Wave Effect

In this paper, a new control system is proposed for dynamic positioning(DP) of marine vessels with unknown dynamics and subject to external disturbances. The control system is composed of a substructure for wave filtering and state estimation together with a nonlinear PD-type controller. For wave filtering and state estimation, a cascade combination of a modified notch filter and an estimation stage is considered. In estimation stage, a modified extended-state observer(ESO) is proposed to estimate vessel velocities and unknown dynamics. The main advantage of the proposed method is its robustness to model uncertainties and external disturbances and it does not require prior knowledge of vessel model parameters. Besides, the stability of the cascade structure is analyzed and input to state stability(ISS) is guaranteed. Later on, a nonlinear PD-type controller with feedforward of filtered estimated dynamics is utilized. Detailed stability analyses are presented for the closed-loop DP control system and global uniform ultimate boundedness is proved using large scale systems method. Simulations are conducted to evaluate the performance of the proposed method for wave filtering and state estimation and comparisons are made with two conventional methods in terms of estimation accuracy and the presence of uncertainties. Besides, comparisons are made in closed-loop control system to demonstrate the performance of the proposed method compared with conventional methods. The proposed control system results in better performance in the presence of uncertainties,external disturbance and even in transients when the vessel is subjected to sudden changes in environmental disturbances.

Feedforward and feedback optimal control for linear time-varying systems with persistent disturbances

The optimal control problem was studied for linear time-varying systems,which was affected by external persistent disturbances with known dynamic characteristics but unknown initial conditions. To damp the effect of disturbances in an optimal fashion,we obtained a new feedforward and feedback optimal control law and gave the control algorithm by solving a Riccati differential equation and a matrix differential equation. Simulation results showed that the achieved optimal control law was realizable,efficient and robust to reject the external disturbances.

Distributed Asymptotic Consensus in Directed Networks of Nonaffine Systems With Nonvanishing Disturbance

In this paper the distributed asymptotic consensus problem is addressed for a group of high-order nonaffine agents with uncertain dynamics,nonvanishing disturbances and unknown control directions under directed networks.A class of auxiliary variables are first introduced which forms second-order filters and induces all measurable signals of agents’states.In view of this property,a distributed robust integral of the sign of the error(DRISE)design combined with the Nussbaum-type function is presented that guarantees not only the desired asymptotic consensus,but also the uniform boundedness of all closed-loop variables.Compared with the traditional sliding mode control(SMC)technique,the main feature of our approach is that the integral operation in the proposed control algorithm is designed to be adopted in a continuous manner and ensures less chattering behavior.Simulation results for a group of Duffing-Holmes chaotic systems are employed to verify our theoretical analysis.

孤岛微电网固定时间分布式鲁棒二次控制

针对孤岛微电网实际运行过程中出现的未知外部扰动,提出了一种固定时间分布式鲁棒二次控制算法,实现了电网频率一致性控制,有效抑制了不确定干扰,提高了系统的鲁棒性能。首先,通过设计基于饱和函数的新型控制算法,有效地解决了现有控制器高频切换引发的抖动问题。同时确保二次控制能够在固定时间内达到稳定状态,且收敛时间上界不依赖于任何初始状态。然后,在设计控制算法的基础上,采用改进的分布式事件触发机制,在满足收敛速度和达到电网频率一致性的基础上减轻了通信负担,减少了控制器更新的频率,显著降低了通信资源的消耗,并排除了Zeno行为。最后,利用Matlab/Simulink仿真平台验证了所提控制算法的有效性。

压力脉冲测试系统滑模抗干扰控制方法

针对压力脉冲测试系统运用滑模控制在体积切换时抖振突出的问题,提出一种滑模抗干扰控制方法。采用奇异值摄动理论对压力脉冲测试系统进行降阶简化,方便控制器的设计以及应用。根据系统降阶模型,构建扩张状态观测器,用于估计系统中的不确定参数和工件体积切换等未知干扰,并将估计的干扰值作为前馈信号补偿给滑模控制器,从而减小干扰不确定上界,减小切换增益来达到抑制抖振的目的。通过选择合适的Lyapunov函数对所提控制方法的稳定性进行了推导证明,使用AMESim、Matlab/Simulink构建的联合仿真平台进行仿真分析,并通过压力脉冲测试台进行了实验验证。研究结果表明:在整体跟踪性能方向,传统滑模控制方法相较于PID方法提升了21.10%,而所提控制方法相较于PID方法提升了30.86%,所提控制方法可以有效估计与补偿未知干扰,实现更小切换增益的同时保持控制精度,在工件体积切换时有效抑制了滑模抖振,提高了系统的抗干扰能力。

Enhanced adaptive nonlinear extended state observer for pure feedback systems with matched and mismatched disturbances

In this paper, an enhanced adaptive nonlinear extended state observer (EANESO) for single-input single-output pure feedback systems in the presence of external time-varying disturbances is proposed. In this paper, a nonlinear system with matched and mismatched disturbances is considered. The conventional extended state observer (ESO) can only be applied to systems that are in the form of integral chains. Moreover, this method has limitations in the face of mismatched disturbances. In the presence of time-varying disturbances, the traditional ESOs cannot estimate the disturbances accurately. To overcome this limitation, an EANESO is proposed in this paper. The main idea is to design the nonlinear ESO (NESO) to estimate the states of the system and multiple disturbances simultaneously. The observer gains are considered time-varying and adjusted with adaptation laws to improve the estimation accuracy and overcome the peaking phenomenon. Next, the proposed controller is designed based on output feedback to eliminate the effects of multiple disturbances and stabilize the closed-loop system. Subsequently, the stability analysis of the closed-loop system and convergence of the observer error are discussed. Finally, the proposed method is applied to the inverted pendulum system. The simulated results show good performance of the proposed method as compared with a recently published scheme in the related literature.

基于扰动观测器的四旋翼无人机自适应姿态控制方法

针对四旋翼无人机携带未知质量载荷对机体姿态控制带来的影响,提出了一种基于扰动观测器的自适应控制方法。该四旋翼无人机在携带未知质量载荷时的动力学模型,针对未知质量载荷对四旋翼无人机造成的干扰,设计了扰动观测器并基于此提出了一种自适应姿态控制器。使用Lyapunov方法证明了该控制器的稳定性。同时,在四旋翼无人机上携带一个未知质量的载荷,分别使用自适应控制器和反步控制器控制四旋翼无人机姿态来进行对比实验,验证控制器的有效性。

Finite-Time Synchronization for Heterogeneous Complex Networks with Time-Varying Delays

This paper studies the problem of finite-time synchronization for a class of heterogeneous complex networks which not only have node time-varying delays and coupled time-varying delays but also contain uncertain disturbance. An appropriate controller is designed such that this type of network can be synchronized within a finite time. By constructing a proper Lyapunov function and using the finite-time stability theory, the sufficient conditions for the network to achieve finite-time synchronization are given and the finite time is estimated. Finally, the conclusions obtained are extended to the case of homogeneous complex networks with time-varying delays and uncertain disturbance.

Fixed-Time Adaptive Time-Varying Matrix Projective Synchronization of Time-Delayed Chaotic Systems with Different Dimensions

This paper deals with the fixed-time adaptive time-varying matrix projective synchronization(ATVMPS)of different dimensional chaotic systems(DDCSs)with time delays and unknown parameters.Firstly,to estimate the unknown parameters,adaptive parameter updated laws are designed.Secondly,to realize the fixed-time ATVMPS of the time-delayed DDCSs,an adaptive delay-unrelated controller is designed,where time delays of chaotic systems are known or unknown.Thirdly,some simple fixed-time ATVMPS criteria are deduced,and the rigorous proof is provided by employing the inequality technique and Lyapunov theory.Furthermore,the settling time of fixed-time synchronization(Fix-TS)is obtained,which depends only on controller parameters and system parameters and is independent of the system’s initial states.Finally,simulation examples are presented to validate the theoretical analysis.

基于新型固定时间稳定方法的一类二阶非线性系统镇定控制

本文研究了受未知外部扰动侵袭的一类二阶非线性系统的固定时间镇定控制问题.首先,提出了一种新的固定时间稳定方法,并给出了收敛时间及其上界估计值的计算公式.理论分析表明,收敛时间的上界与系统初始状态无关,可由系统参数完全确定.然后,基于所提出的固定时间稳定方法设计了新型滑模趋近律和终端滑模面,使得系统状态能够在有界的有限时间内,从任意初始状态收敛至滑模面并沿着滑模面收敛至原点,同时引入了基于系统状态的自适应切换方法,有效避免了终端滑模面导致的奇异问题.最后,通过仿真验证了算法的有效性.

具有预设性能的鲁棒仿射编队机动控制

针对带有未知外部干扰的多智能体系统,提出了一种带有预设性能的鲁棒仿射编队控制算法。在有向图下,利用符号拉普拉斯矩阵,根据领航者的状态,给出了跟随者距离误差动力学模型。然后,利用输入到状态稳定(ISS)和李雅普诺夫稳定性定理,不仅证明了所提控制算法的收敛性和稳定性,抑制了系统的外部干扰,还保证了系统的误差状态收敛到预设的性能函数内,保证系统具有良好的暂态行为。最后,仿真结果验证了跟随者在外部干扰下依然能够跟随领航者,验证了所提算法的有效性。

有色量测噪声下带广义未知扰动的递推上限滤波

针对博弈对抗环境下利用快速采样雷达进行非合作目标跟踪带来的有色噪声和未知干扰共存问题,本文提出有色量测噪声下带广义未知扰动的随机动态系统递推上限滤波.这里,有色量测噪声用于描述由于快速采样或持续干扰带来的噪声相关性,广义未知扰动用于建模博弈对抗对雷达观测带来的异常影响(先验信息缺失).针对所考虑系统,通过参数优化实现状态估计误差协方差上限(而不是理论值)的在线递推,提出有色噪声下上限滤波(CUBF),给出状态估计误差协方差最小上限的近似实现,讨论了所提CUBF的存在性条件.在具有时变未知扰动和有色量测噪声的目标跟踪仿真中验证了所提方法的有效性.

未知初始跟踪条件的无人机自抗扰预设有限时间控制

四旋翼无人机在飞行时的初始状态极易受到未知的外界干扰,影响其飞行稳定性。本文采用一种与初始跟踪条件无关的预设性能控制设计方法,解决四旋翼无人机在初始跟踪状态未知时的预设性能控制器设计问题。基于该方法,将自抗扰技术、预设性能控制和有限时间控制等在设计过程中有机结合,设计无人机的自抗扰预设性能有限时间跟踪控制器,同时保证四旋翼无人机在未知初始跟踪状态下的暂态、稳态和抗干扰性能。仿真结果验证了控制方法的有效性。