Nonsingular terminal sliding mode approach applied to synchronize chaotic systems with unknown parameters and nonlinear inputs

This paper deals with the design of a novel nonsingular terminal sliding mode controller for finite-time synchro-nization of two different chaotic systems with fully unknown parameters and nonlinear inputs. We propose a novel nonsingular terminal sliding surface and prove its finite-time convergence to zero. We assume that both the master＇s and the slave＇s system parameters are unknown in advance. Proper adaptation laws are derived to tackle the unknown parameters. An adaptive sliding mode control law is designed to ensure the existence of the sliding mode in finite time. We prove that both reaching and sliding mode phases are stable in finite time. An estimation of convergence time is given. Two illustrative examples show the effectiveness and usefulness of the proposed technique. It is worthwhile noticing that the introduced nonsingular terminal sliding mode can be applied to a wide variety of nonlinear control problems.

Nanoscale Reciprocating Sliding Contacts of Textured Surfaces:Influence of Structure Parameters and Indentation Depth

Textured surfaces are widely used in engineering components as they can improve tribological properties of sliding contacts, while the detailed behaviors of nanoscale reciprocating sliding contacts of textured surfaces are still lack of study. By using multiscale method, two dimensional nanoscale reciprocating sliding contacts of textured surfaces are investigated. The influence of indentation depth, texture shape, texture spacing, and tip radius on the average friction forces and the running-in stages is studied. The results show that the lowest indentation depth can make all the four textured surfaces reach steady state. Surfaces with right-angled trapezoid textures on the right side are better for reducing the running-in stage, and surfaces with right-angled trapezoid textures on the left side are better to reduce wear. Compared with other textured surfaces, the total average friction forces can be reduced by 82.94%–91.49% for the case of the contact between the tip with radius R = 60rand the isosceles trapezoid textured surface. Besides,the total average friction forces increase with the tip radii due to that bigger tip will induce higher contact areas. This research proposes a detailed study on nanoscale reciprocating sliding contacts of textured surfaces, to contribute to design textured surfaces, reduce friction and wear.

Robust sliding mode control for fractional-order chaotic economical system with parameter uncertainty and external disturbance

This paper presents a modified sliding mode control for fractional-order chaotic economical systems with parameter uncertainty and external disturbance. By constructing the suitable sliding mode surface with fractional-order integral, the effective sliding mode controller is designed to realize the asymptotical stability of fractional-order chaotic economical systems. Comparing with the existing results, the main results in this paper are more practical and rigorous. Simulation results show the effectiveness and feasibility of the proposed sliding mode control method.

Sliding mode control of uncertain systems with distributed time-delay: parameter-dependent Lyapunov functional approach

The robust stability and robust sliding mode control problems are studied for a class of linear distributed time-delay systems with polytopic-type uncertainties by applying the parameter-dependent Lyapunov functional approach combining with a new method of introducing some relaxation matrices and tuning parameters, which can be chosen properly to lead to a less conservative result. First, a sufficient condition is proposed for robust stability of the autonomic system; next, the sufficient conditions of the robust stabilization controller and the existence condition of sliding mode are developed. The results are given in terms of linear matrix inequalities （LMIs）, which can be solved via efficient interior-point algorithms. A numerical example is presented to illustrate the feasibility and advantages of the proposed design scheme.

Numerical Study on Influence of Key Parameters of Aerodynamic Characteristics of Shaftless Ducted Rotor

Shaftless ducted rotor(SDR)is a new type of ducted rotor system designed with ducted-rotor-motor integration,which is quite different from traditional ducted rotor(DR)in aerodynamic characteristics.The sliding mesh based on unstructured grid is used to simulate the aerodynamic characteristics of SDR and DR.Then,the effects of five key parameters,namely,the rotor disk height,the number of blades,the spread angle of the duct,the central hole radius and the ducted lip radius on the aerodynamic characteristics of the SDR are investigated.It is found that the same-sized SDR produces a larger total lift than the DR in hovering,but the lift proportion of its duct is reduced.In the forward flight,a large low-speed region is generated behind the SDR duct,and the reflux vortex in blade root above the advancing blade has the trend for inward diffusion.The rotor disk height has similar effects on SDR and DR.Increasing the number of blades can effectively increase the total lift of SDR,which also increases the lift proportion of duct.Increasing the spread angle of the duct will lead to the rotor lift coefficient decrease,reducing the central hole radius can increase the total lift,but the component lift coefficient decreases.Appropriately increasing the ducted lip radius can increase the total lift,which begins to decrease after reaching a certain value.

Adaptive Gain Tuning Rule for Nonlinear Sliding-mode Speed Control of Encoderless Three-phase Permanent Magnet Assisted Synchronous Motor

In this paper, an adaptive gain tuning rule is designed for the nonlinear sliding mode speed control(NSMSC) in order to enhance the dynamic performance and the robustness of the permanent magnet assisted synchronous reluctance motor(PMa-Syn RM) with considering the parameter uncertainties. A nonlinear sliding surface whose parameters are altering with time is designed at first. The proposed NSMSC can minimize the settling time without any overshoot via utilizing a low damping ratio at starting along with a high damping ratio as the output approaches the target set-point. In addition, it eliminates the problem of the singularity with the upper bound of an uncertain term that is hard to be measured practically as well as ensures a rapid convergence in finite time, through employing a simple adaptation law. Moreover, for enhancing the system efficiency throughout the constant torque region, the control system utilizes the maximum torque per ampere technique. The nonlinear sliding surface stability is assured via employing Lyapunov stability theory. Furthermore, a simple sliding mode estimator is employed for estimating the system uncertainties. The stability analysis and the experimental results indicate the effectiveness along with feasibility of the proposed speed estimation and the NSMSC approach for a 1.1-k W PMa-Syn RM under different speed references, electrical and mechanical parameters disparities, and load disturbance conditions.

利用InSAR形变反演滑坡滑面运动特征——以汶川县布瓦村滑坡为例

当前滑坡滑面运动特征获取多采用接触式手段,费时费力、成本高昂,且仅能获取稀疏点位滑面运动状态。因此,本文提出一种非接触式滑坡滑面运动特征获取方法,其基本思路是:基于位错理论建立滑坡表面形变与滑面运动间的关系模型,同时引入滑面运动平滑约束条件,最终以InSAR等技术获取的地表形变为约束,反演获得滑面运动特征。本文选择四川省汶川县布瓦村滑坡作为研究对象,以时序InSAR技术获取的滑坡坡面升降轨形变数据为约束,基于发展的理论方法反演获得布瓦村滑坡滑面几何与运动学参数,并结合野外勘查、Lidar观测以及模型残差较好地验证了反演结果的可靠性,其中反演升降轨模型残差仅3.1 mm·a^(-1)和3.4 mm·a^(-1)。反演结果显示,布瓦村滑坡滑面位于坡表以下平均~15.0 m深度处,滑面整体以沿坡向运动为主,最大运动量级达~80 mm·a^(-1),同时在坡体西侧中下部发现微量的垂直坡向运动。本文提出方法可方便、快速的获取空间连续的滑坡滑面运动特征,为滑坡灾害预警和失稳风险评估提供更为直接可靠的科学参考。

基于卷积神经网络与可视图像的类滑动放电模式识别

为了提高机器学习算法对类滑动放电模式识别的准确率,提出了一种基于卷积神经网络(convolutional neuralnetworks,CNN)与可视图像识别电晕放电、弥散放电和类滑动放电等模式的方法。通过选取气体体积流量0~16 L/min、电极间隙2~10 mm、脉冲频率0.5~3 kHz等不同条件下的类滑动放电图像构建图像库,搭建CNN模型并优化影响CNN识别性能的超参数,包括网络层数、全连接层(full connected layer,FC)神经元数、卷积核尺寸以及激活函数类型,最后比较了CNN与决策树(decision tree,DT)算法和随机森林(random decision forests,RF)算法的识别效果。结果表明,CNN识别准确率为100%,高于传统机器学习方法。此外,本文还给出了放电模式及条件参数,通过基于反向传播神经网络(back propagation neural networks,BPNN)的聚类分析算法识别弥散放电和类滑动放电,并且准确率为100%。

基于改进型SM-ADRC的PMSM控制策略研究

在永磁同步电机(PMSM)控制中,传统的滑模自抗扰控制(SM-ADRC)能够减小外部负载变化和参数变化导致控制系统性能下降所带来的影响,但是还存在控制器参数太多,整定过于复杂化的问题,故提出一种改进型SM-ADRC方法。设计了一种新型变指数趋近律及新型控制函数将其引入扩展状态观测器(ESO)和非线性状态误差反馈控制律(NLSEF),得到新型滑模状态观测器(SM-ESO)和新型滑模状态误差反馈控制律(SM-NLSEF),减少了SM-ESO和SM-NLSEF待整定参数个数,简化了SM-ADRC参数整定。建立Simulink仿真模型和Links-RT半实物仿真实验平台,仿真和实验结果均表明:与传统SM-ADRC相比,改进型SM-ADRC在简化参数整定的同时提高了系统的响应速度和系统的抗扰性能,减小了电流脉动。

基于自适应非奇异终端滑模自抗扰的ROV控制

ROV浮游工作时由于存在系统模型不确定性和环境干扰导致跟踪效果不佳的问题,因此,提出一种参数变化的非奇异终端滑模自抗扰控制方法;首先,建立ROV的动力学模型;其次,利用非奇异终端滑模控制器代替了传统线性自抗扰的线性控制器,提高了系统的控制性能和抗干扰能力,考虑到引入参数过多问题利用梯度下降的RBF神经网络调整趋近率系数,通过李雅普诺夫定理证明了该系统的稳定性;最后,通过轨迹跟踪仿真实验与线性自抗扰对比,提高了系统响应过程的快速性和平稳性。

微造型形状对滑动轴承摩擦特性的影响

利用激光微造型技术在滑动轴承轴颈表面加工出三角形、圆形和正方形微造型,分析不同形状微造型化滑动轴承的摩擦特性,并表征表面形貌,研究表征参数和摩擦特性的关系。结果表明:与未造型的滑动轴承相比,随着载荷增加,微造型后滑动轴承的摩擦系数逐渐减小,三角形微造型的滑动轴承摩擦系数最小,其次是圆形,最后是正方形。当表面偏态增加,摩擦系数升高,而表面峰态增加时,摩擦系数变化正好相反;当表面谷处和中心处平均空体体积增加时,摩擦系数先降低后升高,表面谷处及中心处平均空体体积分别为6.148×10^(-4)mm^(3)和5.418×10^(-3)mm^(3)时,摩擦系数最低;当表面峰和谷平均体积增加时,摩擦系数降低。在载荷3200 N及600 r/min时,微造型后滑动轴承的摩擦系数随着连通性系数的增加而降低。

单相整流器二次纹波抑制的有源功率解耦控制算法

为了解决单相整流器中LC谐振回路频率适应性差的问题,引入有源功率解耦电路代替LC谐振回路抑制母线电压二次纹波,选择直流母线电容分裂拓扑有利于减小支撑电容容值。首先,对有源功率解耦电路的工作模态进行分析,建立了单相整流器和分裂电容有源功率解耦回路数学模型。其次,传统解耦控制算法间接计算解耦参考电压,为提高功率解耦效果,采用二阶广义积分器直接提取电压纹波作为电压参考,并提出一种基于滑模观测器的无电流传感器控制策略,滑模观测器降低了解耦电路成本,提高了抗干扰能力。然后,根据整流器性能指标和功率解耦要求,给出了有源功率解耦回路电感和电容设计依据。最后,对不同拓扑结构的单相整流器进行了稳态和动态实验对比,实验结果证明了控制算法的有效性。

基于参数估计-滑模阻抗控制的SEA性能分析

重载四足机器人的足部与地面接触过程和步态转换过程中会受到不确定的冲击载荷作用,易导致足部机构载荷过大从而造成结构的冲击损坏。因此,针对使用液压串联弹性执行器(series elastic actuators,SEA)作为足部末端在非结构环境下动态性能差的问题,提出了基于环境参数估计的滑模阻抗控制方法(environmental parameter estimation sliding mode,EPESM)。以阀控液压缸的活塞位移传递函数为基础建立了基于位置内环的SEA阻抗控制模型,并以PID作为基础控制器;为改善SEA阻抗控制的动态性能,根据Lyapunov第二法构建稳定的自适应环境参数估计方法对SEA期望位置进行前馈补偿;为提升自适应环境参数估计方法在SEA工作过程中不同阶段的动态性能和环境变化适应性,使用模糊控制方法对自适应环境参数估计方法中的自适应参数进行寻优;以SEA状态方程为基础构建滑模控制器与PID控制器进行动态性能对比分析。仿真结果表明:在变SEA弹簧刚度工况和变环境刚度下,EPESM阻抗控制的响应速度明显更快,可将调节时间从平均5 s缩短到1 s内,能更快地达到预期位移和预期接触力,且能略微降低稳态误差,使接触力误差保持在±6 N内。在动态跟踪工况下,EPESM阻抗控制的动态性能更好,在快速进入跟踪状态后,可以长时间保持0.2 s以内的相位滞后和5.2%的幅值误差。

弱电网下基于超螺旋滑模的LCL并网逆变器控制研究

针对LCL型滤波器的固有谐振、滤波器参数及弱电网下电网阻抗的波动会严重破坏并网系统稳定性的问题,提出了弱电网下基于超螺旋滑模的LCL并网逆变器控制策略。根据并网系统模型构建超螺旋滑模观测器,对滤波电容电压及逆变器侧输出电流进行估计,消除额外传感器需要,降低成本。采用具有非奇异快速终端滑模面控制(NFTSMC)的超螺旋滑模控制器来快速地跟踪参考给定电流及降低并网系统动稳态误差,且提高并网系统对外界干扰和参数不确定性的全局鲁棒性。仿真结果表明,当滤波参数摄动和电网阻抗变化时,系统表现出较强的鲁棒性,且并网电流的THD值保持在0.5%左右。

基于参数扰动估计的双三相永磁同步电机鲁棒模型预测控制

双三相永磁同步电机因其损耗小、效率高、容错能力强等特点,广泛应用于航空航天技术、电动汽车等领域。为优化双三相永磁同步电机控制性能,采用双d-q坐标变换对双三相永磁同步电机进行数学建模,为减小电流纹波,在传统模型预测电流控制策略基础上,增加延时补偿;考虑电机参数扰动的影响,提出一种能够对参数进行在线估计的滑模观测器,以提高控制系统鲁棒性,最后在MATLAB/Simulink中进行系统抗负载扰动与鲁棒性能仿真分析。仿真结果表明,改进后的控制策略提高了电机的响应速度,超调减小,系统对电机参数扰动的敏感性减弱,系统抗负载能力和鲁棒性增强。

基于分区和滑动时间窗策略的配电网线路参数辨识

针对配电网线路参数辨识困难、不精确的问题,提出了一种基于分区和滑动时间窗策略的配电网线路参数辨识的方法。首先,使用线性解耦潮流模型最小二乘回归得到线路初始辨识参数。然后,将配电网分成若干个区域,并采用滑动时间窗策略,在每个时间窗中对每个区域内的线路参数通过高斯-牛顿法进行精确辨识。最后,对所有时间窗内的辨识结果进行离群值检测,综合各个时间窗的辨识结果得到最终的辨识值。所提方法提高了线路参数的辨识精度,并且可以避免精确辨识时选取到坏数据导致辨识结果偏离真实值。

多参数失配下鲁棒型双馈风机模型预测电流控制

风机系统模型预测电流控制(model predictive current control,MPCC)是基于系统模型实现的,存在系统参数鲁棒性较差的问题。为解决该问题,提出了一种带有新型滑模趋近律(new sliding mode veaching law,NSMRL)的滑模观测器(sliding mode observer,SMO)结合MPCC策略。首先,建立基于电压定向的双馈风机数学模型;其次,建立无差拍模型预测控制系统;最后,构建一种改进的等速伸展项和指数到达项的滑模趋近律,该新型滑模趋近律包括系统状态变量和滑模面函数的功率项,可以以两种不同的形式来表示趋近律,新滑模趋近律的作用是使系统状态更快、抖振更小的收敛到滑模平面,从而提高参数鲁棒性。研究结果表明,该方法与无滑模MPCC和等速趋近律MPCC相比,能有效地抑制系统固有抖振,并提高系统状态到达滑模面的速度。同时,可将平均转矩脉动、电流脉动和相电流总谐波失真(total harmonic distortion,THD)降低10.54%、24.16%和5.12%。因此,所提出的NSMRL-SMO-MPCC方法能够通过在线补偿扰动实现参数失配情况下对电流的可靠预测,从而提升系统的参数鲁棒性。

水库近坝高位滑坡滑带抗剪强度参数综合确定研究

滑坡滑带的抗剪强度参数是进行滑坡稳定性评价和滑坡涌浪等灾害链研究必需的数据基础,科学合理确定滑带物理力学参数至关重要.本研究以澜沧江GS水电站MLS滑坡为依托,采用现场调查、大型原位剪切试验、室内重塑样剪切试验、室内原状样剪切试验、工程地质类比法及参数反分析法,综合确定滑带抗剪强度参数.采用数值模拟软件运用所得参数对滑坡进行变形破坏分析.数值计算结果与现场滑坡监测变形数据相吻合,验证了采用多方法综合选取滑带抗剪强度参数的准确性和合理性.研究成果可为MLS滑坡稳定评估和防治工程设计等提供技术支撑和参考借鉴依据.

基于预测误差补偿的PMSM预测电流控制

为解决永磁同步电机(permanent magnet synchronous motor,PMSM)模型预测电流控制(model predictive control,MPC)参数鲁棒性差的问题,提出一种电流预测误差的补偿策略。首先,引入PMSM局部模型,并采用滑模观测器得到局部模型变量;其次,利用局部模型在一个控制周期内计算出所有电压矢量对应的电流预测误差;最后,采用估计的电流预测误差在线修正预测模型,保证在参数扰动时的预测电流精度。仿真结果证明,相比于传统的MPC,所提出的方法几乎不再受模型参数的影响,在确保控制性能的前提下有效地提高参数鲁棒性。

飞轮储能用磁轴承综述

磁轴承是利用磁场力将转子悬浮于空间,实现定子与转子之间无机械接触的一种新型支承轴承,在飞轮储能领域具有非常广阔的应用前景。阐述了飞轮储能工作原理以及常见的4种磁轴承支承方式,根据偏置磁通产生方式、受控自由度数量、磁极数量对磁轴承结构进行分类介绍,并对磁轴承关键技术参数优化、无传感控制技术以及解耦控制技术进行综述,指出磁轴承关键技术的未来发展趋势是使用智能算法建立模型求最优解。