Chattering analysis for discrete sliding mode control ofdistributed control systems

The chattering characteristic of sliding mode control isanalyzed when it is applied in distributed control systems （DCSs）.For a DCS with random time delay and packet dropout, a discreteswitching system model with time varying sampling period isconstructed based on the time delay system method. The reachinglaw based sliding mode controller is applied in the proposedsystem. The exponential stability condition in the form of linearmatrix inequality is figured out based on the multi-Lyaponov functionmethod. Then, the chattering characteristic is analyzed for theswitching system, and a chattering region related with time varyingsampling period and external disturbance is proposed. Finally, numericalexamples are given to illustrate the validity of the analysisresult.

基于干扰观测器的升力式飞行器改进离散滑模控制研究

升力式飞行器具有飞行空域宽、速度变化范围大、机动性强等特点,是近年来国内外的研究热点。本文针对升力式飞行器模型大不确定及外界干扰强带来的控制难题,提出了一种基于干扰观测器的改进离散滑模变结构控制方法。首先,建立了俯仰通道的离散控制模型。其次,设计了一种基于干扰估计的改进离散滑模变结构控制律,并证明了其稳定性。再次,分析了参数选择对控制系统的影响,验证了控制律的有效性。最后,与传统的离散滑模变结构控制方法进行了比较。仿真结果表明,与传统的离散滑模控制方法相比,本文提出的控制律控制精度更高、鲁棒性更强、滑模面收敛速度更快及抖振更小,可有效提高升力式飞行器的飞行品质,实现复杂任务的稳定控制。

导引头稳定平台离散时间预设性能控制

针对现有离散时间预设性能控制方法对滑模趋近律依赖度高、抖振缺陷明显的难题,通过创建一种摆脱了滑模控制的设计新框架,为拦截弹导引头稳定平台提出了一种离散时间预设性能控制新方法。首先,设计一种离散时间性能函数对跟踪误差的收敛轨迹进行包络约束;然后,定义一种离散时间转换误差并将其用于构造一种新颖的反馈函数;设计离散时间控制律对新开发的反馈函数而不是转换误差进行镇定,不仅保证了所有跟踪误差均具有期望的预设性能,还摆脱了控制算法对滑模趋近律的依赖性,从根本上解决了控制抖振难题;最后,通过数值对比仿真验证了所提方法的有效性与优势。

基于PD-滑模耦合算法的压电智能薄板颤振抑制

针对工件柔性主导的薄壁件铣削颤振问题,提出了一种基于PD–滑模耦合算法的压电智能薄板颤振抑制方法。首先设计了只需位移测量的主动控制算法,基于滑模控制理论处理系统参数不确定性和外部扰动,通过动态补偿器对未知切削状态进行在线近似和补偿;为解决传感误差和系统时滞问题,在滑模控制器中进一步耦合了时空依变PD控制模型,借助ABAQUS仿真拟合控制参数时变函数;最后设计了一套薄壁件主动控制装置,试验结果显示采用主动控制可有效抑制薄壁件铣削颤振,验证了控制方法的可行性。

基于新型趋近律的PMSM模糊滑模控制

针对永磁同步电机的调速系统动态品质易受参数变化、外部扰动以及摩擦力等不确定因素影响而导致伺服性能降低的问题,提出一种改进的幂次指数趋近律,对该趋近律的参数k和ε引入模糊规则控制,有效抑制传统滑模变结构控制中的固有抖振问题,提升收敛速度。为了消除系统内、外部扰动引起的控制精度问题,设计一种新型扰动观测器进行观测。仿真结果表明:该方法能够实现精确的速度控制;与传统的滑模控制相比,在保留其优势的基础上,有效降低了滑模的抖振。

航空薄壁零件切削加工技术研究进展

航空薄壁零件的加工精度和效率直接影响飞机的性能和可靠性。本文系统综述了航空薄壁零件切削加工技术,包括夹具技术、加工变形预测与控制方法、颤振预测与控制技术,以及数字孪生技术应用等多个方面。夹具技术详细研究了各种夹具的操作模式、结构特点、功能与应用等方面。变形预测与控制分析了薄壁件加工变形原因,并介绍了相关的控制技术和方法。颤振预测与控制探讨了切削过程稳定性分析技术和颤振控制技术,包括在线监测与识别、主动与被动控制技术和方法。数字孪生技术的应用部分介绍了该技术在薄壁件加工中的实际应用情况。通过对航空薄壁零件加工技术的系统综述,全面深入地介绍了相关内容,可为学者们的研究提供参考与指导。

永磁同步电机模糊滑模无位置传感器控制

针对滑模量在滑模面切换以及速度非线性变化而致使的系统抖振问题,提出一种超旋转滑模模糊观测器。滑模观测器(SMO)存在的高频抖振会对电机控制系统产生很大的影响,导致电机产生转速波动和稳态误差。为了削弱SMO的抖振问题,首先对滑模动态变量的趋近速度动态变化导致的抖振问题,通过引入模糊逻辑理论使得系统状态量趋动速度智能化,设置模糊规则以达到智能动态化速度,以系统动态变量趋向切换面的距离与状态量动态趋向速度为规则因子,动态智能化趋向速度;其次对系统变换函数导致的系统抖振,进一步采用连续函数F(s)代替不连续的sgn(s)符号函数。该方案有效削弱了系统的抖振问题,相较于SMO控制提高了系统的稳定性。

基于模型不确定性自适应估计的工业机械臂改进TDE控制策略

在对工业机械臂进行控制时,采用传统的基于时延估计的控制(TDEC/TDC)方法难以有效平衡控制精度与输入抖振,针对这一问题,提出了一种基于模型不确定性自适应估计的改进TDEC策略。首先,结合多自由度机械臂动力学模型,构建了时延估计(TDE)控制器;然后,利用动力学模型扰动项的时延估计值及时延估计梯度值,提出了机械臂动力学模型不确定性自适应估计器,并将TDEC及滑模控制作为辅助控制策略,与所提出的自适应估计器相结合,形成了完整的工业机械臂改进TDEC方法;基于Lyapunov方法,对改进的TDEC控制策略进行了稳定性分析;最后,通过仿真分析和实验的方式,验证了改进的TDEC控制方法的优越性。研究结果表明:相较于传统的TDEC方法,改进的TDEC控制策略在机械臂加载/未加载条件下的控制精度平均分别提高了62.29%及45.38%;相较于已有的自适应TDEC方法,改进的TDEC控制策略在机械臂加载/未加载条件下的控制精度平均分别提高了23.31%及36.40%;同时,通过测量计算控制输入能耗的平方值积分,表明了改进的TDEC控制策略能够在保留TDEC优势的基础上有效抑制输入抖振,且能够有效地与已有自适应TDEC方法相结合,提升了对工业机械臂的控制效果,其具有良好的灵活性。

基于疫苗接种策略的流行病学滑模控制方法

为了对流行病学模型进行动态、实时控制,提出了具有控制输入(疫苗接种)策略的易感者-潜伏者-隔离者-感染者-恢复者(susceptible-exposed-quarantined-infected-recovered,SEQIR)流行病学模型,并对其疫苗接种控制律进行滑模控制。首先,对该模型进行了动力学分析。然后,针对SEQIR流行病模型,设计滑模面和相应的接种控制律,使得系统状态移动并收敛到滑模面上,缓解系统的抖振现象。这种滑模控制策略对参数不确定性和扰动具有鲁棒性。此外,采用李雅普诺夫第二方法对闭环系统的稳定性进行了分析。实验表明,滑模控制能够实时、快速地控制流行病的传播,接种疫苗可以减缓流行病的传播速度并降低传播规模,从而减少流行病暴发的风险。结果证明滑模控制策略能够应用在流行病学模型中,并及时、有效地控制疾病流行,同时接种疫苗也是一项非常重要和有效的措施。

一种改进指数趋近律滑模控制器的PMSM矢量控制研究

滑模控制因其具有良好的控制性能,广泛地应用于永磁同步电机高精度调速场合。使用滑模控制设计永磁同步电机矢量控制转速环控制器时,传统的指数趋近律滑模控制器,在系统靠近滑模面时,若参数选取不当,会导致电机抖振。针对这一问题,设计了一种改进指数趋近律,在不影响系统快速性的前提下,使系统状态接近滑模面的速度更为缓慢,稳态性能更好。不同给定转速下的仿真实验证明了所提改进算法的有效性。

基于新型幂次指数趋近律滑模控制算法的研究

针对传统滑模控制存在抖振与收敛速度缓慢的问题,提出一种新型幂次指数趋近律的滑模控制方法。首先上述趋近律结合了双曲正切函数与符号函数的特征进行了切换函数上的改进,滑模系数影响因子引入了系统误差与滑模状态变化量,使其能够自适应调节滑模到达过程的收敛速度并对其进行分阶段调节,还利用切换函数的特征分析了趋近滑模面双侧切换区间的范围;其次分析了自适应新型幂次指数趋近律的收敛区域和收敛时间,并证明了此趋近律的存在性、可达性与稳定性;最后将新型幂次指数趋近律和其它各种传统趋近律运用到经典二阶系统进行了对比,仿真结果表明新型幂次指数趋近律能够更好的提升收敛速率以及削弱抖振的产生。

FUZZY GLOBAL SLIDING MODE CONTROL BASED ON GENETIC ALGORITHM AND ITS APPLICATION FOR FLIGHT SIMULATOR SERVO SYSTEM

To alleviate the chattering problem, a new type of fuzzy global sliding mode controller （FGSMC） is presented. In this controller, the switching gain is estimated by fuzzy logic system based on the reachable conditions of sliding mode controller（SMC）, and genetic algorithm （GA） is used to optimize scaling factor of the switching gain, thus the switch chattering of SMC can be alleviated. Moreover, global sliding mode is realized by designing an exponential dynamic sliding surface. Simulation and real-time application for flight simulator servo system with Lugre friction are given to indicate that the proposed controller can guarantee high robust performance all the time and can alleviate chattering phenomenon effectively.

Fuzzy robust sliding mode control of a class of uncertain systems

Aiming at a class of systems under parameter perturbations and unknown external disturbances, a method of fuzzy robust sliding mode control was proposed. Firstly, an integral sliding mode surface containing state feedback item was designed based on robust H∞ control theory. The robust state feedback control was utilized to substitute for the equivalent control of the traditional sliding mode control. Thus the robustness of systems sliding mode motion was improved even the initial states were unknown. Furthermore, when the upper bound of disturbance was unknown, the switching control logic was difficult to design, and the drawbacks of chattering in sliding mode control should also be considered simultaneously. To solve the above-mentioned problems, the fuzzy nonlinear method was applied to approximate the switching control term. Based on the Lyapunov stability theory, the parameter adaptive law which could guarantee the system stability was devised. The proposed control strategy could reduce the system chattering effectively. And the control input would not switch sharply, which improved the practicality of the sliding mode controller. Finally, simulation was conducted on system with parameter perturbations and unknown external disturbances. The result shows that the proposed method could enhance the approaching motion performance effectively. The chattering phenomenon is weakened, and the system possesses stronger robustness against parameter perturbations and external disturbances.

Limiting Factors for Active Suppression of Structural Chatter Vibrations Using Machine′s Drives

Chatter vibrations are a major limitation for rough milling operations,leading to productivity reduction,low tool life and poor surface finish.It has been shown recently that the machine tool′s own drives can be used to increase the stability limit related to structural modes of the machine.To damp the low frequency modes,a new feedback loop is added to the classical position,velocity and current cascaded control.The objective of this study is to analyse the limitations of this new chatter suppression technique.Constraints related to the non-collocated control are first studied on a simplified three-mass model and then experimentally demonstrated on a three-axis horizontal milling centre.The industrial integration of the new control loop with sampling time constraints and limited drive′s bandwidth is analysed.After determining the appropriate conditions to use this chatter suppression technique,a cutting test demonstrates that the stability limit can be doubled in the low regions of the stability lobes.

Sliding mode control of a new chaotic system

In this paper, a sliding mode controller （SMC） is designed to control a new dynamical system with canonical chaos characters. With the proposed SMC, the new chaotic system can be regulated to a fixed point in the state space. Simulation shows that the chattering phenomenon is greatly alleviated.

Approximation law for discrete-time variable structure control systems

Two approximation laws of sliding mode for discrete-time variable structure control systems are proposed to overcome the limitations of the exponential approximation law and the variable rate approximation law. By applying the proposed approximation laws of sliding mode to discrete-time variable structure control systems, the stability of origin can be guaranteed, and the chattering along the switching surface caused by discrete-time variable structure control can be restrained effectively. In designing of approximation laws, the problem that the system control input is restricted is also considered, which is very important in practical systems. Finally a simulation example shows the effectiveness of the two approximation laws proposed.

Countermeasure Against Regenerative and Forced Chatter of Flexible Workpieces in Milling Processs Using Bi-directional Excitation

A novel extended methodology for chatter suppression in milling process by applying external forced vibrations to the workpiece in two orthogonal directions which are the feed and cross-feed directions.Both the regenerative and forced chatter suppression during the milling process of flexible workpieces are investigated.Here,the workpiece is subject to a sinusoidal periodic force in the feed direction to disrupt the regenerative effect.Additionally,to minimize the forced chatter,the workpiece is subject to the periodic excitation force in cross-feed direction.This force is proportional to the magnitude of the estimated cutting force in cross-feed direction and has a phase opposite to the cutting force to minimize the vibration amplitudes.The effectiveness of the proposed method is evaluated numerically and experimentally,for the spindle speed located in both the local minima and local maxima of the stability lobe diagram.The numerical simulations indicate significant suppression effect in terms of vibration amplitudes,resulting in suppression of both the regenerative chatter and the forced chatter.Experiments were conducted by using a workpiece-mounted active stage composed of flexure hinges and driven by piezoelectric actuators.The experimental results agree qualitatively with the numerical simulations.The proposed method indicates a remarkable vibration reduction effect for both regenerative and forced chatters.

Position Control of Synchronous Motor Drive by Modified Adaptive Two-phase Sliding Mode Controller

A modified adaptive two-phase sliding mode controller for the synchronous motor drive that is highly robust to uncertain- ties and external disturbances is proposed in this paper.The proposed controller uses two-phase sliding mode control (SMC) where the 1st phase mainly controls the system in steady states and disturbed states-it is a smoothing phase.The 2nd phase is used mainly in the case of disturbed states.Also,it is an autotuning phase and uses a simple adaptive algorithm to tune the gain of conventional variable structure control (VSC).The modified controller is useful in position control of a permanent magnet synchronous drive.

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.