IDENTIFICATION OF TIME-VARYING MODAL PARAMETERS USING LINEAR TIME-FREQUENCY REPRESENTATION

A new method of parameter identification based on linear time-frequencyrepresentation and Hubert transform is proposed to identity modal parameters of linear time-varyingsystems from measured vibration responses. Using Gabor expansion and synthesis theory, measuredresponses are represented in the time-frequency domain and modal components are reconstructed bytime-frequency filtering. The Hilbert transform is applied to obtain time histories of the amplitudeand phase angle of each modal component, from which time-varying frequencies and damping ratios areidentified. The proposed method has been demonstrated with a numerical example in which a lineartime-varying system of two degrees of freedom is used to validate the identification scheme based ontime-frequency representation. Simulation results have indicated that time-frequency representationpresents an effective tool for modal parameter identification of time-varying systems.

A Survey of Output Feedback Robust MPC for Linear Parameter Varying Systems

For constrained linear parameter varying(LPV)systems,this survey comprehensively reviews the literatures on output feedback robust model predictive control(OFRMPC)over the past two decades from the aspects on motivations,main contributions,and the related techniques.According to the types of state observer systems and scheduling parameters of LPV systems,different kinds of OFRMPC approaches are summarized and compared.The extensions of OFRMPC for LPV systems to other related uncertain systems are also investigated.The methods of dealing with system uncertainties and constraints in different kinds of OFRMPC optimizations are given.Key issues on OFRMPC optimizations for LPV systems are discussed.Furthermore,the future research directions on OFRMPC for LPV systems are suggested.

Probabilistic Robust Linear Parameter-varying Control of a Small Helicopter Using Iterative Scenario Approach

In this paper, we present an iterative scenario approach (ISA) to design robust controllers for complex linear parameter-varying (LPV) systems with uncertainties. The robust controller synthesis problem is transformed to a scenario design problem, with the scenarios generated by identically extracting random samples on both uncertainty parameters and scheduling parameters. An iterative scheme based on the maximum volume ellipsoid cutting-plane method is used to solve the problem. Heuristic logic based on relevance ratio ranking is used to prune the redundant constraints, and thus, to improve the numerical stability of the algorithm. And further, a batching technique is presented to remarkably enhance the computational efficiency. The proposed method is applied to design an output-feedback controller for a small helicopter. Multiple uncertain physical parameters are considered, and simulation studies show that the closed-loop performance is quite good in both aspects of model tracking and dynamic decoupling. For robust LPV control problems, the proposed method is more computationally efficient than the popular stochastic ellipsoid methods. © 2014 Chinese Association of Automation.

TECHNICAL STABILITY OF NONLINEAR TIME-VARYING SYSTEMS WITH SMALL PARAMETERS

Technical stability:allowing quantitative estimation of trajectory behavior of a dynamical system over a given time interval was considered. Based on a differential comparison principle and a basic monotonicity condition, technical stability relative to certain prescribed state constraint sets of a class of nonlinear time-varying systems with small parameters was analyzed by means of vector Liapunov function method. Explicit criteria of technical stability are established in terms of coefficients of the system under consideration. Conditions under which the technical stability of the system can be derived from its reduced linear time-varying (LTV) system were further examined, as well as a condition for linearization approach to technical stability of general nonlinear systems. Also, a simple algebraic condition of exponential asymptotic stability of LTV systems is presented. Two illustrative examples are given to demonstrate the availability of the presently proposed method.

Improved delay-dependent globally asymptotic stability of delayed uncertain recurrent neural networks with Markovian jumping parameters

In this paper, we have improved delay-dependent stability criteria for recurrent neural networks with a delay varying over a range and Markovian jumping parameters. The criteria improve over some previous ones in that they have fewer matrix variables yet less conservatism. In addition, a numerical example is provided to illustrate the applicability of the result using the linear matrix inequality toolbox in MATLAB.

空间堆线性变参数模型预测控制方法

针对传统PID控制方法在面临复杂负荷需求变化时无法满足空间核反应堆的控制性能需求的问题,提出了基于线性变参数模型的空间堆模型预测控制方法。针对强非线性特性,采用线性变参数模型作为预测模型,对全功率范围内的空间堆运行特性进行预测;针对大时滞的特性,采用串级控制理论结合模型预测方法优化执行机构动作,提升被控量的响应速度。分别设计了电功率和冷却剂温度的预测控制系统,在典型工况下进行控制性能仿真验证,结果表明:相对于串级PID控制系统,所设计的预测控制系统的电功率调节时间减少了68.7%,冷却剂温度调节时间减少了81.7%;电功率和冷却剂温度预测控制系统的核功率的超调量分别减少了22.3%和13.0%,保证了反应堆的安全;控制系统的适用性强,在不同功率水平均具有良好的控制性能;执行机构的动作大幅减少,驱动电机峰值电压下降了84.1%,使用寿命得到延长,系统经济性得到提升。该研究提出的结合串级控制理论基于线性变参数模型的预测控制方法能够用于优化空间堆的控制系统。

电磁阀半主动悬架线性变参数μ综合鲁棒控制

针对电磁阀半主动悬架系统中的非线性和不确定性问题以及多个性能目标之间的矛盾,设计了一种线性变参数(linear parameter varying,LPV)μ综合鲁棒控制器。建立电磁阀非线性阻尼力力学模型并开展台架试验验证模型的准确性,构建了七自由度悬架系统的非线性LPV模型;对悬架参数不确定性和系统建模误差进行分析,并考虑传感器测量噪声的影响,设计了一种基于非线性和混合不确定性的LPV-μ综合鲁棒控制器;最后进行整车电磁阀悬架系统仿真和实车试验。仿真结果表明:在随机扰动下该控制器使车身垂向加速度均方根值降低46.47%,俯仰角加速度降低46.47%,侧倾角加速度降低50.68%,具有良好的抗干扰能力和可控性。试验结果表明:LPV-μ综合控制下车身垂向加速度、俯仰角加速度和侧倾角加速度均方根值分别降低36.6%、30.14%和39.47%,并且保证悬架动挠度小于0.06 m,验证了该控制策略的有效性。

基于LPV-MPC的风电机组功率-载荷协调控制策略

大型风电机组变桨控制是一个复杂的非线性控制任务,如何在系统约束和风速扰动的条件下实现功率调节和载荷降低成为难题。针对该问题,文章采用机理与参数辨识方法构建了一个面向控制的线性变参数(LPV)模型,LPV模型引入间隙度量理论来降低模型复杂度,为控制设计提供了更加精确的线性模型。设计了时变卡尔曼滤波器,实现了风机的最优状态估计,基于获得的最优状态,提出了自适应模型预测(MPC)变桨控制器,MPC控制器能够根据实时风速变化调整预测模型,在满足系统约束的条件下实现大型风电机组功率-载荷的协调控制。OpenFAST对比仿真实例表明了模型与控制器的有效性。

基于变参数模型的智能车辆转向执行器故障诊断

为解决传统车辆研究将纵向车速设为定值的问题,设计一种基于观测器的鲁棒增益调度故障诊断算法.首先,以纵向车速为调度变量,同时考虑执行器故障、模型不确定性以及外部干扰,在传统车辆模型基础上建立四轮转向线性变参数(linear parameter varying,LPV)数学模型.然后,对执行器故障进行状态重构,设计具有可变权重因子的鲁棒增益调度观测器,实现对车辆状态信息及执行器故障信号的双重估计.最后,选取双移线和蛇形工况,通过MATLAB/Simulink和Carsim联合仿真,结果表明,所设计的执行器故障诊断算法能有效处理车辆纵向车速的时变特性,在复杂工况下能及时快速地跟踪车辆的状态及故障信息,突破了原有传统车辆故障诊断算法的局限性.

含参量一阶线性时变常微分系统状态的几个性质

文章针对含参量线性时变常微分系统,研究其参变量对系统状态的影响,并探求含参变量的微分系统状态的性质。基于参变量集合的特点和点集Hausdorff距离,主要得到以下两方面的结果:其一,在参变量集非空条件下,线性时变常微分系统状态集是凸紧的;其二,在Hausdorff距离意义下,含参量时变常微分系统的状态依时间是连续的。

Two freedom linear parameter varying μ synthesis control for flight environment testbed

To solve the problem of robust servo performance of Flight Environment Testbed(FET)of Altitude Ground Test Facilities(AGTF) over the whole operational envelope, a two-degree-offreedom μ synthesis method based on Linear Parameter Varying(LPV) schematic is proposed, and meanwhile a new structure frame of μ synthesis control on two degrees of freedom with double integral and weighting functions is presented, which constitutes a core support part of the paper. Aimed at the problem of reference command's rapid change, one freedom feed forward is adopted, while another freedom output feedback is used to meet good servo tracking as well as disturbance and noise rejection; furthermore, to overcome the overshoot problem and acquire dynamic tuning,the integral is introduced in inner loop, and another integral controller is used in outer loop in order to guarantee steady errors; additionally, two performance weighting functions are designed to achieve robust specialty and control energy limit considering the uncertainties in system. As the schedule parameters change over large flight envelope, the stability of closed-loop LPV system is proved using Lyapunov inequalities. The simulation results show that the relative tracking errors of temperature and pressure are less than 0.5% with LPV μ synthesis controller. Meanwhile, compared with non-LPV μ synthesis controller in large uncertainty range, the proposed approach in this research can ensure robust servo performance of FET over the whole operational envelope.

Adaptive bolus chasing computed tomography angiography by a local linear time and space parameter varying model:modeling,control,identification,and experimental results

A high contrast to noise ratio(CNR)is always desirable for contrast-enhanced computed tomography angiography(CTA).To ensure a high CNR of the vascular images in CTA and potentially reduce the radiation exposure and contrast usage,an adaptive bolus chasing method is proposed and evaluated compared to the existing constant-speed method.The proposed method is based on a local time and space parameter varying model of the contrast bolus.Optimal scan time for the next segment of the vasculature is estimated and predicted in real time and guides the computed tomography(CT)scanner table movement that guarantees that each segment of the vasculature is scanned with the maximum possible enhancement.Simulations and experimental results show that the proposed bolus chasing method outperforms the conventional constant-speed method substantially.

电站锅炉-汽轮机系统的LPV鲁棒H_(∞)/H_(2)变增益控制

采用量子粒子群算法辨识得到机炉协调控制系统的全局线性参数变化(LPV)模型,然后通过极值分解组合得到多胞LPV模型。针对多胞LPV模型,在鲁棒H_(∞)/H_(2)变增益控制中引入松弛变量,设计了保守性更低的机炉协调控制系统鲁棒控制器。结果表明:所设计的控制器具有良好的控制效果。

双线性奇异摄动系统的无源控制器设计

研究了1类不确定变时滞双线性奇异摄动系统的无源控制。通过构造依赖于奇异摄动参数ε的Lyapunov函数,采取线性矩阵不等式和范数有界的方法,获得了使系统渐近稳定和严格无源的时滞依赖的充分条件,进而利用线性矩阵不等式的解给出了无源控制器的设计方法。考虑到系统模型的复杂性,给出了时滞独立的充分条件,从而降低了线性矩阵不等式的阶数。提出了一种奇异摄动参数ε允许上界的估计方法。通过数值仿真验证了以上方法的有效性。

无人直升机LPV控制律设计

针对无人直升机航迹控制要求,提出一种基于线性变参数(LPV)控制理论的无人直升机一体化式飞行控制律设计方法,通过速度、侧滑角、高度和偏航角控制通道的显模型跟踪控制,实现无人直升机航迹控制。建立了无人直升机高阶非线性动力学模型,模型中考虑了旋翼桨叶挥舞和摆振运动、旋翼动态入流、机体运动之间的运动耦合,用于检验直升机高阶运动特性对控制律性能和闭环系统稳定性的影响。由于无人直升机的非线性动力学模型是典型的周期性系统,基于简谐平衡方法进行无人直升机的配平和模型线性化计算,在速度包线内得到用于控制律设计的无人直升机LPV模型,通过凸函数优化方法求解LPV控制律的参数。基于典型直升机机动,采用数值仿真方法对LPV控制律在传感器噪声影响下的控制性能进行检验,仿真结果表明:LPV控制律在速度包线内具有良好的控制性能和鲁棒性,无人直升机闭环系统在机动飞行中满足给定的性能要求。

基于最小二乘支持向量机的火电机组线性参数变化模型辨识研究与应用

火电机组协调控制系统所包含的汽温、汽压等被控对象在不同的负荷下动态特征具有明显的差异,这些非线性特征给提高控制系统运行品质带来了很大的挑战。针对火电机组协调控制系统被控对象在机组全负荷段的建模问题,提出了一种火电机组协调控制系统被控对象的线性参数变化模型辨识方法,建立了全负荷段下过热汽温模型参数随负荷变化的关系曲线。首先将全负荷段机组过热汽温运行数据划分为训练集和验证集,然后使用基于最小二乘支持向量机的线性参数变化模型辨识方法建立了以机组负荷为调度参数的过热汽温被控对象模型,通过最佳拟合率评价不同超参数下的辨识结果,从而保持模型的准确度和泛化能力。辨识结果显示在不同负荷段下被控对象具有不同增益和时间常数等模型特征,并且与过程的先验知识相符,表明了所提出方法的有效性。

基于滑动窗邻域保留投影的工作模态分析

为了识别线性慢时变结构的工作模态参数,提出一种基于滑动窗邻域保留投影(MWNPE)的工作模态参数识别方法。该方法基于“时间冻结”理论,利用固定长度的窗口,将每个窗口内的非平稳信号看作平稳的随机序列,从而将线性时变结构离散成有限个线性时不变结构。在每个窗口内,利用邻域保留投影算法寻找窗口内位移响应数据的低维嵌入,低维嵌入与模态坐标响应矩阵相对应;再利用单自由度识别技术从模态响应矩阵中识别出窗口的模态固有频率;最后,利用最小二乘广义逆估计出变换矩阵,变换矩阵与模态振型矩阵相对应。通过质量慢时变三自由度(DOF)的仿真结构验证表明,所提方法能有效识别出线性慢时变结构的工作模态参数,且识别精度优于滑动窗主成分分析方法和滑动窗等变自适应源分离(EASI)方法。

基于LPV的主动隔振平台单支腿鲁棒控制器设计

利用控制力矩陀螺(CMG)实现敏捷姿态机动控制时,保证机动过程控制输出力矩快速响应的同时,还需要保证机动到位后有效隔离CMG的机械振动以实现高稳定度姿态控制。针对控制CMG主动隔振平台,将控制CMG外框角速度作为变参数,提出单支腿主动隔振平台控制器的一种基于线性变参数(LPV)控制设计实现方法,通过与其他主动隔振控制方法性能比较分析,所提方法在兼顾敏捷姿态机动期间和机动到位后对主动隔振平台不同的力学传递要求方面有更好的性能。

适用于多工作模式Buck-Boost变换器的线性变参数模型与宽运行范围控制

为实现宽范围电压调节,多模式Buck-Boost变换器(multimode Buck-Boost converter,MBBC)能够灵活工作在Buck、Boost与Transition模式,具有升/降压转换能力。然而在多模式变换器建模与控制设计时,传统小信号建模方法将不可避免带来动态响应变差以及潜在失稳问题。为此,该文提出一种面向多模式变换器的线性变参数建模与控制设计方法。基于线性变参数系统模型,能够分析不同Transition模式对变换器动态特性影响,从而构建出一种具备最优开环动态特性的Transition模式。基于闭环控制设计方法,能够保证MBBC多种工作模式的鲁棒稳定性、恢复时间与衰减比等时域指标。通过与传统小信号模型设计实验对比,验证所提多模式变换器控制设计方法有效性。通过与现有Transition模式对比实验,验证所提IBB Transition模式最优暂态性能。

基于不确定LPV系统的变体飞行器姿态控制

针对变体飞行器姿态控制系统,提出一种基于双层多面体描述的LPV多目标控制器,同时考虑调度参数的变化和系统不确定性的影响。第一层多面体用于管理调度参数并在顶点不确定系统上设计增益调度控制器;第二层多面体建立在每个顶点系统上以进行闭环控制系统的鲁棒设计。上述控制器求解问题最终可转化为求解一组有限数量的线性矩阵不等式。仿真结果表明,在所设计控制器作用下,变体飞行器系统可较好的跟踪攻角参考信号,同时具有良好的鲁棒性能。