Robust H∞ filtering for switched linear discrete‐time systems with polytopic uncertainties

In this paper, the problem of robust H_∞ filtering for switched linear discrete‐time systems with polytopic uncertainties is investigated. Based on the mode‐switching idea and parameter‐dependent stability result, a robust switched linear filter is designed such that the corresponding filtering error system achieves robust asymptotic stability and guarantees a prescribed H_∞ performance index for all admissible uncertainties. The existence condition of such filter is derived and formulated in terms of a set of linear matrix inequalities (LMIs) by the introduction of slack variables to eliminate the cross coupling of system matrices and Lyapunov matrices among different subsystems. The desired filter can be constructed by solving the corresponding convex optimization problem, which also provides an optimal H_∞ noise‐attenuation level bound for the resultant filtering error system. A numerical example is given to show the effectiveness and the potential of the proposed techniques. Copyright © 2006 John Wiley & Sons, Ltd.     

The Effect of Uncertainties in the Kuhn-Mark-Houwink-Sakurada Constants on the Quantitative Analysis by Gel Permeation Chromatography

The effect of uncertainties in Kuhn-Mark-Houwink-Sakurada (KMHS) constants on weight average and number average molecular weights and molecular weight distributions of some poly(ethyl methacrylate) samples have been investigated. Parameters were computed by the Weiss and Cohn-Ginsberg method. Whereas errors introduced in M_w, M_n and HI values due to uncertainty in the K value are insignificant, uncertainties in the KMHS exponent present a serious problem. Deviations of ± 3% around a particular a value cause a ± 20% error in M_w and ± 15% error in M_n, values. The effect of deviations in the KMHS exponent on the HI values is dependent on the polydisperity of the sample investigated.     

一类非线性互联系统的H∞模型参考跟踪分散输出反馈模糊控制

本文对一类不确定状态不可测非线性互联系统,给出了一种基于观测器的H_∞模型参考跟踪分散输出反馈模糊控制方法.设计中,首先采用模糊不确定T-S模型对非线性互联系统进行模糊建模,在此基础上,给出模糊分散观测器的H_∞设计和基于观测器的模型参考跟踪分散模糊控制的设计.应用李亚普诺夫和线性矩阵不等式方法给出了模糊分散系统稳定的充分条件.仿真结果进一步验证了所提出的模糊分散控制方法的有效性.     

最近电压稳定临界点的两层规划模型和信赖域算法

考虑了负荷变化的不确定性,提出负荷分布范围的棱锥状模型。建立了求解最近电压稳定临界点的非线性二层规划模型,提出一种求解该问题的信赖域方法。该方法先计算已知负荷增长方向上的电压稳定临界点,然后建立只有上、下界约束的近似模型,基于信赖域方法的思想迭代搜索最近电压稳定临界点,求取临界点时考虑了发电机无功出力的限制。算例分析表明,该算法收敛速度快、鲁棒性好,全局寻优能力强,并可找出系统电压稳定的薄弱区域和母线。     

Adaptive sliding mode current control with sliding mode disturbance observer for PMSM drives

This paper focuses on the current control of a permanent magnet synchronous motor (PMSM) for electric drives with model uncertainties and external disturbances. To improve the performance of the PMSM current loop in terms of the speed of response, tracking accuracy, and robustness, a hybrid control strategy is proposed by combining the adaptive sliding mode control and sliding mode disturbance observer (SMDO). An adaptive law is introduced in the sliding mode current controller to improve the dynamic response speed of the current loop and robustness of the PMSM drive system to the existing parameter variations. The SMDO is used as a compensator to restrain the external disturbances and reduce the sliding mode control gains. Experiments results demonstrate that the proposed control strategy can guarantee strong anti-disturbance capability of the PMSM drive system with improved current and speed-tracking performance.     

Adaptive robust control of fully-constrained cable driven parallel robots

In this paper, adaptive robust control (ARC) of fully-constrained cable driven parallel robots is studied in detail. Since kinematic and dynamic models of the robot are partly structurally unknown in practice, in this paper an adaptive robust sliding mode controller is proposed based on the adaptation of the upper bound of the uncertainties. This approach does not require pre-knowledge of the uncertainties upper bounds and linear regression form of kinematic and dynamic models. Moreover, to ensure that all cables remain in tension, proposed control algorithm benefit the internal force concept in its structure. The proposed controller not only keeps all cables under tension for the whole workspace of the robot, it is chattering-free, computationally simple and it does not require measurement of the end-effector acceleration. The stability of the closed-loop system with proposed control algorithm is analyzed through Lyapunov second method and it is shown that the tracking error will remain uniformly ultimately bounded (UUB). Finally, the effectiveness of the proposed control algorithm is examined through some experiments on a planar cable driven parallel robot and it is shown that the proposed controller is able to provide suitable tracking performance in practice.     

Probabilistic seismic damage assessment of reinforced concrete buildings considering directionality effects

Most of buildings and structures are usually projected according to two main axes. However, the geographical position of these buildings varies randomly. Such random distributions of the azimuthal positions of structures, in most of the cities, generally, are not accounted for when assessing their seismic risk; certainly, the direction of the seismic loads is another highly random variable. Moreover, an additional important source of uncertainty is related to the structural response, mainly due to the random character of the mechanical properties. There is a consensus that uncertainties must be considered for adequately assessing the seismic risk of structures, but these directionality effects have not been deeply explored so far. In this article, the influence of the high uncertainty involved in these input variables on the expected seismic damage is analysed. Thus, an actual earthquake, which affected the southern part of Spain, is studied. Notably, damages on a group of affected buildings, located close to the epicentre, are analysed and discussed in detail. The results show that the influence of the random azimuthal position of structures is an important source of uncertainty and that it should be taken into account when estimating the expected seismic risk in urban areas.     

非匹配条件不确定非线性系统的变结构控制

研究不确定非线性系统的输出跟踪问题。针对系统中的未建模动态和广义的不确定性,基于李亚普诺夫稳定性理论提出了一种变结构控制方案,它不要求系统的不确定性满足匹配条件,仅要求已知不确定性的有界约束。从理论上证明了闭环跟踪系统全局渐近稳定,系统信号保持有界。仿真实例证实了理论结果。     

不确定性高通量筛选系统的双子代数控制

近年来,对于高通量筛选系统的控制,在确定性情形下已进行了不少工作,其中,双子代数框架下的控制策略执行相对更灵活,效率更高.然而,现有的输出反馈优化控制对性能指标期望系统行为还有特殊的构造要求须满足;而且,实际运行中存在有人工干预、设备维护、意外干扰、故障等带来的不确定性.对这两者考虑的缺失限制了目前高通量筛选系统自动控制的效率.为进一步提高这类新兴离散事件系统的控制效率,基于区间双子代数,将该输出反馈控制结构拓展到系统参数不确定的高通量筛选系统,使之对不确定性高通量筛选系统能自动产生优化控制.继而,将输出反馈与预处理补偿相结合.后者对指标的构造并无特殊要求.综合后的控制结构亦避免了原反馈结构下对性能指标构造的限制.最后通过不同实例说明了对不确定性高通量筛选系统应用该控制结构的方法和有效性.