Decentralized decoupling of multivariable control systems with unmodelled interaction

Abstract

This paper presents both state space and frequency domain approaches for the decentralized decoupling of multivariable control systems with unmodelled interaction. The controller has a configuration of two degrees of freedom. The nominal controller is tuned to satisfy the eigenvalue specification of the isolated single variable subsystem. The rejection of unmodelled coupling due to the connections or disconnections of other subsystems is controlled by the decentralized compensator. The method assumes that only local information is acquirable, no information from other subsystems and no interconnection parameters are required. This gives the convenience of single variable design for multi‐variable control applications. The decentralized compensator can also be used to improve the performance of the control system with unmodelled nonlinearity or parameter drifting. The stability of the control system with the decentralized compensator has been investigated. Two numerical examples are given to show the feasibility of the method.     

A proximate-time-optimal-control design and its application to a hard disk drive dual-stage actuator system

We propose a compensator-based strategy for design of a track-seeking and track-following control system for a dual-stage servo actuator in hard disk drives. A well-known decoupling structure is employed to disconnect the control of the primary voice coil motor (VCM) actuator from the loop for a secondary high-bandwidth actuator. The compensator is placed in the secondary loop and suitably combined with a saturation nonlinearity in order to obtain actuator signal boundedness. The design procedure consists of four steps: 1) design of an established nonlinear seek-settle-track following controller for the VCM; 2) design of a linear track following controller for the secondary actuator; 3) observer design; and 4) design of a compensator to retain global stability and to improve performance. The proposed control system improves performance of both long-span seeking (proximate-time-optimal controller) and short-span seeking. In addition, it achieves high-bandwidth track following performance. The experimental results show good track-following performance, and short-span/long-span-seeking performance with fast settling time. The overshoot during track seeking can be made negligible for a suitably tuned VCM-actuator control loop.     

σ‐Stability and characterization of all σ‐stabilizing compensators

Abstract

In feedback stabilizing compensator design for linear systems, mere BIBO (bounded‐input‐bounded‐output) stability is not sufficient since it does not provide a margin of decay rate, e. g., the compensated feedback system may still become insufficiently stable. In this paper, we will define the notion of σ‐stability and will give a complete parametrization of all σ‐stabilizing compensators in terms of a free design parameter via the fractional representation approach. Any σ‐stabilizing compensator will guarantee a decay rate margin σ of the compensated system. Also we will use the state space techniques to obtain the required factors in that parametrization of all σ‐stabilizing compensators.     

Design of a low cross‐talk micro‐coil array for micro‐scale MRI

Design of magnetic resonance micro‐coil arrays with low cross‐talk among the coils can be the main challenge to improve the effectiveness of magnetic resonance micro‐imaging because the electrical cross‐talk which is mainly due to the inductive coupling perturbs the sensitivity profile of the array and causes image artifacts. In this work, a capacitive decoupling network with N(M ? 1) + (N ? 1)(M ? 2) capacitors is proposed to reduce the inductive coupling in an N × M array. A 3 × 3 array of optimized micro‐coils is designed using the finite element simulations and all the needed elements for the array equivalent circuit are extracted in order to evaluate the effectiveness of the proposed decoupling method by assessing the reduction of the coupled signals after employing the capacitive network on the circuit. The achieved results for the designed array show that the high cross‐talk level is reduced by the factor of 2.2–3.4 after employing the capacitive network. By employing this method of decoupling, the adjacent coils in each row and inner columns can be decoupled properly while the minimum decoupling belongs to the outer columns because of the lack of all necessary decoupling capacitances for these columns. The main advantages of the proposed decoupling method are its efficiency and design easiness which facilitates the design of dense arrays with the properly decoupled coils, especially the inner coils which are more coupled due to their neighbors. © 2013 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 23, 353–359, 2013     

Robust nonlinear control of robotic manipulators

Abstract

A robust nonlinear control strategy is proposed to deal with the control problem of robotic manipulators with second order nonlinear actuator dynamics. The control scheme is composed of two stages: the nominal dynamics stage and the perturbed dynamics stage. The control at the nominal dynamics stage and the perturbed dynamics stage. The control at the nominal dynamics stage is aimed at exact linearization and input/output decoupling of the nonlinear actuator‐manipulator system in the task space by nonlinear feedback and nonlinear state space diffeomorphic transformations. The resulting closed‐loop nominal system is capable of precise trajectory following in a desired second‐order linear behavior. To compensate uncertainties in a practical situation, an optimal error correcting compensator is designed to achieve some robustness at the perturbed dynamics stage. Simulation study of a cylindrical robot is given to illustrate the effectiveness of the proposed scheme.     

A multi objective genetic algorithm approach to a design parameter generation for a robot platform on three omnidirectional wheels

Abstract

Superior mobility while ensuring maximum stability is a key requirement for most mobile robots. These requirements are fulfilled if the robot has a well-designed robotic platform that serves as a physical interface between its body and the floor. Although there are different design and development approaches for car-like robotic platforms, there is little design guidance for robot platform on three omnidirectional wheels. Hence, a method for generating optimal design parameters of such robotic platforms is proposed in this work. An objective function relevant to platform stability, the robot mass, and driving torque is formulated to form a min–max optimization problem. Finally, a trade-off between the design variables of the robotic platform is carried out from the result of Multi Objective Genetic Algorithm in Matlab. An omnidirectional wheeled robotic platform is developed to study the stability and mobility analysis of this robotic platform for various maneuver modes. This approach is seen to be effective for generating design variables of omnidirectional three wheels robotic platform that has maximal stability and minimal driving torque while traversing across inclined and flat floors. As a result, this optimization approach can be used to yield better design analysis with reduced reworking cost and manufacturing time.     

Design and analysis adaptivity in multiresolution topology optimization

Multiresolution topology optimization (MTO) methods involve decoupling of the design and analysis discretizations, such that a high-resolution design can be obtained at relatively low analysis costs. Recent studies have shown that the MTO method can be approximately 3 and 30 times faster than the traditional topology optimization method for two-dimensional (2D) and three-dimensional (3D) problems, respectively. To further exploit the potential of decoupling analysis and design, we propose a dp-adaptive MTO method, which involves locally increasing/decreasing the polynomial degree of the shape functions (p) and the design resolution (d). The adaptive refinement/coarsening is performed using a composite refinement indicator that includes criteria based on analysis error, presence of intermediate densities, as well as the occurrence of design artifacts referred to as QR-patterns. While standard MTO must rely on filtering to suppress QR-patterns, the proposed adaptive method ensures efficiently that these artifacts are suppressed in the final design, without sacrificing the design resolution. The applicability of the dp-adaptive MTO method is demonstrated on several 2D mechanical design problems. For all the cases, significant speedups in computational time are obtained. In particular for design problems involving low material volume fractions, speedups of up to a factor of 10 can be obtained over the conventional MTO method.     

Optimum structural design and robust active control using singular value constraints

This paper introduces a methodology for simultaneously designing a minimum weight structure and robust active controls to reduce vibrations in an aircraft structure due to external disturbances. The design problem is posed as a mathematical optimization problem with the principal objective function being the weight of the structure. The robust control design is achieved by specifying appropriate constraints on singular values of the closed-loop transfer matrices. The control approach selected for this purpose is based on designing a dynamic compensator that simultaneously minimizes the upper bound of a quadratic performance index H ₂ and the H norm of a disturbance transfer function of a multi-input/multi-output system. The controller can tolerate both real parameter uncertainty in the structural frequencies and damping, and unmodelled dynamics. The design variables are the crosspsectional areas of the structure and the parameters used in the design of a control system. The method was applied to three structures idealized with membrane elements, shear panels and bar elements with embedded actuators and sensors simulating an active flexible aircraft wing.     

Transition between grid-connected mode and islanded mode in VSI-fed microgrids

This paper investigates the behaviour of a microgrid system during transition between grid-connected mode and islanded mode of operation. During the grid-connected mode the microgrid sources will be controlled to provide constant real and reactive power injection. During the islanded mode the sources will be controlled to provide constant voltage and frequency operation. Special control schemes are needed to ensure proper transition from constant P–Q mode to constant f–V mode and vice versa. Transition from one mode to other will introduce severe transients in the system. Two kinds of transition schemes based on the status of the off-line controller are discussed and a comparative study is presented for various step changes in the load. An additional-pole-placement-based output feedback controller augmentation during transition between the modes is proposed to reduce the transients. A static output feedback compensator design is proposed for the grid connected to island mode transition and a dynamic output feedback compensator design is proposed for resynchronisation. The performance of the output feedback controllers is tested under various operating conditions and found to be satisfactory for the tested conditions.     

基于电流解耦的表贴式永磁同步电机无源控制研究

为了提高表贴式永磁同步电机的电流环频率响应能力和转速响应性能,针对其无源控制器设计过程中因d轴、q轴电流存在耦合而造成期望互联矩阵未知参数过多的问题,结合电压前馈解耦控制,提出了一种基于电流解耦的无源控制器新型设计方法。首先,根据能量平衡原理和电压前馈解耦控制,构建基于电流解耦的表贴式永磁同步电机端口受控耗散哈密顿系统（port control Hamilton system with dissipation, PCHD）模型。然后,通过互联和阻尼配置的无源控制（interconnection and damping assignment passivity-based control, IDA-PBC）方法,完成表贴式永磁同步电机无源控制器的设计,并在设计过程中引入了电压前馈解耦控制,消除了d轴、q轴电流的耦合关系,使期望互联矩阵的未知参数由3个减少为1个。最后,搭建表贴式永磁同步电机测试平台进行实验验证。实验结果表明,当表贴式永磁同步电机的电流环采用基于电流解耦的无源控制器时,q轴电流响应频率由小于250 Hz增大为大于333 Hz;额定转速下的转速响应时间由0.16 s减小为0.11 s,超调量由2.0%减小为0.6%,稳态误差由5.98 r/min减小为1.15 r/min。研究结果可为永磁同步电机的无源控制器设计提供新思路。     

双向解耦平台与结构一体化的混合控制分析

由于传统的混合控制隔振平台在竖直、水平两个方向上存在相互制约作用,从而增加了其在实际工程应用中的难度。因此首先建立了一种对竖直和水平方向双向解耦的新型混合控制隔振平台,将其置于搭建的三层结构厂房模型中,通过数值仿真对比分析了无控制结构楼板和被动隔振平台的响应,验证了该平台模型的合理性和可配置性。在此基础上,对比分析了考虑平台与结构一体化作用对时程响应控制的影响,结果表明,对于精度要求较高的微振动控制,运用双向解耦隔振平台可以大大简化控制设计系统,同时考虑一体化控制有利于进一步深化及优化控制设计。最后运用三分之一倍频程谱对无控、被动及混合控制的速度响应进行频域分析,结果表明该混合控制方案可以有效实现全频域振动的隔离。     

Stabilization and synchronization of 5-D memristor oscillator using sliding mode control

ABSTRACT

This article presents a control design method for asymptotic stabilization, synchronization, and antisynchronization of a five dimensional chaotic memristor oscillator system. Two cases are considered: (i) with known parameters, (ii) and with unknown parameters. When a system’s parameters are known, then controllers are designed using sliding mode approach and when system’s parameters are unknown then controllers are devised using adaptive integral sliding mode control method. Hurwitz surfaces are constructed in both approaches. To employ the integral sliding mode, firstly, the system is transformed into a special structure containing a nominal part and some unknown terms computed adaptively. Then, the system is stabilized using integral sliding mode control. The stabilizing controller, consisting of the nominal control plus some compensator control, is then designed. The compensator controller and the adapted laws are derived in such a way that the time derivative of a Lyapunov function becomes strictly negative. The effectiveness of the proposed scheme is tested through computer simulation.     

Feedforward Control Based on Neural Networks for Hard Disk Drives

We present a novel feedforward control based on neural networks to attenuate the effect of external vibrations on the positioning accuracy of hard disk drives. The neural network compensator, which is an add-on function on top of nominal feedback control, uses the accelerometer signals obtained from a sensor to detect external vibrations. Our feedforward control can be regarded as a nonlinear finite impulse response (FIR) that corresponds to linear FIR when the basis function of the neural network is linear. By neural network learning, the tracking performance of hard disk drives can be improved with no information on disturbance dynamics or sensor model. We have analyzed the stability of the proposed scheme by the Lyapunov criterion. Here, we give simulation results to demonstrate that our control scheme can eliminate the effect of external disturbances on positioning accuracy.      

多旋翼无人飞行器机载光电平台的复合补偿控制方法

为了提高多旋翼无人飞行器机载光电平台的扰动补偿能力,实现机载光电平台的稳定跟踪控制,提出一种基于改进扰动观测器和径向基函数(RBF)神经网络逼近的复合补偿控制方法。首先,对现有扰动观测器结构进行改进,构建基于速度信号的改进型扰动观测器,并分析了干扰补偿能力和稳健性;然后,利用RBF神经网络的函数逼近性质解决非线性未知扰动的补偿问题;最后,基于Lyapunov稳定性原理设计出复合补偿控制结构。实验结果表明,机载光电平台的扰动得到有效补偿。该补偿控制方法具有较高的稳定精度和跟踪控制性能,满足多旋翼无人飞行器机载光电平台的稳定控制要求。     

Function-technology-based product platform formation

Product platforms have been effectively used by many successful companies for product family design. Technological advancements and changes in customer needs pose problems for robustly designing product platforms over a given planning horizon. To date, most product platform formation approaches are directed by structural (subassemblies and components) considerations and are seldom undertaken at the conceptual design stage. We argue that product platform design should commence at the conceptual design stage rather than the detailed design stage. It is noteworthy that physical structures are the end results of designs already frozen at higher level of functional abstraction. Hence, tackling the platform formation problem should start much before structures are materialized. We propose that the product platform formation approach should be considered at two different stages: (i) conceptual design stage; and (ii) detailed design stage. In reference to the Function?–?Behavior?–?Structure model proposed by Gero and Kannengiesser (Gero, J.S. and Kannengiesser, U., Function-behavior-structure: A model for social situated agents. Workshop on Cognitive Modeling of Agents and Multi-Agent Interactions, International Joint Conference on Artificial Intelligence 2003, Acapulco, Mexico, 2003, pp. 101–107), conceptual design would refer to the design of products at function and technology stage, whereas detailed design would refer to the design of products at the structure stage. This paper discusses a method to form product platforms at the Function-Technology stage which can be correspondingly mapped to the structural stages. Thus, forming product platforms at a higher level of abstraction would enable a better understanding of the complications met at structural level. The FT approach uses Function Technology Ant Colony Optimization (FTACO) method to determine product platform configuration(s). We demonstrate the proposed approach using the example of a computer mouse product family.     

Evolutionary feature selection applied to artificial neural networks for wood-veneer classification

This paper presents the application of FeaSANNT, an evolutionary algorithm for optimization of artificial neural networks, to the training of a multi-layer perceptron for identification of defects in wood veneer. Given a fixed artificial neural network structure, FeaSANNT concurrently evolves the input feature vector and the network weights. The novelty of the method lies in the implementation of the embedded approach in an evolutionary feature selection paradigm. Experimental tests show that the proposed algorithm produces high-performing solutions with robust learning results. A significant reduction of the set of veneer features is obtained. Experimental comparisons are made with a previous method based on statistical filtering of the input features and a standard genetic wrapper algorithm. In the first case, FeaSANNT greatly reduces the feature set with no degradation of the neural network accuracy. Moreover, FeaSANNT entails lower design costs, since feature selection is fully automated. In the second case, the proposed algorithm achieves superior results in terms of identification accuracy and reduction of the feature set. FeaSANNT involves also lower computational costs than the standard evolutionary wrapper approach and eases the algorithm design effort. Limited overlapping is observed between the patterns of features selected by the three algorithms. This result suggests that the full feature set contains mainly redundant attributes.     

Detection and classification mean-shifts in multi-attribute processes by artificial neural networks

To monitor the quality of a multi-attribute process, some issues arise. One of them being the occurrence of a high number of false alarms (type I error) and the other an increase in the probability of not detecting defects when the process is monitored by a set of independent uni-attribute control charts. In this paper, based upon the artificial neural network capabilities we develop a new methodology to overcome this problem. We design a perceptron neural network to monitor either the proportions of several types of product nonconformities (instead of using several np charts) or the number of different types of defects (instead of using several c charts) in a product. Moreover, while the proposed method possesses the ability to be applied for small sample sizes, it is also able to diagnose the mean shift online. We present two simulation experiments in which the proportions of several types of nonconformities are monitored. In addition, we present one more simulation experiment in which the number of different types of defect is controlled. We also compare the performance of the proposed methodology with the ones from the Mnp and T ² charts for multi-attribute processes. The results of the simulation studies are encouraging.     

Adaptive backstepping motion control of induction motor drives

Abstract

In this paper, an adaptive backstepping controller is proposed for position tracking of a mechanical system driven by an induction motor. The mechanical system is a single link fixed on the shaft of the induction motor such as a single‐link robot. The backstepping methodology provides a simpler design procedure for an adaptive control scheme and provides a method to define the sliding surface if the robust slidingmode control is applied. Thus, the backstepping control can be easily extended to work as an adaptive sliding‐mode controller. The presented position control system is shown to be stable and robust to parameter variations and external disturbances. The effectiveness of the proposed controllers is demonstrated in experiments.     

Advances in decoherence control

Abstract

I address the current status of dynamical decoupling techniques in terms of required control resources and feasibility. Based on recent advances in both improving the theoretical design and assessing the control performance for specific noise models, I argue that significant progress may still be possible on the road to implementing decoupling under realistic constraints.