Constraint feedforward control for thermal processing of quartz photomasks in microelectronics manufacturing

A feedforward control scheme is designed to improve performance of conductive heating systems used for lithography in microelectronics processing. It minimizes the loading effects induced by the common processing condition of placement of a quartz photomask at ambient temperature on a bake plate at processing temperature. The feedforward control strategy is a model-based method using linear programming to minimize the worst-case deviation from a nominal temperature set-point during the load disturbance condition. This results in a predictive controller that performs a pre-determined heating sequence prior to the arrival of the substrate as part of the resulting feedforward/feedback strategy to eliminate the load disturbance. This procedure is based on an empirical model generated from data obtained during closed-loop operation. It is easy to design and implement for conventional thermal processing equipment. Experimental results are performed for two commercial bake plates and depict an order-of-magnitude improvement in the settling time and the integral-square temperature error between the optimal predictive controller and a feedback controller for a typical load disturbance.     

不确定线性2-D离散系统的鲁棒滑模控制

针对不确定线性离散二维（2-D）系统,研究了其鲁棒稳定性、鲁棒镇定和鲁棒滑模控制问题.基于线性矩阵不等式的方法推导了该系统鲁棒渐近稳定的充分条件,并给出了系统状态反馈镇定器和理想滑动模态存在的充分条件.改进了离散时间滑模控制系统的趋近律方法,使得状态能够到达滑模面上产生理想的滑动模态,并将其推广应用到2-D离散系统中,综合了一类滑模控制器保证闭环系统鲁棒渐近稳定.仿真实例证实了该设计方法的有效性.     

网络环境下切换模糊时滞系统的非脆弱控制

针对一类控制器增益存在摄动的非线性网络切换系统,在系统同时存在随机时变时滞和不确定性的情况下,采用T-S模型建模,研究系统的稳定控制问题。利用平均驻留时间(ADT)法设计系统的切换律及非脆弱状态反馈控制器,并给出网络切换模糊时滞系统指数稳定的平均驻留时间条件。结合李雅普诺夫函数(LKF)法,推导时滞相关的网络切换模糊系统指数稳定的矩阵不等式条件,并将此条件转化为线性矩阵不等式形式。通过数值仿真对比系统在采用ADT法与传统LKF法下的状态曲线,结果表明,ADT法可以使系统收敛速度更快,性能指标更好。     

Reduction-based robust active queue management control

This paper is concerned with the design of improved active queue management (AQM) control schemes for time-delay systems taking into account explicitly the presence of delays in the controller design. A robust controller coping with uncertainties on the network parameters such as round-trip time and load variations is proposed. This is based on an appropriate robust reduction method for time-delay systems. A robust observer for time-delay systems is used to estimate online the average transmission window resulting in a robust output feedback stabilization scheme for AQM. The resulting control law is validated and tested firstly through numerical simulations and then pseudo-experimentally by network simulator (NS-2).     

Stabilization of Nonlinear Systems Under Variable Sampling: A Fuzzy Control Approach

This paper investigates the problem of stabilization for a Takagi-Sugeno (T-S) fuzzy system with nonuniform uncertain sampling. The sampling is not required to be periodic, and the only assumption is that the distance between any two consecutive sampling instants is less than a given bound. By using the input delay approach, the T-S fuzzy system with variable uncertain sampling is transformed into a continuous-time T-S fuzzy system with a delay in the state. Though the resulting closed-loop state-delayed T-S fuzzy system takes a standard form, the existing results on delay T-S fuzzy systems cannot be used for our purpose due to their restrictive assumptions on the derivative of state delay. A new condition guaranteeing asymptotic stability of the closed-loop sampled-data system is derived by a Lyapunov approach plus the free weighting matrix technique. Based on this stability condition, two procedures for designing state-feedback control laws are given: one casts the controller design into a convex optimization by introducing some over design and the other utilizes the cone complementarity linearization idea to cast the controller design into a sequential minimization problem subject to linear matrix inequality constraints, which can be readily solved using standard numerical software. An illustrative example is provided to show the applicability and effectiveness of the proposed controller design methodology.     

Set-point-related indirect iterative learning control for multi-input multi-output systems

A form of iterative learning control (ILC) is used to update the set-point for the local controller. It is referred to as set-point-related (SPR) indirect ILC. SPR indirect ILC has shown excellent performance: as a supervision module for the local controller, ILC can improve the tracking performance of the closed-loop system along the batch direction. In this study, an ILC-based P-type controller is proposed for multi-input multi-output (MIMO) linear batch processes, where a P-type controller is used to design the control signal directly and an ILC module is used to update the set-point for the P-type controller. Under the proposed ILC-based P-type controller, the closed-loop system can be transformed to a 2-dimensional (2D) Roesser s system. Based on the 2D system framework, a sufficient condition for asymptotic stability of the closed-loop system is derived in this paper. In terms of the average tracking error (ATE), the closed-loop control performance under the proposed algorithm can be improved from batch to batch, even though there are repetitive disturbances. A numerical example is used to validate the proposed results.     

太阳能与市电互补LED照明控制系统研究

提出一种基于PIC16F877A为控制核心的太阳能与市电互补LED照明系统。介绍系统的组成和工作原理、系统控制器和直流LED负载,分析了系统的工作状态和程序控制流程。结合现有小区草坪灯、路灯的实际供电情况,提出了太阳能和市电互补照明的设计思想,在实际中具有良好开发和应用前景。     

Controller approximation: approaches for preserving H∞ performance

Investigates the design of reduced-order controllers using an H _∞ framework. Given a stabilizing controller which satisfies a prespecified level of closed-loop H_∞ performance, sufficient conditions are derived for another controller to be stabilizing and satisfy the same level of H_∞, performance. Such controllers are said to be (P,γ)-admissible, where P is the model of the plant under consideration and γ is the required level of prespecified H_∞ performance. The conditions are expressed as norm bounds on particular frequency-weighted errors, where the weights are selected to make a specific transfer function a contraction. The design of reduced-order (P,γ)-admissible controllers is then formulated as a frequency-weighted model reduction problem. It is advantageous for the required weights to be large in some sense. Solutions which minimize either the trace, or the determinant, of the inverse weights are characterized. We show that the procedure for minimizing the determinant of the inverse weights always gives a direction where the weights are the best possible. To conclude, we demonstrate by way of a numerical example, that when used in conjunction with a combined model reduction/convex optimization scheme, the proposed design procedures are effective in substantially reducing controller complexity     

Non-fragile output feedback H∞ vehicle suspension control using genetic algorithm

This paper presents an approach to design static output feedback and non-fragile static output feedback H_∞ controllers for active vehicle suspensions by using linear matrix inequalities and genetic algorithms. A quarter-car model with active suspension system is considered in this paper. By suitably formulating the minimization problem of the sprung mass acceleration, suspension deflection and tyre deflection, a static output feedback H_∞ controller and a non-fragile static output feedback H_∞ controller are obtained. The controller gain is naturally constrained in the design process. The approach is validated by numerical simulation which shows that the designed static output feedback H_∞ controller can achieve good active suspension performance in spite of its simplicity, and the non-fragile static output feedback H_∞ controller has significantly improved the non-fragility characteristics over controller gain variations.     

Periodic Motion Planning and Control for Double Rotary Pendulum via Virtual Holonomic Constraints

Periodic motion planning for an under-actuated system is rather difficult due to differential dynamic constraints imposed by passive dynamics, and it becomes more difficult for a system with higher underactuation degree, that is with a higher difference between the number of degrees of freedom and the number of independent control inputs. However, from another point of view, these constraints also mean some relation between state variables and could be used in the motion planning.We consider a double rotary pendulum, which has an underactuation degree 2. A novel periodic motion planning is presented based on an optimization search. A necessary condition for existence of the whole periodic trajectory is given because of the higher underactuation degree of the system. Moreover this condition is given to make virtual holonomic constraint (VHC) based control design feasible. Therefore, an initial guess for the optimization of planning a feasible periodic motion is based on this necessary condition. Then, VHCs are used for the system transformation and transverse linearization is used to design a static state feedback controller with periodic matrix function gain. The controller gain is found through another optimization procedure. The effectiveness of initial guess and performance of the closed-loop system are illustrated through numerical simulations.      

Robust output regulation of Zeta converter with load/input variations: LMI approach

The output regulation of DC–DC converters is a challenging problem due to the fast switching behavior in the presence of the uncertainty/variation in the model, input, and load. In this paper, the Zeta converter is first analyzed and then using the Linear Matrix Inequality (LMI) theory a robust controller is designed to cope with this issue. Inspired by the photovoltaic applications of the Zeta converter, and due to the nature of the solar cells, not only the load variations but also the input voltage variations are considered in the controller design. Finally, the proposed controller is implemented in a DSP-based controller and its performance is experimentally verified and compared with the widely used PI controller.     

Observer-based H-infinity output feedback control with feedback gain and observer gain variations for Delta operator system

Considering that the controller feedback gain and the observer gain are of additive norm-bounded variations, a design method of observer-based H-infinity output feedback controller for uncertain Delta operator systems is proposed in this paper. A sufficient condition of such controllers is presented in linear matrix inequality （LMI） forms. A numerical example is then given to illustrate the effectiveness of this method, that is, the obtained controller guarantees the closed-loop system asymptotically stable and the expected H-infinity performance even if the controller feedback gain and the observer gain are varied.     

Reliable$rm H_infty $Fuzzy Control for Continuous-Time Nonlinear Systems With Actuator Failures

This paper is concerned with the design of reliable$ H_infty $fuzzy controllers for continuous-time nonlinear systems with actuator failures. The Takagi and Sugeno fuzzy model is employed to represent a nonlinear system. The objective is to find a stabilizing state-feedback fuzzy controller such that the nominal$ H_infty $performance is optimized while satisfying a prescribed$ H_infty $performance constraint in the actuator failure cases. Based on the linear matrix inequality (LMI) techniques, two efficient methods for the design of a suboptimal reliable$ H_infty$fuzzy controller are proposed. Different Lyapunov functions are used during the design for the nominal and actuator failure cases, which lead to a less conservative controller design. In the first method, a single Lyapunov function is used for the actuator failure cases. The second method adopts a parameter-dependent Lyapunov function for the actuator failure cases, which further reduces the conservatism of the design. Finally, numerical simulations on the chaotic Rossler system are given to illustrate the effectiveness of the proposed design methods.     

等式约束的网络化控制系统的稳定性设计

研究了等式约束的网络化控制系统的稳定性问题．在假设网络时滞是随机变化的，并且假设网络化控制系统的被控对象为一个具有等式约束的时滞系统的情况下，将网络化控制系统模型化为一个混合系统．然后采用李亚普诺夫函数、线性矩阵不等式的方法推导出了该混合系统渐近稳定的一个充分条件．根据此充分条件，通过求解一个线性矩阵不等式，较容易地获得系统的最大允许网络时滞以及此时的控制器．最后给出一个具体的数值和仿真实例说明了此设计方法是有效的．     

T-S模糊系统的二次稳定

应用LMI(线性矩阵不等式)方法,研究了T-S模糊系统二次稳定性及控制器设计问题.首先,通过考虑模糊系统隶属函数的性质,将原系统进行变换,给出了T-S模糊系统二次稳定的新条件,并提出了基于LMI的控制器设计方法.与现有结果相比,该方法不仅考虑了各子系统间的关系,还考虑到隶属函数的性质,计算量和保守性较小.仿真算例验证了其有效性.     

Feedforward Control for Wind Turbine Load Reduction with Pseudo-LIDAR Measurement

A gain-scheduled feedforward controller, based on pseudo-LIDAR (light detection and ranging) wind speed measurement, is designed to augment the baseline feedback controller for wind turbine’s load reduction in above rated operation. The pseudo-LIDAR measurement data are generated from a commercial software – Bladed using a designed sampling strategy. The nonlinear wind turbine model has been simplified and linearised at a set of equilibrium operating points. The feedforward controller is firstly developed based on a linearised model at an above rated wind speed, and then expanded to the full above rated operational envelope by employing gain scheduling strategy. The combined feedforward and baseline feedback control is simulated on a 5 MW industrial wind turbine model. Simulation studies demonstrate that the proposed control strategy can improve the rotor and tower load reduction performance for large wind turbines.     

Development of a neural network based integrated control system of 120 ton/h capacity boiler

An integrated control system based on artificial neural network (ANN) is presented in this paper to control a 120 ton/h capacity boiler of the Zia Fertilizer Company Limited (ZFCL), Ashuganj, Bangladesh. The process inverse dynamic modelling technique is applied to design the proposed controller. A multilayer feed-forward neural network is trained to identify the unknown inverse dynamic model of the boiler plant by a well known learning algorithm called backpropagation. The training data were collected from the history file of ZFCL. A new software controller is then developed for integrated control system of the ZFCL boiler using the weights of the trained network. Both the training mode and running mode of the developed controller are presented in this paper. The controller output is also converted into electrical signal using pulse width control technique. The generated signal is used for on-line regulation of the control valve through the parallel port of the computer. The developed controller is tested by using the boiler input–output data that are not used during the training. The output response and performance of the developed controller is compared with those of the existing PID controller of the plant.     

基于事件触发传输机制的非线性系统模糊H∞ 控制

针对离散时间非线性系统, 提出事件触发传输机制下网络化T-S 模糊控制器设计方法. 在事件发生器中引入前提变量偏差触发条件, 从而取消模糊控制器与被控对象的前提变量之间的同步要求. 通过引入一组基于模糊前提变量特性的松弛等式/不等式, 对于无传输时滞和定常传输时滞两种情况, 分别提出具有较小保守性的控制器/事件发生器联合设计算法. 最后, 通过数值算例表明所提出方法的可行性和有效性.

     

基于滑模控制的单域电力系统负荷频率控制

针对一类包含非匹配参数不确定和负荷干扰的电力系统,提出一种负荷频率滑模控制器的设计方法.所设计的积分型切换面有效地改善了系统到达阶段的动态性能,提高了系统的鲁棒性;基于趋近律方法设计了滑模控制器,以保证系统运动轨线在有限时间内到达滑动模态;给出了单区域电力系统仿真模型,分别考虑了不同参数不确定条件下的仿真问题.仿真结果表明了所设计的控制器的有效性和鲁棒性.     

Switching control of an R/C hovercraft: stabilization and smoothswitching

This paper presents stable switching control of an radio-controlled (R/C) hovercraft that is a nonholonomic (nonlinear) system. To exactly represent its nonlinear dynamics, more importantly, to maintain controllability of the system, we newly propose a switching fuzzy model that has locally Takagi-Sugeno (T-S) fuzzy models and switches them according to states, external variables, and/or time. A switching fuzzy controller is constructed by mirroring the rule structure of the switching fuzzy model of an R/C hovercraft. We derive linear matrix inequality (LMI) conditions for ensuring the stability of the closed-loop system consisting of a switching fuzzy model and controller. Furthermore, to guarantee smooth switching of control input at switching boundaries, we also derive a smooth switching condition represented in terms of LMIs. A stable switching fuzzy controller satisfying the smooth switching condition is designed by simultaneously solving both of the LMIs. The simulation and experimental results for the trajectory control of an R/C hovercraft show the validity of the switching fuzzy model and controller design, particularly, the smooth switching condition.