Performance of periodically time-varying controllers for sampleddata control

Analyzes performance of periodically time-varying sampled data controllers for L_p deterministic and uniform disturbance rejection. For a given linear periodic sampled data controller controlling a linear time-invariant continuous-time plant, it is shown that a linear time-invariant controller can be found to give better L _p sampled data control than the time-varying controller. The performance analysis is in time domain using convexity properties of the L_p signal space     

Global H/sub /spl infin// controllers for a class of nonlinear systems

In this note, the problem of state feedback H/sub /spl infin// control for a class of nonlinear systems is considered. The class under study is a generalization of the well-known Lur'e systems. The H/sub /spl infin// problem is addressed via a class of storage functions of the Lur'e-Postnikov type whose integral term is parameterized by a nonlinear scalar function. The related H/sub /spl infin// controllers consist of a linear term, which is designed for the underlying linearized system, plus a nonlinear term which depends on the nonlinear function. A simple geometrical criterion is provided for the characterization of the set of controllers which ensure a given level of L/sub 2/-performance globally. Some guidelines for an effective design of the controller within this set are discussed via two examples.     

Supervised Multi‐Rejector of Periodic Disturbances for Nonlinear Systems Using Decoupled State Multimodel

In this paper, a multi‐rejector of periodic disturbances is proposed for discrete‐time nonlinear systems represented by a decoupled state multimodel. We report a decoupled state multimodel repetitive‐predictive control based on a supervised algorithm to ensure reference trajectory tracking and periodic disturbances rejection. Partial predictors associated to the local controllers make the best choice of the most valid partial controller that meets the desired closed loop performances. The effectiveness of the supervised multi‐rejector is shown via a simulation example. The obtained results are satisfactory and show a good rejection of periodic disturbances and reference trajectory tracking.     

Nonlinear controllers for solar thermal plants: A comparative study

Solar plants have nonlinear dynamics which must be taken into account when a control system is applied to them. The main purpose of the control systems is to maintain the outlet temperature in a desired reference value and, at the same time, attenuate the undesirable transients caused by the disturbances. Linear controllers, like PID ones, are not able to obtain good performance over the whole operation range of these kind of plants. To overcome these limitations two nonlinear controllers, a nonlinear model-based predictive controller and a distributed sliding mode controller, are applied to a solar plant in this work. The performance of these controllers is tested through experimental and simulation results, which show the tracking and disturbance rejection capabilities of the proposed controllers.     

Performance Analysis of Periodic Control for l1 and l∞ Disturbance Rejection

This paper presents a performance analysis of discrete time periodically time varying controllers for the rejection of l_p specific and uniform disturbances. Earlier results on l₂ performance are extended to l₁ and l_∞ performance to present a unified treatment of l_p performance for all p ε [1, ∞]. For a given linear time varying periodic controller, a linear time invariant controller is constructed and necessary and sufficient conditions are presented under which the linear time invariant controller gives strictly better l_p disturbance rejection performance than the time varying periodic controller.     

Limitations of nonlinear discrete periodic control for disturbance attenuation and robust stabilization

This paper presents a performance analysis of nonlinear periodically time-varying discrete controllers acting upon a linear time-invariant discrete plant. Time-invariant controllers are distinguished from strictly periodically time-varying controllers. For a given nonlinear periodic controller, a time-invariant controller is constructed. Necessary and sufficient conditions are given under which the time-invariant controller gives strictly better control performance than the time-invariant controller from which it was obtained, for the attenuation of l_p exogenous disturbances and the robust stabilization of l_p unstructured perturbations, for all p[1,∞].     

低阶时滞过程的伪预测PI／PID控制

基于单位反馈控制结构,根据期望的闭环传递函数设计得到了一种伪预测PI/PID(ADQPI/ADQPID)控制器。这种控制器只有一个可调参数,可调参数与系统动态响应性能和鲁棒稳定性之间存在直接关系,只需单调的调节控制器参数,便可实现系统的动态响应性能与鲁棒稳定性之间的最佳折衷。仿真实例表明,这种控制器在扰动和模型失配的情况下仍然具有良好的控制性能和鲁棒稳定性,是一种值得在实际工程中推广运用的新型控制器。     

Performance analysis of fractional order fuzzy PID controllers applied to a robotic manipulator

A two-link robotic manipulator is a Multi-Input Multi-Output (MIMO), highly nonlinear and coupled system. Therefore, designing an efficient controller for this system is a challenging task for the control engineers. In this paper, the Fractional Order Fuzzy Proportional-Integral-Derivative (FOFPID) controller for a two-link planar rigid robotic manipulator for trajectory tracking problem is investigated. Robustness testing of FOFPID controller for model uncertainties, disturbance rejection and noise suppression is also investigated. To study the effectiveness of FOFPID controller, its performance is compared with other three controllers namely Fuzzy PID (FPID), Fractional Order PID (FOPID) and conventional PID. For tuning of parameters of all the controllers, Cuckoo Search Algorithm (CSA) optimization technique was used. Two performance indices namely Integral of Absolute Error (IAE) and Integral of Absolute Change in Controller Output (IACCO) having equal weightage for both the links are considered for minimization. Numerical simulation results clearly indicate the superiority of FOFPID controller over the other controllers for trajectory tracking, model uncertainties, disturbance rejection and noise suppression.     

H/sub /spl infin// fuzzy output feedback control design for nonlinear systems: an LMI approach

Addresses the problem of stabilizing a class of nonlinear systems by using an H/sub /spl infin// fuzzy output feedback controller. First, a class of nonlinear systems is approximated by a Takagi-Sugeno (TS) fuzzy model. Then, based on a well-known Lyapunov functional approach, we develop a technique for designing an H/sub /spl infin// fuzzy output feedback control law which guarantees the L/sub 2/ gain from an exogenous input to a regulated output is less or equal to a prescribed value. A design algorithm for constructing an H/sub /spl infin// fuzzy output feedback controller is given. In contrast to the existing results, the premise variables of the H/sub /spl infin// fuzzy output feedback controller are not necessarily to be the same as the premise variables of the TS fuzzy model of the plant. A numerical simulation example is presented to illustrate the theory development.     

以幂次吸引的离散多周期重复控制

针对一类多周期干扰的抑制问题,提出一种基于幂次吸引律的离散多周期重复控制方法.多周期干扰由多个周期已知的周期干扰叠加而成.根据周期干扰的对称特性,构造出具有干扰抑制项的幂次吸引律,据此设计出子重复控制器,并以并联方式组合成多周期重复控制器,在消除多周期干扰的同时,有效地抑制慢时变非周期干扰带来的影响,改善控制品质;推导出幂次绝对吸引层和稳态误差带的具体表达式,用于刻画系统跟踪性能.仿真结果验证了所提控制方法的有效性.     

挠性航天器的非线性PID和PI姿态控制器设计

针对存在模型不确性和常值干扰的挠性航天器, 提出一种不依赖于模型参数的非线性PID姿态控制器. 该控制器在小姿态偏差的情况下近似经典的线性PID控制器. 另外, 考虑到航天器上陀螺失效情况, 设计了一种仅需姿态测量信息的非线性PI控制器. 这两种控制器在局部均对常值干扰有抑制作用, 并能使无干扰作用的姿态控制系统半全局渐近稳定. 闭环系统的稳定性证明采用了奇异扰动理论, 以解决积分项的存在带来的稳定性分析问题. 文章最后用数学仿真验证了控制器的性能.     

Nonlinear H/sub /spl infin// controllers for electromagnetic suspension systems

This note presents a unified framework to derive nonlinear H/sub /spl infin// state and output feedback controllers for magnetically levitated (Maglev) vehicles with controlled dc electromagnets, referred to as electromagnetic suspension systems. The theoretical exposition, based on the Taylor series expansion solution to the Hamilton-Jacobi-Isaacs inequality, is followed by an assessment of some of the practical issues in realizing the nonlinear controllers with a digital signal processor and embedded hardware. A select set of experimental results from a single-degree-of-freedom suspension system is included to highlight the effectiveness of the proposed nonlinear stateand output-feedback H/sub /spl infin// controllers to suppress guideway-induced disturbances.     

三相电压型PWM整流器的自抗扰控制研究

三相电压型PWM整流器是一个多输入多输出的强非线性结构,并对三相电压型PWM整流器的数学模型和自抗扰控制器进行了原理分析;为了改善整流系统抗扰性及参数摄动等问题,采用一种改进型的非线性自抗扰控制方案,同时给出了离散形式的表达式;然后,重新构造了常规自抗扰控制器中非线性状态误差反馈控制律(NLSEF)和扩张状态观测器(ESO)的非线性函数,以此来克服非线性函数的不平滑性能,从而减小整流系统输出的高频颤振现象;在MATLAB/Simulink环境下进行仿真和搭建了实验样机来验证,改进型自抗扰控制器与常规自抗扰控制器进行对比分析。结果表明了改进型自抗扰控制策略改善了交流侧电压和负载突变敏感的缺点,并降低了交流侧电流总谐波含量,且直流侧电压具有更好的动静态性和鲁棒性。     

非线性零阶接近有界多模型神经网络自适应控制器

针对一类单变量非线性离散时间系统,提出一种零阶接近有界的多模型神经网络自适应控制器。该控制器包含一个非线性鲁棒自适应控制器和一个非线性神经网络自适应控制器。当系统非线性项放宽到零阶接近有界时,这两个控制器分别用于保证系统的稳定性和提高系统的性能,系统的控制输入由切换机构在两个控制器之间进行切换产生。最后给出了稳定性和收敛性证明,并通过仿真实验验证了该控制器的有效性。     

Optimizing simultaneously over the numerator and denominator polynomials in the Youla-Kuc/spl caron/era parametrization

Traditionally, when approaching controller design with the Youla-Kuc/spl caron/era parametrization of all stabilizing controllers, the denominator of the rational parameter is fixed to a given stable polynomial, and optimization is carried out over the numerator polynomial. In this note, we revisit this design technique, allowing to optimize simultaneously over the numerator and denominator polynomials. Stability of the denominator polynomial, as well as fixed-order controller design with H/sub /spl infin// performance are ensured via the notion of a central polynomial and linear matrix inequality (LMI) conditions for polynomial positivity.     

非线性锅炉-汽轮机系统的鲁棒控制

本文采用环路成形Ｈ∞控制方法对一非性性锅炉－汽轮机系统进行设计,为了能方便地在实际中工程中实现复杂的控制器,本文提出用多变理ＰＩＤ控制器逼近所得控制器的方法,最终简化的由位于主对角通道的三个ＰＩ控制器及位于次对角通道的一个ＰＩ控制器实现,仿真表明所得控制器具有较好的信号跟踪、抗干扰性能,并能在较大范围操作点工作,从而具 鲁棒性。     

Multivariable gain-scheduled fuzzy logic control of an exothermic reactor

Fuzzy logic control frequently exhibits superior performance to classical linear controllers even for ‘hard’, mathematically well defined plants, as described in this paper. The case-study of a highly nonlinear exothermic continuous stirred tank reactor, which poses a multivariable control problem with two interacting loops and open-loop instability, is used. The behaviour of the fuzzy logic controller is compared with that of a PID controller. A smooth, easily tuneable gain-schedule is designed to handle offset-like problems with a fuzzy controller. It is analytically shown that such a gain-schedule is the simpler, intuitive equivalent of a manipulation of the corresponding fuzzy membership functions. The fuzzy controller structure chosen is a parsimonious one, with the choice of Gaussian bell-shaped membership functions generating a smooth input/output surface with nontrivial inferencing spanning the entire input space. This provides a clear, non-heuristic reason to select Gaussian over triangular shapes for membership functions. The gain-scheduled fuzzy controller shows excellent control performance, significantly outperforming the PID controllers in both servo and regulatory modes. The disturbance rejection behaviour of the modified fuzzy controller is observed to be particularly good.     

Predictive controller with estimation of measurable disturbances. Application to an olive oil mill

This paper describes the application of a predictive controller that deals with measurable disturbances in the extraction process in an olive oil mill. The work focuses on the thermal part of the process, where the raw material is prepared for the mechanical separation. The system under consideration can be viewed as composed of several changing-level stirred tanks. The paper shows the development of the controller based upon a model obtained from first principles combined with experimental results and validated with real data. Strong disturbances and large time delays appear in the process, so predictive control strategies have been tested under linear and nonlinear simulation. Finally, they have been implemented on the real plant. A study about the consideration of different models for the estimation of measurable disturbances along the prediction horizon has been carried out, showing that a good performance can be obtained by the use of an appropriate model. A new idea that can improve periodic disturbance rejection in Model Based Predictive controllers is presented.     

An alternative structure for next generation regulatory controllers: Part I: Basic theory for design, development and implementation

Even though employed widely in industrial practice, the popular PID controller has weaknesses that limit its achievable performance, and an intrinsic structure that makes tuning not only more complex than necessary, but also less transparent with respect to the key attributes of the overall controller performance, namely: robustness, set-point tracking, and disturbance rejection. In this paper, we propose an alternative control scheme that combines the simplicity of the PID controller with the versatility of model predictive control (MPC) while avoiding the tuning problems associated with both. The tuning parameters of the proposed control scheme are related directly to the controller performance attributes; they are normalized to lie between 0 and 1; and they arise naturally from the formulation in a manner that makes it possible to tune the controller directly for each performance attribute independently. The result is a controller that can be designed and implemented much more directly and transparently, and one that outperforms the classical PID controller both in set-point tracking and disturbance rejection while using precisely the same process reaction curve information required to tune PID controllers. The design, implementation and performance of the controller are demonstrated via simulation on a nonlinear polymerization process.     

An exact solution to continuous-time mixed H/sub 2//H/sub /spl infin// control problems

Multiobjective control problems have been the object of much attention in the past few years, since they allow for handling multiple, perhaps conflicting, performance specifications and model uncertainty. One of the earliest multiobjective problems is the mixed H/sub 2//H/sub /spl infin// control problem, which can be motivated as a nominal LQG optimal control problem subject to robust stability constraints. This problem has proven to be surprisingly difficult to solve, and at this time no closed-form solutions are available. Moreover, it has been shown that except in some trivial cases, the optimal controller is infinite-dimensional. In this paper, we propose a solution to general continuous-time mixed H/sub 2//H/sub /spl infin// problems, based upon constructing a family of approximating problems, obtained by solving an equivalent discrete-time problem. Each of these approximations can be solved efficiently, and the resulting controllers converge strongly in the H/sub 2/ topology to the optimal solution.