485 research outputs found

    Model predictive control for stochastic systems by randomized algorithms

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    The main topic of this thesis is control of dynamic systems that are subject to stochastic disturbances and constraints on the input and the state. The main motivation for dealing with control of such systems is that there is no method available that adequately deals with this problem, despite the fact that stochastic, constrained systems are often encountered in real world problems. For example, in process industry the margins of physical quantities such as temperature, pressure, concentration, velocity and position can be expressed as amplitude constraints in a natural way. Such constraints are usually persistent in that suitable control actions need to be implemented that respect these constraints irrespective of the presence of uncontrolled disturbances that effect the system. Goals of the thesis are to 1. Formulate a mathematical problem for the synthesis of a controller that will achieve desired performance of the controlled system. More precisely, to minimize a performance measure that captures desired performance while respecting constraints in the face of stochastic disturbances. 2. Deduce verifiable conditions under which the problem formulated in 1. is solvable. 3. Formulate a solution concept for the problem in 1. that is based on the model predictive control technique. 4. Create feasible computational algorithms for the synthesis of controllers that solve control problems from 1. within the solution setup from 3. 5. Investigate convergence properties of the approximate solutions obtained by computational algorithms from 4. The main tool that is used in the thesis to solve the problem formulated in 1. is the model predictive control technique. Model predictive control has had a significant and widespread impact on industrial process control. When dealing with stochastic systems, however, application of the standard model predictive control algorithms results in a significant loss in the controlled system performance. Therefore, to deal with the problem 1. within the model predictive control framework, it was necessary to develop alternative model predictive control techniques. Contributions of the thesis are twofold. The first set of contributions is made with regard to the model predictive control of constrained, stochastic systems. In this thesis, we develop a novel approach to the model predictive control of such systems, that is based on the optimization in closed loop over the control horizon and stochastic sampling of the disturbance i.e. a randomized algorithm. The second set of contributions has been made in more general framework of the optimal control of stochastic systems that are subject to input and state constraints. We present a novel problem setup for control of such systems and give initial results that are concerned with solvability conditions for the posed optimization problem and the characterization of the optimal solution

    Study of numeric Saturation Effects in Linear Digital Compensators

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    Saturation arithmetic is often used in finite precision digital compensators to circumvent instability due to radix overflow. The saturation limits in the digital structure lead to nonlinear behavior during large state transients. It is shown that if all recursive loops in a compensator are interrupted by at least one saturation limit, then there exists a bounded external scaling rule which assures against overflow at all nodes in the structure. Design methods are proposed based on the generalized second method of Lyapunov, which take the internal saturation limits into account to implement a robust dual-mode suboptimal control for bounded input plants. The saturating digital compensator provides linear regulation for small disturbances, and near-time-optimal control for large disturbances or changes in the operating point. Computer aided design tools are developed to facilitate the analysis and design of this class of digital compensators

    EXPERIMENTAL IMPLEMENTATION OF INTEGRATOR BACKSTEPPING AND PASSIVE NONLINEAR CONTROLLERS ON THE RTAC TESTBED

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    Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/57811/1/BenchmarkIJRNCBuppIJRNC1998.pd

    Computer Control: An Overview

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    Computer control is entering all facets of life from home electronics to production of different products and material. Many of the computers are embedded and thus ``hidden'' for the user. In many situations it is not necessary to know anything about computer control or real-time systems to implement a simple controller. There are, however, many situations where the result will be much better when the sampled-data aspects of the system are taken into consideration when the controller is designed. Also, it is very important that the real-time aspects are regarded. The real-time system influences the timing in the computer and can thus minimize latency and delays in the feedback controller. The paper introduces different aspects of computer-controlled systems from simple approximation of continuous time controllers to design aspects of optimal sampled-data controllers. We also point out some of the pitfalls of computer control and discusses the practical aspects as well as the implementation issues of computer control. Published as a Professional Briefs by IFAC

    Design and control of a vibration isolator using a biased magnetorheological elastomer

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    The objective of this work is to explore the capability of a Semi-Active (SA) elastomer and control techniques in the area of shock and vibration isolation. Typical passive isolation methods have short comings in meeting competing objectives. A specific problem is isolating electronic packages mounted to military vehicle walls from shock. Often passive elastomer based isolators are used. The ideal solution for shock isolation is a soft lightly damped isolator. However a soft lightly damped isolator will cause excessive sway during normal driving conditions. Further, vehicle dynamics during normal driving conditions are typically in the range of a few hertz, presenting the possibility of a lightly damped soft system experiencing severe resonance. As a result most elastomer based isolators have significant damping, which decreases their ability to isolate shock. Active systems are able to theoretically reach a optimal compromise between shock isolation and sway, however for several reasons active systems are not practical. SA systems combine the benefits of passive systems, primarily cost and low actuator power input, with the capability of varying system parameters in real-time with performance indexes nearing that of active systems; This work investigates an interesting SA elastomer, a magnetorheological elastomer (MRE), that is able to change its properties with the application of a external magnetic field. Methods of controlling the field to achieve a desired response is discussed. Finally experimental data is presented of a MRE based device using a SA control scheme to isolate a payload from shock and vibration

    Single-stage electrohydraulic servosystem for actuating on airflow valve with frequencies to 500 hertz

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    An airflow valve and its electrohydraulic actuation servosystem are described. The servosystem uses a high-power, single-stage servovalve to obtain a dynamic response beyond that of systems designed with conventional two-stage servovalves. The electrohydraulic servosystem is analyzed and the limitations imposed on system performance by such nonlinearities as signal saturations and power limitations are discussed. Descriptions of the mechanical design concepts and developmental considerations are included. Dynamic data, in the form of sweep-frequency test results, are presented and comparison with analytical results obtained with an analog computer model is made

    ASDTIC control and standardized interface circuits applied to buck, parallel and buck-boost dc to dc power converters

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    Versatile standardized pulse modulation nondissipatively regulated control signal processing circuits were applied to three most commonly used dc to dc power converter configurations: (1) the series switching buck-regulator, (2) the pulse modulated parallel inverter, and (3) the buck-boost converter. The unique control concept and the commonality of control functions for all switching regulators have resulted in improved static and dynamic performance and control circuit standardization. New power-circuit technology was also applied to enhance reliability and to achieve optimum weight and efficiency

    A unified strategy for windup prevention in control systems with multiple saturating actuators

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    Thesis (MScEng)--University of Stellenbosch, 2000.ENGLISH ABSTRACT: A unified method is proposed to treat saturation in both Multi-Input-Multi-Output MIMO and Single-Input-Single-Output controllers. This method offers superior performance over existing MIM 0 anti-saturation schemes. The anti-saturation problem is posed as a linear programming problem. A practical and efficient implementation of the algorithm is developed by transforming the problem into its dual linear programming form. The problem, in dual form, is then solved using the dual simplex method rather than the primal simplex method. The nature of the problem when expressed in dual form and the properties of the dual simplex method are harmonised to guarantee an initial basic feasible solution and an optimal bounded final solution in a finite, predictable and minimal number of iterations. The resultant controller never saturates, hence cannot windup. Furthermore the resultant controller always applies the optimal control effort to the plant to minimise the error signal input as follows: • The controller is governed such that while the future free response combined with the present forced response of the controller results in no saturation limits being exceeded, now or at some time in the future, the normal linear response of the controller prevails. • When the future free response combined with the present forced response of the controller will result in a saturation limit being reached, now or at some time in the future, the present time input signal into the controller is optimally governed to prevent the saturation limit from being exceeded at any future time.AFRIKAANSE OPSOMMING: 'n Metode word voorgestel waarmee versadiging in enkel-inset enkel-uitset en meer-inset meeruitset (MIMU) stelsels beheer kan word. Die metode presteer beter as ander huidige teenversadiging- maatreels vir (MIMU) beheerders. Die teen-versadigings-probleem word as 'n lineere programmeringsprobleem herformuleer. 'n Praktiese en effektiewe implementering van die algoritme word verkry deur die probleem na die duale vorm te transformeer. Die probleem, in duale vorm, word opgelos met die duale simplex metode, in plaas van die direkte metode. Die eienskappe van hierdie formulering is 'n gewaarborgde, aanvanklike, bereikbare oplossing en 'n optimale, begrensde, finale oplossing in 'n eindige, voorspelbare en minimum aantal stappe. Die uiteindelike beheerder versadig nooit nie, en wen gevolglik nie op nie. Die beheerder wend altyd die optimale aanleg-inset aan om die foutsein te minimeer soos volg: • Wanneer die nul-inset gedrag saam met die huidige inset-gedrag geen beperkings nou of in die toekoms saloorskry nie, word geen beperkende aksie geneem nie, en tree die beheerder dus lineer op. • Sodra die toekomstige nul-inset gedrag saam met die huidige inset-gedrag, nou of later versadiging sou veroorsaak, word die huidige inset tot die beheerder optimaal begrens om latere versadiging te voorkom

    Load Reduction Using Rapidly Deployed Trailing-Edge Flaps

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    This thesis details investigations into the aerodynamic properties of a small, rapidlyactuated, actively controlled trailing-edge ap and the potential of such a device to alleviate the unsteady loading experienced by wind turbine blades due to atmospheric turbulence and the atmospheric boundary layer, although such a device would have potential applications in other elds such as rotorcraft. The main goals of this work were to investigate whether aerodynamic loadings could in fact be alleviated by the use of a small trailing-edge ap using only measurements of the unsteady lift on the wing as a control input and to assess such a device's capacity to reject atmospheric disturbances with both numerical and experimental work, carried out in the Aeronautics Department at Imperial College London. The numerical work covered in the thesis comprises the results of linear and nonlinear aerodynamic and control simulations (e.g. PID, LQG controllers) and the results of computational uid dynamics (CFD) simulations using the commercial package FLUENT. The thesis also lays out the results obtained from testing an experimental prototype in the Hydrodynamics Laboratory in the Aeronautics Department. This prototype successfully rejected intentionally introduced ow disturbances from the vortex street of a square block upstream of the wing and the application of control provided a very signi cant reduction in the unsteady loading experienced by the wing. The ndings show the potential of this method of load control for the rejection of unsteady aerodynamic loading by the sole use of measurements of the wing loading and this has been demonstrated both theoretically and experimentally. The work is closed with a conclusion and suggestions for future research proposals

    Intelligent control of nonlinear systems with actuator saturation using neural networks

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    Common actuator nonlinearities such as saturation, deadzone, backlash, and hysteresis are unavoidable in practical industrial control systems, such as computer numerical control (CNC) machines, xy-positioning tables, robot manipulators, overhead crane mechanisms, and more. When the actuator nonlinearities exist in control systems, they may exhibit relatively large steady-state tracking error or even oscillations, cause the closed-loop system instability, and degrade the overall system performance. Proportional-derivative (PD) controller has observed limit cycles if the actuator nonlinearity is not compensated well. The problems are particularly exacerbated when the required accuracy is high, as in micropositioning devices. Due to the non-analytic nature of the actuator nonlinear dynamics and the fact that the exact actuator nonlinear functions, namely operation uncertainty, are unknown, the saturation compensation research is a challenging and important topic with both theoretical and practical significance. Adaptive control can accommodate the system modeling, parametric, and environmental structural uncertainties. With the universal approximating property and learning capability of neural network (NN), it is appealing to develop adaptive NN-based saturation compensation scheme without explicit knowledge of actuator saturation nonlinearity. In this dissertation, intelligent anti-windup saturation compensation schemes in several scenarios of nonlinear systems are investigated. The nonlinear systems studied within this dissertation include the general nonlinear system in Brunovsky canonical form, a second order multi-input multi-output (MIMO) nonlinear system such as a robot manipulator, and an underactuated system-flexible robot system. The abovementioned methods assume the full states information is measurable and completely known. During the NN-based control law development, the imposed actuator saturation is assumed to be unknown and treated as the system input disturbance. The schemes that lead to stability, command following and disturbance rejection is rigorously proved, and verified using the nonlinear system models. On-line NN weights tuning law, the overall closed-loop performance, and the boundedness of the NN weights are rigorously derived and guaranteed based on Lyapunov approach. The NN saturation compensator is inserted into a feedforward path. The simulation conducted indicates that the proposed schemes can effectively compensate for the saturation nonlinearity in the presence of system uncertainty
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