Modern Control Theory is applied to analyze an existing aluminum mill drive, which was originally designed by Classical Methods. The system is studied with Optimal Control and z-transform zero-pole locus tools. The results and also the original design are compared with the performance of simulation. The models are built with the transition matrix and iterative procedures. Conclusions about the appropriated design methods and improvements to the control scheme result from the investigation. / Master of Science / incomplete_metadata

published_or_final_version / abstract / Electrical and Electronic Engineering / Master / Master of Philosophy

Orientador: José Alfredo Covolan Ulson / Banca: Danilo Hernane Spatti / Banca: Fernando de Souza Campos / Resumo: O uso de técnicas de controle preditivo e de sistemas inteligentes na resolução de problemas de controle de grande complexidade tem crescido significativamente na última década. Parte disso se deve ao fato destas abordagens já terem sido utilizadas com sucesso em uma vasta gama de aplicações, demonstrando sua robustez e eficiência. Porém, o uso destas técnicas ainda é pequeno quando comparado com o controle PID (proporcional integral derivativo) clássico, ainda que apresentem resultados melhores. Assim, a maioria das publicações presentes na literatura que utilizam estas técnicas de controle mais sofisticadas tem como objetivo resolver um problema específico de controle. Para isso, em geral, adota-se uma determinada abordagem sem que necessariamente se faça uma avaliação a respeito de qual dos métodos existentes seria o mais eficiente, uma vez que o foco é apenas a resolução do problema. Nesse contexto, o objetivo deste trabalho foi avaliar o desempenho de três das técnicas de controle inteligente e/ou preditivo mais aceitas para o controle de processos industriais frente ao controlador PID clássico, de uso generalizado na indústria. Mais especificamente, optou-se por utilizar o controlador MPC, o controlador Fuzzy e o controlador Neural Preditivo para o controle de um processo industrial e, então, avaliar o desempenho por meio das métricas ISE e ITSE, além de comparar o sobressinal máximo, erro estacionário e tempo de acomodação. Por fim, os resultados de desempenho de cada ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The use of predictive control techniques and intelligent systems in the resolution of complex control problems has increased in the last decade. Part of this is due to the fact that these approaches have already been used successfully in a wide range of applications, demonstrating their robustness and efficiency. However, the use of these techniques is still small when compared to the classic PID (derivative proportional integral) control, although they present better results. Thus, most publications in the literature that use these more sophisticated control techniques aim to solve a specific control problem. For this, in general, a certain approach is adopted without necessarily making an evaluation as to which of the existing methods would be the most efficient, since the focus is only the resolution of the problem. In this context, the objective of this work was to evaluate the performance of three of the most accepted intelligent and / or predictive control techniques for the control of industrial processes against the classical PID controller, widely used in industry. More specifically, it was decided to use the MPC controller, the Fuzzy controller and the Neural Predictive controller to control an industrial process, and then evaluate the performance through the ISE and ITSE metrics, in addition to comparing the maximum overshoot, stationary error and accommodation time. Finally, the performance results of each controller were confronted with the classic PID controller... (Complete abstract click electronic access below) / Mestre

A new and improved stabilizer was developed for the variable speed generation (VSG) system. The VSG system exhibits periodic oscillations which sometimes leads to a loss of synchronism. After careful study, a simple but effective strategy to stabilize the system was implemented with real time digital feedback control. The VSG system consists of an engine, which is the prime mover, driving a doubly fed machine (DFM), which is the generator. The stator of the DFM is directly connected to the grid while the rotor is connected to the grid through a power electronic converter. The converter used in this study is a series resonance converter (SRC), but the proposed method may also be applied to other kinds of converters. The stabilizer senses the RPM of the engine, the feedback signal, and controls the rotor current amplitude and frequency of the doubly fed machine. Control was implemented using the 80C196KB microcontroller. The software consists of a mix of "C" and assembly language. Speed being an important factor in the implementation, care was taken to minimize the control loop times. The important features of the hardware and software developed for the stabilizer are: (1) 12 MHz controller board (2) Real time digital band pass filter (3) Instantaneous rotor speed measurement (4) Interrupt driven measurement and control loops (5) User defined setup parameters (6) IBM PC based real time serial communication The performance of the VSG system was studied with and without the stabilizer. A significant improvement in the stability of the system was noticed over the entire region of operation. / Graduation date: 1991

The Brushless Doubly-Fed Machine (BDFM) has recently become an important research topic in the field of variable-speed AC drives. In recent studies, the BDFM has shown significant potential for improving the reliability and performance of AC drive systems, as well as reducing total system cost. While the BDFM offers several advantages over existing AC drives in steady-state operation, it suffers from dynamic instabilities and slow response times, and a feedback control system is necessary. The mathematics of the BDFM are much more complicated than those of a singly-fed machine, and thus traditional control methods can't be applied. In this thesis, a control method known as "Direct Torque Control" has been adapted from that of a singly-fed induction machine and successfully applied to the BDFM. The thesis begins by discussing the background of the BDFM, its open-loop operating characteristics, and some of the control considerations. The reduced-order system differential equations are introduced, and it is noted that they are coupled and nonlinear. Furthermore, all state variables are time-varying (but periodic), even in steady-state operation. In the controller development, it is found that a linear relationship exists between the desired torque/flux-level change and the d-q voltages to be applied to the control winding of the machine via the power-electronic converter. This linear relationship, together with a one-step-ahead predictor to compensate for computational delay, is successfully used to control the speed and efficiency of the machine, for a wide range of speeds and load torques. Numerous open- vs. closed-loop simulations are compared and summarized, and it is found that the performance of the BDFM is greatly improved in the closed-loop, with faster response and reduced oscillation. Further simulations investigating the robustness of the controller are summarized, and it is found that the controller is reasonably insensitive to errors in most of the the static machine parameters. Hardware implementation is briefly discussed but is not complete; laboratory results are not yet available but should be soon. Future controller considerations are then discussed; included among the recommendations are an on-line parameter estimator for use in adaptive control, and a controller for generator applications of the BDFM. / Graduation date: 1993

The loads on the electrical systems of automobiles are projected to increase significantly in the near future. This will result in a requirement for improved efficiency over the present-day car alternators. An alternative scheme proposed at Oregon State University employs a Brushless Doubly-Fed Machine (BDFM) as an alternator. This thesis begins with a study and characterization of the existing car alternator system. The configuration of the proposed scheme is discussed. In the proposed configuration, the power winding of the machine generates the bulk of the power and the control winding provides the excitation. The power winding feeds a power rectifier, which in turn charges the battery in an automobile. The control winding is supplied through an inverter. Issues related to inverter and rectifier design are discussed. A 3-phase pulse width modulated inverter and a bridge rectifier were developed and tested for performance. A PSPICE simulation model for the rectifier was developed and results are compared with laboratory tests. A Voltage Regulator Circuit (VRC) and an Efficiency Maximizer Unit (EMU) for the system are designed and developed. A prototype alternator system is tested and the principle of efficiency maximization is verified. Finally. the comparative performance of the the existing and the proposed system is discussed and some recommendations for further improvements in the prototype system are made. / Graduation date: 1992

Thesis ( Ph.D.) -- University of Texas at Arlington, 2008.

M. Tech. Electrical Engineering. / Wheeled Mobile Platforms have considerable acceptance and dominance in the field of transportation. While most of these platforms have been designed for able users, very few special designs are available for the physically disabled persons. With increasing numbers of disabled peoples around the world, accommodative and safer displacement means are called for. A normal wheelchair platform with two front castor wheel and two independently driven rear wheels is therefore considered in this study for modelling and control. Based on the nature of persons using wheelchairs, better and much easy to control wheelchair platforms are necessitated. To achieve such objective, this research is focused on two main threads: dynamic modelling and control. In modelling, the aim is to present a dynamic model of wheelchair platform that takes into account slipping parameters and frictional/traction forces experienced on motion. It also intends to account for the effects of gravitational forces that would be experienced by the wheelchair and its effect on the platforms during uphill and downhill movements. Lagrange formalism is utilised in the design of this dynamic model. In control, the objective is to ensure that the platform tracks the reference linear velocity and the reference angular orientation as desired. With such control commands, a simple access device may be employed to ensure that people with severe disability also have a chance of controlling the wheelchair. Since no zero dynamics arise with linear velocity and angular orientation as the platforms outputs, standard input-output feedback linearisation is considered and applied in the linearisation of the model and in the development of the control law. Successfully simulated results demonstrating the performance of the proposed dynamic model and control law are presented for verification. The entire dynamic model and the controller are simulated in a software tool MATLAB and SIMULINK.

Thesis submitted in fulfillment of the requirements for the degree Master of Technology: Electrical Engineering in the Faculty of Engineering at the Cape Peninsula University of Technology 2014 / A new control strategy for control of the nonlinear process of Dissolved Oxygen (DO) concentration in the aerobic tank of wastewater treatment process is proposed. It provides means to improve the performance of the Linear Proportional Integration and Derivative (LPID) controller by extending it to a Nonlinear Proportional Integration and Derivative (NLPID) controller. The aim of the thesis is to develop methods, algorithms and software for design, simulation, and programmable logic controller (PLC) implementation of NLPID controllers in order to control the nonlinear process of dissolved oxygen. The thesis investigates the possibilities the widely used in theory and industry methods for the design of the LPID controllers for linear processes as Ziegler- Nichols and Pole Placement, to be applied to the design of NLPID controllers for the nonlinear process of DO concentration. Three cases are considered: Case 1: Application of the values of the parameters the linear PID controller designed by the Ziegler-Niched method for the linearized DO process model to be used as parameters of the nonlinear PID controllers to control the DO nonlinear process. Case 2: Application of the values of the parameters of the linear PID controller designed by the Pole placement method for the linearized DO process model, to be used as parameters of the nonlinear PID controller to control the nonlinear DO process. Case 3: Novel, proposed in the thesis, method based on the Pole placement method for direct design of the parameters of the linear and nonlinear PID controllers to control the nonlinear DO process. Software is developed to simulate in MATLAB environment the behavior of the closed loop DO process for the considered cases of controller designs. The results of the simulations show that in the Case1 and the Case 2 it is not possible to use the values of the LPID controller parameters designed for the linearized DO process, directly to control the nonlinear process by the NPID controllers. Additional tuning for some of the parameters is needed. The simulation in the Case 3 shows the excellent behaviors of the closed loop system for all linear and nonlinear PID controllers which prove that the new method is effective and applicable. Real-time simulations of the closed loop system are done in a TwinCAT 3 simulation environment of the Bechkoff EX5020 PLC. The deliverables of the thesis are applicable to many type nonlinear processes in chemical, manufacturing, and other industries.

At Mondi Paper Ltd, Merebank, South of Durban, Paper Machine 2 has recently been transferred onto a Distributed Control System (DCS). This was seen as a good opportunity to enhance the control of the pulp feed to the machine. A prime concern in operating a paper machine is to ensure consistent set-point paper properties in the Cross-Direction (CD: ie. across the paper width) and in the Machine-Direction (MD: ie. along the paper length). Sophisticated adjustments are available to ensure an even feed of the stock (consistencies around 2% m/m wood fibres in water) from the head-box across the receiving width of the paper machine. The properties of prime interest as the pulp is pumped through the head-box distributor onto the receiving belt of the machine are the basis weight (fibre mass per unit area) and moisture content (per unit area). However, the distribution system is highly dependent on the properties of the stock as it arrives at the head-box. Variations in upstream chest levels, the supplied pressure, flow-rate and fibre/water ratio, all cause MD and even CD variations. The problems of maintaining steady conditions at the head-box are well known, and are understood to arise from sub-optimal control in the preceding section involving a blend chest and machine chest, amongst other items, where several pulp streams and dilution water are combined. A number of control loops are involved, but appear to require different tuning for different paper grades. Often individual loops are taken off-line. In this study, an understanding of the controller interactions in the stock preparation section has been developed by detailed dynamic modelling, including all of the existing control loops. The model is built up in a modular fashion using a basic element, having one input (which can collect multiple streams originating elsewhere) and four outputs, linked through a vessel of variable volume. Several basic elements are linked together to form the overall system. All of the necessary properties can be defined so that the model allows the simulation of all features of the network: vessels, pipes, junctions, valves, levels and consistencies. A set of first order differential equations is solved which includes total water balance, species mass balances, derivatives of flow controller action, and derivatives of supervisory controller action. Supervisory controllers for consistency or level cascade onto flow controllers. Flow controllers manipulate valves which give a first-order dynamic response of actual flow. Where valves are manipulated directly by the supervisory level, the flow controller is effectively bypassed. This study involves a constraint problem around the blend chest, resulting in a loss of specification at the paper machine. This was solved by the implementation of a static optimiser. Its objective function penalizes deviations from setpoint of five parameters (ratios, consistency and level) using respective weight factors. Both the model and its optimiser were included in a simulator designed with the graphical user interface (GUI) of Matlab. The simulator has then been used to explore control performance over the operating range, by means of a set of scenarios. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2004.