Global Saturated Regulator with Variable Gains for Robot Manipulators

In this paper, we propose a set of saturated controllers with variable gains to solve the regulation problem for robot manipulators in joint space. These control schemes deliver torques inside the prescribed limits of servomotors. The gamma of variable gains is formed by continuous, smooth, and differentiable functions of the joint position error and velocity of the manipulator. A strict Lyapunov function is proposed to demonstrate globally asymptotic stability of the closed-loop equilibrium point. Finally, the functionality and performance of the proposal are illustrated via simulation results and comparative analysis against Proportional-Derivative (PD) control scheme on a two-degrees-freedom direct-drive robot manipulator

Advanced Discrete-Time Control Methods for Industrial Applications

This thesis focuses on developing advanced control methods for two industrial systems in discrete-time aiming to enhance their performance in delivering the control objectives as well as considering the practical aspects. The first part addresses wind power dispatch into the electricity network using a battery energy storage system (BESS). To manage the amount of energy sold to the electricity market, a novel control scheme is developed based on discrete-time model predictive control (MPC) to ensure the optimal operation of the BESS in the presence of practical constraints. The control scheme follows a decision policy to sell more energy at peak demand times and store it at off-peaks in compliance with the Australian National Electricity Market rules. The performance of the control system is assessed under different scenarios using actual wind farm and electricity price data in simulation environment. The second part considers the control of overhead crane systems for automatic operation. To achieve high-speed load transportation with high-precision and minimum load swings, a new modeling approach is developed based on independent joint control strategy which considers actuators as the main plant. The nonlinearities of overhead crane dynamics are treated as disturbances acting on each actuator. The resulting model enables us to estimate the unknown parameters of the system including coulomb friction constants. A novel load swing control is also designed based on passivity-based control to suppress load swings. Two discrete-time controllers are then developed based on MPC and state feedback control to track reference trajectories along with a feedforward control to compensate for disturbances using computed torque control and a novel disturbance observer. The practical results on an experimental overhead crane setup demonstrate the high performance of the designed control systems.Comment: PhD Thesis, 230 page

Model-based control methods to improve the power qualify of grid-connected single-phase inverters.

Power electronic converters are commonly used for interfacing distributing generation sources (DGs) to the electrical power system networks. This is necessary because these DGs usually have different output characteristics and cannot be connected directly to the local load and/or the grid. The power electronic front-end converter is an inverter whose dc link is fed by an ac/dc converter or by a dc/dc converter, according to the DG source type. The commercial front-end inverters are designed to operate either in grid-connected (GC) mode or in stand-alone (SA) mode. In the SA mode, the inverter is connected to local load, but in the GC mode the inverter must be connected to the utility grid and a local load could be connected to this system as well. Based on this, any designed or proposed controller for such systems should work well in both operation modes. The control objective in SA mode is to improve the quality of the local load voltage, and the control objective in GC mode is to inject clean current to the grid with low total harmonic distortion (THD). Most of the control schemes in the literature have been designed to work in one of these operation modes and ensure low THD either for the local load voltage or for the injected grid current. However, some of the existing control schemes in the literature proposed different control architectures for each operation mode. Moreover, there are a few researches have been reported in the literature based on the cascaded control theory to obtain low THD for both the local load voltage simultaneously with the injected current to the grid in the grid-connected mode. Due to the growing penetration of the DG sources in the residential applications, single-phase grid-connected inverters have gained much attention. For this reason, the single-phase grid-connected inverter systems have been chosen in our study. Since such systems have nonlinearity in its behavior, different nonlinear model-based control schemes have been designed in order to improve the quality of the local load voltage while injecting clean current to the grid for single-phase grid-connected inverter systems by using single structure control scheme. Furthermore, the proposed control schemes ensure the seamless transfer between GC and SA operation modes without adjusting the controller structure and with self-synchronization ability

Observation and estimation study for sensorless control of linear vapor compressors.

Linear vapor compressors have become widely investigated for refrigeration applications due to their high efficiency in comparison to the more common rotary type compressors. However, the nature of the linear compressor adds complexity to the control of these machines. The unconstrained motion of the piston in a linear compressor allows for continuous modulation of the compressor output, but requires knowledge of the mechanical dynamics to effectively control the compressor and prevent collision of the piston with the cylinder head. This control is made more difficult by the highly nonlinear nature of the force of gas compression acting against the piston. As this gas force changes so does the resonant frequency of the system. Efficient control of the compressor requires knowledge and tracking of this resonant frequency in addition to other objectives. Sensorless control of the system is preferred for reliability, ease of production, and cost effectiveness. To this end a series of nonlinear observers and a combination of controllers have been developed for the linear vapor compressor

Normas e estabilidade para modelos estocásticos cuja variação do controle e do estado aumentam a incerteza

Orientador: João Bosco Ribeiro do ValDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: Essa dissertação de mestrado gira em torno da discussão sobre controle de sistemas incertos. Modelos matemáticos utilizados como base para o design de controladores automáticos são naturalmente uma representação aproximada do sistema real, o que, em conjunto com perturbações externas e dinâmica não modelada, gera incertezas a respeito dos sistemas estudados. Na literatura de controle, este tema vêm sendo discutido frequentemente, em particular nas sub-áreas de controle estocástico e controle robusto. Dentre as técnicas desenvolvidas dentro da teoria de controle estocástico, uma proposta recente se diferencia das demais por basear-se na idéia de que variações abruptas na política de controle possam acarretar em maiores incertezas a respeito do sistema. Matematicamente, essa noção é representada pelo uso de um ruído estocástico dependente do módulo da ação de controle, e a técnica foi apelidada de VCAI - acrônimo para variação do controle aumenta a incerteza. A definição da política de controle ótima correspondente, obtida por meio do método de programação dinâmica, mostra a existência de uma região ao redor do ponto de equilíbrio para a qual a política ótima é manter a ação de controle do equilíbrio inalterada, um resultado que parece particular à abordagem VCAI, mas que pode ser relacionado a políticas de gerenciamento cautelosas em áreas como economia e biologia. O problema de controle ótimo VCAI foi anteriormente resolvido ao adotar-se um critério de custo quadrático descontado e um horizonte de otimização infinito, e nessa dissertação nós utilizamos essa solução para atacar o problema de custo médio a longo prazo. Dada certa semelhança entre a estrutura do ruído estocástico na abordavem VCAI e modelos utilizados na teoria de controle robusto, discutimos ainda possíveis relações entre a abordagem proposta e controladores robustos. Discutimos ainda algumas possíveis aplicações do modelo propostoAbstract: This work discusses a new approach to the control of uncertain systems. Uncertain systems and their representation is a recurrent theme in control theory: approximate mathematical models, unmodeled dynamics and external disturbances are all sources of uncertainties in automated systems, and the topic has been extensively studied in the control literature, particularly within the stochastic and robust control research areas. Within the stochastic framework, a recent approach, named CVIU - control variation increases uncertainty, for short -, was recently proposed. The approach differs from previous models for assuming that a control action might actually increase the uncertainty about an unknown system, a notion represented by the use of stochastic noise depending on the absolute value of the control input. Moreover, the solution of the corresponding stochastic optimal control problem shows the existence of a region around the equilibrium point in which the optimal action is to keep the equilibrium control action unchanged. The CVIU control problem was previously solved by adopting a discounted quadratic cost formulation, and in this work we extend this previous result and study the corresponding long run average control problem. We also discuss possible relations between the CVIU approach and models from robust control theory, and present some potential applications of the theory presented hereMestradoAutomaçãoMestre em Engenharia Elétrica2016/02208-6, 2017/10340-4FAPES

Model Order Reduction

An increasing complexity of models used to predict real-world systems leads to the need for algorithms to replace complex models with far simpler ones, while preserving the accuracy of the predictions. This three-volume handbook covers methods as well as applications. This third volume focuses on applications in engineering, biomedical engineering, computational physics and computer science

Optimal Planning of Virtual Inertia Installations to Improve the Power System Frequency Response

In recent years, the power system has seen a fast transformation from one primarily based on fossil energy to one where renewable energy, especially wind and solar power, takes a more significant proportion in the energy profile. With the shift in energy profile come the changes in the electricity generation units. The solar panels and wind turbines replace the synchronous generators in electricity generation. Most solar and wind generation units are converter-interfaced. In contrast, the synchronous generator is connected to the power grid directly. For this reason, the future power system of a high level of renewable penetration will exhibit dynamic properties different from the traditional power system, which poses many challenges. One of the challenges is related to frequency stability. The frequency stability of a traditional power system is secured with a three-level frequency control scheme. The scheme is composed of three frequency regulation mechanisms at different time scales. The fastest control mechanism, named primary frequency control, needs about 5 s to be fully deployed to arrest the frequency drops or overshoots. After that, the other two frequency secondary and tertiary frequency control mechanisms are then slowly deployed to bring the system frequency back to the nominal value. Under this control scheme, the overall active power generation and consumption in a power system get balanced, and the power frequency variation is limited within a narrow range around a nominal value. However, before the primary frequency control is sufficiently deployed, the system relies on the natural inertia response of the synchronous generators to maintain the active power balance at the sacrifice of changes in the generators' rotational speeds. As the power frequency is decided collectively by the rotational speeds of all synchronous generators in the system, larger system inertia means smaller power frequency variation when subject to the same disturbance. Since there is no lack of system inertia in a synchronous generator-dominant power system, the power frequency variation with the help of the tertiary control scheme is usually contained within a limited range. For a future power system with more and more synchronous generators being displaced by converter-interfaced generation (CIG) units, the system inertia decreases. The tertiary frequency control scheme alone can no longer limit the power frequency variation within an acceptable range. For this reason, techniques were proposed to emulate inertia response on a converter-interfaced generation unit. Apart from the level of total system inertia, studies show that the spatial distribution of system inertia can also influence the frequency response. Under this context, a well-planned virtual inertia installation at selected locations can achieve a satisfactory level of improvement on frequency response at a low investment cost. This thesis work aims at developing a systematic method to search for the most economical plan of virtual inertia installations while ensuring a satisfactory level of frequency response. In order to derive the most economical plan of virtual installation, a mathematical optimization problem is proposed with constraints formulated with the help of a newly proposed metric of inertia response that quantifies the influence of inertia on the system frequency response. The formulation of the optimization problem considers all possible combinations of loading and renewable generation profiles. Two methods are proposed to solve the optimization problem of the mixed-integer type. The first one is based on the classic scheme of dynamic programming. The second method adopts a relaxation technique based on the sparsity promotion or Majorize-Minimization (MM) method. Furthermore, parallel and cloud programming techniques are used to facilitate computation speed. Other minor contributions include a design of a supplementary controller on top of the inertia emulation control to improve the voltage stability of a converter-interfaced generation unit. Finally, case studies were conducted on a modified Southeast Australian power system against different types of faults to validate the performance and investment cost of the virtual inertia installation plan givens by the proposed method in comparison with two other methods. The result shows that the virtual inertia installation plan given by the proposed method produces better performance while at lower investment costs