Um estudo sobre métodos de determinação de estados e parâmetros de máquinas síncronas de polos salientes

Orientador: Mateus GiesbrechtDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: As máquinas síncronas de polos salientes desempenham um papel fundamental na análise de estabilidade de sistemas elétricos de potência, especialmente em países cuja maior parte da energia gerada provém de fontes hidráulicas. Os modelos elétricos equivalentes que descrevem o comportamento dessas máquinas são compostos por diversos parâmetros, os quais são utilizados em uma ampla gama de estudos. No presente trabalho, estudam-se e propõem-se técnicas de estimação de estados e parâmetros de máquinas síncronas de polos salientes. A princípio, as equações de tensão, de fluxos concatenados, de potência e de movimento são desenvolvidas com as devidas unidades de medida, tanto em variáveis de máquina quanto em variáveis projetadas sobre um plano ortogonal que gira na velocidade elétrica do rotor. Na maior parte da literatura, essas unidades não são explicitadas no equacionamento. Dentre os parâmetros elétricos dos modelos das máquinas síncronas de polos salientes, as reatâncias de magnetização são os que mais influenciam o comportamento da máquina em condições de regime permanente senoidal. Desta forma, apresenta-se uma nova abordagem à estimação do ângulo de carga dessas máquinas e o subsequente cálculo das reatâncias de magnetização a partir de condições de carga específicas -- o desempenho do método proposto é avaliado em dados de simulação e em dados reais de operação de um gerador síncrono de grande porte. Algumas abordagens à determinação de parâmetros requerem que a máquina seja posta fora de operação para que ensaios específicos possam ser realizados. Dentre eles, um dos mais empregados na determinação de parâmetros transitórios e de regime permanente é o ensaio de rejeição de carga; assim, este ensaio também é analisado e aperfeiçoado por um método automatizado de separação de soma de exponenciais baseado em projeção de variáveis. Por tratar-se de um sistema multivariável e altamente não linear, diferentes observadores de estado também são utilizados para se determinarem estados e parâmetros de máquinas síncronas em tempo hábil e com precisão satisfatória. Este trabalho apresenta uma abordagem não linear recursivamente aplicável à estimação de fluxos concatenados, correntes de enrolamentos amortecedores, ângulo de carga e reatâncias de magnetização de máquinas síncronas de polos salientes por meio da filtragem de partículas. Um modelo não linear de oitava ordem é considerado e apenas as medições realizadas nos terminais da armadura e do campo durante regime permanente se fazem necessárias para estimar as referidas grandezasAbstract: Salient-pole synchronous machines play a fundamental role in the stability analysis of electrical power systems, especially in countries where most of the generated energy comes from hydraulic sources. The electrical equivalent models that describe the behavior of these machines are composed of several electrical parameters, which are used in a wide range of studies. In the present work, techniques for estimating states and parameters of salient-pole synchronous machines are studied and proposed. A priori, the voltage, flux linkage, power, and motion equations are developed with the appropriate units included, both in machine variables and in variables projected on an orthogonal plane rotating in the rotor's electrical speed. In most of the literature, these units are not explained in the equation process. Among the electrical parameters, the magnetizing reactances are the ones that most influence the machine behavior under transient and steady-state conditions. In this way, a new approach to estimate the load angle of these machines and the subsequent calculation of the magnetizing reactances from specific load conditions are presented -- the performance of the proposed method is evaluated by means of simulation data and by operating data of a large synchronous generator. Some approaches to determine parameters require the machine to be taken out of operation, so that specific tests may be performed. Among them, one of the most used to determine transient and steady-state parameters is the load rejection test; thus, this test is also analyzed and refined by an automated method based on variable projection for separating the resulting sum-of-exponentials. Since the machines are highly nonlinear, multivariate, dynamic systems, different state observers seek to solve the state estimation problem in a timely manner and with satisfactory accuracy. This work presents a nonlinear and recursive approach for the estimation of flux linkages per second, amortisseur winding currents, load angle, and magnetizing reactances of salient-pole synchronous machines by means of the particle filtering. An eighth-order nonlinear model is considered, and only measurements taken at the machine terminals are necessary to estimate these quantitiesMestradoAutomaçãoMestre em Engenharia Elétrica162015/2018-6CNPq

Efficient Methods for the Study of Eddy-Currents Effects in Medium-Voltage Rotating Electrical Machines

Lo scopo di questa tesi \ue8 presentare alcuni metodi efficienti (dal punto di vista computazionale) per il calcolo degli effetti dovuti alle correnti parassite (eddy currents) in macchine elettriche rotanti in media tensione. Due applicazioni in particolare sono state considerate nel dettaglio. Inizialmente viene analizzato il fenomeno delle correnti parassite indotte nell'albero di motori asincroni a due poli e il conseguente effetto sulle prestazioni della macchina, focalizzandosi in particolare sul fattore di potenza. La seconda parte della tesi concentra la sua attenzione sullo studio dell'avviamento da rete di motori sincroni con rotore massiccio. Per ciascuna applicazione vengono introdotte alcune procedure di calcolo, facenti uso di opportuni modelli numerici basati sul metodo degli elementi finiti, per mezzo delle quali vengono adeguatamente calcolati i parametri dei circuiti equivalenti di macchina, tenendo conto degli effetti legati alle correnti parassite. I modelli numerici sono opportunamente definiti, in modo tale da ridurre al massimo la complessit\ue0 delle geometrie e il conseguente onere computazionale. I risultati delle procedure innovative qui proposte sono confrontati con i dati provenienti da prove sperimentali sulle macchine oggetto di studio e con analoghi risultati di calcolo dedotti tramite le procedure comunemente utilizzate. Il confronto fra questi dati ha dimostrato che gli approcci di calcolo introdotti in questa tesi permettono di ottenere risultati con un elevato livello di accuratezza e una netta riduzione dell'onere computazionale.The efficient computation of eddy-current effects in medium voltage electric machines is discussed in this dissertation. Two particular cases are considered. Firstly, the effects of shaft eddy-currents on two-pole induction motor performance is addressed, with special focus on the power factor. In the second part of the thesis the start-up calculation of a large synchronous motor with solid rotor is analyzed. For each application a special calculation procedure is introduced. These procedures adopt a set of suitable finite-element models to properly compute the machine equivalent circuit parameters that are mainly influenced by eddy-current-related phenomena. By suitably choosing finite-element models boundary conditions and excitations their geometry is simplified to the maximum possible extent, in order to reduce the computational burden. The results of the new calculation methods are compared with experimental data and with analogous results obtained from commonly-adopted calculation procedures. The comparison proves that the proposed approaches can lead to high accuracy levels with very remarkable computational savings

Power system controller tuning considering stochastic variations

Electrical power systems are vulnerable to external disturbances, such as short circuits, that can lead to damage on the equipments and even blackouts. In order to improve the system response to external disturbances, the generators of the power system are equipped with automatic controllers devised to maintain the generators working on a constant operating condition. The tuning of the controllers is performed assuming the system loads do not have time-dependent variations, but such assumption is not realistic as the power system loads are stochastically changing due to the switching on and o of every device (PCs, TVs, cellphones, etc.) connected to it. This work proposes two new methods for the tuning of the generator controllers which takes into account the stochastic nature of the system loads. More speci cally, this work proposes two new methods for the tuning of the governors and AVRs of the power system generators: one focused on the steady state response and the other focused on the fault response. First, the system response as a function of the controller parameters is calculated. As the power system is under the e ect of stochastic loads, the resulting system response is stochastic. Then, a stochastic objective function which measures the quality of the system response is de ned. Each tuning method uses a di erent objective function. Finally, the objective function is optimized using the metaheuristic Cuckoo Search, which is used for global optimization problems and can be used to optimize stochastic functions. The method was tested in di erent benchmark systems showing better system responses

Brushless asynchronous induction machines with leading VAR capability

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A smart power system stabilizer for dynamic reduction of a power system model

This thesis focuses on studying the dynamic stability of power systems and improving them by the addition of smart power system stabilizers (PSSs). A conventional design technique of a power system stabilizer that uses a single machine connected to an infinite bus through a transmission line (SMIB) has been widely used for study of elecromechanical perturbations. This approach requires estimating the external equivalent impedance and the voltage at an external bus for each machine in a multi-machine system. This study will use the conventional mathematical method, which represents a power system with some modifications. The dynamic model is linearized by taking the high voltage side on the generation unit as a reference instead of the infinite bus voltage. By using this modification, several improvements are accomplished, the main ones of which are: the estimation of states is eliminated, the time consumed in estimating calculations is reduced, the parameters of the model are independent of the external system, and the PSS design for each machine is independent in a multi-machine environment system. This strategy enables a PSS to be designed for a single machine and then implemented in a multi-machine system. Power systems have advanced to the point that they now cover vast geographical areas. Consequently, they are not only quite complicated, but the system orders are also high. As the complexity of these systems increases, so does the difficulty of examining their dynamic stability and adjusting their controllers. In this research, to address these issues, the reduced model technique has been employed to mathematically define smaller system models from existing models, such that the properties of both systems are comparable properties. The parameters of the PSS are determined based on a modified Heffron- Phillips model of the power system at certain operating conditions where it can provide reliable performance. Since the power systems are highly nonlinear with configurations and parameters that change with time, a typical PSS design, which is based on a linearized model of the power system, cannot guarantee its performance in practical operating environments. The present study attempts to overcome this limitation by implementing smart power system stabilizers. In the context of this thesis the word smart means novel technique. An artificial neural network power system stabilizer (ANN-PSS), a novel multi input fuzzy logic power system stabilizer (FLPSS), and a modified multi-resolution proportional-integral-derivative power system stabilizer (MMR-PID-PSS), based on the dynamic reduction of a power system model. These PSSs have been developed to refine the power system dynamic performance by adjusting the regulator’s parameters in real-time simulation under various operating conditions. In the first part of this research, the digital simulations results using the proposed ANN-PSS and FLPSS are carried out on a single machine connected to a network and are then compared with conventional Lead-Lag PSS. The results show that the power system with FLPSS has a better dynamic response over a wide range of operating conditions and parameter changes. Next, the digital simulations results using the proposed MMR-PID-PSS is carried out on a single machine connected to the network, a 4-machine 10-bus power system, and a 10-machine 39-bus power system and then compared with FLPSS. The results validate the effectiveness of the proposed MMR-PID-PSS regarding reduced overshoot, undershoot, and settling time under a different type of disturbances

Sensitivity Analysis of Synchronous Generators for Real-Time Simulation

The purpose of this thesis is to validate generator models for dynamic studies of power systems using PSS/E (Power System Simulator for Engineering), EMTP (ElectroMagnetic Transient Program), and Hypersim. To thoroughly evaluate the behavior of a power system in the three specified software packages, it is necessary to have an accurate model for the power system, especially the generator which is of interest. The effect of generator modeling on system response under normal conditions and under faulted conditions is investigated in this work. A methodology based on sensitivity analysis of generator model parameters is proposed aiming to homogenize the behavior of the same power system that is modeled in three software packages. Standard IEEE 14-Bus system is used as a test case for this investigation. Necessary changes in the exciter parameters are made using the proposed methodology so that the system behaves identical across all three software platforms

On-line computer control of turbine generators using state estimation and optimal feedback

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Systematic development of equivalent circuits for synchronous machines.

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