Sensorless speed estimation in induction machines (IMs) presents an attractive proposition for eliminating the need for physical speed measurement sensors and thus avoiding the associated reliability and cost issues, such as the requirement of extra wiring, careful mounting, maintenance and adjustment. In this thesis, the feasibility of utilising the stator current and power signals to establish spectral search based (SSB) sensorless speed estimation schemes in wound rotor induction machines (WRIMs) operating in extended slip and open-loop controlled conditions is investigated. The research is performed on three different industrial WRIM designs. The thesis first investigates the spectral content of WRIM electrical and mechanical signals with the principal aim of identifying spectral patterns that can facilitate the development of real-time sensorless speed estimation. The examination is based on detailed harmonic models of the considered machine designs as well as experimental results obtained from tests performed on laboratory test rigs. A generalised theoretical analysis of the possible spectral content of machine signals that enables the derivation of closed form analytical expressions linking individual spectral frequencies to rotor speed is also undertaken. The results demonstrate that it is possible to clearly identify speed dependent components in the stator current and power signals and map the boundaries of the narrowbands maximised by these for extended slip and open-loop operating conditions. To enable improvement in attainable real time SSB estimation rates a dichotomous search algorithm real-time spectral processing method was employed for frequency tracking in this research. The algorithm performance is evaluated in real-time tests performed on a measured steady-state laboratory machine stator current and power signals. The results demonstrate that the dichotomous routine provides an inherent advantage in the frequency estimation rate without compromising the estimation accuracy and can therefore enable significant estimation rate improvement in SSB speed estimation algorithms. Novel sensorless speed SSB estimation techniques are then proposed for WRIM operation in extended slip and voltage/frequency controlled conditions. The algorithms utilise the reported analysis of electrical signals and are separately defined for each assessed operation mode and the stator current, phase power and three-phase power signals. It is shown that, in principle, power signal based estimation algorithms can offer an inherent capability of estimation rate reduction. A novel adaptive sliding window algorithm is defined for open-loop operating conditions that enable estimation in a wide operating speed range while minimising the potential for undesirable overlap with PWM harmonics. The proposed algorithms have been verified and their performance limitations assessed in real-time experiments on three different industrial WRIM designs. It is shown that reliable real-time speed estimation in steady-state and transient operating conditions is possible at an improved estimation rate while maintaining a low estimation error.

Many utility-scale wind turbine generators use wound-rotor induction machines. By adding an external rotor resistance to the rotor circuit it is possible to control the wind turbine output power and, with proper control, maintain a constant power for wind speeds between rated and cut-out. The external resistance modifies the generator torque-speed curve and changes the angular velocity of the rotor, resulting in a greater power extraction from the wind. A number of control strategies can achieve this objective. These include controlling the rotor resistance to maintain a constant generator equivalent circuit, and control based on the aerodynamic torque. It is also possible to use a lookup table instead of a feedback controller. These options all have the same steady-state result as direct output power control, but differing transient performance. Computer simulations and hardware experiments are used to investigate and characterize the different control methods. / text

Student Number : 0004041J - MSc dissertation - School of Electrical and Information Engineering - Faculty of Engineering / Slip energy recovery (SER) drives are used extensively in industry as they offer cost effective speed control of large wound rotor induction motors. The biggest disadvantage associated with the use of SER drives is the vulnerability of the rotor circuit converters to power system disturbances such as voltage dips. The failure of converters as a result of voltage dips is a problem associated with the use of these particular drives. The aim of this research is to better understand the stresses on rotor circuit converters as a result of voltage dips at the terminals of the motor. The rotor transients developed by a wound rotor induction motor are investigated for a range of three phase and single phase voltage dips. Simulations conducted in the Alternative Transients Program (ATP) supplement measurements conducted on a simplified SER circuit. The results confirm that voltage dips cause significant stresses on the converters in the rotor circuit. Good correlation was obtained between simulated and measured results. This work allows for a better understanding of the response of wound rotor induction motors to voltage dips and identifies the threat that voltage dips impose on the SER rotor circuit converters.

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This thesis investigates a novel induction machine topology that uses a rotating power electronic converter. Steady-state and dynamic performance of the topology is studied to understand its operational principle. Furthermore the potential of improving its efficiency and power factor is investigated. The topology is referred to as wound rotor induction machine with rotating power electronic converter (WRIM-RPEC).     The WRIM-RPEC topology offers the possibility to magnetize the induction machine from the rotor side by introducing a reactive voltage in the rotor. Thus, the power factor of the machine can be improved. Constant speed variable load operation can be achieved by setting the frequency of the introduced voltage. Two options of rotor winding and converter configuration in the WRIM-RPEC system are investigated. The wound rotor windings can either be open-ended and fed by a three-phase back-to-back converter or Y-connected and fed by a single three-phase converter. The dc-link in both converter configurations contains only a floating capacitor. These two configurations give different dc-link voltages at the same torque and speed.     Two analytical steady-state models of the topology are developed in this thesis. The first model can be used to analyze the operating condition of the motor at specific speed and torque. Particularly, the operating range of speed and torque of the topology is investigated. The second model is used to analyze variable power factor operation, including unity power factor operation. Analytical calculations and measurements are carried out on a 4-pole, 1.8kW induction machine and the results are compared.      A dynamic mathematic model is then developed for the WRIM-RPEC system for the back-to-back converter configuration. The mathematic model is then applied in Matlab/Simulink to study the dynamic performance of the system including starting, loading and phase-shifting. The simulation results are compared with measurements on the 4-pole, 1.8kW induction machine. Moreover, the simulation model using the existing Simulink blocks are studied to compare with the results obtained from the mathematic model. Furthermore, the dynamic performance of the WRIM-RPEC system with the single converter configuration is investigated. In addition, harmonic spectra analysis is conducted for the stator and rotor currents.     In the last part of the thesis, efficiency improvement is investigated on the 4-pole induction machine when it is assumed to drive a pump load. It is shown that the efficiency can be further improved by decreasing the rotor resistance. Due to space constraints it is however difficult to decrease the rotor resistance in a 4-pole induction machine. An investigation is thus carried out on a standard 12-pole, 17.5kW squirrel-cage induction machine with inherent low power factor. The cage rotor is redesigned to a wound rotor to enable the connection of converter to the rotor windings. An analytical model is developed to design the wound rotor induction machine. The machine performance from calculations is then compared with FEM simulations with good agreement. The analytical model is further used to design several WRIMs with different dimensions and rotor slot numbers. Power factor and efficiency improvement is then explored for these WRIMs. A promising efficiency increase of 6.8% is shown to be achievable. / <p>QC 20161111</p>

Orientador: Dr. Alfeu J. Sguarezi Filho / Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Engenharia Elétrica, 2014. / Devido as preocupações com a redu¸c¿ao do uso dos recursos f'osseis e das emiss¿oes de CO2 ocasionadas pelos mesmos, o interesse no uso de energias renov 'aveis aumentou, sendo uma destas fontes a energia e'olica. O Gerador de Indu¸c¿ao de Rotor Bobinado (GIRB) tem demonstrado ser uma ferramenta capaz de otimizar o uso da energia e'olica, dada a sua alta efici¿encia, rentabilidade e robustez mec¿anica, ainda assim 'e necess'ario superar os numerosos desafios que est¿ao presentes nesta tecnologia, tais como qualidade da pot¿encia, estabilidade da rede, entre outros. O objetivo desta pesquisa se concentra no estudo de t'ecnicas de controle de pot¿encia fornecida pelo GIRB aplicado a sistemas de gera¸c¿ao e'olica. No presente caso, o sistema de gera¸c¿ao 'e composto por um GIRB com seu estator conectado diretamente 'a rede e seu rotor 'e conectado 'a rede atrav'es de um conversor bidirecional. Prop¿oe-se estudar o m'etodo de controle direto de torque (CDT) com emprego de controladores PI e por modos deslizantes (SMC) mais PI. O controle direto de torque 'e uma t'ecnica de alto desempenho din¿amico e possibilita o controle independente do torque e fluxo do gerador o que possibilitar'a o controle das pot¿encias ativa e reativa do GIRB. Da mesma forma, 'e estudado o conversor para o processamento da energia gerada. As simula¸c¿oes baseadas em modelos matem'aticos destes m'etodos de controle foram revistos, analisados e comparados com as simula¸c¿oes de textos de refer¿encia. Resultados experimentais obtidos em uma bancada validaram o prot'otipo proposto. / Due to concerns about reducing the use of fossil resources and the CO2 emissions caused by them, interest in the use of renewable energy increased, one of these sources is wind energy. The Wound Rotor Induction Generator (WRIG) has been proved to be a tool to optimize the use of wind energy, given its high efficiency, profitability and mechanical robustness, it is still necessary to overcome the many challenges that are present in this technology, such as power quality, grid stability, among others. This research focuses on the study of control techniques for power supply by WRIG applied to wind generation systems. In this case, the generation system consists of a stator WRIG is connected directly to the electrical network and its rotor too, but via a bidirectional converter. It is proposed to study the method of direct torque control (DTC) with the use of PI and sliding mode controllers (SMC) more PI. The direct torque control is a technique of high dynamic performance and enables independent control of torque and flux generator, which will enable the control of active and reactive power ofWRIG. Likewise, it is studied the converter for processing the generated power. The simulations based on mathematical models of these control methods were reviewed , analyzed and compared with simulations of reference texts . Experimental results obtained on a bench validated the proposed prototype.

Tradicionalmente, la detección de faltas en máquinas eléctricas se basa en el uso de la Transformada Rápida de Fourier ya que la mayoría de las faltas pueden ser diagnosticadas con ella con seguridad si las máquinas operan en condiciones de régimen estacionario durante un intervalo de tiempo razonable. Sin embargo, para aplicaciones en las que las máquinas operan en condiciones de carga y velocidad fluctuantes (condiciones no estacionarias) como por ejemplo los aerogeneradores, el uso de la Transformada Rápida de Fourier debe ser reemplazado por otras técnicas. La presente tesis desarrolla una nueva metodología para el diagnóstico de máquinas de inducción de rotor de jaula y rotor bobinado operando en condiciones no estacionarias, basada en el análisis de las componentes de falta de las corrientes en el plano deslizamiento frecuencia. La técnica es aplicada al diagnóstico de asimetrías estatóricas, rotóricas y también para la falta de excentricidad mixta. El diagnóstico de las máquinas eléctricas en el dominio deslizamiento-frecuencia confiere un carácter universal a la metodología ya que puede diagnosticar máquinas eléctricas independientemente de sus características, del modo en el que la velocidad de la máquina varía y de su modo de funcionamiento (motor o generador). El desarrollo de la metodología conlleva las siguientes etapas: (i) Caracterización de las evoluciones de las componentes de falta de asimetría estatórica, rotórica y excentricidad mixta para las máquinas de inducción de rotores de jaula y bobinados en función de la velocidad (deslizamiento) y la frecuencia de alimentación de la red a la que está conectada la máquina. (ii) Debido a la importancia del procesado de la señal, se realiza una introducción a los conceptos básicos del procesado de señal antes de centrarse en las técnicas actuales de procesado de señal para el diagnóstico de máquinas eléctricas. (iii) La extracción de las componentes de falta se lleva a cabo a través de tres técnicas de filtrado diferentes: filtros basados en la Transformada Discreta Wavelet, en la Transformada Wavelet Packet y con una nueva técnica de filtrado propuesta en esta tesis, el Filtrado Espectral. Las dos primeras técnicas de filtrado extraen las componentes de falta en el dominio del tiempo mientras que la nueva técnica de filtrado realiza la extracción en el dominio de la frecuencia. (iv) La extracción de las componentes de falta, en algunos casos, conlleva el desplazamiento de la frecuencia de las componentes de falta. El desplazamiento de la frecuencia se realiza a través de dos técnicas: el Teorema del Desplazamiento de la Frecuencia y la Transformada Hilbert. (v) A diferencia de otras técnicas ya desarrolladas, la metodología propuesta no se basa exclusivamente en el cálculo de la energía de la componente de falta sino que también estudia la evolución de la frecuencia instantánea de ellas, calculándola a través de dos técnicas diferentes (la Transformada Hilbert y el operador Teager-Kaiser), frente al deslizamiento. La representación de la frecuencia instantánea frente al deslizamiento elimina la posibilidad de diagnósticos falsos positivos mejorando la precisión y la calidad del diagnóstico. Además, la representación de la frecuencia instantánea frente al deslizamiento permite realizar diagnósticos cualitativos que son rápidos y requieren bajos requisitos computacionales. (vi) Finalmente, debido a la importancia de la automatización de los procesos industriales y para evitar la posible divergencia presente en el diagnóstico cualitativo, tres parámetros objetivos de diagnóstico son desarrollados: el parámetro de la energía, el coeficiente de similitud y los parámetros de regresión. El parámetro de la energía cuantifica la severidad de la falta según su valor y es calculado en el dominio del tiempo y en el dominio de la frecuencia (consecuencia de la extracción de las componentes de falta en el dominio de la frecuencia). El coeficiente de similitud y los parámetros de regresión son parámetros objetivos que permiten descartar diagnósticos falsos positivos aumentando la robustez de la metodología propuesta. La metodología de diagnóstico propuesta se valida experimentalmente para las faltas de asimetría estatórica y rotórica y para el fallo de excentricidad mixta en máquinas de inducción de rotor de jaula y rotor bobinado alimentadas desde la red eléctrica y desde convertidores de frecuencia en condiciones no estacionarias estocásticas. / Vedreño Santos, FJ. (2013). Diagnosis of electric induction machines in non-stationary regimes working in randomly changing conditions [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/34177 / TESIS