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To reduce torque oscillations in electric motors, harmonic current injection (HCI) has been used in industry for some time. For this purpose, higher harmonic currents calculated in advance are injected into the machine. Since the general conditions for the machine can change during its life cycle, this article presents a method that makes it possible to change the parameters of HCI during operation. For this purpose, sensor signals are used to detect the reaction of the electric motor to small variations of the HCI parameters. The knowledge gained in this way is used to make further suitable variations. FEM simulations were used to verify the effectiveness of the approach. The results show that the algorithm can independently optimize the HCI parameters during runtime and reduces the amplitude of the 6th harmonic in the torque by 87% for a permanent magnet synchronous machine.

CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior Este trabalho apresenta o aperfeiçoamento de um método de controle por ondas não senoidais, que tem o objetivo de gerar variações periódicas de força no eixo de motores de indução lineares trifásicos operando em velocidades próximas de zero. O aprimoramento é desempenhado através da aplicação de um algoritmo de evolução diferencial para a determinação da tensão de alimentação dos motores de indução, sem necessidade da utilização de um equacionamento matemático dispendioso. Para isso, um modelo computacional, baseado nas equações tradicionais do motor de indução, é desenvolvido para atuar como função de avaliação do algoritmo. A validação do trabalho é feita por meio de testes experimentais, durante os quais a tensão aplicada ao motor é controlada por uma Field-Programmable Gate Array (FPGA) conectada a um inversor. Os resultados apresentam melhora em relação a trabalhos anteriores, encontrando valores otimizados de tensão para diferentes tipos de perfis de força. Uma vez comprovada a funcionalidade deste aperfeiçoamento, sua aplicação poderá ser ampliada para diferentes tipos de máquinas elétricas. This work presents an improvement of a non-sinusoidal wave control method, which has the objective of generating periodic variations of force in the shaft of a three-phase linear induction motors operating at speeds near zero. The improvement is performed through the application of a differential evolution algorithm for the determination of the supply voltage of induction motors without the use of an complex mathematical equation. For this, a computational model of the electric motor is developed to act as an evaluation function of the algorithm. The computational model was developed based on the traditional induction motor equations. The improvement of the method is validated through experimental tests, where the voltage applied to the motor is controlled by an FPGA connected to an inverter. The results show an improvement over previous work, finding optimal voltage values for different types of force profiles. Once proven the functionality of this improvement, its application can be extended to different types of electric machines. Tese (Doutorado)

Electrical machines are wide spread because of their intrinsic robustness, versatility and reduced impact on energy and resources. Recently, the demand has focused on specific features: compatibility with power converters and fault tolerance. In fact, a wide range of applications require variable speed drives and high rejection of faults, i.e. safe operation also for non-critical applications. Here, a dual three-phase stator configuration is used, and a novel method for stator fault detection is presented. This method is based on reactive power measurements from both three-phase systems. A differential diagnostic index is defined, that can be used to detect effectively stator faults, isolating them from torque oscillations, load unbalances or other pitfalls.

According to modern grid regulations, doubly fed induction generator (DFIG) needs to operate without losing synchronism during grid faults. But, severe fault leads to rise in stator and rotor current to a higher value and generator will get damaged. Large oscillations in stator real and reactive power are produced and consequently large torque oscillations get developed. To overcome the above affects due to severe faults, enhanced field oriented control technique (EFOC) is adopted in rotor side control of the DFIG. In EFOC technique, rotor flux reference changes its value from synchronous speed to zero or to a smaller value during fault for injecting current at the rotor slip frequency. In this method, DC-offset component of stator flux is controlled to minimize it. This offset decomposition of flux will be oscillatory in a conventional FOC, whereas in EFOC it can damp quickly. The reference frame for rotor during fault changes with EFOC, so as to make the rotor speed not to deviate much from the reference value. This makes the decomposition of flux during fault to be controlled and make the generator winding current not to exceed to higher values. The proposed EFOC technique with fuzzy controller can damp pulsations in electromagnetic oscillations, improve voltage mitigation and limit surge currents and to have sustained operation of DFIG during voltage sags. The performance of the grid connected DFIG system with voltage sag of 40 and 70% of the rated voltage with symmetrical fault occurring at point of common coupling between 0.1 and 0.3 s are analyzed using simulation studies.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior The objective of this thesis is the development of a method to generate a desired time variant force in an induction motor, working on low speed, through the fed voltage waveform manipulation. The mathematical model to the induction motor considers the rotor blocked, once the goal is to apply this method at low speed. Through a mathematical treatment of the model, is possible to obtain the fed voltage of the induction motor as a function of the electromagnetic force. Experimental results obtained in rotative and linear motor prototypes are satisfactorily compared with the teorical results, obtained with the developed method. O objetivo desta tese de doutorado é desenvolver um método para gerar uma variação temporal de conjugado desejado em um motor de indução, em baixas velocidades, por meio da manipulação da forma de onda das tensões de entrada. O modelo matemático para o motor de indução considera seu rotor bloqueado, uma vez que visa aplicações em baixas velocidades. Através de um tratamento matemático do modelo, é possível colocar as tensões de alimentação do motor em função do conjugado eletromagnético. Resultados experimentais obtidos em protótipos de motores rotativo e linear são confrontados satisfatoriamente com os resultados teóricos encontrados na modelagem desenvolvida. Doutor em Ciências

The thesis deals with finite element method simulations of the two-degree of freedom spherical induction actuator performed using the 2D and 3D models. In some cases non-linear magnetization curves, rotor movement and existence of higher harmonics are taken into account. The evolution of the model leading to its simplification is presented. Several rotor structures are tested, namely the one-layer, two-layers and two-layers-with-teeth rotor. The study of some rotor parameters, i.e. teeth number and size, external and internal layer thickness, in order to improve the actuator electromechanical conversion and reduce the torque ripple is performed. The influence of the rotor teeth geometrical form on the electromechanical conversion is shown. General actuator parameters such as the airgap, source current and parameters of the magnetic material are verified as well. Finally the superiority of the two-layers-with-teeth rotor structure over the one-layer and two-layers structures is confirmed. (FSA 3)--UCL, 2005

The main goal in using electronic comutating motors as servo motors is to obtain a smooth torque. To achieve that it is necessary to insure that magnetic flux is as close as possible to a sinusoidal shape. Torque ripple produces vibrations and noise during the running of a motor, especially when the speed of the motor shaft is small. The vibrations can decrease the operational time of the motor. It is desirable to have the torque which is not dependent on the shaft angle, but is only dependent on the excitation function. The position improvement of the servo drive by decreasing the torque oscillations in the brushless PM motors is described.

The aim of this study is to characterize the steady and unsteady flows of a high‐speed axial fan stage and assess its aerodynamic performance parameters. The flow unsteadiness is related to the stator‐rotor interaction originated mainly by two mechanisms: the first is attributed to the potential effect and the second to the wake‐blade interaction and the mixing through the blades' passages. Such effects are dependent on the circumferential positions of blades and inter‐distance between stator and rotor, which could be alleviated by understanding these flow interactions. The pressure waves' main diametrical modes (two blades interacting with two vanes) and their sequences are predicted analytically. FFT analysis of the computed static pressure fluctuations at different monitor points allowed identifying the prevailing modes of interaction and their frequencies and sequence. The assessment of inter‐distance is an important step toward identifying the detrimental effects of axial interdistance on the aerodynamic performance. The closer the blade‐rows of this fan stage can be spaced, the more compact the cooling system of an automotive could be designed.