Modélisation analytique multiphysique pour la conception optimale de moteurs synchrones à aimants permanents

During the last years, permanent magnets synchronous motors have become a reference in the industrial world, both from the economical and the technical point of view, because of their very good performance in both regards. Thus, application of specific methodologies and algorithms during the design phase has become a must. In this thesis, the analytical modelling of permanent magnet synchronous motors for stator configurations with and without teeth is presented. Several physical aspects, such as magnetic, thermal and electrical phenomena, are taken into account. For the magnetic part, several models are presented which all have their own areas of application. Some of them take the magnetic saturation of the ferromagnetic parts into consideration. The simplified thermal model is based on an equivalent Kirchhoff circuit in which convection and radiation are included. Concerning the determination of the electrical characteristics of slotless machine configurations, the determination of the back-emf and of the inductances using the method of images are presented. Special emphasis has been placed that the tendencies of the variations of the modelled phenomena as they are observed with changes in other parameters or criteria are correctly represented. This is almost more significant that the accuracy of the model itself. The models are validated and improved by using finite element simulations. The mathematical expressions of the design problems are taken into account to allow the mathematical optimisation applied to converge towards the optimal solution without failure. Thereby, the objective is to avoid non-continuity of the functions and their first derivatives and to reduce the space where the functions are not mathematically defined. In the "Solar Impulse" project, which aims to realise an around-the-world flight with an airplane using only the solar radiation as energy source, a prototype is optimised and built. A prototype motor has been built and experimentally analysed, to be able to further validate and improve the analytical model used for the optimisation of the machine. The originalities of this thesis can be summarised as follows : modelling of the magnetic phenomena, with several specific models adapted for different configurations ; formulations of the physical phenomena adapted for the design phase ; comparison between analytical and finite element simulations in order to validate or/and improve the analytical models ; use of the method of images to determine the inductances in a slotless motor ; design optimisation by taking into account several physical phenomena where the free parameters are analysed globally ; design and manufacturing of a prototype for a concrete project which allows to completely validate the results of the optimisation and the analytical models.

Analytical design and optimization of ultrasonic vibrational transducers for spinal surgery

John Murphy

Just about every other technical publication you pick up these days makes sweeping statements concerning the pressures on scientists, engineers, and industries as a whole to get to market in less time, with an improved, less expensive product. I am reminded of a slogan used rather ubiquitously by a prior employer : Cheaper, Faster, Better. The mention of this race has become almost blase for most, but for the individuals taking the brunt of the pressure, can be disconcerting if not outright painful. Expected to live up to this ambition, the design engineer is faced with the fact that the door is closing on antiquated methods of trial and error engineering. Unfortunately, most individuals have not been equipped with the necessary skills to enact a more intelligent design process and in many cases when the skills are present, industry, a bit paradoxically, is wary of expending the time and resources needed to fit into this new streamlined paradigm. This thesis could be considered as a case study of a somewhat mature technology coming to grips with this new rushed reality. Typical design methods for ultrasonic transducers, while based on analytical models, have relied heavily on building a transducer from quarter wave segments that have somewhat known characteristics. Prototypes are built, tested and modified until the desired results are obtained. Advances have been made to this method with the introduction of finite element softwares that allow modeling without realizing a prototype. The finite element methodology also permits a limited amount of system optimization, and while this is a definite improvement, it can still take months to realize an acceptable design. In this work, we draw on the analytical models, but abandon the quarter wave approach. We also use finite elements, to a limited extent, to validate results obtained from the analytical models, but do not attempt to use the finite element analysis to perform optimizations. On the contrary, a novel optimization method is developed which uses the analytical models to calculate values for the various cost functions necessary to optimize a transducer and its drive electronics. In this way, system parameters are left free to vary in the search for a maximum or minimum solution. While some systems are not candidates for system optimization as a means to get to market faster with a better product, this is not the case for ultrasonic transducers. The design of ultrasonic transducers is an application that begs for models, for optimization, and characterization. The investment made here in understanding the mathematical models, and in the development of optimization routines and softwares has allowed for a modified method of development for ultrasonic handpieces and their drive electronics. This thesis shows that, given a set of design specifications, the design of a transducer can be done in a very short period of time, a few days, even-and furthermore, the resulting design will function as predicted by the simulations. This work presents analytical models for the transducers elements with analysis and discussion. It then introduces a new method of optimization that is well adapted to optimizing the transducers as well as the drive electronics. The control electronics and a simple method of transducer control, which allow for the operation of the system for testing purposes, are also laid out.

EPFL2007

Méthodologie de conception et optimisation d'actionneurs intégrés sans fer

Igor Stefanini

The growing demand for new technologies in several fields : recreation, medicine, transport, telecommunications and the space industry, etc. is increasingly related to the field of the management, transformation and use of electric power. In this domain, the development of no-ferromagnetic integrated electromechanical actuators finds wide application and thus implies an usefulness over a large diversity of geometries. The absence of ferromagnetic materials does not allow for quick determination of an equivalent electromagnetic circuit for this type of actuator. The interaction of the magnetic induction fields produces phenomenas like the skin effect and the proximity effect which degrade its performance. In such circumstances, there is a compromise to be made between the analytical model's complexity and the precision of the results. Often, a modeling based on numerical approaches, which uses finite element methods, is the best adapted approach. Nevertheless, this type of analysis requires much experience and in particular, the parameterization of the actuator specifications and the exploitation of such a model in the optimized design is not very practical and requires considerable computing time. The use of discretized analytical models constitutes a good compromise between the degree of complexity and the model's correspondence to reality. Accordingly, in this thesis, we propose a suite of discretized analytical models allowing for the design and the optimization of this type of actuator. The development of a general rule to determine the optimal discretization step allows an arbitration between computing time, degree of complexity, and the precision of the results. The identification and the validation of the analytical models describing the skin and proximity effects have made it possible to improve the computation of self-inductance and winding resistance. The development of a design and optimization methodology for this type of actuator permits each application to be optimized in a systematic and efficient way, by proposing one or more possible solutions with their advantages and their disadvantages. Two distinct applications were conceived and optimized adopting this design methodology : the Montrac® system and the Iglus® system. In the Montrac® project, it was a question of modifying the power system of a modular assembly line. This system is composed of a fixed track with motorized shuttles for use in a clean room environment. The replacement of the electrical contacts by a contactless energy transmission system was dimensioned and optimized in order to guarantee an operation compatible with the requirements of the above mentioned environment. In the Iglus® project, a subcutaneous biomedical actuator for glycemic level detection, with the aim of measuring the glucose level of diabetes patients was optimized. The measurements and results from these two applications, made it possible to confirm the validity of the models expounded in this thesis.

EPFL2006

Design methodology and numerical optimization of ultrasonic transducers for spinal surgery

Daniel Porto

Nowadays, the general trend towards to minimally invasive interventions is present in all the medical domains. For the surgical intervertebral spinal disc cutting or removal domain, it is particularly a necessity because the manual methods currently employed are tedious, time consuming and taxing on the hands of the practitioner. In that context, new devices that are small enough to pass through a small opening in the skin or through a small portal are required. A detailed analysis of current cutting methods that are or could be used for disc and disc nucleus removal provided that ultrasonics technology should be investigated as a possible solution. The study of ultrasonics technology to fulfil the overall cutting function needed for spinal annulus and nucleus disc material removal is based on a design methodology that breaks down the overall cutting function in many partial functions. The applied design methodology consists in drawing a complete catalogue of solutions for each partial function. Based on a predetermined choice of criteria for each partial function, the evaluation and the classification of each solution allows determination of the best solutions for each partial function. A new ultrasonic transducer designed device composed of a piezoelectric stack for the source of energy and movement, a transmission partial function with rods or discs, an amplification partial function with exponential horns and the cutting partial function solutions is detailed. Existing analytical methods for the design of ultrasonic transducers are mostly based on quarter wavelength segments used to build the transducer. The modeling of that transducers with a finite element method (FEM) avoids building the prototypes and constitutes progress. Analytical models different from the quarter wavelength approach have already been developed and are very useful when used in an optimization process. Furthermore, when the geometry of the analyzed model is not straightforward, a FEM optimization approach to solve that kind of problems can be a valid solution too. Some existing optimization algorithms and other already developed pseudo-gradient methods applied to optimize the analytical models of the ultrasonic transducers are not valid for numerical optimizations where the computing time is a key factor. This leads to the development a new genetic algorithm (GA) optimization methods. One advantage being that the number of parameters to be optimized does not change the complexity of the algorithm unlike other algorithms. Three GAs with improvements done on different parts are discussed, implemented and tested. One GA is chosen to optimize the transducer model with numerical methods. As the main drawback with FE optimizations is the amount of computation time spent for each simulation, this creates a need to develop numerical 2D models that can be quickly simulated but with accurate results. Ultrasonic transducer prototypes are also built and measured. As the prototype has to be used for the cutting or the removal of spinal disc material, the cutting effect of the prototypes has been tested and evaluated.

EPFL2009