The Brush less Doubly-Fed Machine (BDFM) has the potential to be a more cost effective replacement for conventional induction or synchronous machine drives. The BDFM has two stator windings: a power winding and a control winding. An electronic power converter of variable voltage and frequency is connected to the control winding and allows the speed of the machine to be adjusted synchronously. The power winding, by design, carries the majority of the current needed for operation, the control winding only a fraction of the current, thus enabling the converter rating to be as low as 25% of the rating of the machine depending on the speed range of operation. To date, only one specific stator pole-pair combination has been investigated, namely the 3/1 combination, where 3 and 1 refer to the power winding pole-pairs and the control winding pole-pair, respectively. Since the speed of the machine is dependent on the sum of the pole-pairs of the stator windings, a general pole numbered model is needed to evaluate the performance of such general machines with other pole-pair number machines. The BDFM describing system equations are transformed to the two axis (dq) rotor reference frame using a power invariant transformation. The analysis shows an additional term involving the common bar impedance which was not present in earlier analyses. The dynamic model is simplified to yield a steady state synchronous model. The synchronous frequency of analysis is investigated which results in two equivalent steady state models. The models developed can easily handle excitation of any frequency or sequence on the control winding without the use of an auxiliary model as used in previous analyses. The voltage forced model predictions match data taken for a 5 hp BDFM laboratory prototype, establishing the validity of the analysis. The model is used in illustrating the torque producing capabilities and unity power factor operation of the machine under a variety of inputs. Using the model, predictions are made on a different pole-pair combination machine (4/2 BDFM) for use as a 60 hp pump drive as an alternative to a 3/1 BDFM for the same application. / Graduation date: 1995

Graduation date: 1993

University of Macau / Faculty of Science and Technology / Department of Electromechanical Engineering

No description available.

As high precision data acquisition systems continue to improve their performance and power efficiency to migrate into portable devices, increasing demands are placed on the performance and power efficiency of the analog-to-digital conversion modulator. On the other hand, analog-to-digital modulator performance is largely limited by several major noise sources including thermal noise, flicker noise, quantization noise leakage and internal analog and digital coupling noise. Large power consumption and die area are normally required to suppress the above noise energies, which are the major challenges to achieve power efficiency and cost targets for modern day high precision converter design. The main goal of this work is to study various approaches and then propose and validate the most suitable topology to achieve the desired performance and power efficiency specifications, up to 100 kHz bandwidth with 16-21 bits of resolution. This work will first study various analog-to-digital conversion architectures ranging from Nyquist converters such as flash, pipeline, to the delta sigma architecture. Advantages and limitations of each approach will be compared to develop the criteria for the optimal modulator architecture. Second, this work will study analog sub-circuit blocks such as opamp, comparator and reference voltage generator, to compare the advantages and limitations of various design approaches to develop the criteria for the optimal analog sub circuit design. Third, this work will study noise contributions from various sources such as thermal noise, flicker noise and coupling noise, to explore alternative power and die area efficient approaches to suppress the noise. Finally, a new topology will be proposed to meet all above criteria and adopt the new noise suppression concepts, and will be demonstrated to be the optimal approach. The main difference between this work from previous ones is that current work places emphasis on the integration of the modulator architecture design and analog sub-circuit block research efforts. A high performance stereo analog-to-digital modulator is designed based on the new approach and manufactured in silicon. The chip is measured in the lab and the measurement results reported in the dissertation. / text

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

Not available / text

Not available / text

No description available.

The Anger camera has been used for the last quarter century in many areas of science to image gamma radiation. Some typical applications include medicine, where functionality of organs are studied in vivo, and industrial inspection of fuel rods for nuclear reactors. The standard Anger geometry includes a large scintillation crystal, light guide, photomultiplier array, and analog processing electronics. Even the most modern gamma cameras built today still use the standard Anger design. The work presented here describes an alternative to the standard gamma-camera design that is flexible enough to be used in a wide variety of applications. Especially in single-photon emmission computed tomography (SPECT) applications, the new design has the potential to be more efficient than the standard design. The new design is modular, that is, several small, separate units comprise a system. Each unit consists of a small gamma camera that is optically and electronically independent from other units. The units, called "modular cameras," can be configured around the region of interest so as to provide the maximum amount of information for reconstruction algorithms or direct information to the operator. The theoretical and experimental investigation of this report focuses on the design and construction of the modular cameras. Each modular camera is, in esscence, a small Anger camera. Components of each module include a scintillation crystal, a light guide, and an array of four photomultiplier tubes. Instead of an analog processing network, each module utilizes fast digital circuitry which includes direct analog-to-digital conversion of the photomultiplier signals, a lookup table which maps detector responses to position estimates of the scintillation flashes in the crystal, and an image memory which accumulates the position estimates and forms an image of the radiation incident on the faceplate of the camera. The digital electronics are necessary because analog techniques fail to give satisfactory estimates of scintillation position when the flashes occur near the sides of the crystal. The contents of the lookup table are determined from the statistical properties of the detected signals as a function of scintillation position. Experiments are described in which "best" estimates of position are found by processing data collected from an array of point-source positions in contact with the crystal. Alternative methods for construction of the lookup table are also discussed, which involve computer generation of the estimates. Both maximum-likelihood and mimimum-mean-square-error estimation rules are used, and the results are compared. A mathematical bound on the performance of the estimators is calculated assuming Poisson statistics for the detection process. The bound, which is a Cramer-Rao lower bound, is used to compare module geometries before lookup tables are constructed. A one-dimensional module, which accumulates information along one axis of the faceplate, is designed first. The one-dimensional module provides proof-of-principle evidence for the estimation techniques and is used to determine critical parameters for modular-camera design. The results of the experiments with the one-dimensional camera are extended to two-dimensional designs, which yield position estimates along both axes of the camera faceplate. Several two-dimensional cameras are tested, and an optimum geometry is constructed and tested for spatial resolution and bias of the estimators.