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Thesis (Ph. D.)--University of Hong Kong, 2005. / Also available in print.

The evaluation of the stray-load losses in induction motors is an important part of the efficiency estimation process. However, stray-load losses have several components which are difficult to isolate and calculate. Consequently, they are more readily determined by test. IEEE Standard 112-1996 recommends the testing of electrical induction motors at a rated mode (nominal frequency and voltage). Thus, the IEEE 112 test does not provide us with information about the motor efficiency and stray load losses at supply frequencies which are different from the rated value. At the same time, this information is very important for the correct evaluation of the efficiency of the motors, controlled by the Adjustable Speed Drives (ASDs). This work is dedicated to the investigation of the relation between the motor efficiency, stray-load loss and the supply frequency. The voltages to be applied for the specific values of the frequency were chosen to keep the value of the relative slip constant at 100% load torque. After performing the series of load tests, it was found that the SLL is proportional to the square of the load and the dependency between SLL and frequency for different load levels is close to linear. The comparison of the efficiency values obtained by the methods IEEE 112 B and 112 E has shown a good correlation of the results. / Graduation date: 2004

Basic operation, as well as successful development, of the Brush less Doubly-fed Machine (BDFM) has been documented, and research has turned from proof of concept and early development to the more practical direction of increased manufacturability to prove industrial viability. Previous research centered on using standard induction motor stators along with a manufactured BDFM rotor. The more recent efforts center around a ground up design of an optimized BDFM prototype system including a custom converter, a custom die-cast rotor, and a custom stator, all designed specifically for a BDFM system. This paper presents the design process involved in the development of the rotor and stator of a pre-production optimized 5 hp BDFM with a die-cast rotor, from the initial evaluation of the desired specifications to design, simulation, construction, and finally to testing. Using the results of the 5 hp BDFM design, a 15 hp BDFM was designed and manufactured, and the results of that effort are included in this paper as well. This complete process, from design to testing, enables a closed loop analysis of the design techniques and tools used; the successes of the design can be affirmed and the shortcomings identified and corrected. While the primary goal of this paper is to produce two successful BDFM prototypes, the secondary goal is to improve the BDFM design process. / Graduation date: 1998

This thesis presents the development of dynamic control strategies for the brushless doubly-fed machine (BDFM). A simple open-loop scalar controller is first investigated and its response is found to be oscillatory. Using the speed feedback signal, an improved closed loop scalar control algorithm is designed. Steady state performance is controlled by the magnitude of the BDFM control winding current. Simulation and experimental results demonstrate that the closed loop algorithm has a slow response and is suitable for low performance drive applications. A model reference adaptive control algorithm is investigated in simulation, attempting to improve the BDFM dynamic response and assure its robustness against system parameter variations. Further investigations reveal that the field orientation principle for conventional induction machines can be adapted for the BDFM. This enables the design of a rotor flux oriented control algorithm, based on a newly established synchronous reference frame model. Simulation results illustrate the algorithm's fast dynamic response and robustness against parameter variations. The verification of various control algorithms is carried out on a laboratory system consisting of an experimental BDFM, a power converter and associated control hardware. An Intel 80196Kr microprocessor is used to implement inverter switching and current regulation for the BDFM control winding. The rotor flux oriented control algorithm is implemented using an Intel 80960KB floating point microprocessor, achieving a control bandwidth in the kHz-order. Evaluation of a BDFM synchronous angle shows its significance in control design, and it is incorporated into the later control algorithm development in order to eliminate electric torque estimation. This simplifies control algorithm design and is verified experimentally. Consequently, the control algorithm for the BDFM can approach the simplicity of equivalent induction machine control techniques. / Graduation date: 1996

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Multi-phase motors have several advantages over the traditional three-phase motors. In this study, the additional degrees of freedom available in five-phase permanent magnet motors have been used for three purposes: 1) enhancing the torque producing capability of the motor, 2) improving the reliability of the system, and 3) better adjusting of the torque and flux linkages of the five-phase direct torque controlled system. 1) Due to the fact that space and time harmonics of the same orders will contribute positively to output torque, a five-phase permanent magnet motor with quasi-rectangular back-EMF waveform is supplied with combined fundamental and third harmonic of currents. For modeling and analysis of the motor a 0 3 3 1 1 q d q d frame of reference is defined where 1 1q d rotates at the synchronous speed and 3 3q d rotates at the three times synchronous speed. Based on the mathematical model in the 0 3 3 1 1 q d q d frame of reference, it is shown that this system while having a higher torque density with respect to a conventional permanent magnet synchronous machine, is also compatible with vector control algorithm. 2) A resilient current control of the five-phase permanent motor with both sinusoidal and trapezoidal back-EMF waveforms under asymmetrical fault condition is proposed. In this scheme, the stator MMF is kept unchanged during healthy and faulty condition. Therefore, the five-phase permanent magnet motor operates continuously and steadily without additional hardware and just by modifying the control algorithm in case of loss of up to two phases. The feature is of major importance in some specific applications where high reliability is required. 3) High torque and flux ripple are the major drawbacks of a three-phase direct torque controlled system. The number of space voltage vectors directly influences the performance of DTC system. A five-phase drive, while benefiting from other advantages of high order phase drives, has inherently 32 space voltage vectors which permits better flexibility in selecting the switching states and finer adjustment of flux and torque. A sensorless direct torque control of five-phase permanent magnet motor is implemented. Speed information is obtained based on the position of stator flux linkages and load angle. Experiments have been conducted on a 5kW five-phase surface mount permanent magnet motor and a 3kW five-phase interior permanent magnet motor by using TMS320C32 DSP. The results obtained are consistent with theoretical studies and simulation analysis, which further demonstrate the feasibility and practical significance of the five-phase permanent magnet motor drives.

Thesis (M.S.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains viii, 112 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 110-112).

Thesis (M. Sc.)--University of Hong Kong, 1964. / Mimeographed.

With the growing interests and high requirements in low-speed linear drives, the linear machines possessing high force density, high power density and high efficiency feature become in great demands for the linear direct-drive applications. There are many available linear machine topologies, but their performances for exhibiting the high-force density capability dissatisfy the industrial requirements. In order to solve this problem, the new machine topologies emphasizing on high force density are explored and studied. The objective of this thesis is to present the design, analysis, and application of permanent magnet (PM) linear machines which can offer a higher force density at the same magnetic loading and electric loading than the conventional machines. Although in recent years there are many emerging advanced PM rotational machines for direct-drive rotational drives, the development of advanced PM linear machines for direct-drive linear drives is sparse. In spite of the motion type of electric machines, the inherent operating principle is the same. By studying and borrowing concepts of the high torque density rotational electric machines, the linear machine morphologies of the promising candidates are designed and analyzed. The problems and side effects resulting from the linearization are discussed and suppressed. Two main approaches for machine design and analysis are developed and applied, namely the analytical calculation and the finite element method (FEM). By analytically solving the magnetic field problem, the relationships between the field quantities and the machine geometry are unveiled. With the use of analytical calculation, the machine design and dimension optimization are conveniently achieved. With the use of FEM, the machine design objective and its electromagnetic performance are verified and evaluated. Finally, the proposed low-speed PM linear machine is applied for direct-drive wave power generation. By mathematically modeling the wave power, generation system and the generator, the conditions for maximum power harvesting are determined. By using the vector control, the generator output power is maximized which is verified by the simulation results. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy