No description available.

This thesis evaluates an electric vehicle with four independently-controlled in-wheel electric motors. The electric vehicle investigated in this work requires a main con- troller that not only coordinates with each individual motor drive controller, but is also needed to distribute torque and power to each in-wheel motor. The controller adjusts the speed of each motor to the driving conditions according to the require- ments and emulates the behavior of a mechanical di erential. Then, in addition to the electronic di erential controller, a simple yet robust control strategy for maximiz- ing traction force between tire and road is developed and presented. Moreover, the controller continuously senses the yaw rate and prevents over- and under-steering by adjusting the torque on the right or left wheels. Simulation and experimental results validate the proposed strategy.

There is no abstract available for this thesis.

The ideal squirrel cage motor should have a varying rotor resistance; large at standstill, and decreasing as the speed rises. Overseas - designed high impedance rotors try to fulfil these conditions - mostly used are double cage rotors and die cast aluminium rotors. However, in the South African coal-mining industry these rotors recorded high rate failures with heavy financial losses. As a result, the need for an alternative rotor type that was able to comply with basic conditions ignored before appeared on the market: • Higher reliability with extended life expectancy • Lower total ownership costs • Easy re-manufacturing with components available on the market • Specific performance stability at competitive price. Over the years, only two principles were tacitly accepted in designing squirrel cage rotors: 1. For a single cage rotor, in a circumferential direction around the rotor the squirrel cage bars are placed in the same cylindrical shell, with the same shape and same conductivity. 2. For a double cage rotor, the same rule as above applies; however, in the radial direction, the bars have different shapes and typically different conductivities. The Invention is based on a new principle, i.e. "in a circumferential direction around the squirrel cage rotor, squirrel cage bars may have different conductivities and same shapes, or different conductivities and different shapes”. Mixed Conductivity Fabricated Rotors (MCFR) are designed and manufactured based on this new principle, and are able to withstand the harsh South African mining conditions. Since patented, the invention has been materialised in a set of special rotors powering continuous miners of a reputable coal-mining house, which was spending about R5 million annually on replacing specific imported die cast aluminium rotors only. Fully complying with the above-mentioned basic conditions, the patent offers a large variety of technical and economical advantages, increasing mining processes efficiency beyond expectations. The thesis describes the MCFR's design adaptability by altering the rotor design to meet the demands of a specific engineering application as a base line of drives design. The patent is part of the new South African trend of increasing processes efficiency. It offers large possibilities of designing dedicated motors with a positive impact on the South African economy. Some socio-economical advantages are worthy of considerable study: • Being locally manufactured, the MCFR may reduce the country's economical dependence. • Requiring no special expertise, the MCFR can be produced in any quantity and size without excessive investment. • The MCFR offers an alternative option (product interchangeability) on the market as well as sound competition (with export potential). • The patent ensures business sustainability conditions which diffuse financial constraints on motor manufacturers and end-users during the re-capitalisation process (very loaded in South African economic and industrial environment). / Thesis (Ph.D. (Electrical Engineering))--North-West University, Potchefstroom Campus, 2007.

No description available.

The alternators in today's automobiles are of the claw-pole or Lundell construction, which is a readily manufactured, low-cost derivative of the conventional rotating dc field synchronous generator. The efficiency of the Lundell system is low due to a complicated magnetic circuit of predominantly solid steel and a high windage rotor structure. As the number of electrical devices in a car increases, so does the demand on the generator system. The Lundell alternator is not able to meet the demands and numerous alternative systems are under investigation. This led to the development of the brushless doubly-fed alternator system with the advantages of regulation over a wide speed range, competitive system cost based on inexpensive machine construction, low rating controller, diode rectifier and robust, low maintenance configuration. The conventional alternator has only one degree of control (de excitation), whereas the doubly-fed alternator has three control quantities: excitation magnitude, frequency and phase sequence. Excitation magnitude is used to regulate the output voltage, which leaves two control parameters to optimize efficiency over the alternator speed range. Simulation tools were developed for conducting design studies on the BDFM alternator system. Various stator and rotor configurations were studied through simulation and a few prototypes were built. A proof-of-concept prototype built in an existing induction machine frame achieved comparable efficiency characteristics to the Lundell System and exceeded the Lundell performance over part of the speed range. Significant performance improvements are expected for a new, optimized prototype which will not rely on the induction machine laminations, but will utilize custom components designed for this low voltage, high frequency application. Since the increase in automotive power demand is likely to be coupled with an increase in system voltage, a 24V, 2kW alternator system is investigated and simulation results are presented. / Graduation date: 1993

[Truncated Abstract] This thesis describes investigations carried out in the development of a wind powered generation system suitable for interconnection with a power grid ... The simplicity and flexibility exhibited by the induction machines in providing electromechanical energy conversion make it the most favoured choice for wind-powered systems operated in parallel with an existing powers system. Although not as common as the ‘squirrel cage’ induction machine, the slip-ring type has several attractive features in providing constant-frequency ac power when driven from a varaible-speed source such as a wind turbine. The fundamental energy conversion properties of the induction machine system are studied in order to determine the suitability of these systems for constant-frequency variable-speed electric power generation. Two distinct control policies are formulated: (i) optimising power from the wind when the generator is connected to an ‘infinite’ bus bar and, (ii), scheduling a constant output power irrespective of fluctuations in wind speed when the generator is operated in parallel with a ‘weak grid’.

Dissertation (Ph.D.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographic references.

Thesis (M.S.)--Ohio University, August, 1999. / Title from PDF t.p.

Thesis (M.E.) -- University of Adelaide, Department of Electrical Engineering, 1978. / Typescript (photocopy).