The loads on the electrical systems of automobiles are projected to increase significantly in the near future. This will result in a requirement for improved efficiency over the present-day car alternators. An alternative scheme proposed at Oregon State University employs a Brushless Doubly-Fed Machine (BDFM) as an alternator. This thesis begins with a study and characterization of the existing car alternator system. The configuration of the proposed scheme is discussed. In the proposed configuration, the power winding of the machine generates the bulk of the power and the control winding provides the excitation. The power winding feeds a power rectifier, which in turn charges the battery in an automobile. The control winding is supplied through an inverter. Issues related to inverter and rectifier design are discussed. A 3-phase pulse width modulated inverter and a bridge rectifier were developed and tested for performance. A PSPICE simulation model for the rectifier was developed and results are compared with laboratory tests. A Voltage Regulator Circuit (VRC) and an Efficiency Maximizer Unit (EMU) for the system are designed and developed. A prototype alternator system is tested and the principle of efficiency maximization is verified. Finally. the comparative performance of the the existing and the proposed system is discussed and some recommendations for further improvements in the prototype system are made. / Graduation date: 1992

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