Brushless Self-Excited Synchronous Field-Winding Machine With Five- and Higher-Phase Design Using Independently Controlled Spatial Harmonics

Abstract

Electric machines used in a variety of sustainable energy applications need to possess high power density, high efficiency, and low manufacturing cost. While permanent-magnet machines and synchronous field-winding machines are the popular option for variable-speed drives, these topologies have undesirable aspects. The magnets in permanent-magnet machines are typically made of rare-earth materials which have high price volatility and are prone to demagnetization, risking machine operation. The synchronous field-winding machines require additional electrical and mechanical components requiring regular maintenance and replacement and add extra volume, weight, and cost to the drive system. In this dissertation, a novel brushless self-excitation scheme for synchronous field-winding machines is presented. This scheme uses an AC stator with five or higher phases to create two independently controlled rotating magnetic fields at different spatial harmonics, allowing indepen- dent magnetic coupling with different rotor windings. The rotor of the proposed machine possesses a field winding, transformer windings, and a diode rectifier that converts induced AC voltages in the transformer windings into a DC voltage for the field winding. A design for a five-phase sta- tor configuration is developed using finite-element analysis tools, and simulation results are pre- sented. Torque and power characteristics of the design are compared with similarly-sized interior permanent-magnet and induction machines.