Design of a novel field controlled constant voltage axial flux permanent magnet generator for enhanced wind power extraction

Abstract

Wind energy systems with permanent magnet generators, especially axial flux permanent magnet generators (AFPMG), have been quite popularly studied and employed recently. However, a known shortcoming of such systems is that they can operate efficiently only in a very limited range of wind speeds, which corresponds to about 70 to 110% of the rated speed of the generator employed and the energy available outside of this wind speed bracket is not accessed at all, and in fact, wasted. Moreover, the absence of any means of excitation control to maintain a regulated output voltage under varying speed conditions calls for expensive power converters. This study presents a novel methodology to obtain a constant output voltage from an AFPMG under varying wind conditions, through the integration of field poles and their control, along with modifications in stator winding. This significantly enhances the power extraction capability of the system over a much wider operational range (corresponding to 25–125% of the rated speed) while eliminating the requirement of a DC–DC converter to maintain constant output voltage. The details of the design of the constant voltage AFPMG and the results establishing the effectiveness of the methodology have also been presented.