Modification of the Single-Phase AC Induction Motor to the Low-Speed Single-Phase AC Permanent Magnet Generator

Abstract

This paper discusses the design of the low-speed single-phase AC permanent magnet generator through the modification of a squirrel cage single-phase AC induction motor. Both rotor and stator of the single-phase AC induction motor are modified. Eight permanent magnet poles are embedded in the rotor so that generator will rotate at a relatively low speed of 750 rpm and produce an sinusoidal AC voltage with a frequency of 50 Hz. The total number of stator windings and slots remains the same: four stator windings and 36 stator slots. However, the number of turns for each stator winding is increased to 600 turns. Therefore, each stator slot is housing 150 conductor turns. The permanent magnet generator is expected to generate an sinusoidal AC output voltage with a magnitude in the range of 110 -115 V when it rotates at 750 rpm. Laboratory tests with a constant speed of electric motor drive have been conducted. Results of the no-load test show that generator output voltage is 110 V when it rotates at 749.3 rpm. However, the output voltage generated is not sinusoidal as indicated by its total harmonic distortion (THD) value of 15.8%. Results of the on-load test show that generator voltage drops vary from 8.2% to 29.1% and 4.5% to 26.4% respectively on linear resistive and non-linear load. On the same loading condition, the generator efficiency varies from 53.5% to 66.7% and 32.6% to 67.5%.