Improvement of start up torque of three phase induction motor operating with single phase supply

This paper addresses a new single-phase starting technique of a three phase induction motor. Indeed, three-phase induction motors operating with a single-phase ac supply are not self starting of their own, hence an external device must be used to get them started. The former starting technique with capacitor is often used. So, in this paper a simple and low cost single-phase to three-phase converter is proposed in order to start up a three phase induction motor operating with a single-phase ac supply. The goal is to improve the starting performances such as high starting torque and low inrush current. The device is based on the use of naturally firing thyristor or ac bidirectional switches (triacs), from which rotating magnetic field is created using the Discrete Frequency Control (DFC) of the switches. Instead to start up with capacitor, a low generated frequency with a single phase supply allows start up with high starting torque. The effectiveness of the proposed starting method has been verified by both simulation and experimental results.