A quick transition electronic winding changeover technique for extended speed ranges

In many applications it is often needed to extend the constant power range of an induction motor. In order to extend the constant power range without sacrificing the torque capability at higher speeds, the wye/delta switchover method was adopted and still remains popular in spindle drives for machine tools. Other techniques for extending the constant power range include use of modified machines with taps that are selected to achieve the desired speed-torque characteristic. All techniques that employ mechanical contactors have limited life and are associated with dead time in the range of tens to hundreds of milliseconds due to mechanical constraints. Power electronic versions for the contactors have been proposed but most methods are rather complicated and involve many switching devices. Pole amplitude modulation (PAM) and pole phase modulation (PPM) have also been proposed but these techniques require additional inverters. This paper describes a novel and simple switching technique involving only two three-phase diode bridges and two IGBT switches to extend the constant power range of induction motors. The proposed method requires a center tap to be placed in each phase of the motor and access to the ends and the center tap making the motor a nine-lead machine. The proposed method and the circuit used to extend the constant power range is described and supported by experimental results.