A novel technique for AC supply voltage and frequency modulation of induction motor drives

The paper presents a novel scheme for speed regulation, smooth starting and fast braking of induction motor drive system. The novel technique is based on inserting a chopper MOSFET switch across a six-pulse diode bridge at the neutral point of stator windings. The essence of the technique is that by chopping the stator current in an ON/OFF synchronized fashion with supply phase voltage, the stator applied voltage and its frequency are modulated causing the motor speed to change. The advantage of the new scheme is the utilization of only one controlled device switch compared with other methods which employ more than one switch. The novel speed control scheme is used to smooth-start the induction motor without large inrush current as well as control of the induction motor speed. Furthermore, the proposed scheme is attempted to brake the induction motor in fast time. Both digital simulation and experimental prototype system results of an induction motor driven by the novel scheme are presented under different loading conditions.