ABSTRACT
The synchronous speed and hence the rotor speed of a given induction motor depends solely on the stator voltage and stator frequency for specific load torque. When an ac voltage regulator is introduced between an ac source and motor, the motor terminal voltage can be conveniently changed to allow variable-speed operation. This scheme is simple and economical, and it is used to control the speed of fan and pump drives and to allow smooth starting of induction motors. This chapter describes theoretical concepts behind stator voltage-controlled induction motors and circuits for ac/ac conversion, as well as a discussion on speed control range with constant load torque and fan/pump drives. This chapter also features rotor resistance control and slip power recovery schemes.
