An Improved Scalar Controlled Drive Based on Steady State Model of Vector Controlled Drive for Squirrel Cage Induction Motor

An improved scalar controlled induction motor drive is proposed. The improvement is based on the incorporation of the steady state model of the rotor flux oriented vector drive into the scalar drive. This is achieved by dropping the time varying terms in the dynamic vector model of the motor to zero and then merging the reduced model into the scalar model. As a result, it becomes possible to formulate close form expressions for the stator voltages encapsulating the motor parameters and to keep the magnetizing current constant without putting any constraint on the voltage to frequency ratio. As a result, the magnetizing current can be controlled more precisely in a close loop scalar control drive with speed feedback, and it becomes feasible to start the motor with full load torque applied which is difficult to achieve in the conventional scalar control. Simulation and experimental results are presented using a fractional horsepower squirrel cage induction motor coupled to a dc generator. A comparison of the proposed drive with the conventional scalar drive is also given.