A CURRENT SOURCE INVERTER-FED CONSTANT AIR GAP FLUX CONTROLLED SQUIRREL CAGE INDUCTION MOTOR DRIVE

ABSTRACT

In this thesis, a current source inverter fed squirrel cage induction motor drive at constant air gap flux is presented. The drive scheme is conceived to take advantage of the short circuit withstand capability of the current source inverter and the ruggedness (even under harsh conditions) of the squirrel cage induction motor. The variable inverter input dc link current is derivable from either a controlled ac to dc converter or a controlled dc to dc converter. The constant motor air gap flux control drive scheme has inner dc link current control loop and an outer motor speed control loop that maintains the motor slip frequency constant for a given motor load torque. The closed loop control parameters are selected such that negligible torque pulsation and relatively fast motor speed response are obtained without the need for an inverter output capacitor filter. A 400V, 10hp, 1440rpm, 50Hz squirrel cage induction motor is used to simulate the motor drive scheme in Matlab-Simulink environment. For step changes in demand (reference) speed at no load torque and at load torque equals to or less than the motor rated torque, the drive response has relatively fast settling time and acceptably low overshoot/undershoot over the motor speeds not exceeding the rated value.