The rugged and relatively inexpensive Induction Motor is becoming increasingly important for use in high performance servo motor systems. This thesis describes the complete design and implementation of an all digital Field Oriented Controller for a 1.5 KW Squirrel Cage Induction Motor. The classical steady state motor model and dynamic models in both D.Q. and Space Vector format are presented. A specific controller structure is selected, and tuned using Discrete-time design techniques. The Field Weakening technique is analytically investigated. Methods for rotor air-gap flux vector determination are reviewed. The sensitivity of the controller forward path to variations in the rotor time constant is studied. Equations for the corresponding errors in the torque and in the machine excitation level are derived. Simulation results, predicting the overall performance of the controller on the full, non-linear and cross-coupled D.Q. model of the motor are given. The influences o f Rotor Time Constant variations and P.W.M. amplifier non-linearities on the Stall Torque dynamics are experimentally evaluated. Steady state oscillations are found to exist in the developed Stall Torque. It is shown that these are caused by the Cross Over Delays introduced by the P.W.M. amplifier and represent the key problem in the use of Induction Motor based servo systems in Low Speed and Position Control applications. Further, it is proven that these non-linear effects have major implications on the stability o f Field Oriented Controllers with the Voltage Source Inverter Fed Induction Motor.
Metadata
Item Type:
Thesis (Master of Engineering)
Date of Award:
1988
Refereed:
No
Supervisor(s):
McCorkell, Charles and Devitt, Frank
Uncontrolled Keywords:
Engineering design; Induction motors; Control systems