Robust Design for the Microprocessor-Based Indirect Field Orientation Control of a Squirrel-Cage Induction Motor

A robust design method for the microprocessor-based indirect field orientation control of a squirrel-cage induction motor is presented. The dynamic behavior of the induction motor which is controlled by usig the technique of indirect field-oriented decoupling is approximated by a mathematical model as for a shunt dc motor. The robustness of the system with respect to model uncertainty, imperfect decoupling and load variation is achieved by attaching an interaction compensator to adapt the quadrature voltage delivered by the PWM power driver. The goal of the interaction compensator which is designed by using model following technique with high gain feedback is to maintain the induction motor behaving as a precribed model as closely as possible. The time lag in measurement and computation is considered and compensated as a one-step time delay. Consequently, the indirect field orientation control is not necessarily depend on precise modelling of the motor system especially the precise measurement of the rotor time constant. Using a sixteen-bit microcomputer and a voltage source, PWM-type, power driver with current feedback, a robust motion control system is implemented for a three horse power induction motor. Results from both experiments and computer simulations are demonstrated.