ABSTRACT

Nur Aminah, Induction Motor Speed Control System Design with a Quantitative Feedback Theory (QFT) Method (supervised by Rhiza S. Sadjad and Muhammad Tola).

The Quantitative Feedback Theory (QFT) method of robust control system design is implemented to an Indirect Field Oriented Control (FOC) model of a three-phase 3 X 280 VA, 380 V induction motor. The linearized model of the plant derived from its steady-state dq-model is an open-loop second order transfer function relating the output of speed w to the reference input current iqs. The dynamic effects of load variations and input-output disturbances are shown by a simulation.

The structure of the controller consists of a feedback path of the speed w compared to the pre-filtered reference input and a compensator. The QFT method is applied to determine the pre-filter and the compensator transfer functions. The feedback gain is assumed to be unity, the robust margin bound is 1.2, and the input disturbance rejection is set to be less than 0.01 for w < 10 rad/sec. The simulation of the control system shows that the dynamic effects of load variations and input-output disturbances are significantly reduced. However, the introduction of noise in the feedback path cannot be avoided.