Indirect Field Oriented Control of an Induction Motor Sensing DC-link Current with PI Controller

This paper describes an analysis method for achieving control torque and speed with indirect field oriented control for induction motors. An indirect field-oriented output feedback motor PI controller is presented; it is suitable for low-cost applications. A current model control is used to sense back electromotive force (back-EMF) by means of an analog to digital converter; its simulation and filtering are discussed. A Current model is the core of this work, but other system modules are analyzed such the proportional-integrative (PI) controller, the indirect field control with pulse width modulation and others. The paper also shows that PI controller is not an intelligent controller nor is the slip calculation accurate. Therefore, changes in rotor time constant degrade the speed performance. Another main problem in variable speed ac drives is the difficulty of processing feedback signal of the outer loop in the presence of harmonics.