Comparison Between Direct and Indirect Field Oriented Control of Induction Motor

Vector control, also called fieldoriented control (FOC), is a Variable frequency Drive (VFD) control method in which the stator currents of a 3 phase induction motor are identified as two orthogonal components that can be visualized with a vector. The vector control of induction motors is one of the most suitable and popular speed control technique presently used. The vector control technique decouples the two components of stator current space vector: one providing the control of flux and the other providing the control of torque. The two components are defined in the synchronously rotating reference frame. With the help of this control technique the induction motor can replace a separately excited dc motor. The scalar control technique is simple to implement but have the coupling effect ultimately responsible for the sluggish response, which leads to instability due to higher order system effect. The DC motor needs time to time maintenance of commutator, brushes and brush holders. The main effort is to replace DC motor by an induction motor and merge the advantages of both the motors together into variable speed brushless motor drive and eliminate the associated problems. The squirrel cage induction motor being simple, rugged, and cheap and requiring less maintenance, has been widely used motor for fixed speed application. The induction motor is transformed from a non-linear to linear control plant. It is expected that with increasing computational power of the DSP controllers, it will eventually nearly universally displace scalar volts -per-Hertz (V/f) control. In this paper we will come to know the concept of vector control and different types of vector control techniques available. And finally we will be able to compare them. Key words-Induction Motor, Vector Control, Scalar Control, Sluggish, Higher Order System Effect, DSP.