Abstract:
It has become a common practice for the industry to use vector control technique in
induction motor control.In this method stator current space vector is decoupled into
two components in synchronously rotating reference frame where one component pro-
vides control over
ux and the other controls the torque in an independentent way like
a DC machine.That is why, With the help of this control technique the induction mo-
tor can ll the role of a separately excited dc motor.Existence of commutator, brushes,
brush holders in dc motor makes dc motor drive less reliable as it calls for time to
time maintenance.Henceforth the main e ort is to replace DC motor by an induction
motor and merge the advantages of both the motor together into the variable speed
brushless motor drive and eliminate the associated problems. The squirrel cage induc-
tion motor being simple, rugged, and cheap, and requiring less maintenance , has been
widely used for xed speed applications.So implementation of vector control technique
ia an attractive solution for creating two independent channel so as to control
ux and
torque independently which in turn makes the induction motor from a non-linear to
linear plant.However, the essential requirement for the proper operation of the vector
controller is precise knowledge of rotor
ux position which demands a speed sensors (e.g
shaft mounted tacho-generators, resolvers,search coils or digital shaft position encoder).
These cause the system to be less reliable and loses beni ts of an induction motor drive
as well. Sensorless vector control came as a solution of the aforesaid problem in which
the speed is estimated using some of the estimation methods rather than using speed
sensors. In this dissertation work a scheme of open loop speed estimator using stator
voltage and current and MODEL REFERENCE ADAPTIVE SYSTEM(MRAS) based
speed estimators are proposed and simulated in Simulink/Matlab environment and per-
formance of these schemes are evaluated on various operating conditions.
