Abstract:
Speed control of Induction Motors has been widely carried out with the aim of
saving on energy, cost reduction and performance improvement of the motors and
various methods have been used. Scalar control method which involves magnitude
variation of the control variable is easy to implement. Its performance is however
sluggish due to coupling e ect of torque and
ux which are functions of current
and frequency. A big drop in torque also occurs at lower speeds due to higher
drop in the stator impedance. Vector control method which involves magnitude
and phase variation of the control variable improves on the dynamic performance
of the motors. To implement this method, rotor speed has to be measured and a
speed sensor is therefore required. Introduction of the speed sensor increases the
cost, size and complexity of the motor drive system. A sensorless vector control
system has also been developed where the rotor speed is estimated rather than
measured. This method requires the model equations of the motor which, for
the Single Phase Induction motor (SPIM), are complex due to unequal resistance
and inductance in the main and auxiliary windings. The estimation process also
introduces errors in the system and this has an e ect on the overall e ciency of
the system. This work presents a practical approach which aims at addressing
the problems encountered in the already existing methods. The method involves
the design and implementation of a Fuzzy Logic speed controller for the SPIM
with magnetostrictive amorphous wire as the speed sensor. The sensor is in form
xvi
of a thin magnetostrictive amorphous wire in a pick-up coil and therefore it is
expected that the issues of motor drive cost, size and complexity will be addressed.
The performance of the sensor is tested and compared to the conventional digital
tachometer. Fuzzy logic control technique is employed due to its ability to handle
non-linearities, its independence on the plant's model and fast response. The
controller is tested for di erent speeds of the SPIM at no load condition. The
volts per hertz with feedback scalar control is employed in this work due to its
ease of implementation.
