DISTINCTION BETWEEN SWITCHED
RELUCTANCE MOTOR AND THE VARIABLE RELUCTANCE STEPPER MOTOR
The
conduction angle for phase currents is controlled and synchronized with the
rotor position, usually by means of a shaft position sensor.
Thus SR
motor is exactly like a brushless dc motor. But the stepper motor is usually
fed with a square-wave of phase current without rotor position feedback.
SR motor
is designed for efficient power conversion at high speeds comparable with those
of the PM brushless dc motor. The stepper motor is usually designed as a torque
motor with a limited speed range.SR motor is more than a high-speed stepper
motor. Its performance and low manufacturing cost make it a competitive motor
to PM brushless dc system.
1. Merits of SRM
1. Construction
is simple and robust, as there is no brush.
2. Rotor
carries no windings, no slip rings and brush-less maintenance.
3. No
permanent magnet, neither in the stator nor in the rotor.
4. Ventilating
system is simpler as losses takes place mostly in stator.
5. Power
semiconductor switching circuitry is simpler.
6. No
shoot-through fault is likely to happen in power semiconductor circuits.
7. Torque
developed does not depend upon the polarity of the current in the phase
winding.
8. The
operation of the machine can be easily changed from motoring mode to generating
mode by varying the region of conduction.
9. It is
impossible to have very high speeds.
10. Depending
upon the requirement, the desired torque speed characteristics can be tailor
made.
11.
It is a self-starting machine.
12. Starting
torque can be very high without excessive inrush currents.
2. Demerits of SRM
1. Stator
phase winding should be capable of carrying the magnetizing current also, for
setting up
the flux
in the air gap.
2. For high
speed operations, the developed torque has undesirable ripples. As a result it
develops undesirable acoustic losses (noise).
3. For high
speeds, current waveform also has undesirable harmonics. To suppress this
effect alarge size capacitor is to be connected.
4. The air
gap at the aligned axis should be very small while the air gap at the
inter-polar axis should be very large. It is difficult to achieve. No
standardized practice is available.
5. The size
of the motor is comparable with the size of variable speed induction motor
drive.
6. Number of
power wires between power semiconductor circuitry and the motor and the number of
control cables from one controller to the power semiconductor circuitry are
more and all to be properly connected.
7. It
requires a position sensor.
3. Application of SRM
1. Washing
machines
2. Vacuum
cleaners
3. Fans
4. Future
automobile applications
5. Robotic
control applications
Related Topics
Privacy Policy, Terms and Conditions, DMCA Policy and Compliant
Copyright © 2018-2024 BrainKart.com; All Rights Reserved. Developed by Therithal info, Chennai.