PULSE WIDTH MODULATED
INVERTER FED INDUCTION MOTOR
Due to disadvantage of cyclo converter
drive it is better to prefer PWM technique which is free from low speed torque
pulsations, low harmonic content with high efficiency.
* The main drawback of PWM technique is complex circuit and switching loss. This problem is minimized by varying output voltage, hence inverting operation is possible at all frequencies.
Frequency ratio = Inverting switching
frequency/ Inverter output
The
reduction in harmonic current is shown in wave forms compared to quasi square
wave inverter wave form.
PWM
features:
1. The
Inverter has constant circuit link voltage and eliminate harmonic.
2. The
filter can be reduced.
3. The
transfer switches used instead of thyristors.
4. By using
harmonic techniques, low order harmonics are eliminated.
5. Parallel
operation is possible on same bus.
6. The
system efficiency is effected by switching losses/
7. Torque
pulsations are minimized.
8. The drive
application is for low to medium power upto 450KVA commercial drive is available.
9. This
drive posses good transient and dynamic response.
10. There is
difficulty in controlling.
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