Industrial electronics
Before / after
Motor Speed Control Before and After VFDs
Before VFDs, factories wasted energy just to slow a motor down
Quick check · tap an answer to continue
Lesson notes
Key points
- Before, induction motors ran at fixed speed, so flow was throttled with valves while the motor kept drawing full power.
- A VFD rectifies AC to DC, then a PWM inverter rebuilds AC at any frequency, so motor speed follows frequency.
Takeaway: VFD: rectify, smooth, invert at a chosen frequency to set speed.
Quick check: What quantity does a VFD vary to change induction motor speed?
- Supply frequency
- Rotor resistance
- Number of poles
Induction motor synchronous speed is proportional to supply frequency.
Fixed-speed motorsVariable frequency drive
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