Industrial Engineer · phase 10 of 16
PWM
Pulse-Width Modulation, an inverter switching method that controls effective motor voltage and frequency by varying pulse timing.
The Explain card
- Plain English
- Pulse width modulation is how the inverter makes a variable voltage out of a fixed DC bus. It switches the bus on and off very quickly, and the width of each pulse sets the average voltage the motor feels.
- Example
- To make a sine wave, the drive sends wide pulses near the peak and narrow pulses near the zero crossing. The motor's inductance smooths the pulses into a nearly sinusoidal current.
- Why it matters
- PWM is why a drive is efficient and why its output is a train of sharp edges rather than a clean sine. Those edges are the source of reflected waves, bearing currents and the whine you hear from the motor.
- Hook
- Fast on and off, averaged into whatever voltage you asked for.
Where it sits in the deck
Phase 10: VFD Electrical and Motor Fundamentals
The physics under the parameters: slip, torque, flux, and the relationship between frequency and voltage that every drive is really controlling.
