Pulse-width modulation (PWM)
The technique that lets discrete switches synthesise a smooth voltage waveform.
- Explain pulse-width modulation (pwm) at engineering level
- Read the numbers that define the behaviour
- Apply the idea to a real drive unit
Overview
Pulse-width modulation is how an inverter, using switches that are either fully on or fully off, produces an effective voltage that can be anything in between.
In depth
Lab: Adjust PWM
Trade current ripple, audible noise and switching loss against each other.
Pulse-width modulation synthesises a sine wave from a chopped DC bus. The duty cycle sets the average voltage; the carrier frequency sets how finely it is chopped. A higher carrier gives lower ripple and pushes acoustic noise above the audible band, but every extra transition costs energy.
Carrier frequency trade-offs
A higher carrier (switching) frequency gives smoother current, lower audible noise (pushed above the audible range) and finer control — but every additional switching event burns energy, so switching loss rises roughly linearly with carrier frequency.
Key takeaways
- PWM builds an effective analogue voltage from discrete switch states.
- Higher carrier frequency smooths current but raises switching loss.
- Space-vector PWM extracts more usable voltage from the same DC bus.
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