Carrier Signal — PWM (Carrier)
The periodic sawtooth or triangle wave that the speed reference is compared against to generate the PWM pulses. Its frequency sets the switching frequency; its shape affects where the pulses sit within the period and therefore the shape of the current ripple.
Generating PWM is really just a comparison: if the instantaneous value of the carrier is below the reference, the output is on; if it is above, the output is off. As the reference rises the pulse widens and the duty cycle increases.
The carrier shape offers two main options. With a sawtooth carrier the pulse is anchored to one end of the period; it is simple to generate and the edge always occurs at the same instant. With a triangle (symmetric) carrier the pulse sits in the middle of the period and the two edges are symmetric about it. The symmetric placement lowers the peak of the current ripple somewhat and makes the noise spectrum more predictable.
Another practical detail is shifting the carriers relative to one another in multi-channel drivers. Channels that switch at the same instant draw one large current pulse from the supply line; shifted carriers spread that pulse out in time, reducing the load on the bus capacitor and the voltage ripple on the supply line. This also helps RF receivers working next to the motor cable.
Where this term is used: DC Motor Driver Selection Guide
Do not confuse: what is described here is the sawtooth or triangle wave that generates the PWM pulses in a motor driver. For the carrier in radio communication, see the Carrier Signal (RF Carrier) entry.