Current Ripple
It is the oscillation of the motor current around its average value within the PWM period. Its amplitude is roughly determined by ΔI = V × t / L: it shrinks as the switching frequency rises or as the motor inductance grows. It directly affects heating and torque oscillation.
The motor current rises during the on phase of the PWM and falls during the off phase. The sawtooth-shaped oscillation these two movements create is an additional component riding on the average current. Although motor torque depends on the average current, the heating effect depends on the effective (RMS) value; large ripple means more heat at the same average current.
Three factors determine its amplitude: the applied voltage, the pulse duration and the winding inductance. Using 24 V instead of 12 V increases the ripple at the same frequency. Doubling the frequency, on the other hand, halves the pulse duration and so reduces the ripple by roughly half.
In practice, keeping the ripple in the range of 10–30 percent of the average current is a common design target. Above that, vibration at low speeds and audible hum become noticeable. In small, low-inductance motors a higher switching frequency is needed to keep the ripple at an acceptable level, and that in turn increases the driver's heat budget.
Context where this term is used: DC Motor Driver Selection Guide