Article: What is Torque Ripple and Cogging Torque in Electric Motors

Measuring torque is a very important aspect of the electric machine industry. Torque ripple is periodic disturbances in torque, and causes noise vibration. Noise vibration is an important factor to control in machines and so identifying and analyzing torque accurately is essential in the work of electrification engineers.

What is Torque Ripple?

Torque ripple is a periodic disturbance in torque, and so it is not a static value. Torque is often seen as an average value, such as that which is shown by the black line in the top graph. However, torque has a frequency component and an amplitude component. It is an AC imposed over DC value, caused by excitation and construction.

Torque is often misunderstood because it is looked at when heavily filtered. The bottom graph shows a load step for a torque signal. But by looking at the instantaneous torque in red, it is clear that the torque has frequency and amplitude.

Even when approaching the steadier state, the torque ripple has frequency and amplitude. If this signal is heavily filtered, which we see in the black, all of these frequency and amplitude details are missed, as well as dynamics. Even a little filtering can distort the torque ripple signal and cause missed information.


EPT Measuring Torque Ripple