Electric Motor Torque Ripple

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.

Electric motor torque ripple.

The power produced by the motor depends on the speed of the motor and is zero at 0 speed and. It is an issue with all motors but there are differences. What is torque ripple and cogging torque in electric motors. Torque ripple is a periodic disturbance in torque and so it is not a static value.

Torque ripple is created by harmonics in the electromagnetic torque which exist in all electric machines regardless of type or design. Measuring torque is a very important aspect of the electric machine industry. The harmonics are created by non idealities in the electromagnetic fields produced by the rotor and stator interaction. Torque is often seen as an average value such as that which is shown by the black line in the top graph.

Most commonly the rotor is attached to the load and spins as a result of repulsion between the magnetic field of the rotor and the magnetic field of the stator see figure 1. However torque has a frequency component and an amplitude component. In electric machines we often want to understand the efficiency and dynamics. Due to the nature of the interaction between the magnetic fields of the rotor and the stator described above torque ripple varies sinusoidally.

Torque ripple is an effect seen in many electric motor designs referring to a periodic increase or decrease in output torque as the motor shaft rotates. The driving force of an electric motor is torque not horsepower. It is an ac imposed over dc value caused by excitation and construction. In a motor the magnitude of this lorentz force a vector represented by the green arrow and thus the output torque is a function for rotor angle leading to a phenomenon known as torque ripple since this is a two pole motor the commutator consists of a split ring so that the current reverses each half turn 180 degrees.

The torque is the twisting force that makes the motor running and the torque is active from 0 to 100 operating speed. Torque ripple is periodic disturbances in torque and causes noise vibration. In order to keep the motor turning the magnetic orientation for the rotor must switch directions periodically. Since torque is not a static value it is preferred to have a highly accurate averaged measurement.

Measuring torque with high accuracy bandwidth and resolution is particularly important for designing a controller and implementing an electric motor solution. Torque ripple the result of cogging torque is a variation in torque production referred to as torque ripple that occurs when the motor is energized with constant current. Measuring torque ripple hbk provides industry leading testing and measurement equipment for evaluating torque ripple and analyzing the surrounding complexities.