Electric Motor Torque Ripple

It is an issue with all motors but there are differences.

Electric motor torque ripple.

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. Torque ripple is periodic disturbances in torque and causes noise vibration. 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. It is an ac imposed over dc value caused by excitation and construction.

Since torque is not a static value it is preferred to have a highly accurate averaged measurement. Torque is often seen as an average value such as that which is shown by the black line in the top graph. What is torque ripple and cogging torque in electric motors. 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.

In electric machines we often want to understand the efficiency and dynamics. The power produced by the motor depends on the speed of the motor and is zero at 0 speed and. However torque has a frequency component and an amplitude component. 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 webinar will present topics including torque ripple background and measurement the impact on electric power measurements and correlation to nvh. Torque ripple is a periodic disturbance in torque and so it is not a static value. Torque ripple although the specifics of motors vary widely the basic components are a rotor and a stator see tutorial. Measuring torque is a very important aspect of the electric machine industry.

The torque is the twisting force that makes the motor running and the torque is active from 0 to 100 operating speed. Due to the nature of the interaction between the magnetic fields of the rotor and the stator described above torque ripple varies sinusoidally. Measuring torque with high accuracy bandwidth and resolution is particularly important for designing a controller and implementing an electric motor solution. 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.

The harmonics are created by non idealities in the electromagnetic fields produced by the rotor and stator interaction. In order to keep the motor turning the magnetic orientation for the rotor must switch directions periodically. The driving force of an electric motor is torque not horsepower.