What is the cogging effect of a motor What is the effect of cogging effect on a motor

Current generators all use a cogging structure, and the teeth are used to guide the magnetic field lines.

To reduce the magnetic resistance, the groove is used to inlay the windings and cross-link with the magnetic field lines in the teeth, and permanent magnet generators are no exception. The different magnetic permeability of the teeth and grooves causes the rotor to have an unequal number of magnetic field lines at different positions, aligning the stator at the poles.

The position of the teeth, ferromagnetically attracted, so that it hinders the rotation of the rotor of the permanent magnet generator, which is called the "cogging effect" and "cogging resistance moment" of the permanent magnet generator.

Because the motor adopts the cogging structure, the tooth is used to guide the magnetic field lines, reduce the magnetic resistance, the groove is used to inlay the winding and cross-link with the magnetic field lines in the tooth, the different magnetic permeability of the tooth and the groove makes the rotor have an unequal number of magnetic field lines in different positions, and the magnetic pole is aligned with the position of the stator tooth, the ferromagnetic attraction hinders the rotation of the motor rotor, which is called the cogging effect and cogging resistance torque of the motor.

Although appropriate measures can be taken to reduce the cogging effect in the design and manufacture of existing motors, it is completely impossible to completely eliminate the cogging resistance torque in the existing motor structure. The cogging effect increases the starting resistance of the motor and makes the motor run unstable, which will reduce the efficiency of the motor.

Cogging torque is the torque generated in the circumferential direction by the interaction between the magnetic field of the permanent magnet of the rotor and the cogging of the stator core. This torque is independent of the current of the stator, which always tries to position the rotor in certain positions. In variable speed drives, the vibration and noise generated by the cogging torque are amplified when the torque frequency coincides with the mechanical resonance frequency of the stator or rotor.

The presence of cogging torque also affects the low-speed performance of the motor in the speed control system and the high-precision positioning in the position control system. The method to solve the problem of cogging torque ripple mainly focuses on the optimal design of the motor body.

There are two ways to reduce the cogging effect, one is that the magnetic pole has a certain inclination relative to the main shaft, and the other is to adopt a fractional groove design structure.

Chute method: The stator chute or rotor chute is one of the most effective and widely used methods to suppress cogging torque ripple, which is mainly used for motors with a large number of stator slots and a long axial direction. In order to produce a constant electromagnetic torque, the back EMF waveform must be an ideal trapezoidal wave with a flat top width greater than 120°, and the sinusoidization of the winding back EMF caused by the chute or oblique pole will increase the electromagnetic torque ripple.

Therefore, choosing the right chute angle is the key to effectively suppressing the cogging torque ripple.

Fractional groove method: This method can increase the frequency of the cogging torque fundamental, so that the cogging torque ripple is significantly reduced. However, after the use of fractional slots, the distribution of windings under each pole is asymmetrical, so that the effective torque component of the motor is partially canceled, and the average torque of the motor will be reduced accordingly.

At present, generators all adopt a cogging structure, the tooth is used to guide the magnetic field lines and reduce the magnetic resistance, and the groove is used to inlay the windings and cross-link with the magnetic field lines in the teeth, and the permanent magnet generator is no exception. The different magnetic permeability of the tooth and the groove makes the rotor have an unequal number of magnetic field lines at different positions, and at the position of the stator tooth where the magnetic pole is aligned, the ferromagnetism is attracted, which is quietly high and even hinders the rotation of the rotor of the permanent magnet generator, which is called the "cogging effect" and "cogging resistance torque" of the permanent magnet spring generator motor. Although appropriate measures can be taken to reduce the "cogging effect" in the design and manufacture of existing generators, it is completely impossible to completely eliminate the "cogging torque" in the existing motor structure.

The cogging effect "increases the starting resistance of the generator, and also makes the operation of the motor unstable, which will reduce the efficiency of the generator. Especially in low-speed wind power applications, the "cogging effect" can greatly increase the difficulty of starting low-speed power generation, increase the threshold of breeze power generation, reduce power generation efficiency, and reduce the energy obtained by generators from the wind.