Elevator Motor Magnets

Elevator motor magnets have become very popular options in elevator applications. This is due to their increased efficiency and performance characteristics. However, this type of PM motors require a variable frequency drive (VFD) to know the position of the rotor in relation to a stator pole pair to modulate at the correct commutation angle to produce maximum torque output.

The VFD uses the encoder to determine the position of the rotor and then calculates the commutation angle necessary to maximize torque output by applying current to the motor at the right amplitude. If the encoder is incorrectly mounted or if the phasing of the encoder channels is mismatched, this can cause the VFD to have difficulty knowing the rotor's position in relation to the stator pole pairs and may result in the motor drawing high current or not turning at all.

As the number of poles increases in a permanent magnet synchronous motor, the mechanical degrees between pole pairs must decrease in order to achieve the same torque output. For example, a 6-pole motor will have 120 mechanical degrees between pole pairs and a 20-pole motor will have 36 mechanical degrees between pole pairs.

Therefore, it is important to shift the torque ripple frequency of the permanent magnet synchronous motor during constant-speed running from the resonance frequency of the mechanical system of the elevator in order to avoid car vibration and reduce passenger discomfort. This can be achieved in the prior art by increasing the number of poles and the number of slots of the permanent magnet synchronous motor.

In addition, it is also possible to increase the frequency of cogging torque and torque ripple by selecting the number of salient poles. Then, the frequencies of these two types of torque ripple and cogging torque can be shifted from the resonance frequency of the mechanical system in order to prevent the car vibration that is generated during constant-speed running.

Furthermore, it is possible to improve the stability of the permanent magnet synchronous motor in terms of the ability to stop. This can be done by selecting the number of salient poles in the permanent magnet synchronous motor and ensuring that the frequency of the torque ripple and the cogging torque of the permanent magnet synchronous motor match the resonance frequency of the mechanical system at a speed of about 1/2 or less of the rated speed.

It is a very simple technique to implement and the results are quite impressive. In general, it is only a matter of choosing the number of poles and the number of salient poles so that the torque ripple and cogging torque of the permanent magnet synchronized motor will match the resonance frequency of the mechanical system at the rated speed of the elevator.

In the embodiment of this invention, an embedded permanent magnet is used in the rotor back yoke of the permanent magnet synchronous motor. This structure allows the permanent magnet to be directly fixed in the rotor back yoke without requiring a dedicated mounting member or an adhesive. It can save manufacturing time and cost and also provides a more stable permanent magnet synchronous motor.