Method for reducing cogging torque effects of an electrical permanent magnet machine

A system, comprising:

• an electrical permanent magnet machine including a rotor and a stator;
• a drive coupled to the machine;
• a sensor configured to generate a vibration signal representing vibrations resulting from cogging torque;
• a processor coupled to the drive, the machine, and the sensor;
• wherein the processor is configured to:
• run at least two tests of the machine with at least two different cogging compensation signals from the drive, one of the tests being designated an “a” test and another of the tests being designated a “b” test;
• determine the amplitude and phase responses of the signal for each of the tests;
• multiply a complex cogging amplitude of the cogging compensation signal applied during the “a” test with a complex amplitude of the vibration signal generated during the “b” test to compute a first value;
• multiply a complex cogging amplitude of the cogging compensation signal applied during the “b” test with a complex amplitude of the vibration signal generated during the “a” test to compute a second value;
• divide a difference between the first value and the second value by a difference between the complex amplitudes of the vibration signals generated during the “b” test and the “a” test to compute a desired complex cogging amplitude;
• and
• apply a cogging compensation torque to the machine based on the desired complex cogging compensation amplitude.

An apparatus, comprising:

• an electrical permanent magnet machine;
• a drive configured to control the speed of the machine;
• a controller coupled to the drive, the controller configured to monitor the speed and load of the machine, and to provide cogging compensation values to the drive, each cogging compensation value being based on:
• a quotient of
• a difference of
• a product of a complex cogging amplitude of a compensation signal applied during a first test of the machine with a complex amplitude of a vibration signal measured during a second test of the machine and
• a product of a complex cogging amplitude of a compensation signal applied during the second test with a complex amplitude of a vibration signal measured during the first test;
• and
• a difference of the complex amplitudes of the vibration signals measured during the second test and the first test.