Patent ID: 8541968

Claim:
A method for reducing cogging torque effects of an electrical permanent magnet machine where the machine is connected to a drive, and where the drive includes a feature of adding a torque component independent of a torque generated by a speed regulator, the machine having a rotor and a stator, the method comprising: measuring an angular position of the rotor relative to the stator and an angular speed of the rotor by use of a sensor; running at least two tests with at least two different cogging compensation signals from the drive where one of the tests is designated an “a” test and another of the tests is designated a “b” test; analyzing a received signal from the sensor to find corresponding amplitude and phase responses of a vibration signal for said tests; calculating a first value by multiplying a complex cogging amplitude of the compensation signal applied for the “a” test with a complex amplitude of the vibration signal representing vibrations resulting from cogging torque of the “b” test; calculating a second value by multiplying a complex cogging amplitude of the compensation signal applied for the “b” test with a complex amplitude of the vibration signal representing vibrations resulting from cogging torque of the “a” test; calculating a desired complex cogging compensation amplitude by dividing the difference between said first value and said second value by a difference between the complex amplitudes of the vibration signals representing vibrations resulting from the “b” test and the “a” test; and applying a cogging compensation torque to the machine based on the desired complex cogging compensation amplitude.