Control methods for quiet operation of permanent magnet synchronous motors

The method employed to minimize pulsating torque in permanent magnet synchronous motors (PMSM) was to measure each motor imperfection as it leaves the production line. Motor imperfections responsible for the pulsating torque include cogging torque caused by the magnets on the rotor and current. The most effective method of measuring motor imperfections was to split up the total motor noise into individual components. The pulsating torque decoupling (PTD) was done by applying a least square minimization between the electromagnetic torque generated by the current and the measured torque. The pulsating torque levels were calculated as the root mean squared value (RMS) of pulsating torque divided by the rated torque of the motor. The PTD method was found to be the best method that was capable of reducing the pulsating torque to less than 1% of rated torque. The method revealed that if the motor imperfections can be adequately determined, the noisy motor can be made to run smoothly.