Characterisation of the mechanical motor parameters for a permanent magnet synchronous motor using induced torque harmonics

Determination of mechanical motor parameters is often desirable for accurate control of permanent magnet synchronous motors. A good example where these parameters are needed is when the torque is reconstructed from velocity measurements as in [3]. The method proposed in this paper allows the determination of the mechanical motor parameters while the motor is operating. This is done by inducing torque harmonics at frequencies that are not excited by the normal operation of the motor and measuring the velocity response. By using the reference current waveform methods described in [6] this excitation can be done without the use of a torque sensor. Results show that the determined moment of inertia varies by a standard deviation of less than 1 % over the operating range. The viscous friction, once normalised by the velocity and torque setpoints also varies by a standard deviation of less than 1%. The accuracy of this method has been further demonstrated by comparing the torque reconstructed using the determined parameters with the measured torque.