Velocity fluctuation suppression of non-ideal PM synchronous motors

The problem with indirect torque control of brushless motors is that the commutator issues high frequency control signals which may not be precisely followed by the current controller due to its finite bandwidth. As a result, pulsation torque may appear at high velocities even though the commutator is calibrated to perfectly compensate the motor´s position nonlinearity. This paper describes a modification to the commutation law based on Fourier coefficients in order to eliminate the velocity induce torque ripple. This is made possible by expressing the motor´s current waveform as a function of not only the rotor angle but also the velocity and taking into account the amplifier dynamics model in the control design. A case study is appended that illustrates the proposed commutator nested inside a motion controller is able to eliminate the pulsation torque and velocity fluctuation at high velocities even if a low bandwidth amplifier is employed.