Ripple Suppression of BLDC Motors With Finite Driver/Amplifer Bandwidth at High Velocity

Abstract

The excitation currents of a brushless dc motor can be preshaped by an electronically controlled commutator based on position feedback so that the motor delivers ripple-free torque and simultaneously minimizes copper losses. However, at high rotor velocity, the commutator issues high frequency control signals which may not be precisely followed by the motor driver/amplifier 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 brief 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.