Torque-ripple minimization in dc-brushless drives using a predictive control technique adapted to generic air-gap flux-density distribution

For a three-phase DC-brushless drives, the paper presents a control technique able to maintain practically constant the motor torque in steady-state operations. This optimized feature can be obtained whatever is the waveform of the air-gap flux density distribution generated by rotor magnets. Isotropic machine are considered with respect to the air-gap armature field (surface mounted magnets). On the basis of no-load induced voltages waveforms measured at constant speeds in off-line tests, simple control algorithms are carried out for either ldquotwo phase onrdquo or ldquothree phase onrdquo operating conditions; i.e. they are active also during the commutation between two consequent armature phases. These algorithms evaluate the instantaneous currents suitable to remove ripples in the torque time-behaviour. In cascade, a predictive algorithm computes the correspondent voltage reference values for the feeding VSI. For DC-brushless motors the voltage predictive algorithm is rather simple and is efficacious both in low and high speed (or load) operating conditions. An accurate numerical investigation and some experimental results are presented in order to validate the proposed control technique.