An effective control technique for shaft-torque smoothing in DC-brushless drives with arbitrary shape of air-gap magnetic field

An high performance control technique of dc-brushless drives is presented in the paper, with the aim to considerably reduce current and torque ripples. The proposed control algorithms are very simple and are separately pointed out for “two phase on” and “three phase on” operations, i.e. either far or during the commutation of two consequent armature phases. They can be successfully used in those dc-brushless drives which uses permanent magnet motors with any arbitrary shape of the air-gap flux-density distribution generated by rotor magnets. A magnetically isotropic motor configuration can be considered with respect to the air-gap field generated by the armature m.m.f. The smoothing torque control procedure is a “current control technique” operating in two cascaded phases. As first step it evaluates the value of the instantaneous reference current able to reduce to zero the torque oscillations magnitude. Afterwards, a simple model-based predictive algorithm computes the voltage reference values for the PWM motor supplying inverter. As in many other applications, the voltage predictive control provides better performance than PI or hysteresis controller because more homogeneous results can be yield for low and high speed (or load) operating conditions. Some cases-study are numerically investigated in order to validate the proposed control technique.