Reduction of torque pulsations by inductance harmonics identification of a permanent-magnet synchronous machine

It is usual, for controlling permanent-magnet synchronous machines, to assume the electromotive forces (emf), the self and mutual inductances variations sinusoidal with respect to the angular rotor position. This leads to sinusoidal fed currents. However, such an assumption is not valid in practice and leads to torque ripples. In this paper we propose a nonlinear current control strategy which reduces the torque pulsations. Firstly, we show that nonlinear control which consists in imposing sinusoidally fed currents is not suitable to obtain a constant torque which is free of pulsations. The adopted approach imposes fed currents references computed on the basis of a model with nonsinusoidal variations of the e.m.f. and of the inductances of the machine. Then a nonlinear control law is designed for the instantaneous fed currents in the (d,q) rotating frame based on a simplified model of the machine. Furthermore, as the inductance harmonics are not well known, an identification scheme for its dominant parameters based on the synchronous detection technique is presented. Finally, the performances of the proposed scheme are illustrated by computer simulations.