Effects of approximating back emf of a brushless DC motor from trapezoidal to sinusoidal

Modelling of brushless dc motors has received wide attention in literature over the last three decades. Many of the reported works in this area have approximated the trapezoidal back emf of the machine as sinusoidal. This work investigates the effects of this approximation on average torque, torque ripple, rms torque, % torque ripple, speed ripple, rms speed, % speed ripple and rms current. The result show that the parameters vary with load except for average torque and speed. The rippling components vary drastically with load and the approximation doesn´t have any prominent effect on dynamic torque vs. speed characteristics.