Synchronous servomotor fed by a PWM inverter-analysis and compensation of the low frequency torque ripple

In the classical control of electrical drives fed by a pulse-width modulation (PWM) power converter, the inverter is considered as a simple transmission gain corresponding to the average modelling approach. This modelling is reasonable in many cases but shows its limits as the PWM period increases and becomes significant compared to the electrical and mechanical time constants of the machine. In this case, with classical controllers (PI, for example), a low frequency torque ripple appears