Minimum torque ripple pulse width-modulation with reduced switching frequency for multi-megawatt motor drive

In this paper, the characteristics of ripple current of multi-megawatt induction motor fed by a PWM inverter is investigated. And, based on the investigation a novel PWM scheme is devised to reduce the switching loss of the inverter under the same torque ripple of the induction motor. The proposed PWM is composed with two parts. One is Minimum Torque Ripple Pulse-Width Modulation (MTRPWM) which is optimized in terms of minimum torque ripple in high Modulation Index. The other is a part to decide a minimum switching frequency while keeping the average torque ripple under the allowable value at the various operating conditions. It is named RSF. Consequently, only changing PWM method from conventional fixed switching frequency CPWM to the proposed PWM with RSF, the switching loss of inverter driving 3.5MW induction motor has been reduced by 51.6%, when MI is 1.12.