OPTIMAL LOW SWITCHING FREQUENCY MODULATION OF A FRONT-END INVERTER FEEDING INDUCTION MOTORS

In power converters, PWM techniques generally offer acceptable spectral shapes for load currents only if high switching frequencies are adopted. In medium-high power applications, in order to reduce the EMI and commutation losses, the basic goal of the modulation strategies must be the minimization of the harmonic distortion by keeping, at the same time, the switching frequency to a low value. In the paper, this feature is achieved for an ac drives by adopting a front-end inverter structures. In fact, the possibility of achieving variable dc link voltages allows to perform an optimization procedure which drastically reduce the motor current harmonics working with very low value of the switching frequency. The proposed technique has been validated by means of an experiment analysis and a performance comparison with a traditional space vector modulation technique. A full EMC analysis is also performed to evaluate radiated and conducted emissions.