Pulse width modulation technique with harmonic injection in the modulating wave and discontinuous frequency modulation for the carrier wave to reduce vibrations in asynchronous machines.

Abstract

A new carrier-based pulse-width modulation (PWM) technique to control power inverters is presented in this study. To generate the output waveform, this technique compares a harmonic-injection modulating wave and a frequency-modulated triangular carrier wave. The instantaneous frequency for the carrier wave is adjusted according to a periodic function synchronised with the fundamental term of the modulating wave. The main motivation for using this technique compared to a classic PWM sinusoidal technique revolves around the reduction of total harmonic distortion, the reduction of the distortion factor and the shift of temporal harmonics to higher frequencies for any modulation frequency order. Experimental results show that it is possible to optimise the time harmonics generated to minimise vibrations produced by an induction motor when it is fed with a DC/AC converter controlled by the proposed control strategy. This is made possible by using a control parameter that modifies the instantaneous frequency of the carrier wave without modifying the number of pulses per period of the modulating wave, i.e. the mean value of the carrier wave frequency. The proposed technique is applied to an open loop-controlled inverter that operates an induction motor, helping to reduce the vibration levels produced.