Application of Slope PWM Strategies to Reduce Acoustic Noise Radiated by Inverter-Fed Induction Motors

In this paper, two strategies based on the slope pulsewidth modulation (PWM) technique are applied to acoustic noise reduction in inverter-fed induction motors. This generated technique uses a trapezoidal modulator wave with a triangular or a sinusoidal carrier signal. The main advantage of the proposed method is that only two control parameters are necessary to achieve a voltage spectrum configuration that helps reduce radial electromagnetic forces. One of them modifies the amplitude of the modulated output of the inverter, and the other controls the frequency spectrum distribution. Small changes to these parameters can yield a wide range of electrical spectra that allow for selective acoustic harmonic reduction. Thus, it is possible to avoid the overlap of radial forces produced by the MMF time harmonic frequencies of the inverter and the radial forces produced by the MMF space harmonic frequencies due to the discretized distribution of stator winding in slots of the motor, maintaining the number of pulses per period chosen. Also, it can help to avoid activating the resonances due to the mechanical natural frequencies. Results are checked experimentally and compared to those of other PWM techniques.