Discontinuous PWM Strategy with Frequency Modulation for Vibration Reduction in Asynchronous Machines

Abstract

The aim of this paper is to present our research into the reduction of vibrations in induction motors. The use of power inverters results in the generation of electrical harmonics, which increase the level of the mechanical vibrations of electrical machines. To reduce these harmonics, we present a discontinuous pulse-width modulation (PWM) control strategy based on carrier-wave modulation applied to multilevel inverters. Using the proposed modulation technique, the amplitude of the electrical harmonics is reduced, as compared to other conventional techniques. These current harmonics produce the MMF (magnetomotive force) harmonics in the air gap, which are one of the main sources of vibrations. The control strategy makes it possible to vary the electrical spectrum at the output of a multilevel inverter by modifying a control parameter of the carrier wave in the PWM, thus avoiding the natural frequencies of mechanical resonance. The proposed technique also has the feature of attenuating the total harmonics distortion of the voltage of the multilevel inverters, as well as the achievement of a higher RMS value of the output voltage for the same DC level. Laboratory results for an induction motor with different modulation strategies, applied in a multilevel inverter and compared to the strategy presented, are attached.

Optimal Hybrid Pulse Width Modulation for Three-Phase Inverters in Electric Propulsion Ships

“…Discontinuous pulse-width modulation (DPWM) has been an optimal solution to these problems [13][14][15][16][17]. It can reduce the number of switchings and, hence, losses by clamping the switch to ON or OFF depending on the position of the reference signal.…”

“…DPWM has been applied to reduce motor noise, wherein the switching frequency was set to a higher audible frequency range [13]; however, this increased the switching losses. A DPWM that reduces noise and switching losses [14] was utilized to reduce the vibrations in induction motors. DPWM minimizes the motor's magnetomotive force (MMF), thereby preventing mechanical resonance and reducing vibration.…”