Increasing awareness of industrial noise pollution and emerging stricter standards have made noise an important topic of research in electric machines. This work is a state-of-the-art review on the identification of noise sources and techniques to mitigate noise. It points the reader to relevant research in the past on acoustic noise identification and mitigation techniques. The paper also describes the current standards and practices and some of the suggestions in literature to intensify these standards. The paper summarizes the emerging future directions in acoustic noise mitigation studies.

Noise in electric machines: a review

A novel randomized control strategy for three-phase voltage source inverters, based on voltage space vectors, is described. An implicit asymmetrical modulating function results in switching losses in the inverter being reduced by about half in comparison with those using the classic space vector pulsewidth PWM method. The pulse rate is varied within individual 60/spl deg/ sectors of the vector plane, so that the power spectra of the output voltage are spread over a wide frequency range and acquire a continuous part. Relevant theoretical analyses, computer simulations and experimental results are presented.

Space vector PWM technique with minimum switching losses and a variable pulse rate [for VSI]

A novel PWM technique for three-phase voltage-controlled power inverters, based on the concept of voltage space vectors, is described. The minimum-loss, variable pulse rate (MLVPR) strategy, employing an implicit asymmetrical modulating function, results in the switching losses in the inverter reduced by half in comparison with the classic space vector PWM method. The pulse rate is varied from one 60/spl deg/ sector of the vector space to another, which produces spread, partly continuous spectra of the output voltage of the inverter. Theoretical analysis and results of experimental investigation of a prototype modulator are presented. >

Space vector PWM technique with minimum switching losses and a variable pulse rate

Voltage source inverters (VSIs) supply nonsinusoidal voltages to induction motor drives, leading to line current distortion and torque pulsation. Conventional space vector pulsewidth modulation (PWM) techniques are widely used in VSIs on the account of good waveform quality and high dc bus utilization. In a conventional space vector PWM technique, the switching sequence begins with one zero state and ends with the other zero state in a subcycle. Some novel switching sequences have been proposed, which employ only one zero state but apply one of the two active states twice in a subcycle. One pair of such special switching sequences has recently been shown to reduce the pulsating torque considerably. In this paper, the conventional and special switching sequences are compared experimentally in terms of acoustic noise. In the low- and medium-speed ranges, the special switching sequence is seen to reduce the amplitude of the tonal component of noise at the switching frequency considerably and is also found to result in spread spectrum.

Experimental Investigation on the Effect of Advanced Bus-Clamping Pulsewidth Modulation on Motor Acoustic Noise

Random pulse width modulation (RPWM) approaches can make the harmonic spectrum of inverter output voltage be continuously distributed without affecting the fundamental frequency component, and thus the acoustic noise and mechanical vibration of an inverter-fed AC motor drive are greatly reduced. However, the analysis and design of the RPWM mechanisms are generally not so trivial for practical engineers that their applications are limited. In this paper, a random frequency PWM (RFPWM) inverter and its practical design procedure are presented. First, the effects of the attributes of a random signal on the inverter output harmonic spectrum distribution characteristics are analyzed using an intuitive concept, then based on which, the quantitative design. Simulink simulation and implementation of the proposed RFPWM inverter are introduced. The proposed RFPWM inverter is employed to power an indirect field-oriented induction motor drive. The simulated and measured results indicate that the uniform random distribution of inverter output harmonic spectrum and thus smaller acoustic noise and mechanical vibration are obtained by the proposed RFPWM scheme.

Analysis, design, and implementation of a random frequency PWM inverter

The first part of the paper describes the relationship between inverter output voltage and radial magnetic force on the inner surface of the stator, which generates vibrations of the stator and causes the magnetic noise. The theoretical results are verified experimentally. In the second part the authors derive the frequency components of the pulse width modulated (PWM) and pulse frequency modulated (PFM) voltage and of the magnetic noise. This is the basis for a calculable spreading of the spectrum by means of PFM, shown in the third part. The purpose is noise reduction and elimination of selected harmonics to avoid mechanical resonances. >

T. Eilinger

Papers

Spectral analysis of the sinusoidal PWM with variable switching frequency for noise reduction in inverter-fed induction motors