## 1 Introduction  
Induction Machines (IMs) are promising electrical motors used in industry and for electric vehicles thanks to their performance, high efficiency, low cost and almost free maintenance. Recently, the systems including power converters and electric motors have been widely used for electric vehicles. The acoustic noise generated by the IM drive as a variable-speed drive becomes a problem for the living environment, and even a slight noise may cause discomfort. The audible range of humans is generally from 20 Hz to 20 kHz. In recent years, the acoustic noise emitted by electric motors has been the subject of numerous studies. The acoustic noise sources can be grouped into four types: mechanic, aerodynamic, magnetic, and electronic [1, 2, 3]. Our work focuses on the study of electronic noise and accordingly in switching harmonics sources. The flux harmonics in the air gap of an IM create radial forces in the stator frame. Thus, these harmonics cause excitation forces that have a detrimental effect on the machine structure. Consequently, the considerable emission of vibration and noise can be engendered, which makes the machine more troublesome to operate. Generally, there are three main reasons for the harmonics in the air-gap flux reported in the literature:  
* Spatial harmonics due to the non-sinusoidal repartition of coils in the stator and the rotor. * Harmonics in the air-gap permeance, which depend on the number and geometry of the stator and rotor slots, the geometry of the teeth in both the stator and the rotor, and the permeation in the iron core. * Harmonic current in the stator coil. IM-driven solid-state inverter drive systems are full of harmonics since their power voltages are non-sinusoidal. The harmonics absorbed by the stator coils generate additional stator flux density components--hence the additional force waves to be produced. Voltage-Source Inverter (VSI)-fed IMs produce disagreeable acoustic noise caused by current harmonics at the inverter output. Consequently, these harmonics are narrow-band components located around the inverter switching frequency and its multiples. Furthermore, an analysis of the harmonic spectrum of the voltage or current can determine and define the frequencies and amplitudes of the different harmonics at the inverter output. In fact, noise intensity depends on the harmonic spectrum of the inverter output, which is also correlated to the Pulse Width Modulation (PWM) strategy control applied to the inverter. Motor drives modulated with such PWM methods invariably emit discrete/tonal noise, which is irritating to the human ear. Numerous PWM techniques have been developed and proposed in the literature. Sine PWM (SPWM) and Space Vector PWM (SVPWM) are well-known fixed-switching frequency PWM methods applied in industry. Using the SPWM strategy, the inverter harmonic is concentrated in distinct zones located around the switching frequency and its integer multiples. However, the SVPWM strategy has the advantage of high voltage utilization and can offer reduced current. Moreover, the harmonics are decreased and are concentrated around the integer multiples of the VSI switching frequency compared to the SPWM strategy. The acoustic noise emitted by an IM fed by a PWM inverter remains very interesting, considering the numerous articles published lately. The author in [4; 5] elaborated on an experimental procedure to determine the acoustic and vibration behavior of SVPWM-modulated IM drives over a range of carriers and modulation frequencies. An advanced SVPWM scheme with a special type of switching sequence was also reported in [6] to reduce the acoustic noise in low and medium-speed ranges of the motor drive. A lot of researchers have recently published and investigated the Random PWM (RPWM) technique in order to reduce the tonal bands around the multiple of the switching frequency with fixed PWM and disperse them over a wide range of frequencies.