Vincent Lanfranchi

Characterization and Reduction of Audible Magnetic Noise Due to PWM Supply in Induction Machines

This paper derives the analytical characterization of the Maxwell radial vibrations due to pulsewidth modulation (PWM) supply in induction machines and, particularly, in traction motors supplied with an asynchronous switching frequency. The number of nodes and the velocity of these particular force waves are experimentally validated by visualizing some operational deflection shapes of the stator. It is shown that according to the switching frequency, these forces can be responsible for high magnetic-noise levels during starting and braking. A simple rule to avoid PWM noise is then proposed and applied to an industrial traction motor. Experimental results show that the choice of the switching frequency can have a 15-dB impact on the sound power level emitted by the motor during starting and that a lower switching frequency can sometimes lead to lower magnetic noise. In agreement with analytical predictions, the new proposed switching frequency that avoids resonances between PWM exciting forces and corresponding stator modes reduces the magnetic noise of 5 dB during starting.

Multiphysics Modeling: Electro-Vibro-Acoustics and Heat Transfer of PWM-Fed Induction Machines

The design of variable-speed electrical machines involves several fields of physics, such as electromagnetism, thermics, mechanics, and also acoustics. This paper describes the analytical multiphysics models of a computer-aided-design software which is applied to inverter-fed traction induction machines. The electromagnetic model computes rotor and stator currents, the induction-machine traction characteristics, and the radial air-gap flux density. The mechanical and acoustic models compute the motors audible magnetic noise level due to Maxwell forces. The thermal model based on 3-D nodal network computes the transient temperature of different parts of the motor. These fast models make it possible to couple the software with some optimization tools. Some simulation results are presented on a self-ventilated closed motor and compared to experiments.

Multiobjective Optimization of Induction Machines Including Mixed Variables and Noise Minimization

Induction motor design requires making numerous tradeoffs, especially when including electromagnetic noise criterion besides usual criteria like efficiency and cost. Moreover, adding the noise objective significantly increases computational time as it must be evaluated at variable speed in order to take into account resonance effects. In that case, the application of multiobjective optimization algorithms can be hard for their computational cost as for the difficulty to interpret multidimensional results in both design variables and objectives spaces. This paper first describes a fast analytical model of a variable-speed induction machine which calculates both motor performances and sound power level of electromagnetic origin. This model is then coupled to Nondominating Sorting Genetic Algorithm (NSGA-II) in order to perform global constrained optimizations with respect to several objectives (e.g., noise level, efficiency and material cost). As induction machine design involves both continuous and discrete variables, a modified NSGA-II algorithm handling mixed variables is detailed. Finally, some optimization results are presented and analyzed by the aid of several visualization tools.

Coupled Numerical Simulation Between Electromagnetic and Structural Models. Influence of the Supply Harmonics for Synchronous Machine Vibrations

An automatic and fast numerical coupling method between 2-D electromagnetic and 3-D structural FEM software is presented. The described coupling method permits to compute the electromagnetic noise in electric machines for different realistic alimentation currents. Thanks to this tool, the strong influence of the supply harmonics on the acoustic level of a synchronous machine is clearly shown. This method has been developed for a wound rotor synchronous machine (WRSM) but can be applied for any non-skewed machines. First of all, the global principle of the study and the magnetic noise theory is briefly introduced. Then, computation algorithms coupling magnetic forces to structural mesh are developed and finally simulation results show the influence of supply harmonics on global vibration levels.

Characterization and Reduction of Magnetic Noise Due to Saturation in Induction Machines

This paper derives the analytical characterization of Maxwell radial vibrations due to saturation effects in induction machines, and especially in traction motors. The number of nodes and the velocity of these particular force waves are experimentally validated by visualizing some operational deflection shapes of the stator. It is shown that according to the stator and rotor slot numbers, and stator natural frequencies, these forces can be responsible for high magnetic noise levels during starting and braking. A simple rule to avoid saturation magnetic noise is then proposed, and applied to an industrial motor. Simulation results show that the new proposed motor improves magnetic noise level up to 20 dB, whereas experiments give a 15 dB improvement.

Optimal Slot Opening Width for Magnetic Noise Reduction in Induction Motors

This paper presents a method to characterize the main magnetic force waves occurring in a sinusoidally fed induction machine. Three main force types are identified: slotting force waves, winding force waves, and saturation force waves. Slotting force waves are characterized in terms of number of nodes, velocity, propagation direction, and magnitude. On the ground of the expression of these forces magnitude, a method to cancel a given magnetic force wave by properly choosing the rotor slot or stator slot opening width is presented. This new method is validated with both simulations and experiments. Contrary to the common design rule that advices to decrease rotor and stator slot openings width in order to reduce magnetic noise, it is shown that a wider slot opening can lower the global noise level when properly chosen.

Multiphysics modeling: electro-vibro-acoustics and heat transfer of induction machines

The design of electrical machines involves several fields of physics, such as electromagnetism, thermics, mechanics but also acoustics. This paper describes the analytical multiphysics models of a computer-aided design (CAD) software which is applied to inverter-fed traction induction machines. The electromagnetic model computes rotor and stator currents, the induction machine traction characteristics, and the radial airgap flux density. The mechanical and acoustic model computes the motor audible magnetic noise level due to Maxwell forces. The thermal model based on 3D nodal network, computes the transient temperature of different parts of the motor. These fast models make it possible to couple the software with some optimization tools. Finally, some simulations are presented on a self-ventilated closed motor, and an example of multi-objective optimization is exposed.

Influence of temperature on the vibro-acoustic behavior of claw-pole alternators

Audible noise of automotive alternators is a key point for future cars. Its reduction requires a multiphysic approach including electromagnetic, vibro-acoustic and thermal aspects. In this perspective, this paper investigates the influence of stator temperature on the acoustic noise of a claw-pole alternator. Experimental results show a clear reduction of sound power level and change in noise peak frequencies with an increased temperature. An experimental modal analysis of the stator is carried out to explain this effect. Based on these measurements, a model is developed to predict the resonant frequencies of the wound stator at different temperatures.

Vibro-Acoustic Simulation and Optimization of a Claw-Pole Alternator

This study aims at minimizing the acoustic noise from a magnetic origin of a claw-pole alternator. This optimization is carried out through a multiphysics simulation, which includes the computation of magnetic forces, vibrations, and the resulting noise. Therefore, a mechanical model of the alternator has to be developed to determine its main modes. Predicted modal parameters are checked against experimental results. Based on this model, the sound power level is simulated and compared with measurements. Finally, the rotor shape is optimized and a significant reduction of the noise level is found by simulation.

Vibro-acoustic simulation and optimization of a claw-pole alternator

This study aims at minimizing the acoustic noise from a magnetic origin of a claw-pole alternator. This optimization is carried out through a multiphysic simulation which includes the computation of magnetic forces, vibrations and the resulting noise. Therefore, a mechanical model of the alternator has to be developed to determine its main modes. Predicted modal parameters are checked against experimental results. Based on this model, the sound power level is simulated and compared with measurements. Finally, the rotor shape is optimized and a significant reduction of the noise level is found by simulation.