Michel Hecquet

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.

Modeling of a claw-pole alternator using permeance network coupled with electric circuits

We propose in this paper, a modeling and simulation method of electrical machines by electric-magnetic coupled network, based on the Bond-Graph models and permeance network. The proposed approach allows us to easily take into account nonlinearities such as saturation and simple hysteresis effects, and to obtain forces applied on the teeth, with a simulation time very weak compared to the finite element method. This method is very interesting for three dimensional studies of typical machines, as for example: a claw-pole alternator. >

Prediction of Audible Magnetic Noise Radiated by Adjustable-Speed Drive Induction Machines

This paper presents a fully analytical model of the electromagnetic and vibro-acoustic behavior of variable-speed squirrel-cage induction machines. This model is integrated in a fast simulation tool that can be used to design motors with low magnetic noise level on their whole speed range.

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.

Design and simulation of turbo-alternators using a coupled permeance network model

The modeling of a turbo-alternator using permeance network is described. This approach allows implementing electrical and magnetic coupling as well as mechanical coupling. Such processes as saturation, movement, and three-dimensional (3-D) effects are taken into account. The aim of this study is to set up a design model of 10-100mW turbo-alternators. The method of taking into account of 3-D effects is described. The first results of simulation were obtained. The experimental measurements validate the model

Simulations of synchronous machines using a electric-magnetic coupled network model

A dynamic modelling and simulation method of electrical machines by an electric-magnetic coupled network is presented. Its main advantages are to take into account many phenomena such as saturation effects and the rotor movement, with a good compromise between calculation time and accuracy of results. A general dynamic model is implemented using a new solver specifically developed for a coupled permeance network. It was applied to the study of two kinds of machine, a permanent-magnet motor and a claw-pole alternator. Main results are presented and compared to experiments.

Time variation of forces in a synchronous machine using electric coupled network model

Radial forces between the stator teeth and rotor claw inside a claw-pole alternator are investigated. Typically three dimensional, the complete machine has been modelled as a coupled electric and magnetic circuit, with the aim of saving simulation time. Radial forces are obtained for several rotation speeds and stator currents. These results are compared with those of a 3D finite element analysis package, considered as reference results. A few typical results are also compared with measurements. Accuracy is sufficient to assess that the permeance network models, taking into account nonlinearities such as magnetic saturation, electronic commutations and rotor movement, realise a good compromise between simulation time and precision.