Jérome Legranger

Combination of Finite-Element and Analytical Models in the Optimal Multidomain Design of Machines: Application to an Interior Permanent-Magnet Starter Generator

This paper proposes to apply optimal multiphysic models to the design of highly constrained electrical machines, such as interior permanent-magnet (IPM) machine intended for an automotive integrated starter generators. One of the main problems in the use of such optimal approaches remains the accuracy of the models used by the optimizer. In a recent study, we proposed a design model linked to three strong hypotheses: 1) Iron losses are calculated according to the flux density fundamental (sinusoidal approach); 2) flux densities are estimated with a saturated but decoupled d,q reluctant circuit model neglecting the cross saturation effect; and 3) thermal states are indirectly treated with a current density limit. This paper improves these models by using first the finite element method for the determination of flux and iron losses in the machine and then an equivalent thermal steady-state lumped-parameter network. These models are included in the optimization loop and so are evaluated at each iteration. The optimization method uses standard sequential quadratic programming algorithm and Sequential Simplex algorithm. A comparison between the design of an IPM machine with the previous model and the new one will be performed.

General Analytical Model of Magnet Average Eddy-Current Volume Losses for Comparison of Multiphase PM Machines With Concentrated Winding

This paper studies magnet eddy-current losses in permanent-magnet (PM) machines with concentrated winding. First, space harmonics of magnetomotive force (MMF) and their influence on magnet losses in electrical machines are investigated. Second, an analytical model of magnet volume losses is developed by studying the interaction between MMF harmonics wavelengths and magnet pole dimensions. Different cases of this interaction are exhibited according to the ratio between each harmonic wavelength and magnet pole width. Then, various losses submodels are deduced. Using this analytical model, magnet volume losses for many slots/poles combinations of three-, five-, and seven-phase machines with concentrated winding are compared. This comparison leads to classify combinations into different families, depending on their magnet losses level. Finally, in order to verify the theoretical study, finite-element models are built and simulation results are compared with analytical calculations.

Slot/pole combinations choice for concentrated multiphase machines dedicated to mild-hybrid applications

This paper presents multiphase permanent magnet machines with concentrated non-overlapped winding as a good candidate for automotive low voltage mild-hybrid applications. These machines often require a trade-off between low speed performances such as high torque density and high speed performances like flux weakening capabilities. This paper describes how to choose a key design parameter to ease this compromise, the slots/poles combination, according to three parameters: winding factor including harmonics factor, rotor losses amount thanks to a comparison factor, and radial forces balancing. The comparison criterions are based on both analytical formula and Finite Element Analysis.

Design of a Brushless Rotor Supply for a Wound Rotor Synchronous Machine for Integrated Starter Generator

Wound rotor synchronous machines present interesting performances for integrated starter generator. Nevertheless, the lack of reliability of their gliding contacts remains their main drawback. The following paper proposes to replace the gliding contacts of such a wound rotor synchronous machine by an iron silicon axial rotary transformer operating as a contactless transmission power system. The design process is based on an accurate non-linear multidisciplinary analysis model divided into a magnetic, thermal and electrical part, optimized thanks to a sequential quadratic programming algorithm. The method is applied to a particular wound rotor synchronous machine and the electromagnetic and thermal performances are subsequently confirmed using the finite element method (FEM). The optimal result indicates that the rotary transformer is a good challenger to gliding contacts in term of compactness. Other advantages and limitations of the optimal rotary transformer are discussed.

Combination of Finite Element and Analytical Models in the Optimal Multi-Domain Design of Machines : Application to an Interior Permanent Magnet Starter Generator

This paper proposes to apply optimal multiphysics models to the design of highly constrained electrical machines, such as interior permanent magnet machine (IPM) intended for an automotive integrated starter generators (ISG). One of the main problems in the use of such optimal approaches remains the accuracy of the models used by the optimizer. In a previous paper, we proposed a design model linked to three strong hypotheses : (1) Iron losses are calculated according to the flux density fundamental (sinusoidal approach); (2) Flux densities are estimated with a saturated but decoupled d,q reluctant circuit model neglecting the cross saturation effect; (3) Thermal states are indirectly treated with a current density limit. The present paper improves theses models by using first the finite element method (FEM) for the determination of flux and iron losses in the machine and then an equivalent thermal steady state lumped parameter network. These models are included in the optimization loop and so are evaluated at each iteration. The optimization method uses standard sequential quadratic programming algorithm (SQP) and sequential simplex algorithm. A comparison between the design of an IPM machine with the previous model and the new one will be performed.

Comparison of Two Optimal Rotary Transformer Designs for Highly Constrained Applications

The lack of reliability of gliding contacts in highly constrained environments induces manufacturers to develop contactless transmission power systems such as rotary transformers. The following paper proposes an optimal design methodology for rotary transformers supplied from a low-voltage source at high temperatures. The method is based on an accurate multidisciplinary analysis model divided into magnetic, thermal and electrical parts, optimized thanks to a sequential quadratic programming method. The technique is used to discuss the design particularities of rotary transformers. Two optimally designed structures of rotary transformers : an iron silicon coaxial one and a ferrite pot core one, are compared.

Analytical model of magnet eddy-current volume losses in multi-phase PM machines with concentrated winding

This paper studies magnet eddy-current losses in permanent magnet (PM) machines with concentrated winding. First of all, space harmonics of magnetomotive force (MMF) and their influence on magnet losses in electrical machines are investigated. Secondly, analytical model of magnet volume losses is developed by studying the interaction between MMF harmonics wavelengths and magnet pole dimensions. Different cases of this interaction are studied according to the ratio between each harmonic wavelength and magnet pole width (following flux density variation). Then various losses sub-models are deduced. Finally, using this analytical model, magnet volume losses for many slots/poles combinations of 3, 5, and 7 phase machines with concentrated winding are compared. This comparison leads to classify combinations into different families depending on their magnet losses level. Besides, in order to validate the theoretical study, Finite Element models are built and simulation results are compared with analytical calculations.

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.