Convertisseurs parallèles entrelacés : étude des pertes fer dans les transformateurs inter-cellules

La recherche de performances élevées (densité de puissance, efficacité, dynamique,…) a conduit ces dernières années à l'apparition de convertisseurs entrelacés utilisant des transformateurs inter-cellules. La minimisation de la taille et la réduction de pertes des transformateurs inter-cellules sont les objectifs principaux de cette étude. Les transformateurs inter-cellules deviennent encombrants à cause des fortes concentrations de flux existantes dans certaines branches du circuit magnétique. Dans les convertisseurs parallèles entrelacés, la séquence des phases d'alimentation des bobinages constitue un degré de liberté. En fonction de la topologie de transformateurs inter-cellules adoptée, deux procédés de permutation des phases d'alimentation sont proposés, visant la minimisation des flux magnétiques. Le gain obtenu en termes de pertes fer a été évalué théoriquement et expérimentalement. Les résultats obtenus valident qualitativement l'avantage de l'alimentation permutée devant l'alimentation classique. Enfin, la réalisation pratique d'un prototype de convertisseur de puissance utilisant des transformateurs inter- ellules a été abordée. Il s'agit de douze cellules permettant de réaliser un bras d'onduleur à douze cellules entrelacées ou la mise en opposition de deux bras à six cellules chacun. ABSTRACT : During the last years, high performance requirements (power density, efficiency, dynamic behavior,…) in power converters lead to the development of interleaved converters using intercell transformers. Minimization of the size of intercell transformers and the reduction of losses that occur in such transformers are the main objectives of this study. Intercell transformers become bulky because of the existing flux hotspots in certain branches of the magnetic circuit. In interleaved converters, the sequence of the phase voltages applied to the windings is a degree of freedom. Depending on the topology of intercell transformers, two methods of permutation of the phase voltages are proposed, pointing at a decrease of the magnetic fluxes. The reduction of core losses was evaluated theoretically and experimentally. The results obtained confirm the advantage of the permuted supply against the standard supply. At last, the implementation of a power converter using intercell transformers is shown. It is about twelve interleaved commutation cells which allow performing a single phase voltage inverter or testing, with opposition method, two voltage-inverter legs containing six cells each on

Convertisseurs parallèles entrelacés (étude des pertes fer dans les transformateurs inter-cellules)

La minimisation de la taille et la réduction de pertes des transformateurs inter-cellules sont les objectifs principaux de cette étude. Les transformateurs inter-cellules deviennent encombrants à cause des fortes concentrations de flux existantes dans certaines branches du circuit magnétique. Dans les convertisseurs parallèles entrelacés, la séquence des phases d'alimentation des bobinages constitue un degré de liberté. En fonction de la topologie de transformateurs inter-cellules adoptée, deux procédés de permutation des phases d alimentation sont proposés, visant la minimisation des flux magnétiques. Le gain obtenu en termes de pertes fer a été évalué théoriquement et expérimentalement. Les résultats obtenus valident qualitativement l'avantage de l'alimentation permutée devant l'alimentation classique. Enfin, la réalisation pratique d'un prototype de convertisseur de puissance utilisant des transformateurs inter-cellules a été abordée.Minimization of the size of intercell transformers and the reduction of losses that occur in such transformers are the main objectives of this study. Intercell transformers become bulky because of the existing flux hotspots in certain branches of the magnetic circuit. In interleaved converters, the sequence of the phase voltages applied to the windings is a degree of freedom. Depending on the topology of intercell transformers, two methods of permutation of the phase voltages are proposed, pointing at a decrease of the magnetic fluxes. The reduction of core losses was evaluated theoretically and experimentally. The results obtained confirm the advantage of the permuted supply against the standard supply. At last, the implementation of a power converter using intercell transformers is shown. It is about twelve interleaved commutation cells which allow performing a single phase voltage inverter or testing, with opposition method, two voltage-inverter legs containing six cells each one.TOULOUSE-ENSEEIHT (315552331) / SudocSudocFranceF

Practical model of the axial magnetic field in the end region of large turbo-generators

International audiencePurpose The axial magnetic field occurs in the end-region of large turbo-generators is known to induce hot points or voltages between laminations, that may cause insulation breakdown and thus stator faults. Design/methodology/approach It is important to dispose of simple methods for estimating the axial flux rapidly with regard to the operating point of the machine. Findings The authors provide a practical model of the axial magnetic field based on a simplified vector diagram. The parameters required to build the vector composition of the flux densities are assessed with a limited number of finite element method simulations of the whole end-region of the machine. These simulations were validated by an experimental test on a real turbo-generator. Then the axial flux density was simply estimated for various operating points. Originality/value The originality of the paper concerns the practical model of the axial magnetic field based on a simplified vector diagram

Practical model of the axial magnetic field in the end region of large turbo-generators

International audiencePurpose The axial magnetic field occurs in the end-region of large turbo-generators is known to induce hot points or voltages between laminations, that may cause insulation breakdown and thus stator faults. Design/methodology/approach It is important to dispose of simple methods for estimating the axial flux rapidly with regard to the operating point of the machine. Findings The authors provide a practical model of the axial magnetic field based on a simplified vector diagram. The parameters required to build the vector composition of the flux densities are assessed with a limited number of finite element method simulations of the whole end-region of the machine. These simulations were validated by an experimental test on a real turbo-generator. Then the axial flux density was simply estimated for various operating points. Originality/value The originality of the paper concerns the practical model of the axial magnetic field based on a simplified vector diagram

3D computation and analysis of magnetic field in the end-region of turbo-generators

This paper presents a 3D finite element model of the end region of a large turbo-generator. The analysis focuses on the axial magnetic field distribution, and its sources. This axial component may cause severe deterioration of the stator core (insulation breakdown, overheating)