Advanced Model for Multiphase Generators

The current development of generators and power electric drives is characterized by increased power electronic integration. This evolution concerns particularly the variable speed power units allowing both a higher performance and substantial savings on cost but nevertheless, it implies new constraints and difficulties in term of interaction between the various components: generator, converter and network. The design and optimization of such generators is no longer possible with the same approach and same tools as for conventional machines directly connected to a symmetrical three-phase network. This Ph.D. study is related to an industrial project which was developed by ALSTOM in the same time frame in which this thesis work was prepared. Since the project relies on a new high power synchronous generator topology (a multiphase turbo-generator connected to a three phase network via a power electronic converter), not many studies were done especially because of the enormous financial resources required by such studies and limitations in respect of the maximum power that a power electronic device can commute. The goal of this study is the development of an advanced multiphase machine model which can be used in a complex system comprising power electronic elements. The model has to accurately consider the physical phenomena which are taking place in a machine while functioning in such conditions. The selected approach for the development of the machine model is a combined numerical-analytical approach. This solution was preferred since it can take benefit from the precision, a property which is characteristic to the numerical Finite Element Methods (FEM), but also from the fast computation times which is a property of the analytical models. The model presented in this thesis is based on the differential inductance parameter. The differential inductances are calculated analyzing the results of FEM simulations and are used afterwards in analytically expressed circuit equations. The machine circuit equations, having as parameters the differential inductances, are afterwards solved numerically. In order to take advantage of the existing elements necessary for the analysis of the electrical power networks (including power electronic converters), the developed method was integrated into a network simulation software package. This simulation software package was designed for industrial use where a short computation time is desired; the module with the integrated machine model is respecting this principle.