Design and analysis of a brushless doubly fed induction machine with rotary transformer

This paper analyses design and performance aspects of a brushless doubly fed three-phase induction machine with wound rotor circuit accessed by rotary transformer. It focuses firstly on the advantages of substituting brushes and slip-rings by rotary transformers. Secondly it shows the device operation conditions and rotary transformer calculation by using Finite Element Software in 2D domain. In sequence are presented analytical dynamic and steady state models for prediction of machine behavior. The analytical dynamic model is obtained by transforming the equations written in machine variables into equations written in arbitrary reference frame. The steady state model considers electrical circuit techniques to obtain information about current, power factor and efficiency on load. Design data of a 90kW prototype were considered for numerical results presented on this study.