Universal Coupled-Circuit Modelling Approach applied to the Brushless Doubly-Fed Induction Machine

Abstract:
This paper presents a universal coupled-circuit model for induction machines. The modelling technique is applied to the brushless doubly-fed induction machine, which is a type of induction machine with two stator windings and a special cage rotor to couple in both stator fields. The linear model considers the fields in the machine’s air gap neglecting saturation, reluctance and slotting effects. Starting from the analytic description of the windings and its current sheet distributions using a fourier-series approach, the magnetic flux density is derived and the inductance matrix is calculated. From this universal approach, a new equivalent circuit structure for the machine is derived, which shows great similarity to the equivalent circuit of the standard doubly-fed induction machine with slip rings and brushes. This proves the similar behaviour of the two machine types on a structural level. For experimental verification, measurements of no-load tests and circle diagrams with dual stator supply have been taken with a good agreement to the model.