Design and Analysis of a Brushless Doubly-Fed Induction Machine With Dual-Stator Structure

This paper explores the feasibility of an intuitive solution for torque density improvement of conventional brushless doubly-fed induction machine by introducing dual-stator structure. A general purpose torque density equation for dual-stator topologies is developed to initialize the key dimensions and, more importantly, evaluate the torque capability of specific designs. The topological requirements for enhancing torque capability are derived. The relationship between torque capability and key design parameters, such as pole pair combination, split ratio, and turn ratio between outer and inner rotor windings, is revealed. A design example with detailed design procedure is presented to provide the designer a practical way to make initial calculation of machine dimensions and parameters. Moreover, finite element analysis is carried out to deduce the characteristics of the machine. Experimental results of a 7.5-kW prototype machine are given to verify the design and analysis.