Analytical Analysis and Performance Characterization of Brushless Doubly Fed Machines With Multibarrier Rotors

The brushless doubly fed reluctance machine (BDFRM) with a multibarrier rotor has shown great promise in applications where high reliability and low maintenance cost are required, such as offshore wind turbines. This paper presents a systematic analytical analysis and performance characterization of the BDFRM with a multibarrier rotor. First, the airgap magnetomotive force distributions under both open circuit and loaded condition are detailed, based on which a more practical rule than the widely accepted vertical bar p(1) - p(2)vertical bar not equal 1 is derived to effectively avoid the unbalanced magnetic pull in suchmachines. Analytical formulas different from those for slip-ring doubly fed induction machines are then obtained to estimate inductance parameters for circuit modeling and control purposes. Design equations for initial sizing and torque density comparison are also developed, with achievable torque density discussed. Both finite-element analysis and experimental tests are conducted to validate the effectiveness of the presented analysis.