Qualitative analysis: Brushless Wound-rotor [Synchronous] Doubly-Fed Electric Machine for electric propulsion

Experts theorized that a Brushless Wound-rotor [Synchronous] Doubly-fed Electric Machine System (BWRSDF), which can symmetrically motor or generate with variable speed, provides higher efficiency, higher power density, higher torque density, and lower cost than any other electric machine system, including the permanent magnet electric machine system, but only with the discovery of a practical brushless real time control solution for its known issues of instability and the multiphase slip-ring assembly that continually eludes state-of-art control methods, such as Field Oriented Control (FOC). Comprising a dual-ported transformer circuit topology with the attractive characteristics common to the advanced induction electric machine system, such as versatility, robustness, field weakening, practically unconstrained torque and power rating, simplicity, and low cost, etc., but with higher efficiency and torque than the permanent magnet electric machine system, the fully electromagnetic core of the BWRSDF uses readily available technology and materials without the market volatility, safety and reliability issues of rare-earth permanent magnets.