Performance Analysis of a Brushless Doubly Fed Machine with Asymmetrical Composite Flux Barrier/Magductance Rotor

In this article, an asymmetrical composite rotor featuring flux barrier and short-circuited coil magductance is proposed for the brushless doubly fed machine (BDFM). A qualified magnetic field modulation effect, cross-coupling capability, and reduction of unproductive high-order summation modulated harmonics under asynchronous modulations are provided by the design. First, compensation for the phase shift caused by the magductance of short-circuited coils from the rotor is achieved through an asymmetrical configuration based on the newly proposed vector magnetic circuit theory. On this basis, the operating principle, modulation operator, and modulation capability of the proposed composite rotor are evaluated. Analytical investigation such as various airgap field harmonics prediction is accomplished. In addition, torque contributions of effective airgap harmonics and torque component composition are achieved based on the theoretical evolution. For further improvement of modulation airgap field and cross-coupling efficiency, as well as reduction of output torque ripple, parameter adjustments are considered globally. Thus, a typical 4/2 pole pair BDFM featuring asymmetrical composite flux barrier/magductance rotor is subjected to multiobjective optimization based on sensitivity analysis. A proof-of-concept prototype of the optimized BDFM is fabricated, and the corresponding experimental results are provided to verify the effectiveness of theoretical analyses.