A novel rotor configuration for brushless doubly-fed induction generators

Brushless Doubly-Fed Induction Generator has attractive features to be the first choice in next generation of wind generators. However, its efficiency and power-to-weight ratio are slightly lower in comparison to induction machine with the same rating. Considerable part of these imperfections arises from the rotor design, which produces magnetic field with considerable undesirable spatial harmonics. This paper proposes a novel rotor configuration to reduce spatial harmonic distortion of air-gap magnetic field as well as improving some drawbacks of the conventional structure, including unequal magnitudes of rotor bar currents, teeth saturation at low average air gap magnetic fields, high core loss and inefficient magnetic material utilization. The rotor loops are connected in series in the new scheme rather than nested arrangement of the conventional design. Furthermore, the Imperialist Competitive Algorithm is used for optimising the conductor distributions in order to improve spatial distribution of the rotor magneto-motive force. The rotor current is evaluated in each iterative step using electric equivalent circuit. The analytical procedure of determining the circuit parameters is modified for the case of series loops. Effectiveness of the novel configuration is verified by comparing the results of optimised and conventional designs in several experimental and simulation studies.