Design of a Low-Harmonic-Content Wound Rotor for the Brushless Doubly Fed Generator

The rotor structure is one of the key factors affecting the performance of the brushless doubly fed machine (BDFM). This paper presents a “double-sine” wound rotor for the brushless doubly fed generator to reduce the harmonic contents of the rotor winding. Ideally, so-called double sine is to make the magnetomotive force (MMF) space vector in one set of three-phase symmetric windings only containing two sinusoidal-waveform magnetic fields of different pole pairs. According to the principles of tooth harmonic and sinusoidal winding, the double-sine winding is designed to be constituted by double-layer unequal-turn coils. The design procedure and rules are given in detailed with the design example. The steady-state performance of a 60 kW prototype generator with double-sine wound rotor is analyzed by the simulation and experimental test, and the validity of the design method for proposed rotor structure is verified.