Practical Evaluation of a Brush-less DFIG Employing a Rotary Transformer

Doubly fed induction generators (DFIGs) traditionally employ slip-ring and brush assemblies for rotor excitation, requiring frequent maintenance and impacting reliability. This study explores the use of contact-less energy transfer systems like rotary transformers as alternatives. Due to the low rotor frequency (<15 Hz), the rotary transformers can be quite large as its size is inversely proportional to its operating frequency. Alternatively, connecting the DFIG in rotor-tied configuration to the grid can increase rotor frequency, enabling the use of more compact rotary transformers. This paper presents measurement results of a three-phase rotary transformer coupled with an 18.5kW DFIG, highlighting advantages of stator-tied and rotor-tied configurations over traditional slip-ring operation.