This study presents the performance analysis and testing of a 250 kW medium-speed brushless doubly-fed induction generator (DFIG), and its associated power electronics and control systems. The experimental tests confirm the design, and show the system's steady-state and dynamic performance and grid low-voltage ride-through capability. The medium-speed brushless DFIG in combination with a simplified two-stage gearbox promises a low-cost low-maintenance and reliable drivetrain for wind turbine applications.

5A design procedure for the Brushless Doubly Fed machine is based on equations derived from a simplified equivalent circuit. 6The method allows the many variables in the design of this machine to be handled in straightforward way. Relationships are 7 given for the division of slot area between the two stator windings and for the design of the magnetic circuit. The design method 8 is applied to a frame size 180 machine. In particular, calculated values for flux densities in the machine have been verified by 9 time stepping finite element analysis for actual operating conditions. The approach outlined can also be used as part of a design 10 optimization routine.

A procedure has been established for obtaining equivalent circuit parameters for the Brushless Doubly Fed Machine (BDFM), also known as the Brushless Doubly Fed Induction Machine (DFIM), by transforming a reduced coupled-circuit model into a sequence component form. This approach takes advantage of the model reduction procedure's ability to reduce a complex rotor structure to a single equivalent loop without significant loss of accuracy. An alternative method based on winding factors has also been developed and includes coupling via harmonic fields. Parameters determined in both ways are in close agreement with those determined from Finite Element Analysis (FEA) and experimentally. The advantages of each method is discussed in the conclusion section.