A Brushless Doubly Fed Machine for use in an Integrated Motor/Converter, Considering the Rotor Flux

The Brushless Doubly Fed Machine (BDFM) has received considerable attention recently, particularly in respect of analysis and performance as it has potential application where variable speed operation is required but limitations of cost and size demand a reduced-size converter. Any application of the BDFM in this way must accept a reduced speed range. A low rating use of such technology could be as an Integrated BDFM Motor/Converter where the application does not require a full speed range. This paper explores this application by assembling a prototype Integrated BDFM Motor/Converter from a commercial two-speed induction Motor, with modified rotor, and a commercial, first quadrant, PWM Converter. The design of the Motor affects the rating and operation of the Converter, in particular the balance between the stator winding MMFs, the design of the rotor slotting & winding to optimise the machine air gap flux. This paper investigates these issues on the prototype, using experimental test results & FE modelling to confirm the magnetic flux in the rotor.