Selection of Power and Control Windings Pole numbers of Brushless Doubly-Fed Induction Machine in Wind Generator Application with 500 rpm Synchronous Speed

Up to now, several configurations have been proposed and implemented in wind turbine. The structure based on Doubly-Fed induction Generator (DFIG) is used widely because of its technical and economic benefits. Among other structures, Brushless Doubly-Fed Induction Generator (BDFIG) has interesting properties to be used as wind generator such as brushless operation, robust structure with higher reliability and lower operating and maintenance costs, needing partially rated converter and a gear box with lower speed ratio and also, better low voltage ride through capability. There are two 3-phase windings on stator namely power winding (PW) and control winding (CW) and one special cage winding on the rotor which is called nested loop winding. An important design issue is selection of PW and CW pole pair numbers in order to achieve good performance characteristics. In this paper, the analysis carried out using electric equivalent circuit model and 2D finite element model reveals that the 2 and 4 pole pairs combination for PW and CW respectively, results in the best performance for medium speed rotational speeds around 500 rpm.