The BDFM as a Generator in Wind Turbines

Abstract

The Brushless Doubly-Fed Machine (BDFM) is attractive for use in wind turbines, especially offshore, as it offers high reliability by virtue of the absence of brushgear. Critical issues in the use of the BDFM in this role at a system level include the appropriate mode of operation, the sizing of associated converter and the control of the machine. At a machine level, the design of the machine and the determination of its ratings are important. Both system and machine issues are reviewed in the light of recent advances in the study of the BDFM, and preliminary comparisons are made with the well-established doubly fed wound rotor induction generator.

Effects of Rotor Winding Structure on the BDFM Equivalent Circuit Parameters

“…This is in contrast to the result obtained in [1]. The reason for this change is using an alternative approach of B sum limit instead of peak flux density of √ 2B sum .…”

“…The reason for this change is using an alternative approach of B sum limit instead of peak flux density of √ 2B sum . The actual values of n r o p t are 0.71 and 0.63 for the 4/8 BDFM from (5) and [1], respectively. An optimum rotor for the purpose of maximum machine rating has minimum resistance and leakage inductance with a turns ratio close to an optimum value.…”

“…Their main advantages over other generator systems, notably permanentmagnet synchronous generators (PMSGs), is their lower cost. The brushless doubly fed machine (BDFM), as a new generation of DFIG, offers promising advantages such as improved reliability and reduced capital and maintenance costs [1]. Similar to low-cost DFIG systems, the BDFM only requires a fractionally rated converter and does not use permanent magnet materials.…”

A double concentric wound rotor brushless doubly fed generator

“…The rotor winding (RW) is particularly designed to realize the indirect energy exchange and transmission between the PW and CW. The potential application of the BDFG is therefore in environments where the absence of the brush is highly beneficial, such as in a ship or in a wind turbine . The frequency converter capacity accounts for only a small part of the total capacity of the system.…”

A Study of Unbalanced Magnetic Pull in Brushless Doubly Fed Machines

“…The coupling between the windings is therefore through the rotor [2]. The rotor is specially designed to couple to the two air-gap fields associated with the two stator windings, the nested-loop design being commonly used [3]. The normal mode of BDFM operation is as a synchronous machine with the rotor rotating at a speed determined by the winding pole numbers and the mains and converter frequencies [2].…”