Abstract
Brushless Doubly-Fed Machine has attracted considerable attention in recent years due to its advantages. It has the robustness of the squirrel cage induction machine, and the speed and power factor controllability of the synchronous machine as well as the absence of brushes and slip rings, and using a fractionally rated frequency converter. Hence, there are considerable benefits over the conventional machines, when the machine is applied to applications such as a wind turbine generator or high power adjustable speed drive. However, these benefits are obtained in slightly more complex structure, higher cost and larger dimensions in comparison to the conventional induction machine. This paper presents fundamental aspects of the three modes of operation of brushless doubly fed machine, i.e. simple induction mode, cascade induction mode, and synchronous mode. The investigation is performed by analyzing the spatial harmonic contents of the rotor magnetic flux density. The direct cross couplings between stator and rotor fields as well as, indirect cross coupling between stator fields by the special rotor of this machine is described. Furthermore, loss analysis of the machine in various modes is presented and the torque-speed curves for asynchronous modes are obtained. A 2-D magnetodynamic finite element model based on the D-180 4/8 pole prototype machine is extracted and simulated to verify the results.
Highlights
The conceptual idea of the machines with two stator windings can be traced to some publications in the 1900s [1,2,3]
This paper presents fundamental aspects of the three modes of operation of brushless doubly fed machine, i.e. simple induction mode, cascade induction mode, and synchronous mode
This paper presents the characteristics of the brushless doubly-fed machine (BDFM) in simple induction, cascade induction and synchronous modes of operation and describes the direct and indirect cross coupling by simple electromagnetic relations
Summary
The conceptual idea of the machines with two stator windings can be traced to some publications in the 1900s [1,2,3]. The split-wound dual-winding machine was proposed to improve the power capability of large synchronous generators and to achieve better drive reliability resulting from its inherent redundancy [5]. The second type, the self-cascaded machine or the brushless doubly-fed machine (BDFM), with two sets of stator windings, which do not couple directly but via the intermediate action of a special rotor, was introduced by Hunt in 1907 [2]. The rotor should couple the power and control windings magnetic fields, in the appropriate manner. This paper presents the characteristics of the BDFM in simple induction, cascade induction and synchronous modes of operation and describes the direct and indirect cross coupling by simple electromagnetic relations. A 2-D magnetodynamic finite element model of the D-180 frame prototype BDFM is used for verification
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