Design and Performance Comparisons of Brushless Doubly Fed Generators With Different Rotor Structures

Abstract

Abstract-The Brushless Doubly-Fed Generator (BDFG) shows the great potential for use in large variable speed wind turbines due to its high reliability and cost benefits of a partially-rated power electronics converter. However, it suffers from the compromised efficiency and power factor in comparison with conventional doubly fed induction or synchronous generators. Therefore, optimizing the BDFG, especially the rotor, is necessary for enhancing its torque density and market competitiveness. In this paper, a novel cage-assisted magnetic barrier rotor, called the hybrid rotor, is proposed and analyzed. The detailed analytical design approaches based on the magnetic field modulation theory are investigated. In addition, the machine losses and mutual inductance values using the proposed rotor designs are calculated and their performance implications evaluated. Finally, the comparative experimental results for two BDFG prototypes are presented to verify the accuracy and effectiveness of the theoretical studies.

Sensorless variable speed operation of doubly‐fed reluctance wind generators

“…The d s -axis position (θ s ) and the rotor 'electrical' angle (θ r ) estimates are further obtained by means of (15)- (17), the fairly obvious i s angle relationships in α − β and d s − q s frames that can be derived from Fig. 4, and the angular position version of (1):…”

“…• The secondary dq control currents, i sd and i sq , formulated by (16) and (17), are estimated using the primary flux and current dq components in the ω p frame (Fig. 4).…”

“…• The BDFRG is almost fully-saturated by the grid-tied primary winding, so L m , and hence L p = L m + L lp , can hardly change making (16) and (17) insensitive to their on-line variations. This is further reinforced by the comparatively higher leakage inductances (L lp ) intrinsic to the machine [10,11].…”

“…brushless doubly fed induction generator (BDFIG)) can be of special nested-loops cage or wound structure with short-circuited coils [1,2,8,9], whereas its cage-less reluctance companion, the brushless doubly-fed reluctance generator (BDFRG), may have an axially or radially laminated design [10,11] offering the superior efficiency, fewer parameter-dependent dynamic models [12], and the possibility for decoupled field-oriented control of real and reactive power [13,14] similar to DFIG [4]. More optimised hybrid rotor prototypes of higher torque densities and efficiencies have likewise been reported recently to combine the individual BDFIG and BDFRG advantages in a single machine [15][16][17]. Besides, the usually 30% rated 'backto-back' converter of the BDFG is not only cheaper but less susceptible to failures than its full-scale version with synchronous wind turbine generators [18], sharing so the DFIG's economic benefits in this sense [19].…”

Loss Estimation of Brushless Doubly-Fed Generator With Hybrid Rotor Considering Multiple Influence Factors

“…2, a cage-assisted magnetic barrier rotor (i.e., hybrid rotor) which has better magnetic field modulation capacity than the commonly used rotors has been proposed [10]- [12]. In [10], the detailed analytical design approaches based on the magnetic field modulation theory are investigated. The influence of various parameters on the rotor modulating capability was fully considered in the design process.…”