Windrive has led to important outcomes in the industrialization of the medium-speed Brushless DFIG drivetrain for wind turbine applications. The publications resulted from the research findings are provided here and can be downloaded. The Adobe Acrobat Reader is required to open the documents.

A Study of Converter Rating for Brushless DFIG Wind Turbines
This paper studies the converter rating requirement of a Brushless DFIG for wind turbine applications by considering practical constraints such as generator torque-speed requirement, reactive power management and grid low-voltage ride-through (LVRT). Practical data has been used to obtain a realistic system model of a Brushless DFIG wind turbine using steady-state and dynamic models. A converter rating optimization is performed based on the given constraints. The converter current and voltage requirements are examined and the resulting inverter rating is compared to optimization algorithm results. In addition, the effects of rotor leakage inductance on LVRT performance and hence converter rating is investigated.
A Study of Converter Rating for a Brushl[...]
Adobe Acrobat document [2.0 MB]
Design and performance analysis of a 6 MW medium-speed brushless DFIG
The paper presents the design and performance analysis of a 6 MW medium-speed Brushless Doubly-Fed Induction Generation (Brushless DFIG) for a wind turbine drivetrain. Two machines with different frame sizes have been designed to show the flexibility of the design procedure. The medium speed Brushless DFIG in combination with a two stage gearbox offers a low-cost, low-maintenance and reliable drivetrain for wind turbine applications.
Design and Performance Analysis of a 6 M[...]
Adobe Acrobat document [597.8 KB]
Investigation of Magnetic Wedge Effects in Large-Scale BDFMs
This paper studies the effects of magnetic wedges on the equivalent circuit parameters of the Brushless Doubly-Fed Machine (BDFM). Magnetic wedges are used in slot openings of large electrical machines to reduce magnetizing currents, but the study of their effects on the BDFM performance is not straightforward due to the complex magnetic fields in the BDFM. Equivalent circuit and FE models have been developed for a 250 kW BDFM taking into account the effects of wedges and verified experimentally.
Investigation of Magnetic Wedge Effects [...]
Adobe Acrobat document [2.5 MB]
Vector-Controlled Grid Synchronization for the Brushless Doubly-Fed Induction Generator
To further demonstrate the applicability of the brushless doubly-fed induction generator for wind turbine applications, a grid synchronization procedure is developed. Vector control of the converter-side stator winding is used to induce a voltage on the grid-side stator winding. A detector is developed to automatically connect the machine to the grid when the voltages are synchronized. Experimental results show that synchronization occurs within 0.4 seconds while the rotor is accelerating
2013 - IET PRG Proc - Vector controlled [...]
Adobe Acrobat document [173.3 KB]
A Novel Analytical Approach and Finite Element Modelling of a BDFIM
This paper presents a method of analytically evaluating the brushless DFIM. This is done by analyzing the flux density produced by the two stator windings and the interaction with the nested loops of the rotor. Subsequently FEM is used to verify the analytical findings and analyze the behaviour of the machine. Several design parameters of the BDFIM such as the pole pair combinations and the number of loops per nest are evaluated.
A Novel Analytical Approach and finite E[...]
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Brushless Doubly-Fed Induction Machines: Magnetic Field Modelling
This paper develops an analytical magnetic field model for the brushless DFIM. Since the brushless DFIM rotor construction has a rich space harmonic spectrum, attention is paid to the effects of winding space-harmonics. The developed model is validated by FE calculations.
Brushless Doubly-Fed Induction Machines [...]
Adobe Acrobat document [493.6 KB]
Brushless Doubly-Fed Induction Machines: Torque Ripple
This paper focuses on torque ripple in the brushless DFIM. The causes and origin of torque ripple are discussed and an analytical model is developed that derives the torque ripple from the air-gap magnetic field distribution. Furthermore, a FE method for torque ripple calculation is presented. Both methods are used to calculate the torque response of a case study machine. Results are compared and the
accuracy of the analytical model is validated with good result. The analytical model is then used to further analyse the torque ripple, resulting in exact torque ripple frequencies and additional insight in the cause of the torque ripple.
Brushless Doubly-Fed Induction Machines [...]
Adobe Acrobat document [804.2 KB]
Effects of Rotor Skew on the Performance of Brushless Doubly-Fed Induction Machine
Undesired space harmonics exist in the brushless DFIM because the specially designed rotor needs to couple both two stator windings which have different pole-pair numbers and different frequencies. These rich space harmonics lead to a larger torque ripple compared to the standard normal induction machine. This paper uses a 2D multi-slice finite element (FE) method to study the effect of the rotor skew on the performance of the BDFIM in the cases without and with saturation. The results show the torque ripple is reduced significantly by skewing the rotor both in those two situations. But the rotor skew has negligible influence on the harmonics due to the saturation effect. Furthermore, the rotor skew has little influence on the total amount of losses
Effects of Rotor Skew on the Performance[...]
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Finite Element Based Multi-Objective Optimization of a Brushless Doubly-Fed Induction Machine
A static brushless DFIM FE model is used in conjunction with a NSGA-II multi-objective optimization algorithm. The result is an accurate and fast brushless DFIM design optimization tool. Optimization results of different brushless DFIM construction variations are compared. The best designs of each construction variation are then analysed in more detail using a time-stepping brushless DFIM FE model. This provides good insight in the effects of different construction variations on torque ripple and induced time-harmonics.
Finite Element Based Multi-Objective Opt[...]
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Finite Element Modeling of Brushless Doubly-Fed Induction Machine Based on Magneto-Static Simulation
TThe brushless doubly-fed induction machine (BDFIM) is a potentially attractive choice for a variable-speed wind generator. Finite element (FE) modelling of the brushless doubly-fed induction machine (BDFIM) allows the the machine performance, including saturation effects to be evaluated. A long computing time makes the FE model difficult to combine with an optimization program. This paper presents an alternative method to predict the BDFIM performance by using the magneto-static FE solutions and the space-time transformation. The simulation time can then be reduced significantly making it possible to search in a large design space for the optimization purpose.
Finite Element Modeling of Brushless Dou[...]
Adobe Acrobat document [522.3 KB]
LVRT Performance of Brushless Doubly Fed Induction Machines - A Comparison
The Brushless Doubly Fed Induction Machine (BDFIM) shows promise for use in wind turbine drivetrains. This paper discusses the performance of this machine under symmetric low voltage dips and compares this with the performance
of two other machines - the Permanent Magnet Synchronous Machine (PMSM) and the Doubly-Fed Induction Generator (DFIG).
LVRT Performance of Brushless Doubly Fed[...]
Adobe Acrobat document [518.6 KB]