The state of the art of wind energy conversion systems and technologies: A review

This study presents the performance analysis and testing of a 250 kW medium-speed brushless doubly-fed induction generator (DFIG), and its associated power electronics and control systems. The experimental tests confirm the design, and show the system's steady-state and dynamic performance and grid low-voltage ride-through capability. The medium-speed brushless DFIG in combination with a simplified two-stage gearbox promises a low-cost low-maintenance and reliable drivetrain for wind turbine applications.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-rpg.2012.0234

Performance analysis and testing of a 250 kW medium-speed brushless doubly-fed induction generator

The brushless doubly-fed induction machine (DFIM) provides an interesting alternative to the commonly applied conventional DFIM in modern multi-megawatt (MW) wind turbines. This study presents a literature survey on the brushless DFIM. The evolution of the cascaded induction machine into the modern brushless DFIM is discussed, as well as several theories explaining this machines complex operating principles. Nowadays, brushless DFIM research is mainly focused on the development of a commercially competitive brushless DFIM-based drive for multi-MW wind turbine applications. An overview of the latest developments in the fields of brushless DFIM modelling, design, and control is provided. Based on this, a qualitative comparison is presented of the brushless DFIM and other well-established generator systems for wind turbines and the challenges for future research are explored.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-epa.2016.0118

Brushless doubly-fed induction machines for wind turbines: developments and research challenges

In this paper, the operational envelops and efficiency maps of an electrically excited (EE) machine with/without employing flux weakening control via armature current and/or with/without the field excitation regulating are obtained and comprehensively compared for electric vehicle applications. It shows that even in EE machines, only using the field excitation regulating but without the flux weakening armature current control, the maximum power at high speed is not constant but inversely proportional to the machine speed. Only by employing the flux weakening armature current control, the maximum constant power operation at high-speed region can be achieved while the operational high-speed region can be greatly extended. The maximum efficiency in this extended high-speed region can be achieved when both the field excitation and flux weakening ${d}$ -axis armature current change proportionally. The main benefit of the field excitation regulating is that the efficiency in low-torque region can be significantly improved. All the analyses are validated analytically.

Investigation on Operational Envelops and Efficiency Maps of Electrically Excited Machines for Electrical Vehicle Applications

The brushless doubly fed reluctance machine consists of a stator containing two winding sets if different pole number linked by a reluctance type of rotor. This paper studies the magnetic performance of machines with different pole combinations aimed for use in a 2 MW wind turbine. This paper investigates the use of high-flux-density steels in order to observe the influence on torque density. An increase of 27% in performance is observed. In the second part of this paper, the unbalanced magnetic pull on the rotor is investigated. It has been suggested that a 4/6 pole may be suitable for this application, but it is illustrated that the rotor experiences high radial forces that may negate the use of this type of machine due to excessive bearing wear over a prolonged period.

Improvements in Brushless Doubly Fed Reluctance Generators Using High-Flux-Density Steels and Selection of the Correct Pole Numbers

The performances of three types of magnetic gears (MGs), which are radial-flux MGs, transverse-flux MGs, and axial-flux MGs, are quantitatively analyzed and compared using 3-D finite-element method of magnetic field and mechanical motion coupled computation. To fairly compare the torque capability of different topologies of MGs, all the MGs under study have the same gear ratio, the same outer diameter, and the same axial stack length. To maximize the torque density, several important structure parameters are optimized. Scenarios using different iron core materials and different magnetization directions of permanent magnets are also studied. Based on the comparative analysis, appropriate topologies of MGs that can achieve a torque density as high as 198 kNm/m
 3
 are suggested. The results in this paper give a good review of the torque density levels of different MGs, and hence they can be used as application guidelines.

A Quantitative Comparison Analysis of Radial-Flux, Transverse-Flux, and Axial-Flux Magnetic Gears

In this paper, a novel doubly excited brushless machine (DEBM) with the radially laminated magnetic barrier rotor (RLMB-rotor) for wind power generator application is designed and built. The performance studies of the prototype RLMB-rotor DEBM with 10 rotor pole numbers by using the 2D transient finite element analysis model and the experimental method are presented. The magnetic fields, the no-load and loaded characteristics, the electromagnetic torque characteristics of the prototype machine are investigated. The experiment results validate the theoretical analysis results and all studies in this paper show that the prototype RLMB-rotor DEBM is a high efficiency wind power generator.

Design and performance analysis of a doubly excited brushless machine for wind power generator application

A 1000 kW/19 200 rpm wound-rotor synchronous machine has been designed as a draft based on 2-D transient finite-element method (FEM). The magnetic fields distribution, the iron losses, the electromagnetic torque and the terminal characteristics of the prototype machine are investigated in this paper by using 2-D finite element analysis. The d-axis inductance Ld and the q-axis inductance Lq of the sample machine are predicted in analytical models. All studies indicate that the wound-rotor synchronous machine is potential to apply in high speed generator or motor application.

Finite Element Analysis of 1 MW High Speed Wound-Rotor Synchronous Machine

Rotor pole numbers of a Doubly Excited Brushless Reluctance Machine (DEBRM) system profoundly affect its magnetic coupling between the primary and secondary windings, and torque capability. This paper presents a comparison study of a DEBRM with 3 different pole numbers by using two analytical models, the winding function linear model and the 2D transient nonlinear model. The magnetic fields and torque production of the DEBRM are investigated. The results are used to reveal the significant impact of different pole numbers to the interaction of the primary/secondary windings and torque production.

Comparison study of Doubly Excited Brushless Reluctance Machine with different rotor pole numbers

The brushless doubly fed machines (BDFM) have been widely researched. The BDFM system has lots of advantages such as brushless, simplicity, robustness and reliability, and a much smaller power electronic converter compared to a conventional AC induction machine. The BDFM as a new type of AC machine and is attractive for converter-fed variable speed drive applications and variable-speed constant-frequency (VSCF) wind power generation systems. This paper presents a BDFM respectively with radial laminated reluctance and nested-loop cage rotors of the same size, and the BDFM with radial laminated reluctance rotor hasn't been studied before. The voltage of power windings and air-gap flux harmonic order of both motors are analyzed on no-load operation; the BDFM torque capabilities are investigated with 5-pole rotor machines, and the voltage harmonic order of the power winding which used as generators at negative maximum torque are researched. All these results are based on finite element method and provide insights into the control of BDFM used in wind power generation system.

Huijuan Liu

Papers

A Quantitative Comparison Analysis of Radial-Flux, Transverse-Flux, and Axial-Flux Magnetic Gears

Design and performance analysis of a doubly excited brushless machine for wind power generator application

Finite Element Analysis of 1 MW High Speed Wound-Rotor Synchronous Machine

Comparison study of Doubly Excited Brushless Reluctance Machine with different rotor pole numbers

Comparative Study of Brushless Doubly Fed Machine with Different Rotor Structures Used in Wind Power Generation System