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The brushless doubly fed induction generator (BDFIG) has been proposed as a viable alternative in wind turbines to the commonly used doubly fed induction generator (DFIG). The BDFIG retains the benefits of the DFIG, i.e. variable speed operation with a partially rated converter, but without the use of brush gear and slip rings, thereby conferring enhanced reliability. As low voltage ride-through (LVRT) performance of the DFIG-based wind turbine is well understood, this paper aims to analyze LVRT behavior of the BDFIG-based wind turbine in a similar way. In order to achieve this goal, the equivalence between their two-axis model parameters is investigated. The variation of flux linkages,... 

The brushless doubly-fed induction generator (BDFIG) has substantial benefits, which make it an attractive alternative as a wind turbine generator. The aim of this work is to present a nodal-based magnetic equivalent circuit (MEC) model of the BDFIG which provides performance characteristics and flux density distributions. The model takes into account stator winding distributions, special configuration of rotor bars, slotting effects, teeth saturation, flux fringing and current displacement effects. The real flux tubes are considered for creating an MEC network and calculating its non-linear elements. A method for simplifying the rotor magnetic network has been applied and Gauss elimination... 

Variable speed wind turbines are widely used in the modern power industry. These turbines that are usually driven by doubly fed induction generators (DFIGs) contain two groups of controlling variables; mechanical variables like pitch angle and electrical variables like rotor voltage. During the turbine operation, with variable wind velocity, power must be managed in two regimes; power optimisation and power limitation. In the current research, initially a non-linear simulation, based on the general wind turbine dynamic model is presented. Then, the desired controllers for both pitch angle and generator voltage components are constructed. After designing the controller, in order to... 

The Brushless Doubly-fed Induction Generator (BDFIG) has high potential for wind energy systems, especially for offshore applications where minimum maintenance is vital. The machine low voltage ride through (LVRT) capability in the light of current grid code requirements was investigated using a precise dynamic model. This is particularly important for future multi- MW BDFIGs. This paper shows the necessity for improvements of the BDFIG LVRT capability with presenting a comprehensive analytical study during asymmetrical voltage dips. Analytical studies are conducted to extract a more precise equivalent circuit model of the BDFIG used for analyzing machine dynamic behavior under various fault... 

This paper is aimed at proposing a current based vector control model of the brushless doubly fed induction generator, modelling the presented control method, as well as implementing the proposed algorithm by DSP. In order to achieve the purpose, by presenting a detailed coupled circuit model of BDFIG, the vector model and then the current based vector control algorithm of the mentioned machine are acquired. The way of independent control of torque and power, and also the structure of speed controller amongst the proposed control model are discussed. Additionally, the concepts behind the proposed structure of the speed control system and the way of determining the model parameters are... 

Brushless doubly fed induction generators (BDFIGs) show commercial promise for wind-power generation due to their lower capital and operational costs and higher reliability as compared with doubly fed induction generators. This paper presents a vector-control scheme for a BDFIG operating as a variable-speed generator. The proposed vector controller is developed on the power-winding stator-flux frame and can be used to control both the speed and the reactive power. The machine model and the control system are developed in MATLAB. The test results show that the proposed controller has good dynamic performance when changes in speed and reactive power are applied. © 2009 IEEE  

The brushless doubly fed induction generator (BDFIG) has substantial benefits, which make it an attractive alternative as a wind generator. However, it suffers from lower efficiency and larger dimensions in comparison with the doubly fed induction generator. A major part of drawbacks arises from undesirable spatial harmonics of air-gap magnetic field. Calculation of core loss is an important issue in optimal design studies to improve the performance characteristics. The iron loss is higher and has a more complex nature in BDFIGs in contrast with conventional machines. Furthermore, additional losses cannot be ignored due to a high level of spatial harmonics distortion. This paper aims to... 

In this paper the direct power control methods of doubly fed induction generator in wind turbine applications are studied. In the methods under study, the proper voltage space vector of the rotor side converter is selected using a switching table which is derived from flux position and the difference between the measured and reference stator active and reactive powers. Various simulations are performed in Matlab/Simulink software on a DFIG system in order to investigate the dynamic performance and robustness of the proposed control methods against machine internal parameters variations  

The brushless doubly fed induction generator has been proposed for use in wind turbines as a more reliable alternative to the more commonly used doubly fed induction generator. To realize the commercial promises of the brushless doubly fed induction generator in this role, it must meet the existing grid connection codes, particularly with respect to low-voltage ride-through. In this article, the application of series dynamic resistors is proposed to enhance brushless doubly fed induction generator low-voltage ride-through capability, and the required analysis is provided. Three locations for series dynamic resistors are suggested in the brushless doubly fed induction generator circuit and... 

Due to the proliferation of wind turbines in power networks, participation of doubly-fed induction generator (DFIG)-based wind turbines in the frequency regulation task is attracting more attention during recent decades. It is a challenge to design an effective DFIG's auxiliary frequency controller, since back-to-back converters used in DFIG make the possibility of large deviations in current and speed of rotor during frequency support period. Hence, it is necessary to use exact expression of DFIG's output power in the frequency-related studies. This paper addresses this challenge by developing a nonlinear dynamic model for the DFIG's output power integrated into the dynamic model of power... 

Doubly-fed induction generator (DFIG) is the most commonly used technology for wind power generation due to the variable speed performance, decoupled control of active and reactive powers, and high efficiency. However, the DFIG originally cannot participate in damping of power system oscillations since it is not synchronously connected to the power system. This paper proposes an optimal and robust additional damping controller for the DFIG wind turbine to contribute it to damp power system oscillations. It is a fuzzy logic controller that its parameters are optimally tuned using the genetic algorithm (GA). The proposed controller modifies the DFIG active power output by using feedback from... 

In this paper, application of a five-leg converter in Doubly Fed Induction Generator (DFIG) for Wind Energy Conversion Systems (WECS) is investigated. The five-leg structure and its PWM control are studied and performances are compared with the classical six-leg topology. The main drawback of five-leg converter with respect to the six-leg back-to-back converter is the need to increase the dc-link voltage for the same operation point, i.e. the same powers in case of WECS. So, different methods for the reduction of the required dc-link voltage in the five-leg case are studied. The five-leg converter is used to replace the conventional six-leg one, with the same ability. For the performance... 

This paper first discusses dynamic characteristics of wind turbines with doubly fed induction generator (DFIG). Rotor back electromotive force (EMF) voltages in DFIG reflect the effects of stator dynamics on rotor current dynamics, and have an important role on rotor inrush current during the generator voltage dip. Compensation of these voltages can improve DFIG ride-through capability and limit the rotor current transients. It is found that the electrical dynamics of the DFIG are in nonminimum phase for certain operating conditions. Also, it is shown that the dynamics of DFIG, under compensation of rotor back EMF and grid voltages, behave as a partially linearizable system containing... 

Brushless doubly fed induction generator (BDFIG) has substantial benefits, which make it an attractive alternative as a wind turbine generator. However, it suffers from lower efficiency and larger dimensions in comparison to DFIG. Hence, optimizing the BDFIG structure is necessary for enhancing its situation commercially. In previous studies, a simple model has been used in BDFIG design procedure that is insufficiently accurate. Furthermore, magnetic saturation and iron loss are not considered because of difficulties in determination of flux density distributions. The aim of this paper is to establish an accurate yet computationally fast model suitable for BDFIG design studies. The proposed... 

The use of brushless doubly-fed induction generator has been recently proposed for wind turbines because of its variable speed operation with fractional size converter without the need to brush and slip ring. This paper introduces a control scheme to improve low voltage ride-through capability of doubly-fed induction generator considering grid code requirements. The proposed control strategy is based on analysis of flux linkages and back electromotive forces and intends to retain the control-winding current below the safety limit (typically 2pu) during severe voltage dips. The time-domain simulations validate effectiveness of the proposed scheme to protect the converter against failure as... 

The use of brushless doubly-fed induction generator has been recently proposed for wind turbines because of its variable speed operation with fractional size converter without the need to brush and slip ring. This paper introduces a control scheme to improve low voltage ride-through capability of doubly-fed induction generator considering grid code requirements. The proposed control strategy is based on analysis of flux linkages and back electromotive forces and intends to retain the control-winding current below the safety limit (typically 2 pu) during severe voltage dips. The time-domain simulations validate effectiveness of the proposed scheme to protect the converter against failure as... 

This paper proposes effective approach for determining appropriate crowbar resistance value to be able to improve the brushless doubly fed induction generator ride through capability during any asymmetrical voltage dip scenarios. The brushless DFIG has great potential for wind power plants particularly in offshore applications where maintenance is a major concern. Dynamic behavior of the machine is studied using two axis model and a more precise equivalent circuit model is extracted for analyzing machine behavior under fault conditions. Important limits and constraints in the use of crowbar are identified and discussed in detail. It is shown that large crowbar values can lead to considerable... 

This article proposes a bang-bang auxiliary frequency control scheme for doubly-fed induction generator (DFIG)-based wind turbines. It results in the DFIGs emulate the primary frequency control of conventional units and, thus, increases the power system frequency stability. Indeed, the suggested hysteresis controller causes to deliver the maximum extractable kinetic energy of DFIGs to the grid and consequently further enhance the power system frequency. This is accomplished using different frequency deviation indices, which determine the size of power mismatch and lead to an appropriate frequency response by the DFIGs. The operational constraints of the DFIGs are taken into account in the...