Dynamic analysis of the brushless doubly-fed induction generator during symmetrical three-phase voltage dips

The Brushless Doubly-Fed Induction Generator (BDFIG) shows commercial promise as replacement for doublyfed slip-ring generators for wind power applications by offering reduced capital and operational costs due to its brushless operation. In order to facilitate its commercial deployment, the capabilities of the BDFIG system to comply with grid code requirements have to be assessed. This paper, for the first time, studies the performance of the BDFIG under grid fault ride-through and presents the dynamic behaviour of the machine during three-phase symmetrical voltage dips. Both full and partial voltage dips are studied using a vector model. Simulation and experimental results are provided for a 180 frame BDFIG.

Study of iron saturation in Brushless Doubly-Fed induction machines

This paper presents an analytical modelling approach for the Brushless Doubly-Fed Machine (BDFM) taking iron saturation into account. A generalised coupled-circuit model is developed which considers stator and rotor teeth saturation effects. A method of calculating the machine inductance parameters is presented which can be implemented in time-stepping simulations. The model has been implemented in MATLAB/Simulink and verified by Finite Element analysis and experimental tests. The tests are carried out on a 180 frame size BDFM. Flux search coils have been utilised to measure airgap and teeth flux densities. © 2010 IEEE.

Characterising rotors for brushless doubly-fed machines (BDFM)

The brushless doubly fed machine (BDFM) is a robust alternative to the doubly fed induction generator (DFIG) which is widely used in wind turbines but suffers from failures associated with its brushes and sliprings. The rotor plays an important part in a BDFM, coupling the two stator fields. To date, the nested loop has been almost exclusively used in modern BDFMs, but this approach is not ideally suited to large machines in which a form wound rotor is likely to be preferable from a manufacturing point of view. This paper gives a comparative study of two rotor windings. The performance of the rotors has been predicted from theory for a frame size 160 BDFM. Actual rotors have been built, using identical rotor laminations, and tested, giving results which accord well with predictions. The results give insight into the design issues of rotors both from electrical and manufacturing viewpoints. ©2010 IEEE.

Dynamics of RNA with A6 bulge loop

In order to understand the behavior of RNAs with large bulges In solution, molecular dynamics was performed on the RNA molecule in water with A6 bulge. The result of simulation showed that nonstacked conformation Is the main conformation in large bulges, and the backbone of large bulge is of great conformational flexibility, but bulges-induced bends are relatively rigid. The fluctuation in bulge has little influence on the bend angle of RNAs.

Statistical correlation between protein secondary structure and messenger RNA stem-loop structure

Anew integrated sequence-structure database, called IADE (Integrated ASTRAL-DSSP-EMBL), incorporating matching mRNA sequence, amino acid sequence, and protein secondary structural data, is constructed. It includes 648 protein domains. Based on the IADE database, we studied the relation between RNA stem-loop frequencies and protein secondary structure. It was found that the alpha-helices and beta-strands on proteins tend to be preferably "coded" by mRNA stem region, while the coils on proteins tend to be preferably "coded" by mRNA loop region. These tendencies are more obvious if we observe the structural words (SWs). An SW is defined by a four-amino-acid-fragment that shows the pronounced secondary structural (alpha-helix or beta-strand) propensity. It is demonstrated that the deduced correlation between protein and mRNA structure can hardly be explained as the stochastic fluctuation effect. (C) 2003 Wiley Periodicals, Inc.

Symmetrical low voltage ride-through of the Brushless Doubly-Fed Induction Generator

The Brushless Doubly-Fed Induction Generator (BDFIG) shows commercial promise for wind power generation due to its lower cost and higher reliability compared to the Doubly-Fed Induction Generator (DFIG). For the purposes of commercialisation, the BDFIG must meet grid codes at all times. Nowadays, all new wind generators have to ride through certain grid faults, and the Low-Voltage Ride Through (LVRT) capability has become one of the most important points on which to assess the performance a generator. This paper, for the first time, proposes a control scheme to enable the the BDFIG to ride through symmetrical voltage dips. Simulation results and experimental results on a prototype BDFIG show that the proposed scheme gives the capability to ride through low voltage faults. © 2011 IEEE.

Spontaneous induction of the uniform lying helix alignment in bimesogenic liquid crystals for the flexoelectro-optic effect

Using in-plane electric fields, the electrical induction of the uniform lying helix (ULH) alignment in chiral nematic liquid crystals is reported. This process permits spontaneous induction of the ULH alignment to give an in-plane optic axis, without the need for complex processing. Flexoelectro-optic switching is subsequently obtained by holding the in-plane electrodes at a common voltage and addressing via a third, plane-parallel electrode on a second, or upper, substrate to give a field across the device in the viewing direction. For this device, in optimized bimesogenic materials, we demonstrate full intensity modulation and sub-millisecond response times at typical device temperatures. © 2012 American Institute of Physics.

A comparison of cage and nested-loop BDFM rotors

The Brushless Double-Fed Machine (BDFM) is a type of variable speed generator or drive. Using theoretical analysis of simple BDFM rotors this paper establishes trends in how rotor structures determine the rotor's equivalent circuit resistance, leakage inductance and turns ratio. The variation in measured parameters of five prototype rotors is then analysed in light of the trends found. Both the theory and experimental results suggest a significant performance advantage in using cage+loops type rotors as opposed to the simple nested loop type more usually employed.

线粒体D-loop序列变异与东方鲀属鱼类系统发育

东方鲀属的红鳍东方鲀(Takifugu rubripes)是后基因组时代的一种重要模式生物。本研究中,利用东方鲀属11种鱼类(18尾)的D-loop基因序列,对东方鲀属鱼类的系统发育关系进行研究。经序列比对排定后,分析中D-loop序列有841个位点,其中395个位点为可变位点,267个位点为系统发育信息位点。分别采用邻接法(NJ)、最大简约法(MP)、最大似然法(ML)和贝叶斯方法构建了分子系统树。研究结果表明:(1)东方鲀属鱼类为一单系类群;(2)由横纹东方鲀(T. oblongus)和铅点东方鲀(T

Inverse induction motor modelling of a submarine propulsion system

An inherent trade-off exists in simulation model development and employment: a trade-off between the level of detail simulated and the simulation models computational cost. It is often desirable to simulate a high level of detail to a high degree of accuracy. However, due to the nature of design optimisation, which requires a large number of design evaluations, the application of such simulation models can be prohibitively expensive. A induction motor modelling approache to reduce the computational cost while maintaining a high level of detail and accuracy in the final design is presented. © 2012 IEEE.

Crowbarless fault ride-through of the brushless doubly fed induction generator in a wind turbine under symmetrical voltage dips

The brushless doubly fed induction generator (BDFIG) shows commercial promise for wind power generation due to its lower cost and higher reliability when compared with the conventional DFIG. In the most recent grid codes, wind generators are required to be able to ride through a low-voltage fault and meet the reactive current demand from the grid. A low-voltage ride-through (LVRT) capability is therefore important for wind generators which are integrated into the grid. In this paper, the authors propose a control strategy enabling the BDFIG to successfully ride through a symmetrical voltage dip. The control strategy has been implemented on a 250-kW BDFIG, and the experimental results indicate that the LVRT is possible without a crowbar. © 1982-2012 IEEE.