Quantitative Control Approach for Wind Turbine Generators to Provide Fast Frequency Response with Guarantee of Rotor Security

Wind generation is expected to reach substantially higher levels of penetration in the near future. With the converter interface, the rotor inertia of doubly-fed induction generator (DFIG) based wind turbine generator is effectively decoupled from the system, causing a reduction in inertial response. This can be compensated by enabling the DFIG to provide fast frequency response. This paper proposes a quantitative control approach for DFIG to deliver fast frequency response in the inertial response time scale. A supplementary power surge function is added to the active power reference of DFIG. The exact amount of power surge that is available from DFIG-based wind turbine is quantified based on estimation of maximum extractable energy. Moreover, the operational constraints such as rotor limits and converter over-load limit are considered at the same time. Thus, the proposed approach not only provides adequate inertial response but also ensures the rotor speed is kept within a specified operating range. Rotor safety is guaranteed without the need for an additional rotor speed protection scheme.Comment: 5 page

Towards optimisation of load-time conditions for producing viscoelastically prestressed polymeric matrix composites

A viscoelastically prestressed polymeric matrix composite (VPPMC) is produced by applying a tensile creep load to polymeric fibres, the load being released before the fibres are moulded into a polymeric matrix. The viscoelastically recovering fibres induce compressive stresses within the matrix, which can improve mechanical properties by up to 50%. This study investigates the feasibility of reducing the creep loading period for VPPMC production. By using nylon 6,6 fibres, we have demonstrated that the previously adopted viscoelastic creep strain, requiring 330 MPa for 24 h, can be achieved over a shorter duration, tn, using increased creep stress. Thus tn was 92 min at 460 MPa and 37 min at 590 MPa. Subject to avoiding fibre damage however, it may be possible to reduce tn further. From the three creep settings, elapsed recovery strain values were similar, as were the Charpy impact test data from corresponding VPPMC samples; i.e. there were no significant differences in impact energy absorption, these being ∼56% greater than their control (unstressed) counterparts

A bistable morphing composite using viscoelastically generated prestress

Elastically generated prestress within polymeric composites can be used to create bistable morphing structures; i.e. they can ‘snap through’ between one of two states. In this paper, a morphing bistable structure has been produced, utilising viscoelastically generated prestress. Here, polymeric fibres are subjected to a tensile (viscoelastic) creep load which is released before the fibres are moulded into a matrix. Following curing, the previously strained fibres continue to attempt viscoelastic recovery, creating compressive stresses within the matrix that are counterbalanced by residual tension in the fibres. The bistable structure consists of prestressing strips bonded to the sides of a thin, flexible resin-impregnated fibre-glass sheet. Bistability is achieved through pairs of strips orientated to give opposing cylindrical configurations within the sheet. It is envisaged that viscoelastically prestressed morphing structures may overcome the potential limitations of elastic prestressing; i.e. production flexibility and product longevity

Superconductivity near Itinerant Ferromagnetic Quantum Criticality

Superconductivity mediated by spin fluctuations in weak and nearly ferromagnetic metals is studied close to the zero-temperature magnetic transition. We solve analytically the Eliashberg equations for p-wave pairing and obtain the normal state quasiparticle self-energy and the superconducting transition temperature $T_c$ as a function of the distance to the quantum critical point. We show that the reduction of quasiparticle coherence and life-time due to scattering by quasistatic spin fluctuations is the dominant pair-breaking process, which leads to a rapid suppression of $T_c$ to a nonzero value near the quantum critical point. We point out the differences and the similarities of the problem to that of the theory of superconductivity in the presence of paramagnetic impurities.Comment: 4 pages, 1 figure, revised version to appear in Phys. Rev. Let

Idiosyncratic Consumption Risk and the Cross-Section of Asset Returns

This paper investigates the importance of idiosyncratic consumption risk for the cross-sectional variation in average returns on stocks and bonds. If idiosyncratic consumption risk is not priced, the only pricing factor in a multiperiod economy is the rate of aggregate consumption growth. We offer evidence that the cross-sectional variance of consumption growth is also a priced factor. This demonstrates that consumers are not fully insured against idiosyncratic consumption risk, and that asset returns reflect their attempts to reduce their exposure to this risk. We find that over the sample period the resulting two-factor consumption-based asset pricing model significantly outperforms the CAPM. The model's empirical performance also compares favorably with that of the Fama-French three-factor model. Moreover, in the presence of the market factor and the size and book-to-market factors, the two consumption based factors retain explanatory power. Together with the results of Lettau and Ludvigson (2000), these findings indicate that consumption-based asset pricing is relevant for explaining the cross-section of asset returns. Cet article analyse l'importance du risque idiosyncratique de la consommation individuelle pour la variance transversale des rendements moyens des actifs et des obligations. Lorsque l'on n'attribue pas de prix au risque idiosyncratique de la consommation individuelle, le seul facteur d'évaluation dans une économie à plusieurs horizons est le taux de croissance de la consommation agrégée. Nous montrons que la variance transversale de la croissance de la consommation est également un facteur dont le prix est déterminé. Ceci démontre que les consommateurs ne sont pas complètement assurés contre le risque idiosyncratique de la consommation et que les rendements des actifs reflètent leurs efforts à réduire leur exposition à ce risque. Pour la période considérée, nous trouvons que le modèle d'évaluation d'actifs à deux facteurs basés sur la consommation donne de meilleurs résultats que le CAPM. De plus, la performance empirique du modèle se compare favorablement avec celle du modèle à trois facteurs de Fama-French. Par ailleurs, en présence du facteur de marché et des facteurs taille et ratio valeur comptable/cours, les deux facteurs basés sur la consommation conservent leur pouvoir explicatif. Combiné aux résultats de Lettau et Ludvigson (2000), ces résultats indiquent que l'évaluation d'actifs à partir de la consommation sert à expliquer l'intégralité des rendements d'actifs.cross-sectional asset pricing; consumption-based model; idiosyncratic consumption risk; incomplete markets; measurement error, évaluation d'actifs transversale, modèle basé sur la consommation, risque de consommation idiosyncratique, marchés incomplets, erreur de mesure

Forecasting dairy herd development in China

With the rapid development of the Chinese dairy industry, various researchers have examined the industry from many perspectives related to supply and demand. One of the most important factors for this industry is the total number of dairy cows and it is this aspect that will be addressed in this paper. This paper examines how economic and biological factors influenced the size of the Chinese dairy herd population using an autoregressive distributed lag model and a dairy herd inventory model. The estimated results showed that the biological process was dominating the development of the Chinese dairy herd. The ratio of milk to corn price, as an economic variable, is another factor that had an impact. Beef price, which was found to be an influential variable for the United States dairy cattle inventory did not have a significant impact on the Chinese dairy industry. This is expected to change as the dairy industry in China develops. Results from this study also suggest that Chinese farmers have a positive expectation in the long term towards the dairy industry and that there are high adjustment costs in dairy production in China. Finally, the projection results showed that it is very likely that the dairy cattle numbers in China would double between 2005 and 2010.dairy herd, China, cattle inventory model, projection, Livestock Production/Industries,

Snap-through behaviour of a bistable structure based on viscoelastically generated prestress

A novel form of shape-changing bistable structure has been successfully developed through the use of viscoelastically generated prestress. Bistability is achieved through pairs of deflecting viscoelastically prestressed polymeric matrix composite (VPPMC) strips, which are orientated to give opposing cylindrical configurations within a thin, flexible resin-impregnated fibreglass sheet. This arrangement enables the structure to ‘snap through’ between one of two states by external stimulation. Deflection from the VPPMC strips occurs through compressive stresses generated from the non-uniform spatial distribution of nylon 6,6 fibres undergoing viscoelastic recovery. In this study, snap-through behaviour of the bistable structure is investigated both experimentally and through finite element (FE) analysis. By using experimental results to calibrate FE parameter values, the modelling has facilitated investigation into the development of bistability and the influence of modulus ratio (fibreglass sheet: VPPMC strip) on the snap-through characteristics. Experimental results and FE simulation show good agreement with regard to snap-through behaviour of the bistable structure and from this, the bistability mechanisms are discussed

Efficacy of common laboratory disinfectants and heat on killing trypanosomatid parasites

The disinfectants TriGene, bleach, ethanol and liquid hand soap, and water and temperature were tested for their ability to kill bloodstream forms of Trypanosoma brucei, epimastigotes of Trypanosoma rangeli and promastigotes of Leishmania major. A 5-min exposure to 0.2% TriGene, 0.1% liquid hand soap and 0.05% bleach (0.05% NaOCl) killed all three trypanosomatids. Ethanol and water destroyed the parasites within 5 min at concentrations of 15-17.5% and 80-90%, respectively. All three organisms were also killed when treated for 5 min at 50 degrees C. The results indicate that the disinfectants, water and temperature treatment (i.e. autoclaving) are suitable laboratory hygiene measures against trypanosomatid parasites

Discriminative Segmental Cascades for Feature-Rich Phone Recognition

Discriminative segmental models, such as segmental conditional random fields (SCRFs) and segmental structured support vector machines (SSVMs), have had success in speech recognition via both lattice rescoring and first-pass decoding. However, such models suffer from slow decoding, hampering the use of computationally expensive features, such as segment neural networks or other high-order features. A typical solution is to use approximate decoding, either by beam pruning in a single pass or by beam pruning to generate a lattice followed by a second pass. In this work, we study discriminative segmental models trained with a hinge loss (i.e., segmental structured SVMs). We show that beam search is not suitable for learning rescoring models in this approach, though it gives good approximate decoding performance when the model is already well-trained. Instead, we consider an approach inspired by structured prediction cascades, which use max-marginal pruning to generate lattices. We obtain a high-accuracy phonetic recognition system with several expensive feature types: a segment neural network, a second-order language model, and second-order phone boundary features