Sliding mode control law for a variable speedwind turbine

Modern wind turbines are designed in order to work in variable speed operations. To perform this task, wind turbines are provided with adjustable speed generators, like the double feed induction generator. One of the main advantage of adjustable speed generators is improving the system efficiency compared to fixed speed generators, because turbine speed can be adjusted as a function of wind speed in order to maximize the output power. However this system requires a suitable speed controller in order to track the optimal reference speed of the wind turbine. In this work, a sliding mode control for variable speed wind turbines is proposed. An integral sliding surface is used, because the integral term avoids the use of the acceleration signal, which reduces the high frequency components in the sliding variable. The proposed design also uses the vector oriented control theory in order to simplify the generator dynamical equations. The stability analysis of the proposed controller has been carried out under wind variations and parameter uncertainties by using the Lyapunov stability theory. Finally simulated results show, on the one hand that the proposed controller provides a high-performance dynamic behavior, and on the other hand that this scheme is robust with respect to parameter uncertainties and wind speed variations, that usually appear in real systems.

An adaptive sliding mode control law for the power maximization of the wind turbine system

POWERENG 2011

Civil framework of the Internet : Law n°. 12.965, of April 23, 2014, which establishes the principles, guarantees, rights and duties for use of the Internet in Brazil

Traz atualizado o texto do Marco Civil Brasileiro da Internet, a Lei nº 12.965, de 23 de abril de 2014.

Mechanics of adhesive contact on a power-law graded elastic half-space

We consider adhesive contact between a rigid sphere of radius R and a graded elastic half-space with Young's modulus varying with depth according to a power law E = E-0(z/c(0))(k) (0 < k < 1) while Poisson's ratio v remaining a constant. Closed-form analytical solutions are established for the critical force, the critical radius of contact area and the critical interfacial stress at pull-off. We highlight that the pull-off force has a simple solution of P-cr= -(k+3)pi R Delta gamma/2 where Delta gamma is the work of adhesion and make further discussions with respect to three interesting limits: the classical JKR solution when k = 0, the Gibson solid when k --> 1 and v = 0.5, and the strength limit in which the interfacial stress reaches the theoretical strength of adhesion at pull-off. (C) 2009 Elsevier Ltd. All rights reserved.

Adhesive behavior of two-dimensional power-law graded materials

In this paper, we investigate the adhesive contact between a rigid cylinder of radius R and a graded elastic half-space with a Young's modulus varying with depth according to a power-law, E = E-0(y/c(0))(k) (0 < k < 1), while the Poisson's ratio v remains constant. The results show that, for a given value of ratio R/C-0, a critical value of k exists at which the pull-off force attains a maximum; for a fixed value of k, the larger the ratio R/c(0), the larger the pull-off force is. For Gibson materials (i.e., k = 1 and v = 0.5), closed-form analytical solutions can be obtained for the critical contact half-width at pull-off and pull-off force. We further discuss the perfect stick case with both externally normal and tangential loads.

Investment prospects in inland capture fisheries with special reference to small reservoirs: the exclusive fishing right licence model

The paper discusses simple methods of estimating fish yield from small reservoirs and establishes 2 indices of fish yield based on: 1) the relationship between the catch per boat in artisanal commercial fish landings and the catch per unit effort in experimental gill-net survey; and also, 2) the relationship between standing crop of fish in reservoirs and catch per unit effort in experimental gill-net survey. The paper then elaborates on the methods of utilizing these simple relationships in managing small reservoirs in Nigeria based on the principle of exclusive fishing right licence with the objective of attracting investors into this viable inland fishery investment project hitherto untapped

Investment prospects in marine capture fisheries

An examination is made of investment prospects in the Nigerian marine fisheries, considering the following sectors: inshore demersal fishery; inshore pelagic fishery; and the offshore pelagic fishery. The marine fisheries resources of countries with which Nigeria has bilateral fishing rights agreements are discussed, considering Equatorial Guinea, Guinea Conakry, Guinea Bissau, Senegal and Mauritania. Fishing gear and methods for the marine fishery sectors are outlined. Market potentials for fish products and profitability are also examined

Investment prospects in inshore trawling in Nigeria

Commercial trawling for finfish in Nigeria's inshore water is a recent activity. Intensive industrial trawling started when the Federal Government distributed trawlers to viable fishermen cooperatives during the Third National Development Plan Period (1975-80). Hitherto, industrial fisheries development in the country focused on the assessment of the potential fish stock on Nigeria's continental shelf and measures to increase artisanal production. As a result of increasing demand for fish and shortage of foreign exchange to import fish, measures to increase fish supply leaned towards industrial exploitation of the fisheries potentials of Nigeria's continental shelf. Based on this background, this paper examines the investment prospects of trawling for fish in inshore waters. The fisheries potentials of the inshore zone of Nigeria are identified. Catch efficiency and profitability of inshore trawling are estimated. Measures that can safeguard the longterm interest of the trawling industry are recommended

Artisanal canoe fishing industry of the Rivers State: its economic viability and investment potentials

Consequent upon the present national call in Nigeria for all to go back to agriculture including fishing, most retrenched workers and unemployed youths from the riverine areas are taking up fishing as a legitimate and gainful livelihood. To sustain this tempo and attract more investment, the economic viability of such projects must be known. This study is an attempt to document the profitability and investment potential of artisanal canoe fishing. Socio-economic information including catches, operational cost and returns were obtained through a personal interview questionnaire survey of 240 randomly selected artisanal canoe fishermen from Bonny, Brass and Degema Local Government Areas (LGA) of the State and analyzed. With an investment cost of about 8,135, 8,490 and 6,571 and operation cost of 750, 776 and 627, the analysis showed an average monthly gross income of 1,869, 3,221 and 1,775 for the three local government areas respectively. A benefit-cost-ratio of 1:8, net present value of 400, 603 and internal rate of return greater than 50% were obtained. Since capital invested in fisheries is not tied up for long before benefits start flowing, coupled with the high IRR, it is concluded that artisanal canoe fishing would be an economically viable venture if well managed

Investment prospects in inland capture fisheries -- revolving loan scheme to artisanal fishermen

Fishing inputs in the form of the netting materials, boats and outboard engines were issued to 20 fishermen on revolving loan basis at 2 centres - Shagunu. and Monai along the western bank of Kainji Lake, Nigeria. The agreement was that the recipients should sell all their catches to the Institute and surrender 20% as part payment of the loan, until they offset the loan after which the inputs would become theirs'. The scheme was monitored for 5 years during which time most recipients had completed payment. It was observed that adequate revenue could be made from the scheme provided there was effective supervision. A proposal has been made for large scale supply of fishing inputs to one hundred fishermen. The scheme is laudable as a means of improving the lot of the fishermen and implementing management proposals in water bodies through the recipients

Investment opportunities in fish seed technology

An examination is made of the requirements for the commercial propagation of carp and tilapia in Nigeria. It is concluded that the operation of a successful Fish Hatchery and fry production system will depend on the following factors: 1) Correct initial planning for intended production (both species and intended numbers); 2) Design of the appropriate facilities to enable required production; 3) Selection of top calibre, dedicated and experienced hatchery staff; and, 4) The ethical responsibility taken by the hatchery management to produce only the highest quality seed under the best possible conditions. Purchasing farmers are dependent on this

Investment prospects in the production of the common carp (Cyprinus carpio) fingerlings in freshwater ponds

Since the introduction of Common carp Cyprinus carpio in Oyo State (Nigeria) from Israel in 1964, various local breeding methods have been employed in carp rearing to improve the survival rate at all stages of development during breeding. The physico-chemical parameters of the ponds which were simultaneously investigated for carp rearing in this study includes temperature (t), dissolved oxygen (DO) and hydrogen-ion concentration (pH). However, high rates of water displacement in the breeding ponds were unfavourable to the development of zooplankton which play important role in the food web of C. carpio. The survival rates of 15.88-69.50% and 19.60-33.83% obtained for the egg-hatchling and hatchling-fingerling stages respectively were encouraging. A breeding performance of this magnitude was found to be viable, breaking even in the fourth year. However, an increase in size of this trial project would be more profitable and increase fingerling supply as well as provide employment opportunities. This study thereby provides some baseline information on some local techniques and progress in the propagation of C. carpio and scope for further improvement

Investment prospects in fish feed technology

The author endeavours to analyse the recent trend in the local production of fish by sector over a period of 5 years, 1980-1985 and the data available to the author on the Nigerian fish imports. The present and future deficit in fish production in Nigeria could only be met from the capture fishery and the fish farm industry but more likely from the latter. The production techniques involved in fish feed industry are illustrated in this paper with standard feed formulations to arrive at a suitable fish diet. Associated problems of fish feed industry and their possible solutions are highlighted. A case study of investment prospects in fish feed industry as well as the production of brine shrimps are suggested as possible areas of investments in the industry. The unit production cost of fish feed is about 700/ton, while in the case of artemia (brine shrimp), the estimated unit cost if about 400/ton

Investment opportunity in aquarium technology. Export marketing of tropical aquarium fishes

A brief account is given of the demand for ornamental fish, providing also estimates of world trade volume. The major importing countries are the USA, Japan, Germany, the UK and the Netherlands. Present supply patterns are outlined; although Nigeria has vast natural resources of tropical aquatic life and the right climate for breeding, current exports are estimated at only 5% of the total potential. Recommendations for the promotion of exports of tropical aquarium fish in Nigeria are included

Investment prospects in integrated fish and poultry farming project: The Kainji Lake Research Institute integrated fish and poultry farm model

The paper examines the feasibility of a small-scale integrated fish and poultry farming project based on an existing experimental model currently in operation at the Kainji Lake Research Institute, New Bussa, Nigeria. Financial analysis reveals a viable investment based on the output from a 2 ha fish pond or reservoir