煤矿局部通风机瓦斯浓度自动调节及节能控制研究

文章研究一款局部通风机瓦斯浓度自动调节及节能控制系统,通过传感器来检测矿井内瓦斯的浓度,利用PLC控制系统控制变频器来控制通风量自动调节,达到降低矿井内瓦斯浓度、节约电能的作用。

湘潭钢铁厂炼铁分厂煤粉制备系统阻力损失测试及节能改造

本文对湘潭钢铁厂炼铁分厂煤粉制备系统每个单元与阀门的实际阻力损失值进行了测量,测量结果表明,该系统运行总效率低于30%,本文通过对实际阻损值进行分析研究,提出了用一台风机代替目前两台风机串联运行的技术改造方案,改造后,取得了较好的经济效益。图2,表2,参3。

Dynamic modelling and robust current control of wind-turbine driven DFIG during external AC voltage dip

Doubly-Fed Induction Generator （DFIG）, with vector control applied, is widely used in Variable-Speed Constant- Frequency （VSCF） wind energy generation system and shows good performance in maximum wind energy capture. But in two traditional vector control schemes, the equivalent stator magnetizing current is considered invariant in order to simplify the rotor current inner-loop controller. The two schemes can perform very well when the grid is in normal condition. However, when grid disturbance such as grid voltage dip or swell fault occurs, the control performance worsens, the rotor over current occurs and the Fault Ride-Through （FRT） capability of the DFIG wind energy generation system gets seriously deteriorated. An accurate DFIG model was used to deeply investigate the deficiency of the traditional vector control. The improved control schemes of two typical traditional vector control schemes used in DFIG were proposed, and simulation study of the proposed and traditional control schemes, with robust rotor current control using Internal Model Control （IMC） method, was carded out. The validity of the proposed modified schemes to control the rotor current and to improve the FRT capability of the DFIG wind energy generation system was proved by the comparison study.

Adaptive rotor current control for wind-turbine driven DFIG using resonant controllers in a rotor rotating reference frame

This paper proposes an adaptive rotor current controller for doubly-fed induction generator (DFIG), which consists of a proportional (P) controller and two harmonic resonant (R) controllers implemented in the rotor rotating reference frame. The two resonant controllers are tuned at slip frequencies ωslip+ and ωslip-, respectively. As a result, the positive- and negative-sequence components of the rotor current are fully regulated by the PR controller without involving the positive- and negative-sequence decomposition, which in effect improves the fault ride-through (FRT) capability of the DFIG-based wind power generation system during the period of large transient grid voltage unbalance. Correctness of the theoretical analysis and feasibility of the proposed unbalanced control scheme are validated by simulation on a 1.5-MW DFIG wind power generation system.

Experimental study on performance of contra-rotating axial flow fan

Contra-rotating axial flow fan is a kind of the vital equipment in coal mines. Their work conditions directly affect the safety of staff and production. In the paper, the performance of the contra-rotating axial flow fan is experi- mentally investigated. The study is focused on the fan performance, the shaft power and the match between the motor and fan efficiency at different blade angles. The results show that the blade angle 43°/26° has the best aerodynamic perfor- mance. The first engine has a greater impact on the fan than the second one. The blade angle with the best aerodynamic performance does not necessarily correspond to the one with the best match between the motor and fan efficiency. The blade angle 43°/24° is the best choice for the operation of the fan in the present study.

Functional design of wind turbine airfoils based on roughness sensitivity characteristics

To improve aerodynamic performance of wind turbine airfoils,the shape profile characteristic of the airfoil is investigated.Application of conformal transformation,one functional and integrated expression of wind turbine airfoils is presented.Using the boundary layer theory,the aerodynamic model with roughness of wind turbine airfoils is introduced by studying flow separation around the airfoil.Based on the shape expression and aerodynamic performance of airfoils,the function design of wind turbine airfoils is carried out that the maximum lift-drag ratio and low roughness sensitivity are designed objects.Three wind turbines airfoils with different thickness are gained which are used at tip part of blades.As an example,the aerodynamic performance of one designed airfoil with relative thickness of 15%is simulated in different conditions of clean surface,rough surface,laminar flow and turbulent flow.The comparison of aerodynamic performance between the designed airfoil and one popular NACA airfoil is completed which can verify the better performance of the designed airfoil and reliability of the designed method.

Investigation on Installation of Offshore Wind Turbines

Wind power has made rapid progress and should gain significance as an energy resource,given growing interest in renewable energy and clean energy.Offshore wind energy resources have attracted significant attention,as,compared with land-based wind energy resources,offshore wind energy resources are more promising candidates for development.Sea winds are generally stronger and more reliable and with improvements in technology,the sea has become a hot spot for new designs and installation methods for wind turbines.In the present paper,based on experience building offshore wind farms,recommended foundation styles have been examined.Furthermore,wave effects have been investigated.The split installation and overall installation have been illustrated.Methods appropriate when installing a small number of turbines as well as those useful when installing large numbers of turbines were analyzed.This investigation of installation methods for wind turbines should provide practical technical guidance for their installation.

Perspectives of China’s wind energy development

Wind energy is a kind of clean renewable energy, which is also relatively mature in technology, with largescale development conditions and prospect for the commercialization. The development of wind energy is a systematic project, involving policy, law, technology, economy, society, environment, education and other aspects. The relationship among all the aspects should be well treated and coordinated. This paper has discussed the following relationships which should be well coordinated: relationship between wind resources and wind energy development, relationship between the wind turbine generator system and the components, relationship between wind energy technology and wind energy industry, relationship between off-grid wind power and grid-connected wind power, relationship between wind farm and the power grid, relationship between onshore wind power and offshore wind power, relationship between wind energy and other energies, relationship between technology introduction and self-innovation, relationship among foreign-funded, joint ventured and domestic-funded enterprises and relationship between the government guidance and the market regulation, as well as giving out some suggestions.

Effect of blade pitch angle on aerodynamic performance of straight-bladed vertical axis wind turbine

Wind energy is one of the most promising renewable energy sources, straight-bladed vertical axis wind turbine(S-VAWT) appears to be particularly promising for the shortage of fossil fuel reserves owing to its distinct advantages, but suffers from poor self-starting and low power coefficient. Variable-pitch method was recognized as an attractive solution to performance improvement, thus majority efforts had been devoted into blade pitch angle effect on aerodynamic performance. Taken into account the local flow field of S-VAWT, mathematical model was built to analyze the relationship between power outputs and pitch angle. Numerical simulations on static and dynamic performances of blade were carried out and optimized pitch angle along the rotor were presented. Comparative analyses of fixed pitch and variable-pitch S-VAWT were conducted, and a considerable improvement of the performance was obtained by the optimized blade pitch angle, in particular, a relative increase of the power coefficient by more than 19.3%. It is further demonstrated that the self-starting is greatly improved with the optimized blade pitch angle.

Study on switched reluctance generator

The linear and non-linear math models of the switched reluctance generator (SRG) in generator mode were established in this work. The phase current and energy conversion process during generator operation were simulated by the linear math model. The non-linear math model was used to analyze the characteristics of the SRG operation in self-excitation mode and in separately-excitation mode. Some important findings on how the SRG is operated and controlled were obtained in this study, which provides theoretical basis for further design and experimental study.

On Advanced Control Methods toward Power Capture and Load Mitigation in Wind Turbines

This article provides a survey of recently emerged methods for wind turbine control. Multivariate control approaches to the optimization of power capture and the reduction of loads in components under time-varying turbulent wind fields have been under extensive investigation in recent years. We divide the related research activities into three categories： modeling and dynamics of wind turbines, active control of wind turbines, and passive control of wind turbines. Regarding turbine dynamics, we discuss the physical fundamentals and present the aeroelastic analysis tools. Regarding active control, we review pitch control, torque control, and yaw control strategies encompassing mathematical formulations as well as their applications toward different objectives. Our survey mostly focuses on blade pitch control, which is considered one of the key elements in facilitating load reduction while maintaining power capture performance. Regarding passive control, we review techniques such as tuned mass dampers, smart rotors, and microtabs. Possible future directions are suggested.

Layered Multi-mode Optimal Control Strategy for Multi-MW Wind Turbine

The control strategy is one of the most important renewable technology,and an increasing number of multi-MW wind turbines are being developed with a variable speed-variable pitch(VS-VP)technology.The main objective of adopting a VS-VP technology is to improve the fast response speed and capture maximum energy.But the power generated by wind turbine changes rapidly because of the continuous fluctuation of wind speed and direction.At the same time,wind energy conversion systems are of high order,time delays and strong nonlinear characteristics because of many uncertain factors.Based on analyzing the all dynamic processes of wind turbine,a kind of layered multi-mode optimal control strategy is presented which is that three control strategies:bang-bang,fuzzy and adaptive proportional integral derivative(PID)are adopted according to different stages and expected performance of wind turbine to capture optimum wind power,compensate the nonlinearity and improve the wind turbine performance at low,rated and high wind speed.

A Case Study on the Utilization of Wind Energy Potential on Remote and Isolated Small Wastewater Plants

Small WWTP （wastewater treatment plants） are frequently located, by necessity, in remote and isolated sites, which increases the difficulty of its energy supply. This paper describes a case study which is a step by step procedure concerning the evaluation of the wind potential of sites that are dependent of in-situ energy generation, as well as, on the utilization of the potential wind energy in Magoito WWTP. The adopted methodology comprised the collection of one year of in-situ wind data and its validation by comparison with historical data of more than 10 years of a nearby anemometric station. The data provided by the two anemometric stations was statistically treated and allowed the analysis of the results from the two stations. These results are promising in terms of wind availability and velocity. Finally, the study comprised the simulation of the local wind conditions for a considerable larger area in order to find the best site for locating a wind turbine.

Wind Energy Potential Assessment in Republic of Macedonia

The paper presents the measurement campaign of wind energy potential undertaken in Republic of Macedonia on four sites from the middle of 2006. The wind data analysis has been performed for one site, following with the assessment of energy production of simulated wind park with six wind turbine generators.

Particular evolution in a 72-year-old diabetic patient with acute coronary syndrome

Diabetes mellitus is an important risk factor for coronary atherosclerosis and many patients present extensive coronary stenosis at coronarography. However, in patients with diabetes, endothelial and microvascular dysfunction also participate in chronic and acute myocardial ischemia. Although the majority of diabetic patients with myocardial infarction have angiographic evidence of significant coronary artery disease.

Numerical Investigations on the Aerodynamic Performance of Wind Turbine： Downwind Versus Upwind Configuration

Although the upwind configuration is more popular in the field of wind energy, the downwind one is a promising type for the offshore wind energy due to its special advantages. Different configurations have different aerodynamic performance and it is important to predict the performance of both downwind and upwind configurations accurately for designing and developing more reliable wind turbines. In this paper, a numerical investigation on the aerodynamic performance of National Renewable Energy Laboratory （NREL） phase V1 wind turbine in downwind and upwind configurations is presented. The open source toolbox OpenFOAM coupled with arbitrary mesh interface （AMI） method is applied to tackle rotating problems of wind turbines. Two 3D numerical models of NREL phase VI wind turbine with downwind and upwind configurations under four typical working conditions of incoming wind velocities are set up for the study of different unsteady characteristics of the downwind and upwind configurations, respectively. Numerical results of wake vortex structure, time histories of thrust, pressure distribution on the blade and limiting streamlines which can be used to identify points of separation in a 3D flow are presented. It can be concluded that thrust reduction due to blade-tower interaction is small for upwind wind turbines but relatively large for downwind wind turbines and attention should be paid to the vibration at a certain frequency induced by the cyclic reduction for both configurations. The results and conclusions are helpful to analyze the different aerodynamic performance of wind turbines between downwind and upwind configurations, providing useful references for practical design of wind turbine.

Organ dysfunction as a risk factor for early severe acute pancreatitis

We read with interest the review paper by Tao et al. on thetopic of early severe acute pancreatifis (EASP, defined as severeacute pancreatitis according to the Altanta criteria, with organdysfunction within 72 h after the start of symptoms) in a recentissue of the World Journal of Gastroenterology. It addressesan important problem in patients with severe acute pancreatitis,namely early organ dysfunction and its effect on outcomes.

Development of testing techniques for mine fan performance

Three progressive stages of testing techniques are elaborated,which are en-tirely manual operating,taking separate instruments testing and computer program con-trolling.The testing method and principle are detailed based on the testing process formeteorological parameters,air pressure,air quality and rotating velocity.And every testingtechnique is analyzed.Finally, the technique outlook is viewed.All this plays a leading rolein development of the testing techniques.

Performance evaluation methods and instrumentation for mine ventilation fans

Ventilation fans are one of the most important pieces of equipment in coal mines. Their performance plays an important role in the safety of staff and production. Given the actual requirements of coal mine production,we instituted a research project on the measurement methods of key performance parameters such as wind pressure,amount of ventilation and power. At the end a virtual instrument for mine ventilation fans performance evaluation was developed using a USB interface. The practical performance and analytical results of our experiments show that it is feasible,reliable and effective to use the proposed instrumentation for mine ventilation performance evaluation.

Heating and Cooling Performance of Earth-Tube Heat Exchanger in a Mechanical Ventilated Farrowing House

Earth tempering of stable air has attracted great attention as a sustainable air conditioning method in pig houses. At summer time air cooling of income air strongly reduces heat stress and required ventilation rate. At winter time heating costs can be reduced. The effect of air condition using geothermal energy was investigated in a farrowing house. Underneath the foundation of the farrowing house 88 non perforated ribbed tubes （diameter： 20 cm） were piped in a depth of 1.6-2.0 m. Over a period of 12 month following data were recorded at hourly intervals and analyzed： outside air temperature, as well as air temperature in the air supply duct and in the compartments. Incoming air （supply duct） was heated up to 20 ℃ during winter time and in summer time cooled by up to 15 ℃ compared to the outside air temperature. In contrast to the outside air diurnal variation, temperature fluctuations of the incoming air were reduced by 90%. Due to cooling of the incoming air at summer time the stable inside temperature could be limited to maximal 29 ℃（maximum outside temperature was 35℃）. Earth-tube heat exchangers with non perforated ribbed tubes were very efficient for air conditioning in farrowing houses. They were a cost effective supplement for sustainable cooling and heating of farrowing houses.