Meeting future world energy needs while addressing climatic changes has led to greater strain on conventional power sources. One of the viable sustainable energy sources is wind. But the installation large scale wind farms has a potential impact on the climatic conditions, hence a decentralized small scale wind turbines is a sustainable option. This paper presents review of on different types of small scale wind turbines i.e., horizontal axis and vertical axis wind turbines. The performance, blade design, control and manufacturing of horizontal axis wind turbines were reviewed. Vertical axis wind turbines were categorized based on experimental and numerical studies. Also, the positioning of wind turbines and aero-acoustic aspects were presented. Additionally, lessons learnt from various studies/countries on actual installation of small wind turbines were presented.

A review on small scale wind turbines

Performance evaluation of 3D printed miniature electromagnetic energy harvesters driven by air flow

Locally manufactured wind power technology for sustainable rural electrification

The inertia of wind turbines causes a reduction in their output power due to their inability to operate at the turbine maximum co-efficient of performance point under dynamic wind conditions. In this paper, this dynamic power reduction is studied analytically and using simulations, assuming that a steady-state optimal torque control strategy is used.

The concepts of the natural and actual turbine time-constant are introduced, and typical values for these parameters are examined. It is shown that for the typical turbine co-efficient of performance curve used, the average turbine speed can be assumed to be determined by the average wind speed. With this assumption, analytical expressions for the power reduction with infinite and then finite turbine inertia are determined for sine-wave wind speed variations. The results are then generalized for arbitrary wind speed profiles.

A numerical wind turbine system simulation model is used to validate the analytical results for step and sine-wave wind speed variations. Finally, it is used with real wind speed data to compare with the analytical predictions. Copyright © 2012 John Wiley & Sons, Ltd.

Dynamic wind turbine output power reduction under varying wind speed conditions due to inertia

The expansion of the railway industry has increased the demand for the three-dimensional modeling of railway tracks. Due to the increasing development of UAV technology and its application advantages, in this research, the detection and 3D modeling of rail tracks are investigated using dense point clouds obtained from UAV images. Accordingly, a projection-based approach based on the overall direction of the rail track is proposed in order to generate a 3D model of the railway. In order to extract the railway lines, the height jump of points is evaluated in the neighborhood to select the candidate points of rail tracks. Then, using the RANSAC algorithm, line fitting on these candidate points is performed, and the final points related to the rail are identified. In the next step, the pre-specified rail piece model is fitted to the rail points through a projection-based process, and the orientation parameters of the model are determined. These parameters are later improved by fitting the Fourier curve, and finally a continuous 3D model for all of the rail tracks is created. The geometric distance of the final model from rail points is calculated in order to evaluate the modeling accuracy. Moreover, the performance of the proposed method is compared with another approach. A median distance of about 3 cm between the produced model and corresponding point cloud proves the high quality of the proposed 3D modeling algorithm in this study.

https://www.mdpi.com/1424-8220/20/18/5220/pdf

Rail Track Detection and Projection-Based 3D Modeling from UAV Point Cloud

A case study was performed on a commercially available low cost wind turbine. The turbine was tested in a wind tunnel with up to 13 m/s wind speed. The blade characteristics were measured as a function of wind speed, yaw angle, with and without a nose cone, and compared to theoretical models. Practical issues are noted as required for reliable operation, in particular the design of blades and their attachment to the turbine.

A Low Cost Wind Turbine and Blade Performance

This paper describes measurements of the shape of a 900 mm long, hand-carved timber blade for a 500 W three-bladed horizontal axis wind turbine. Four blades were hand-carved in Nepal by reference to a master blade cut in Australia on a numerically controlled milling machine. A high definition three-dimensional scanner was used to determine the surface of one hand-carved blade as a series of profiles at 50 mm intervals along the blade's length. A surface model generated from these profiles was compared to the designed blade shape in terms of the three fundamental blade design parameters: chord, twist, and profile shape. The measured twist and chord were less that the design values, particularly in the hub region. This is consistent with the poor starting performance of the turbine when mounted with the remaining hand-carved blades. Assessment of the differences in profile shape would require a detailed computational analysis, which has not been undertaken.

The Shape and Performance of Hand-Carved Small Wind Turbine Blades

Insulated Gate Bipolar Transistors (IGBTs) are semiconductor devices used in power modules for inverters and in many other applications. The challenge however is that these devices do not last their estimated life span of about 20 years and experience different failure mechanisms. It is of interest to study the failure mechanisms to give a better understanding of how to improve reliability of these devices as well as model and accurately predict the lifetime of IGBTs. The IGBT circuitry is encapsulated in silicone gel and the presence of this silicone gel prevents visual inspection of the type of failure mechanism that was experienced by the IGBT. When using a scanning electron microscope to examine the failed module, the sample may need to be gold plated and will be placed in a vacuum. Any silicone gel remaining on the IGBT module under investigation will vaporise and coat parts of the electron microscope thus damaging the microscope. Hence there is need to be able to remove all the silicone gel from the IGBT module before proper investigation into the mechanism that caused failure can begin. The results of these experiments show a practical approach on how to remove silicone in the laboratory from IGBT modules without causing any further corrossive damage to the modules under investigation.

Experimental Investigation of IGBT Silicone Gel Removal

Nonlinear loads draw a distorted current from the supply containing both nonzero and zero sequence harmonic amplitudes. In a three phase four wire network, such loads would also result in a high neutral current. This paper compares the design and performance of four branch shunt passive filter topologies in a three phase four wire stiff grid to selectively filter both nonzero and zero sequence harmonics. The results have shown the effectiveness of the filter to attenuate nonzero sequence harmonics and the limitation, due to system resonance, to attenuate zero sequence harmonics. A modified passive filter with a supply side neutral impedance is presented in this paper to improve filter performance. Computer simulation as well as experimental setup were implemented for the comparison and results have shown the effectiveness of the modified passive filter to selectively filter both nonzero and zero sequence harmonics.

Design and Comparison of Four Branch Passive Harmonic Filters in Three Phase Four Wire Systems

Informal settlements are often temporary settlements which exist without the usual residential infrastructure, including no electricity. This paper presents a case study for a particular informal settlement in terms of 3 possibilities of a styles of electrification, consisting of grid connection, photovoltaic systems for large household solar and small household solar systems. The effect of no land tenure is shown to be an overriding factor.

Comparison of informal settlement electrification: A case study at seaview, eastern cape, South Africa

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