Current Issue : April - June Volume : 2019 Issue Number : 2 Articles : 5 Articles
This paper proposed a probabilistic load flow technique of AC/VSC-MTDC (Alternate\nCurrent/Voltage Source Control-Multiple Terminal Direct Current) hybrid grids based on an\nimproved stochastic response surface method. The applied traditional stochastic response surface\nmethod is inherent with the capability to tackle correlated normal variables; however, the accuracy\nis poor in the case of correlated diverse distributions. To address this issue, NATAF transformation\nwas adopted to transform the correlated wind speeds and loads following arbitrary distributions\ninto the variables that are subject to standard normal distributions. The collection points could be\nselected to establish the polynomial relationship among the independent standard normal variables\nand the output responses. Then, the probability distributions and statistics of the responses could\nbe accurately and efficiently estimated. The modified IEEE 14-bus system, involving an additional\nVSC-MTDC system, wind speeds following various distributions, and diverse consumer behaviors,\nwas used to demonstrate the validity and capability of the proposed method....
Due to fundamental temporal mismatches between renewable energy generation and demand load, a long-duration energy storage system is required to power Prince Edward Islandâ??s (PEI) electricity system exclusively from on-island wind and solar resources. While a very large lithium battery is a technically capable solution, todayâ??s battery technology is not cost effective; even as wind and solar generation costs become increasingly competitive with fossil fuel alternatives. To explore alternative storage technologies this comparative study utilizes the established hybrid optimization model for multiple energy resources (HOMER) techno-economic modeling tool to perform an application-based high-level comparison of an efficient but costly lithium battery technology solution with a much less efficient but lower-cost thermal-storage with steam-turbine concept; both capable of enabling a 100% wind and solar powered electricity supply for the island. Interestingly, the thermal storage turbine concept is shown to be competitive, at least in principle, with projected cost reductions in lithium battery technologies while also offering a number of distinct practical advantages...
Wind tunnel measurements of two-dimensional wing sections, or airfoils, are the building\nblock of aerodynamic predictions for many aerodynamic applications. In these experiments, the forces\nand pitching moment on the airfoil are measured as a function of the orientation of the airfoil relative\nto the incoming airflow. Small changes in this angle (called the angle of attack) can create\nsignificant changes in the forces and moments, so accurately measuring the angle of attack is critical\nin these experiments. This work describes the implementation of laser displacement sensors in a\nwind tunnel; the sensors measured the distance between the wind tunnel walls and the airfoil, which\nwas then used to calculate the model position. The uncertainty in the measured laser distances, based\non the sensor resolution and temperature drift, is comparable to the uncertainty in traditional linear\nencoder measurements. Distances from multiple sensors showed small, but statistically significant,\namounts of model deflection and rotation that would otherwise not have been detected, allowing for\nan improved angle of attack measurement....
Megawatt-scale wind turbine technology is nowadays mature and, therefore, several\ntechnical improvements in order to optimize the efficiency of wind power conversion have been\nrecently spreading in the industry. Due to the nonstationary conditions to which wind turbines\nare subjected because of the stochastic nature of the source, the quantification of the impact of\nwind turbine power curve upgrades is a complex task and in general, it has been observed that\nthe efficiency of the upgrades can vary considerably depending on the wind flow conditions at the\nmicroscale level. In this work, a test case of wind turbine control system improvement was studied\nnumerically and through operational data. The wind turbine is multi-megawatt; it is part of a wind\nfarm sited in a complex terrain in Italy, featuring 17 wind turbines. The analyzed control upgrade is\nan optimization of the revolutions per minute (rpm) management. The impact of this upgrade was\nquantified through a method based on operational data: It consists of the study, before and after the\nupgrade, of the residuals between the measured power output of the wind turbine of interest and an\nappropriate model of the power output itself. The input variables for the model were selected to be\nsome operational parameters of the nearby wind turbines: They were selected from the data set at\ndisposal with a stepwise regression algorithm. This work also includes a numerical characterization\nof the problem, by means of aeroelastic simulations performed with the FAST software: By mimicking\nthe pre- and post-upgrade generator rpmâ??generator torque curve, it is subsequently possible to\nestimate how the wind turbine power curve changes. The main result of this work is that the two\nestimates of production improvement have the same order of magnitude (1.0% of the production\nbelow rated power). In general, this study sheds light on the perspective of employing not only\noperational data, but also a sort of digital replica of the wind turbine of interest, in order to reliably\nquantify the impact of control system upgrades....
This paper presents a new operational strategy for a large-scale wind farm\n(WF) which is composed of both fixed speed wind turbines with squirrel cage\ninduction generators (FSWT-SCIGs) and variable speed wind turbines with\npermanent magnet synchronous generators (VSWT-PMSGs). FSWT-SCIGs\nsuffer greatly from meeting the requirements of fault ride through (FRT), because\nthey are largely dependent on reactive power. Integration of flexible ac\ntransmission system (FACTS) devices is a solution to overcome that problem,\nthough it definitely increases the overall cost. Therefore, in this paper, a new\nmethod is proposed to stabilize FSWT-SCIGs by using VSWT-PMSGs in a\nWF. This is achieved by injecting the reactive power to the grid during fault\ncondition by controlling the grid side converter (GSC) of PMSG. The conventional\nproportional-integral (PI)-based cascaded controller is usually used\nfor GSC which can inject small amount of reactive power during fault period.\nThus, it cannot stabilize larger rating of SCIG. In this paper, a suitable fuzzy\nlogic controller (FLC) is proposed in the cascaded controller of GSC of PMSG\nin order to increase reactive power injection and thus improve the FRT capability\nof WF during voltage dip situation due to severe network fault. To evaluate\nthe proposed controller performance, simulation analyses are performed on a\nmodified IEEE nine-bus system. Simulation results clearly show that the proposed\nmethod can be a cost-effective solution which can effectively stabilize the\nlarger rating of SCIG compared to conventional PI based control strategy....
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