Upravljanje vjetroagregatom otporno na me.uzavojske kvarove statorskog namota generatora

Faults of wind turbine generator electromechanical parts are common and very expensive. This paper introduces a generator fault-tolerant control scheme for variable-speed variable-pitch wind turbines that can be applied regardless to the AC generator used. The focus is on generator stator isolation inter-turn fault that can be diagnosed and characterised before triggering the safety device. An extension of the conventional wind turbine control structure is proposed that prevents the fault propagation while power delivery under fault is deteriorated as less as possible compared to healthy machine conditions. Fault-induced and inherent asymmetries of the generator are estimated and respected by the field-oriented control of the generator to eliminate torque oscillations. An approach for asymmetry detection based on an unscented Kalman filter is proposed. Presented fault-tolerant control strategy is developed taking into account its modular implementation and installation in available control systems of existing wind turbines to extend their exploitable life span and increase energy production. Simulation results for the case of a megawatt class wind turbine are presented.Kvarovi elektromehaničkih dijelova generatora vjetroagregata česti su i izrazito skupi. U ovom radu predstavljen je koncept na kvarove otpornog upravljanja generatorom vjetroagregata s promjenjivom brzinom vrtnje i zakretom lopatica primjenjiv bez obzira na tip korištenog izmjeničnog generatora. Naglasak je stavljen na oštećenje izolacije unutar namota jedne faze statora generatora koje se može dijagnosticirati i okarakterizirati prije aktiviranja sustava zaštite. Predložena je nadogradnja postojećeg sustava upravljanja vjetroagregatom koja sprječava širenje kvara i pritom postiže čim manje smanjenje proizvodnje električne energije u odnosu na normalan režim rada. Tako.er je prikazano vektorsko upravljanje generatorom koje uzima u obzir nesimetrije generatora, kako one nastale uslijed djelovanja kvara, tako i one inherentne. U radu je prikazan pristup za otkrivanje nesimetrija generatora zasnovan na nederivacijskom Kalmanovu filtru. Predstavljena strategija upravljanja razvijena je uvažavajući mogućnost modularnog nadovezivanja na postojeće algoritme upravljanja već postavljenih vjetroagregata s ciljem produženja njihova životnog vijeka i povećanja proizvodnje energije. Dani su simulacijski rezultati za slučaj vjetroagregata iz megavatne klase

An analytical study for low voltage ride through of the brushless doubly-fed induction generator during asymmetrical voltage dips

The Brushless Doubly-fed Induction Generator (BDFIG) has high potential for wind energy systems, especially for offshore applications where minimum maintenance is vital. The machine low voltage ride through (LVRT) capability in the light of current grid code requirements was investigated using a precise dynamic model. This is particularly important for future multi- MW BDFIGs. This paper shows the necessity for improvements of the BDFIG LVRT capability with presenting a comprehensive analytical study during asymmetrical voltage dips. Analytical studies are conducted to extract a more precise equivalent circuit model of the BDFIG used for analyzing machine dynamic behavior under various fault conditions. In addition, a comparison between different voltage dips is performed to identify critical operating points for LVRT assessment. The results of the study are verified by coupled-circuit model, simulated in MATLAB/Simulink for a BDFIG prototype

Risk analysis and risk ranking in tunneling: A case study

Constructing tunnels underground is generally described as a high-risk activity owing to the fact that conditions in the surrounding area tend to be unpredictable. This would create unique dangers in every situation. It is important to gain a deep understanding of the risks associated with tunneling, in order to reduce the likelihood of their occurrence and severity of their consequences, should they occur. For this to be achieved, different risks should first be evaluated and ranked according to their relative importance and criticality. Amir Kabir tunnel is considered to be one of the most dangerous tunnels in Tehran, Iran in terms of the risks involved in its excavation and their potential consequences. In particular, part T4 of the tunnel passes through a zone of different strata and a compound of various soils. This paper studies part T4 of Amir Kabir tunnel from a risk analysis and risk management point of view. In doing so, factors increasing total cost of the project, causing delay in the project completion time, decreasing the operation rate and downgrading project quality were identified and ranked according to their importance, using the aggregate primary index risk method. For this purpose, a comprehensive questionnaire was designed and completed by experts within the field of tunneling. By responding to the questionnaires, the experts determined the relative likelihood of occurrence of the studied factors and their potential consequences. As a result, the experts suggested several alternatives to reduce the risks involved in this particular study. Moreover, the experts completed new questionnaires whilst taking into account different alternatives. In the next step, the risks before and after applying the alternatives were compared. As a result of performing the said analyses, it was concluded that firstly, the aggregate primary index risk is an effective tool in identifying the risks involved in such projects. Secondly, it was concluded that by taking into account different alternatives when analyzing and ranking the risks, severity of the said risks can potentially be reduced. By taking into account such matters when analyzing the risks of tunneling, the efficiency of tunneling projects can greatly increase as a result of reducing the risks that threaten all financial and human resources involved in tunneling project execution. The approach introduced in this paper, together with the methodology described, can be adopted by the mining design engineer in all similar situations. They will be of particular advantage in such methods as room and pillar where the number of similar tunnels required is high

Electromagnetic-thermal design optimization of the brushless doubly fed induction generator

In view of its special features, the brushless doubly fed induction generator (BDFIG) shows high potentials to be employed as a variable-speed drive or wind generator. However, the machine suffers from low efficiency and power factor and also high level of noise and vibration due to spatial harmonics. These harmonics arise mainly from rotor winding configuration, slotting effects, and saturation. In this paper, analytical equations are derived for spatial harmonics and their effects on leakage flux, additional loss, noise, and vibration. Using the derived equations and an electromagnetic-thermal model, a simple design procedure is presented, while the design variables are selected based on sensitivity analyses. A multiobjective optimization method using an imperialist competitive algorithm as the solver is established to maximize efficiency, power factor, and power-to-weight ratio, as well as to reduce rotor spatial harmonic distortion and voltage regulation simultaneously. Several constraints on dimensions, magnetic flux densities, temperatures, vibration level, and converter voltage and rating are imposed to ensure feasibility of the designed machine. The results show a significant improvement in the objective function. Finally, the analytical results of the optimized structure are validated using finite-element method and are compared to the experimental results of the D180 frame size prototype BDFIG. © 1982-2012 IEEE

Failure Modes and Effects Analysis (FMEA) for wind turbines

The Failure Modes and Effects Analysis (FMEA) method has been used to study the reliability of many different power generation systems. This paper now applies that method to a wind turbine (WT) system using a proprietary software reliability analysis tool. Comparison is made between the quantitative results of an FMEA and reliability field data from real wind turbine systems and their assemblies. These results are discussed to establish relationships which are useful for future wind turbine designs. The main system studied is an existing design 2 MW wind turbine with a Doubly Fed Induction Generator (DFIG), which is then compared with a hypothetical wind turbine system using the Brushless Doubly Fed Generator (BDFG) of the same rating. The software reliability analysis tool used for these studies was Relex Reliability Studio 2007 Version 2

A novel modeling approach for design studies of brushless doubly fed induction generator based on magnetic equivalent circuit

Brushless doubly fed induction generator (BDFIG) has substantial benefits, which make it an attractive alternative as a wind turbine generator. However, it suffers from lower efficiency and larger dimensions in comparison to DFIG. Hence, optimizing the BDFIG structure is necessary for enhancing its situation commercially. In previous studies, a simple model has been used in BDFIG design procedure that is insufficiently accurate. Furthermore, magnetic saturation and iron loss are not considered because of difficulties in determination of flux density distributions. The aim of this paper is to establish an accurate yet computationally fast model suitable for BDFIG design studies. The proposed approach combines three equivalent circuits including electric, magnetic and thermal models. Utilizing electric equivalent circuit makes it possible to apply static form of magnetic equivalent circuit, because the elapsed time to reach steady-state results in the dynamic form is too long for using in population-based design studies. The operating characteristics, which are necessary for evaluating the objective function and constraints values of the optimization problem, can be calculated using the presented approach considering iron loss, saturation, and geometrical details. The simulation results of a D-180 prototype BDFIG are compared with measured data in order to validate the developed model. © 1986-2012 IEEE

Assessing the effect of wind farm layout on energy storage requirement for power fluctuation mitigation

Optimization of wind farm (WF) layout has been studied in the literature with the objective of maximizing the wind energy capture. Based on the power spectrum density (PSD) theorem, this paper shows that the WF layout affects not only the total harvested energy but also the level of power fluctuation, which in turn influences required capacity of battery energy storage system (BESS) needed to mitigate the inherent power fluctuation of the wind farms. Since both harvested energy level and BESS capacity directly influence the profit of WF owner, the effect of WF layout on these quantities are taken into account simultaneously and WF layout optimization problem is redefined. Genetic algorithm (GA) is then employed in order to optimize the resulting objective function. The proposed method and optimization process are performed on the layout of an actual offshore WF using real wind data. A new index is introduced to quantify the power fluctuations, and energy curtailment is assessed. The comparative analysis between the actual layout performance and the optimal layout in different scenarios is conducted, showing the reduction of power fluctuations and improvement of energy curtailment. In addition, different BESS technologies have been analyzed to study the impact of their parameters on the optimization results

Reliability comparison of direct-drive and geared-drive wind turbine concepts

This paper proposes for wind turbines (WTs) an analytical reliability method, used on other engineering systems, to compare the reliability of different turbine concepts. The main focus of the paper is to compare the reliability of geared generator and direct-drive concept WTs. Modification methods are also recommended for improving the availability of WTs and geared generator concept incorporating doubly fed induction generator

Wind turbine productivity considering electrical subassembly reliability

This paper proposes a reliability model for the electrical subassemblies of geared wind turbine systems with induction generators. The model is derived considering the failure of main subassemblies and their parameters are calculated. A productivity comparison is performed between the selected wind turbine systems including reliability issues. Two methods of modification for variable-speed wind turbines with Doubly Fed Induction Generators (DFIG) to improve their availability are finally suggested