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1
Ling, Yu, Zhenlan Dou, Qiang Gao i Xu Cai. "Improvement of the Low-Voltage Ride-through Capability of Doubly Fed Induction Generator Wind Turbines". Wind Engineering 36, nr 5 (październik 2012): 535–51. http://dx.doi.org/10.1260/0309-524x.36.5.535.
Pełny tekst źródłaStreszczenie:
So far, active crowbars are a preferred technique for doubly fed induction generator (DFIG) wind turbines, which is used to protect the power converter against over-current and undesirably high dc link voltage during voltage dip. However, its main drawbacks are that (1) the DFIG absorbs reactive power from the grid during grid voltage dips, (2) the crowbar activation increases the acceleration of the rotor and so, deteriorates the dynamic stability of DFIG, and (3) the control is not flexible for long-time voltage sags. In the paper, three different initiating logic control methods of crowbar protection are compared, and how low-voltage ride-through (LVRT) characteristics of DFIG wind turbines with active crowbar are affected by different switching logic control modes of the crowbar are investigated. According to the comparison results, an improved crowbar switching control strategy is proposed to reduce its operation time and improve the LVRT capability of DFIG wind turbines. In addition, an emergency pitch blade angle control scheme to reduce the acceleration of the rotor and prevent the over-speeding of rotor is presented in detail, and as a result, the LVRT capability of DFIG wind turbines is enhanced even during long-time voltage sags. Finally, the presented control strategies are validated in simulation tool Matalab/Simulink for a 1.5MW generator.
2
Rihan, Mahmoud, Mahmoud Nasrallah, Barkat Hasanin i Adel El-Shahat. "A Proposed Controllable Crowbar for a Brushless Doubly-Fed Reluctance Generator, a Grid-Integrated Wind Turbine". Energies 15, nr 11 (25.05.2022): 3894. http://dx.doi.org/10.3390/en15113894.
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Brushless doubly fed reluctance generators (BDFRGs) are hopeful generators for using inside variable speed wind turbines (VSWTs), as these generators introduce a promising economical value because of their lower manufacturing and maintenance costs besides their higher reliability. For integrating WT generators, global networks codes require enabling these generators to stay connected under grid disturbances. The behavior of the BDFRG is strongly affected by grid disturbances, due to the small rating of the used partial power converters, as these converters cannot withstand high faults currents which leads to quick tripping of BDFRG. VSWTs can be safeguarded against faults using the crowbar. Usually, the conventual crowbar is shunt connected across the converter to protect it, but this configuration leads to absorbing reactive power with huge amounts from the grid, leading for more voltage decaying and more power system stability deterioration. This study proposes a simpler self-controllable crowbar to enhance the ability of the BDFRG to remain in service under faults. The operation technique of the proposed crowbar is compared to other crowbar operation techniques, the effectiveness of the proposed system would be analyzed. Through the simulation results and behavior analysis, the proposed crowbar technique demonstrates a decent improvement in the conduct of the studied system under faults.
3
Li, Yin Xing, Peng Hui Liu i Jun Li Zhang. "Research on Low Voltage Ride-Through Technique in DD-PMSG Wind Power Generator System". Applied Mechanics and Materials 300-301 (luty 2013): 108–11. http://dx.doi.org/10.4028/www.scientific.net/amm.300-301.108.
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In order to achieve the power grid voltage default ride-through, the permanent magnet direct-drive type wind power generator system is employed. The Crowbar resistance and the STATCOM operation mode are two effective methods to control the DC capacitor voltage not to rise and to help the power grid voltage restoration. The power grid voltage default is little and the STATCOM operation mode is applied. The Crowbar resistance is invested to the wind power generator system when the voltage default is large. The methods introduced in this paper are applied in other variable speed fixed frequency wind power generator system.
4
Zhang, Dahai, Ying Chen, Jing Yang, Ming Tan, Xiandong Ma i Wei Li. "Fault Ride-Through Analysis and Protection of a 2-MW DFIG Tidal Current Turbine". Marine Technology Society Journal 49, nr 5 (1.09.2015): 49–57. http://dx.doi.org/10.4031/mtsj.49.5.1.
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AbstractThe purposes of this article are to report on a study of fault ride-through (FRT) capability improvements of a tidal current turbine with a doubly fed induction generator (DFIG) and to investigate protection schemes for power electronic converters without disconnection during grid faults. A dynamic model of a DFIG tidal current turbine is described in the article, taking into account the effect of crowbar protection on the system when subjected to disturbances, such as short circuit faults. Investigations into the dynamic behavior of tidal current turbines are made through extensive simulations via PSCAD/EMTDC software. The research demonstrates that both the timing of crowbar removal and the value of crowbar resistance have a significant impact on the system voltage recovery following grid faults. The article also demonstrates that the selection of an appropriate crowbar resistor value is critical in order to ensure that the DFIG returns to normal operation with active and reactive power control as quickly as possible.
5
Su, Yinsheng, Sijia Tu, Guanghu Xu, Ligang Zhao, Haicheng Yao, Guanbiao Huang i Bao Li. "Short-circuit Current Engineering Calculation Method Considering Crowbar Operation Priority Degree of DFIG". Journal of Physics: Conference Series 2496, nr 1 (1.05.2023): 012031. http://dx.doi.org/10.1088/1742-6596/2496/1/012031.
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Abstract When fault occurs in high wind power proportion grid, the control strategy and external characteristics of the wind power plant are affected by voltage drop of grid, so the traditional short-circuit current engineering calculation is difficult to converge. A short-circuit current engineering calculation method for high wind power proportion grid, considering grid node importance evaluation and crowbar protection of DFIG(double-fed induction generator), is proposed. This paper proposes the external equivalent model of the DFIG when fault occurs in grid, considers voltage drop degree and node importance indexes, and determines the weight of each index through Delphi method. The DFIG crowbar operation priority is evaluated to ensure the successful convergence of calculation and the maximum voltage support of wind power plants. The study case shows that proposed method is superior to the traditional method.
6
G, SENTHIL KUMARAN, KUMAR V J F i DIVAKER DURAIRAJ C. "Bio-mechanical analysis on selected agricultural hand tools". Madras Agricultural Journal 91, March (2004): 5–9. http://dx.doi.org/10.29321/maj.10.a00056.
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Bio-mechanical analysis of agricultural hand tools viz. crowbar, hand hoc, spade and sickle was conducted. Pertinent anthropometric parameters of male and female farm workers of the southern districts of Tamil Nadu were measured. A bio- mechanical analysis on the work posture indicated that the reaction force on neck. for the operation of crowbar, different spades, hand hoes and sickle were 21.8, 24- 26, 17-21 and 18.9 kg respectively. The crowbar and spade caused 21.8 kg and 88- 110 kg of reaction forces respectively on biceps. The same for hand hoe and sickle was 41 and 2.6 kg respectively. The reaction force due to hand grip was 4.8 and 1-1.3 kg for crow bar and spade respectively. The reaction force on lumbosacral joint for spade, hand hoe and sickel was 248-394, 311-388 and 280 kg respectively. It was negligible for crow bar.
7
Le, Thai Hiep, i Duong Hoang Phuc Tran. "Study on operating modes of doubly fed induction generator with a short circuit fault on grid near the wind power plant". Journal of Science, Quy Nhon University 15, nr 1 (25.02.2021): 37–44. http://dx.doi.org/10.52111/qnjs.2021.15104.
Pełny tekst źródłaStreszczenie:
In this paper, the operating mode of a doubly fed induction generator (DFIG) wind turbine is studied in order to evaluate its fault ride-through and transient stability with a grid’s short circuit fault at near the wind power plant. Based on the structure of DFIG, external resistors are directly connected to rotor windings, then the generator operates as a wound rotor induction generator (WRIG) when there is a short circuit fault on the grid. According to the simulation results in Matlab, the active power is consumed on the crowbar resistor, causing the active power characteristic of generator is changed from high to low. As a result, the amount of excess mechanical energy is not much, so the generator be not accelerated significantly. These simulation results show that it is appropriate to use the crowbar resistor to change the power characteristic of the DFIG. Thanks to this change, the generator is still connected to the grid, stable operation both during and after a short circuit.
8
Yang, Xi Yun, Li Xia Li i Ya Min Zhang. "Control for Dc-Bus Voltage Using Grid Voltage Feed-Forward and Crowbar Circuit". Applied Mechanics and Materials 448-453 (październik 2013): 1727–31. http://dx.doi.org/10.4028/www.scientific.net/amm.448-453.1727.
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The DC bus voltage is key variable for the operation of converter system in a wind power system. When grid voltage drops, a control of the DC bus voltage is needed to keep the smoothness of DC bus voltage for avoiding generator cutting off grid. A combined control method based on the grid voltage information feedforward with a crowbar circuit is proposed for a direct-drive wind power system in the paper. The unbalanced energy of the DC bus can be unleashed by the crowbar circuit during the dropping of grid voltage. At the same time, the output power of motor-side converter can be controlled to decrease according to the grid-side voltage information, and the mechanical speed of wind turbine and generator can be suppressed by the pitch angle regulation when the output power reduces. Thus, the DC-bus voltage can keep smooth. Results based on Matlab/Simulink simulation shows that this method not only improves dynamic response performance of DC bus voltages control, but also reduces the action time of crowbar circuit. It is benefit to the ability of the wind power system riding through the grid fault.
9
Chen, Jiming, Yuanhao Wang, Mingxiao Zhu, Qianyu Yu i Jiacai Li. "Improved Rotor Braking Protection Circuit and Self-Adaptive Control for DFIG during Grid Fault". Energies 12, nr 10 (24.05.2019): 1994. http://dx.doi.org/10.3390/en12101994.
Pełny tekst źródłaStreszczenie:
This paper introduces an improved rotor braking protection circuit configuration and the corresponding self-adaptive control strategy to enhance the low voltage ride-through (LVRT) capability of the doubly-fed induction generator (DFIG). The proposed protection circuit consists of a crowbar circuit and a series rotor braking resistor array, which guarantees the safe operation of wind generators under the LVRT. Moreover, to adapt the proposed protection and further enhance the performance of the improved configuration, a corresponding self-adaptive control strategy is presented, which regulates the rotor braking resistor and protection exiting time automatically through calculating the rotor current in the fault period. The LVRT capability and transient performance of the DFIG by using the proposed method is tested with simulation. Compared with the conventional crowbar protection or the fixed rotor braking protection, the proposed protection and the control strategy present several advantages, such as retaining the control of the rotor side converter, avoiding repeated operation of the protection and accelerating the damping of stator flux linkage during a grid fault.
10
Onishi, Koji, Yingxiao Li, Kenta Koiwa, Fang Liu, Tadanao Zanma i Kang-Zhi Liu. "Analysis on the operation of crowbar in doubly fed induction generators". Electric Power Systems Research 215 (luty 2023): 108950. http://dx.doi.org/10.1016/j.epsr.2022.108950.
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Meng, Yan Feng, Shu Ju Hu i Hong Hua Xu. "Research on an Improved Control Strategy for Enhancing LVRT Ability of DFIG System". Applied Mechanics and Materials 291-294 (luty 2013): 467–71. http://dx.doi.org/10.4028/www.scientific.net/amm.291-294.467.
Pełny tekst źródłaStreszczenie:
Aiming at operation problems of DFIG under grid fault condition, the improved control strategy of coordinating control rotor converter and Crowbar circuit switching logic for enhancing LVRT ability is proposed. The over-current cause on the stator and rotor of DFIG under grid fault is analyzed and complete improved control strategy flow chart is given during entire voltage dip. Experimental verification results show that adopting this improved control strategy can effectively suppress the generator stator and rotor over-current and over-voltage, enhance wind turbine operation ability, and provide important theoretical basis and reference for large-scale wind turbine to respond to grid transient fault.
12
Xing, Zuo Xia, Lei Chen, Li Chen Xue i Yong Xing Zhang. "The Research of Verifying Low Voltage Ride through of Double-Fed Wind Turbine Generator System and Voltage Dropping Simulation". Advanced Materials Research 347-353 (październik 2011): 2380–85. http://dx.doi.org/10.4028/www.scientific.net/amr.347-353.2380.
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In order to maintain the stable operation of grid system, the grid company requires wind turbine generator system with low-voltage ride through (LVRT) capability. With this issue, the article builds a double-fed wind turbine generator system model, Crowbar circuit strategy model to protect rotor-side inverter and fault pitch control strategy model to inhibition rotor speed during grid fault. Then all the models and strategies are verified by the simulation of grid low voltage. The simulation results show that these models can complete LVRT.
13
Xie, Zhen, i Xue Li. "The Virtual Resistance Control Strategy for HVRT of Doubly Fed Induction Wind Generators Based on Particle Swarm Optimization". Mathematical Problems in Engineering 2014 (2014): 1–11. http://dx.doi.org/10.1155/2014/350367.
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Grid voltage swell will cause transient DC flux component in the doubly fed induction generator (DFIG) stator windings, creating serious stator and rotor current and torque oscillation, which is more serious than influence of the voltage dip. It is found that virtual resistance manages effectively to suppress rotor current and torque oscillation, avoid the operation of crowbar circuit, and enhance its high voltage ride through technology capability. In order to acquire the best virtual resistance value, the excellent particle library (EPL) of dynamic particle swarm optimization (PSO) algorithm is proposed. It takes the rotor voltage and rotor current as two objectives, which has a fast convergence performance and high accuracy. Simulation and experimental results verify the effectiveness of the virtual resistance control strategy.
14
Kalyani, V. Mohana, J. Preetha Roselyn, C. Nithya i D. Devaraj. "Enhanced Crowbar Protection for Fault Ride through Capability of Wind Generation Systems". International Journal of Power Electronics and Drive Systems (IJPEDS) 7, nr 4 (1.12.2016): 1366. http://dx.doi.org/10.11591/ijpeds.v7.i4.pp1366-1376.
Pełny tekst źródłaStreszczenie:
Due to increasing demand in power, the integration of renewable sources like wind generation into power system is gaining much importance nowadays. The heavy penetration of wind power into the power system leads to many integration issues mainly due to the intermittent nature of the wind and the desirability for variable speed operation of the generators. As the wind power generation depends on the wind speed, its integration into the grid has noticeable influence on the system stability and becomes an important issue especially when a fault occurs on the grid. The protective disconnection of a large amount of wind power during a fault will be an unacceptable consequence and threatens the power system stability. With the increasing use of wind turbines employing Doubly Fed Induction Generator (DFIG) technology, it becomes a necessity to investigate their behavior during grid faults and support them with fault ride through capability. This paper presents the modeling and simulation of a doubly fed induction generator according to grid code compatibility driven by a wind turbine connected to the grid. This paper analyses the voltage sag due to a three-phase fault in the wind connected grid. A control strategy including a crowbar circuit has been developed in MATLAB/SIMULINK to bypass the rotor over currents during grid fault to enhance the fault ride through capability and to maintain system stability. Simulation results show the effectiveness of the proposed control strategies in DFIG based grid connected wind turbine system.
15
Sadara, Wara, i Bunlung Neammanee. "Dynamic Behavior of Flexible Drive Train Models and Back-to-Back Converter for DFIG Wind Turbines during Voltage Sags". Applied Mechanics and Materials 704 (grudzień 2014): 170–79. http://dx.doi.org/10.4028/www.scientific.net/amm.704.170.
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This paper proposes an accurate complete model of a DFIG wind turbine composed of the flexible drive train model, the DFIG, the back-to-back converter, the protection systems, and the control techniques. The simulations use the Matlab/Simulink program to investigate the dynamic behavior of these parts on the 2 MW wind turbine. The simulations show the complete dynamic behavior of electrical and mechanical under normal operation, and voltage sags. Moreover the control logic of an active crowbar protection during high rotor current, and the control logic of a DC-chopper protection during high DC-bus voltage are presented. It can be seen that both protection schemes can limit the current and DC-bus voltage as well as generator torque. The demagnetization control technique also reduces the high transient rotor current and the generator torque during recovery process.
16
YAMADA, Manabu, Masaki HAYATSU, Kouichi KAJIWARA, Yasutaka TAGAWA i Daisuke YAMAGUCHI. "2P2-D11 Development of rescue devices designed for citizen : Development of power-assisted hoist and crowbar jack for rescue operation". Proceedings of JSME annual Conference on Robotics and Mechatronics (Robomec) 2006 (2006): _2P2—D11_1—_2P2—D11_4. http://dx.doi.org/10.1299/jsmermd.2006._2p2-d11_1.
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Qin, Kaina, Shanshan Wang i Zhongjian Kang. "Research on Zero-Voltage Ride Through Control Strategy of Doubly Fed Wind Turbine". Energies 14, nr 8 (19.04.2021): 2287. http://dx.doi.org/10.3390/en14082287.
Pełny tekst źródłaStreszczenie:
With the rapid increase in the proportion of the installed wind power capacity in the total grid capacity, the state has put forward higher and higher requirements for wind power integration into the grid, among which the most difficult requirement is the zero-voltage ride through (ZVRT) capability of the wind turbine. When the voltage drops deeply, a series of transient processes, such as serious overvoltage, overcurrent, or speed rise, will occur in the motor, which will seriously endanger the safe operation of the wind turbine itself and its control system, and cause large-scale off-grid accident of wind generator. Therefore, it is of great significance to improve the uninterrupted operation ability of the wind turbine. Doubly fed induction generator (DFIG) can achieve the best wind energy tracking control in a wide range of wind speed and has the advantage of flexible power regulation. It is widely used at present, but it is sensitive to the grid voltage. In the current study, the DFIG is taken as the research object. The transient process of the DFIG during a fault is analyzed in detail. The mechanism of the rotor overcurrent and DC bus overvoltage of the DFIG during fault is studied. Additionally, the simulation model is built in DIgSILENT. The active crowbar hardware protection circuit is put into the rotor side of the wind turbine, and the extended state observer and terminal sliding mode control are added to the grid side converter control. Through the cooperative control technology, the rotor overcurrent and DC bus overvoltage can be suppressed to realize the zero-voltage ride-through of the doubly fed wind turbine, and ensure the safe and stable operation of the wind farm. Finally, the simulation results are presented to verify the theoretical analysis and the proposed control strategy.
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Tuka, Milkias. "Investigation of Voltage Dip Problems during Faults on a Grid-Tied Doubly Fed Induction Generator in a Wind Energy System". Jordan Journal of Electrical Engineering 9, nr 2 (2023): 209. http://dx.doi.org/10.5455/jjee.204-1669028936.
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A voltage dip is a sudden drop of voltages - generally between 10 and 90 % of the rated RMS value - during a period lasting from half a cycle to a few seconds on the phases of the power lines. It is one of the most important power quality problems affecting the stability of the Doubly Fed Induction Generator (DFIG) in Wind Energy Conversion System (WECS) and hence needs to be analyzed for a given machine for its performance analysis under grid disturbances. When a voltage dip problem happens in the given power as of faults, the magnitude of the rotor and stator currents of DFIG get increased, and hence disturbs steady state operation of the system. Therefore, in this paper, the worst voltage dip of 90 % is tested for grid faults on a 5 kW DFIG to validate its performance under this phenomenon. Based on the results of the simulation - along with its experimental validation - the machine is found to be robust for faults staying a shorter period without disconnecting it from the grid. On the other hand, operating a machine for a longer period while keeping it connected to a grid during a heavy dip, may result in its degradation as the rated limits are violated. To rectify and mitigate the aforesaid problems, a control system - with and without a crowbar - is developed for symmetrical faults to tackle such a problematic situation, and to discuss its fulfillment of the current grid code requirements. Finally, a complete model of the DFIG coupled with the grid is developed, modeled, analyzed and simulated using MATLAB/Simulink user-defined function toolbox block.
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Nduwamungu, Aphrodis, Etienne Ntagwirumugara, Francis Mulolani i Waqar Bashir. "Fault Ride through Capability Analysis (FRT) in Wind Power Plants with Doubly Fed Induction Generators for Smart Grid Technologies". Energies 13, nr 16 (17.08.2020): 4260. http://dx.doi.org/10.3390/en13164260.
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Faults in electrical networks are among the key factors and sources of network disturbances. Control and automation strategies are among the key fault clearing techniques responsible for the safe operation of the system. Several researchers have revealed various constraints of control and automation strategies such as a slow dynamic response, the inability to switch the network on and off remotely, a high fault clearing time and loss minimization. For a system with wind energy technologies, if the power flow of a wind turbine is perturbed by a fault, the intermediate circuit voltage between the machine side converter and line side converter will rise to unacceptably high values due to the accumulation of energy in the DC link capacitor. To overcome the aforementioned issues, this paper used MATLAB simulations and experiments to analyze and validate the results. The results revealed that fault ride through capability with Supervisory Control and Data Acquisition (SCADA) viewer software, Active Servo software and wind sim packages are more adaptable to the variations of voltage sag, voltage swell and wind speed and avoid loss of synchronism and improve power quality. Furthermore, for protection purposes, a DC chopper and a crowbar should be incorporated into the management of excess energy during faults and a ferrite device included for the reduction of the electromagnetic field.
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Loulijat, Azeddine, Najib Ababssi i Mohammed Makhad. "DFIG use with combined strategy in case of failure of wind farm". International Journal of Electrical and Computer Engineering (IJECE) 10, nr 3 (1.06.2020): 2221. http://dx.doi.org/10.11591/ijece.v10i3.pp2221-2234.
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In the wind power area, Doubly Fed Induction Generator (DFIG) has many advantages due to its ability to provide power to voltage and constant frequency during rotor speed changes, which provides better wind capture as compared to fixed speed wind turbines (WTs). The high sensitivity of the DFIG towards electrical faults brings up many challenges in terms of compliance with requirements imposed by the operators of electrical networks. Indeed, in case of a fault in the network, wind power stations are switched off automatically to avoid damage in wind turbines, but now the network connection requirements impose stricter regulations on wind farms in particular in terms of Low Voltage Ride through (LVRT), and network support capabilities. In order to comply with these codes, it is crucial for wind turbines to redesign advanced control, for which wind turbines must, when detecting an abnormal voltage, stay connected to provide reactive power ensuring a safe and reliable operation of the network during and after the fault. The objective of this work is to offer solutions that enable wind turbines remain connected generators, after such a significant voltage drop. We managed to make an improvement of classical control, whose effectiveness has been verified for low voltage dips. For voltage descents, we proposed protection devices as the Stator Damping Resistance (SDR) and the CROWBAR. Finally, we developed a strategy of combining the solutions, and depending on the depth of the sag, the choice of the optimal solution is performed.
21
Jawaid, Saad, i Dan Cody. "Crowbar impalement: the PHEM perspective". BMJ Case Reports 11, nr 1 (grudzień 2018): e227293. http://dx.doi.org/10.1136/bcr-2018-227293.
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A man in his 50s suffered an impalement on a crowbar after falling from the roof of a domestic shed. A helicopter-based prehospital emergency medical service team was called to assist in the patient’s care. The crowbar had entered from the left-upper quadrant and was tenting the skin of the right iliac fossa. Analgesia and prehospital sedation were provided to facilitate extrication. A series of improvisations were carried out to support the logistics of transferring the patient using an air ambulance to the regional major trauma centre with the crowbar in situ. The patient was taken to the operating theatre without any imaging and a section of perforated bowel was removed. He made a full recovery and was discharged home 9 days postincident.
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Zhai, Jia Jun, Bu Han Zhang, Kui Wang, Wen Shao i Cheng Xiong Mao. "Symmetrical Short Circuit Current Characteristics of Doubly Fed Induction Generator Wind Turbine with Crowbar Protection". Advanced Materials Research 512-515 (maj 2012): 782–87. http://dx.doi.org/10.4028/www.scientific.net/amr.512-515.782.
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Doubly fed induction generator (DFIG) is now becoming one of most widely used wind turbines in global market for wind power generation, due to its outstanding advantages. However, the DFIG is sensitive to grid faults. The DFIG will have to be removed from the grid if there’s no protection appliance in it. Therefore, the crowbar protection is widely used in the world for improving the low voltage ride-through ability of wind turbines. This paper analysed the operating characteristics and short-circuit current of DFIG under symmetrical short-circuit fault with respect to different sags to grid voltage, which on the basis of DFIG wind turbine with crowbar protection. And the expressions of short-circuit current under symmetrical short-circuit fault for DFIG were derived. The effectiveness of the expression was simulated in PSCAD/EMTDC.
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Loulijat, Azeddine, Hamid Chojaa, Mouncef El marghichi, Naoufl Ettalabi, Abdelilah Hilali, Abderrahman Mouradi, Almoataz Y. Abdelaziz, Zakaria M. Salem Elbarbary i Mahmoud A. Mossa. "Enhancement of LVRT Ability of DFIG Wind Turbine by an Improved Protection Scheme with a Modified Advanced Nonlinear Control Loop". Processes 11, nr 5 (8.05.2023): 1417. http://dx.doi.org/10.3390/pr11051417.
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One of the problems with the doubly-fed induction generator (DFIG) is its high vulnerability to network perturbations, notably voltage dips, because of its stator windings being coupled directly to the network. As the DFIG’s stator and rotor are electromagnetically mated, the stator current peak occurs during a voltage dip causing an inrush current to the critical converter back-to-back and an overload of the DC-link capacitor. For this purpose, a series of researchers have achieved a linear and non-linear controller with a crowbar-based protection scheme. With this type of protection, the Rotor Side Converter (RSC) is disconnected momentarily, and consequently, its control of both the active and reactive output power of the stator is totally lost, leading to incorrect power quality at the point of common coupling (PCC). In this document, a robust nonlinear controller by Advanced Backstepping with Integral Action Control (ABIAC) is initially employed to monitor the rotor and the network side converters under normal network operations. In the presence of a network fault, an improved protection scheme (IPS) is tacked on to the robust nonlinear control to help enforce the behavior of the DFIG system to be able to overcome the fault. The IPS, which is formed by a crowbar and an RL series circuit, is typically located in the space between the rotor coils and the RSC converter. Compared to a standard crowbar, the developed scheme is successful to limit the rotor transient current and DC-link voltage, also an RSC disengagement to rotor windings can be prevented during the fault. Furthermore, the controllers of both the RSC and the Network Side Converter (NSC) are modified to boost the supply voltage at the PCC. A comparative study is also performed between the IPS without and with modification of the reactive power control loops. The simulation results mean that with the modified controllers during the fault, the amount of reactive power sustainment with ABIAC at the PCC is optimized to 17.5 MVAr instead of 15 MVAr with proportional-integral control (PIC). Therefore, the voltage at the PCC is fort increased in order to comply with the voltage requirements of the farm and absolutely to maintain the connection to the network in case of voltage dip.
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Butkus, Paulius, Sonata Tolvaišienė i Sebastjanas Kurčevskis. "Validation of a SPICE Model for High Frequency Electroporation Systems". Electronics 8, nr 6 (23.06.2019): 710. http://dx.doi.org/10.3390/electronics8060710.
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In this paper, we present an analysis and a validation of a simulation program with integrated circuit emphasis (SPICE) model for a pulse forming circuit of a high frequency electroporation system, which can deliver square-wave sub-microsecond (100–900 ns) electric field pulses. The developed SPICE model is suggested for use in evaluation of transient processes that occur due to high frequency operations in prototype systems. A controlled crowbar circuit was implemented to support a variety of biological loads and to ensure a constant electric pulse rise and fall time during electroporation to be independent of the applied buffer bioimpedance. The SPICE model was validated via a comparison of the simulation and experimental results obtained from the already existing prototype system. The SPICE model results were in good agreement with the experimental results, and the model complexity was found to be sufficient for analysis of transient processes. As result, the proposed SPICE model can be useful for evaluation and compensation of transient processes in sub-microsecond pulsed power set-ups during the development of new prototypes.
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Memon, Ahsanullah, Mohd Wazir Mustafa, Shadi Khan Baloch, Attaullah Khidrani i Touqeer Ahmed. "Dynamic response enhancement of BDFIG using vector control scheme based internal model c ontrol". Indonesian Journal of Electrical Engineering and Computer Science 23, nr 1 (1.07.2021): 90. http://dx.doi.org/10.11591/ijeecs.v23.i1.pp90-97.
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Doublefed induction generator(DFIG) has shown tremendous success inwind turbines due to its flexibility and ability to regulate the active andreactive power. However, the presence of brushes and slip rings affects itsreliability, stability, and power quality. Furthermore, itdoes not providepromising outcomes in case of faults even in presence of the crowbar circuit.In contrast, thebrushless doubly fed induction generator(BDFIG) is a morereliable option for wind turbines than its mentioned counterpart due to theabsence of the brushes and slip rings. This research work as such attempts toimprove the dynamic performance of thevector control(VC)oriented powerwinding (PW) stator flux-based BDFIG by optimally selecting theproportional-integral(PI) gains throughinternalmodel control(IMC)approach. The proposed control scheme is utilized to regulate the speed,torque, and reactive power of the considered BDFIG independently. Contraryto the previous literature where the “trial and error method” is generallyutilized, the current research work uses the IMC for selecting the mostsuitable PI parameters, thus reduces the complexity, time consumption, anduncertainty in optimal selection. The considered BDFIG based wind turbinewith the proposed control scheme provides a better BDFIG control designwith an enhanced dynamic response as compared to that of the same withDFIG under identical operating conditions and system configurations.
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Verma, Rishi, J. M. V. V. S. Aravind, Pankaj Deb, J. N. Rao, P. Dey, A. K. Dubey, R. Shukla i in. "Modular electromagnetic railgun accelerator for high velocity impact studies". Review of Scientific Instruments 93, nr 12 (1.12.2022): 124703. http://dx.doi.org/10.1063/5.0104365.
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A modular electromagnetic railgun accelerator facility named “RAFTAR” (i.e., Railgun Accelerator Facility for Technology and Research) has been commissioned and its performance has been characterized for high velocity impact testing on materials in a single-shot mode. In the first tests, RAFTAR demonstrated an acceleration of more than 1000 m/s for an 8 g solid aluminum-7075 armature projectile. The current fed was 220 kA, having a muzzle time of about 1.75 ms. It is a single pulse breech-fed rectangular bore (14 × 13 mm2) railgun, and its 1.15 m long barrel assembly consists of two parallel copper bars with an inter-gap of 13 mm that are encased within 50 mm thick high strength reinforced fiberglass sheets (Garolite G10-FR4) and bolted from both the sides. RAFTAR is powered by two capacitor bank modules that have a maximum stored energy of 160 kJ each (containing eight 178 μF/15 kV capacitors), two high power ignitron switches, and a pulse shaping inductor. To obtain consistent acceleration of the armature inside the barrel, reversal of driving current is prevented, and its pulse duration is stretched by tactical integration of the crowbar switch and bitter coil inductor in the circuit. Armature projectile velocity measurement in-bore and outside in free space was performed by the time-of-flight technique using indigenously made miniature B-dot sensors and a novel shorting-foil arrangement, respectively. The time resolved measurement of the in-bore armature evidenced a velocity-skin-effect in the high acceleration phase. There is good agreement between the experimentally measured and theoretically predicted efficiency, confirming the optimal choice of operating parameters. The conclusion summarizes important experimental findings and analyzes the underlying causes that limit the performance of railguns.
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Kelevišius, Kęstutis, Jonas Amšiejus i Šarūnas Skuodis. "THE INFLUENCE OF CHANGING SHAFT FRICTION OF THE PILE TO WAVE PROPAGATION". Engineering Structures and Technologies 3, nr 2 (30.06.2011): 64–71. http://dx.doi.org/10.3846/skt.2011.08.
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In most cases, the bearing capacity of the pile under natural conditions can be determined by applying static and dynamic pile tests as well as the numerical modelling of a dynamic test. The integrated business problem is employed for calculating vertical displacements. This integral is calculated using the summing method. In the majority of cases, real pile strength capacity can be investigated referring to the adapted means of testing applying the mathematical model that can calculate static or dynamic investigations. The idealized scheme of a pile test is presented including a hammering system and soil properties. Moreover, information on the analysis and work of the scheme is disclosed. The article also describes pile hammering models and the equation for Smith method improved by Edwards, Holloway, Briaud and Trucker, Rieke and Crowser, ”GRL“, including the advantages and disadvantages of the introduced method. Smith realized the mathematical analysis of wave propagation supported by a real hammer-pile-soil scheme by discretic elements interaction. Basing on this for classical one dimensional method of wave propagation (that is programmed in computer program MW87) the code of the computer program was changed by authors of this article. When using a computer program, an algorithm for an integral equation was created. The introduced algorithm was made for counting experimental displacement the growth of which along the pile was analyzed. All obtained results were compared with the engineering method indicating that diff erence in results made less than 2%. Using computer program MW87, a diff erent distribution of shaft friction along the pile was studied when the total shaft friction in all cases was constant, because, the results of numerical modelling disclosed that the shaft friction of the pile in one diameter above the pile’s toe was larger than that in the middle or at the top. The hammer-pile-soil system was analyzed with reference to the impact of the returning wave at the top of the pile. Wave propagation in the pile is vertical: the first wave moves from the top to the bottom of the pile. When the bottom is reached, impact wave returns to the top of the pile. All information about the pile of the returning wave is useful as then we can analyze the integrity and bearing capacity of the pile. All this information received from the returning wave is integrated and later shown in the scheme where we can see all steps of performed operations. This article investigates soil deformations and these deformations in soil influence for a hammering pile. A pile of 0,8 m in diameter and 3 m in height, which is in sand, is an object of investigation in this article. For calculation purposes, the pile is divided into 20 segments. Changes in velocities and displacements of pile segments during analysis are graphically shown. Aft er calculating tests on pile dynamics considering diff erent masses of hammers, falling heights of hammers, contribution of shaft friction and static resistances of the piles, a nomograme for determining static resistance of the pile was made. The article explains how the use of the nomograme determines static resistance of the pile and what data on conducting a pile test are needed.
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Onishi, Koji, Yingxiao Li, Kang-Zhi Liu, Fang Liu, Kenta Koiwa i Tadanao Zanma. "Analysis on the Operation of Crowbar in Doubly Fed Induction Generators". SSRN Electronic Journal, 2022. http://dx.doi.org/10.2139/ssrn.4116247.
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Nadour, Mohamed, Ahmed Essadki i Tamou Nasser. "Improving low-voltage ride-through capability of a multimegawatt DFIG based wind turbine under grid faults". Protection and Control of Modern Power Systems 5, nr 1 (grudzień 2020). http://dx.doi.org/10.1186/s41601-020-00172-w.
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AbstractLarge integration of doubly-fed induction generator (DFIG) based wind turbines (WTs) into power networks can have significant consequences for power system operation and the quality of the energy supplied due to their excessive sensitivity towards grid disturbances. Under voltage dips, the resulting overcurrent and overvoltage in the rotor circuit and the DC link of a DFIG, could lead to the activation of the protection system and WT disconnection. This potentially results in sudden loss of several tens/hundreds of MWs of energy, and consequently intensifying the severity of the fault. This paper aims to combine the use of a crowbar protection circuit and a robust backstepping control strategy that takes into consideration of the dynamics of the magnetic flux, to improve DFIG’s Low-Voltage Ride Through capability and fulfill the latest grid code requirements. While the power electronic interfaces are protected, the WTs also provide large reactive power during the fault to assist system voltage recovery. Simulation results using Matlab/Simulink demonstrate the effectiveness of the proposed strategy in terms of dynamic response and robustness against parametric variations.
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Yin, Jun. "Research on Short-Circuit Current Calculation Method of Doubly-Fed Wind Turbines Considering Rotor Dynamic Process". Frontiers in Energy Research 9 (28.05.2021). http://dx.doi.org/10.3389/fenrg.2021.686146.
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With the enlarging scale of doubly-fed induction generators (DFIGs) connected to power systems, it is important to analyze the influence of a short-circuit current to system relay protection. Due to the correct evaluation of the protection operation characteristics, the DFIG short-circuit current needs to be calculated accurately. But the current research on the short-circuit current of DFIG is based on the following assumption: the rotor excitation current is zero after the rotor crowbar is put, and the influence of its dynamic process is ignored. This will bring errors to the calculation results. This paper takes into account the influence of rotor current dynamics by studying the mechanism of the potential transient change of DFIG. The stator rotor flux linkage of DFIG in the event of a three-phase short-circuit is accurately calculated, and an improved RMS calculation method of doubly-fed wind turbine short circuit current is proposed. A physical experiment platform with an actual controller of a doubly-fed fan is established, based on RTDS. It can be seen from the experiment that the short-circuit current calculation method proposed in this paper is more accurate than those methods that ignore the rotor dynamic process. This study lays a foundation for further study of the influence of DFIG on the protection operation characteristics.
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Shan, Haoqi, Moyao Huang, Yujia Liu, Sravani Nissankararao, Yier Jin, Shuo Wang i Dean Sullivan. "CROWBAR: Natively Fuzzing Trusted Applications Using ARM CoreSight". Journal of Hardware and Systems Security, 15.06.2023. http://dx.doi.org/10.1007/s41635-023-00133-3.
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AbstractTrusted execution environments (TEE) are deployed on many platforms to provide both confidentiality and integrity, and their extensive use offers a secure environment for privacy-sensitive operations. Despite TEE prevalence in the smartphone and tablet market, vulnerability research into TEE security is relatively rare. This is, in part, due to the strong isolation guarantees provided by its implementation. In this paper, we propose a hardware assisted fuzzing framework, CROWBAR, that bypasses TEE isolation to natively evaluate trusted applications (TAs) on mobile devices by leveraging ARM CoreSight components. CROWBAR performs feedback-driven fuzzing on commercial, closed source TAs while running in a TEE protected environment. We implement CROWBAR on 2 prototype commercial-off-the-shelf (COTS) smartphones and one development board, finding 3 unique crashes in 5 closed source TAs that are previously unreported in the TrustZone fuzzing literature.
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Safwat, Ayman, Mohiy E. Bahgat, A. M. Abdel-Ghany i Helmy M. El Zoghby. "Crowbar Protection and Blades Pitch Angle Control of a Wind Turbine at Severe Faulty Conditions using Adaptive Neuro-Fuzzy Inference System". Recent Advances in Electrical & Electronic Engineering (Formerly Recent Patents on Electrical & Electronic Engineering) 16 (3.11.2022). http://dx.doi.org/10.2174/2352096516666221103102058.
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Background: Due to their superior efficiency, stability, and ability to produce maximum power under various typical operating situations, wind turbines driving doubly fed induction generator systems are frequently utilized in wind power extraction. These systems face stability problems especially at severe faulty conditions Objective: To protect the rotating parts of the system from over speeding when the fault occurs and to ensure that the generator does not deviate from stability by adjusting the aerodynamic torque of the wind turbine. In addition, to protect electrical parts of the system, especially DC bus voltage and power electronics converters. Methods: Using Adaptive Neuro-Fuzzy Inference System (ANFIS). The proposed ANFIS technique detects the faulty conditions from the measured voltages and currents at the terminals of the generator. In case of faulty cases, an ANFIS technology activates the wind turbine's pitch angle controller and the crowbar resistance. Results: A comparison between the behavior of DFIG at faulty conditions without any fault controller and with the proposed ANFIS technique is applied. When the ANFIS technique is used, the wind system's performance and response are improved Conclusion: The proposed ANFIS control system has proven its effectiveness in protecting the DFIG in the event of a grid fault.