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This work examines the analysis of temporary behaviors and crowbar hardware layout for enhancing the fault ride-through capability (FRTC) in doubly fed induction wind generators (DFIWGs) A crowbar that is linked in parallel to the rotor side converter (RSC) is a feature found on the majority of DFIWGs these days to safeguard the RSC and DC-bus capacitor (DCBC). Previous studies demonstrated that the crowbar resistance has an impact on the DFIWG transient response's oscillations and peak values. In order to satisfy the FRTC criterion, the article initially methodically examines the DFIWG dynamics with and without a crowbar during a 100% voltage dip and studies the effects of two resistance values on the DCBC. It has been demonstrated that choosing a crowbar resistance greater than the permitted range may cause the DFIG FRT performance to decline. By actively addressing grid faults and improving performance, stability, and dependability, this integrated crowbar shows the potential of state-of-the-art control approaches for the dependable and efficient use of DFIWGs. MATLAB/Simulink is used to run robust simulations, and the results unambiguously show that the proposed model may significantly improve the FRTC of DFIWGs. [ABSTRACT FROM AUTHOR]

[Introduction] Facing the rapid transfer of extreme fault energy of the HL-3 fusion scientific apparatus, it is required to configure a large-capacity bypass switch for short-circuit protection. [Method] Based on the parameters of HL-3 magnet power supply, and in combination with power electronic converter technology and thyristor trigger application foundation, this paper integrated the practical experience of power electronic converter engineering, and used the following means and methods at the harsh working conditions of multi-parallel thyristor consistency conduction and stable current sharing in fast impact application: the equal length type improvement of parallel branch conductive circuit; consistency screening of parallel component parameters, differential selection of component position and parameters in parallel arm; physically forced current sharing by adding a series resistance on the side of the silicon controlled rectifier, calculation of the thermal stability of the additional resistance, and checking calculation of the electrodynamics impact of the parallel bridge arm; thyristor high-frequency pulse train strong trigger. [Result] A stable crowbar bypass protection electronic switch system for high-capacity fusion of 220 kA class of thyristor was deduced and designed, which was verified by experimental simulation and 160 kA impact test under actual load, and the matching requirements of large-capacity bypass switch for HL-3 protection were realized. [Conclusion] Under thermal and stability checking calculation, it is completely feasible to realize the matching application of large-capacity crowbar in fusion by adopting comprehensive means such as circuit improvement, additional physical force current sharing, component parameter screening and assembly, and trigger mode adjustment.

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Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In a system where wind farms are connected to the grid via a bipolar flexible DC transmission, the occurrence of a short-time fault at one of the poles results in the active power emitted by the wind farm being transmitted through the non-faulty pole. This condition leads to an overcurrent in the DC system, thereby causing the wind turbine to disconnect from the grid. Addressing this issue, this paper presents a novel coordinated fault ride-through strategy for flexible DC transmission systems and wind farms, which eliminates the need for additional communication equipment. The proposed strategy leverages the power characteristics of the doubly fed induction generator (DFIG) under different terminal voltage conditions. By considering the safety constraints of both the wind turbine and the DC system, as well as optimizing the active power output during wind farm faults, the strategy establishes guidelines for the wind farm bus voltage and the crowbar switch signal. Moreover, it harnesses the power regulation capability of the DFIG rotor-side crowbar circuit to enable fault ride-through in the presence of single-pole short-time faults in the DC system. Simulation results demonstrate that the proposed coordinated control strategy effectively mitigates overcurrent in the non-faulty pole of flexible DC transmission during fault conditions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this study, improving fault-ride through capacity of the DFIG under symmetrical and asymmetrical voltage dips has been investigated. Initially, a crowbar protection circuit has been designed for the rotor side converter (RSC). With the help of the crowbar, the fault ride-through (FRT) ability of the wind energy conversion systems (WECS) has been increased, while the capacitors, rotor windings, and converters are protected from critical damage caused by the voltage dip. Then, the crowbar has been equipped with a fuzzy logic controller (FLC) to increase the FRT capacity. The switching time of the crowbar circuit has also been improved to protect the WECS from this serious damage. The suggested WECS has been designed and analyzed in Matlab/Simulink under symmetrical/asymmetrical voltage dips. DC bus voltage, electromagnetic torque, grid currents, crowbar current, and terminal voltage results of DFIG have been obtained. The simulation results of the DFIG have been compared. The results have also been contrasted with related studies. The obtained results demonstrated the robustness, applicability, and dependability of the suggested system. [ABSTRACT FROM AUTHOR]

In this paper, a heuristic approach to doubly fed induction generator (DFIG) protection and low voltage ride through (LVRT) is carried out. DFIG-based wind systems are rapidly penetrating the power generation section. Despite their advantages, their direct coupling grid makes them highly sensitive to symmetrical faults. A well-known solution to this is the crowbar method of DFIG protection. This paper provides a method to determine the optimal crowbar resistance value, to ensure a strong trade-off between the rotor current and DC voltage transients. Further, since the crowbar method requires disconnection from the grid, the linear quadratic regulator (LQR) is applied to the system. This is to ensure fault ride through compliance with recent grid code requirements. The well-known PSO, as well as the recently developed African vultures optimization algorithm (AVOA), was applied to the problem. The first set of results show that for severe symmetrical voltage dips, the AVOA provides a good option for crowbar magnitude optimization, whereas PSO performed better for moderately severe dips. Secondly, when the LQR was optimized via the AVOA, it exhibited superiority over the conventional PSO-based PI controller. This superiority was in terms of rotor current transient magnitude, DC voltage transient magnitude, and reactive power steady-state ripple and were in the order of 67.5%, 20.35%, and 37.55%, respectively. When comparing the crowbar method and the LQR, it was observed that despite the LQR exhibiting superiority in terms of transient performance, the crowbar method offered a unanimously superior settling time. [ABSTRACT FROM AUTHOR]

In a system where wind farms are connected to the grid via a bipolar flexible DC transmission, the occurrence of a short-time fault at one of the poles results in the active power emitted by the wind farm being transmitted through the non-faulty pole. This condition leads to an overcurrent in the DC system, thereby causing the wind turbine to disconnect from the grid. Addressing this issue, this paper presents a novel coordinated fault ride-through strategy for flexible DC transmission systems and wind farms, which eliminates the need for additional communication equipment. The proposed strategy leverages the power characteristics of the doubly fed induction generator (DFIG) under different terminal voltage conditions. By considering the safety constraints of both the wind turbine and the DC system, as well as optimizing the active power output during wind farm faults, the strategy establishes guidelines for the wind farm bus voltage and the crowbar switch signal. Moreover, it harnesses the power regulation capability of the DFIG rotor-side crowbar circuit to enable fault ride-through in the presence of single-pole short-time faults in the DC system. Simulation results demonstrate that the proposed coordinated control strategy effectively mitigates overcurrent in the non-faulty pole of flexible DC transmission during fault conditions.

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. [ABSTRACT FROM AUTHOR]

Zafarana Wind Park is considered the largest wind farm in Middle East. By the year 2022, Zafarana wind farm will inject 545 MW to Egypt national electric network (ENEN). This wind farm has been connecting to ENEN in stages (eight stages) from ten years ago. Each stage represents a project of wind farm. Hence, the impact of the emergency condition of ENEN on the performance of the installed stage of Zafarana Wind Park should be studied. Moreover, determining the possible method to reduce the side effects of the emergency condition of ENEN on the installed stage of Zafarana Wind Park becomes an important issue. In this paper, a combination between Static Synchronous Series Compensator (SSSC) and crowbar (Cro-SSSC) is used to enhance the performance of the one installed stage of Zafarana Wind Park. The studied stage of Zafarana Wind Park is Zafarana Z1 wind farm (Z1). Zafarana Z1 wind farm represents that first stage of Zafarana Wind Park that was connected to ENEN. Hence, the paper takes Zafarana Z1 wind farm as the studied case to examine the impact of Cro-SSSC. The crowbar is used to protect the power components of the SSSC from the high current during grid fault condition. Also, in this paper multi-objective lightning attachment procedure optimization algorithm (LAPO) and the sine cosine algorithm (SCA) are used to evaluate and tune the control gains of SSSC and the value of crowbar's resistance. This step is important in order to determine the values of the control's gains of SSSC and the value of crowbar resistance which suit the studied system (one installed stage of Zafarana Wind Park). The sliding mode control (SMC) is used as an example of nonlinear control of SSSC. Also, a hybrid of LAPO and SMC is used to improve the performance of Zafarana Z1 during faults. The results of LAPO, SCA and SMC are compared during three-phase fault and single line to ground fault applied to the studied system. [ABSTRACT FROM AUTHOR]

In this work, a novel electroporation system (electroporator) is presented, which is capable of forming high frequency pulses in a broad range of parameters (65 ns–100 µs). The electroporator supports voltages up to 3 kV and currents up to 40 A and is based on H-bridge circuit topology. A synchronized double crowbar driving sequence is introduced to generate short nanosecond range pulses independently of the electroporator load. The resultant circuit generates pulses with repetition frequencies up to 5 MHz and supports unipolar, bipolar, and asymmetrical pulse sequences with arbitrary waveforms. The shortest pulse duration step is hardware limited to 33 ns. The electroporator was experimentally tested on the H69AR human lung cancer cell line using 20 kV/cm bipolar and unipolar 100 ns–1 μs pulses. Based on a YO-PRO-1 permeabilization assay, it was determined that the electroporator is suitable for applied research on electroporation. The system offers high flexibility in experimental design to trigger various electroporation-based phenomena. [ABSTRACT FROM AUTHOR]

In this paper, a heuristic approach to doubly fed induction generator (DFIG) protection and low voltage ride through (LVRT) is carried out. DFIG-based wind systems are rapidly penetrating the power generation section. Despite their advantages, their direct coupling grid makes them highly sensitive to symmetrical faults. A well-known solution to this is the crowbar method of DFIG protection. This paper provides a method to determine the optimal crowbar resistance value, to ensure a strong trade-off between the rotor current and DC voltage transients. Further, since the crowbar method requires disconnection from the grid, the linear quadratic regulator (LQR) is applied to the system. This is to ensure fault ride through compliance with recent grid code requirements. The well-known PSO, as well as the recently developed African vultures optimization algorithm (AVOA), was applied to the problem. The first set of results show that for severe symmetrical voltage dips, the AVOA provides a good option for crowbar magnitude optimization, whereas PSO performed better for moderately severe dips. Secondly, when the LQR was optimized via the AVOA, it exhibited superiority over the conventional PSO-based PI controller. This superiority was in terms of rotor current transient magnitude, DC voltage transient magnitude, and reactive power steady-state ripple and were in the order of 67.5%, 20.35%, and 37.55%, respectively. When comparing the crowbar method and the LQR, it was observed that despite the LQR exhibiting superiority in terms of transient performance, the crowbar method offered a unanimously superior settling time.

The calculation of short-circuit currents is critical for the design of protection systems and electrical equipment rating. The short-circuit current contribution of traditional synchronous generators, which depends on common machine parameters, has been validated in recent decades. In this sense, the increasing penetration of wind power generation in current power systems means that network operators need to evaluate the response of wind turbines when a fault occurs. The recent publication of Edition 2 of IEC 60909-0 in 2016 defined a formulation to represent the short-circuit contribution for modern wind turbines, such as doubly-fed and full-converter technologies. Nevertheless, both the IEC and the ANSI/IEEE guidelines are based on new parameters that must be provided by the wind turbine manufacturer. This paper develops a methodology to calculate the parameters that define the short-circuit contribution of doubly-fed wind turbines for both international guidelines, IEC 60909-0 Ed. 2 and ANSI/IEEE. Field measurements and simulations are used for the validation of the developed method. Furthermore, some of the shortcomings of the IEC short-circuit calculation method are identified and alternative approaches are proposed and evaluated. [ABSTRACT FROM AUTHOR]

The main problem of the Doubly-Fed Induction Generator (DFIG) is its sensitivity to network disturbances especially voltage dip due to its stator windings being directly linked to the network. A voltage dip in the network results from high current peaks in the stator windings, since the stator and rotor are electromagnetically coupled, so these peaks provoke inrush current hard at the delicate back-to-back converters and an overcharge of the DC-LINK capacitor. In this perspective, several researchers are realized a linear and nonlinear controller with a passive protection method (PPM). The objective of this paper is to develop modelling and control models based on a true DFIG model considering the effect of all the parameters of a stator winding. The Second- Order Sliding Mode controller (SOSMC) is the non-linear control strategy used to control the dynamics of the DFIG through the rotor-side and network-side power converters under normal network conditions. When a voltage dip is detected, the Kalman observer (KO) contributes to a non-linear controller and the latter is coupled to a passive protection method that contains crowbar and DC-chopper circuits to improve the dynamics of the DFIG system to cross the network fault. Also, a comparative study is carried out between the developed controller and other linear,non-linear approaches exist in the literature. The results obtained, under a maximum voltage dip (100%) on the 60 kV network, confirm its robustness and superiority in terms of limiting the DFIG graders at the beginning and on termination of a fault. In terms of Ir and Vdc values during a voltage dip, our control strategy does not exceed 1.45p.u and 1.2p.u, on the contrary, the ABC with HGO which is developed recently reaches 2.2p.u and 0.4p.u. [ABSTRACT FROM AUTHOR]

Nowadays, most of the doubly fed induction generators (DFIGs) are equipped with rotor crowbar for the requirement of low voltage ride through (LVRT). The crowbar resistance is an important parameter, and it is selected taking rotor overcurrent and dc link overvoltage limits into consideration. However, the impact of grid impedance on the LVRT performance of DFIG and crowbar resistance is not adequately researched. This paper proposed an improved method to analyze the LVRT performance of DFIG system with rotor crowbar taking the influence of the grid impedance to fill this gap. The impedance of the present grid would be decreased in the future due to the installation of more wind farms to the grid. As a consequence, the performance of DFIG under LVRT with rotor crowbar is degraded. So the design rules of the crowbar resistance need to be reconstructed. Additionally, the analytical expression of the crowbar resistance is derived considering the grid impedance. The effectiveness of the proposed method is validated through theoretical analysis and MATLAB simulations.

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.

The grid codes define low voltage ride-through (LVRT) as capability of wind turbine generator (WTG) to support the grid voltage by injecting reactive power and suppress the rise of DC-link voltage and inrush rotor current in the rotor side converter (RSC) of the doubly fed induction generator (DFIG) during a fault. Moreover, the rotor current increases significantly during severe disturbances if any protection schemes are not employed. Therefore, the protection schemes must be used to avoid the damage to the converter during a fault. This paper proposes an enhanced LVRT control scheme of a DFIG employing a crowbar in the RSC side and braking chopper across the DC-link capacitor. The DFIG is highly delicate to grid voltage fluctuation during a fault because the DFIG is directly linked to the grid via stator. During severe fault the crowbar regulates the rotor current within an acceptable range and the braking chopper discharges the DC-link capacitor via resistor within a safe limit. The proposed LVRT control scheme is performed for a 2.4-MW DFIG using a MATLAB/SIMULINK simulator. The results delineate that the proposed control scheme is able to rapidly decrease the rotor current and repress the escalation in DC-link voltage during a grid fault. [ABSTRACT FROM AUTHOR]

In this work, a novel electroporation system (electroporator) is presented, which is capable of forming high frequency pulses in a broad range of parameters (65 ns–100 µs). The electroporator supports voltages up to 3 kV and currents up to 40 A and is based on H-bridge circuit topology. A synchronized double crowbar driving sequence is introduced to generate short nanosecond range pulses independently of the electroporator load. The resultant circuit generates pulses with repetition frequencies up to 5 MHz and supports unipolar, bipolar, and asymmetrical pulse sequences with arbitrary waveforms. The shortest pulse duration step is hardware limited to 33 ns. The electroporator was experimentally tested on the H69AR human lung cancer cell line using 20 kV/cm bipolar and unipolar 100 ns–1 μs pulses. Based on a YO-PRO-1 permeabilization assay, it was determined that the electroporator is suitable for applied research on electroporation. The system offers high flexibility in experimental design to trigger various electroporation-based phenomena.

Abstract This paper proposes a novel controllable crowbar based on fault type (CBFT) protection technique for doubly fed induction generator (DFIG) wind energy conversion system connected to grid. The studied system consists of six DFIG wind turbines with a capacity of 1.5 MW for each of them. The operation mechanism of proposed technique is used to connect a set of crowbar resistors in different connection ways via activation of controllable circuit breakers (CBs) depending on the detected fault type. For each phase of DFIG, a crowbar resistor is connected in parallel with a controllable CB and all of them are connected in series to grid terminals. The adaptive neuro-fuzzy inference system (ANFIS) networks are designed to detect the fault occurrence, classify the fault type, activate the CBs for crowbar resistors associated with faulted phases during fault period, and deactivate them after fault clearance. The effectiveness of proposed CBFT protection technique is investigated for different fault types such as symmetrical and unsymmetrical faults taking into account the single-phase to ground fault is the most frequently fault type that occurs in power systems. Also, a comparison between the behaviours of studied system in cases of using traditional parallel rotor crowbar, classical outer crowbar, and proposed CBFT protection techniques is studied. The fluctuations of DC-link voltage, active power, and reactive power for studied system equipped with different protection techniques are investigated. Moreover, the impacts of different crowbar resistance values on the accuracy of proposed technique are studied. The simulation results show that, the proposed technique enhances the stability of studied wind turbine generators and contributes in protection of their components during faults.

To enhance the Low-voltage Ride Through (LVRT) capability of large-scale centralized wind farms is essential for the safety of the wind farm and the security of the power system. However, the LVRT capability enhancement coordinating the control and protection of individual wind generators merits consideration. To contribute in this way, a Coordinated Sequential Control (CSC) strategy is proposed in this manuscript. Regarding different voltage disturbance scenarios, the goal of voltage control is determined in real-time. To keep as many wind turbines operating grid-connected as possible, a multi-staged coordination strategy is set according to the critical time to ride through the fault. The reactive power control and the shedding of the wind turbines are coordinated in the three stages of the CSC. According to the simulation results, more wind turbines can be kept grid-connected by using the proposed control strategy. Comparison studies are made among several types of coordinating strategies, emphasizing the advantages of the proposed method in terms of both validation and real-time performance. [ABSTRACT FROM AUTHOR]

High-voltage power supplies (HVPSs) are widely used to drive vacuum tubes, inherently susceptible to vacuum arc faults. Owing to the considerable cost of vacuum tubes, the HVPS should enjoy a reliable, fast protection mechanism. A common protection mechanism against vacuum arc faults is the shunt crowbar. The crowbar diverts the energy stored in the elements of the HVPS through itself as a parallel path, thereby protecting vacuum tubes from irrecoverable damages. Among all types of the shunt crowbar, the thyristor-based crowbar along with the fault current limiter (FCL) resistors attracts more attention because of its more reliable operation. The absence of the comprehensive design procedure providing an insight into selecting the key components of the crowbar is strongly felt. This article presents a comprehensive design procedure for selecting these components. All constraints which should be satisfied by the protection mechanism and key components are elaborated. By doing so, the upper and lower limits of the FCL resistors, the thyristor specifications, and their series inductance are specified. It is shown that thyristors with high nominal peak current cannot contribute to the operation of the crowbar. The intersection area of the constraints and optimum values are determined for one case study. The simulations and experimental tests are exploited to evaluate the effectiveness of the presented design procedure. [ABSTRACT FROM AUTHOR]

Many applications that use high-energy plasma are realized using microwave tubes (MWT) that operate at peak power in the range of hundreds of MW and frequency in GHz. One failure mode of the MWT is due to the excess energy in the tube during internal arcing events. Crowbar is used to protect the MWT by diverting the energy during fault. To compute the energy released into the MWT, the dc fault current model and the MWT model are essential. An equivalent fuse wire model is utilized for the MWT for the crowbar applications. The paper proposes a model for the dc fault current, the analysis for which is based on Joules Integral energy concept. The model provides flexibility to choose a range of practically observed reactance to resistance ratio ($X{/}R$) of transformer and also allows the use of a range of dc current-limiting resistances that are utilized in the high-voltage (HV) power supply circuits in microwave applications. The nonlinearity of the system due to the multipulse diode rectifier is also considered by introducing a correction factor in the model. This paper shows that the same correction factor can be applied for both dc side parallel- and series-connected rectifier circuits. Both dc fault current and MWT models are verified experimentally. Using the model, a 10 kV, 1 kA crowbar is built to limit the energy in MWT below 10 J. [ABSTRACT FROM AUTHOR]

A new upper divertor is proposed for the ASDEX Upgrade (AUG) tokamak experiment. It is planned to be equipped with internal coils for investigation of alternative magnetic configurations like e.g. "snowflake" (Herrmann et al., 2017 [ 1 ]). Since the coils are close to the plasma, high induced and very stiff voltages are expected during disruption events. Because only very vague analytical estimates of voltages, forces and coupling factors were available, an improvement by the help of Finite Element Method (FEM) was envisaged. Therefore, recorded measurements of currents, plasma position, plasma profile and the geometry were integrated in an electromagnetic simulation as boundary conditions to calculate resulting field distributions during selected AUG disruptions. The time resolution can be better than 100 μs and the required computing resources are comparably small due to the assumption of 2D axis-symmetry. The results were compared with magnetic probe measurements integrated into the tokamak ultimately observing good agreement. After this, the FE model was modified including the new divertor to calculate all relevant parameters. The output of these calculations has strong implications for the coil and power supply design: i) The power supply will be protected by a new kind of crowbar to avoid damage of the power supply due to overvoltage and uncontrolled current and force rise of the coils. The concept of this so called "ripping crowbar" is introduced, which is now under development. ii) The coil cable should be coaxial shaped to monitor isolation faults and to become inherently safe against single-turn shortcuts, identified as destructive fault scenario. [ABSTRACT FROM AUTHOR]

High-voltage power supplies (HVPSs) are widely used to supply vacuum tubes. The amount of delivered energy from the HVPS to the tube is an important issue during the vacuum arc in the tube. The conventional protection mechanism consists of a shunt crowbar which diverts the fault current from the tube to itself as a parallel path. The crowbar circuit is usually built of the devices without the turn-off capability. It is a drawback since the output of the power supply is shortened for a long time. Thus, the restoration time of these power supplies is excessive. This demerit can have detrimental effects on mission-critical applications. In this paper, the insulated-gate bipolar transistor (IGBT)-based crowbar structure is studied to overcome this issue. In the proposed protection mechanism, the crowbar can be reopened intentionally after closing. A theoretical analysis is presented to compare power supply performance in the presence of the conventional crowbar with the IGBT-based crowbar. The experimental results are presented to demonstrate the practical considerations of the proposed crowbar structure and its appropriate performance. This paper shows that HVPS has more fault resiliency and less restoration time with the proposed IGBT-based crowbar. [ABSTRACT FROM AUTHOR]

Abstract Doubly-fed induction generator (DFIG) is sensitive to the disturbance of grid voltage, and its low voltage ride-through (LVRT) technology is still a hotspot issue. Rotor side crowbar is widely used to realize LVRT. However, traditional fixed crowbar can't strike a balance between the limitation of rotor over current and DC-bus over voltage, and the crowbar is usually activated repeatedly due to the inappropriate deactivation strategy. Based on the analysis of rotor current considering crowbar operations, an improved LVRT method that dynamically adjusting crowbar resistance and adaptively deactivating the crowbar circuit is proposed. The corresponding adaptive control strategy and the resistance setting method are given. With the proposed scheme, both the rotor current and DC-bus voltage can be controlled within the restriction. Besides, the crowbar can be deactivated in the least time under the precondition of avoiding being reactivated, which will effectively reduce the absorbed reactive power from the system and benefit the service life of switching devices. The effectiveness of proposed LVRT scheme is verified by MATLAB/Simulink simulation. [ABSTRACT FROM AUTHOR]

In this work, we present a novel electroporator which is capable of generating single and bursts of high power (3 kV, 60 A) square wave pulses of variable duration (100 ns to 1 ms) with predefined repetition frequency (1 Hz to 3.5 MHz). The proposed synchronized crowbar implementation ensures a constant pulse rise and fall times, which are independent from the load, thus highly relevant in electroporation. The electroporator was successfully tested for the inactivation of the human pathogen Candida albicans. The device is compatible with standard commercial electroporation cuvettes.

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.

The output unit of the Angara-5-1 installation was upgraded in order to increase megabar pressure. Upgrading was carried out taking into account those fact that pressure was created using the magnetic field of the current flowing through the specimen. To increasing the power impulse acting on the flyer from the side of the magnetic field, variants of increasing the time duration of the magnetic field were considered by controlled current shorting (crowbar). In accordance with the mathematical simulation when extending the current pulse, it is possible to increase the flyer velocity by a factor of two. [ABSTRACT FROM AUTHOR]

With the increasing capacity of wind farms integrated into the power grid, the short-circuit current analysis for wind farms becomes more and more important. Since the wind turbine is usually integrated into the power grid via power electronic devices, the "crowbar" is installed in the wind turbine to protect the power electronic devices and to improve the fault ride through capability. The impact of the crowbar has to be considered during the short-circuit current analysis for the wind farm. In order to fully analyze the short-circuit current characteristics of a wind farm, the short-circuit currents for a doubly-fed induction generator (DFIG) wind turbine under symmetrical and asymmetrical faults considering the crowbar action characteristic are derived firstly. Then the action situation of the crowbar of a DFIG wind turbine is studied and the action area curve is obtained. Taking the crowbar action, or not, as the grouping criterion, wind turbines in the wind farm are divided into two groups, and the wind farm is aggregated into two equivalent wind turbines. Using the equivalent model, the short-circuit current of a wind farm can be calculated accurately. Finally, simulations are performed in MATLAB/Simulink which is the commercial math software produced by the MathWorks company in Natick, Massachusetts, the United States to verify the proposed short-circuit current calculation method for the DFIG wind farm. [ABSTRACT FROM AUTHOR]

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.

High-voltage high-power pulse switches are built with semiconductor devices, preferably thyristor, due to the superior performance that they offer. Triggering methods classify the thyristor as electrically triggered thyristor (ETT) and light triggered thyristor (LTT). Due to the specialized gate constructions and many build-in protections, the cost of LTT is much higher than ETT. The operating modes in applications, such as crowbar, do not require all these build-in protections. In this paper, the operation of a crowbar is analyzed, and the build-in protections of LTT are reviewed. This paper proposes three experiments for the design selection of thyristor, between ETT and LTT, for crowbar applications. The experiments cover the electrical performance as well as electromagnetic emissions in a 10-kV, 1-kA crowbar built with both ETT as well as LTT, which can be used to benchmark the performance of the crowbar circuit. From the three experiments, the performance of ETT-based crowbar is found to be comparable with LTT-based crowbar. Based on the experiments carried out with the proposed benchmarking approaches, this paper shows that ETT-based crowbar is a cost-effective solution for crowbar applications. [ABSTRACT FROM PUBLISHER]

Semiconductor devices in power electronic converters of the doubly-fed induction generator (DFIG) are susceptible to significant junction temperature variations when operating around synchronous speed, thereby reducing the lifetime of the converters. This is due to the fact that the frequency of the rotor current in a DFIG is determined by the stator flux frequency and rotor speed, and hence will lead to low rotor current frequency when operating closer to the synchronous speed, and ultimately result in significant thermal stress on semiconductor devices. In this paper, a multimode operation control strategy is proposed for the DFIG to prevent operating around the synchronous speed (within a predefined deadband); thus, the proposed control strategy can avoid the thermal stress problem. The proposed strategy engages the existing crowbar scheme for DFIG-based wind energy conversion system to intentionally alter the operating mode of the generator between DFIG and induction generator (IG). Smooth transition between the two operating modes can be achieved with the supplementary control strategies. Unity power factor can also be maintained in both operating modes by using the grid side converter as a static synchronous compensator (STATCOM) to fulfill the reactive power requirement of the DFIG in IG mode. [ABSTRACT FROM PUBLISHER]

The energy sector is evolving rapidly, namely due to the increasing importance of renewable energy sources. The connection of large amounts of wind power generation poses new challenges for the dynamic voltage stability analysis of an electric power system, which has to be studied. In this paper, the traditional Doubly-Fed Induction Generator model is employed. Based on this model, a crowbar and chopper circuit is set up to protect the turbine during the short-circuit period. The EUROSTAG software package was used for the simulation studies of the system, and numerical results were obtained. Conclusions are drawn that provide a better understanding of the influence of crowbar and chopper protection on Doubly-Fed Induction Generators (DFIG), during low voltage ride through, in a system with wind power generation.

With the increasing capacity of wind farms integrated into the power grid, the short-circuit current analysis for wind farms becomes more and more important. Since the wind turbine is usually integrated into the power grid via power electronic devices, the “crowbar” is installed in the wind turbine to protect the power electronic devices and to improve the fault ride through capability. The impact of the crowbar has to be considered during the short-circuit current analysis for the wind farm. In order to fully analyze the short-circuit current characteristics of a wind farm, the short-circuit currents for a doubly-fed induction generator (DFIG) wind turbine under symmetrical and asymmetrical faults considering the crowbar action characteristic are derived firstly. Then the action situation of the crowbar of a DFIG wind turbine is studied and the action area curve is obtained. Taking the crowbar action, or not, as the grouping criterion, wind turbines in the wind farm are divided into two groups, and the wind farm is aggregated into two equivalent wind turbines. Using the equivalent model, the short-circuit current of a wind farm can be calculated accurately. Finally, simulations are performed in MATLAB/Simulink which is the commercial math software produced by the MathWorks company in Natick, Massachusetts, the United States to verify the proposed short-circuit current calculation method for the DFIG wind farm.

Crowbar is a popular device used to facilitate the fault ride-through of doubly fed induction generator (DFIG), which protects the power converter from the damage of overcurrent/overvoltage. The crowbar is activated once an overcurrent/overvoltage is detected, and it is desirable to release the crowbar as soon as possible in order to output active/reactive powers to the grid. But releasing the crowbar at an inappropriate timing may result in the recurrence of overcurrent. So, it is important to release the crowbar at an adequate timing. To this end, we analytically investigate the behavior of rotor current, and reveal that the current amplitude fluctuates periodically with a decaying magnitude. Hence, there is a set of release timings which may prevent overcurrent/overvoltage. Further, it is shown that these release timings are robust to the variations of voltage dip depth, generator parameters as well as wind speed. This analysis not only provides a justification for existing release algorithms, but also forms a solid basis for further improvement of crowbar operation. Finally, an algorithm is proposed for the crowbar operation which can prevent overcurrent/overvoltage while minimizing the adverse impact on the grid. The analysis is validated and compared via detailed simulations. • Analytic solutions derived and analyzed for DFIG fluxes and currents. • Biases of dc-component of rotor current are in a descending order from single-phase dip, double-phase dip to three-phase dip. • dominant harmonics in the amplitude fluctuation of rotor current revealed. • Candidate release timings are exposed and are robust to the parameter variations. • Algorithm provided for crowbar operation ensuring overcurrent/overvoltage prevention and grid code compliance. [ABSTRACT FROM AUTHOR]

The ride-through control of a doubly-fed induction generator (DFIG) for the voltage sags on wind farms utilizing crowbar circuits by which the rotor side converter (RSC) is disabled has being reported in many literatures. An analysis and calculation of the transient current when the RSC is switched off are of significance for carrying out the low voltage ride through (LVRT) of a DFIG. The mathematical derivation is highlighted in this paper. The zero-state and zero-input responses of the transient current in the frequency domain through a Laplace transformation are investigated, and the transient components in the time domain are achieved. With the characteristics worked out from the linear resolving without modeling simplification, the selection of the resistance in the linear crowbar circuit and the value conversion from a linear circuit to a nonlinear one is proposed to setup the attenuation rate. In terms of grid code requirements, the theoretical analysis for the time constant of the transient components attenuation insures the controllability when the excitation of the RSC is resumed and it guarantees the reserved time for the response of the reactive power compensation. Simulations are executed in MATLAB/SIMPOWER and experiments are carried out to validate the theoretical analysis. They indicate that the calculation method is effective for selection of the resistance in a crowbar circuit for LVRT operations. [ABSTRACT FROM AUTHOR]

In this work, we present a novel electroporator which is capable of generating single and bursts of high power (3 kV, 60 A) square wave pulses of variable duration (100 ns to 1 ms) with predefined repetition frequency (1 Hz to 3.5 MHz). The proposed synchronized crowbar implementation ensures a constant pulse rise and fall times, which are independent from the load, thus highly relevant in electroporation. The electroporator was successfully tested for the inactivation of the human pathogen Candida albicans. The device is compatible with standard commercial electroporation cuvettes. [ABSTRACT FROM AUTHOR]

This paper have studied the dynamic of a 2.0MWDoubly Fed Induction Generator (DFIG) during a severe voltage sag. Using the dynamic model of a DFIG, it was possible to determine the current, Electromagnetic Force and flux behavior during three-phase symmetrical voltage dip. Among the technologies of wind turbines the DFIG is widely employed; however, this machine is extremely susceptible to disturbances from the grid. In order to improve DFIG Low Voltage Ride-Through (LVRT), it is proposed a novel solution, using Superconducting Current Limiter (SCL) in two arrangements: one, the SCL is placed between the machine rotor and the rotor side converter (RSC), and another placed in the RSC DC-link. The proposal is validated through simulation using PSCAD™/EMTDC™ and according to requirements of specific regulations. The analysis ensure that both SCL arrangements behave likewise, and are effective in decrement the rotor currents during the disturbance. [ABSTRACT FROM AUTHOR]

• Doubly fed induction generator has a complex fault signature with crowbar operation. • Abrupt shift in both magnitude and angle needs to be considered. • Accurate and concise stator and rotor currents are analytically obtained. • The analytical stator expressions are useful for relay and breaker ratings. • The analytical rotor expressions are useful for fault ride through design. The fault current characteristics of Doubly Fed Induction Generator (DFIG) based wind turbine generator (WTGs) differ from those of traditional generators. Although asymmetrical faults are far more frequent, the studies on transient current characteristics of DFIG-based WTGs are mainly focused on symmetrical faults and consider the variations in voltage magnitude only. This paper presents highly accurate and concise analytical expressions for the stator and rotor currents of DFIG-based WTGs under crowbar protection considering the variations in magnitude and phase angle of both the positive- and negative-sequence voltages during asymmetrical faults. The proposed expressions are validated using a detailed simulation model of a 1.5 MW DFIG-based WTG. The expressions can be directly integrated into protection tools for the evaluation of dynamic performance of relays and design of fault ride through (FRT) solutions. [ABSTRACT FROM AUTHOR]