Crowbar Circuit Research Articles

Control of Grid Voltage Feed-Forward and Crowbar Circuit for DC-Bus Voltage

The DC bus voltage is the main criteria to reflect whether the converter system is working properly or not, and the stability control of the DC bus voltage is the key to ensure that wind power generators not take off the grid when grid voltage drops. This paper had done research on a direct-drive wind power system and proposed a coordinated control method based on the grid voltage information feedforward with a crowbar circuit. The hardware was combined with the improved control strategy in this method. When the grid voltage drops, the extra energy of the DC bus can be unleashed by the crowbar circuit, at the same time, the output power of motor-side can be controlled according to the grid-side information, and the mechanical speed of motor-side can be suppressed by the pitch angle regulation when the output power reduces. Thus, the DC-bus voltage can be keep stability. Results based on Matlab/Simulink simulation shows that this method not only improves the stability and dynamic response performance of the DC bus voltage, but also effectively maintains the output power of generator and reduces the action time of crowbar circuit. The ability of the wind power system riding through the grid fault has been effectively improved.

The Virtual Resistance Control Strategy for HVRT of Doubly Fed Induction Wind Generators Based on Particle Swarm Optimization

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.

Control for Dc-Bus Voltage Using Grid Voltage Feed-Forward and Crowbar Circuit

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.

Research of Driving Circuit in Coaxial Induction Coilgun

Power supply is crucial equipment in coaxial induction coil launcher . Configuration of the driving circuit directly influence s the efficiency of the coil launcher.This paper gives a detailed analysis of the properties of the driving circuit construction based on the capacitor source. Three topologies of the driving circuit are compared including oscillation , crowbar and half-wave circuits. It is proved that which circuit has the better efficiency depends on the detailed parameters of the experiment, especially the crowbar resistance. Crowbar resistor regulates not only efficiency of the system, but also temperature rise of the coil. Electromagnetic force (EMF) applied on the armature will be another problem which influence s service condition of the driving circuits. Oscillation and crowbar circuits should be applied to both of the synchronous and asynchronous induction coil launchers, respectively. Half-wave circuit is seldom used in the experiment. Although efficiency of the half-wave circuit is very high , the speed of the armature is low. A simple independent half-wave circuit is proposed in this paper. In general, the comprehensive property of crowbar circuit is the most practical in the three typical circuits. Conclusions of the paper could provide guidelines for practice.

Analysis and Enhancement of Low-Voltage Ride-Through Capability of Brushless Doubly Fed Induction Generator

This paper discusses the dynamic behavior of the brushless doubly fed induction generator during the grid faults which lead to a decrease in the generator's terminal voltage. The variation of the fluxes, back EMFs, and currents are analyzed during and after the voltage dip. Furthermore, two alternative approaches are proposed to improve the generator ride-through capability using crowbar and series dynamic resistor circuits. Appropriate values for their resistances are calculated analytically. Finally, the coupled circuit model and the generator's speed and reactive power controllers are simulated to validate the theoretical results and the effectiveness of the proposed solutions. Moreover, experiments are performed to validate the coupled circuit model used.

Research on an Improved Control Strategy for Enhancing LVRT Ability of DFIG System

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.

An Investigation of the Low Voltage Ride through Function of GE DFIG Wind Turbines for Electro-Mechanical Simulations

Doubly-fed induction generator (DFIG) wind turbine has become the most widely used wind turbine in wind farms, since it presents noticeably advantages such as decoupled controls of active and reactive powers, and the use of a power converter with a rated power of 25% of total system power. As the penetration of wind power in power system increases, it is required that the wind turbine remained connected and actively contributed to the system stability during and after faults and disturbance. One common approach for a DFIG to obtain such low voltage ride through (LVRT) function is to install a crowbar circuit across its rotor terminals, which short circuit the rotor side converter when over-current is detected in the rotor. A detailed model of LVRT function normally requires electromagnetic simulations. However, the time consuming computational process is prohibitive for the studies of the integration of wind farms into large scale power systems. Electromechanical simulations are more suitable for such engineering applications. GE has incorporated the LVRT function into its recently released DFIG wind turbine model for Electro-mechanical simulations. This paper has implemented this model and verified the effectiveness of the LVRT function.

대전류 펄스 성형이 가능한 150MW급 펄스파워 시스템의 설계 및 동작특성

본 논문은 트리거 시간을 조절하여 펄스 성형이 가능한 150 MW 펄스 파워 시스템의 설계와 동작특성을 알아보았다. 이 시스템은 2개의 커패시터 뱅크 모듈로 구성되어 있고, 각 커패시터 뱅크 모듈은 병렬로 연결되어 있다. 그리고 커패시터 뱅크 모듈은 메인스위치, 커패시터, 에너지 덤프회로, 크로바 회로, 펄스 성형 인덕터로 구성되어 있다. 또한 이 시스템의 모듈 선택과 트리거 시간은 트리거 제어부에서 조정된다. Pspice 시뮬레이션은 실험회로의 결과를 예측하고, 시스템의 구성품의 파라미터를 결정하기 위한 것으로 사용하였다. 실험 결과, 시뮬레이션은 실험결과와 잘 일치하였다. 출력 전류의 펄스폭은 커패시터 뱅크 모듈에서의 순간적 점화 시간 제어로 300~650 us의 펄스폭이 형성되었다. 그리고 최대 전류값은 2개의 커패시터 뱅크 모듈이 동시에 트리거 되었을 때 약 40 kA 정도이다. 이 150 MW 펄스 파워 시스템은 파암 전원, Rail Gun, Coil Gun, 나노분말 제조, HPM 등과 같은 대전류 펄스 파워 시스템에 적용할 수 있다. This paper presents design and operational characteristics of 150 MW pulse power system for high current pulse forming network to control trigger time. The system is composed of two capacitor bank modules. Each capacitor bank module consist of a trigger vacuum switch, 9k 33kJ capacitor, an energy dump circuit, a crowbar circuit and a pulse shaping inductor and is connected in parallel. It is controlled by trigger controller to select operational module and determine triggering time. Pspice simulation was conducted about determining parameters of components such as crowbar circuit, capacitor, pulse forming inductor, trigger vacuum switch and predicting results of experiment circuit. The result of the experiment was in good agreement with the result of the simulation. The various current shapes with 300~650 us pulse width is formed by sequential firing time control of capacitor bank module. The maximum current is about 40 kA during simultaneous triggering of two capacitor bank modules. The developed 150 MW pulse power system can be applied to high current pulse power system such as rock fragmentation power sources, Rail gun, Coil gun, nano-powers, high power microwave.

Control strategies of doubly fed induction generator-based wind turbine system with new rotor current protection topology

A protection scheme of a doubly fed induction generator (DFIG) based wind turbine system during faults is crowbar activation. With this protection, the rotor side converter (RSC) is temporarily disconnected, and its vector control over the stator active and reactive power is lost, leading to poor power quality at the point of common coupling (PCC). This paper presents a new protection scheme for transient rotor current to improve the performance of DFIG during grid disturbance. The new scheme, consisting of a crowbar and series circuit, is connected between the rotor windings and RSC to enhance the low voltage ride-through capability of DFIG. The proposed scheme successfully limits the transient rotor current and dc-link voltage, and a disconnection of RSC from the rotor windings is avoided during fault. Additionally, RSC and grid-side converter controllers are modified to improve the voltage at PCC. Simulations on matlab/Simulink verify the effectiveness of the proposed scheme.

Design of a 135 MW Power Supply for a 50 T Pulsed Magnet

At the Wuhan National High Magnetic Field Center (WHMFC) a 50 T/100 ms flat-top long-pulse magnet consisting of two coaxially nested coils is designed. The power and energy to operate the magnet is provided by a 100 MVA/185 MJ inertial energy storage motor-generator set. To accommodate the needs of this and future magnets, two 67.5 MW power supply modules based on 12-pulse converters are designed to convert the ac-power produced by the generator into controlled dc-power. The modules can operate independently as well as in parallel or in series. Each module consists of a combined input disconnect/grounding switch, two rectifier transformers, two parallel-connected 6-pulse rectifiers, a crowbar circuit, and a reversing switch. Two different transformer tap settings allow the module to provide no-load voltages of 3.2 kV and 2.7 kV and full-load voltages of 2.7 kV and 2.25 kV at the rated current of 25 kA for a 2 second pulse once every half hour. All components of the power supply modules are now under construction, with complete delivery and installation expected in early 2012. The design of the power supply components is described in detail. Digital simulation results of the power supply driving the 50 T/100 ms magnet are presented.

Novel Scheme for Improving the Performance of a Wind Driven Doubly Fed Induction Generator during Grid Fault

Enhancement of fault ride-through (FRT) capability and subsequent improvement of rotor speed stability of wind farms equipped with doubly fed induction generator (DFIG) is the objective of this paper. The objective is achieved by employing a novel FRT scheme with suitable control strategy. The proposed FRT scheme, which is connected between the rotor circuit and dc link capacitor in parallel with Rotor Side Converter, consists of an uncontrolled rectifier, two sets of IGBT switches, a diode and an inductor. In this scheme, the input mechanical energy of the wind turbine during grid fault is stored and utilized at the moment of fault clearance, instead of being dissipated in the resistors of the crowbar circuit as in the existing FRT schemes. Consequently, torque balance between the electrical and mechanical quantities is achieved and hence the rotor speed deviation and electromagnetic torque fluctuations are reduced. This results in reduced reactive power requirement and rapid reestablishment of terminal voltage on fault clearance. Furthermore, the stored electromagnetic energy in the inductor is transferred into the dc link capacitor on fault clearance and hence the grid side converter is relieved from charging the dc link capacitor, which is very crucial at this moment, and this converter can be utilized to its full capacity for rapid restoration of terminal voltage and normal operation of DFIG. Extensive simulation study carried out employing MATLAB/SIMULINK software vividly demonstrates the potential capabilities of the proposed scheme in enhancing the performance of DFIG based wind farms to fault ride-through.

Comparative Study between Two Protection Schemes for DFIG-based Wind Generator Fault Ride Through

Fixed speed wind turbine generators system that uses induction generator as a wind generator has the stability problem similar to a synchronous generator. On the other hand, doubly fed induction generator (DFIG) has the flexibility to control its real and reactive powers independently while being operated in variable speed mode. This paper focuses on a scheme where IG is stabilized by using DFIG during grid fault. In that case, DFIG will be heavily stressed and a remedy should be found out to protect the frequency converter as well as to allow the independent control of real and reactive powers without loosing the synchronism. For that purpose, a crowbar protection switch or DC-link protecting device can be considered. This paper presents a comparative study between two protective schemes, a crowbar circuit connected across the rotor of the DFIG and a protective device connected in the DC-link circuit of the frequency converter. Simulation analysis by using PSCAD/EMTDC shows that both schemes could effectively protect the DFIG, but the latter scheme is superior to the former, because of less circuitry involved.

ENHANCEMENT OF FAULT RIDE THROUGH CAPABILITY OF A WIND DRIVEN DFIG CONNECTED TO THE GRID

Enhancement of fault ride-through (FRT) capability and subsequent improvement of rotor speed stability of wind farms equipped with doubly fed induction generator (DFIG) is the objective of this paper. The objective is achieved by employing a novel FRT scheme with suitable control strategy. The proposed FRT scheme, which is connected between the rotor circuit and dc link capacitor in parallel with Rotor Side Converter, consists of an uncontrolled rectifier, two sets of IGBT switches, a diode and an inductor. In this scheme, the input mechanical energy of the wind turbine during grid fault is stored and utilized at the moment of fault clearance, instead of being dissipated in the resistors of the crowbar circuit as in the existing FRT schemes. Consequently, torque balance between the electrical and mechanical quantities is achieved and hence the rotor speed deviation and electromagnetic torque fluctuations are reduced. This results in reduced reactive power requirement and rapid reestablishment of terminal voltage on fault clearance. Furthermore, the stored electromagnetic energy in the inductor is transferred into the dc link capacitor on fault clearance and hence the grid side converter is relieved from charging the dc link capacitor, which is very crucial at this moment. The converter in this case can be utilized to its full capacity for rapid restoration of terminal voltage and normal operation of DFIG. Extensive simulation study carried out employing MATLAB/SIMULINK software demonstrates the potential capabilities of the proposed scheme in enhancing the performance of wind farms DFIG to fault ride-through.

The Research of Verifying Low Voltage Ride through of Double-Fed Wind Turbine Generator System and Voltage Dropping Simulation

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.

High Voltage Series Switch and Crowbar Protection in RF Heating

Plasma is the fourth state of matter. High temperature is essential to sustain the plasma in ionic form. The RF heating system used to provide the required temperature may get damaged due to occurrence of arcing. Series switch (circuit breaker) is one of the most effective and efficient methods of protecting RF generators. The series switch must be operated within stipulated time after the occurrence of electric fault and therefore the triggering circuit of series switch must be designed carefully to obtain optimum results. This paper presents the designs of high voltage series switch and crowbar circuit developed for the protection of RF heating system. An optimum triggering scheme is designed to obtain the triggering with the delay of only 4.8 μS as compared to the safety margin of 10 μS. The importance of optical triggering and utilization of fiber optic has been justified. The designs are well supported with the experimental results.

Reactive Power Generation and Optimization during a Power System Fault in Wind Power Turbines Having a DFIG and Crowbar Circuit

For variable-speed constant-frequency (VSCF) wind power generation, a doubly fed induction generator (DFIG) equipped with a crowbar circuit is becoming more widely used in electrical transmission networks. This prevents potentially damaging over-voltage and/or over-current conditions in the DFIG during a power system fault. The response of a DFIG based wind turbine system to voltage dips at the point of common coupling is studied in this paper. A crowbar circuit can limit the surge current as well as protect the rotor side converter and DC-link capacitor. When the crowbar is cut in, the rotor side converter is disconnected from the rotor windings, which makes the DFIG behave as an asynchronous induction generator with high rotor impedance. It is suggested that use of a crowbar circuit can reduce the reactive power absorbed by the stator and also assist in voltage recovery of the grid by injecting reactive power into the grid. This paper analyzes the influence of the AC crowbar resistors or inductors on the reactive power consumption of the stator during grid voltage dips. In addition, the paper presents a current-limiting method to control the grid side converter and the rotor side converter, which provides reactive power to the grid and thus enhance the capability of low voltage ride-through (LVRT). In the simulation studies presented, AC crowbars with different resistor and inductor values are selected. The simulation results show that the stator reactive power absorption can be controlled, while the rotor side converter and grid side converter can be controlled to inject reactive power into the grid to enhance voltage restoration and fault recovery.

Novel scheme for enhancement of fault ride-through capability of doubly fed induction generator based wind farms

Enhancement of fault ride-through (FRT) capability and subsequent improvement of rotor speed stability of wind farms equipped with doubly fed induction generator (DFIG) is the objective of this paper. The objective is achieved by employing a novel FRT scheme with suitable control strategy. The proposed FRT scheme, which is connected between the rotor circuit and dc link capacitor in parallel with Rotor Side Converter, consists of an uncontrolled rectifier, two sets of IGBT switches, a diode and an inductor. In this scheme, the input mechanical energy of the wind turbine during grid fault is stored and utilized at the moment of fault clearance, instead of being dissipated in the resistors of the crowbar circuit as in the existing FRT schemes. Consequently, torque balance between the electrical and mechanical quantities is achieved and hence the rotor speed deviation and electromagnetic torque fluctuations are reduced. This results in reduced reactive power requirement and rapid reestablishment of terminal voltage on fault clearance. Furthermore, the stored electromagnetic energy in the inductor is transferred into the dc link capacitor on fault clearance and hence the grid side converter is relieved from charging the dc link capacitor, which is very crucial at this moment, and this converter can be utilized to its full capacity for rapid restoration of terminal voltage and normal operation of DFIG. Extensive simulation study carried out employing PSCAD/EMTDC software vividly demonstrates the potential capabilities of the proposed scheme in enhancing the performance of DFIG based wind farms to fault ride-through.

Ensuring Fault Ride Through for Wind Turbines with Doubly Fed Induction Generator: a Model Predictive Control Approach

AbstractThis paper proposes a novel control strategy, based on Model Predictive Control (MPC), which ensures Fault Ride Through (FRT) for wind turbines with Doubly Fed Induction Generators (DFIGs). During large voltage dips, large currents are induced in the rotor that can destroy the rotor converter. The common approach used to protect the rotor converter is to disable the converter and to dissipate the rotor power via a crowbar circuit. This approach is currently not accepted by most grid codes which dictate that grid connected wind turbines should remain connected to the grid during severe faults with full control over their active and reactive power. The proposed strategy ensures FRT for DFIG grid connected wind turbines without using a crowbar and therefore meets recent grid codes requirements. This is achieved by using a Dynamic Series Resistance and an MPC controller incorporating most of the DFIG's constraints.

10/350-$\mu\hbox{s}$ Crowbar Pulse Current System

This paper presents a novel crowbar system of 10/350-μs pulse current. The crowbar pulse current system includes a crowbar pulse current waveform forming circuit, a controlling unit, and a measuring unit. The crowbar pulse current circuit consists of a main air triggered switch, a triggered vacuum switch (TVS) which is used as the crowbar switch, and two trigger signal generators. A kind of TVS is designed and fabricated. Its triggering characteristics are tested, and experimental results show that, compared with other reported similar switches, the TVS has excellent characteristics such as wide operating voltage scope from 1.3 to 120 kV, short discharging delay time with maximum delay time at 400 ns, and its jitter at ±10 ns. Based on the TVS, the crowbar 10/350-μs pulse current circuit and its controlling circuit are designed. With a 36-μF storage capacitor <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> and a 6-μH waveform forming inductance <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> , a 10/350-μs pulse current waveform with a maximum of 150 kA can be generated.

A High-Voltage and High-Current Triggered Vacuum Switch

High-power and high-current test technology has many requirements for a discharging switch, such as high hold-off voltage, wide operating voltage scope, short discharging delay time and jitter, strong charge transfer ability, and long lifetime. A high-voltage and high-current triggered vacuum switch (TVS) with a surface flashover trigger device has been designed, and the trigger device is made from a material whose relative dielectric constant ε <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> is around 2500. The experimental circuits are set up, and the experiments are performed. The experimental results showed that the TVS can be used at a maximum voltage of up to 120 kV, the minimum operation voltage is 1.3 kV, the maximum discharging delay time is less than 400 ns, and the minimum discharging delay time and jitter reach to 100 and 10 ns, respectively. The maximum current switched is about 180 kA, and the maximum transfer charge per shot is larger than 2.5 C. The switch can satisfy the main demands of crowbar circuit applications and can be used on high-voltage and high-current application situations.