Short circuit fault analysis in a grid connected DFIG based wind energy system with active crowbar protection circuit for ridethrough capability and power quality improvement (original) (raw)
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IET Generation, Transmission & Distribution, 2017
A hybrid scheme for enhancing fault ride through (FRT) capability of doubly fed induction generator under symmetrical and asymmetrical grid faults is presented. The hybrid strategy is composed of switch type fault current limiter (STFCL), braking chopper and energy storage system (ESS). The hybrid scheme guarantees the safety and controllability of rotor side converter and DC-link capacitor. The proposed FRT scheme has ability to overcome the transients and oscillation produced during the voltage dip. The hybrid strategy is capable of keeping the fault current, DC-link voltage, rotor current and voltage and electromagnetic torque within the limits and damps the oscillations during the voltage dip. The results of hybrid scheme are compared with STFCL only and are found better for the former case. MATLAB/Simulink is used for simulation of 9 MW wind turbine interfaced with grid.
Dynamic performance of DFIG based WECS under different voltage sag
At the present time Doubly Fed Induction Generator (DFIG) based wind energy conversion systems are widely used for large wind power plants. DFIG offers many advantages for instance reduced rating power converter, low cost and reduced losses with the better efficiency, easy in realization of power factor correction schemes, variable speed operation and four quadrants active and reactive power control capabilities. Due to operate under variable speed mode total energy output is much more, so capacity utilization factor is enhanced and cost of per unit energy is cheap. But the main disadvantage of DFIG is that it is very susceptible to grid disturbance or fault, particularly for the voltage dip. As the doubly-fed induction generator (DFIG) has been broadly used in wind energy conversion systems, the Fault Ride through (FRT) or Low Voltage Ride through (LVRT) expertise of the DFIG has been investigated extensively in recent times. This paper focuses the fault ride-through capability of DFIG based WECSs under different voltage sag. The paper also gives an overview on the interaction between variable-speed DFIG based WECSs and the power system subjected to disturbances/fault. The dynamic performance of WECS based on DFIG under grid faults is simulated and assessed. This paper also discusses major grid problems and grid codes for operation & grid connection of wind farms and gives brief introduction about the solutions for FRT/LVRT available in market today.
International Journal of Emerging Electric Power Systems, 2016
In this paper a three phase fault analysis is done on a DFIG based grid integrated wind energy system. A Novel Active Crowbar Protection (NACB_P) system is proposed to enhance the Fault-ride through (FRT) capability of DFIG both for symmetrical as well as unsymmetrical grid faults. Hence improves the power quality of the system. The protection scheme proposed here is designed with a capacitor in series with the resistor unlike the conventional Crowbar (CB) having only resistors. The major function of the capacitor in the protection circuit is to eliminate the ripples generated in the rotor current and to protect the converter as well as the DC-link capacitor. It also compensates reactive power required by the DFIG during fault. Due to these advantages the proposed scheme enhances the FRT capability of the DFIG and also improves the power quality of the whole system. Experimentally the fault analysis is done on a 3hp slip ring induction generator and simulation results are carried ou...
Comparative Study between Two Protection Schemes for DFIG-based Wind Generator Fault Ride Through
Journal of international Conference on Electrical Machines and Systems, 2012
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.
Analysis of Protection Scheme for Grid Connected DFIG System under Symmetrical Fault Condition
2016
This paper deals with the protection scheme of Doubly Fed Induction Generator (DFIG) based wind energy conversion system (WECS) for Low Voltage Ride Through (LVRT). The ability of Wind Turbine to stay connected to the grid during voltage dips is termed as the low-voltage ride-through (LVRT) capability. During voltage dip, two major concerns comes into picture, first one is the overcurrent in stator and rotor circuits and other one is the dc link overvoltage. Both issues are dangerous to DFIG operation. The overvoltage in dc link and overcurrent in rotor circuit is dangerous for rotor converters, as less capacity of rotor converters is used in DFIG wind turbines. To prevent this situation dc chopper is inserted in dc link circuitry to regulate the dc link voltage and active crowbar is inserted in rotor circuit which helps to prevent the rotor circuitry from overcurrent.
Fault Ride through Capability Improvement of DFIG Using SMES Unit during Short Circuit
International Journal of Mechanical Engineering and Robotics Research
Catastrophic impacts of conventional based power plants on the environment has forced many nations to concern more on exploring renewable energy (RE) source for power plants. One of the most popular RE sources is wind, where the wind has been installed about 430 GW in 2015. Among wind turbines generator that available in the market niche, Doubly Fed Induction Generator (DFIG) is the most popular type. DFIG type dominates the total wind turbine installed capacity by about 17.5% in 2015 according to the report of JRC (Joint Research Center). Although DFIG is capable in extracting 5% more energy if compared to the fixed speed type, it is however, very sensitive to the fault that may violate the Fault Ride Through (FRT) which leads to the disconnecting of the DFIG from the grid. In this paper, a Superconducting Magnetic Energy Storage (SMES) unit is applied to improve the FRT capability of the system with DFIG during a short circuit event in the distribution lines. A Fuzzy Logic Type-2 is employed on the SMES to obtain the most optimum response of the DFIG during the fault.
IEEE Transactions on Applied Superconductivity, 2013
Wind power generation is growing rapidly. However, maintaining the wind turbine connection to grid is a real challenge. Recent grid codes require wind turbines to maintain connected to the grid even during fault conditions which increases concerns about its sensitivity to external faults. So, researchers have given attention to investigating the impact of various external faults, and grid disturbances such as voltage sag and short circuit faults, on the fault ride through (FRT) capability of the doubly fed induction generator (DFIG). However, no attention has been given to the impact of internal faults on the dynamic performance of the machine when the fault occurs within the voltage source converters (VSCs) that interface the DFIG with the grid. This paper investigates the impact of the rotor side converter (RSC) IGBT flashover fault on the common coupling (PCC) reactive power and the FRT capability of the DFIG. A proper STATCOM controller to mitigate the effects of the flashover fault on the FRT is proposed. The DFIG compliance with numerous and recently released FRT grid codes under the studied fault, with and without the STATCOM are examined and compared. Furthermore, the capability of a proposed controller to bring the voltage profile at the point of PCC to the nominal steady-state level; maintain the unity power factor operation; and, maintain the connection of the wind turbine to the grid are examined.
In suggested protection technique, an advanced Active Crowbar Protection system is proposed for Doubly-Fed Induction Generator (DFIG) coupled Wind Energy Conversion System (WECS). An active Crowbar Protection system with relay components is designed for DFIG based Wind Turbine for analysis of Low Voltage Ride through (LVRT) at different fault conditions. DFIG controlled model is connected to utility based substation in standalone mode and assumed to be connected to large grid by taking substation as programmable voltage source. A large number of lumped load can be connected to the line. DFIG performance analysis with and without Crowbar protection is done for all kinds of faults and effectiveness of proposed fault protection technique have been demonstrated by the results. This work has motivated by the controlling of DFIG and behavior analysis at the time of fault.
Impact of DFIG based wind energy conversion system on fault studies and power swings
2016 National Power Systems Conference (NPSC), 2016
The integration of renewable energy sources into power systems changes the transient and fault current characteristics of the conventional grid. The variation in the system response during grid disturbance like sudden load changes or fault would cause the failure of traditional protection and control. Since the operating condition of DFIG depends on the characteristics of the grid and its control, the short circuit current in the system becomes more complex. This paper analyzes the short circuit characteristics of DFIG and develops an analytical expression for the three phase fault current. Depending on the severity of the fault in terms of voltage drop, the fault current responses are developed with and without crow bar resistance. The power swings that originates in the system when the fault is cleared are also analyzed in the paper. The transient simulation studies are performed in PSCAD/EMTDC by integrating DFIG to WSCC system. Case studies are performed to analyze the impact of location of fault to the power swing and fault current contribution.
—The stabilized operation of Doubly Fed Induction Generator (DFIG) during symmetrical faults is a demanding problem for power system engineers. Transient peaks, oscillations, and higher-order frequency harmonics in DC link voltage and rotor circuitry will lead to the violations of the grid-code objectives during grid faults. Control actions must be taken to ensure safe operation of the Wind Energy Conversion System (WECS) during voltage sags/dips or short-circuit conditions without affecting system reliability. Based on the analysis, we propose a hybrid Fault-Ride-Through (FRT) strategy, considering grid-code specifications and converters control functions. Our work also presents a comparative and critical analysis of active FRT schemes under symmetrical faults. Moreover, our work discusses the effect of voltage and current parameters on the steady-state performance and stability of WECS. Furthermore, we analyze transient response of various performance parameters for the comparison of aforesaid schemes, such as rotor voltages and currents, DC link voltage, electromagnetic torque, active and reactive power support, and rotor speed. We used IEEE 5 Bus System interfaced with 9MW DFIG-Wind Turbine (WT) for the FRT performance evaluation in MATLAB/Simulink. keywords—Fault-Ride-Through (FRT), Wind energy, Doubly-Fed Induction Generator (DFIG), PI Control, Power control.