PhD student , University of Tasmania
I am studying on fault ride through capability enhancement of different types of wind turbine.
Regarding new grid code requirements, wind turbines should remain connected to the grid, depending on the level of voltage sag to satisfy the grid code requirements. This behavior is known as fault ride-through (FRT) capability of wind turbine.
Due to many significant characteristics of Doubly-Fed Induction Generator (DFIG) based wind turbines, they are widely employed in the power system especially for the multi-MW applications. In the configuration of the DFIG, the stator of the DFIG is directly connected to the grid and the rotor circuit is linked to the network by a partial scale back-to-back voltage source converters. During the fault condition, transient over-current goes through the rotor circuit towards the Rotor Side Converter (RSC). The rotor over-current can either trip out the DFIG or damage the power electronic devices. Therefore, keeping the DFIG based wind turbine connected to the utility and preventing the equipment from damage are important during the fault.
By now, many methods have been introduced to enhance the FRT capability of the DFIG. One of these techniques is Fault Current Limiters (FCLs). A new approach of application of the resistive type FCLs is studied in this research. The proposed FCL is capable of inserting a controllable resistance in fault current pass of the stator side to not only restrict fault current level and compensate voltage sag in the stator terminal but also consume pre-fault output active power of the DFIG regarding wind speed variation. Simulation and experimental results are also presented to prove effectiveness of the operation of the proposed approach.
Meanwhile, for Fixed Speed Wind Turbine (FSWT), the research has proposed an optimum resistive type FCL (OR-FCL) to improve the fault ride-through capability of the FSWT during symmetrical and asymmetrical grid faults. A dedicated control circuit is designed for the proposed OR-FCL. By means of this control circuit, the OR-FCL calculates an optimum resistance value with respect to all pre-fault operation conditions, including the fault location and the pre-fault output active power of the induction generator. The calculated value of optimum resistance enters the fault current path through the use of the special switching pattern with the frequency of fs and the optimum duty cycle. In this way, the proposed OR-FCL limits the fault current efficiently and guarantees the maximum FRT capability of the FSWT during various grid faults.
Seyed Behzad Naderi (S'10) received the B.S. and M.Sc. degrees in power engineering from the University of Tabriz, Tabriz, Iran, in 2008 and 2011, respectively. He is currently PhD Fellow at the School of Engineering and ICT, University of Tasmania, Australia and working with Prof Michael Negnevitsky. Meanwhile, he was also with Department of Energy Technology as a guest visiting PhD student at Aalborg University, Denmark and cooperating with Prof Frede Blaabjerg. He is the author and coauthor of more than 20 journal and conference papers. His current research interests include fault current limiters, power system transient stability, power quality, flexible ac transmission systems, and renewable energy.
Abstract: Publication date: March 2017 Source:International Journal of Electrical Power & Energy Systems, Volume 86 Author(s): Amin Jalilian, Seyed Behzad Naderi, Michael Negnevitsky, Mehrdad Tarafdar Hagh, Kashem M. Muttaqi Doubly-fed induction generator (DFIG)-based wind turbines utilise small-scale voltage sourced converters with a limited overcurrent withstand capability, which makes the DFIG-based wind turbines very vulnerable to grid faults. Often, modern DFIG systems employ a crowbar protection at the rotor circuit to protect the rotor side converter (RSC) during grid faults. This method converts the DFIG to a squirrel cage induction generator, which does not comply with the new grid codes. The recent grid codes need wind turbines to stay connected to the utility grid during and after power system faults, especially in high penetration level of wind power. Furthermore, the crowbar switch is expensive. This paper proposes a novel DC-link switchable resistive-type fault current limiter (SRFCL) to improve the LVRT capability of the DFIG. The proposed SRFCL is employed in the DC side of the RSC. The SRFCL solves crowbar protection activation problems and eliminates subsequent complications in the DFIG system. The proposed SRFCL does not have any significant impact on the overall performance of the DFIG during normal operation. Whenever the fault, whether symmetrical or asymmetrical, occurs, the SRFCL not only limits rotor over-currents but also prevents rotor speed acceleration and restricts high torque oscillations even during zero grid voltage, as recommended by some grid codes. To prove the effective operation of the SRFCL on the RSC fault current limitation, analytical analysis is performed in each switching interval. The proposed approach is compared with the crowbar-based protection method. Simulation studies are carried out in PSCAD/EMTDC software. In addition, a prototype is provided to demonstrate the main concept of the proposed approach.
Pub.: 16 Nov '16, Pinned: 27 Jul '17