“Analysis of Sub-synchronous Resonance in Wind Farms Interfaced with Series Compensated Transmission Lines”
Dr. Hossein Ali Mohammadpour, Postdoctoral Fellow, University of South Carolina

Mon. March 9th, 2015 from 3:05 – 3:55 p.m. in WEB 1230


Nowadays, it is well-understood that the burning of fossil fuels in electric power stations has a significant influence on global climate due to greenhouse gas emissions. In many countries, the use of cost-effective and reliable low-carbon electricity energy sources is becoming an important energy policy. Among different kinds of clean energy resources- such as solar power, hydro-power, ocean wave power and so on, wind power is the fastest-growing form of renewable energy at the present time.

The adjustable speed generator wind turbine (ASGWT) has key advantages over the fixed-speed generator wind turbine (FSGWT) in terms of reduced mechanical stress, improved power quality, high system efficiency, and reduced acoustic noise. One important class of ASGWT is the doubly-fed induction generator (DFIG), which has gained significant attention from the electric power industry due to its advantages over the other class of ASGWT, i.e. fully rated converter-based wind turbines. Because of increased integration of DFIG-based wind farms into electric power grids, it is necessary to transmit the generated power from wind farms to the existing grids via transmission networks without congestion.

Series capacitive compensation of DFIG-based wind farm is an economical way to increase the power transfer capability of the transmission line connecting the wind farm to the grid. However, a factor hindering the extensive use of series capacitive compensation is the potential risk of sub- synchronous resonance (SSR). The SSR is a condition where the wind farm exchanges energy with the electric network, to which it is connected, at one or more natural frequencies of the electric or mechanical part of the combined system, comprising the wind farm and the network. The frequency of the exchanged energy is below the fundamental frequency of the system. This phenomenon may cause severe damage in the wind farm, if not prevented, as occurred in the ERCOT power transmission network event of 2009, which damaged both wind generators and the series capacitors.

This seminar deals with the SSR phenomena in a capacitive series compensated wind farm. A DFIG-based wind farm, which is connected to a series compensated transmission line, is considered as a case study. The small-signal stability analysis of the system is presented, and the eigenvalues of the system are obtained. Using both modal analysis and time-domain simulation, it is shown that the system is potentially unstable due to the SSR mode.

Then, two different possibilities for the addition of SSR damping controller (SSRDC) are investigated. The SSRDC can be added to (1) gate-controlled series capacitor (GCSC), or (2) DFIG rotor-side converter (RSC) and grid-side converter (GSC) controllers. The first case is related to the series flexible AC transmission systems (FACTS) family, and the second case uses the DFIG back-to-back converters to damp the SSR. The SSRDC is designed using two methods including (1) residue-based analysis supported by root locus method, and (2) an observed-state feedback controller tuned through an optimal quadratic controller design technique. In this work, MATLAB/SIMULINK is used for eigenvalue analysis and PSCAD/EMTDC for time-domain simulations, respectively.


Dr. Hossein Ali Mohammadpour (IEEE S ’2009– M ’2015) received both the B.Sc. and the M.Sc. degrees in electrical engineering – power systems from the Department of Electrical Engineering, Iran University of Science and Technology (IUST), Tehran, Iran, in 2006 and 2009, respectively. During and after his M.Sc., until 2010, he has been with the Iran University of Science and Technology (IUST) as an instructor.

He received the Ph.D. degree in electrical engineering, with emphasis on electric power systems and renewable energy, from the Department of Electrical Engineering, the University of South Carolina, Columbia, SC, USA, in 2014. He is currently a Postdoctoral Fellow with the University of South Carolina.

He has published over fifty papers in power systems, power electronics, and renewable energy resources in international journals and conference proceedings. His research interests include power systems stability and control, control of power electronics systems, renewable energy, smart grid, Flexible AC Transmission System (FACTS) technologies, and micro grid electric ship system modeling and analysis.