ORCID Identifier(s)


Graduation Semester and Year




Document Type


Degree Name

Doctor of Philosophy in Electrical Engineering


Electrical Engineering

First Advisor

Wei-Jen Lee


Power systems have recently become more susceptible to Sub-Synchronous Control Interaction (SSCI) due to the increasing penetration of renewable generation resources and series compensated lines. Any contingency which results in a radial condition between renewable generation resources and near-by series compensated lines might trigger an undamped SSCI oscillation. This is a purely electrical phenomenon which has potential to grow rapidly. Undamped SSCI oscillation can cause serious damage to the renewable generation resources and transmission elements and consequently leads to cascading outages. Due to the importance of the phenomena and its potential impacts, this research has focused on two aspects of this event as listed below: • Detail modeling of Doubly-Fed Induction Generators (DFIGs) as the most vulnerable type of wind generator to SSCI • Proposing a novel algorithm for the detection of SSCI Firstly, a novel state-space based modeling approach for Doubly Fed Induction Generator (DFIG) is proposed which allows for the inclusion of the Phase Locked Loop (PLL) controller in a detail dual d-q state-space model. Eigenvalue analysis as well as time domain transient simulations are performed using the proposed nonlinear state-space model to study the impact of PLL parameters on SSCI oscillations. The results are indicative that faster PLL control parameters can increase the risk and severity of SSCI. To validate and interpret the results, the closed loop d-q sub-synchronous impedance model of the DFIG including impedance transfer function of the proposed PLL model is extracted. Bode diagrams of the DFIG and transmission system are then plotted for different scenarios utilizing different PLL parameters. In line with the eigenvalue and time domain transient analysis, the impedance model depicts that faster PLL control parameters leads to smaller phase margin and consequently higher SSCI risk. Secondly, an effective algorithm is proposed to detect SSCI within 45ms and reliably send a trip signal within 95ms. Initially, a comprehensive SSCI analysis is suggested to improve the pre-processing of the measured signal. The proposed algorithm then utilizes mode identification approaches in conjunction with a moving FFT to capture the frequency and magnitude of oscillations and process them to issue a reliable trip command in the case of a SSCI event. To evaluate the algorithm, a portion of ERCOT grid with relatively higher penetration of renewable resources is utilized to simulate the SSCI phenomenon. The proposed detection algorithm was implemented on a real-time target device. The SSCI signal observed in the detailed EMT simulation of the ERCOT grid was injected to the device to test the algorithm under real-time operating conditions. The results indicate the efficiency and accuracy of the method in successful detection within the acceptable time frame.


Sub-synchronous resonance, Detection, DFIG


Electrical and Computer Engineering | Engineering


Degree granted by The University of Texas at Arlington