Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Electrical and Computer Engineering (Holcomb Dept. of)

Committee Member

Dr. Elham B. Makram, Committee Chair

Committee Member

Dr. Richard Groff

Committee Member

Dr. Taufiqar Khan

Committee Member

Dr. Anthony Martin

Committee Member

Dr. Ramtin Hadidi


Small signal stability has become a major concern for power system operators around the world. This has resulted from constantly evolving changes in the power system ranging from increased number of interconnections to ever increasing demand of power. In highly stressed operating conditions, even a small disturbance such as a load change can make the system unstable resulting in small signal instability. The main reason for small signal instability in power systems is an inter-area mode/s becoming unstable. Inter-area modes involve a group of generators oscillating against each other. Traditionally, power system stabilizers installed on the synchrous machines were used to damp the inter-area modes. However, they may not be very suitable to perform the job since they use local I/O signals which do not have a good controllability/observability of the inter-area modes. Recent advancements in phasor measurement technology has resulted in fast acquisition of time-synchronized measurements throughout the system. Thus, instead of using local controllers, an idea of a wide area controller (WAC) was proposed by the power systems community that would use global signals. This dissertation demonstrates the design of a WAC using eigenstructure assignment technique. This technique provides the freedom to assign a few eigenvalues and corresponding left or right eigenvectors for Multi-Input-Multi-Output (MIMO) systems. This technique forms a good match for designing a WAC since a WAC usually uses multiple I/O signals and a power system only has a few inter-area modes that might lead to instability. The last chapter of this dissertation addresses an important aspect of controller design, i.e., robustness of the controller to uncertainties in operating point and time delay of feedback signals. The operating point of a power system is highly variable in nature and thus the designed WAC should be able to damp the inter-area modes under these variations. Also, a transmission delay is associated due to routing of remote signals. This time delay is known to deteriorate the performance of the controller. A single controller will be shown to achieve robustness against both these uncertainties.



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