Today’s power systems are becoming heavily loaded and operating close to their stability
limit. This raises issue of voltage security and small signal stability, which may lead to
the system being forced to operate way below its rated capacity. The impact of renewable
technology such as wind and other technologies are likely to further strain existing power
networks and infrastructure, hence, likely to adversely affect voltage stability of the power
network. The intermittency associated with these sources could also adversely affect on
the damping of the system’s oscillatory modes.
The work presented in this thesis develops techniques for identifying which controls are
effective to improve voltage security margins. Using distributed series impedance, a
device that can either increase or reduce line impedance, and margin sensitivity, it is
shown that voltage stability margin can be effectively enhanced. Validation is performed
on a 39 bus system following a major line outage contingency. Ways of improving the
accuracy of margin sensitivity with respect to various controls are presented.
Techniques for designing controllers to improve system mode damping have been developed. Unlike techniques using predominately state-space method, these which utilise
polynomial methods, yield robust controller of low order and whose structure can be
pre-specified. Three techniques are presented. The first uses Kharitonov’s theorem and
results in bilinear matrix inequality (BMI) stability conditions. The second uses the theory of positive polynomials which results in linear matrix inequality (LMI) conditions for
stability. The last uses conic programming to the controller design problem as a two part
problem, first involving phase compensation design, then gain tuning. The effectiveness
of the techniques is validated by designing controller for an 68 bus test system model.