Coordinated Voltage Control in Electric Power Systems

Abstract: This thesis deals with various aspects of coordinated voltage control in electric power systems. It consists of an introduction and six papers. The introduction contains a summary of the thesis and tutorials on voltage control and the search methods that have been applied. The first part deals with the coordination of cascaded tap changers in radial distribution feeders. A tuning rule for the conventional (local) controllers as well as two new (centralized) schemes are proposed: firstly, an optimal controller based on on-line optimization and secondly, a rule based controller based on a fuzzy inference system. A prototype of the fuzzy-rule based controller has been installed and successfully tested in a distribution feeder in the south of Sweden. The second part of the thesis describes a coordinated system protection scheme (SPS) against voltage collapse based on model predictive control. Using combinatorial optimization and predictions of the system's future behaviour, the SPS optimally coordinates dissimilar and discrete controls such as generator, tap changer and load shedding controls in presence of load dynamics and constraints on controls as well as voltages and currents in the network. Modelling of power systems has also been addressed. The third part describes a freely available power system library called ObjectStab intended for voltage and transient stability analysis and simulation written in Modelica--a general-purpose object-oriented modelling language. All component models are transparent and can be modified or extended. Power system topology and parameter data are entered in one-line diagram form using a graphical editor. The component library has been validated using comparative simulations with Eurostag.