Dynamic Control of Static Converters: Dynamic Control Methods for a Static Converter Model in PSCAD for a Traction Power System
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- Institutt for elkraftteknikk 
The Norwegian traction power system is a 15 kV single-phase 16 2/3 Hz power system. The traction power system is mainly supplied by rotary frequency converters that convert three-phase 50 Hz power from the utility grid to single-phase 16 2/3 Hz power. In recent times, static frequency converters (power electronic converters) have also been introduced. Parts of the traction power system are quite weak; consisting of long, radial lines with high impedance. Since the 1990s, the introduction of advanced rail vehicles has revealed a poorly damped eigenmode around 1.6 Hz in the rotary converters used to supply power to the system. In weak parts of the traction power system, the advanced rail vehicles can excite this eigenmode with their fast control systems, creating low frequency voltage oscillations in the traction power system. This thesis presents the work in investigating whether the static converters in the traction power system could be used to dampen low frequency oscillations and stabilise the traction power system. A central part of the work is the developing a model of a static converter in the PSCAD/EMTDC software, including a control system.For the purpose of recreating the low frequency oscillation problem, a rotary converter is also modelled, modifying synchronous machine models in the PSCAD model library.The traction power system is synchronised with the 50 Hz utility grid, so a control algorithm governing the frequency and phase angle of the static converter is implemented in the static converter control system, to allow both the static converter and rotary converter model to maintain synchronism and operate in parallel. An existing advanced rail vehicle model developed in  and implemented in PSCAD in  is also added, forming a small model of a traction power system. The model of a static converter, rotary converter and advanced rail vehicle are combined to form a test-bench to study the how the static converter control system can be used to mitigate the low frequency oscillation problem. A Power Oscillation Damping (POD) controller is implemented in the static converter's control system and tested. The static converter is found to provide extra stability to the traction power system when interconnected with a rotary converter, compared to situations were only rotary converters are present in the system, or worse, when a rotary converter operates in stand-alone mode.Implementation of a POD controller was also found to be effective in adding additional damping to the low frequency oscillations, but also revealed potential negative interaction issues with advanced rail vehicles.