This paper proposes to model and simulate a unified power flow controller (UPFC) in power system computer aided design and electromagnetic transient direct current (PSCAD/EMTDC) environment. The series converter of the UPFC controls the transmission line real/reactive power flow and the shunt converter of the UPFC controls the UPFC bus voltage/shunt reactive power and the DC link capacitor voltage. The real power demand of the series converter is supplied by the shunt converter of the UPFC via the DC link capacitor. The control of transmission line reactive power flow leads to excessive voltage excursion of the UPFC bus voltage. In this proposed work, we have considered two system cases. The first case is to cause a sudden increase in the system load. The second case is to introduce a transient fault in the system. In both cases, excessive bus voltage excursions occur. A UPFC is modeled and designed to reduce these bus voltage excursions, and also proper coordination between the series and shunt converter controllers of the UPFC is maintained to limit the collapse of DC capacitor voltage. PSCAD/EMTDC software is utilized to design and simulate the model.
Key words: Unified power flow controller (UPFC), coordinated control, proportional integral (PI), power system computer aided design and electromagnetic transient direct current (PSCAD/EMTDC).
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