Performance improvement of power systems using Hybrid Power Flow Controller

This paper discusses the applicability of Hybrid Power Flow Controller (HPFC) as an alternative to Unified Power Flow Controller (UPFC) for improvement of power system performance. UPFC is a flexible AC transmission system (FACTS) device containing two switching converters, one in series and one in shunt. To configure the HPFC, one of the switching converters of the UPFC is replaced by thyristor controlled variable impedances, thus reducing the cost. In this paper, the HPFC has been configured by multilevel Voltage Source Converter (VSC) used for the shunt compensation branches and a thyristor controlled variable impedance used for series compensation. It is shown that with suitable control the HPFC can inject a voltage of required magnitude in series with the line at any desired angle, just like UPFC. This helps in providing compensation equivalent to UPFC and improving the steady state stability limits of the power system.