Dynamic analysis of an ePFC (enhanced Power Flow Controller) with conduction angle control

Majority of ongoing investigations in the field of power transmission systems are concerned with the use of naturally commutated, thyristor switched circuits such as Static VAr Compensators (SVC) and Thyristor Controlled Series Capacitors (TCSC). The enhanced Power Flow Controller (ePFC) is a distributed version of TCSC topology and is an improvement on Distributed Series Impedance (DSI) circuit. This paper addresses stability analysis of an ePFC which consists of a series connected Thyristor Controlled Reactor (TCR) with a fixed capacitor in parallel. This is a periodically controlled non-linear circuit and hence employing 1^st order (assumes sinusoidal voltage across compensation capacitor) and 2^nd order (assumes sinusoidal current in the transmission line) fundamental impedance model are shown to be inaccurate methods to analyze effective impedance inserted by ePFC. Instead, a new mathematical model that is based on sinusoidal voltage difference between two end buses is used that provides more accurate steady state impedance results. Likewise, to analyze the stability of this system, Poincare mapping of entire bus-to-bus system is employed and the resultant dynamic model of an ePFC is systematically derived in this paper. Finally, eigen values of this system are mapped as a function of conduction angle and regions of instability are identified for the enhanced Power Flow Controller which are in turn verified through computer simulations.