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This paper introduces a hybrid flow controller (HFC) as a new member of flexible ac transmission system (FACTS) controllers for steady-state and power-flow control of power transmission lines. HFC is a hybrid compensator (i.e., provides series and/or shunt compensation). Structurally, an HFC unit is composed of a mechanically switched phase-shifting transformer, a mechanically switched shunt capacitor, and multimodule, series-connected, thyristor-switched capacitors and inductors. This paper describes the steady-state operation, single-phase equivalent circuit, power-flow model, and V-I and P-Q characteristics of the HFC. This paper highlights the steady-state technical features of the HFC for power-flow control of a study system and also provides a quantitative comparison of the HFC, UPFC, and PST. Index Terms--Flexible ac transmission system (FACTS), power flow, thyristor-switched series capacitor (TSSC), thyristor-switched series reactor (TSSR), unified power-flow controller (UPFC).

This paper presents a control algorithm for a voltage-sourced converter-based back-to-back (VSC-BTB) tie which enables a 'transient free' load transfer between the tie sides. The studies were performed for the recently commissioned Eagle-Pass VSC-BTB interconnecting the Electric Reliability Council of Texas (ERCOT) transmission network in the USA to the Comision Federal De Electricidad (CFE) transmission network in Mexico. The objective of the algorithm is realization of the transfer of load from one side of VSC-BTB to the other side of the tie without interruption of the power supply to the Eagle-Pass load. The developed algorithm has been validated through simulation studies, describing the load transfer process. Index Terms--Angle synchronization, back-to-back (BTB), frequency matching, load restoration, load transfer, phase-locked loop (PLL), switching sequence, voltage-sourced converter (VSC).

This paper examines the enhancement of power system stability properties by use of thyristor controlled series capacitors (TCSCs) and static var systems (SVCs). Models suitable for incorporation in dynamic simulation programs used to study angle stability are analyzed. A control strategy for damping of electromechanical power oscillations using an energy function method is derived. Using this control strategy each device (TCSC and SVC) will contribute to the damping of power swings without deteriorating the effect of the other power oscillation damping (POD) devices. The damping effect is robust with respect to loading condition, fault location and network structure. Furthermore, the control inputs are based on local signals. The effectiveness of the controls are demonstrated for model power systems. Index Terms--Control strategy, energy function, interaction, local variables, POD, power swings, SVC, TCSC.