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Due to their ability to provide reactive power support and control active power flow, voltage-sourced-converter (VSC)-based flexible ac transmission system controllers can be used to improve the power transfer capability of congested transmission lines. A converter-based controller structure has the inherent feature to be used to provide shunt or series compensations. This inherent feature is utilized in the convertible static compensator installed at the New York Power Authority's Marcy substation, which can operate in 11 configurations of shunt and series compensations. Moreover, each configuration can be operated in different control modes. The paper presents a novel approach to model converter-based transmission controllers for load-flow calculations. The paper focuses on modeling converter-based controllers when two or more VSCs are coupled to a dc link (e.g., unified power-flow controller (UPFC), interline power-flow controller, and a generalized unified power-flow controller). This approach also allows efficient implementation of various VSC operating limits, where one or more VSCs are loaded to their rated capacity. A computer program incorporating this approach is developed to illustrate the maximum dispatchability of UPFC and IPFC in a large power system. Index Terms--Flexible ac transmission systems (FACTS), interline power-flow controllers (IPFCs), Newton-Raphson algorithm, rated-capacity operation, unified power-flow controllers (UPFCs), voltage-sourced converters (VSCs).

For a system with a unified power-flow controller (UPFC), maximum power transfer capability is often achieved when the UPFC is operated at its rated capacity and conventional voltage and line-flow setpoint regulation is no longer possible. This paper uses injected voltage sources to directly model a UPFC and impose the rating limits in a Newton-Raphson load-flow algorithm. A dispatch strategy is proposed for a UPFC operating at rated capacity in which the power circulation between the shunt and series converters is used as the parameter to optimize the power transfer. Voltage-stability curves for two test systems are shown to illustrate the effectiveness of this proposed strategy. Index Terms--Flexible ac transmission system (FACTS) controllers, Newton-Raphson algorithm, unified power-flow controllers (UPFCs), voltage-source converters (VSCs), voltage stability.

The paper investigates the use of sensitivity methods to identify the parameters of reduced transformer models. The reduced model retains the structure of the original model. The identification is performed in both the time domain and the frequency domain. The technique is applied to a lumped-linear model of an experimental coil, and the results are promising. Keywords: Transformer modeling, frequency-domain identification, time-domain identification, parameter sensitivities

Dynamic regulation models for voltage-sourced converter (VSC) based flexible ac transmission system (FACTS) controllers are described in this paper. The dynamic models can then be used to analyze these FACTS controller's capability to improve the capability of a power transfer path. The contributions of this paper include showing that the benefits of FACTS controllers are proportional to the MVA ratings and the benefits of multiple FACTS controllers are cumulative. Furthermore, the coupling of dc buses allowing active power circulation between multiple VSC FACTS controllers may offer additional improvement in transfer capability. [ABSTRACT FROM AUTHOR]

Due to their ability to provide reactive power support and control active power flow, voltage-sourced-converter (VSC)-based flexible ac transmission system controllers can be used to improve the power transfer capability of congested transmission lines. A converter-based controller structure has the inherent feature to be used to provide shunt or series compensations. This inherent feature is utilized in the convertible static compensator installed at the New York Power Authority's Marcy substation, which can operate in 11 configurations of shunt and series compensations. Moreover, each configuration can be operated in different control modes. The paper presents a novel approach to model converter-based transmission controllers for load-flow calculations. The paper focuses on modeling converter-based controllers when two or more VSCs are coupled to a dc link (e.g., unified power-flow controller (UPFC), interline power-flow controller, and a generalized unified power-flow controller). This approach also allows efficient implementation of various VSC operating limits, where one or more VSCs are loaded to their rated capacity. A computer program incorporating this approach is developed to illustrate the maximum dispatchability of UPFC and IPFC in a large power system. [ABSTRACT FROM AUTHOR]