Monday, November 12, 2012

Distributed Flexible AC Transmission System Controllers

Widespread use of conventional FACTS controllers has not extensively occurred due in part to size, expense, and installation effort. Technology improvements since the inception of FACTS allow the genre of power flow control concepts to be revisited. The use of distributed flexible AC transmission system (D-FACTS) devices may facilitate the realization of a comprehensively controllable power system. Large-scale power flow control may finally be achievable.

DSSCs are series power flow control D-FACTS devices which change the effective impedance of transmission lines through the use of active impedance injection with a synchronous voltage source (SVS) . DSSCs are comprised of a low-rated single phase inverter and a single turn transformer and provide control similar to the SSSC, but are smaller and will be less expensive. Hereafter, DSSCs will only be referred to as D-FACTS devices.

A D-FACTS device changes the effective line impedance actively by producing a voltage drop across the line which is in quadrature with the line current. Thus, a D-FACTS device provides either purely reactive or purely capacitive compensation. D-FACTS devices do not change the line’s resistance at all since doing so would imply the ability of the device to create real power. Hereafter, when we refer to the ability of D-FACTS devices to change line impedances, we are only referring to the reactive line impedance, As line impedance-changing devices D-FACTS devices have an impact on states, power flows, losses, and more. One attractive feature of D-FACTS devices is their potential capability to send and receive signals wirelessly through a built-in wireless transceiver. D-FACTS may receive commands for desired impedance injection changes. The impact on the system caused by D-FACTS devices on different lines working together can be coordinated to achieve some desired control objective. Although communication is desirable in order to achieve advanced control objectives, D-FACTS devices may be configured to operate autonomously in certain situations such as during transients, faults, or when communications are lost.

Ref. - D. M. Divan, W. E. Brumsickle, R. S. Schneider, B. Kranz, R. W. Gascoigne, D. T. Bradshaw, M. R. Ingram, and I. S. Grant, “A distributed static series compensator system for realizing active power flow control on existing power lines,” IEEE Transactions on Power Delivery, vol. 22, no. 1, pp. 642-649, Jan 2007

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