28-11-2012, 01:31 PM
MODELLINGOF UNIFIED POWER FLOW CONTROLLER
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FACTS DEVICES
•What is FACTS?
•FACTS is flexible ac transmission systems.
•FACTS is a new technology, the principle role of enhancing controllability & power transfer capability in ac systems.
•With the increasing demand of power, the power system networks are becoming more complex from the point of view of operation & control. The existing networks are mostly mechanically controlled but these devices are slow in operation & another problem is that control cannot be initiated frequently. That’s why we use FACTS as control devices.
Operating principle of upfc
•Consists of two voltage source inverters (VSIs) sharing a common dc storage capacitor.
•VSIs are connected to the power system through coupling transformers.
–One VSI is connected in shuntto the transmission system via a shunt transformer.
–The other one is connected in seriesthrough a series transformer.
Componentsseries inverter
•It injects an AC voltage VPQwith controllable magnitude and phase angle ρ(0 ≤ ρ ≤ 360) in series with the line.
•The line current flowing exchanges the real and reactive power between it and ac system
•The reactive power exchanged is internally generated by the inverter.
•The real power must be supplied to it.
Shunt converter
•It supplies the real power demanded by the series device at the dc link.
•It can also absorb or generate the controllable reactive power.
•It is used for voltage regulation at the point of connection injecting an opportune reactive power flow into the line.
•Balances the real power flow exchanged between the series inverter and the transmission line.