Flexible AC Transmission System Overview

Flexible AC Transmission System Alternating current transmission systems incorporating power electronics-based and other static controllers to enhance controllability and increase power transfer capability

Constraints on Useable Transmission Capacity Dynamic: Transient and dynamic stability Subsynchronous oscillations Dynamic overvoltages and undervoltages Voltage collapse Frequency collapse

Steady-State: Uneven power flow Excess reactive power flows Voltage capability Thermal capability

FACTS Controllers Static VAR Compensator - SVC Thyristor Controlled Series Compensator - TCSC Thyristor Controlled Phase Angle Regulator - TCPAR Static Synchronous Compensator - StatCom Solid State Series Compensator - SSSC Unified Power Flow Controller - UPFC

US FACTS Installations AEP/ Unified Power Flow Controller /100 MVA/ EPRI NYPA/ Convertible Static Compensator/ 200 MVA Vermont Electric/ STATCOM/ 130 MVA/ Mitsubishi San Diego G&E/ STATCOM/100 MVA Mitsubishi Northeast Utilities/ STATCOM/ 150 MVA/ Areva (Alstom) TVA STATCOM/ 100MVA EPRI Eagle Pass (Texas) Back-to-back HVDC 37 MVA/ ABB Austin Energy STATCOM/ 100MVA ABB CSWS (Texas) STATCOM/ 150 MVA / W-Siemens

Power Flow Control Power transfer between areas can be affected by adjusting the net series impedance. Transmission line capability can be increased by installing a series capacitor which reduces the net series impedance.

UPFC

UPFC may control voltage, impedance, and angle impacts active and reactive power flow in line

Basic Operation

UPFC Capabilities Increase transmission line capacity Direct power flow along selected lines Powerful system oscillation damping Voltage support and regulation Control of active and reactive power flow at both sending- and receiving-end

Operation Reactive power is generated or absorbed by the shunt inverter to control bus voltage Reactive power is generated or absorbed by the series inverter to control the real and/or reactive power flow on the transmission line

Cont’d A portion of the real power flow on the transmission line is drawn from the bus by the shunt inverter to charge the DC capacitor. Real power is inserted into the line through the series inverter.

Power flow in a transmission line and To increase PSR, increase

- + - +

How is Vinj created? + b1 a2 a1 b2 c1 c2

+ + + a1 on, b1 on, c1 off Vab=0, Vbc=V, Vca = -V a1 on, b1 off, c1 off Vab=V, Vbc=0, Vca = -V a2 b2 c2 + a1 b1 c1 a1 on, b1 off, c1 on Vab=V, Vbc=-V, Vca = 0 a2 b2 c2

Sine-triangle PWM