1. UNIT-VIII COMBINED COMPENSATORS

2. Contents UPFC Basic operating principle
Independent real and reactive power flow controller
Control structure

3. UPFC
The basic conception of the UPFC was proposed by Nabavi-Niaki and Iravani in It is made up of two voltage source controllers sharing the same capacitor at their dc voltage controlled side.
One voltage source controller is in parallel with one side of a transmission line and the other voltage source controller in the UPFC is in series connect to the other side of the same transmission line. The basic structure of the UPFC is shown in the Figure .
The UPFC can simultaneously control the active and reactive power flow and voltage magnitude. How ever it has little effect on voltage angle.
UPFC= STATCOM + SSSC

7. UPFC May Control Voltage, Impedance and Angle
Impacts Active And Reactive Power Flow In Line

8. Basic Operation

9. 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

10. 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.

11. 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

12. UPFC

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

14. + + + 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

16. Sine-triangle PWM

17. Different roles of various FACTs devices

19. CONCLUSION