UNIT-VIIICOMBINED COMPENSATORS

Contents

• UPFC• Basic operating principle• Independent real and reactive power flow

controller• Control structure

UPFC• The basic conception of the UPFC was proposed by Nabavi-

Niaki and Iravani in 1996. 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

UPFC

• May Control Voltage, Impedance and Angle• Impacts Active And Reactive Power Flow In Line

Basic 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

Operation

• 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.

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

UPFC

How is Vinj created?

V+b1

a2

a1

b2

c1

c2

V+b1

a2

a1

b2

c1

c2

a1 on, b1 on, c1 offVab=0, Vbc=V, Vca = -V

a1 on, b1 off, c1 offVab=V, Vbc=0, Vca = -V

V+a1 b1 c1

c2b2a2

V+a1 b1 c1

c2b2a2

a1 on, b1 off, c1 onVab=V, Vbc=-V, Vca = 0

Sine-triangle PWM

0 100 200 300 400 500 600 700-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

0 100 200 300 400 500 600 7000

0.5

1

Va

0 100 200 300 400 500 600 7000

0.5

1

Vb

0 100 200 300 400 500 600 700-1

0

1

Vab

Different roles of various FACTs devices

CONCLUSION