MODELLING OF UNIFIED POWER FLOW CONTROLLERby

Alan Jose Kuriappan(B070322EE)

Joyal Dominic Aerath(B070505EE)

Nirmal George(B070199EE)

Nithin Das.K(B070593EE)

FACTS DEVICES

Based on power electronic switching converters Enhances -system utilization

-power transfer capacity

-stability, security, reliability

-power quality of AC system Complex power systems require new devices for

controlling power flow in transmission

VARIOUS FACTS DEVICES

Static VAR Compensator Thyristor Controlled Series Capacitor Thyristor Controlled Phase shifting

Transformer Static Synchronous Compensator Static synchronous Series Compensator Unified Power Flow Controller Interline Power Flow controller

USES OF FACTS DEVICES

Facts devices in ac lines - power flow control. - increase of transmission capability. - voltage control. - reactive power compensation. - stability improvement. - power quality improvement

UPFC

Universal and most flexible of all other facts devices

Combination of 3 compensators-impedance -voltage magnitude -phase angle

Consists of two voltage source converters;-series converter-shunt converter

Converters are connected by a common dc link.

UPFC-SCHEMATIC DIAGRAM

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 shunt to the

transmission system via a shunt transformer. The other one is connected in series through a

series transformer.

COMPONENTSSERIES INVERTER

It injects an AC voltage VPQ with 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.

DC LINK

A capacitor works as a dc link between the two voltage source inverters.

CONTROL FUNCTIONS

1. Voltage regulation-

Achieved by injecting a voltage V1, in phase (or out of phase) with VS

The magnitude of the sending bus voltage Vs is increased (or decreased)

CONTROL FUNCTIONS

2. Series reactive compensation-

It is obtained by injecting a voltage V2, orthogonal to the line current

The effective voltage drop across the line impedance X is decreased (or increased)

CONTROL FUNCTIONS

3. Phase shift-

A desired phase shift is achieved by injecting a voltage V3

Shifts VS by + θ or - θ while keeping its magnitude constant as shown in Fig.

OPERATING MODES OF SERIES CONVERTER

Direct voltage injection modeThe series converter generates the voltage VPQ with the

magnitude and phase requested by the reference input Line impedance compensation modeThe injected voltage is controlled is in proportion to the

magnitude of line current Phase angle regulation modeVoltage is controlled with respect to the input voltage so

that output voltage is phase shifted Bus voltage regulation modeInjected voltage is kept in phase with input and its

magnitude is controlled to maintain output at a reference value

OPERATING MODES OF SHUNT CONVERTER

Reactive power control mode - The shunt converter control translates the

var ref in to corresponding shunt current request

-It adjusts the gating of the converter to establish the desired current

Automatic voltage control mode The reactive current is automatically

regulated to maintain the line voltage to a ref value

POWER CONTROL MODE

CONTROL STRUCTURE

It can be of two types -internal control -functional operational control Internal control -Operates the converter to produce required

injected voltage -converter responds to internal reference

variables Functional control -responsible for generating internal

references

BASIC UPFC CONTROL SCHEME

PULSE WIDTH MODULATION

The converter output voltage can be controlled using various control techniques

Pulse Width Modulation (PWM) techniques can be designed for the lowest harmonic content

When sinusoidal PWM technique is applied turn on and turn off signals for GTOs are generated comparing a sinusoidal reference signal Vr of amplitude Ar with a saw tooth carrier waveform Vc of amplitude Ac as shown

Vr > Vc results in a turn on signal for the device one and gate turn off signal for the device four

Vr<Vc results in a turn off signal for the device one and gate turn on signal for the device four.

UPFC-INJECTION MODEL

UNCOUPLED MODEL

IDEAL TRANSFORMER MODEL

WORKS COMPLETED

Detailed study of FACTS devices and its applications

Studied the principle and working of UPFC 

WORKS TO BE COMPLETED

Simulation of UPFC in three phase network Case study of UPFC in power transmission

system

REFERENCE

Understanding FACTS- NARAIN G HINGORANI Narain G. Hingorani, Laszlo Gyugyi,

“Understanding FACTS: Concepts and Technology of Flexible AC Trnasmission Systems,” IEEE Press Marketing, 1999, pp. 297-352, pp. 407-424.

Unified Power Flow Controller (UPFC) – An Introduction,Suresh Kumar K.S,AP,EED,NIT CALICUT