basic upfc paper

8/3/2019 Basic Upfc Paper

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European Journal of Scientific Research

ISSN 1450-216X Vol.30 No.4 (2009), pp.677-684

EuroJournals Publishing, Inc. 2009http://www.eurojournals.com/ejsr.htm

Single Phase Unified Power Flow Controller

(UPFC): Simulation and Construction

Nashiren.F. Mailah

Department of Electrical and Electronic Engineering, Faculty of Engineering

Universiti Putra Malaysia, 43400 UPM Serdang, Selangor

E-mail: [email protected]

Senan M. Bashi

Department of Electrical and Electronic Engineering, Faculty of Engineering

Universiti Putra Malaysia, 43400 UPM Serdang, Selangor

E-mail: [email protected]

Abstract

Unified Power Flow Controller (UPFC) is used to control the power flow in the

transmission systems by controlling the impedance, voltage magnitude and phase angle.

This controller offers advantages in terms of static and dynamic operation of the power

system. It also brings in new challenges in power electronics and power system design. The basic structure of the UPFC consists of two voltage source inverter (VSI); where one

converter is connected in parallel to the transmission line while the other is in series with

the transmission line. The main scope of this paper involves the designing of a single phaseUPFC using Matlab and Simulink software, and constructing a lab scale model of the

UPFC. A microcontroller program has been developed to provide the required phase shift.The experimental result which has been obtained from a lab scale system showed a goodagreement with the simulation result.

1. IntroductionAs the power systems are becoming more complex, it requires careful design of the new devices for theoperation of controlling the power flow in transmission system, which should be flexible enough to

adapt to any momentary systems conditions. The operation of an ac power transmission line, are

generally constrained by limitation of one or more network parameters and operating variables [1].

Flexible Alternating Current Transmission System or FACTS is a technology introduced byElectrical Power Research Institute (EPRI) in the 80s [2]. Its principle role is to increase the

transmission capacity of the ac lines and to control power flow over designated transmission lines.

FACTS technologies involve conversion and switching of power electronics in the range of a few tensto few hundred megawatts [3]. New solid state self commutating devices such as MOSFETs, IGBTs,

GTOs and also other suitable power electronic devices are used as controlled switches in FACTS

devices [4].The universal and most flexible FACTS device is the Unified Power Flow Controller (UPFC).

UPFC is the combination of three compensators characteristic; i.e. impedence, voltage magnitude and

phase angle, that are able to produce a more complete compensation.In this paper, the work revolves on the development of a single phase UPFC, drawn and

simulated through Matlab and Simulink software. The effect of the phase shift, produced by theUPFC are noted and compared with the results obtained from the lab scale model of the UPFC. The


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Single Phase Unified Power Flow Controller (UPFC): Simulation and Construction 678

required phase shift of the model is generated from a Programmable Interface Controller (PIC). A goodagreement has been obtained between the simulation and experimental results.

2. UPFC ConstructionThe UPFC consists of two voltage source converters; series and shunt converter, which are connected

to each other with a common dc link. Series converter or Static Synchronous Series Compensator

(SSSC) is used to add controlled voltage magnitude and phase angle in series with the line, while shuntconverter or Static Synchronous Compensator (STATCOM) is used to provide reactive power to the ac

system, beside that, it will provide the dc power required for both inverter. Each of the branchesconsists of a transformer and power electronic converter. These two voltage source converters shared a

common dc capacitor [5].

The energy storing capacity of this dc capacitor is generally small. Therefore, active powerdrawn by the shunt converter should be equal to the active power generated by the series converter.

The reactive power in the shunt or series converter can be chosen independently, giving greater

flexibility to the power flow control. The coupling transformer is used to connect the device to the

system. Figure 1 shows the schematic diagram of the three phase UPFC connected to the transmissionline.

Figure 1: Schematic diagram of three phase UPFC connected to a transmission line [2]

Control of power flow is achieved by adding the series voltage, VS with a certain amplitude,

VS and phase shift, to V1. This will gives a new line voltage V2 with different magnitude andphase shift. As the angle varies, the phase shift between V2 and V3 also varies. Figure 2 shows thesingle line diagram of the UPFC and phasor diagram of voltage and current.


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679 Nashiren.F. Mailah and Senan M. Bashi

Figure 2: Single line diagram of UPFC and phasor diagram of voltage and current

With the presence of the two converters, UPFC not only can supply reactive power but also

active power. The equation for the active and reactive power is given as follows:-

sin12

2112

X

VVP = (1)

)1(cos12

21

12 += X

VVQ (2)

3. MethodologyThe focus of this work is to design a single phase UPFC and simulate it using Matlab and Simulink

software. A lab scale model will then being constructed and its performance are compared to the

simulated ones. The effect of phase shift, of VS to the supply voltage, V1 are investigated.Based on the schematic diagram of the three phase UPFC in Figure 1, a simulation model of a

single phase UPFC is drawn in Simulink and is illustrated in Figure 3.

Figure 3: Simulinks simulation model

A lab scale model is constructed using H-bridge voltage source inverter to act as SSSC. Figure

4 shows the block diagram of the lab scale model.


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Figure 4: Block diagram of lab scale model

Programmable Interface Controller (PIC) is being programmed to generated PWM signals tothe gate drive that will send the signals to trigger the IGBTs. The comparator provides a reference

signal to the PIC controller board to generate triggering signals in synchronization with the supplyvoltage. Figure 5 shows the flow chart of the program used to find zero crossing and to generate the

required pulses.

Figure 5: Flow chart of the program used to find zero crossing and to generate the required pulses.


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Figure 7: Supply voltage and output voltage

V1

V

As the phase shift value, is increased, the output voltage is shifted more to the left. Whennegative phase shift in implemented, the output voltage will be shifted to the right in comparison to the

supply voltage.

Figure 8: Output voltage with 30 phase shift with ac supply

V1

V

The UPFCs output voltage, VS is then being added to the ac supply voltage, V1 to obtain V2.

The resultant waveform is not pure sinusoidal due to the triggering signal which is of pulsed type as

shown in Figure 9. Filters need to be added in order to get a smooth resultant voltage to reach the ideal.The ideal output of an UPFC as shown in Figure 10 where sinusoidal waveform of the output

voltage is added to the ac supply voltage in 50Hz. When both the output voltage is added to the supply

voltage, a sinusoidal waveform with magnitude and phase shift will be observed as explained in thevector diagram of Figure 2.


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683 Nashiren.F. Mailah and Senan M. Bashi

Figure 9: Sum of output voltage waveform with 30 phase shift from the supply voltage

Figure 10: Ideal sinusoidal output voltage

Figure 11 shows the result obtained from the lab scale model. The sinusoidal waveform

represents the ac supply waveform while the square waveform represents the PWM signal. When there

is no phase shift, set in the program, the PWM signal generated is in synchronization with the acsupply. However, when a phase shift, is applied, the signals will be shifted with angle .

Figure 11: Output and ac supply waveform with delay


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4. ConclusionIn power system transmission, it is desirable to maintain the voltage magnitude, phase angle and line

impedance. Therefore, to control the power from one end to another end, this concept of voltage

injection is applied. The magnitude of this V is constant and the variable is the phase shift, . This project covers the scope of designing the single phase UPFC, where its function is to generate the

phase shift, . When the designed voltage injection is added to the sending end voltage, V1, voltage, V2

at the receiving end with a phase shift of is obtained. From the power flow equation, sin12

21

X

VVP = ,

phase shift is varied to vary the power, P. The output voltage of the H-Bridge inverter, VS can be

controlled to be in synchronization or with some delay with the ac supply. The delay is programmed

into the PIC in order to get a phase shift with respect to the ac supply.The experimental result which has been obtained from a lab scale model showed a good

agreement with the simulation results in term of phase shift, of the UPFC.

References[1] N. G. Hingorani and L. Gyugyi, Understanding FACTS, IEEE Press, 2000.[2] Narain G. Hingorani, Laszlo Gyugyi, Understanding FACTS: Concepts and Technology ofFlexible AC Trnasmission Systems, IEEE Press Marketing, 1999, pp. 297-352, pp. 407-424.[3] Edvina Uzunovic, Claudio A Canizares, John Reeve, Fundamental Frequency Model of

Unified Power Flow Controller, North American Power Symposium (NAPS), Cleveland,

Ohio, October 1998, pp 294-299.

[4] M. Toufan, U.D. Annakkage, Simulation of The Unified Power Flow Controller PerformanceUsing PSCAD/EMTDC, Electrical Power System Research Vol. 46, 1998, pp 67-75

[5] L. Xu and V.G. Agelidis, Flying Capacitor Multilevel PWM Converter Based UPFC, IEEProc. Of Electronic Power Application, Vol. 149, No. 4, July 2003. Page(s) 304-310.

basic upfc paper

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