Analysing The Performance Of A Dynamic Voltage … or short circuit current on the customer ... modelled using the Simulink toolbox provided by Matlab. ... SIMULINK MODEL OF DVR TEST

International Journal of Scientific Research and Engineering Studies (IJSRES)

Volume 2 Issue 3, March 2015

ISSN: 2349-8862

www.ijsres.com Page 124

Analysing The Performance Of A Dynamic Voltage Restorer For

Eliminating Power Quality Issues In Power Distribution Network

Abstract: A Dynamic Voltage Restorer is a custom

power device that finds application in the modern power

distribution system, for mitigating power quality issues like

voltage sag, voltage swell and harmonics. For improving

the system performance for distribution system and with

the growing development of the power semiconductor

technology, the concepts of custom power was introduced

to distribution systems. In this paper, a new control strategy

for modelling a Dynamic Voltage Restorer is introduced. The

performance and accuracy of the system subject to different

power quality disturbances will be analysed.

Index Terms: Power Quality, Custom Power Devices, Dynamic Voltage Restorer, Voltage Sag, Voltage Swell, Matlab- Simulink.

I. INTRODUCTION

In modern electrical power systems, electricity is

produced at generating stations, transmitted through a high

voltage network, and finally distributed to consumers. Due to

the quick increase in power demand, electric power systems

have developed broadly during the 20th

century, resulting in

today’s power industry probably being the largest and most

complex industry in the world. Electricity is one of the key

elements of any economy, industrialized society or country. A

modern power utility should be capable of furnishing reliable,

good quality and uninterruptible power to its customers at a

rated voltage and frequency within constrained variation

limits. If the supply quality suffers a reduction and is outside

those predefined limits, sensitive equipment might trip, and

any motors connected on the system might stall. The electrical

system should not only be able to provide cheap, protected and

secure energy to the buyer, but also to compensate for the

continually changing load demand. During that process the

quality of power could be distorted by faults on the system, or

by the switching of heavy loads within the customers

facilities.

Now-a-days, modern loads that use power electronics

based control strategy are more sensitive to power system

parameter variations than the loads that were used long ago. In

early days, distortion or power system parameters variation

did not impose any severe problems to end users or utilities.

But gradually professionals started to realise that, most of the

interruptions and faults that were occurring in the electrical

equipments, were due to power quality disturbances. Highly

interconnected transmission and distribution lines have

highlighted the previously small issues in power quality due to

the wide propagation of power quality disturbances in the

system. The reliability of power systems has improved due to

the growth of interconnections between utilities. In the modern

industrial world, many electronic and electrical control

devices are part of automated processes in order to increase

energy efficiency and productivity. However, these control

devices are characterized by tremendous sensitivity in power

quality disparity, which has led to growing concern over the

quality of the power supplied to the user

In order to increase the quality of power and to protect the

consumer equipments from failure due to deviation in voltage,

current or frequency, different custom power devices were

introduced. A dynamic voltage restorer is a PE converter-

based custom power device that can protect sensitive loads

from all supply-side disturbances other than outages. It is

connected in series with a distribution feeder and is also

capable of generating or absorbing real and reactive power at

its AC terminals. In the following section different

components of a dynamic voltage restorer and their functions

will be discussed.

Bhaskar Lodh

M.Tech in Electrical Engineering,

AMIE Department of Electrical Engineering,

Jalpaiguri Government Engineering College Jalpaiguri,

West Bengal, India



ISSN: 2349-8862


II. DIFFERENT COMPONENTS OF DYNAMIC

VOLTAGE RESTORER

A typical Dynamic Voltage Restorer has the following

components-

An injection/ Booster Transformer

Harmonic Filter

Storage Devices

A Voltage Source Converter

DC Charging Circuit

DVR Control System

INJECTION / BOOSTER TRANSFORMER: The Injection

/ Booster transformer is a specially designed transformer

that tries to bound the coupling of noise and transient

energy from the primary side to the secondary side. The

key duty of an Injection Transformer is to connect the

DVR to the distribution network via the HV-windings. It

transforms the injected compensating voltages generated

by the voltage source converters to the incoming supply

voltage. Apart from this the transformer serves the

purpose of separating the load from the system.

HARMONIC FILTER: A harmonic filter keeps the

harmonic content generated by the voltage source

converter to an allowable level.

STORAGE DEVICES: The reason of using a storage

device is to bring necessary energy to the VSC by means

of a dc link. The different types of energy storage devices

that are in use today are- Superconductive Magnetic

Energy Storage (SMES), Capacitors, batteries etc.

VOLTAGE SOURCE CONVERTER: A voltage source

converter has a storage device and switching devices

associated to it. It can produce sinusoidal voltage at any

required frequency, magnitude and phase angle. The

voltage source converter generates part of the supply

voltage that is absent during the time of sag. The main

power electronic devices that are in use today as voltage

source converter are MOSFET, GTO, IGBT and IGCT.

IGCT (Integrated Gate Commutated Thyristor) is a

recently developed power electronics device. This device

is very compact and reliable. Even, voltage dips can be

compensated by the use of IGCT now a day when it’s

used in a DVR.

DC CHARGING CIRCUIT: The DC Charging circuit

charges the energy storage device after a sag

compensation event. It also maintains the dc link voltage

at a nominal level.

CONTROL AND PROTECTION SYSTEM: The control

instrument of the general configuration typically consists

of hardware with programmable logic. All protective

functions of the DVR should be implemented in the

Software. Differential current protection of the

transformer, or short circuit current on the customer

load side are only two examples of many protection

functions possibility.

III. EQUIVALENT CIRCUIT OF DVR

The equivalent circuit of a Dynamic voltage Restorer is

show in the figure below-

Figure1: Equivalent Circuit of DVR

The system impedance Zth depends on the fault level of

the load bus. When the system voltage (Vth) drops, the DVR

fetch a series voltage VDVR through the injection transformer

so that the desired load voltage magnitude VL can be

maintained. The series injected voltage of the DVR can be

written as-

Here,

VL = Desired Load voltage Magnitude

Z TH= Load Impedance

IL= Load current

VTH= System Voltage during Fault condition

Here the Load current is given by,

The reference equation can be written as

Here, are the angles of

respectively. given by, ;

The complex power injection of the DVR can be written as -

. It requires the injection of only reactive

power and the DVR itself is capable of generating the reactive

power.

IV. MODELLING DVR WITH MATLAB SIMULINK

TOOLBOX

In this section, a Dynamic Voltage Restorer will be

modelled using the Simulink toolbox provided by Matlab.

Simulink is a toolbox package provided by Math Works Inc. It

is an integral part of MATLAB software. It is nothing but a

graphical extension of MATLAB software, in which the

system is constructed on screen by using blocks available in

Simulink library browser. Hence, this package will be best

suited for modelling the proposed system of Dynamic Voltage



ISSN: 2349-8862


Restorer. Due to its utility and flexibility, Simulink has

become an obvious choice for researchers and engineers in the

fields of power system, control system and power electronics.

The single line diagram of the proposed system will be as

shown in the figure below. The model is tested for voltage sag

of around 50 % for duration of 0.2 Second and again for a

voltage Swell of 50% for duration of around 0.2 Seconds. The

results came out of the simulation was pretty much

satisfactory.

Figure 2: Single Line Diagram of the System

The dqo transformation or Park’s transformation is used

to control of DVR. The dqo method gives the sag depth and

phase shift information with start and end times. The

quantities are expressed as the instantaneous space vectors.

Firstly convert the voltage from a-b-c reference frame to d-q-o

reference. For simplicity zero phase sequence components is

ignored. Following figure shows the flow chart for proposed

detection method of voltage sag and generating signal for

PWM.

Figure 3: Flow chart for control technique of DVR based

on dq0 transformations

The control is based on the comparison of a voltage at the

supply and receiver end (Va,Vb,Vc).The voltage sags is

detected when the supply drops below 90% of the reference

value whereas voltage swells is detected when supply voltage

increases up to 25% of the reference value. The error signal is

used as a modulation signal that allows generating a

commutation pattern for the power switches (IGBT’s)

constituting the voltage source converter. The commutation

pattern is generated by means of the sinusoidal pulse width

modulation technique (SPWM); voltages are controlled

through the modulation.

V. PRINCIPLE OF OPERATION OF THE DVR

DVR is connected in series with the line between main

supply and load as shown in the single line diagram. The main

function of the DVR is to boost up the voltage at load side so

that equipments connected at the load end is free from any

power disruption. In addition to voltage sag compensation.

DVR also carry out other functions such as line voltage

harmonic compensation, reduction of transient voltage and

fault current.

Pulse Width Modulation (PWM) control technique is

applied for inverter switching so as to produce a three phase

sinusoidal voltage. The magnitude of supply end voltage is

compared with reference voltage and if any difference is there

error signal will be generated, which is an actuating signal.

This error signal is used for triggering the IGBT inverter.

In this model, the dq0 transformation or the Parks

transformation is used for voltage calculation where the three

phase stationary co-ordinate system is converted to the dq0

rotating quantity. The dq0 transformation technique is used to

give the information of the depth (d) and phase shift (q) of

voltage sag/ swell with starting and ending time. The V0, V d

and Vq are obtained as-

...........................................(1)

In the simulink model a three phase programmable

voltage source will be used as supply voltage. This is available

in the simulink library browser. The purpose of using this

block is- a voltage sag or swell of desired value can be

implemented manually in the test system. For injecting the

generated voltage, a three phase 12 pulse transformer will be

used. The inverter circuit will be modelled by an IGBT with a

filter circuit for eliminating the harmonics.

The Flow Chart for Modelling the DVR test system is

shown in the figure below-



ISSN: 2349-8862


Figure 4.Flow chart for the overall test system

VI. SIMULINK MODEL OF DVR TEST SYSTEM

Following figure shows the power circuit diagram of the

proposed DVR test system-

Figure 5: Power Circuit model of DVR

The control circuit will be as shown in the figure below-

Figure 6: Control Circuit model of DVR

The IGBT based inverter circuit will be modelled in the

following way-

Figure7: Model of IGBT based Inverter

VII. PARAMETERS FOR THE DVR TEST SYSTEM

All the specifications of the system quantities are shown

in the table below-

Sl

No.

System Quantities Standards

1. Source Voltage

3Phase,450 V, 50 Hz

2. Line Impedance

0.0001296 Ohm/Phase

3. Three Phase

Breaker

Breaker resistance 0.1 Ohm,

Snubber Resistance- 1 Mega

Ohm



ISSN: 2349-8862


4. Three Phase Load

230 Volt, 50 Hz, 10 kW.

5. 12-Pulse

Transformer rating

Turns Ratio 1:1

6. Battery Voltage 600 Volt

7. LC Filter

Inductance &

Capacitance

0.1 mH, 1𝜇F

8. Inverter

Specification

IGBT based, 3Arm, 6 Pulse,

Carrier Frequency 3 kHz.

Table1: Parameter of the DVR Test system

VIII. RESULT OF SIMULATION

In the first simulation voltage sag of 50% is provided in

the programmable voltage source block in the test system. The

sag is kept for duration of 0.1 to 0.3 seconds with duration of

0.2 Seconds. The results of simulation is as follows-

Figure 8: Source Voltage(p.u.) with 50 % Sag

Figure 9: Simulation result for frequency, angle (𝜔𝑡) and

function Sin_Cos

Figure 10: Source Voltage in dq reference frame with 50

% Sag

Figure 11: Referance voltage in p.u.

Figure 12: Referance voltage in dq reference frame.

Figure 13: Triggering pulse generated by PWM

generator



ISSN: 2349-8862


Figure 14: Compensating Voltage injected by Inverter

Figure 15: Load Voltage after sag mitigation

In the first simulation three phase voltage sag is simulated

and a 50% three-phase voltage sag occurring at the utility grid

is shown in Figure-8. It is also shows 50% voltage sag

initiated at 0.1 s and it is kept until 0.3 s, with total voltage sag

duration of 0.2s. Figures-15 shows the corresponding load

voltage with compensation. As a result of DVR, the load

voltage is kept at 1 p.u. Before DVR operation the phase

voltage of source will be as shown below-

Figure 16: Phase voltage before DVR operation

Figure 17: Total Harmonic Distortion before DVR

operation

Figure 18: Phase Voltage of Load after DVR operation

Figure 19: Total Harmonic Distortion after DVR

operation

Total Harmonic Distortion (THD); which came out to be

0.41 % before DVR operation has been reduced to 0 % after

successful operation of DVR. In the next simulation a voltage

swell of magnitude 50% will be given for duration of 0.1 to

0.3. The following figure represents the source voltage

waveform with swell-

Figure 20: Source Voltage with 50% swell

Figure 21: Simulation result for frequency, angle (𝜔𝑡)

and function Sin_Cos



ISSN: 2349-8862


Figure 22: Source Voltage in dq reference frame

Figure 23: Compensating Voltage waveform

Figure 24: Load Voltage after Swell mitigation

Figure 25: Phase Voltage of Source end

Figure 26: THD before DVR operation

Figure 27: Phase Voltage of Load after DVR operation

Figure 28: THD after swell mitigation

Total Harmonic Distortion (THD); which came out to be

0.43 % before DVR operation has been reduced to 0 % after

successful operation of DVR.

IX. CONCLUSION

In this context, a distinct control strategy for mitigating

voltage sag and swell using Dynamic voltage restorer is

shown. In the constructed simulation model, a 12 pulse

transformer based DVR is built. It is evident from the

simulation result that, in occurrence of both voltages sag and

swell, the DVR was able to mitigate the power quality related

issues successfully. The Voltage waveform was restored to its

original shape. That is the lost voltage was compensated by

the DVR efficiently. Also the harmonic distortion was

mitigated promptly.



ISSN: 2349-8862


REFERENCES

[1] Roger C. Dugan, Mark F McGranham, Surya Santoso, H.

Wayne Beaty “Electrical Power System Quality,”

McGraw Hill , 2010.

[2] A.K. Tyagi, “MATLAB and Simulink for Engineers”,

New Delhi, Oxford University Press, 2012

[3] K.R. Padiyar, “FACTS Controllers in Power

Transmission and Distribution”, New Age International

Publishers

[4] S. LEELA, S. S. DASH, CONTROL OF THREE LEVEL

INVERTER BASED DYNAMIC VOLTAGE

RESTORER, Journal of Theoretical and Applied

Information Technology, January 2005.

[5] Chris Fitzer, Mike Barnes, Member IEEE, Peter Green,

Member IEEE, Voltage Sag Detection Technique for a

Dynamic Voltage Restorer; © 2002 IEEE

Documents

Analysing The Performance Of A Dynamic Voltage … or short circuit current on the customer ... modelled using the Simulink toolbox provided by Matlab. ... SIMULINK MODEL OF DVR TEST