dstatcom and dvr in power system

7/28/2019 dstatcom and dvr in power system

1/50


2/50

2

1.2LITERATURE SURVEYSeveral research papers and reports addressed the subject of improving power quality

in distribution system by the use of custom power devices. The followings present a brief

review of the work undertaken so far.

N.G.Hingorani, prstesents the concept of custom power is now becoming familiar.

The book describes the value- added power that electric utilities and other service providers

will offer their customers in the future. The enhanced level of reliability of this power, in

terms of problem, of which a prominent feature will be the application of power electronics

controllers to utility distribution system and at the supply end of many industrial and

commercial customer and industrial parks.

Olimpo Anaya-Lara and E. Acha,et al [3] This paper presents the modeling and

analysis of custom power controllers, Graphics-based models suitable for electromagnetic

transient studies are presented for the following three custom power controllers: the

distribution static compensator (D-STATCOM), the dynamic voltage restorer (DVR), and the

solid-state transfer switch (SSTS). Comprehensive results are presented to assess the

performance of each device as a potential custom power solution

M.H.J.Bollen, et al. [4] presents the influence of sags that leads to an interruption of

plant operation. The assumption that voltage sag is not correct in a power system with large

loads. After fault- clearing, they will accelerate again, drawing a high reactive current from

the supply, causing extended post fault of some voltage sags in an example power system is

shown and discussed. The influence of faster protection and of reduced transformer

impedance on the table is presented. A simple model is implemented in a method for

including interruptions due to voltage sag in the reliability of power systems.

H.P.Tiwari, et al [8] presents dynamic voltage restorer against voltage sag. A

dynamic voltage restorer (DVR) is a custom power device used to correct the voltage sag by

injecting voltage as well power into the system. The mitigation capability of these devices is

generally influence by the maximum load; power factor and maximum voltage dip to becompensated. Voltage dip on a feeder is a main task for DVR system operation and

appropriate desired voltage sag compensation. This paper is intended to assimilate the

amount of DC energy storage depends on voltage dip. It is available in a convenient manner

for DVR power circuit.

Arindam Ghosh, et al [6] presents the performance of voltage-source converter-

based shunt and series compensators used for load voltage control in electrical power

distribution system has been analyzed and compared, A distribution static compensator (D-

STATCOM) as shunt device and a dynamic voltage restorer (DVR) as a series device are


3/50

3

considered in the voltage control mode for the comparison. The effect of various system

parameters on the control performance of the compensator studied using the proposed

analysis. The experimental verification of the analytical result derived has been obtained

using a laboratory model of the single-phase D-STATCOM and DVR.

Arindam Ghosh, et al. [7] presents the Dynamic Voltage Restorer (DVR) with ESS

based PI Controller method to compensate balanced voltage sag. Voltage sag is one of the

major power quality problems which result in a failure of end use equipments. Sensitive

industrial load and utility distribution networks all suffer from various types of outages and

service interruptions which can cost significant financial loss per event. The aim therefore is

to recommend measures that can improve voltage sag.

C.S.Chang, et al [9] presents performance of voltage sag mitigation devices such as

the Dynamic voltage restorer(DVR) has been analyzed in highly simplified electrical

environment consisting of simple line and load models. The negative influence of dynamic

load on the existing voltage disturbance, such as post- fault sags, further during fault phase

angle deviations, during- fault and post-fault voltage fluctuations have often been unnoticed.

First, the influence of load operation on the during-fault and post-fault waveforms will be

discussed. After which ability of the DVR to dynamically respond to the various types of

voltage sag condition at the terminals of a dynamic load and restore the sagging voltage to its

pre-fault conditions is presented.

1.3SCOPE OF WORKFrom the literature review, it is observed that the work on the investigation on power

with compensating devices have the wide area. However it is observed that there is scope to

investigate the effectiveness of compensating devices for different loads and with different

loading conditions in distribution system. As the distribution system locates the end of power

system and is connected to the customer directly, so the reliability of power supply is

increasing day by day, so the reliability of the distribution system has to be increased.

Electrical distribution network failures account for about for the average customer

interruptions. So it is highly required to increase the reliability of the distribution system.

The objective of proposed work is to improve the power quality or reliability in the

distribution system with the use of custom power devices like D-STATCOM and DVR.

Different fault conditions are applied the load to analyzed the comparative operation of D-

STATCOM and DVR for the improvement the power quality in distribution system.


4/50

4

1.4ORGANIZATION OF THESISChapter-1 Provide introduction and work in this field which has been carried out till date. It

also includes scope of work and organization of the thesis.

Chapter-2 gives the fundamentals of power quality, power quality problem and their

associated solutions.

Chapter-3 presents the concept and need of custom power devices.

Chapter-4 presents the operation, modeling and applications of Dynamic voltage Restorer

(DVR).

Chapter-5 presents the operation, modeling and applications of D-STATCOM.

Chapter-6 gives the ideas of proposed controller.

Chapter-7 presents DVR test system and simulation results.

Chapter-8 presents D-STATCOM test system and simulation results.

Chapter-9 present the conclusion of the work presented in this thesis. It also presents the

future scope of this work.

Chapter-10 References.


5/50


6/50

6

Voltage sags; it may be define as A decrease to between 0.1 and 0.9 pu in rms voltage or

Current at the power frequency for durations of 0.5 cycles to 1 minute. Voltage sags are

mostly cause be system faults and may be occurred from 3 cycles to 30 cycles depending on

the fault clearing time. Starting of large induction motor, transformer energies, load switching

etc can cause the voltage sag.

Voltage swells; it maybe define as, An increase to between 1.1 pu and 1.8 pu in rms

voltage or current at the power frequency durations from 0.5 to 1 minute . Similarly as sag

swell is also associate with system faults. A single line to ground fault can result in a voltage

swell in the healthy phases. Swell can also result from energizing a large capacitor banks.

2.3.2 Voltage fluctuation and flicker

Voltage fluctuations are systematic variation of the voltage or a series of random

changes in the voltage magnitude which lies in the range of 0.9 to 1.1 p.u. High power loads

that draw fluctuating current, such as large motor drives and arc furnaces, cause low

frequency cyclic voltage variation that result in flickering of light sources like incandescent

and fluorescent lamps which can cause significant irritation in human beings. The voltage

flicker can also affect stable operation of electrical and electronics devices.

2.3.3 Frequency variations

Power frequency variations are defined as the variation of the system frequency from

its value of 50 Hz. The frequency variations start from the change in the load and the

response of the generators to meet the load.

2.4 SOLUTION OF POWER QUALITY PROBLEMS

The power quality problems can be solving by considering two approaches.

According to first approach the solution to the power quality problems can be done from the

utility side. This approach is called as load conditioning, in which the equipment is

considered less sensitive to power disturbances, allowing the operation even under significant

variation distortion.

In second approach, install line conditioning system that suppresses the power system

disturbances. In this approach the compensating devices is connect to low and medium

voltage distribution system in shunt or in series. Shunt power filters operate as a controllable

current source and series active power filters operates as controllable voltage source. Both

schemes are implemented with voltage source PWM inverters, with a dc source having a

reactive element such as a capacitor. Apart from this there are many approaches to nullified

the problems, but in this thesis concentration on shunt and series controller only.


7/50

7

3.1 INTRODUCTION

STATCOM, SSSC, IPFC and UPFC etc are the FACTS devices and these are design

for the transmission system. But today, more attention has to be given on the distribution

system for the improvement of power quality. Hence, these devices are modified and known

as custom power devices. The custom power is the value- added powers that given to the

customers. The value added power consists of the application of high power electronic

controllers to distribution system, at the supply end of industrial, commercial consumers.

The custom power devices which are used in distribution system to maintain the

power quality are distribution static synchronous compensator (D-STATCOM), dynamic

voltage Restorer (DVR), active filter (AF), unified power quality conditioner (UPQC) etc. All

are base on voltage source converter (VSC). The DVR is similar to SSSC where as UPQC is

similar to UPFC. In spite of the similarities, the control techniques are quite different for

improving power quality. A DVR can work as a harmonic isolator to prevent the harmonics

in the source voltage reaching the load in addition to balancing the voltage and providing

voltage regulation. A D-STATCOM is utilized to eliminate the harmonics from the source

current and also balance them in addition to providing reactive power compensation to

improve power factor or regulate the load bus voltage. To solve the power quality problem,

custom power devices used here are D-STATCOM and DVR. D-STACOM DVR are the

most efficient and effective modern customs power device used in power distribution

networks.

3.2 BENEFIT OF CUSTOM POWER DEVICES

1. They contribute to best possible system operation by improving voltage profile and

reducing power losses.

2. Improve the power flow in critical lines.

3. The transient stability limit is improved thereby improving dynamic security of the system

and reducing the incidence of blackouts caused by cascading outages.

4. The problem of voltage fluctuations and in, dynamic over voltages can be overcome by

these controllers.

5. The problem of voltage sag and voltage swell in case of industrial loads like motor,

switching, transformer energies etc. can be reduced by these devices.


8/50

8

4.1 INTRODUCTION

The DVR is a solid state dc to ac switching power converter that injects a set of three

single phase ac output voltages in series with the distribution feeder and in synchronism with

the voltages of the distribution system. By injecting voltages of controllable amplitude, phase

angle and frequency (harmonic) into the distribution feeder in instantaneous real time via a

series injection transformer, the DVR can restore the quality of voltage at its load side

terminals when the quality of the source side terminal voltage is significantly out of

specification for sensitive load equipment.

The reactive power exchanged between the DVR and distribution system is internally

generated by the DVR without any ac passive reactive components, i.e. reactors and

capacitors. For large variations in the source voltage, the DVR supplies partial power to the

load from a rechargeable energy source attached to the DVR dc terminal. The DVR, with its

three single phase independent control and inverter design is able to restore line voltage to

critical loads during sags caused by unsymmetrical as well as symmetrical three phase faults

on adjacent feeders or disturbances that may originate many miles away on the higher voltage

interconnected transmission system. Connection to the distribution network is via three

single-phase series transformers there by allowing the DVR to be applied to all classes of

distribution voltages. At the point of connection the DVR will, within the limits of its

inverter, provide a highly regulated clean output voltage.


9/50

9

4.2 WORKING PRINCIPLE OF DVR

The DVR is a solid state dc to ac switching power converter that injects a set of three

single phase ac output voltages in series with the distribution feeder and in synchronism with

the voltages of the distribution system. A DC to AC inverter regulates this voltage by

sinusoidal PWM technique. By injecting voltages of controllable amplitude, phase angle and

frequency (harmonic) into the distribution feeder in instantaneous real time via a series

injection transformer, the DVR can restore the quality of voltage at its load side terminals

when the quality of the source side terminal voltage is significantly out of specification for

sensitive load equipment.

The reactive power exchanged between the DVR and distribution system is internally

generated by the DVR without any ac passive reactive components, i.e. reactors and

capacitors. For large variations in the source voltage, the DVR supplies partial power to the

load from a rechargeable energy source attached to the DVR dc terminal. The DVR, with itsthree single phase independent control and inverter design is able to restore line voltage to

critical loads during sags caused by unsymmetrical as well as symmetrical three phase faults

on adjacent feeders or disturbances that may originate many miles away on the higher voltage

interconnected transmission system. Connection to the distribution network is via three

single-phase series transformers there by allowing the DVR to be applied to all classes of

distribution voltages. At the point of connection the DVR will, within the limits of its

inverter, provide a highly regulated clean output voltage.


10/50

10

4.3 BASIC CONFIGURATION OF DVR

The general configuration of the DVR consists of,

1. An Injection/ Booster transformer

2. A Harmonic filter

3. Storage Devices

4. A Voltage Source Converter (VSC)

5. DC charging circuit

6. A Control and Protection system

4.3.1 Voltage Injection/ Booster transformer

The primary side of the injection transformer is connected in series to the distribution

line, while the secondary side is connected to the DVR power circuit. 3 single phase

transformers can be used for 3 phase DVR. Basically the injection transformer is a step up

transformer which increases the voltage supplied by filtered VSI output to a desired level and

it also isolates the DVR circuit from the distribution network. Winding ratios are very

important and it is predetermined according to the required voltage at the secondary side.

High winding ratios would mean high magnitude currents on the primary side which may

affect the components of inverter circuit. When deciding the performance of DVR, the rating

of the transformer is an important factor. The winding configuration of the injection

transformer is very important and it mainly depends on the upstream distribution transformer.

In case of a -Y connection with the grounded neutral there will not be any zero sequence

current flowing into the secondary during an unbalance fault or an earth fault in the high

voltage side.

4.3.2 DC charging unit

The dc charging circuit is used after sag compensation event, the energy source is

charged again through dc charging unit. It is also used to maintain dc link at the nominal dc

link voltage.

4.3.3 Voltage Source Converter (VSC)

A voltage source converter is a power electronic system consists of a storage device

and switching devices, which can generate a sinusoidal voltage at any required frequency,

magnitude and phase angle. It could be a three-phase three-wire voltage source converter. In

this thesis two level converters are used for both DVR and D-STATCOM. The VSC is used

to momentarily replace the supply voltage or to generate the part of the supply voltage which

is absent (missing voltage). There are four main types of switching devices: Metal Oxide

Semiconductor Field Effect Transistor (MOSFET), Gate Turn-Off thyristor (GTO), Insulated


11/50

11

Gate Bipolar Transistor (IGBT), and Integrated Gate Commutated thyristor (IGCT). Here,

IGBT based two level six pulse voltage source converter is used.

4.3.4 Simulink result of proposed two levels VSC.

The following fig.4.3 represents the out of proposed voltage source converter. Here, the

input given to the inverter is 6.2 KV DC and the alternating output of nearly 6.2 KV is getting

at output side.

Figure 4.3 output of proposed two level voltage source converters.

4.3.5 Pulse Width Modulation Generator (PWM)

As we well known the operation of PWM that by comparing the carrier signal and

reference signal, required pulse are generated by this discrete PWM generator. The

modulated signals are compared against a triangular signal in order to generate the switching

signals which are shown in fig.4.4. The main parameters of sinusoidal PWM generator are

amplitude modulation index and frequency modulation index. The amplitude modulation

index is kept 1p.u and frequency modulation index depend upon the ratio of carrier frequency

and fundamental frequency. The modulating signal is applied to the PWM in phase A, the

angle for phase B and C are shifted by -120 and +120 respectively.

Figure 4.4 Pulse generated by Discrete PWM Generator.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-8000

-6000

-4000

-2000

0

2000

4000

6000

8000

Time

V

oltage

(K

V

)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Time

Voltage(p.u

)


12/50

12

4.3.4 Harmonic filter

As DVR consist of power electronic devices, the possibility of generation self

harmonics is there so harmonic filter is also become a part of DVR. In order to achieve this it

is necessary to eliminate the higher order harmonic components during DC to AC conversion

in Voltage Source Inverter which will also distort the compensated output voltage. Thesefilters which play a vital role can be placed either on high voltage side i.e. load side or on low

voltage side i.e. inverter side of the injection transformers. We can avoid higher order

harmonics from passing through the voltage transformer by placing the filters in the inverter

side. Thus it also reduces the stress on the injection transformer. One of the problems which

arise when placing the filter in the inverter side is that there might be a phase shift and

voltage drop in the inverted output. So this could be resolved by placing the filter in the load

side. But this would allow higher order harmonic currents to penetrate to the secondary side

of the transformer, so transformer with higher rating is essential.

4.4 OPERATING MODE OF DVR

4.4.1During the normal operation

During the normal operation as there is no sag, DVR will not supply any voltage to

the load. It will be in a standby mode or it operates in the self charging mode if the energy

storage device is fully charged. The energy storage device can be charged either from the

power supply itself or from a different source.

4.4.2During a voltage sag/swell on the line

The difference between the pre sag voltage and the sag voltage is injected by the DVR

by supplying the real power from the energy storage element and the reactive power. The

DVR injects the difference between the pre-sag and the sag voltage, by supplying the real

power requirement from the energy storage device together with the reactive power. Due to

the ratings of DC energy storage and the voltage injection transformer ratio the maximum

capability of DVR is limited. The magnitude of the injected voltage can be controlled

individually in the case of three single-phase DVRs. With the network voltages the injected

voltages are made synchronized (i.e. same frequency and the phase angle).


13/50

13

4.4.3 During a short circuit or fault in the downstream of the distribution line

In this case we have seen before that a bypass switch (crossbar switch) will be

activated and it will bypass the inverter circuit in order to protect the electronic components

of the inverter.

4.5 COMPENSATION TECHNIQUES

4.5.1 Pre-sag Compensation

Pre-sag compensation is a method which is generally used for non linear loads such as

thyristor controlled drives. In non linear loads the voltage magnitude as well as he phase

angle needs to be compensated. Figure 4.5 below describes the pre-sag compensation

technique. A higher rated energy storage device and voltage injection transformers are

needed for this technique.

4.5.2 In-phase Compensation

This technique of compensation is generally used for active loads. Only compensation

for voltage magnitude is required whereas no phase compensation is required. In this

particular method the compensated voltage is in phase with the sag voltage. It is clear from

the Figure 4.6, that there is a phase shift between the voltages before the sag and after the sag.

In above both the techniques required both real and reactive power for the compensation and

the DVR is supported by an Energy storage device.


14/50

14

4.6 EQATIONS RELATED TO DVR

The injected voltage and load impedance Zth depends on the fault level of the load bus.

When the system voltage (Vth) drops, the DVR injects 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,

VDVR=VL+ ZthIL-Vth (1)Here, IL is load current and is given by

IL =( +)

When VL is considered as a reference, equation -1 can be written as

VDVR = VL 0+ ZthIL (- ) -Vth

Here , and are the angle of VDVR, Zth andVth respectively, is the load power factor angle,

= tan-1 (QL/PL)

the complex power injection of the DVR can be written as,

SDVR=VDVRIL*


15/50

15

5.1 INTRODUCTION

This chapter presents the operating principles of DSTATCOM. The DSTATCOM is

basically one of the custom power devices. It is nothing but a STATCOM but used at the

Distribution level. The key component of the DSTATCOM is a power VSC that is based on

high power electronics technologies.

The Distribution STATCOM is a versatile device for providing reactive compensation

in ac networks. The control of reactive power is achieved via the regulation of a controlled

voltage source behind the leakage impedance of a transformer, in much the same way as a

conventional synchronous compensator. However, unlike the conventional synchronous

compensator, which is essentially a synchronous generator where the field current is used to

adjust the regulated voltage, the DSTATCOM uses an electronic voltage sourced converter

(VSC), to achieve the same regulation task. The fast control of the VSC permits the

STATCOM to have a rapid rate of response.

The DSTATCOM is the solid-state based power converter version of the SVC.

Operating as a shunt connected SVC, its capacitive or inductive output currents can be

controlled independently from PWM technique. Because of the fast-switching characteristic

of power converters, the DSTATCOM provides much faster response. DSTATCOM is a

shunt connected, reactive compensation equipment, which is capable of generating and or

absorbing reactive power whose output can be varied so as to maintain control of specific

parameters of the electric power system. DSTATCOM employ solid state power switching

devices, hence, it provides rapid controllability of the three phase voltages, both in magnitude

and phase angle.


16/50

16

5.2 PRINCIPLE OF DSTATCOM

Basically, the DSTATCOM system is comprised of three main parts: a VSC, a set of

coupling reactors and a controller. The basic principle of a DSTATCOM connected in a

power system is the generation of a controllable ac voltage source by a voltage source

converter (VSC) connected to a dc capacitor (energy storage device). The ac voltage source,

in general, appears behind a transformer leakage reactance. The active and reactive power

transfer between the power system and the DSTATCOM is caused by the voltage difference

across this reactance. The DSTATCOM is connected in shunt with the power networks at

customer side, where the voltage-quality problem is a concern. All required voltages and

currents are measured and are fed into the controller to be compared with the commands. The

controller then performs feedback control and outputs a set of switching signals to drive the

main semiconductor switches (IGBTs, which are used at the distribution level) of the power

converter accordingly. The basic diagram of the DSTATCOM is illustrated in Fig5.2

The ac voltage control is achieved by firing angle control. Ideally the output voltage of the

VSC is in phase with the bus voltage. In steady state, the dc side capacitance is maintained at

a fixed voltage and there is no real power exchange, except for losses.


17/50

17

5.3 PRINCIPLE OF VOLTAGE REGULATION

5.3.1 Voltage regulation without D-Statcom

Consider a simple phasor as shown in fig. 5.4. It consists of a source voltage Vs, VL is

the load voltage and load current IL. Without a voltage compensator the load voltage drop

caused by the load current IL. The change in load voltage is V.

V=Vs-VL=Zs*IL

IL=()

V=(Rs+jXs)*(()

)

V= Vr+ Vx

So, the voltage change has a component Vr in phase with Vth and component Vx having

lagging phase difference.


18/50

18

5.3.2 Voltage regulation with DSTATCOMNow consider a compensator connected to the system. It is as shown in Fig 5.3.2 shows

vector diagram with voltage compensation. By adding a compensator in parallel with the load,

it is possible to supply voltage equal to Load voltage by controlling the current of the

compensator.

Is =Ish + IL

Vth

IL

Vs

IsRth

jIsXth

Figure 5.5phasor diagram for compensated

IsIsh


19/50

19

6.1 INTRODUCTIONA controller is required to control or to operate both D-Statcom and DVR during the

fault condition only. Load voltage is sensed and passed through a sequence analyzer. The

magnitude of the actual voltage is compared with reference voltage i.e Vref. Pulse width

modulated(PWM) control system is applied for inverter switching so as to generate a three

phase 50Hz sinusoidal voltage at the load terminals. Switching frequency in the range of few

KHz. The IGBT Inverter is controlled with PI controller in order to maintain 1p.u voltage at

the load side. An advantage of proportional pulse integral controller is an actuating signal

which is the difference between the reference voltage and feedback load voltage. Output of

the controller is in the form of an angle , which introduces additional phase-lag/lead in the

three-phase voltage. The output of error detector is the missing voltage. The controller output

when compared at PWM signal generator hence, the result in the desired firing sequence.

6.2 PHASE MODULATION

The sinusoidal signal Vcontrol phase modulated by means of the angle are,VA=Sin (t + ) VB=sin (t + -2/3) VC =sin (t ++2/3)

Figure 6.2 phase modulation of the control angle .

This modulated signal is compaired with triangular signal and generates the switching signals

for the converter valves. The main parameters of the sinusoidal PWM scheme are the

amplitude modulation index of signal, and the frequency modulation index of the triangular

signal. The modulating angle is applied to the PWM generator in phase A. the angles for

Phase B and phase C are shifted by 120 and 240 lagging respectively. The speed of

response is clearly shown in the simulation result shown.


20/50

20

7.1 PARAMETERS OF DVR TEST SYSTEM

The test system consists of 13KV, 50Hz generation system (considered to be source).

This source, feeding two transmission lines through a three winding transformer connected in

Y// 13/115/115 KV. Such transmission lines feed two distribution network through two

transformer connected in /Y, 115/11KV.

Table-7.1 system parameters

Sr. No. System Quantities Standards

1 Source 13KV, 50Hz 100MVA

2 Three winding transformer 100MVA,Y// 13/115/115 KV

3 Impedance of transmission line1 R1=0.05/Km, L1=0.4806 H/Km

4 Impedance of transmission line2 R2=1m/Km, L2=5mH/KM

5 Two winding transformer 100MVA,50Hz, /Y 115/11 KV

6 Injection transformer 100MVA, 50Hz,/Y 11/11KV

7 Load on bus1 P=6.05MW(resisitive load)

8 Load on bus2 P=3.4922KW Q=2MVAR(highly inductive)

9 Inverter parameters IGBT based, 3 arms, 6 pulse, carrier

Frequency=1080Hz

10 PI controller Kp=0.5, Ki=50, Sample time=50s

7.2 SINGLE LINE DIAGRAM OF THE DVR TEST SYSTEM


21/50

21

In the above test system we have a generating unit of 13KV, 50Hz which is considered as

source of 100MVA. The test system is constructed with concerning the DVR actuation. The

output from the source is fed to the primary of tertiary winding transformer. Now, further two

parallel feeders of 11KV each are drawn with the help of two winding transformer. In one of

the feeder (L2) DVR is connected in series and on other line fault is applied to creat sag or

swell.

7.3 SIMULINK MODEL OF TEST SYSTEM AND RESULTS

7.3.1 Simulation of test system without fault and without DVR

This simulink model presents the test system without any fault and without

connecting custom device like DVR.

Figure 7.2 Simulink model of test system without fault and without DVR


22/50

22

7.3.2 Simulation Results without fault and without DVR

The following result shows the system when considering no fault and no connection

ofDVR. RMS value of Voltage in p.u, instantaneous voltages, line to line voltage and phase

voltage of the simulation result shown in the following figure.7.3, 7.4, 7.5 and 7.6

respectively. The line to line voltage is 11KV and phase voltage is 6.3508V is measured.

Figure 7.3 Voltage Vrms( p.u) at load side.

Figure 7.4 Instantaneous value in p.u at load side.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.2

0.4

0.6

0.8

1

1.2

Time

V

olta

g

e(P

.U

)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Time

V

olta

g

e

(P

.U

)


23/50

23

Figure 7.5 line to line voltage (KV) at load side

Figure 7.6 Phase Voltage (KV) at load side.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-2

-1.5

-1

-0.5

0

0.5

1

1.5

2x 10

4

Time

V

o

lta

g

e

(K

V

)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1

-0.5

0

0.5

1x 10

4

Time

V

o

lta

g

e

(K

V

)


24/50

24

7.3.3 Simulink model of test system with fault but without DVR

In this simulink model we have system which fed the two buses or feeders through

two winding transformer as shown. On the upper bus we are applying the 3phase Line to

ground fault(3LG) , here we are not considering the presence of DVR and have to observe the

effect on voltages on the lower bus(second bus or second feeder).

Figure 7.7 Simulink model withfault without DVR

7.3.4 Simulation Result of test system with fault and without DVR

From the following results it is observed that during the fault time i.e 0.4-0.6 sec, thevoltage sag to some finite value. Since the fault is on upper bus, hence sag may be 70-80% .

The sag on the lower bus at the load side is nearly 10-15% , and measured the line to line

voltage value and phase voltage value during fault time is 10.1KV and 6.01KV respectively.

Such observation can be found from the following figures.


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.2

0.4

0.6

0.8

1

1.2

Time(sec)

V

oltage(P.U

)


25/50

25



0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Time (sec)

V

o

lta

g

e

(P

.U

)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-2

-1.5

-1

-0.5

0

0.5

1

1.5

2x 10

4

Time(sec)

V

o

lta

g

e

(K

V

)


26/50

26


7.3.5 Simulink model of test system with fault and with DVR

In this simulink model we have system which fed the two buses or feeders through

two winding transformer as shown. On the upper bus we are applying the three phase Line to

ground fault (3LG). And on the lower bus we have connected the DVR because in this bus

sag is low and custom device can compensate easily. The system is shown in following fig.

Figure 7.12 simulation test system with DVR

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1

-0.5

0

0.5

1x 10

4

Time

V

o

lta

g

e

(K

V

)


27/50

27

7.3.6 Simulation Results with fault and with DVR

From the following results it is clear that the DVR compensate the voltage sag during

the fault time 0.4-0.6 sec. the compensated results of sag with respective rms value of

voltage, instantaneous value, line to line voltage and phase voltages are shown in fig, 7.13,

7.14, 7.15 and 7.16 respectively. The fig.7.17 shows the amount of voltage injected by the

DVR which is nearly 0.5KV. The battery voltage is found to be 6.2KV.


Figure 7.14 instantaneous values in p.u at load side.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.2

0.4

0.6

0.8

1

1.2

Time

V

oltage(P.U

)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1.5

-1

-0.5

0

0.5

1

1.5

Time

V

o

lta

g

e

(P

.U

)


28/50

28



Figure 7.17 Injected voltage by DVR

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-2

-1.5

-1

-0.5

0

0.5

1

1.5

2x 10

4

Time

V

oltage(P.

U

)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1

-0.5

0

0.5

1x 10

4

Time

V

oltage(P.U

)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1

-0.5

0

0.5

1x 10

4

Time

V

oltage(K

V

)


29/50

29

7.3.7 Simulation of test system for voltage swells without DVR

The following simulink model represent the creation of swell for the time 0.4-0.6 sec.

to create the swell capacitor switching is proposed on lower bus.

Figure 7.18 simulink model of test system for voltage swell.

7.3.8 Simulation Results for voltage swell without DVRDuring the capacitor switching the voltage is swell to 10-15% of its normal value at

the interval of 0.4-0.6, which are shown in the following fig. 7.19, 7.20, 7.21 and 7.22

represent rms value of voltage in p.u, three phase instantaneous value in p.u, line to line

voltage and phase voltage in KV respectively. The line to line voltage and phase voltage

during the 0.4-0.6 are 0.77KV and 0.445KV respectively.


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.2

0.4

0.6

0.8

1

1.2

Time

Voltage(P.U

)


30/50

30


Figure 7.21 line to line voltage (KV) at load side.


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Time

Volt

age(P.

U)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1

-0.5

0

0.5

1x 10

4

Time

V

oltage(K

V

)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-2

-1.5

-1

-0.5

0

0.5

1

1.5

2x 10

4

Time

V

oltage(K

V

)


31/50

31

7.3.9 Simulation of test system for voltage swells with DVR

In the following simulink model we are considering the working of DVR to eliminate

the swell during the capacitor switching.

Figure 7.23 simulation test system for voltage swell with DVR.

7.3.10 Simulation Results for voltage swell with DVR

From the following results it is clear that the DVR compensate the voltage swell

during the switching time 0.4-0.6 sec. the compensated results of swell with respective rms

value of voltage, instantaneous value, line to line voltage and phase voltages are shown in fig,

7.24, 7.25, 7.26 and 7.27 respectively.


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.2

0.4

0.6

0.8

1

1.2

Time

V

oltage(P.U

)


32/50

32




0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Time

Volta

ge(P.

U)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-2

-1.5

-1

-0.5

0

0.5

1

1.5

2x 10

4

Time

V

oltage(K

V

)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1

-0.5

0

0.5

1x 10

4

Time

V

oltage(

K

V

)


33/50

33

8.1 PARAMETERS OF D-STATCOM TEST SYSTEM

The test system consists of 230KV, 50Hz transmission line (considered to be source).

This source, feeding two distribution network through a three winding transformer connected

in Y// 230/11/11 KV.

Table-8.1 system parameters

Sr. No. System Quantities Standards

1 Source 230KV, 50Hz 100MVA

2 Three winding transformer 100MVA,Y/Y/Y 230/11/11 KV

3 Load on bus1 P=1.776MW, Q= 65.26MVAR(highly inductive)

4 Load on bus2 P=385.124KW Q=2MVAR(highly inductive)

5 Injection transformer 100MVA, 50Hz,/Y 11/11KV

6 Inverter parameters IGBT based, 3 arms, 6 pulse, carrier

Frequency=1080Hz

8.2 SINGLE LINE DIAGRAM OF THE DVR TEST SYSTEM

In the above test system we have a transmission line of 230KV, 50Hz which is considered as

source of 100MVA. The test system is constructed with concerning the D-Statcom actuation.

The source is fed to the primary of tertiary winding transformer. Now, further two parallel

feeders of 11KV each are drawn from secondary winding the transformer. In one of the

feeder D-STATCOM is connected in shunt and on other line two parallels loads are

connected. The fault is applied at load side to create sag or swell.


34/50

34

8.3 SIMULINK MODEL OF TEST SYSTEM AND RESULTS

8.3.1 Simulation of test system without fault and without D-STATCOM

This simulink model presents the test system without any fault and no connecting

custom device like DVR.

Figure 8.2 simulink mode without fault and without D-STATCOM.

8.3.2 Simulation Results without fault and without D-STATCOM

The following results shows the system when considering no fault and no connection

of D-STATCOM rms value of Voltage in p.u, instantaneous voltages, line to line voltage and

phase voltage of the simulation result shown in the following figure.8.3, 8.4, 8.5 and 8.6

respectively. The line to line voltage and phase voltage are nearly11KV and 6.3508V is

measured.


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.1

0.2

0.3

0.4

0.5

0.6

0.70.8

0.9

1

Time

V

oltage(P.U

)


35/50

35




0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Time

V

oltage(P.

U

)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-2

-1.5

-1

-0.5

0

0.5

1

1.5

2x 10

4

Time

V

oltage(P.U

)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1

-0.5

0

0.5

1x 10

4

Time

V

oltage(P.U

)


36/50

36

8.3.3 Simulation of test system with fault but without D-STATCOM

In this simulink model we have system in which source is connect to primary side of

tertiary transformer as shown. The load is connected to the secondary sides of 11KV.the sag

is create here by providing the switching for the interval of 0.4-0.6 sec.

Figure 8.7 simulation test system without D-STATCOM

8.3.4 Simulation Results with fault but without D-STATCOM

From the following results it is observed that during the fault time i.e 0.4-0.6 sec, the

voltage sag to some finite value.The sag during the fault at the load side is nearly 10-15% ,

and measured the line to line voltage value and phase voltage value during fault time is

10.25KV and 6.01KV respectively. Such observation can be found on the following figures.


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.2

0.4

0.6

0.8

1

Time

V

oltage(P.U

)


37/50

37




0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Time

V

oltage(P

.U

)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-2

-1.5

-1

-0.5

0

0.5

1

1.5

2x 104

Time

V

oltage(P.U

)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1

-0.5

0

0.5

1x 10

4

Time

Voltage(KV)


38/50

38

8.3.5 Simulation of test system with D-STATCOM

In this simulink model we have system which fed the load through secondary winding

of tertiary transformer as shown. Out of two parallel loads, sag is created by providing the

switching on one of load. The D-STATCOM is connected to one of the secondary winding of

tertiary transformer .The system is shown in following fig.8.12

Figure 8.12 simulation test system with D-STATCOM

8.3.6 Simulation Results with fault and with D-STATCOM

From the following results it is clear that the D-STATCOM compensate the voltage

sag during the fault time 0.4-0.6 sec. the compensated results of sag with respective rms value

of voltage, instantaneous value, line to line voltage and phase voltages are shown in fig, 8.13,

814, 8.15 and 8.16 respectively. The battery voltage is found to be 28KV.


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.2

0.4

0.6

0.8

1

Time

Voltage(P.U

)


39/50

39

Figure 8.14 instantaneous values in p.u at load side with fault but without D-STATCOM

Figure 8.15 line to line voltage (KV) at load side. with fault but without D-STATCOM

Figure 8.16 Phase Voltage (KV) at load side. with fault but without D-STATCOM

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Time

V

oltage(P

.U

)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-2

-1.5

-1

-0.5

0

0.5

1

1.5

2 x 10

4

Time

V

oltage(K

V

)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1

-0.5

0

0.5

1x 10

4

Time

V

oltage(P.U

)


40/50

40

8.3.7 Simulation of test system for voltage swells without D-STATCOM

The following simulink model represent the creation of swell for the time 0.4-0.6 sec.

to create the swell switch is closed for the interval of 0.4-0.6 sec. As shown in following fig.

Figure 8.17 Simulation of test system for voltage swells without D-STATCOM.

8.3.7 Simulation Results for voltage swell without D-STATCOM

The voltage swell is created by closing the switch during 0.4-0.6 sec. The swell of 10-15% of

its normal value is found at the interval of 0.4-0.6 sec, which is shown in the following fig.

8.18, 8.19, 8.20 and 8.21 representing rms value of voltage in pu, three phase instantaneous

value in p.u, line to line voltage and phase voltage in KV respectively. The line to line

voltage and phase voltage during the 0.4-0.6 are 0.93KV and 0.588KV respectively.


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.2

0.4

0.6

0.8

1

Time

V

oltage(P.U

)


41/50

41



0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Time

V

o

lta

g

e

(P

.U

)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-2

-1.5

-1

-0.5

0

0.5

1

1.5

2x 10

4

Time

V

o

lta

g

e

(K

V)


42/50

42


8.3.8 Simulation of test system for voltage swells with D-STATCOM

In the following simulink model we are considering the working of D-STATCOM to

eliminate the swell during the switching of load.

Figure 8.22 simulation test system for voltage swell with D-STATCOM

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1

-0.5

0

0.5

1x 10

4

Time

V

o

lta

g

e

(K

V

)


43/50

43

8.3.9 Simulation of test system for voltage swells with D-STATCOM

From the following results it is clear that the DVR compensate the voltage swell

during the switching time 0.4-0.6 sec. the compensated results of swell with respective rms

value of voltage, instantaneous value, line to line voltage and phase voltages are shown in fig,

8.23, 8.24, 8.25 and 8.26 respectively.



0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.2

0.4

0.6

0.8

1

Time

V

oltage(P.U

)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Time

V

o

lta

g

e

(P

.U

)


44/50

44



0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1.5

-1

-0.5

0

0.5

1

1.5x 10

4

Time

V

o

lta

g

e

(K

V

)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1

-0.5

0

0.5

1x 10

4

Time

V

o

lta

g

e

(K

V

)


45/50

45

9.1 CONCLUSION

The thesis has presented the study and simulation model of custom power equipment,

namely D-STATCOM and DVR, and applied them for power quality problem such as voltage

sag and voltage swell. The highly develop graphic facilities available in MATLAB is used to

conduct all the aspect of model implementation and to carry out extensive simulation studies.

A controller which is based on closed loop technique is used which generate error signals and

this signals are used to trigger the switches of inverter using pulse width modulation (PWM)

scheme in the D-STATCOM and DVR, this PWM control scheme only requires voltage

measurements. The simulations are carried out for both sag and swell on 11KV feeder using

both D-Statcom and DVR as custom power devices and it has been found that DVR provide

excellent voltage regulation capabilities. It is also observed that the DVR capacity for power

compensation and voltage regulation depends mainly on two factors that is, the rating of the

dc storage device and the coupling transformer.

9.2 FUTURE SCOPE

The following point can be consider for future extension of work

The control circuit can be change. The other controller like fuzzy, PQ techniqueand adaptive PI fuzzy controller may employ in the compensation scheme.

Result can be improve by considering the operation with multi-level inverter Both custom devices can be established for active loads like wind turbine and

solar source.


46/50

46

REFERENCES

[1] N.G.Hingorani,Flexible AC Transmission, IEEE Spectrum, vol. 30, pp.40-44,1993.

[2] N.G.Hingorani, Introducing Custom Power, IEEE Spectrum, vol. 32 pp.41-48,1995.

[3] Anaya-Lara O, Acha E., Modeling and analysis of custom power system by

PSCAD/EMTDC, IEEE Transactions on Power Delivery, Vol.17, and Issue: 1, Jan.2002. Pp.266-272.

[4] M.J.H.Bollen, Voltage sags in three-phase system Power Engineering Review,

IEEE, Vol.21 Issue:9, Sept.2001.pp.8-11.

[5] Haque. M.H, Compensation of distribution system voltage sag by DVR and D-

STATCOM. Power Tech. proceeding. 2001IEEE Porto, vol.11, Issue: Sept. 2001

pp.10-13

[6] Arindam Ghosh, Performance Comparision of VSC-Based Shunt and Series

Compensators Used for Load Voltage Control in Distribution System.IEEE

Transaction on power delivery, vol.26, No.1, Jan, 2011. pp.268-278.

[7] Arindam Ghosh, Copensation of Distribution System Voltage Using DVR. IEEE

Transaction on power delivery, vol.17, No.4, Oct. 2002. pp.1030-1036.

[8] H.P Tiwari and Sunil Kumar Gupta Dynamic Voltage Restorer against Voltage Sag

International of Innovation, Management and Technology vol.03, pp. 232-237,2010.

[9] C.S Chang, Y.S Ho, The Influence of Motor Load on the Voltage Restoration

Capability of Dynamic Voltage Restorer. Power System Technology, Proceedings,

Power Con, International Conference, vol.2,pp. 637-642,2000.

[10] M.H. Rashid, Power Electronics 2nd edition, Elsevier, Inc, Publication, Californial,

U.S.A 2007.

[11] Rakosh Das Begamudre, Extra High Voltage AC Transmission Engineering, 2nd

Edition, New Age International Limited, New Delhi 1990.

[12] Majid Moradlou and Hamid R. Karshenas, Design Strategy for Optimum RatingSelection of Interline DVRIEEE, VOL. 26, NO. 1, Jan, 2011.


47/50

47

LIST OF PUBLICATIONS

Sr.

No.

Authors Title of Paper Name of

International

Journals /

International

Conference

Place and date of

Publication with

Citation Index

1

Akil

Ahemad,

Prof. N.T.

Sahu

Simulation of DVR

in power system.

National Conference

On Advances In

Engineering And

Technology.

Anjuman College of

Engineering &

Technology. Sadar,

Nagpur-440001

March 13, 2012

2

Akil

Ahemad,

Prof. N.T.

Sahu

Performance of

DVR in Power

system.

International

conference on

Interdisciplinary

Research and

Development in

Management,

Engineering,Technology and

Social Sciences

(ICMETSS) 2012.

Choice Institute of

Management Studies

& Research, Pune.

28th and 29th April,

2012.


48/50

48


49/50

49


50/50

.

dstatcom and dvr in power system

Documents