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Distribution Static Synchronous Compensator (DSTATCOM) is a shunt compensating device which is us...

Distribution Static Synchronous Compensator (DSTATCOM) is a shunt compensating device which is used

to improve current profile by exchanging of reactive power with unbalanced and nonlinear load. DSTATCOM is a

shunt compensating device used for power quality improvement in distribution systems. Relevant solutions are

applied for harmonics, fluctuation of voltage, voltage deviation, unbalance of three phase voltage and current and

frequency deviation. Different controlling schemes such as Phase Control Method (PCM), Fryze Power Theory

(FPT), Synchronous Reference Frame Theory (SRFT) and Instantaneous Reactive Power Theory (IRPT) are used

for reactive power compensation with the help of Voltage source Inverter (VSI). In this project we are going to

balance the source current using different control schemes. The results of different source currents are compared

with a different control schemes in terms of active and reactive power and in terms of Total Harmonic Distortion

(THD) for nonlinear load using Fryze Power Theory (FPT) and Instantaneous Reactive Power Theory (IRPT).

Reference currents are generated by the different control schemes have been dynamically traced in a hysteresis

current controller. The performance of DSTATCOM for different control schemes is validated for load balancing

and harmonic elimination by using simulation models in MATLAB/SIMULINK

- International Journal of Engineering and Techniques - Volume 2 Issue 2, Mar – Apr 2016

RESEARCH ARTICLE

OPEN ACCESS

Load Balancing and Harmonic Elimination

Using Distribution Static Synchronous

Compensator (DSTATCOM)

AnkurGheewala1, Jay Chanawala2,Nikhil Jadav3,Modi Rishit4, Chirag Machhi5,Jenish

Rana6

(Electrical Engineering Department, Shroff S. R. Rotary Institute of Chemical Technology,Ankleshwar)

Abstract:

Distribution Static S ynchronous Compensator (DS TATCOM) is a shunt compensating device which is used

to improve current profile by exchanging of reactive power with unbalanced and nonlinear load. DSTATCOM is a

shunt compensating device

used for power quality improvement in distribution systems. Relevant solutions are

applied for harmonics, fluct

uation of voltage, voltage deviation, unbalance of three phase voltage and current and

frequency deviation. Differ

ent control ing schemes such as Phase Control Method (PCM), Fryze Power Theory

(FPT), Synchronous Refere nce Frame Theory (SRFT) and Instantaneous Reactive Power Theory (IRPT) are used

for reactive power compensation with the help of Voltage source Inverter (VSI). In this project we are going to

balance the source current using different control schemes. The r esults of different source currents are compared

with a different control schemes in terms of active and reactive p ower and in terms of Total Harmonic Distortion

(THD) for nonlinear load using Fryze Power Theory (FPT) and Instantaneous Reactive Power Theory (IRPT).

Reference currents are generated by the different control schemes have been dynamical y traced in a hysteresis

current control er. The performance of DSTATCOM for different control schemes is validated for load balancing

and harmonic elimination by using simulation models in MATLAB /SIMULINK

Keywords—DSTATCOM, Unbalanced load, Nonlinear load, Reactive power compensation, Reference

currents, Load balancing, Harmonic elimination

I.

INTRODUCTION

Power systems voltage and current waveforms are

control er devices used for improving the power

deteriorates by highly use of power converters and nonlinear quality are as fol ows:

loads. Harmonics are generated because of high frequency of

Static VAR Compensators (SVC)

switching of power electronics converters. The presence of

Thyristor Control ed Series Capacitors (TCSC)

harmonics in voltage and current waveforms increases the

power loss.The unbalanced load current with large reactive

Static Compensators (STATCOM)

components leads results in voltage fluctuations and

Static Series Synchronous Compensators (SSSC)

unbalance due to the source (system) impedances. Because of

Unified Power Flow Controllers (UPFC)

unbalanced current the harmonic components increases and

reduction in power factor of distribution network. A shunt Among of the various distribution FACTS control ers,

compensator also helps to reduce voltage fluctuation sat the Distribution Static Compensator (DSTATCOM) is an

point of common coupling (PCC). If the source voltages are important shunt compensator which has the capability to solve

unbalanced and varying, it is also possible for a shunt power quality problems faced by distribution systems.

compensator to achieve this[1]. In distribution system the DSTATCOM has effectively replaced a Static VAR

power quality can be improved by custom power devices Compensator (SVC), as it takes large response time in

which can able to exchange of extra demanded reactive power addition it is connected with the passive filter banks and

which are also cal ed FACTS devices. The commonly FACTS capable only steady state reactive power compensation. A

DSTATCOM is a Voltage Source Inverter (VSI) based

ISSN: 2395-1303 http:/ www.ijetjournal.org

Page 184 - FACTS controller sharing similar concepts with a STATCOM

used at transmission level. Moreover SVCs which have been

largely used in arc welding plants for voltage flicker

mitigation have been replaced by DSTATCOMs because

SVCs exhibit limited reduction of instantaneous flicker

level.A DSTATCOM is basical y a Voltage Source Converter

(VSC) based FACTS control er sharing many similar concepts

with that of a STATCOM used at transmission level. A

STATCOM at the transmission level handles only

fundamental reactive power and provides voltage support

while as a DSTATCOM is employed at the distribution level

or at the load end for power factor improvement and voltage

regulation. DSTATCOM have similar functionality as

compared to shunt active filter, it can work as a shunt active

filter to eliminate unbalance and distortion in source current

and supply voltage.

The performance of the DSTATCOM depends on the control

algorithm i.e. the extraction of the current components. So, for

this, there are various control algorithms for the control of

DSTATCOM block depending on various theories and

strategies like phase shift control, instantaneous PQ theory,

Fig.1 Single line diagram of DSTATCOM

and synchronous frame theory. Each of the algorithms

specified have their own merits and demerits. In this The main principle of DSTATCOM is as fol ow:

dissertation there are five control strategies have been 1. Vi > VM → DSTATCOM will supply the reactive power

implemented to compensate the required reactive power at the 2. Vi < VM → DSTATCOM will absorb the reactive power

load side. Phase control method has used for enhancement of 3. Vi=VM → DSTATCOM wil not exchange the reactive

power transmission system performance. The other control

power which is also a balanced condition.

strategies are Synchronous frame theory, instantaneous PQ Where, Vi = Inverter voltage in volt

theory and fryze method used for compensation of the

VM = Point of common coupling voltage in volt

unbalanced linear load and nonlinear power electronic load. VS = Source voltage in volt

The hysteresis current control strategy has implemented to

compensate reactive power requirement of single-phase load.

Eachcontrol algorithm calculatesthe compensated

current of compensator to supply or absorb the reactive power.

II.

Distribution STATCOM

The compensated current is given by

The DSTATCOM is a voltage source inverter which is

used for the modification of bus voltage sags. DSTATCOM is

IC = IL – IS

(A)

connected to the distribution network through a standard Where, IC = Compensated current in ampere

distribution power transformer. The DSTATCOM is IL = Load current in ampere

continuously monitoring the line waveform and provide IS = Source current in ampere

leading or lagging compensating current. The single line

diagram of DSTATCOM is shown in fig.1. DSTATCOM

III.

Control Algorithms

consists of a dc capacitor, one or more converter modules, an

The basic block diagram of compensator is as shown in

L-C filter, a distribution transformer and a PWM control fig.2. The main function of any control scheme is to generate

technique. In this implementation, a voltage-source inverter required reference currents by sensing the load current and

converts a dc voltage into a three-phase ac voltage that is source current. Reference currents are faded to the hysteresis

synchronized with, and connected to, the ac line through a current controller. Hysteresis current controller generates the

smal tie reactor and capacitor (L-C filter).

pulses which are injected to the gate of IGBT switches.

According to these pulses the compensator supply or absorb

the current and make the system balanced. The compensator

can give desired performance as long as its bandwidth is

sufficient to track the fluctuations in the load. In this

configuration VSC is used with the dc storage capacitor. Two

IGBT switches are used in one leg and three legs are

connected in paral el with the dc capacitor. In this operation

the capacitor must be precharged to a sufficient value such

that it can give the bet er tracking performance to generate

reference currents. Interfacing of filter resistance Rf and

ISSN: 2395-1303 http:/ www.ijetjournal.org

Page 185 - inductance Lf are used to filter the high frequency components

p0 V0

0

0

of compensating current. The value of inductance L

I

f controls

0

the switching frequency of converter.

p

0

V

V I

q

0 V V

I

In three phase three wire system, io = 0 this implies

po= 0. Equation (3) would be reduced to

p

V V

i

q V V i

When the system is balanced, the instantaneous

active and reactive powers p and q can be decomposed into an

average and an oscillatory component. pdc and qdc are average

components and pac and qac are oscillatory part of real and

reactive instantaneous powers. The compensating currents are

calculated to compensate the instantaneous reactive power and

the oscil atory component of the instantaneous active power.

In this case the source transmits only the non-oscil ating

component of active power. Therefore the reference source

Fig.2 Basic block diagram of compensator

currents in α-β co-ordinates are expressed as,

(1)Instantaneous Reactive Power Theory (IRPT):

*

is

V

V

p

This control scheme was invented by H. Akagi. The

*

dc

is

V V

basic block diagram of IRPT is as shown in fig. 3. In this

0

algorithm instantaneous source voltages and load currents are

These currents can be transformed in a-b-c quantities

sensed and are transformed from a-b-c to α-β-0, which is to find the reference currents in a-b-c coordinate.

cal ed Clark’s transformation [2].

1

1

0

i *

2

sa

i

*

2 1

1

3 0

i sb

3

2

2

2 i

i *

sc

1

1

3 i

2

2

2

(2) FRYZE Power Theory (FPT):

The block diagram of this control algorithm is as shown in

fig.4 [3]. In this control ing algorithm the load current and the

source voltages are sensed and the active fryze conductance

Ge is calculated by,

Fig.3 Basic block diagram of IRPT

V i V i V i

sa La

sb La

sc Lc

e

G

2

2

2

The Clark’s transformation of source voltage is given by

s

V a s

V b s

V b

1

1

1

Where,

V

iLa; iLb; iLc = Load current of phase a, phase b and phase c

0

2

2

2

V

2

1

1 a

V

respectively

1

3

2

2 V b

V

sa; Vsb; Vsc = Source voltage of phase a, phase b and phase c

V

3

3 V c

respectively

0

2

2

Then this signal Ge is fed to the LPF which is

1

1

1

denoted by Ḡe. The active instantaneous currents are

calculated as shown below:

I0

2

2

2

I

2

1

1 a

iwa = isa = Ḡe Vsa

I

i

1

wb = isb = Ḡe Vsb

3

2

2

Ib

I

i

wc = isc = Ḡe Vsc

3

3 I c

0

Where,

2

2

iwa; iwb; iwc = Active instantaneous current of phase a, phase b

and phase c respectively

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Page 186 - isa; isb; isc = Source current of phase a, phase b and phase c

respectively

(i i)

Fig.4 Basic block diagram of FPT

Then the reference current are calculated by,

i*Ca = iLa - iwa

i*Cb = iLb - iwb

i*Cc = iLc - iwc

Where,

iCa; iCb; iCc = Measured compensating current of phase a ,b and

c respectively

i*Ca; i*Cb; i*Cc = Calculated compensating current of phase a, b

and c respectively

This calculated compensated current is compared by

measured compensated current and the generated error signal

is given tothe voltage source inverter which is generated

(iv)

triggering pulses and is fed to the gate of the inverter.

Fig.5 Waveform of (i) load, source and compensated

current v/s time (i ) active and reactive power v/s time (i i)

IV.

SIMULATION RESULTS AND DISCUSSION source voltage and current of phase of phase-a v/s time (iv)

power factor v/s time (nonlinear load) for IRPT

(i)

(i)

(i )

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Page 187 - (i )

(i )

(i i)

(i i)

(iv)

Fig.6 Waveform of (i) load, source and compensated

current v/s time (i ) active and reactive power v/s time (i i)

source voltage and current of phase of phase-a v/s time (iv)

(iv)

power factor v/s time (linear unbalanced Δ-connected Fig.7 Waveform of (i) load, source and compensated

load)for IRPT

current v/s time (i ) active and reactive power v/s time (i i)

source voltage and current of phase of phase-a v/s time (iv)

power factor v/s time (nonlinear load) for FPT

(i)

(i)

ISSN: 2395-1303 http:/ www.ijetjournal.org

Page 188 - current v/s time (i ) active and reactive power v/s time (i i)

source voltage and current of phase of phase-a v/s time (iv)

power factor v/s time (linear unbalanced Δ-connected load)

for FPT

V.

CONCLUSIONS

After implement of these two algorithms successful y,

there is a making comparison between IRPT and FPT in terms

of rms value of source current. From table-I results the

conclusions are made as shown in table-II.

(i )

TABLE II: Comparison of IRPT and FPT

Control Scheme

Objectives of Compensation

IRPT

FPT

Computational Complexity

High

Simple

Reactive Power Compensation

Good

Excel ent

Load Balancing

Excel ent

Good

Harmonics Mitigation

Good

Excel ent

APPENDIX

(i i)

PARAMETERS

VALUE

Source parameters

VS (rms value) = 415 V, RS =

0.01 Ω, LS = 2 mH

Compensators parameters

Cdc = 500 μF, Rf = 0.01 Ω,

Lf = 15 mH

Linear unbalanced Δ-

Zlab = 50+ j 62.8 Ω,

connected load

Zlbc = 25+ j 54.95 Ω,

Zlca = 50 + j 70.65 Ω

(iv)

Fig.8 Waveform of (i) load, source and compensated

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Page 189 - REFERENCES

1. K.R. Padiyar, ``FACTS CONTROLLERS IN POWER

TRANSMISSION AND DISTRIBUTION”.

2. HIROFUMI AKAGI, YOSHIHIRA KANAZAWA AND

AKIRA NABAE, “Instantaneous Reactive Power

Compensators Comprising Switching Devices

without Energy Storage Components ", IEEE

TRANSACTIONS ON INDUSTRY APPLICATIONS,

VOL. IA-20, NO. 3, MAY/JUNE 1984.

3. Jaruppanan P, Kanta Mahapatra, Jeyaraman.K and

Jeraldine Viji, “Fryze Power Theory with Adaptive-

HCC based Active Power Line Conditioners",

International Conference on Power and Energy

Systems (ICPS), Dec 22-24, 2011, IIT-Madras.

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