Reducing Harmonics Distortion in Distribution Network Against the Induction Motor Drive Non Linear Load

8/12/2019 Reducing Harmonics Distortion in Distribution Network Against the Induction Motor Drive Non Linear Load

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International Journal for Science and Emerging ISSN No. (Online):2250-3641Technologies with Latest Trends 9(1): 27-32 (2013) ISSN No. (Print): 2277-8136

Reducing Harmonics Distortion in Distribution Network AgainstThe Induction Motor Drive Non Linear Load

Mani Bansal* and Navneet Singh Bhangu**

*, ** Department of Electrical Engineering, Guru Nanak Dev Engineering College

Ludhiana, INDIA

(Received 27 June 2013 Accepted 3 July 2013)

-AbstractPower quali ty is a major concern f or electrical engineers and researchers now days. Var ious power quali ty problems are

voltage sag, swell, in terruptions, harmoni cs etc. Thi s paper di scusses the problem of harmon ics and its reduction in distr ibution

network against the induction motor drive load. Harmonics distortion is reduced using Distribution static compensator

(DSTATCOM) modeli ng in the MATLAB/ Simulin k environment. The control technique used is Instantaneous power theory whichcalculates the requir ed cur rent inj ected into the power system. The simu lated resul ts show the effectiveness of DSTATCOM in

reducing harmon ics distortion.

Keywords- Power quality, harmonics, DSTATCOM , I nstantaneous power theory, MATLAB.

1. Introduction

The intensive use of power electronic convertersand non linear loads resulted in the deteriorationof power quality which ultimately causeseconomical losses. Non linear loads poseharmonics into the power system which deviate

the sinusoidal voltage and current waveform tonon sinusoidal one. This distortion in thewaveform is measured in term of index known asTotal harmonics Distortion (THD).THD may bedefined as the ratio of the square root of the sumof squares of the rms value of harmoniccomponent to the rms value of the fundamentalcomponent [2].

ITHD =

According to IEEE 519 standard, The THD levelfor current harmonics should be less than 5%. Inthis paper, the effort is made to reduce theharmonics as per standards. In order to achievethis, a custom power device called DistributionStatic Compensator (DSTATCOM) is modeledusing MATLAB/Simulink. DSTATCOM is avoltage source converter (VSC) based powerelectronic device [8]. Usually, this device is

supported by short term energy stored in a dccapacitor [3]. The DSTATCOM proposed in this

paper is employed to provide harmonicscompensation. The control technique used for theDSTATCOM control is Instantaneous reactive

power theory (IRP) [1].2. Distribution Static Compensator

The DSTATCOM is a voltage source converterbased static compensator that is used for thecorrection of line currents [8]. It is connected inshunt to the distribution network via couplingtransformer [6].

Fig.1 Schematic Diagram of DSTATCOM


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Fig.1 shows the schematic configuration ofDSTATCOM. DSTATCOM system consists of astandard three-phase Insulated Gate BipolarTransistor (IGBT) based three legs VSC bridgewith the input ac inductors and a dc energystorage device to obtain a self-supporting dc bus[5].The DSTATCOM is capable of generating

continuously variable inductive or capacitiveshunt compensation at a level up its maximumMVA rating [10]. The DSTATCOMcontinuously checks the line waveform withrespect to a reference ac signal, and therefore, itcan provide correct amount of leading or laggingreactive current compensation to reduce theamount of voltage fluctuations [10]. TheDSTATCOM has been utilized for voltageregulation, correction of power factor andelimination of current harmonics [11]. In this

paper, the performance of DSTATCOM isanalysed for elimination of current harmonics.

3. Voltage Source Converter

A voltage-source converter is a power electronicdevice, which can generate a sinusoidal voltagewith any required magnitude, frequency and

phase angle[7].A basic VSC structure is shownin Fig.2 where Rs and Ls represent the resistanceand inductance between the converter ac voltage

(VC) and the ac system voltage (V) and is is thecurrent injected into the grid. A dc capacitor isconnected on the dc side to produce a smooth dcvoltage. The switches in the circuit representcontrollable semiconductors, such as IGBT or

power transistors [7, 8]. Depending on theconverter rating, series-connected IGBT valvesare arranged in either a three-phase two-level orthree-level bridge. Each IGBT position isindividually controlled and equipped withintegrated antiparallel diodes [8]. For converter

the most important part is the sequences ofoperation of the IGBTs. The IGBTs signals arereferred to the Pulse Width Modulation (PWM)that will generate the pulses for the firing of theIGBTs. IGBTs are used in this simulation

because it is easy to control the switch on and offof their gates and suitable for the DSTATCOM[9].

Fig.2 Voltage source converter [5]

Fig.3 MATLAB based model of voltage sourceconverter (DSTATCOM)

4. Control of DSTATCOM

The control technique investigated in this paper

is Instantaneous Power Theory which is based

on instantaneous values in three phase power

systems with or without neutral wire. This is

valid for steady state or transitory operations as

well as for generic voltage and current

waveforms. It consists of an algebraic

transformation of the three phase voltages in the

a-b-c coordinates to the --0 coordinates. Thistransformation is called Clarke transformation. It

is then followed by the calculation of the p-q

theory instantaneous power components [12].

The mathematical computation of the powercomponents are as shown below:

(1)

Where Va, Vb, Vc are phase voltages. Identical

relations hold for line currents ia, ib and ic. The

instantaneous three phase power is given by:

p3(t) = vaia+ vbib+ vcic= vi+ vi+v0i0=pa(t) +pb(t) +pc(t)

28 Bansal* and Bhangu**


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=p(t) +p(t) +p0(t) =p(t) +p0(t)

(2)

Where p= p+ p is instantaneous real power;

and p0 (t) = v0i0 is the instantaneous zero

sequence power.

There is an advantage of using the

transformation of --0 is to separate the zerosequence component of the system.

The reactive power measurement can be given

by:

q (t) vivi(3)

Rewritten in terms of a-b-c components as

q= - [(va-vb) ic+ (vb-vc) ia+ (vc-va) ib]/ 3

The powers p and q can be rewritten as

(4)

From this matrix equation, = v2 + v

2

(5)

Separating the Active and Reactive parts

(6)

Where, the current components are

ip= vp/ , iq= vq/ (7)

ip= vp/ , iq= v q/ (8)

Power in phases and can be separated as

(9)

Where, the power components are

pp= vip= v2

p/ (10)

pq= viq= -v vq/ (11)

pp= vip= v2p/

(12)

pq= viq= vvq/ (13)

Therefore, the three phase active power can be

rewritten as

p3(t) =p+p+p0=pp +pq +pp +pq +

p0=pp +pp +p0(14)

Thus from equations (11) and (13)

pq +pq = 0

(15)

Thus,pp = axis instantaneous active power.

pp = axis instantaneous active power.pq = axis instantaneous reactive power.pq = axis instantaneous reactive power.

From above equations, it is observed that the

reactive power corresponds to the parts of

instantaneous power, which is dependent on the

instantaneous power q, in each independent

phase and vanishes when added (pq +pq = 0), in

a two phase (-) system[12].Instantaneous real power p, gives the net energy

per second being transported from source to load

and vice- versa at any time, which is dependentonly on the voltage and currents in phases and and has no zero sequence present.

5. Modeling of Control Strategy

Firstly, the three phase voltages and current are

transformed from a-b-c coordinates to the --0coordinates as shown in Fig.4. Then the real

power is calculated using - coordinates.

Fig. 4 MATLAB computation using Clarketransformation

The next step is to calculate the which iscomputed using above said theory as shown

below in Fig.5.

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Fig.5 Computation of

Next is the calculation of current injected into

the system as per algorithm. The current

computed in this way is the two coordinates.

This requires the transformation of two

coordinates (-) into the a-b-c coordinates asthe system will take three phase currents. This is

accomplished by using inverse Clarketransformation. Then this current is injected into

the power system with the help of pulse

generators as the IGBTs accepted the signals in

the form of pulses. The computation of current

in - coordinates and a-b-c coordinates isshown in Fig. 6 & 7 respectively.

Fig.6 Calculation of injection current

Fig.7 Inverse Clarke transformation

6. MATLAB/SIMULINK Based Power

System Model

A power system model is developed in the

Simulink in which the load connected to the

three phase source is the direct torque control

(DTC) Induction motor drive which keeps thetorque and flux, hence speed of the motor within

their tolerant bands by proper switching of the

transistors as shown in Fig.8. These transistors

are power electronic equipments which cause the

harmonics in the system and deviates the system

from sinusoidal currents and voltages. The

harmonics produced in the system should be

within the permissible limits otherwise the

system operation will become malfunctions

which results in the discontinuity of supply to

the consumers. In this model, two parallelfeeders are shown, one is connected to shunt

connected compensation device and the other is

left as it is. DSTATCOM is connected with six

pulse generators which provided gating signals

to six IGBT/Diode with a delay time.

Fig.8 MATLAB based Proposed Test model



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6.1 Parameters of the Test system

TABLEI

6.2 Results and Discussion

Fig. 9 Load current before compensation

Fig. 10 Load current after compensation

A non linear industrial drive is considered in the

proposed model and the distribution staticcompensator control is modeled in such a way

that the harmonics distortion in the current is

mitigated. This is clearly shown in Fig.11 & 12

below:

Fig.11 THD for Load current before compensation

Fig.12 THD for Load current after compensation

According to IEEE harmonics standards, for

distribution systems (120V to 69000V), the

Total Harmonics Distortion should be less than

5%. In this case while considering non linear

load as DTC induction motor drive, the

harmonics distortion is 5.70% which violates the

IEEE standards. After the implementation of

DSTATCOM at the point of common coupling,

The THD obtained is less than 5% i.e. 4.39%.

7. Conclusion

In this paper, model of DSTATCOM is

developed using Simulink in MATLAB. A

comprehensive control technique is simulated

which is based on the algebraic transformation

of the three phase voltages and currents in the a-

b-c coordinates to the --0 coordinates. Then,injection current is calculated as per algorithm

and the simulated results showed the

effectiveness of DSTATCOM (custom power

device) in mitigating the current harmonics.

Bansal* and Bhangu** 31


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America, pp. 01-50.[3] Arindam Ghosh and Gerard Ledwich, Load compensatingDSTATCOM in weak AC systems, IEEE transactions

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2278-1676 Vol.1, Issue 2, pp. 01-09, 2012.[10] Michael D. Stump, Gerald J. Keane and Frederick K.S.Leong, The role of custom power products in power

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About the Authors:

Mani Bansal was born at Ludhiana on 02 October, 1987. He obtained the B.Tech degree in

Electrical Engineering from DAV institute of Engineering & Technology, Jalandhar, Punjab, India in

2010. Currently pursuing M.Tech degree in Power Engineering from Guru Nanak Dev Engineering

College, Ludhiana, Punjab, India. His interest area includes power quality improvement, custom

power and robust control.

Navneet Singh Bhangu obtained B.E. degree in Electrical Engineering from Guru Nanak Dev

Engineering College, P.U., Chandigarh, India. He did his M.Tech in 2001. He has various

publications in National and International conferences/ Journals. His interest area includes Power

system, Energy management and reliability engineering.


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Reducing Harmonics Distortion in Distribution Network Against the Induction Motor Drive Non Linear Load