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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)
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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.
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REFERENCES
[1] Bhim Singh and Jitendra Solanki, A comparison of controlalgorithms for DSTATCOM, IEEE Transactions on
Industrial Electronics, Vol.56, No.7, July 2009.
[2] Mahesh M. Swamy, Understanding input harmonics andtechniques to mitigate them, Yasakawa Electric
America, pp. 01-50.[3] Arindam Ghosh and Gerard Ledwich, Load compensatingDSTATCOM in weak AC systems, IEEE transactions
on Power Delivery, Vol. 18, No. 4, October 2003.[4] C. Sankaran, Power quality, CRC Press, ISBN- 0-8493-1040-7, 2002.[5] S.Suresh, N.Devarajan, M.Geetha and V. Rajasekaran, Investigation on DSTATCOM operation for power quality
improvement in a three phase three wire distribution systemwith a new control strategy, Control theoryand
informatics, ISSN 2224-5774, Vol 1, No.2, pp. 06-13,
2011.[6] Satyaveer Gupt, Ankit Dixit, Nikhil Mishra and S.P. Singh,Custompower devices for power quality improvement:
a review, International Journal of Research in Engineeringand Applied Sciences, ISSN- 2249-3905, Vol.2, Issue2,
pp.1646-1659, 2012.[7] Y. Hu, member IEEE, Zhe Chen, senior member IEEE andH.Mckenzie, Volatge source converters in distributed
generation Systems, DRPT 2008, Nanjing China.[8] Rodda Shobha Rani and B. Jyothi, VSC basedDSTATCOM & pulse-width modulation for power quality
improvement, International Journal of EngineeringTrends and Technology- Vol.2, Issue2, pp. 38-41, 2011.[9] Pradeep Kumar, Niranjan Kumar and A.K.Akella, Reviewof DSTATCOM for stability analysis,IOSR Journal of
Electrical and Electronics Engineering (IOSRJEEE), ISSN:
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
quality improvement at industrial facilities, IEEEcatalogue no. 98EX137, pp. 507-517,1998.[11] R. Heera Singh, N. Ravi, H.O. Gupta, Impacts of custompower device on the dynamic performance of power
network,.[12] Moinuddin K Syed and DR. BV Sanker Ram, Instantaneous power theory based active power filter: aMATLAB/ SIMULINK approach, Journal of Theoretical andApplied Information Technology, 2005 - 2008 JATIT.
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.
32 Bansal* and Bhangu**
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