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HARMONIC MITIGATION AND REACTIVE COMPENSATION
BY SRF/MCPWM CONTROL OF MLI-STATCOM IN POWER
DISTRIBUTION NETWORK 1M.Sathiskumar, 2K.Kannadasan, P. Avirajamanjula3
1 Assistant Professor, Department of EEE, PMIST, Vallam, India,
2 PG scholar, Department of EEE, PMIST, Vallam, India, [email protected]
3Professor, Dept of EEE, PRIST Deemed University, Thanjavor
Abstract:
Electric Power Quality is term which has captured increasing attention in Power
Engineering in the recent years. Usually Power quality refers to maintaining a
sinusoidal waveform of bus voltages at rated voltage and frequency. But due to
Nonlinear loads, the harmonics and distortion current create reactive power problems.
The harmonic voltage drops across the network impedance that affects power factor.
This paper discus with a five-level diode clamped Multilevel Inverter based
Distribution STATCOM (MLI-DSTATCOM) with Synchronous Reference Frame
based control. The mathematical modelling of the control structure to the D-
STATCOM, Nonlinear load and the modelling of 5 level Cascaded H Bridge Inverter
with Phase shifted PWM technique is presented It is proved that the CHB based
multilevel inverter mitigates the harmonics in the source current at distribution
system. These harmonics are mitigating the Power Quality Enhancement in
distributed system. Here the device called STATCOM is one of the FACTS Devices
which can be used to mitigate the harmonics and reactive power compensation. In this
paper we implement with SRF based STATCOM control. SRF theory is implemented
for the generation of controlling reference current signals for controller of STATCOM.
The Matlab\Simulink based model is developed and simulation results are found. The
hardware is implemented and the results were compared with the simulated outputs.
Keyword: Nonlinear loads, Harmonics, Distortion current, MLI-D-STATCOM, SRF,
FACTS.
1.Introduction:
International Journal of Pure and Applied MathematicsVolume 118 No. 20 2018, 4875-4886ISSN: 1314-3395 (on-line version)url: http://www.ijpam.euSpecial Issue ijpam.eu
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Nonlinear loads such as diode/thyristor, rectifier, Switched Mode Power Supplies
(SMPS), Welding Equipments, incandescent light is degrading power quality in
transmission and distribution grid system. These nonlinear loads result in harmonic
or distortion current and create reactive power problems. These harmonics induce
malfunctions in sensitive equipments, overvoltage by resonance, increased heating in
the conductors and harmonic voltage drop across the network impedance that affects
power factor. As technology advances, nonlinear loads are multiplying in numbers and
the resulting complexity throws tremendous challenge to the quality of power supply
[1]. The levels of harmonics are on the rise and polluting more and more of the
electrical network. Because of the strict requirement of power quality at the input a.c
mains, Various harmonic standards and engineering recommendation are there such
as IEC 1000-3-2, IEEE 519(USA), AS2779, ER G(5/4) (UK) etc. To comply with these
harmonic standards installations utilizing power electronic and nonlinear loads often
use one of the growing numbers of harmonic mitigation techniques. Traditionally
harmonics was suppressed by passive filters. This conventional passive filter consists
of R, L and C components. It has many disadvantages like filter size requirement
becoming bulky for low frequency components, ageing, tuning problems and could
resonate with supply impedance.
Today these Problems have even higher impact on reliable and secure power
supply in the world of Globalization and Privatization of electrical systems and energy
transfer. The development in fast and reliable semiconductors devices (GTO and
IGBT) allowed new power electronic Configurations to be introduced to the tasks of
power Transmission and load flow control. [2] The FACTS devices offer a fast and
reliable control over the transmission parameters, i.e. Voltage, line impedance, and
phase angle between the sending end voltage and receiving end voltage. On the other
hand, the custom power is for low voltage distribution, and improving the poor quality
and reliability of supply affecting sensitive loads. Custom power devices are very
similar to the FACTS. Most widely known custom power devices are DSTATCOM,
UPQC, DVR among them DSTATCOM is very well known and can provide cost
effective solution for the harmonic mitigation, compensation of reactive power and
unbalance loading in distribution system. The performance of the DSTATCOM
depends on the control algorithm i.e. the extraction of the current components. For
this purpose, there are many control schemes, which are reported in the literature and
some of these are instantaneous reactive power (IRP) theory, instantaneous
compensation, instantaneous symmetrical components, synchronous reference frame
(SRF) theory, computation based on per phase basis, and scheme based on neural
network. Among these control schemes, instantaneous reactive power theory and
synchronous rotating reference frame are most widely used [3]. This technique would
also Compensate for reactive power requirement thereby increasing the transmittable
power. The paper proposes a five level cascaded H-bridge Multi Level Inverter based
Distribution STATCOM (MLI-DSTATCOM) with MCPWM Control. A three-phase
system with nonlinear load is designed and simulated in Matlab/Simulink for
performance analysis of proposed MLI-DSTATCOM. The results provide evidence of
restricting harmonic currents at load end and prevent from entering into source
International Journal of Pure and Applied Mathematics Special Issue
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effectively. The performance of a five-level diode-clamped Multi Level Inverter based
Distribution STATCOM (MLI-DSTATCOM) with Synchronous reference frame
control is also compared.
2. Literature review
2.1 Harmonics mitigation techniques:
In Dec 1996 H. Akagi, discussed about “New trends in active filters for power
conditioning. In 1999 Bhim Singh, K. Al-Haddad and et al discussed about A Review
of Active Filters for Power Quality Improvement,” In 2010 C. Sciences, M. R. Amer,
discussed about Drives and Energy Systems. In March 2016 G.S. Mahesh, K.
Hemachandra Reddy and et al discussed about Harmonics Mitigation using
DSTATCOM through a Current Control technique. In September 2016 Venkata Reddy
Kota and et al analyzed about various harmonics mitigation methods in power
systems[4]
2.2 Synchronous Reference Frame:
In 2014 Bhasha Shaik Mohammad and B. Lalitha spoke about “Comparison of Control
Algorithms for Shunt Active Filter for Harmonic Mitigation,” In 2015 S. M.
Shembekar and K. L. Deshmukh, analyzed about “Analysis of Reference Current
Generation for Shunt Active Power Filter Using SRF Algorithm to Compensate
Harmonic Current,” In 2015 C. Sciences, M. R. Amer, et al discussed about “A Simple
Algorithm for SRF Theory with Three Phase Shunt Active Power Filter,” [5] . In 2016
T. Trivedi, C. Gupta et al spoke about “Energy Procedia Implementation of
Synchronous Reference Frame Theory based Shunt Active Power Filter using DSP
Controller,”
2.3 MLI Based STATCOM in power distribution Network:
In 2008 M. G. Molina and P. E. Mercado, spokes about “Dynamic Modeling and Control
Design of DSTATCOM with Ultra-Capacitor Energy Storage for Power Quality
Improvements”, for achieving efficient power transmission. In 2011 S. Chanda, B. Das,
discussed about “Identification of weak buses in a power network using novel voltage
stability indicator in radial distribution System”, for distribution systems
improvement. In 2012 S. M. S. Hussain, N. Visali, discussed about “Identification of
weak buses using Voltage Stability Indicator and its voltage profile improvement by
using DSTATCOM in radial distribution systems”, In 2015 P.Avirajamanjula,
P.Palanivel, analyzed about “Investigation of Line Current Harmonics in Cascaded
Multi-Level Inverter Based Induction Motor Drive and an Adaptive on-line Selective
Current Harmonic Elimination Algorithm”, to improve the MLI performance.[6]
3.Existing System:
The nonlinear loads result in harmonic or distortion current and create reactive power
problems. These harmonics induce malfunctions in sensitive equipments, overvoltage
by resonance, increased heating in the conductors and harmonic voltage drop across
International Journal of Pure and Applied Mathematics Special Issue
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the network impedance that affects power factor. As technology advances, nonlinear
loads are multiplying in numbers and the resulting complexity throws tremendous
challenge to the quality of power supply. The levels of harmonics are on the rise and
polluting more and more of the electrical network.
Traditionally harmonics was suppressed by passive filters. This conventional
passive filter consists of R, L and C components. Even though It can handle large
voltage, current and power and do not need additional DC power supply, it has many
disadvantages.
• Resonate with supply impedance
• There is no isolation b/w input and output.
• These circuits cannot provide any gain.
• There is always some loss of signal, it can be in the passband.
• Circuit becomes bulky if inductors are used.
• There is no clear demarcation between Passband and stopband but actually it
(Passband & Stopband) get mixed up.
• In this frequency response is not sharp as no sudden change in the output
when switching from passband to stopband.
• Source loading can take place.
Active Power Filters give superior performance when compared to Conventional
Passive filter, but still an improvement is required. This Project make use of Cascaded
H Bridge Inverter Based DSTATCOM, instead of Diode Clamped Inverter Based
DSTATCOM, Since Cascaded H Bridge inverter require very minimum components
and give better performance in Harmonic Mitigation. A Study of Both type inverter
based STATCOM is done.
4. PROPOSED SYSTEM:
This project present novel harmonic mitigation techniques in Power
Distribution Network. i.e., MCPWM Technique and by synchronous reference frame-
based control of MLI-STATCOM. This technique would also Compensate for reactive
power requirement thereby increasing the transmittable power. This paper proposes
a five level Cascaded H-Bridge Multi Level Inverter based Distribution STATCOM
(MLI-DSTATCOM) with MCPWM Control. A comparison of this is made with a
synchronous reference frame-based control of five level Diode Clamped Multi Level
Inverter STATCOM (MLI-DSTATCOM). A three-phase system with nonlinear load is
designed and simulated in Matlab/Simulink for performance analysis of proposed
MLI-DSTATCOM. The results provide evidence of restricting harmonic currents at
load end and prevent from entering into source effectively.
Custom Powered Devices (CPD) later introduced gave improved performance
over the passive filters and are very useful for maintaining the present power quality
levels. To suppress harmonics and other power quality issues related to current,
Distribution Static Compensator (DSTATCOM) connected across load is widely
researched and proved to be effective. Other FACTS devices also have been researched
widely to improve power quality, flexibility, controllability and stability. Reactive
power control or compensation is of importance for stability, control and quality in
International Journal of Pure and Applied Mathematics Special Issue
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power system. DSTATCOM also have a significant role to play for reactive power
control in distribution network. Performance of any CPDs is greatly depending on the
gating pulses and the control algorithm to generate estimated reference currents. Few
control algorithms mostly employed are
• Feed forward training
• SRF theory
• Instantaneous active and reactive power theory,
• Lyapunov-function control and the
• Non-linear control technique etc.
Performance of MLI-DSTATCOM is analyzed in this paper with nonlinear load. With
the proposed MCPWM and SRF control methods, load currents, source currents and
source voltages are measured. Total Harmonic Distortion (THD) of supply currents
with five-level MLI-DSTATCOM is developed and analyzed in Matlab/Simulink
software. This study has been expanded to active and reactive power flow analysis.
5.1. CONTROL TECHNIQUES.
5.1.1 SYNCHRONOUS REFERENCE FRAME CONTROL
Synchronous Reference Frame Control is one of the efficient controls to
suppress voltage and current harmonics. It refers d-q technique, in which
transformations and its inverse transformations of a-b-c to d-q-0 are used. The basic
SRF Control technique to generate reference currents from nonlinear
balanced/unbalanced load is depicted in Fig. 5.1. The load currents of abc coordinates
(I Labc ) are transformed into d-q-0 coordinates with the help of modified PLL according
to the equation (1). These d-q-0 coordinates comprises of an oscillatory component
(I~oSd and I~oSq ) and averaged component ( I~ASd and I~ASq ) resulting to oscillatory in
nature. In order to avoid oscillatory response and maintain only averaged components
of d-q-0 coordinates, a 2nd ordered Butterworth LPF is used. These averaged
components are stable in nature and are referred to as source current averaged
component ( I~SdL).[6]-[7]
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Fig. 2. Simulink Model of Proposed System
Hard-ware module:
Fig.2. Shunt Controller using SRF
International Journal of Pure and Applied Mathematics Special Issue
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For proper compensation, voltage of DC link capacitor must be kept constant at rated
value (i.e. 1200V in this case). The PI controller or fuzzy controller is therefore used
to compensate the loss component of active current (IDloss ). Using Ziegler-Nichols’
method, proportional gain (Kp) and Integral gain (Ki) are estimated and are fine tuned
to values of 0.003 and 0.0025. The d-axis component of supply current including the
active power loss component for capacitor voltage balancing can be represented by
Considering these currents as d-axis component, d-q-0 coordinates are transformed
into a-b-c coordinates with reference to equation (3) and are taken as reference supply
currents.[8]
These reference currents ( IrefSa , IrefSb and IrefSc ) are compared with load currents ( ILa , ILb and ILc ) to generate DSTATCOM reference currents iShabc_ref . The currents of the
DSTATCOM are maintained at reference values using Hysteresis current controller.
The hysteresis current controller is operated with a lower band 0.25A and higher band
of 0.5A to generate switching pulses to a five level diode clamped MLI-
DSTATCOM.[9]-[11]
International Journal of Pure and Applied Mathematics Special Issue
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TABLE I. Comparison of Phase Shifted and Level Shifted Modulation.
6.RESULTS AND DISCUSSIONS:
Fig. 6.6 Output of Multi Level Inverter (Five Level) STATCOM
International Journal of Pure and Applied Mathematics Special Issue
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Fig. 6.7. THD- 26.37% With non linear load with out DSTATCOM
Fig. 6.11 THD- 5.32% With non linear load with Diode Clamped MLI Statcom
7.CONCLUSION
International Journal of Pure and Applied Mathematics Special Issue
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The design and Analysis of the DSTATCOM has been presented using
MATLAB/SIMULINK software to test its efficacy in mitigating harmonics and
Reactive Compensation. Multi level Inverters have been employed for DSTATCOM to
reduce harmonics. Operating conditions like fault switching are analyzed and tested.
The DSTATCOM presented has shown great performance in alleviating the
harmonics. It can be deduced from the results obtained that MLI DSTATCOM
improves power quality and mitigates harmonics.
In this paper, Multi Carrier Pulse Width Controlled Cascaded H-Bridge Five level
Inverter and Synchronous Reference Frame Controlled Diode Clamped Five level
Inverter based DSTATCOMs have been modelled and simulated with the objective of
mitigating harmonics occurring due to Non linear loads at power distribution system.
The use MLI in the custom power applications which has not been the focus of many
researchers for a long time due various reasons is explored through this paper. From
the simulation results of this model, it is learnt that the harmonics at the distribution
level voltage under load perturbation has been successfully mitigated by MLI based
DSTATCOM system. This paper will pave the way for encouraging the application of
the MLI topology in other types of custom power devices for solving power quality
problems. Some examples of the possible power quality problems where MLI topology
[12] can replace the VSC include voltage swells, unbalance, harmonics and power
factor correction.
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