harmonic mitigation and reactive compensation by … · inverter statcom (mli -dstatcom ). a three...

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,

[email protected]

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

4875

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


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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


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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


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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]


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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


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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


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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.

REFERENCES

[1] Ucar Mehmet, Ozdemir Engin, “Control of a 3-phase 4 leg active power filter under

non-ideal mains voltage condition,” Electr Power Syst Res 2008:58–73.

[2] Phipps JK, Nelson JP, Sen PK., “Power quality and harmonic distortion on

distribution systems,” IEEE Trans Ind Appl 1994;30:476-84.

[3] Lee TL, Hu SH, “Discrete frequency-tuning active filter to suppress harmonic

resonances of closed-loop distribution power systems,” IEEE Trans Power Electr

2011;26(1):137–48.

[4] Ghosh A, Ledwich. G., Power Quality Enhancement Using Custom Power Devices,

London, U.K.: Kluwer;2002.

[5] Lee Tzung-Lin, hushang-Hung, chanyu-Hung., “DSTATCOM with positive-

sequence admittance and negative-sequence conductance to mitigate voltage

fluctuations in high-level penetration of distributed generation systems,” IEEE

Trans. Ind. Electron. 2013; 60(4):1417–28.

[6] P.Avirajamanjula, P.Palanivel, “Normalized Least Mean Square based selective

Current Harmonic Elimination in Voltage Source Inverters”, International


4884

Review on Modelling and Simulations (IREMOS),Vol.7 No.3, June 2014, pp-394-

400.

[7] Jing X, Cheng L., “An optimal-PID control algorithm for training feed forward

neural networks,” IEEE Trans. Ind. Electron2013;60(6):2273- 83.

[8] P. Rao, M.L. Crow, Z. Yang, “STATCOM control for system voltage control

applications,” IEEE Trans. Power Delivery 15 (4) (2000) 1311- 1317.

[9] P.S. Sensarma, K.R. Padiyar, V. Ramanarayanan, “Analysis and performance

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[10] Benysek Grzegorz, Pasko Marian., Power theories for improved power quality,

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[11] Benhabib MC, Saadate S., “New control approach for four-wire active power filter

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73(3):353-62.

[12] P.Avirajamanjula, P.Palanivel, “Corroboration of Normalized Least Mean Square

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Adaptive Selective Current Harmonic Elimination in Voltage Source Inverter Using

DSPProcessor”, International Journal of Power Electronics and Drives

Systems,Vol.6, No.1, March 2015, pp-178-184.


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harmonic mitigation and reactive compensation by … · inverter statcom (mli -dstatcom ). a three...

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