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Procedia Computer Science 47 ( 2015 ) 153 – 167

Available online at www.sciencedirect.com

1877-0509 © 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Peer-review under responsibility of organizing committee of the Graph Algorithms, High Performance Implementations and Applications (ICGHIA2014)doi: 10.1016/j.procs.2015.03.194

ScienceDirect

Simulation of Artificial Intelligent Controller based DVR for Power Quality Improvement

N. Srinivasa Raoa , Dr. A. Selwin Mich Priyadharsonb , Dr. J. Praveenc

a Research Scholar, School of Electrical, Vel Tech Rangarajan Dr. Sagunthala, R&D Institute of Science and Technology, Chennai, India.

bAssociate Professor, School of Electrical, Vel Tech Rangarajan Dr. Sagunthala R&D Institute of Science and Technology, Chennai, India.

c Professor& HOD, Department of EEE,GRIET, Hyderabad, India.

Abstract— This paper Presents Simulation study of Dynamic Voltage Restorer based on Photovoltaic system. A Photovoltaic based DVR is used to mitigate the problems of voltage sag and swell. The Maximum Power Point Tracking Algorithm and DC-DC converter is used to extract maximum power from the Photovoltaic system. A Hysteresis based Control strategy is adopted for switching the voltage source Inverter of DVR. Perturb and Observation method is used as MPPT algorithm. When the grid is in normal operation DVR works for reducing the problems of voltage sag and swell, when the grid fails DVR works as Uninterrupted power supply(UPS) The proposed system is simulated in MATLAB/SIMULINK and the simulation results show that the proposed PV based DVR can efficiently reduce the problems of Voltage sags and swells. © 2015 The Authors. Published by Elsevier B.V.

Peer-review under responsibility of organizing committee of the Graph Algorithms, High Performance Implementations and Applications (ICGHIA2014).

Keywords— Dvr, Sag, Swell, Pv cell, power quality.

I.INRODUCTION The rapid trend of industrialization of nations, increased interest in environmental issues led recently to explore the use of renewable forms such as solar energy. Photovoltaic (PV) generation is gaining increased importance as renewable source due to its advantages like absence of fuel cost, no noise and wear due to absence of moving parts and little maintenance etc. There is very small work done until now related to PV based Dynamic Voltage Restorer until now. sinusoidal voltage at the contracted magnitude and frequency. However, in practice power system

© 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Peer-review under responsibility of organizing committee of the Graph Algorithms, High Performance Implementations and Applications (ICGHIA2014)

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154 N. Srinivasa Rao et al. / Procedia Computer Science 47 ( 2015 ) 153 – 167

especially the distribution system, have numerous non linear loads, which are significantly affect the quality of power supply. As a result, the purity of waveform of supply lost. This ends up producing many power quality problems. To improve power quality, custom power devices are used. In 1995 the concept of custom power is first explained by Hingorani [1].

The thought of custom power (CP) identifies with the utilization of electronic controllers for power system network. There are number of custom power units which are given below, Distribution Statcom (DSTATCOM), Dynamic Voltage Restorer (DVR), Unified power quality conditioner (UPQC), Active Power Filters, Battery Systems (BESS), Distribution Series Capacitors (DSC), Surge Arresters (SA), Un-interruptible Power Supplies (UPS), Solid State Fault Current Limiter (SSFCL), Solid-State Transfer Switches (SSTS), and Static Electronic Tap Changers (SETC)[2]. Dynamic Voltage Restoration (DVR) is a method and apparatus used to sustain, or restore, an *Coresponding Author Email: [email protected] operational electric load during sags, or spikes, in voltage supply[2-4]. DVRs are a class of custom power devices for providing reliable distribution power quality. They employ a series of voltage boost technology using solid state switches for compensating sags/swells.

This paper presents PV based Dynamic voltage restorer for mitigating the problems of voltage sags and

swells. Perturb and observation based MPPT algorithm is used to extract maximum power from the PV system. A DC-DC converter is used to step up the voltage from PV system and fed to Voltage source inverter(VSI) of Dynamic voltage restorer. This papers is organized as follows, Section II represents the block diagram and working principle of PV based dynamic voltage restorer

II a) DYNAMIC VOLTAGE RESTORER

Dynamic voltage restorer is overall suited to secure susceptible or delicate load from short span voltage

dips and swells. Whenever a short circuit happens in a power system network, a sudden voltage dip will show on nearby feeders[5,6]. With a DVR introduced on a load feeder, the line voltage is restored to its normal level within the reaction time of a few milliseconds. Hence power interruption is avoided. The below figure 1 shows the typical DVR connected distributed system.

Fig. 1. Typical DVR-connected distribution system


In this paper the storage unit in figure 1 is replaced with Photovoltaic source and MPPT controlled DC/DC

converter is employed to extract maximum Voltage from PV system. The block diagram of the Proposed DVR is shown below figure 2.

Fig 2: Proposed PV based DVR

b)PV CELL MODELLING AND MPPT

A PV cell is the basic structural unit of the PV module that generates current carriers when sunlight falls on it[11]. The power generated by these PV cell is very small. To increase the output power the PV cells are connected in series or parallel to form PV module[12]. The equivalent circuit of the PV cell is shown in fig: 2.

Fig.3 Equivalent circuit of the PV cell.

The main characteristics of the PV cell are given by:


Where, I and V- Cell output current and voltage; Io- Cell reverse saturation current; T- Cell temperature in Celsius; K- Boltzmann’s constant; q- Electronic charge; Ki- short circuit current/temperature coefficient; G- Solar radiation in W/m2; Gn- nominal solar radiation in W/m2; Eg- energy gap of silicon; Io,n- nominal saturation current; Tn- nominal temperature in Celsius; Rs- series resistance; Rsh- shunt resistance; α- ideality factor between 1.0 to 1.5; Ipv- light generated current; The I-V characteristic of a PV module shown in Fig.4 is highly non-linear in nature. This characteristics drastically changes with respect to changes in the solar radiation and temperature. Whereas the solar radiation mainly affects the output current, the temperature affects the terminal voltage. The I-V characteristics of the PV module under varying solar


radiation at temperature T=250 is shown below[12].The data of the PV system used in this are taken from msx60i type of

panels.

Fig. 4 Current versus voltage at constant cell temperature T=250,irradiation G=100,250,500,750,1000w/m2 Fig.5 shows the I-V characteristics of the PV module under varying cell temperature at constant solar radiation (1000 W/m2).

Fig.5 Current versus voltage at constant solar radiation G = 1000 W/m2,t=25,50,75,100deg cent

MAXIMUM POWER POINT TRACKING (MPPT) The PV array will be having only one point on its current and voltage characteristics, and that point is called as the Maximum Power Point. The systems which are connected directly will not operate at MPP. So significant amount of enegy is wasted because of this problem. But systems which have a DC-DC converter as a controller to match PV array to Pump set will definitely act at MPP[8-10]. Several MPPT strategies have been proposed in the past like

1) Voltage Reference MPPT 2) Perturb and Observe(P&O) MPPT 3) Incremental Conductance(INC) MPPT


In this paper Perturb and Observe type of MPPT is used for calculating the Duty Cycle for the DC-DC converter. The flowchart of the MPPT algorithm is shown below in fig 6. .

Fig.6 Flow chart of P&O MPPT Algorithm The below figure 7 shows the working behavior of P&O based MPPT method.

Fig.7 MPPT Tracking

When compared with the other MPPT algorithms P&O algorithm is simpler to implement and it does not need much knowledge of the previous PV array and details about irradiance and temperature. There are two methods of P&O algorithm

a) Reference Voltage Perturbation b) Direct Duty ratio Perturbation

The block diagrams of each method are discussed below fig 8 and fig 9. In the reference voltage control taking the inputs of voltage and current of the PV system, then implementing to MPPT algorithm, the reference PV voltage


is found out. The obtained reference voltage is compared with the actual PV voltage and error is given to PI controller to calculate the duty cycle for DC-DC converter.

Fig.8 Block Diagram of Reference Voltage based MPPT

In the Direct Duty Ratio control method the voltage and current inputs from the PV array are taken and the flowchart shown is implemented to calculate the duty cycle for DC-DC converter. When compared with the reference voltage method duty cycle method have several advantages like better stability characteristics and good energy utilization performance.

Fig.9 Block Diagram of Direct Duty Ratio based MPPT

III Control of DVR The aim of the control scheme is to maintain constant voltage magnitude at the sensitive load under voltage disturbance condition. The proposed control scheme based on comparison of actual supply voltage and desired load voltage. The error is determined dynamically based on difference between desired and measured value. The control system employs abc to dqo transformation to dq0 voltages. During normal condition and symmetrical condition, the voltage will be constant and d-voltage is unity in p.u. and q-voltage is zero in p.u. but during the abnormal conditions it varies. After comparison d-voltage and qvoltage with the desired voltage error d and error q is gereted. These error component is converted into abc component using dq0 to abc transformation. Phase Locked Loop

PLL) is used to generate unit sinusoidal wave in phase with main voltage. This abc components are given to generate three phase Pulses using Pulse Width Modulation(PWM)technique. Proposed control technique block is shown in figure10.


Fig 10: Control Diagram of DVR

V.MATLAB/SIMULINK VALIDATION

The below figure 11 shows the simulation circuit of the PV based Dynamic voltage restorer for compensating sags and swells.

Fig.11Matlab/Simulink circuit of proposed DVR


The below figure 12 shows the DVR circuit diagram which consists of PV system, MPPT controller, DC/DC converter, Inverter and

Filter. Fig.12 Matlab/Simulation Circuit Of proposed DVR The below figure 13 shows the source voltage waveform where there is a sag occurred from the time 1.5 sec to 1.8 sec.

Fig.13Supply voltage waveform during sag condition


The below figure 14 shows the output voltage waveform. Eventhough as shown in above figure there is a sag occurred in source voltage, the output voltage waveform is constant in magnitude because DVR is injecting the voltage.

Fig.14 Output voltage waveform during Sag

The figure 15 below shows the injected voltage of the DVR. It shows that when a sag that is occurred at 1.5 sec to 1.8 sec DVR is acted at that particular time and is injecting voltage into the line through transformers.

Fig.15 DVR injected voltage during sag condition


Case II:SWELL The below figure 16 shows the source voltage waveform when there is a voltage swell during the time period of 0.5 sec to 0.8 sec.

Fig.16 Supply Voltage during Swell

The below figure 17 shows the output voltage waveform which shows that it is constant throughout the time even there is a swell in the source voltage.

Fig.17 Output voltage waveform during Swell


The below figure 18 shows the DVR injected voltage during the time 0.5 sec to 0.8 sec when there is a swell occurred in the supply voltage.

Fig.18 DVR Injected Voltage Waveform during swell Case III OPERATING UNDER FUZZY CONTROLLER The below figure 19 shows the source voltage waveform where there is a sag occurred from the time 0.06 sec to 0.14 sec.

Fig.19 Supply voltage waveform during sag condition


The figure 20 below shows the injected voltage of the DVR. It shows that when a sag that is occurred at 0.06 sec to 0.14 sec Fuzzy-DVR is acted at that particular time and is injecting voltage into the line through transformers.

Fig.20 DVR injected voltage during sag condition The below figure 21 shows the output voltage waveform. Eventhough as shown in above figure there is a sag occurred in source voltage, the output voltage waveform is constant in magnitude because Fuzzy-DVR is injecting the voltage.

Fig.21 Output voltage waveform during Sag


CONCLUSION

This work shows how a conventional DC storage system can be replaced with Photovoltaic system and can be used as dc source for DVR in mitigating voltage sags and swells. The Transformation based control strategy is employed to control the Inverter of DVR while MPPT technique is used to control the DC/DC converter. The Proposed Fuzzy-DVR successfully compensated the problems of voltage sags and swells as shown in the above simulation results. This Proposed DVR can also suppress the problems of unbalanced sags and swells.

REFERENCES [1] J. A. Martinez and J. Martin-Arnedo, “Voltage sag studies in distribution networks- part II: Voltage sag assessment,”IEEE Trans. PowerDel., vol. 21, no. 3, pp. 1679–1688, Jul. 2006. [2] J. A. Martinez and J. M. Arnedo, “Voltage sag studies in distribution networks- part I: System modeling,”IEEE Trans. Power Del., vol. 21, no. 3, pp. 338–345, Jul. 2006. [3] P. Hcine and M. Khronen, “Voltage sag distribution caused by power system faults,”IEEE Trans. Power Syst., vol. 18, no. 4 , pp. 1367–1373, Nov. 2003. [4] S. S. Choi, B. H. Li, and D. M. Vilathgamuwa, “Dynamic voltage restoration with minimum energy injection,”IEEE Trans. Power Syst., vol. 15, no. 1, pp. 51–57, Feb. 2000. [5] C. Fitzer, M. Barnes, and P. Green, “Voltage sag detection technique for a dynamic voltage restore,”IEEE Trans. Ind. Appl., vol. 2, no. 1, pp. 203–212, Jan./Feb. 2004. [6] C. Benachaiba and B. Ferdi, “Voltage quality improvement using DVR,”Electt. Power Qual. Utilisation, Journal, vol. XIV, no. 1, 2008. [7] D. M. Vilathgamuwa, H. M. Wijekoon, and S. S. Choi, “A novel technique to compensate voltage sags in multiline distribution system-the interline dynamic voltage restorer,”IEEE Trans. Ind. Electron., vol. 53, no. 5, pp. 1603–1611, Oct. 2006. [8] J. G. Nielsen, M. Newman, H. Nielsen, and F. Blaabjerg, “Control and testing of a dynamic voltage restorer (DVR) at medium voltage level,” IEEE Trans. Power Electron., vol. 19, no. 3, pp. 806–813, May 2004. [9] PNK Sreelatha, Dr J Praveen, Dr V Kamaraju,” Voltage Sag Compensation with DVR for Different types of faults at a remote place on a remote feeder”, accepted for presentation at Eight Control Instrumentation System International Conference CISCON-2011, Modeling and Simulation in Engineering Applications , 3-6th November, Manipal Institute of Technology, Manipal, Karnataka

[10] P.N.K Sreelatha, J.Praveen, V.Kamaraju, ‘Effect of Unsymmetrical faults on Distribution lines with Different Line X/R ratios and Voltage Restoration using DVR with Space Vector Control’ published in the proceedings of International Conference on Computing, Electronics and Electrical Technologies-ICCEET-2012 held on 21-22 March,2012 organized by Noorul Islam Centre for Higher Education, Kumaracoil, Thuckalay, Tamilnadu. pp.14

[11] Dr J Praveen, “Direct Power Control Strategy in the DVR for enhancing power quality” presented at a National Conference on Electrical Power Engineering and Industrial Drives during May 18-19,2012 Organized by Sreenidhi Institute Science and Technology (Autonomous), Hyderabad.

[12] P.N.K.Sreelatha, J.Praveen, V.Kamaraju “Voltage sags in Distribution Systems with Induction motor loads fed by Power converters and voltage mitigation using DVR and D-STATCOM” published in International Journal of Electrical Engineering (IJEE) journal ISSN 0974-2158 Volume 5, Number 7 (2012), pp. 889-901.

[13] Y. W. Li, D. M. Vilathgamuwa, P. C. Loh, and F. Blaabjerg, “A dualfunctional medium voltage level DVR to limit downstream fault currents,” IEEE Trans. Power Electron., vol. 22, no. 4, pp. 1330–1340, Jul. 2007.


AUTHORS PROFILE

N.Srinivasa Rao did his M.tech at J.B.I.E.T Hyderabad with specialization of Electrical Power systems. He Received Gold medal for his academic Excellence. He is currently Research Scholar and present working as Associate Professor in EEE department at Narasimha Reddy Engineering College, Hyderabad. His research interests include Power Systems, Power Quality, Power Electronics.

Dr. A. Selwin Mich Priyadharson obtained his Diploma in Instrumentation & Control Engineering from Government Polytechnic, Udhagamandalam, India. Graduated B.E (Instrumentation & Control Engineering) affiliated to M.K University and completed his M.E (Control & Instrumentation Engineering) affiliated to Anna University, from Arulmigu Kalasalingam College of Engineering Srivilliputhur, India. He has obtained his Ph.D degree in Electronics Engineering from Sathyabama University, Chennai. Currently he is working as Associate Professor in School of Electrical, Vel Tech Rangarajan Dr. Sagunthala R&D Institute of Science and Technology, Avadi, Chennai, Tamil Nadu, India. His area of interest

encompasses automation, adaptive, predictive, neural networks, fuzzy logic, expert systems, networking, modeling and simulation.

Dr. J. Praveen completed his B. Tech (EEE) from Osmania University College of Engineering, Hyderabad In 1998, M. Tech (ES) from JNTU, Hyderabad, Andhra Pradesh in 2000 and completed Ph.D. (Power Electronic) from Osmania University, Hyderabad in 2007. He has 15 years of teaching experience. He is presently working as Professor and HOD, Gokaraju Rangaraju Institute of Engineering and Technology, Hyderabad. He has published more than 65 papers in International and National Conferences and Journals. His research interests are Power Electronics and Power Quality

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