 Open Access
 Total Downloads : 826
 Authors : Shahab Uddin Baqar, Mrs Jayanti Choudhary
 Paper ID : IJERTV2IS90378
 Volume & Issue : Volume 02, Issue 09 (September 2013)
 Published (First Online): 14092013
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
Power Quality Improvment by UPQC Using ANN Controller
Shahab Uddin Baqar
Mtech Electrical Engineering National Institute Of Technology Patna
Patna, India
Mrs Jayanti choudhary
Assistant Professor Electrical Engineering National Instate Of Technology Patna Patna, India
AbstractOne of the major concerns in electricity industry today is power quality. It becomes especially important with the introduction of advanced and complicated devices, whose performance is very sensitive to the quality of power supply. The electronic devices are very sensitive to disturbances and thus industrial loads become less tolerant to power quality problems such as voltage dips, voltage sags, voltage flickers, harmonics and load unbalance etc. At present, a wide range of very flexible controllers, which capitalize on newly available power electronics components, are emerging for custom power applications. Among these, the distribution static compensator, dynamic voltage restorer and unified power quality conditioner which is based on the VSC principle are used for power quality improvement. In this project, Neural Network controller with reference signal generation method is designed for UPQC and compared its performance with proportional integral based controller. This is used to compensate current and voltage quality problems of sensitive loads. The results are analyzed and presented using matlab/simulink software.
KeywordsUPQC, Shunt APF, Series APF, PCC, Harmonics, ANN,

INTRODUCTION (Heading 1)
Unified power quality control was widely studied by many researchers as an eventual method to improve power quality of electrical distribution system [13]. The function
of unified power quality conditioner is to compensate supply voltage flicker/imbalance, reactive power, negativesequence current, and harmonics. In other words, the UPQC has the capability of improving power quality at the point of installation on power distribution systems or industrial power systems. Therefore, the UPQC is expected to be one of the most powerful solutions to large capacity loads sensitive to supply voltage flicker/imbalance [2]. The UPQC consisting of the combination of a series active power filter (APF) and shunt APF can also compensate the voltage interruption if it has some energy storage or battery in the dc link [3].
The shunt APF is usually connected across the loads to compensate for all currentrelated problems such as the reactive power compensation, power factor improvement, current harmonic compensation, and load unbalance compensation [12], whereas the series APF is connected in
a series with the line through series transformers. It acts as controlled voltage source and can compensate all voltage related problems, such as voltage harmonics, voltage sag, voltage swell, flicker, etc.follow.

UPQC CONTROL ALGORITHM
The UPQC consists of two voltage source inverters connected back to back with each other sharing a common dc link. One inverter is controlled as a variable voltage source in the series APF, and the other as a variable current source in the shunt APF. Fig. 1 shows a basic system configuration of a general UPQC consisting of the combination of a series APF and shunt APF. The main aim of the series APF is harmonic isolation between load and supply; it has the capability of voltage flicker/ imbalance compensation as well as voltage regulation and harmonic compensation at the utilityconsumer PCC. The shunt APF is used to absorb current harmonics, compensate for reactive power and negativesequence current, and regulate the dclink voltage between both APFs.
Fig 1:Unified Power Quality Conditioner

Reference Voltage Signal Generation for Series APF
The function of the series APF is to compensate the voltage disturbance in the source side, which is due to the fault in the distribution line at the PCC. The series APF control algorithm calculates the reference value to be injected by the series APF transformers, comparing the positivesequence component with the load side line voltages. The proposed series APF reference voltage signal generation algorithm is shown in Fig. 3. In equation (1), supply voltages vSabc are transformed to dq0 coordinates.
The function of the series APF is to compensate the voltage disturbance in the source side, which is due to fault in the distribution line al the point of coupling. The series APF control algorithm calculates the reference value to be injected by the series APF transformers, comparing the positive sequence component with the load side line voltages. In equation (3.1), supply voltages VSabc are transformed to dqO coordinate.
1
The voltage in d axes (Vsd) given in (2) consists of average and oscillating components of source voltages ( Vsd and V Sd ).
The average voltage VSd is calculated by using second order LPF (low pass filter).
2
The load side reference voltages v*Labc are calculated as given in equation (3). The switching signals are assessed by comparing reference voltages ( v*Labc ) and the load voltages ( vLabc ) and via sinusoidal PWM controller.
.3
These produced threephase load reference voltages are compared with load line voltages and errors are then processed by sinusoidal PWM controller to generate the required switching signals for series APF IGBT switches.
Fig: series APF voltage generation and shunt APF current signal generation

Reference Current Signal Generation for Shunt APF
. The above figure shows the control diagram of shunt active filter. The shunt active filter compensates the current harmonics and reactive power generated by the nonlinear load. The instantaneous active power (pq) theory is used to control of shunt APF in real time. In this theory, the instantaneous threephase currents and voltages are transformed to apO coordinates. The instantaneous three phase current and voltages are transformed to –0 coordinates as shown in the equation (4) and (5).
.4 ..5
The source side instantaneous real and imaginary power components are calculated by using source currents and phase neutral voltages as given in (6). The instantaneous real and imaginary powers include both oscillating and average components as shown in (7). Average components of p and q consist of positive sequence components ( p and q ) of source current. The oscillating components (p and q ) of p and q include harmonic and negative sequence components of source currents. In order to reduce neutral current, p0 is calculated by using average and oscillating components of imaginary power and oscillating component of the real power; as given in (8) if both harmonic and reactive power compensation is required. is* , is* and is0* are the reference currents of shunt APF in – 0 coordinates. These currents are transformed to threephase system as shown in (9).
.6 .7
8 9
The reference currents are calculated in order to compensate neutral, harmonic and reactive currents in the load. These reference source current signals are then compared with sensed threephase source currents, and the errors are processed by hysteresis band PWM controller to generate the required switching signals for the shunt APF switches.


TRAINING OF ANN
An ANN is essentially a cluster of suitably interconnected nonlinear elements of very simple form that possess the ability of learning and adaptation. These networks are characterised by their topology, the way in which they communicate with their environment, the manner in which hey are trained and their ability to process information.
Their ease of use, inherent reliability and fault tolerance has made ANNs a viable medium for control. An alternative to fuzzy controllers in many cases, neural controllers share the need to replace hard controllers with intelligent controllers in order to increase control quality [19]. A feed forward neural network works as compensation signal generator. This network is designed with three layers. The input layer with seven neurons, the hidden layer with 21 and the output.
:
Fig: Network topology of ANN
The training algorithm used is LevenbergMarquardt Backpropagation (LMBP).
Training is given as follows: net=newff(minmax(P),[7,21,3],
{tansig,tansig,purelin},trainlm); net.trainParam.show =50;
net.trainParam.lr = .05;
net.trainParam.mc = 0.95;
net.trainParam.lr_inc = 1.9;
net.trainParam.lr_dec = 0.15;
net.trainParam.epochs = 1000; net.trainParam.goal = 1e6; [net,tr]=train(net,P,T); a=sim(net,P);
gensim(net,1);
The compensator output depends on input and its evolution. The chosen configuration has seven inputs three each for reference load voltage and source current respectively, and one for output of error (PI) controller. The neural network trained for outputting fundamental reference currents [20]. The signals thus obtained are compared in a hysteresis band current controller to give switching signals. The block diagram of ANN compensator is as shown in the figure

AIMMULATION AND RESULTS
The circuit is simulated using Matlab/Simulink .The matlab diagram of series and shunt APF with pi controller and ANN controller is as follow
Fig: the shunt APF with pi controller
The above matlab diagram is of the shunt active power filter. Here the dq0 transform is used to convert the three phase
voltage and three phase current into two phase voltage and current. The three phase PLL is used to generate the sine cosine term. The sine and cosine term is used in abc to dq0 transform and then again dq0 to three phase transform. The transformed dq0 is feed into the pq generation. The p term is feed into the low pass second order filter to filter out the harmonics. The q term is left out. Now this filter out P term is feed into the pq to dq0 transform. Now again this signal is feed into the dq0 to three phase transform. This transformed three phase signal is treated as reference signal. Now this reference signal and three phase current signal is feed into the hysteresis current controller. The generated signal is given into the inverter.
Fig:shunt APF with ANN control
The waveforms obtained from both of the controller is as
Fig: the uncompensated current waveforms
Fig:the current waveform odtained through pi controller
Fig:the current waveform obtained through the ANN controller
The THD of the unconpensated current obtained without the UPQC in operation is 27.63% which is quit high. The IEEE standerd is that it should be below 5%. The current obtained the UPQC is in the operation with the proportional integral controller is 1.76% which is quit low and satisfy trhe IEE standerd. And when the UPQC is in operation with the Artificial Neural Network controller the THD is 0.67% which much more less than the pi contrioller.
CONCLUSION
A simple control technique based on unit vector templates generation is proposed for UPQC. Proposed model has been simulated in MATLAB. The result after simulation compensate the input voltage harmonics and current harmonics caused by nonlinear load effectively by the control strategy. The closed loop control schemes of direct current control, for the proposed UPQC have been described. A suitable model of the UPQC has been developed with different shunt controllers (PI and ANN) and simulated results are compared.
The performance of harmonic current filtration is shown in Figs. 5.15 and 5.16. The load current in both cases is found to be content of all odd harmonic minus triplen, providing a total harmonic distortion (THD) of 27.82%. It is observed from the figure that the THD of the source current at
0.15 s is 0.69% in the case of the PI controller while it is 0.63% in the case of the ANN controller scheme. Similarly, the THD of the source current at .25 s is 0.7% in case of the PI controller while it is 0.59% in case of the ANN controller scheme. Thus by seeing the result obtained through the simulation of UPQC with both the controller PI and ANN it can be conclude that for the same load the THD obtained is less as compared to the conventional PI controller. Hence the ANN controller is better option than the conventional controller
REFERENCES

C. Sankaran, Power Quality, CRC Press LLC, 2002.

Alexander Kusko and Marc T.Thompson, Power Quality in Electrical Systems, McGrawHill, 2007.

Roger C. Dugan, Mark F. McGranaghan, Surya Santoso and H.Wayne Beaty, Electrical Power Systems Quality, The McGrawHill, Second Edition, 2004.

K. R. Padiyar, Facts Controllers in Power Transmission and Distribution, New Age International Publishers, 2007.

H. Hingorani, Introducing Custom Power IEEE Spectrum, Vol.32, Issue: 6, Page(s): 4148, June 1995.

Juan W. Dixon, Gustavo Venegas and Luis A. Moran, A Series Active Power Filter Based on a Sinusoidal CurrentControlled VoltageSource Inverter IEEE Transactions on Industrial Electronics, Vol. 44, Issue: 5, Page(s): 612 – 620, October 1997.

Yash Pal, A. Swarup, and Bhim Singh, A Review of Compensating Type Custom Power Devices for Power Quality Improvement 2008 Joint International Conference on Power System Technology (POWERCON) and IEEE Power India Conference New Delhi, India Page(s): 1 – 8, October 2008.

Arindam Ghosh and Gerard ledwhich, Power Quality Enhancement Using Custom Power Devices, Kluwer Academic Publishers, 2002.

Angelo Baggini, Handbook of Power Quality, John Wiley & Sons Ltd, 2008.

T. A. Short, Distribution Reliability and Power Quality, Taylor & Francis Group, CRC Press, 2006, June 2009.

Mojtaba Nemati, Hesam Addin Yousefian and Rouhollah Afshari,
Recognize the Role of DVR in Power Systems, International Journal of Recent Trends in Engineering, Vol. 2, Page(s): 13 – 15, November 2009.

J. Barros, M. de Apraiz, and R. I. Diego, Measurement of Subharmonics In Power Voltages, Power Tech, IEEE Lausanne, Page(s): 1736 1740, 2007.

Mahesh Singh and Vaibhav Tiwari, Modeling analysis and solution of Power Quality Problems, http://eeeic.org/proc/papers/50.pdf.

Chellali Benachaiba and Brahim Ferdi, Voltage Quality Improvement Using DVR, Electrical Power Quality and Utilisation, Journal Vol. XIV, No. 1, 2008.

R.N.Bhargavi, Power Quality Improvement Using Interline Unified Power Quality Conditioner, 10th International Conference on Environment and Electrical Engineering (EEEIC), Page(s): 1 – 5, 2011.

K. Palanisamy, J Sukumar Mishra, I. Jacob Raglend and D. P. Kothari,
Instantaneous Power Theory Based Unified Power Quality Conditioner (UPQC), 25th Annual IEEE Conference on Applied Power Electronics Conference and Exposition (APEC), Page(s): 374 379, 2010.

G. Siva Kumar, P. Harsha Vardhana and B. Kalyan Kumar,
Minimization of VA Loading of Unified Power Quality Conditioner (UPQC), Conference on POWERENG 2009 Lisbon, Portugal, Page(s): 552 – 557, 2009.

V. Khadkikar , A. Chandra, A.O. Barry and T.D Nguyen, Conceptual Study of Unified Power Quality Conditioner (UPQC), IEEE International Symposium on Industrial Electronics, Vol. 2, Page(s): 1088 1093, 2006.

V. Khadkikar , A. Chandra, A.O. Barry and T.D. Nguyen, Power quality enhancement utilising singlephase unified power quality conditioner: digital signal processorbased experimental validatio Conference on Power Electronics, Vol. 4, Page(s): 323 331, 2011.

M. Faridi, H. Maeiiat, M. Karimi, P. Farhadi and H. Mosleh, Power System Stability Enhancement Using Static Synchronous Series Compensator (SSSC) Conference on Computer Research and Development (ICCRD) Vol. 3, Page(s): 387 391, 2011.

B. Singh, V. Verma, A. Chandra and K. AlHaddad, Hybrid Filters for Power Quality Improvement, IEE Proceedings Generation, Transmission and Distribution, Vol.152, Page(s): 365 – 375, 2005.

V. Khadkikar , A. Chandra, A.O. Barry and T.D.Nguyen, "Application of UPQC to Protect a Sensitive Load on a Polluted Distribution Network", IEEE PES General Meeting, 2006. [23] Ahmed M. A. Haidar, Chellali Benachaiba,
Faisal A. F. Ibrahim and Kamarul Hawari, Parameters Evaluation of Unified Power Quality Conditioner, IEEE International Conference on Electro/Information Technology (EIT), page(s):1 – 6, 2011.

M. Tarafdar Haque, and S.H. Hosseini, "A Novel Strategy for Unified Power Quality Conditioner (UPQC)", Conference on Proceedings of Power Electronics Specialists, Vol. 1, Page(s): 94 – 98, June 2002.

Jiangyuan Le, Yunxiang Xie, Zhang Zhi and Cheng Lin, A Nonlinear control strategy for UPQC, International Conference on Electrical Machines and Systems, Page(s): 2067 – 2070, 2008.

A. Mokhtatpour and H.A. Shayanfar Power Quality Compensation as Well as Power Flow Control Using of Unified Power Quality Conditioner, Asia Pacific Power and Energy Engineering Conference (APPEEC), Page(s): 1 – 4, 2011.

Metin Kesler and Engin Ozdemir A Novel Control Method for Unified Power Quality Conditioner (UPQC) Under NonIdeal Mains Voltage and Unbalanced Load Conditions, 25th Annual IEEE Applied Power Electronics Conference and Exposition (APEC), Page(s): 374 379, 2010.

Luis F.C. Monteiro, Mauricio Aredes and Joao A. Moor Neto A Control Strategy for Unified Power Quality Conditioner, IEEE International Symposium on Industrial Electronics, vol. 1, Page(s): 391 – 396, 2003.

R.V.D. Rama Rao, Subhransu and Sekhar Dash, Power Quality Enhancement by Unified Power Quality Conditioner Using ANN with Hysteresis Control International Journal of Computer Applications (0975 8887) Vol. 6, Page(s): 915, Sep. 2010