The term ‘power quality’ [1-2] refers to the purity of the voltage and current wave-form, and a power quality disturbance is a deviation from the pure sinusoidal form. Harmonics superimposed on the fundamental are one cause of such deviations. Power quality problems [1-2] like voltage harmonics, voltage flickers, voltage sags and voltage swells, current harmonics, current unbalance, reactive current etc. are studied.Conventionally passive L-C filters [3] were used to reduce harmonics and capacitors were employed to improve the power factor of the AC loads. However, the demerits of passive filters are fixed compensation, large size and resonance. The increased severity of harmonic pollution in the power networks has attracted the attention of power electronics to develop the dynamic and adjustable solutions to the power quality problems, generally known as active filters [3]. Classification of active power filters [3-4] based on converter type, topology, and the number of phases are presented.Active power filters use power electronic switches such as Thyristors, MOSFET’S, IGBT’S etc. They use 3-phase inverters for generating compensating signals which are controlled by gate pulses generated by pulse width modulated controller[5].Unified Power Quality Conditioner [6, 9] which is a combination of series active power filter and shunt active power filter ,is used to mitigate voltage and current harmonics. The compensating principle of UPQC and its steady state analysis [1] is studied. The control techniques PI,PSO and GA are studied and applied in this work and compared with performance of FUZZY and ANN controllers [1, 7, 8and 9]... The theory about optimization techniques is studied and their applications to UPQC [11,12] is also studied.

1. R.V.D Rama Rao, Dr.SubhransuSekhar Das ‘Enhancement Of Power Quality by using Unified Power Quality Conditioner with PID and Fuzzy Logic Controller’, International journal of Computer Applications, Vol.5, No. 7, August 2010.
2. Math H.J.Bollen – ‘Understanding power quality problems’.
3. Bhim Singh, kamal Al-Haddad, ‘A Review of Active Filters for Power Quality Improvement’, IEEE Transactions on industrial Electronics, VOL. 46, No. 4, October 1999.
4. Hirofumi Akagi, ‘New Trends in Active Power Filters for Power Conditioning’, IEEE Transactions on Industry Applications, Vol. 32, No. 6, November/December 1996.
5. Muhammad H. Rashid- 'Power Electronics’.
6. Khadkikar, V.,Aganval, P.,Chandra, A., Bany, A.O. and Nguyen, T.D ’A Simple new Control Technique For Unified Power Quality Conditioner (UPQC)’, 11th International Conference on Harmonics and Quality of Power, Lahe Placid, NewYork, USA, Sept 2004.
7. Chirag Pate, RanjitMahanty,’ Unified Power Quality Conditioner using Fuzzy Logic Controller’,International journal of emerging Electric Power Systems: Vol. 11:Iss. 4, Article 5, 2010.
8. Timothy J Ross – ‘Fuzzy Logic with Engineering Application’.
9. A.J aya Lakshmi, G.Tulasi Ram Das and K.Uma Rao, ‘Role of PI and Fuzzy Controllers in Power Quality Improvement’.
10. Unified Power Quality Conditioner, APRN Journal of Engineering and Applied Sciences, VOL.2, No. 2, April 2007.
11. Optimization of parameters of the unified power quality conditioner using genetic algorithm method Chellalibenachaiba, Ottmaneabdelkhalek, Samira dib, Mohamed haidas
12. Mitigation of Voltage Sags With Phase Jumps by UPQC With PSO-Based ANFIS G. Siva Kumar, Student Member, IEEE, B. Kalyan Kumar, Member, IEEE, and Mahesh K. Mishra, Senior Member, IEEE
13. Application of PI, Fuzzy Logic and ANN in Improvement of Power Quality using UPQC, K.S.Ravi Kumar, S.V.A.R. Sastry, International Conference on Sustainable Energy and Intelligent Systems (SEISCON 2011), Publication Year: 2011 , Page(s): 316 - 319

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