[Dabhade* et al., 5(8): August, 2016] ISSN: 2277-9655 IC™ Value: 3.00 Impact Factor: 4.116 http: // www.ijesrt.com © International Journal of Engineering Sciences & Research Technology [63] IJESRT INTERNATIONAL JOURNAL OF ENGINEERING SCIENCES & RESEARCH TECHNOLOGY RESOLVEMENT OF POWER QUALITY PROBLEMS BY UNIFIED POWER QUALITY CONDITIONER (UPQC) Ms. Rohini. R. Dabhade*, Prof. C. Veeresh * Department of Electrical Engineering, SND COE & RC, Yeola Department of Electrical Engineering, SND COE & RC, Yeola ABSTRACT In this project presents a Design of a Unified Power Quality conditioner (UPQC) connected to three phase four wire system (3P4W). The neutral of series transformer used in the fourth wire for the 3P4W system. The neutral current that may flow toward transformer neutral point is compensated by using a four-leg voltage source inverter topology for shunt part. The series transformer neutral will be at virtual zero potential during all operating conditions. In this simulation we observe the power quality problems such as unbalanced voltage and current, harmonics by connecting non linear load to 3P4W system with Unified Power Quality conditioner. A new control strategy such as unit vector template is used to design the series APF to balance the unbalanced current present in the load currents by expanding the concept of single phase P-Q theory. KEYWORDS: Unified power quality conditioner,Series active power filter,Shunt active power filter,Power quality INTRODUCTION Electrical power system is design to provide high quality power for satisfactory operation of various electrical equipment. However the extensive use of non-linear loads in modem power system is becoming highly vulnerable to power quality and contributing to increased power quality issues. The main issues of a poor power quality are harmonic currents, poor power factor, supply-voltage variations; etc.It has been always a challenge to maintain The quality of electric power within the acceptable limits. The adverse effects of poor power quality may result into increased power losses, abnormal and undesirable behavior of equipments, interference with nearby communication lines, and so forth. The term active power filter (APF) is a widely used terminology in the area of electric power quality improvement. APFs have made it possible to mitigate some of the major power quality problems effectively. The UPQC is one of the APF family members where shunt and series APF functionalities are integrated together to achieve superior control over several power quality problems. The function of unified power Control strategy plays a vital role in the overall performance of the power conditioner. Rapid detection of disturbance signal with high accuracy, fast processing of the reference signal and high dynamic r e s p on s e of the controller are the prime requirements for desired compensation. Generation of appropriate swi tching Pattern or gating signal with reference to command compensating signal determines the control strategy of the UPQC. PROPOSED SCHEME In proposed system easy expansion of 3P3W system to 3P4W system. The neutral current, present if any, would flow through this fourth wire toward transformer neutral point. This neutral point current can be compensated by using a split capacitor. This neutral current achievement is used the method P-Q Theory in UPQC. The UPQC consisting of the combination of a series active power filter (APF) and shunt APF.