IOSR Journal of Electrical and Electronics Engineering (IOSR-JEEE) e-ISSN: 2278-1676,p-ISSN: 2320-3331, Volume 9, Issue 4 Ver. IV (Jul – Aug. 2014), PP 36-50 www.iosrjournals.org www.iosrjournals.org 36 | Page Power Quality Improvement by IUPQC with Fuzzy Control Technique N. Prasad 1 , K.Vasantha Sena 2 , K. Durga Syam Prasad 3 , K. Sravanthi 4 1 (PG STUDENT, Department of EEE, DIET College of Engineering, Anakapalle, Visakhapatnam, India) 2 (Assistant Professor, Department of EEE, DIET College of Engineering, Anakapalle, Visakhapatnam, India) 3 (Sr. Assistant Professor, Department of EEE, DIET College Of Engineering, Anakapalle, Visakhapatnam, India) 4 (Assistant Professor, Department of EEE, Vignan’s Institute of Information Technology, Visakhapatnam, India) Abstract: This paper proposes a new connection for a unified power quality conditioner (UPQC) to improve the power quality of two feeders in a distribution system. A UPQC consists of a series voltage-source converter (VSC) and a shunt VSC both joined together by a common dc bus. It is demonstrated how this device is connected between two independent feeders to regulate the bus voltage of one of the feeders while regulating the voltage across a sensitive load in the other feeder. Since the UPQC is connected between two different feeders (lines), this connection of the UPQC will be called an interline UPQC (IUPQC). The structure, control and capability of the IUPQC with PI and FUZZY controller technique are discussed in this paper. The efficiency of the proposed configuration has been verified through simulation studies using MATLAB. Index Terms: distribution static compensator (DSTATCOM), distribution system, dynamic voltage restorer (DVR), fuzzy logic controller, power quality (PQ), Interline unified power quality conditioner (IUPQC) . I. Introduction Voltage Source Converter (VSC) based custom power devices are increasingly being used in custom power applications for improving the power quality (PQ) of power distribution systems. Devices such as distribution static compensator (DSTATCOM) and dynamic voltage restorer (DVR) are the facts devices. A DSTATCOM can compensate for distortion and unbalance in a load such that a balanced sinusoidal current flows through the feeder. It can also regulate the voltage of a distribution bus. A DVR can compensate for voltage sag/swell and distortion in the supply side voltage such that the voltage across a sensitive/critical load terminal is perfectly regulated .A unified power quality conditioner (UPQC) can perform the functions of both DSTATCOM and DVR. The UPQC consists of two voltage-source converters (VSCs) that are connected to a common dc bus. One of the VSCs is connected in series with a distribution feeder, while the other one is connected in shunt with the same feeder. The dc links of both VSCs are supplied through a common dc capacitor. It is also possible to connect two VSCs to two different feeders in a distribution system. In, a configuration called IDVR has been discussed in which two DVRs are connected in series with two separate adjacent feeders. The dc buses of the DVRs are connected together. The IDVR absorbs real power from one feeder and maintains the dc link voltage to mitigate 40% (about 0.6p.u.) voltage sag in the other feeder with balanced loads connected in the distribution system. It is also possible to connect two shunt VSCs to different feeders through a common dc link. This can also perform the functions of the two DVRs mentioned above, albeit with higher device rating. This paper presents a new connection for a UPQC called interline UPQC (IUPQC). The single-line diagram of an IUPQC connected distribution system is shown in Fig. 1. Fig.1: Single-line diagram of an IUPQC-connected distribution system. Two feeders, Feeder-1 and Feeder-2, which are connected to two different substations, supply the system loads L-1 and L-2. The supply voltages are denoted byV s1 and V s2 It is assumed that the IUPQC is