International Electrical Engineering Journal (IEEJ) Vol. 5 (2014) No.12, pp. 1673-1679 ISSN 2078-2365 http://www.ieejournal.com/ 1673 Author et. al., xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Abstract— Flexible AC Transmission System (FACTS) became very popular for control of power flow in transmission lines. The Load changes the voltage Variation in transmission lines must be limited, otherwise the consumer’s equipments are damaged at distributed side. For reducing this voltage variation a FACTS device called Distributed Power Flow Controller (DPFC) and Distributed Interline Power Flow Controller (DIPFC) is used. The DPFC is derived from the unified power- flow controller (UPFC). The DPFC (Distribute Power-Flow Controller) modified from UPFC for increasing system reliability and reducing costs. The DPFC can be considered as UPFC with an eliminated common DC link, to enable the independent operation of the shunt and the series converters which enhances the effective placement of the series and shunt converters. The active power exchange between the two converters, which is through the common dc link in the UPFC, is now through the transmission lines at the third-harmonic frequency in the DPFC and DIPFC. In DPFC three-phase series converter is divided to several single-phase series distributed converters through the transmission line and in DIPFC three single phase series converters are placed in between the two transmission lines. This paper consists of both active and reactive variations, using MATLAB/SIMULINK is simulated and its effects on the transmission lines observed. The simulated results are analyzed and validated with the real time results for the system considered. Index Terms— FACTS, DPFC, DIPFC, UPFC, Power Quality I. INTRODUCTION Nowadays the power system becomes very complex due to the increasing load demand of the electricity and the aging of the networks. There is a great desire for the power flow control in the transmission lines with fast operation and reliability [1]. A Power Quality problem can be defined as deviation of magnitude and frequency from the ideal sinusoidal wave from. Good power quality is benefit to the operation of electrical equipment, but poor power quality will produce great harm to the power system [1]. Harmonics are defined as sinusoidal wave form having a frequency equal to an integer multiple of the power system fundamental frequency. It is a component of a periodic waveform. If the fundamental frequency multiple is not an integer, then we are dealing with inter harmonics [1]. Most of the electronic equipments such as personal computers, telecommunication equipment, microprocessors, and microcontrollers etc; are generally responsible to Power Quality problems. A poor power quality has become a more important issue for both power suppliers and customers. Poor power quality means there is a deviation in the power supply to cause equipment malfunction or may failure. To solve the power quality problem the power electronic devices such as flexible alternating-current transmission system (FACTS) and custom power devices (DVR) which are used in transmission and distribution control, respectively, should be developed [2], [3], [4]. The Distributed Power Flow Controller (DPFC) which is shown in figure 1, is one of the device with in FACTS family, which is derived from the UPFC. As compared with the UPFC, DPFC has the same controlling capability to change all the parameters within the transmission system. In case of DPFC the commonly connected DC link between series and shunt converter is eliminated and application of D-FACTS [6] concept to series converter shown in Fig.2.The active power exchange between the converters is at 3rd harmonic frequency. The D-FACTS concept not only reduces the ratings of the devises but also improves the reliability of the system because of redundancy and reducing the cost of high voltage isolation. Simulation of Distributed Interline Power Flow Controller (DIPFC) for Power Quality Improvement in Distribution System Kotipalli Vineela Chandrika, Palakaluri Venkatesh kotipallivineela@gmail.com, venki249@gmail.com