Experimental Verification and Matlab Simulation of UPFC for Power Quality Improvement

Abstract

This paper aims in presenting the importance of presence of Unified Power Flow Controller(UPFC) for enhancement of power quality of existing transmission network.UPFC is used for controlling varioustransmission parameters such as series impedance, shunt impedance, line voltage, current, active and reactive power, oscillation damping etc. Experimental controlled reading of UPFC is obtained with the help of lab model for various parameters.Controlling is done with the help of IGBT based converters through DSP kit(for controlling firing angle of converters).This paper also presents the study of UPFC using MATLAB 7.9 and lab prototype is also setup. Effect of presence of UPFC on various parameters is obtained and is compared with parameters without UPFC for real system through simulation using MATLAB 7.9. With the increase in load demand, we have to increase the generation & require proper channel to transfer electrical power from generating end to receiving end which is highly efficient in nature (i.e transmission line). But when we try to add one or more number of generator to the existing transmission network then system suffers from large number of problems such as reduction in power , voltage dip, interruption , over voltage etc which can cause ill effect to the power system quality. It is necessary to maintain or enhance the quality of the network in order to get efficient power flow. Adding large number of generating to the existing transmission makes it more and more complex. Hence designing of such system is really a hectic job or we have to redesign the whole system by selecting the proper filter rating, power system stabilizer etc. We can use the traditional controller also for controlling power flow of this lines but frequent tuning is again a problem. Hence to overcome from above mention problem, we can use the fast acting power electronics controllers called FACTS devices. In late 1980's ,Electric power research institute introduce the new technology called Flexible AC Transmission Technology and the controller used for controlling power flow is known as FACTS devices. Deregulated environment is again one of the major cause of making line network more and more bulky. The AC system cannot be preferable for long transmission of power because of high transmission losses but by using this technology we can able to transfer the AC power for long distance. Unified Power Flow Controller Gyugyi proposed the Unified Power Flow Controller (UPFC) concept in 1991. The UPFC was devised for the real time control and dynamic compensation of ac transmission systems, providing multifunctional flexibility required to solve many of the problems facing the delivery industry. Within the framework of traditional power transmission concepts, the UPFC is able to control, simultaneously or selectively, all the parameters affecting power flow in the transmission line (i.e., voltage, impedance and phase angle), and this unique capability is signified by the adjective unified in its name. Alternatively, it can independently control both the real and reactive power flows in the line. The UPFC not only performs the functions of STATCOM, TCSC and phase angle regulator but also provides additional flexibility by combining some of the functions of these controllers. The Unified Power Flow Controller (UPFC) consists of two voltage sourced converters using power switches, which operates from a common DC circuit of a DC-storage capacitor. This arrangement functions as an ideal ac to ac power converter in which the real power can freely flow in either direction between the ac terminals of the two converters and each converter can independently generate (or absorb) reactive power at its own ac output terminal. The UPFC (Fig.1) is a combination of an STATCOM and an SSSC, sharing a common dc link. The UPFC can control both the active and reactive power flow in the line. It can also independently provide controllable shunt reactive compensation. In other words, the UPFC can provide simultaneous control of all the basic transmission line parameters.