International Journal of Engineering Research & Science (IJOER)
[Vol-1, Issue-1, March.- 2015]
Enhancement of UPFC performance using Fuzzy Logic based intelligent controller Sudip Halder 1, Debanjan Mukherjee2, S. Saha3, Aniruddha Mukherjee4 Electrical Engineering Department, University of Engineering and Management, Jaipur, Rajasthan, India Abstract—In today's highly complex and interconnected power systems, sometimes made of thousands of buses and hundreds of generators, there is a great need to improve electric power utilization while still maintaining reliability and security. In order to meet the ever-growing power demand, utilities prefer to rely on already existing generation instead of building new transmission lines that are subject to environmental and regulatory policies. On the other hand, power flows in some of the transmission lines are well below their thermal limits, while certain lines are overloaded, which has as an overall effect of deteriorating voltage profiles and decreasing system stability and security. In addition, existing traditional transmission facilities in most cases are not designed to handle the control requirements of complex highly interconnected power systems. This overall situation requires the review of traditional transmission methods and practices, and the creation of new concepts which would allow the use of existing generation and transmission lines up to their full capabilities without reduction in system stability and security. If the oscillatory response of a power system during the transient period following a disturbance is damped and the system settles in a finite time to a new steady operating condition, we say the system is stable. If the system is not stable, it is considered unstable. This primitive definition of stability requires that the system oscillations should be damped.
Damping control function of a static synchronous series compensator (SSSC) installed in power systems has also been analyzed [3]. The linearized model of the SSSC integrated into power systems is established and methods to design the SSSC damping controller are proposed. Control strategy for suppressing undesirable electromechanical oscillations in power system with FACTS devices [4] with several FACT devices like STATCOM, SSSC and Unified Power Flow Controller (UPFC). Also their performance in power system has been compared which shows that most effective and flexible control can be achieved with the use of UPFC. Several references in technical literature can be found on development of UPFC steady state, dynamic and linearized models. Steady state model referred as an injection model is described in [5]. UPFC is modeled as a series reactance together with the dependent loads injected at each end of the series reactance. A nonlinear fuzzy PI controller is proposed reference [6], which has the advantage of fuzzy controller while maintaining the simplicity and robustness of classical PI controller. To overcome these difficulties better control techniques have been proposed in this dissertation to make the power system more reliable and more stable
Keywords—UPFC, Fuzzy logic controller and
The UPFC is placed between two busses referred to as the UPFC sending bus and the UPFC receiving bus. It consists of two voltage sourced converters (VSC) as mentioned before with a common DC link. For the fundamental frequency model, the VSCs are replaced by two controlled voltage sources as shown in the figure bellow. The voltage source at the sending bus is connected in shunt and will therefore be called the shunt voltage source. The second voltage source i.e. the series voltage source is placed between the sending and the receiving busses. The UPFC is placed on high voltage transmission lines. This arrangement requires step-down transformer in order to allow the use of power electronics devices for the UPFC.
Proportional-Integral (PI) Controller I.
INTRODUCTION
Much of industry effort and interest related to system stability since the 1960’s has been considered on transient stability. Significant improvement in transient stability performance have been achieved through use of high speed fault clearing device, high initial response exciters , series capacitors and FACT devices [1]. A STATCOM can also be used in stabilizing sub synchronous resonance oscillation of a large turbine generator set [2]. Here a STATCOM along with a PI controller is used to effectively damp all SSR (Sub Synchronous Resonance oscillation) and to improve system stability. The proposed control system is simple cost effective easy to implement and technically sound.
II.
UPFC DESCRIPTION AND OPERATION
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