Transient Stability of Power System using Facts Device-UPFC

IJSRD Found one good reserch article on Electrical Engineering Department

Abstract— This paper is based on Occurrence of a fault in a power system causes transients. To stabilize the system, The Flexible Alternating Current Transmission (FACTS) devices such as UPFC are becoming important in suppressing power system oscillations and improving system damping. The UPFC is a solid-state device, which can be used to control the active and reactive power.. By using a UPFC the oscillation introduced by the faults, the rotor angle and speed deviations can be damped out quickly than a system without a UPFC. The effectiveness of UPFC in suppressing power system oscillation is investigated by analyzing their oscillation in rotor angle and change in speed occurred in the two machine system considered in this work. A proportional integral (PI) controller has been employed for the UPFC. It is also shown that a UPFC can control independently the real and reactive power flow in a transmission line. A MATLAB simulation has been carried out to demonstrate the performance of the UPFC in achieving transient stability of the two-machine five-bus system.

I. INTRODUCTION

The UPFC is the most versatile of the FACTS devices. The main function of the UPFC is to control the flow of real and reactive power by injection of a voltage in series with the transmission line. Both the magnitude and the phase angle of the voltage can be varied independently. Real and reactive power flow control can allow for power flow in prescribed routes, loading of transmission lines closer to their thermal limits and can be utilized for improving transient and small signal stability of the power system.  

Fig. Schematic diagram of UPFC

The UPFC consists of two branches. The series branch consists of a voltage source converter, which injects a voltage in series through a transformer. The inverter at the input end of the UPFC is connected in shunt to the AC power system and the inverter at the input end of the UPFC is connected in series with the AC transmission circuit. Since the series branch of the UPFC can inject a voltage with variable magnitude and phase angle it can exchange real power with the transmission line. However the UPFC as a whole cannot supply or absorb real power in steady state (except for the power drawn to compensate for the losse.

The Unified Power Flow Controller (UPFC) was proposed' for real turn-off time control and dynamic compensation of ac transmission systems, providing the necessary functional flexibility required to solve many of the problems facing the utility industry. The Unified Power Flow Controller consists of two switching converters, which in the implementations considered are voltage sourced inverters using gate thyristors valves, as illustrated in Fig. These inverters, labeled "Inverter1" and "Inverter 2" in the figure, are operated from a common dc link provided by a dc storage capacitor. 

This arrangement functions as an ideal auto ac power converter in which the real power can freely flow in either direction between the ac terminals of the two inverters and each inverter can independently generate (or absorb) reactive power at its own ac output terminal since the series branch of the UPFC can inject a voltage with variable magnitude and phase angle it can exchange real power with the transmission line. However a UPFC as a whole cannot supply or absorb real power in steady state (except for the power drawn to compensate for the losses). Unless it has a power source at its DC terminals. Thus the shunt branch is required to Transmission Line Shunt Transformer VSC2 VSC1 Control Transient Stability of Power System Using Facts Device-UPFC (IJSRD/Vol. 1/Issue 3/2013/0025) All rights reserved by www.ijsrd.com 507 compensate (from the system for any real power drawn/supplied by the series branch and the losses. if the power balance is not maintained, the capacitor cannot remain at a constant voltage. Shunt branch can independently exchange reactive power with the system. 

For full article Click Here

For More detail about research work

visit us : www.ijsrd.com