Control and analysis of a unified power flow controller

This paper presents a control scheme and comprehensive analysis for a unifi ed power flow controller (UPFC) on the basis of theory, computer simulation , and experiment. This developed theoretical analysis reveals that a conven tional power-feedback control scheme makes the UPFC induce power fluctuatio n in transient states, The conventional control scheme cannot attenuate the power fluctuation, and so the time constant of damping is independent of a ctive- and reactive-power feedback gains integrated in its control circuit. This paper proposes an advanced control scheme which has the function of s uccessfully damping out the power fluctuation. A UPFC rated at 10 kVA is de signed and constructed, which is a combination of a series device consistin g of three single-phase pulsewidth modulation (PWM) converters and a shunt device consisting of a three-phase diode rectifier. Although the dynamics o f the shunt device are not included, it is possible to confirm and demonstr ate the performance of the series device. Experimental results agree well w ith both analytical and simulated results and show viability and effectiven ess of the proposed control scheme.