Modeling and Implementation of D-q Control System for a Unified Power Flow Controller

The Unified Power Flow Controller (UPFC) can provide simultaneous control of all basic power system paramaters (transmission voltage, impedance and phase angle). The controller can fulfill functions of reactive shunt Compensation, series compensation and phase shifting, meeting multiple control objectives. From a functional perspective, the objectives are met by appliying a cross coupling control strategy which is based on d-q axis theory is presented by simulation. In this control system, the transformation of a three phase system to the d-q, 2 axis system is done through which real and reactive power can be controlled individually, also regulating the local bus voltage. The performance of the proposed control system is checked by applying various faults across a transmission line to which UPFC is connected. A generalized pulse width modulation switching technique is used to generate firing pulses for both the converters of the UPFC. Simulation was carried out using Matlab/ Simulink software to validate the performance of the UPFC connected to a transmission line with different faults. Simulation results show that the proposed control scheme is effective in damping the power swings in transient states.