Control system for a UPFC in a transmission line

This paper focuses on the control of the power flow through a transmission line using a PWM.based UPFC. The dynamic model of the UPFC has been developed using the space-vector representarion of the instantaneous three-phase variables. The Park’s transformation and the reference frame selected reduce the control of the real- and reactive-power flows to the control of the d- and q-axis currents, respectively. The proposed control scheme produces fast and decoupled response of the real- and the reactive-power flow through a transmission line. The system performance has been simulated under normal operation condition and under fault conditions. A 15 kVA prototype with 750 Hz switching frequency has been built to illustrate the main contributions. Experimental results agree with the theoretical analysis and the simulation results. Finally, the bandwidth of the UPFC has been characterized. The theoretical closed-loop transfer function agrees with the experimental one. It is shown that the bandwidth of the UPFC is high enough to damp the main perturbations of a power system. Under fault conditions in a typical scenario, power system oscillations can be damped quickly with the UPFC.