Control system for a UPFC in a transmission line

This paper presents a detailed investigation of a UPFC control system. The dynamic model of the UPFC has been developed using the space-vector representation of the instantaneous three-phase variables using Park's transformation. 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 control loops and the algorithms to ensure instantaneous power control decoupling are explained in detail. The controller also maintains constant the voltage at the DC-link of the back to back inverters. The problems derived from the discrete inverter output control are taken into account when using space-vector PWM. A simulator has been developed to illustrate the main results before building a prototype. A continuous-time model has been used for the power system and the control has been implemented in discrete time. The inverters have been simulated using ideal switches with 0.5 kHz switching frequency.