Double closed loop control and analysis for shunt inverter of UPFC

The paper presents an in-depth analysis for the dynamic performance of the shunt inverter of unified power flow controller (UPFC). The goal of the shunt inverter is stabling the node voltage and the dc-link capacitor voltage. The d-q math model of shunt invert based on three phase PWM converter is established in the paper. In order to improve the dynamic performance and control precision, the paper propose a double closed loop decoupling control scheme and briefly introduce the proceeding of control system design. Node voltage outer loop control system adopts indirect current droop control, which consists of PI regulation and scaling factors of droop characteristic. A current feed-forward link is introduced into dc-link capacitor voltage regulation. The simulation model is constructed by using MATLAB and the simulation results for a case study indicate that dc-link capacitor voltage and node voltage can be controlled efficiently, attest that control scheme and controller design are viable and effective. Furthermore, the proposed control scheme is validated by the experimental results on a 15-KVA laboratory-scale setup