Cross-coupling Control Scheme and Performance Analysis for Power Flow Control of UPFC

The paper investigates the power flow control ability of unified power flow controller (UPFC). By analyzing active and reactive power balance, power flow control characteristic of UPFC system, power operation surface plots of UPFC in a three-dimensional space are presented. It provides an intuitionistic measure for choosing effectively power capability of UPFC and judging the feasibility of UPFC power control scheme. A cross-coupling control system with three control loops is adopted. The series converter injected voltage of UPFC is decomposed into two components in the synchronous rotating d-q frame. The d-axis component controls the transmission line reactive power flow. The q-axis component regulates the transmission line active power flow. The PI regulator parameters of power loop are obtained by a frequency characteristic method. The performance of UPFC with the above control scheme was tested in a 15kVA laboratory UPFC setup. Experimental results show that UPFC holds prominent ability in controlling power flow.