The series converter of unified power flow controller (UPFC) may be damaged when a short circuit fault occurs in the power systems. So, a topology of UPFC with fault current limiting (UPFC-FCL) was proposed by scholars of Zhejiang University, which can protect the series converter from being damaged by fault current. But before the thyristors of FCL turn off completely, the fault current can flow through the diode of IGBT-Module and cause the voltage rise of DC-Capacitor to exceed the voltage level of IGBT-Module, which can also damage the series converter. This paper analysed the path of short circuit current when short circuit fault occurs. Then the mathematical model of short circuit for UPFC-FCL was established. After a brief analysis on the mechanism of the voltage rise of DC-Capacitor when a short circuit occurs, a novel improvement topology of UPFC-FCL was proposed. PSCAD/EMTDC simulation results demonstrate that this new topology can avoid the voltage rise of DC-Capacitor as well as limit the fault current when a short circuit occurs．
LV Wen-tao,SHEN Chen,JIANG Dao-zhuo,GUI Fan,FAN Yu,WU Zhao-lin. UPFC with fault current limiting and capacitor voltage limiting. JOURNAL OF ZHEJIANG UNIVERSITY (ENGINEERING SCIENCE), 2014, 48(5): 877-881.
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