Research On Parameters Design And Control Strategy In Unified Power Flow Controller With Solid-state Fault Current Limiter

The unified power flow controller with fault current limiting (UPFC-FCL) is a new flexible AC transmission system devices, which combined traditional UPFC with solid-state fault current limiting (SSFCL). During normal operation, UPFC can exchange power with the system. When short circuit fault occurs, FCL can limit the short-circuit current and isocate the faults quickly, and improve the operation safety and stability of UPFC device.A parameter design method is proposed which is combined with UPFC working principle, and maximum compensation voltage is chosen based on maximum compensation capacity and rated current, and then DC bus rated voltage is determined, and the value range of filter inductance is chosen based on compensation capacity target, and current-limiting inductance is selected based on short circuit current level. According to the design method above, this paper proposes a design example that the rated voltage is10kV and the maximum compensation capacity is1MVA, and it provides maximum compensation voltage which comes from series converter, DC bus rated voltage, series converter and shunt converter filter inductance, current-limiting inductance.After an analysis of the shortage of existing power control strategies in UPFC-FCL, a power system model with UPFC-FCL is established, and a power control strategy based on line current control is proposed. Analysed the start-stop process of UPFC-FCL, then a complete start-stop control scheme is proposed. In start process, the charging rate of DC capacitor is limited by current-limiting resistance, which prevented overvoltage or overcurrent of equipment. In stop process, the design requirements of discharge resistance can be reduced because the energy of DC capacitance is part released through shunt converter. PSCAD/EMTDC simulation results demonstrate that the UPFC-FCL power control strategy based on line current control has a good dynamic and steady performance, and the start-stop control scheme is reasonable and effective.Finally, an experiment prototype of380V UPFC-FCL is developed. The results of starting experiment, power flow adjustment experiments and short circuit experiments demonstrate that the topology structure, parameter design and control strategy is effective and rational.