Research On A Novel Multi-functional Solid-State Fault Current Limiter

With the fast construction and development of power grid, short-circuit capacitykeep on increasing, seriously restrict the further development of power system, somust take effective measures to limit short-circuit current to reduce the damage to thepower system caused by the short-circuit fault. Installing Fault Current Limiter(FCL)is a kind of very effective measures to limit fault current, which has been getting moreattention in recent years. Especially the Solid-State Fault Current Limiter(SSFCL)which is based on power electronic technology has become one of the researchhotspots with the development of power electronic technology at home and abroad.However, SSFCL is in the idle state for a long time since the probability of systemfailure is very small, the equipment utilization and economy benefit is low. Soresearch on multi-functional SSFCL to improve equipment utilization and economybenefit is required. And power quality issue is also one of the facto rs greatly threatensthe effective and reliable operation of power system, effective measures must be takento control it. So a novel Multi-functional SSFCL(MSSFCL) with functions of powerquality control and fault current limit is researched in this thesi s, which can be used toimprove power quality during normal operation of power system and limit the faultcurrent under short circuit conditions.(1)This paper has summarized the problems to be solved for the research ofMSSFCL at first by comparing the similarities and differences of typical SSFCL andtypical power quality control devices and analyzing the existing multi-functionalSSFCLs. On the basis of this, the topology of single-phase MSSFCL is proposed, andthe design thought of the novel topology is described in detail. Then the topology ofthree-phase MSSFCL suitable for both isolated neutral power system and neutraldirectly grounding power system is proposed, and its detailed working principle isanalyzed.(2)Then, the integrated control strategy of MSSFCL is studied, a compoundcontrol method based on the judgment of state is proposed focusing on the compoundcontrol of multifunctional composite circuit of power quality control and fault currentlimit. It can control the working mode of MSSFCL according to the running state ofpower system, that is, work in power quality control mode when power system isnormal, while work in fault current limit mode under fault state. The technology of composite compensation on power quality issues such as voltage sag, harmonicvoltage and etc is studied. And an instruction calculation method based on theoptimization of ability to compensate the voltage sag is put forward. Furthermore, arapid detection algorithm suitable for MSSFCL is proposed in this thesis for state ofpower system.(3)Finally, the main circuit parameters design method of MSSFCL is analyzedwith specific voltage level and load capacity of power system, and simulations withthe parameters designed are carried out to study the performances of MSSFCL inisolated neutral power system and neutral directly grounding power systemrespectively. The results show that the MSSFCL proposed can effectively achieve theimprovement of power quality and restriction on short circuit current, which verifiedthe validity of MSSFCL and the correctness of the theories studied in this thesis.