Research On Solid-state Current Limiter Of Medium Voltage Based On IGCT

With the development of modern power systems, the fault current level of each grid keeps rising, which threats the system safety seriously. Therefore, measures must be taken to limit the fault current level within a reasonable range. In recent years, the fault current limiters become a hot research point, a lot kinds of fault current limiters were proposed. Among all types of fault current limiters, the solid-state type based on high-power power electronic devices is most close to the requirements of ideal fault current limiters in terms of action speed, recovery time and control flexibility. But the solid-state current limiter has a larger conduction loss due to the restriction of the current level of the power electric devices, and to realize a higher power level, the power electronic devices must be connected in series and parallel, which brings voltage and current sharing issues in the device use.The solution to those problems depends on the development and application level of solid state power electronic devices.On one aspect, high power electronic devices of low on state losses must be developed. On the other aspect, the devices of certin ratings must be fully used by better protection starategy and better topology. This paper studies the the topology and the parallel connection of devices and its protection problems.In terms of topology, this paper first introduces the evolution process of high-power power electronic devices and solid-state current limiter topology, and then summarizes the advantages and disadvantages of all kinds of devices and topology. This part explores the possibility of rasing the power ratings of solid state current limiters by using new devices and topologies.In the device appliction research, the IGCT is selected as the research object. A lump-charge model of IGCT is established in the Saber software first, and the correctness of the model is verified according to the experiment results. The experiment of parallel connection of IGCT and varistor is carried out based on the simulation with the IGCT model. For the parallel connection of IGCT device, the impact of the snubber circuit and the dynamic avalanche breakdown characteristics on the current sharing issue of IGCT is analyzed. And the reasons for the transient phenomenon at the end of current tail process of asymmetric type IGCT is discussed in detail. In the varistor parallel protection experiment part, the simulation and experiment waveforms of different varistor combination are presented, which proves the possibility of separation of overvoltage suppression and energy absorption when the varistor of different parameters are used in parallel.At last,the basic current limiting experiment is completed using resistance as the current limiting element. The effect of the different parameters of resistor and the circuit stray inductance on current transfer process is analyzed at last.Based on the study of this article, a device level simulation platform of IGCT is established, the limit turn off current of IGCT in parallel and its protection problems are explored, the law of the influence of different protection mode of IGCT turn-off is concluded, these rules are helpful for the parameter design of solid-state current limiter, and will also make sense in the application of high-power power electronic devices in other devices.