ITER PF in Series AC/DC Converters Starting Mechanism Assisted by External Bypass

The International Thermonuclear Experimental Reactor (ITER) Poloidal Field (PF) in series AC/DC converters are composed by three converter units in series to supply megawatt energy to PF coil. With the characteristics that high power, complex operating mode, large amount of snubber capacitors and thyristor branch busbar inductances, starting failure could give rise to overvoltage and damage the converter. Therefore, it is imperative to analyze the starting mechanism of ITER PF in series AC/DC converters. In this paper, assisted by the external bypass the starting mechanism is proposed to activate the ITER PF in series AC/DC converters securely and reliably. The starting failure overvoltage of three starting mechanisms including the impact of resistance-capacitance absorption is calculated. According to the calculated results, a starting mechanism that starts two converter units firstly and then start the third one is optimal for ITER PF in series AC/DC converters. The effectiveness and superiority of the proposed starting mechanism is testified by the simulation.