New thyristor platform with voltage ratings 6.7 kV, 7.2 kV and 8.5 kV was developed to enable an optimal design of converter valves with the DC link rating voltages over 1000 kV. Silicon resistivity and wafer thickness were chosen to fulfill the demands laid on the blocking capability of UHVDC application. A proper choice of electron irradiation energy and dose for Qrr banding provides the optimal technology curve between the VT and Qrr. Full utilization of six inch wafers and the optimized layout of amplifying gate and cathode improved the ON-state current ratings by ca. 20% compared to prior art thanks to the reduced ON-state voltage by ca. 10%. Together with the low value of circuit commutated recovery time tq, the new thyristor platform provides more efficient and stable converter valves for the next generation UHVDC systems to be operated at the rating power breaking the level of 10 GW.
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