Katsunori Azuma

Critical current test results of 13 T–46 kA Nb3Al cable-in-conduit conductor

In the framework of ITER-EDA, a 13 T-46 kA Nb3Al conductor with stainless steel jacket has been developed in order to demonstrate applicability of an Nb3Al conductor with react-and-wind technique to ITER-TF coils. Using a 3.5 m sample consisting of a pair of conductors with 0% and 0.4% bending strain, the critical current performances of the Nb3Al conductors were studied to verify that the conductor achieves the expected performance and the bending strain of 0.4% does not originate degradation. The critical currents were measured at background magnetic fields of 7, 9, 10 and 11 T at temperatures from 6 to 9 K. The expected critical currents were evaluated taking into account the variation of the strain in the cross-section due to the bending strain as well as self-field and non-uniform current distribution as results of an imbalance in the joint resistance and inductances. The calculation results indicate that the current distribution is almost uniform and the experimental results showed good agreement with the expected critical currents. Accordingly, we can conclude that the fabrication process of this conductor is appropriate and the react-and-wind technique using the Nb3Al conductor is applicable to ITER-TF coils. In addition, the critical current of the Nb3Al conductor is expected to be 108 kA at 13 T and 4.5 K, resulting in a sufficient margin against the nominal current of 46 kA. Furthermore, it was found that the decrease in the critical current by thermal strain can be made small by applying the bending strain to the conductor so as to reduce the compressive strain at higher fields, i.e. inner side of the coil, in the conductor cross-section

Novel 3.3-kV advanced trench HiGT with low loss and low dv/dt noise

Novel 3.3-kV trench IGBT with low loss and low dv_AK/dt noise was developed. The structural feature of the IGBTs is deep p-WELL layers separated from trench gates. This structure suppresses excess V_GE overshoot and then reduces recovery dv_AK/dt. Moreover, this effect is enhanced by reducing the resistance of the deep p-WELL layers (R_FP). It was found that, for the first time, the trade-off characteristics between V_CEsat and recovery dv_AK/dt were drastically improved by separating p-WELL layers from trench gates and decreasing R_FP. The recovery dv_AK/dt could be reduced by 79% more than that for the conventional trench IGBT, maintaining a small V_CEsat and E_on equal to the conventional one.

Suppression of reverse recovery ringing 3.3kV/450A Si/SiC hybrid in low internal inductance package: Next high power density dual; nHPD2

Suppression of reverse recovery ringing from 3.3kV Si-IGBT SiC Schottky barrier diode hybrid was verified. Reducing loop inductance, consisting of internal module, busbar connection and capacitor, is effective. To realize low inductance within the module and external connection with busbar, the gap between p and n terminal is minimized whilst maintaining the creepage and clearance required by regulation standards. Functional isolation is adopted instead of basic isolation. We achieved an inductance value 9nH for a 3.3kV, 450A dual IGBT, that leads to the extinction of reverse recovery oscillation. Details of switching characteristics of Si + SiC hybrid module is compared with that of Si IGBT module with low inductance.