Compensation of NI Behaviors in Synchronous Motors With NI HTS Field Winding Using Harmonic Current Injection

Focusing on the improved operation reliability of no-insulation (NI) high-temperature superconductor (HTS) coils, various attempts are being conducted to replace conventional superconductor coils with NI HTS coils for industrial and energy conversion purposed applications. When applying NI techniques, unique behaviors of NI HTS coils due to the removal of turn-to-turn insulation should be considered with given operating conditions, because it could affect the overall characteristics of the machines. In particular, in the case of synchronous motors to which NI HTS field winding is adopted, it has been reported that periodic turn-to-turn leak currents were identified even in steady-state operation due to harmonic components, which may result in torque and loss characteristics changes. Here we report a method to offset these additional NI behaviors that may appear when NI HTS field winding is applied to synchronous motors. A brief mechanism of the proposed method was presented, and the proposed method was applied to an example model through finite element analysis. As a result, it was shown that turn-to-turn contact loss could be reduced to 2.18% without adverse effect on torque characteristics.