Our group is researching High Temperature Superconducting Induction/Synchronous Motor (HTS-ISM) in which the squirrel-cage rotor windings of induction motors are composed of the HTS conductors [1]. By effectively utilizing the zero resistance as well as the nonlinear resistance associated with magnetic flux-flow of the HTS windings, the HTS-ISM can achieve excellent rotational characteristics such as high efficiency, high power density, and stable transient characteristics.
On the other hand, the HTS-ISM is driven by applying a three-phase balanced voltage to the three-phase winding of the stator. Therefore, if the above-mentioned nonlinear resistance in the squirrel-cage HTS winding appears in the stator winding, it becomes very difficult to control, resulting in, for example, a three-phase unbalance and a risk of burnout.
In this study, the above problems were investigated experimentally and theoretically for 20 kW class HTS-ISM. First, after connecting voltage taps to multiple HTS rotor-bars in the HTS squirrel-cage winding, the rotor was excited under its locked condition and the nonlinear voltage associated with the magnetic flux-flow was measured. As a result, the stator current was a beautiful sinusoidal waveform without distortion even under the condition that the HTS rotor-bar generated nonlinear flux-flow voltage. Furthermore, the above experimental results were proved by convoluting the local nonlinear induced electromotive force of the HTS rotor-bar considering the spatial distribution of the windings giving the magnetomotive force. The above results suggest that the HTS-ISM has both excellent rotational characteristics and easy controllability.
[1] G. Morita, T. Nakamura and I. Muta, Supercond. Sci. Technol., 19(6) (2006) 473
I would like to thank Mr. Jun Matsuura and Mr. Takuro Ogasa for their cooperation in the experiments. This work was supported by JSPS KAKENHI under Grant No. 22H01471.