Control the Output of an HTS Dynamo With a DC Background Field

This paper proposed and demonstrated a feedback control method for a high temperature superconducting (HTS) dynamo, which was based on an additional DC coil. This method was based on the theory of macroscopic magnetic coupling effects (MMCE) discovered by Wang and Coombs, "Macroscopic magnetic coupling effect: The physical origination of a high-temperature superconducting flux pump," Phys. Rev. Appl., by using this theory, we had realized very flexible and accurate control of the pumped current in the HTS closed-loop. In this experiments, we had shown that the DC background field has a significant impact on the DC output of HTS dynamo, for instance, by applying a reversed DC bias field to the AC travelling wave generated by the HTS dynamo, we had managed to reverse the pumped current from 69.5A to -28.7A in the YBCO coil, without changing the rotation of HTS dynamo. Based on this experiment, we had developed a feedback control system, i.e., by controlling the direction of the DC bias field, we had managed to control the direction of HTS dynamo's DC output. By doing this, we had realized the adaptive control of the pumped current in the HTS closed-loop, with the control accuracy reached up to about 0.15A. This work verified that the state of superconducting magnetic flux quanta plays an important role in HTS dynamo's DC output, as had been explained in the theory of MMCE. This work had proven the "four-quadrant control" method proposed in MMCE, which may have important implications in HTS applications, especially in applications with high current accuracy such as in magnetic resonance imaging, etc.