Test of a YBCO thin film based over current limiter employed in battery unit of SMES-battery HESS during charging process

This paper proposes a novel over current protection strategy based on YBa ₂Cu ₃O _7-x (YBCO) thin film current limiter, to improve the over current stability of the battery unit in superconducting magnetic energy storage (SMES)-battery hybrid energy storage system (HESS) during charging process. The conventional over current protection strategy for battery unit is based on cutting off the operation of the battery unit to remove the fault. Especially, during the charging process, once the battery unit circuit is cut off, the stability and reliability of the HESS will be also reduced. Hence, considering the features of the YBCO thin film in both superconducting state and quench state, it can be deployed as the over current limiter, to keep the stability of the battery unit against the over current fault during the charging process. In this paper, we designed and fabricated the YBCO thin film over current limiter, meanwhile, the preliminary verification experiment was carried out in our laboratory. It can be found from the experimental results that the over current in battery unit can be limited effectively by its quench resistance without cutting off the whole circuit. Besides, the charge voltage fluctuation of the battery unit can be also compensated by using the proposed protection strategy. Thus, the stability and reliability of the battery unit against the over current fault in charging process can be further improved.