A fast AC loss calculation method for high temperature superconducting magnetic energy storage magnet via critical state driven current identification

Superconducting Magnetic Energy Storage (SMES) systems are power type energy storage for grid stability control. Advantages such as millisecond scale response and very low operational loss are offered. Nonperiodic charging and discharging currents generate significant AC loss that constrains thermal stability, so rapid and reliable assessment is required. A physics based, system level real time evaluation framework for high temperature superconducting tapes is presented. Current history is respected by identifying the critical state and reconstructing the current density distribution. A penetration depth loss map of the target wound magnet is produced by a finite element algorithm, which separates electromagnetic states during charge and discharge. Local loss of micro elements at different penetration depths is evaluated through a superposition scheme, and then aggregated into the total loss. The method is applied to solenoid magnets with energy from 150 kJ to 10 MJ using practical operating conditions of SMES. Agreement with a finite element model is achieved. The interval error is 1.75%. For three solenoid magnets the errors are 2.49, 3.04, and 8.63%. Evaluation time is reduced from 2 h 4 min and 5 h 8 min to 0.17 and 0.20 s. AC loss assessment for SMES is therefore fast, reproducible, and suitable for engineering application when current history from the critical state is considered. The method supports thermal margin design and the co design of control for grid services. A consistent benchmark for future comparative studies is also provided.