Equivalent Circuit Extraction of MI-HTS Coil Including High-Frequency Region for Electromagnetic Transient Simulation With Voltage-Source Converter

Combining metal-insulation high-temperature superconductor (MI-HTS), power electronics presents a promising potential to implement reliable magnetic energy storage systems. A modern power converter, typically implemented as a voltage-source converter (VSC), utilizes power semiconductors with switching frequencies ranging from several kHz to hundreds of kHz. From a VSC design perspective, analyzing the current flowing into power semiconductors at the microsecond timescale is essential to prevent converter failure due to overcurrent. Thus, to reduce the risk of operation failure of VSC, it is crucial to simulate the operation of VSC with MI-HTS not only the long-term behavior but also the short-term dynamics before commissioning. This article presents a practical method to develop an equivalent circuit of MI-HTS, enabling the replication of its current response at the microsecond timescale within electromagnetic transient simulations. This circuit can be used to verify the operation of MI-HTS and VSC, including control algorithms, by considering characteristics of leakage currents in MI-HTS under pulsed voltage from the VSC. The proposed method utilizes measured frequency response data and a rational approximation algorithm to extract an equivalent circuit. The proposed procedure is validated through a comparison of simulated and experimental results from closed-loop current control of a 37.2 mH MI-HTS coil driven by a VSC with a switching frequency of 2 kHz.