Influence of Harmonic Distortion on AC Losses in Converter-Fed Superconducting Electrical Machines

Accurate estimation of ac losses is crucial to successfully implement high-temperature superconductors (HTS) in the armature of electric machines. In this estimation, a purely sinusoidal current is often assumed. However, the connection to power electronic converters will introduce harmonics in the transport current, generally leading to higher losses. In this article, four separate distorted current waveforms produced by space vector modulation were implemented to assess how harmonics from power electronics influence the HTS ac losses in a 2.5 MW superconducting aviation motor. By varying the switching frequency between 5 and 40 kHz, the amount of harmonic distortion was varied between the four cases. The ReBCO and copper layers were both modeled using a multilayer H-A-formulated model. While the harmonic distortion was found to have a minor impact on ReBCO layer hysteresis losses, it increased eddy current losses in the copper stabilizer by between 250% and 471%, depending on the amount of distortion. Consequently, the total losses increased by between 60% and 123%, with a higher copper loss fraction.