Comparison of the AC Loss of MgB₂ Superconductors and HPAL Cryogenic Composites for Rotating Machine Applications

High-power electric aircraft motors and generators require high current density conductors to meet the required performance metrics, which are beyond those achievable using ambient temperature metals. <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{MgB}_{2}$</tex-math></inline-formula> superconductors and high-purity aluminum (HPAL) hyperconductors are being considered for this work because of their combination of high current density/ampacity in combination with relatively low AC loss and their ability to work at the temperature of liquid hydrogen and above. In this work, we calculated the AC losses of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{MgB}_{2}$</tex-math></inline-formula> and HPAL conductors of various wire architectures in applied magnetic fields of 0.5 T and frequencies, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i>, up to 1 kHz. In particular, we estimated the contributions of several AC loss components, including eddy current and coupling losses, in AC magnetic fields and frequencies relevant to AC motors and generators in electric aircraft. The losses were then summed up and presented in terms of power loss per length, per unit current [W/(m*A)] in order to fairly compare the AC losses of superconductors to hyperconductors over various frequency regimes. Additionally, we accounted for the anomalous magnetoresistance component of the HPAL conductor, using data from a newly developed composite, measured at 20 K in fields up to 9 T in a PPMS. We conclude that for a 0.5 T, externally applied, time varying field, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{MgB}_{2}$</tex-math></inline-formula> is the lowest loss conductor for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> < 180 Hz, while multifilamentary HPAL conductors are better for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> > 180 Hz (explored up to 1 kHz), based on our chosen conductor design assumptions. However, the best place to transition from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{MgB}_{2}$</tex-math></inline-formula> to HPAL composites lies somewhere in the 200 Hz to 1 kHz regime, depending on the parameters of the conductors, the value of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$B_{m}$</tex-math></inline-formula>, and the relative tradeoffs in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$J_{e}$</tex-math></inline-formula> and power loss per unit volume the application demands.