Electromagnetic and Thermal Design of Partially HTS Linear Motor: Analysis of Thrust Ripple Harmonics and Thermal Optimization

The acceleration and heat loss of superconducting linear motors are the main limitations in their development. The electromagnetic and thermal design methods of a partially high-temperature superconducting linear motor (HTSLM) are proposed to increase acceleration and reduce heat loss. The electromagnetic design is based on a two-dimensional (2D) analytical model and a three-dimensional (3D) finite element model (FEM), whereas the thermal design is performed using a thermal network model (TNM) and a 3D FEM, under steady-state conditions. In this paper, both the mover and the stator are placed in a cryostat to reduce the air gap and increase the acceleration up to 9 g. After the proposed HTSLM system reaches thermal equilibrium, the stator operates at 52 K. The electromagnetic thrust is analytically derived and decomposed into the fundamental and ripple components. The harmonic analysis indicates that the ripple originates from the coupling between the AC and the (6i$\pm$1)-order harmonics of the air-gap field. The TNM and the 3D FEM are used to analyze the heat flow paths and to calculate the heat losses. The parametric effects of the mover temperature and the heat loss are studied. The parameters of the TNM and the 3D FEM are then improved to optimize the thermal design and to guide the selection of a cryocooler. The 2D model proposed in this paper for electromagnetic design, as well as the TNM for thermal design, have certain generality and can be used in the design of planar and rotary motor systems.