High-temperature superconducting (HTS) linear synchronous motor (LSM) with coreless stator presents numerous advantages, among which we stress the high thrust density, large electromagnetic gap as well as the absence of iron losses. This paper aims to investigate the magnetic fields and forces in a coreless HTS LSM and the AC losses in the REBCO coil serving as the excitation system therein. First, a three-dimensional analytical model to calculate the magnetic fields and forces is derived, based on the Biot-Savart law and the Lorenz equations. Secondly, the air-gap magnetic fields and forces are calculated by the analytical model and its effectiveness was confirmed by comparison with the finite element method (FEM) model and experimental measurement. Lastly, the AC losses in the REBCO secondary coil are calculated by a two-dimensional FEM model combined with the three-dimensional analytical model. These results prove that the analytical model presents several advantages of high computational accuracy and less computing-time consumption.

Introduction

The coreless high-temperature superconducting (HTS) linear synchronous motor (LSM), due to its high thrust density, large electromagnetic gap and the absence of iron losses, has attracted growing attention in the high-speed transportation systems, such as the highspeed train with wheel-rail support [1,2] and the electrodynamic suspension (EDS) train [3,4]. The EDS train consists of the suspension system and the driving system in which the coreless HTS LSM is used because of its unique advantages, for instance, the robust driving stability and increasing suspension stability with lateral displacements [5]. In order to promote the development of the EDS train and wheel-rail train in the high-speed transportation, a systematical examination of the electromagnetic properties of coreless HTS LSM is essential. Several studies on the electromagnetic properties of coreless HTS LSM have been carried out in recent years. A 7-kW air-core-type HTS LSM prototype has been designed and installed in a bogie on a 10-m track, and the test results have verified the effectiveness of the coreless HTS LSM for high-speed trains [2]. More recently, the comparison of electromagnetic forces generated by two types of small-scale HTS LSMs with air-core stator and iron-core stator respectively was performed, and it proved that the coreless HTS LSM can provide better thrust and normal force [6]. Besides, based on the Genetic Algorithm method and virtual displacement method, two analytic models were developed in parallel to calculate and optimize the electromagnetic forces of the coreless HTS LSM for the EDS train [5,7]. The obtained results show that the racetrack magnet with elliptical sides can improve thrust and normal force, and the thrust fluctuation can be mitigated by using the optimal parameters of the propulsion coil.