## 1 Introduction  
Although magnetic bearings have solved the rotor support problem in high-speed motors [1], they still have the disadvantages of high power consumption for magnetic levitation control, long rotor shafts, and limited critical speed, etc. [2, 3]. A bearingless motor is a new type of magnetic levitation motor that integrates rotary drive and rotor levitation functions [4]. It not only overcomes the shortcomings of AC motors with magnetic bearings, such as low power density, high power consumption of the control system, and high cost, but also has the advantages of a high critical rotational speed and ease of microminaturization [2, 5]. Therefore, it has broad application prospects in the fields of advanced manufacturing, flywheel energy storage, aerospace engineering, etc. [2, 6, 7, 8, 9]. Currently, bearingless motors generally adopt a dual-winding structure; that is, the torque winding and levitation winding are simultaneously embedded in the stator to achieve radial levitation and rotational drive control of the bearingless rotor, respectively [2; 7]. However, the existence of independent levitation windings reduces the slot occupancy rate of torque winding, thereby reducing the motor power density. Therefore, the development of a single-winding structure for bearingless motors has become an inevitable trend [2; 9; 10; 11]. The single-winding structures of bearingless motors includes bridge winding [10], parallel DPNV winding [11], midpoint injected winding [9], multiphase winding [12], etc. Among them, multiphase bearingless permanent magnet synchronous motors (BPMSMs) not only have high working efficiency, excellent speed regulation performance, and the high reliability characteristics of permanent magnet synchronous motors, but also offer the advantages of multiphase motors, such as multiple degrees of freedom and less harmonic content. Thus, they have gradually become an international research hotspot in the field of high-speed motors [2; 12; 13]. Reference [12] investigated a five-phase BPMSM with 30 slots and 4 poles, established an inductance model, and performed validation analysis. For the two-pole torque system and four-pole levitation system of a six-phase BPMSM, reference [13] proposed a structure and control strategy for a parallel dual three-phase BPMSM with 24 slots and 4 poles. In the low-power field, stator structures with 12 or fewer slots are most commonly adopted [14; 15; 16]. Reference [14] studied a six-phase BPMSM with 6 slots and 2 poles, analyzed the fault-tolerant performance advantages of the multiphase BPMSM, and experimentally proved the correctness of the mathematical model. Reference [15] proposed a dual three-phase control method for a single-winding BPMSM with a two-pole torque system and a four-pole suspension system, carried out electromagnetic characteristic tests on a prototype machine, and gave the calculation results of the control parameters. Reference [16] studied a five-phase motor with 10 slots and 8 poles and optimized the levitation performance using a harmonic injection method. However, the magnetic levitation force waveform of a BPMSM usually has obvious fluctuations, meaning that the rotor levitation performance can only be improved through an external closed-loop control system. This makes it inconvenient for the promotion and application of bearingless motor technology in the low-power field [2]. In this work, to meet the requirements for single-winding bearings motor technology in the low-power field, a six-phase distributed single-winding BPMSM with 12 slots and 2 poles (six-phase DSW-12/2-BPMSM) is researched, and detailed modeling and electromagnetic characteristic analyses are conducted. First, the control principles of electromagnetic torque and magnetic levitation force are analyzed, and mathematical models of the inductance matrix, electromagnetic torque, and magnetic levitation force are established.