Abstract
In this paper, a new type of hybrid stepping motor (HSM) with permanent magnets (PMs) embedded in the stator, namely the stator-permanent-magnet hybrid stepping motor (SHSM), is presented. It has the same operation principles as the traditional HSM, with a 2-D distributed magnetic field nature and superiorities such as simpler rotor structure, easier PM cooling, higher torque and power density, and higher power grade. Its structural topology and operation principles are initially presented. Then an investigation on the performance comparison between the HSM and the SHSM, in terms of PM flux density, PM torque, detent torque, positional holding accuracy, stator core saturation issue, PM flux leakage, and PM utilization rate is carried out theoretically to make an assessment of the performance superiorities of the SHSM. A prototype of a 2-phase 8-pole 50-rotor-tooth SHSM is fabricated and experimentally compared with the HSM by using finite element analysis (FEA) to verify the motor’s operational feasibility and the theoretical analysis. The FEA and experimental results show that the proposed SHSM has performance advantages such as higher torque density, higher power grade, and higher pull-out torque, holding torque, and torque-speed property, although it has performance defects such as higher torque ripple and relatively lower positional holding accuracy in the open-loop operation than the conventional HSM. Consequently, this novel SHSM is more suitable for electromechanical energy conversion applications rather than positioning mechanisms, especially taking into account the open-loop control advantage.
Highlights
Stepping motors are typically classified into three categories: variable-reluctance (VR), permanent-magnet (PM), and hybrid (HSM)
One is the stator-permanent-magnet hybrid stepping motor (SHSM) with the configuration shown in Figure seen that the calculation result can well predict the measured one, which is of significant importance in computing the motor’s dynamic performance
The other one is the hybrid stepping motor (HSM) with the configuration shown in Figure 8a and the same dimensions as the SHSM except for the permanent magnets (PMs) surface area
Summary
Stepping motors are typically classified into three categories: variable-reluctance (VR), permanent-magnet (PM), and hybrid (HSM). The HSM benefits merit its use over the PM and VR stepping motors It can achieve small step sizes along with a simpler magnet structure, and requires less excitation to achieve a given torque, due to the utilization of PMs [1]. It is quite suitable for high-precision and high-torque positioning applications, becoming so far the most widely used stepping motor type in automation applications. It still suffers from some defects mainly due to the rotor-permanent-magnet structure and the 3-D distributed magnetic field nature, which limits its performance improvement, capability enhancement, and its further development. The PM field has to travel vertically through core laminations and inter-lamination air-gaps to form a closed magnetic circuit [2], leading to a low utilization rate of the PM and core materials; it is difficult to control the temperature rise of the rotor-PM, which increases the risk of irreversible demagnetization; since the PM size is restricted by the rotor’s diameter, the multi-stack rotor and more than one PM should be adopted to supply an adequate
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