In high-speed surface-mounted permanent magnet (SPM) brushless machines, time- and space-harmonic excitations can induce significant eddy currents flowing in the rotor conductive parts. An effective measure to suppress the eddy currents is to employ a copper shield between the magnets and the retaining sleeve. In this article, a Fourier-based analytical model is proposed to evaluate the rotor eddy current losses. The model is set up in the cylindrical coordinate system and is able to compute the eddy current fields and losses in all rotor domains, that is, the sleeve, shield, magnets, and shaft. Although it is generally believed that both ordinary Bessel functions (OBFs) and modified Bessel functions (MBFs) are workable for solving the magnetic vector potential, it is argued in this article that only the MBF-based models are numerically stable when the high-conductivity domain (e.g., the copper shield) exists, while the OBF-based models may result in irrational results. Both the OBF- and MBF-based analytical models for a prototype motor are established and comparatively studied, with verification of the finite-element (FE) method. Moreover, the cause of losing analysis accuracy in the OBF-based models is revealed.

This paper proposes a novel online maximum torque per ampere (MTPA) control method for permanent magnet synchronous motors (PMSMs), addressing nonlinearities such as magnetic saturation and cross-coupling effects. A flux linkage based nonlinear PMSM model is developed to improve torque control under dynamic conditions. The proposed gradient projection descent (GPD) method is introduced as a computationally efficient solution specifically tailored for real-time applications. It is evaluated alongside the Levenberg-Marquardt algorithm (LMA), renowned for its high accuracy and rapid convergence. Compared with LMA method, the proposed GPD method achieves an optimal balance between computational efficiency and control accuracy, making it suitable for embedded systems with limited resources. Notably, the method can support online experimental characterization and online parameter estimation techniques to capture real operating conditions, such as temperature and load variations, providing a significant advantage for dynamic PMSM applications. Extensive simulations and experimental validations using a 1.3 kW interior PMSM prototype and a TMS320F28375S control platform demonstrate the effectiveness of the proposed methods. Results demonstrate that GPD ensures real-time feasibility while maintaining acceptable levels of torque accuracy. These findings highlight the potential of GPD as a practical solution for high-performance motor control applications, especially in resource-limited embedded systems, with future work planned to explore online characterization and estimation for enhanced adaptability.

In conventional permanent magnet-assisted synchronous reluctance machines, the permanent magnet (PM) torque and reluctance torque are coupled with each other due to the rotor structure, and the ripples of these two torque components are superposed, with few design solutions being applicable to reduce the overall torque ripple. In this paper, an axially-segmented permanent magnet-assisted synchronous reluctance machine, which has a reluctance segment and a PM segment on the rotor, is studied. A method of torque ripple reduction using harmonics superposition is proposed, in which the two torque components generated by the two rotor segments are matched in such a way that their main harmonics have appropriate amplitudes and phases to cancel each other. Motor optimizations with surrogate models based on neural network fitting and interpolation are performed to achieve maximum suppression effect of the torque ripple. Finite element analysis and prototype experiments are conducted, confirming the effectiveness of the method.

In this paper, a fast rotor design method for synchronous reluctance machines (SynRM) is proposed, utilizing partly concentric circular flux barriers. The parametrization model exhibits a design freedom between the classic model with concentric flux barriers and the complete model with non-concentric ones. Moreover, a simple yet efficient equation between the end span angle and thickness of each flux barrier is introduced, based on the Joukowski formulation, which expands the parameter scan range while avoiding redundant rotor geometries, thereby improving time efficiency of the motor optimization. Three models, viz. the classic, complete and proposed, are applied to a same SynRM design and optimization process, employing Evolutionary Algorithm combined with the response surface method. The proposed methodology demonstrates significantly higher fitting accuracy compared to the complete model and achieves superior motor performance relative to the classic model. Finally, a prototype based on the proposed design method is manufactured and tested, validating the effectiveness of the method.

In this paper, the impact of parameter matching on the steady-state performance of permanent magnet-assisted synchronous reluctance motors (PMaSynRM) under vector control is analyzed and discussed. First, based on the mathematical model of motors under the maximum torque per ampere (MTPA) control strategy, an analysis is conducted concerning two main parameters, i.e., the matching relationship between the back electromotive force (back-EMF) and the saliency ratio. The impact of these two parameters on the operational status of the motor is investigated. Then, the motor’s voltage operating conditions are examined, and the operating curve under minimum voltage is derived. Furthermore, in the overvoltage region under the MTPA control strategy, the operation of the motor under the maximum torque per voltage (MTPV) control strategy is explored. This analysis illuminated the patterns of influence exerted by the back-EMF and the saliency ratio on the motor’s voltage operating condition. Between these two control strategies, there remains scope for the motor to operate at its limits. An enhanced understanding of the effects of the back-EMF and saliency ratio within this range on motor performance was achieved, resulting in the optimal matching curve for the back-EMF and saliency ratio. Finally, a 45 kW PMaSynRM was designed, prototyped, and tested to validate the correctness of the design techniques, with the motor achieving IE5 efficiency.

This paper presents an improved rotor topology aiming at torque enhancement for high-speed synchronous reluctance motors (SynRMs). Conventional high-speed SynRM rotor requires both tangential and radial ribs for mechanical integrity. However, the ribs increase flux leakage and reduce rotor saliency, consequently deteriorate the torque density. Ribless designs with extra connecting structures have been proposed, which come with high manufacturing and assembly cost. In the proposed structure, symmetrical inner ribs are employed to maintain rotor robustness without the need for additional structures. Moreover, tangential ribs are cut off with the design of asymmetric rotor island tips to improve rotor saliency ratio and reduce torque ripple. Sensitivity analysis of design parameters is performed for staged optimization of the proposed machine. Analysis results demonstrate that the proposed rotor topology delivers higher torque compared to the conventional design while maintaining similar maximum rotor stress. Finally, static and load experiments are conducted, validating the superiority of the proposed rotor topology.