The high-performance control of permanent magnet synchronous motors hinges on precise rotor position information. However, traditional mechanical sensors are plagued by high costs, large dimensions, and low reliability. As a result, position sensorless control technology has emerged and is becoming a research hotspot in the field of motor control. This article comprehensively reviews the existing position sensorless control technologies for permanent magnet synchronous motors. First, the fundamental principles of classical methods based on the motor’s fundamental wave model and saliency effect are analyzed in detail. Second, the advantages, disadvantages, and applicable scenarios of various position sensorless control methods are summarized. Finally, the key issues that need to be addressed in future research are pointed out.

Aiming at the characteristics of machine-side output instability and the wide-range variation in the tidal energy PMSG-PWM power generation system, we propose a control scheme with a high anti-interference capability applied to the PWM rectifier. The outer voltage loop adopts sliding mode control (SMC) with the variable exponential convergence law based on expanded state observer (ESO). By compensating the perturbation observation value into the sliding mode controller in advance, it improves the robustness and response speed of the system and suppresses the direct current (DC)-side voltage jitter phenomenon. The current inner loop combines model prediction (MP) with direct power control (DPC). By introducing time-delay compensation, it improves the control accuracy, reduces the machine-side harmonic content, and enables the system to maintain unit power factor operation despite external disturbances. Simulation and experiment results show that, under the wide range of PMSG output, the PMSG-PWM power generation system adopting the “ESO_SMC+MDPDC” scheme has a fast dynamic regulation of DC output voltage, obvious vibration suppression effect, low harmonic content of the current on the PMSG side, and fast current tracking speed, which verify the feasibility of applying this system to the field of tidal energy generation.

Thanks to the magnetic field modulation effect, the magnetic field modulation motor (MFMM) significantly improves torque density and magnetic field harmonic utilization by breaking the constraints of traditional motor excitation and armature pole number matching. This advantage enhances its development potential in fields such as new energy vehicles, aerospace, power generation, and the military. This article first starts with the basic principle of magnetic field modulation, and adopts the excitation unit position classification method to systematically summarize the evolution laws of major MFMM topology structures such as the permanent magnet synchronous motor, switch magnetic flux motor, and flux reversal motor in recent years. It also analyzes the research progress of key performance such as the torque characteristics and power factor of these motors. Research has pointed out that the MFMM still faces core challenges such as high torque ripple, complex structure, low power factor, and multiple losses. Based on a review of the main achievements in the field, the future development direction of MFMMs is proposed to promote its development in the fields of precision drive and efficient energy conversion.

This paper presents a 10 kW outer-rotor field-modulated permanent magnet vernier generator tailored for low-speed direct-drive applications. It employs an outer-rotor Spoke-array configuration, which effectively mitigates the leakage flux between adjacent pole pairs. First, the topology and operating principle of the proposed generator are elaborated. Analytical calculations of key design parameters are then performed to accelerate the modeling process. A systematic parametric sweep is conducted to optimize the motor parameters, based on which a 2D finite element analysis model is established. Comprehensive FEA simulations are carried out to investigate its flux regulation capability, static and dynamic characteristics, and permanent magnet demagnetization risk. The results demonstrate that the Spoke-array permanent magnet array effectively suppresses leakage flux, achieving a volumetric power density of 387.5 kW/m³, and the no-load back electromotive force achieves a peak amplitude of 270 V with a total harmonic distortion as low as 3.7%, which is significantly higher than that of conventional permanent magnet vernier generators. Finally, a 30-slot/23-pole prototype is fabricated and tested. The experimental results show excellent agreement with the simulation predictions, validating the effectiveness of the proposed design.

The rim-driven device (RDD) integrates the motor and the impeller, which can achieve shaftless, modular, and integrated operation of the turbomachinery system and has broad application prospects. To reduce the axial length and radial thickness of the RDD, a motor with a thin-yoke wide-tooth fractional slot concentrated winding stator and a coreless Halbach permanent magnet array rotor is designed. Theoretical and finite element simulation analyses of its air gap magnetic field characteristics were carried out. The results show that, for the thin-yoke wide-tooth fractional slot concentrated winding permanent magnet motor, the harmonic magnetic field generated by the magnetic poles should mainly consider the magnetic field components produced by the interaction between the harmonic magnetomotive force of the magnetic poles and the constant air gap specific magnetic permeability, as well as the magnetic field components generated by the interaction between the fundamental magnetomotive force of the magnetic poles and the fundamental and second-order harmonic air gap specific magnetic permeability. The harmonic magnetic field generated by the current should mainly consider the magnetic field components produced by the interaction between the harmonic magnetomotive force with a small number of pole pairs (NOPP) and large amplitude generated by the current and the constant air gap specific magnetic permeability. Compared with radial magnetic flux density, tangential magnetic flux density has the same NOPP and frequency components, with a phase difference of 90°. The fundamental amplitude difference between them is larger, while the harmonic amplitude difference between them is smaller.