In this paper, a novel coaxial magnetic gear (MG) is proposed, in which both permanent magnet and consequent poles are employed on the inner and outer rotors. The MG is expected with improved torque transmission capability by increasing the effective magnetic flux and offering additional reluctance torque. Air-gap field distribution and torque-angle characteristic of this MG are analyzed and compared with the conventional MG which adopts dual surface-mounted permanent magnet rotors. To maximize the torque density, several key design parameters are investigated using finite element method. Analysis results indicate that the proposed MG with ferrite magnets can largely improve the pull-out torque. In addition, end effect and power losses with different rotor structures are analyzed. Performance of two optimized MGs is then validated with test. Also, the MG cost effectiveness with different magnet materials is presented.

A rotor retaining sleeve is usually essential in high-speed permanent magnet (PM) motors to firmly retain the magnets and ensure the rotor integrity. The structure and material of retaining sleeve have a significant effect on rotor losses, especially on the rotor eddy current loss. On the other hand, heat dissipation from the rotor is difficult, therefore, any excessive rotor loss may lead to over temperature and cause irreversible demagnetization of the magnets. In this paper, the influence of retaining sleeve with different structures and materials on the rotor eddy current loss in high-speed PM motors will be comprehensively investigated, with both 3-D finite element method (FEM) simulations and experiments. Particularly, the proposed experiments are carried out with a stationary rotor. The study reveals that the equivalent conductivity of the retaining sleeve has a significant influence on the rotor eddy current loss, and countermeasures can be made accordingly so as to reduce the rotor eddy current loss.

This paper proposes a modified model-free predictive current control (M-MFPCC) integrated with a modified extended state observer (MESO). The goal is to reduce torque ripple and improving current distortion caused by inverter nonlinearity and other system disturbances. The disturbances are precisely observed with unity gain and zero phase delay. Adaptive gain updating of the proposed observer is implemented to track the frequency of the disturbance and sustain the noise suppression performance under various operating conditions. The proposed M-MFPCC can eliminate the high frequency harmonic disturbances without requiring additional information about inverter nonlinearity or necessitating extra parameter tuning. Experimental results confirm the proposed method's efficacy in suppressing current Total Harmonic Distortion (THD) and torque ripple under a variety of load conditions.

Dual permanent magnet (PM) machines have attracted numerous interests due to the high torque density and compact volume . This article investigates a synergistic PM machines with the synergies of flux switching and flux reversal effects. The flux-reversal and flux-switching PM (FSPM) flux paths circulate from two sides of the split teeth separately, which avoid the over-saturation with dual PM excitations. The preferred stator and rotor pole number is derived from a simplified analytical model and the influence of leading parameters is analyzed as design guidelines. Furthermore, the synergistic stator PM machine is optimized and compared with FSPM machines. It is revealed that the synergistic stator PM machine exhibits ∼20%, ∼10%, and ∼17% higher torque density than conventional FSPM machine, C-core FSPM machine, and E-core FSPM machine, respectively. Besides, good flux weakening capability is achieved with a larger inductance than conventional FSPM machine, and higher efficiency is obtained at both low-speed and high-speed operations. Finally, an experimental prototype is fabricated to validate the proposed concepts.

The most common method to suppress electromagnetic vibration is to weaken the electromagnetic force harmonics, which are the vibration sources. Clearly, vibration is related to some other factors, too. Therefore, in this article, a modal analytical model and the transmission function of a permanent magnet synchronous motor are studied, based on which a fast analytical method of predicting the electromagnetic vibration is proposed, so that the vibration can be preliminarily evaluated during the machine electromagnetic design. The time-consuming 3-D finite-element method is not needed when predicting the vibration. Moreover, using the fast prediction method, a 15-D multiobjective optimization problem for vibration, torque, and efficiency performances is solved in stages. After optimization, the vibration is greatly reduced, and the torque performance is improved. The proposed methods are also proved to be applicable for different operating conditions and types of motors with various slot–pole combinations.

Given the wide-range applications of bidirectional dual-active-bridge series-resonant converter (DABSRC), its complex nonlinear dynamic behavior is an interesting phenomenon that deserves attention of power electronics engineers. It is observed that if the control variables (i.e., phase-shift angles) are directly updated through conventional transient modulation, large-amplitude transient oscillations and dc offsets will be induced in the high-frequency-link voltages and currents during transient stage, which can ultimately degrade the converter's waveform quality significantly. The relatively few prior works in studying the transient oscillatory behavior of DABSRC have only focused on single-phase-shift modulation. In this article, a new transient modulation method referred to as generalized trajectory-switching modulation (GTSM) is first proposed for enhancing the transient performance of multiphase-shift modulated DABSRC. GTSM can simultaneously mitigate the problems of transient oscillations and dc offsets regardless of operation modes and power-flow directions, thus always ensuring safe transient operation. It also enables the resonant voltages and currents as well as magnetizing current to seamlessly reach the desired new steady-state values swiftly. Finally, the said theoretical claims are verified experimentally under both open loop and closed loop with model predictive control, and the influence of deviations from nominal resonant tank's parameters on GTSM is also considered.