Fractional-slot concentrated windings (FSCWs) are widely utilized in six-phase fault-tolerant permanent-magnet synchronous machines (PMSMs). However, FSCWs cause abundant space harmonics of stator magnetomotive force (MMF) and increase the losses of the machine. In this article, in order to suppress the space harmonics of a six-phase PMSM, the six-phase winding is regarded as a combination of two sets of three-phase windings, and the effect of phase-shifting between two sets of three-phase windings on the MMF harmonic suppression is investigated. To achieve more effective suppression of the MMF harmonics, the low-space-harmonic oriented design is further extended to phase-shifting between double six-phase windings while the phase number is not doubled. A low-space-harmonic double-six-phase 15°-shifting winding is designed, in which both J-pole-pair and 5-pole-pair MMF harmonics are suppressed, and its characteristics of losses, permanent-magnet (PM) torque, and reluctance torque are evaluated. A prototype of 24-slot/14-pole double-six-phase 15°-shifting PMSM is manufactured, and the experiments are carried out to verify the performance of the machine.
This study focuses on the phenomenon of rotor beat frequency vibration (BFV) in a 2-pole magnetic levitation induction machine (MLIM), systematically investigating its dynamic mechanisms and subsequently applying an established method for its suppression. First, the BFV synthesis process is described. Subsequently, three primary disturbance sources in the magnetic bearing (MB) system are identified and analyzed, including rotor unbalance, unbalanced magnetic pull (UMP) and magnetostrictive effect. Through numerical solution of a four-degree-of-freedom (4-DOF) rotor dynamic model, the theoretical analysis reveals that MLIM -induced BFV consists of three spectral components: (i) rotor rotational frequency (RRF), (ii) electrical fundamental frequency (EFF), and (iii) the sum of EFF and slip frequency (EFF+SF). Building on these findings, we propose the adoption of a well-established notch filtering technique as an effective means to suppress the BFV. The experimental results confirm the correctness of the analysis of the BFV generation mechanism, and in particular of the EFF disturbance mechanism, and also demonstrate the effectiveness of the vibration suppression method.
This paper investigates an aggregated design and optimization method for permanent magnet hub (PMH) motors, guided by permeance harmonics, to meet low-speed, high-torque requirements. The key lies in establishing the correlation between stator and rotor permeance harmonics and torque. Firstly, contribution equations describing the influence of stator and rotor permeance harmonics on torque are derived. It reveals that the contribution degree is affected by harmonic amplitude and phase. Then, the selection criteria for stator and rotor topology are formulated. The amplitude and phase characteristics of the permeance harmonic group are considered in criteria, which aim to achieve the aggregated design from a permeance harmonic perspective. Furthermore, based on the identified aggregated permeance harmonics, the airgap flux density harmonics directly linked to permeance harmonics are determined. Taking these harmonics as the goal, they are involved in the optimization process for high torque density. Sensitivity analysis and response surface analysis are adopted, respectively, to lock the design variables and their parameter ranges. Then, the motor topology with characteristics of high torque density is obtained through multi-objective optimization. Finally, a prototype experiment is conducted on the optimized PMH motor.
Sustainable motor design is crucial for improving energy efficiency and reducing material consumption. This paper introduces a novel asymmetric interior permanent magnet (IPM) rotor design using topology optimization (TO). The study employs a two-stage TO approach to design IPM rotor. In the first stage, a multi-objective electromagnetic TO is conducted to enhance the average torque and reduce the mass of the magnetically active rotor zone. In the second stage, structural TO is performed to minimize the mass of the magnetically inactive rotor zone while maintaining mechanical integrity, ensuring the rotor withstands operational mechanical stresses. The asymmetric topology-optimized IPM (ATO-IPM) machine is analyzed and benchmarked against the conventional IPM design and the symmetric topology-optimized IPM (STO-IPM) design. The results indicate that the asymmetric flux barriers enhance the torque performance. The ATO-IPM design offers significantly more efficient utilization of permanent magnets (PMs) and improved torque density by approximately 13.3% compared to the conventional IPM motor. Moreover, ATO-IPM design supports the advancement of sustainability by improving efficiency by 2.3% compared to conventional design. Furthermore, ATO-IPM designs save about 46.7% of the amount of silicon steel of the conventional topology.
With the development of onshore power grid projects in desert, Gobi and desertified regions as well as offshore wind power projects, electric energy requires long-distance transmission due to insufficient local consumption. Modular multilevel converter based high-voltage direct current (MMC-HVDC) has become the mainstream transmission technology for large-scale remote wind farm integration. However, MMC-HVDC electrically decouples wind farms from the main grid, and its interaction with wind farms can trigger various oscillations. In addition, the MMC-HVDC connected wind farm system differs from single-converter grid-connected systems in structure, equipment complexity, and fault evolution, leading to problems such as low inertia, wideband oscillations and poor fault ride-through. To address these issues, coordinated control strategies considering dynamic interactions between wind farms and MMC-HVDC have been widely studied. This paper thus reviews such coordinated control strategies from three aspects: first, introducing common engineering symmetrical monopole/bipolar MMC-HVDC system structures; second, summarizing grid frequency sensing methods and inertia support control strategies for MMC-HVDC and wind farms; third, discussing coordinated oscillation suppression and fault ride-through control strategies, considering direct current (DC)-side faults, alternating current (AC)-side grid faults, and wind farm area faults. Finally, it summarizes deficiencies of existing studies for each challenge and prospects future research directions for MMC-HVDC connected wind farm systems.
