Analytical method for vibration and noise prediction in electrical machines is computationally efficient and widely used. In conventional analytical approaches, the slotted stator is simplified as a cylinder, and it is generally believed that the vibration is more sensitive to the air-gap forces with low spatial orders, hence, those high-order air-gap forces are usually neglected. In this paper, the force distribution on the slotted stator is analyzed using a force transformation model and a new phenomenon, i.e., the modulation effect, is found, which indicates that a high-order air-gap force could also induce a low-mode stator vibration with a large amplitude. As a result, the conventional analytical methods are not so accurate for machines with a strong modulation effect, such as fractional-slot concentrated-winding machines. The existence condition for the modulation effect is also discussed in this paper. Finite-element analysis and experiments have been done to verify the analysis results.

High-speed permanent-magnet (PM) machines are promising for many industrial applications. The main design challenge of high-speed PM machines comes from the PM rotor design due to the low strength and high thermal sensitivity of PM materials. In this paper, the mechanical constraints and speed limits for a high-speed rotor topology are derived with analytical equations. Thereafter, a case study is done to design an 80 kW, 80,000 rpm PM machine. Analysis results show that the high rotor eddy-current loss is one of the key factors contributing to the overheat of the PMs. Hence, a hybrid sleeve topology, which contains an inner titanium cylinder and an outer cylinder made of carbon fiber composite (CFC), is proposed to suppress the rotor eddy-current losses. The optimal dimensions of the hybrid sleeve are obtained by finite element analysis (FEA). Thereafter, a comparison among the proposed and two other sleeve topologies, namely, the copper clad sleeve and grooved sleeve, is done from the point of view of their rotor eddy-current losses, rotor temperature rise, mechanical stress and critical speed. The results indicate that the hybrid sleeve gains an advantage over the other two topologies. For the designed case, the rotor eddy-current losses and temperature rise are decreased by 66.4% and 73 °C, respectively, by using the hybrid sleeve. Furthermore, a reduction of 14.5% for the rotor maximum stress is obtained with the hybrid sleeve, while the rotor's first critical speed has little reduction.

The requirement for electrical machines with high power/torque density has stimulated the development of high efficient cooling systems to dissipate the heat within the machines. This paper presents a new water cooling topology for thermal management of a permanent magnet synchronous machine (PMSM) with concentrated windings. The advanced cooling configuration consists of several water cold plates (WP) radially inserted into the core laminations. Therefore, the heat sources in laminations and windings are close to the coolant. 3-D electromagnetic finite element analysis (FEA) and the computational fluid dynamics (CFD) are used to evaluate the performance of the PMSM. In order to evaluate the effectiveness of the proposed cooling configuration, one PMSM with the proposed cooling configuration and the other with the regular water jacket (WJ) are designed and built under the similar sizes and specifications. The simulated and tested results shows that the winding temperature can be reduced by over 20oC using this cooling technique compared to using the WJ at the rated condition.

With the development of vibration mechanism research on electrical machines, the tooth modulation effect was found recently. Besides, the tangential effect, which contains both the air-gap tangential force's effect and the influence of tangential magnetic field on the radial force, was also proved to be of great importance. Nevertheless, these effects are still not found to be considered in the analytical or hybrid vibration synthesis methods, which are quite efficient for machine vibration analysis. Hence, this article proposes a hybrid vibration synthesis method for electrical machines taking both these two effects into account to improve the accuracy. The electromagnetic force processing and transfer function construction processes of the proposed method are presented in detail. By applying this hybrid model to a permanent magnet machine and conducting an experimental study, the accuracy of this method is validated. Moreover, based on the proposed method, the influences of tooth modulation and tangential effects on the machine's vibration are analyzed. The result proves the significance of these two effects and highlights the contribution of this article.

In this paper, a novel flux switching permanent- magnet machine (FSPM) with consequent-pole magnets and flux bridges in the stator core is proposed to improve the torque capability of FSPMs with high pole ratios. The stator yoke and flux bridges adjacent to the magnets can provide magnetic paths for the main working harmonic field, thus the magnetic reluctance of the working harmonic field is reduced, and the flux modulation effect, winding back-electromotive force (EMF) and output torque of the proposed FSPM can be significantly improved compared to the regular FSPM with high pole ratios. The operation principles and stator-slot/rotor-slot combinations of the proposed FSPM are introduced. Then, the influences of pole ratio, split ratio, slot opening ratio and PM width on torque density of the proposed FSPM is investigated using finite element analysis (FEA). Moreover, after the investigations, a proposed FSPM is compared to a regular FSPM in terms of back-EMF, rated torque, power factor, etc. Finally, to verify the theoretical analysis, a 12-stator-slot/14-rotor-slot FSPM is built and tested.

Stator-permanent magnet (PM) machines are gaining more research interest in recent decades. Since the permanent magnets (PMs) are moved from the rotor side to the stator side and salient rotor structure is adopted, it is claimed that the stator-permanent magnet machines exhibit several promising features, such as simple and robust rotor, being suitable for high speed operation, and good ability of heat dissipation as the main losses are located in the stator. On the other hand, to improve the shortcomings of inherent limited magnetic field adjustment ability, hybrid excitation PM machines with additional field windings are proposed. However, the complexity of the machine structure is increased inevitably. At present, it is found that both the stator PM and the stator DC current excited vernier machines operate with the flux modulation principle, and generally, the armature windings of the stator PM machines are fed with pure sinusoidal current. In this paper, a novel hybrid excitation, stator permanent magnet vernier machine (HE-VPM) is analyzed. In addition to the features of salient rotor structure, stator located PMs, and concentrated armature windings, the novelty of this machine is DC-biased sinusoidal phase current, which contains an alternating current (AC) component and a direct current (DC) component. The fundamental theories of stator PM machines fed with DC-biased current are researched, operation principle and slot/pole combination is concluded, and the optimal current configuration is studied theoretically and by finite element analysis (FEA). Finally, a prototype was designed and manufactured, the experimental tests were done to validate the proposed analysis.