In this paper, a superhigh-speed permanent-magnet generator (SHSPMG) which has an alloy sleeve on the rotor outer surface is investigated. The purpose of the sleeve is to fix the permanent magnets and protect them from being destroyed by the large centrifugal force. However, the sleeve material characteristics have much influence on the superhigh-speed machine, and therewith, most of rotor eddy-current losses are generated in the alloy rotor sleeve, which could increase the device temperature. Taking a 117-kW 60 000-r/min SHSPMG as an example, the influence of the sleeve on the generator output performance is analyzed when the generator sleeve is made of stainless steel, carbon fiber, copper-iron alloy, and copper. In addition, the eddy-current loss distributions could be gotten, and therewith, the variations of the eddy-current losses in different kinds of sleeves are analyzed. Based on the 3-D coupling field between the fluid and temperature, the temperature distributions were obtained when the sleeve adopts different materials. Moreover, the temperature variations of the permanent magnets are further analyzed. The obtained conclusions may provide some references for the design and analyses of the SHSPMG.

A new kind of induction motor with compound cage rotor (IMCCR) is proposed in this paper, in which rotor bars are composed of upper parts made of alloy (conductor for electric and magnetic) and lower parts made of cast aluminum. Calculation models for IMCCR electromagnetic field and whole region (including stator and rotor) temperature field analyses are established. From a motor electromagnetic analysis using the finite-element method, loss distributions are obtained, which are taken as the heat source in thermal analysis. In this paper, the starting and thermal performances of IMCCR operating under rated load are studied. From the comparison of the obtained results with test data, it can be seen that IMCCR would be a better choice for the driving system in electrical vehicles (EVs) and plug-in hybrid EVs (PHEVs). Furthermore, the influences of compound bar material on motor temperature distribution are analyzed, which would be helpful for the research on electrical materials used in machines. Considering the working conditions of motor used in PHEV and EV, the effects of ambient temperature and output load on motor thermal performance also have been studied.

Alloy rotor sleeves are used extensively in high-speed permanent-magnet machines since they could fasten the permanent magnets availably. However, it is inevitable that eddy-current losses will be generated in the sleeve, which may make the permanent magnets overheated. In order to reduce the rotor eddy-current losses, this paper focuses on the influence of the rotor-sleeve electromagnetic characteristics. Taking a high-speed permanent-magnet generator (HSPMG) as an example, the variations of output performance and rotor eddy-current losses were analyzed when the generator adopts the steel sleeve and the copper-iron alloy sleeve, respectively, and therewith, the principles of the variations were exposed. Then, the rotor eddy-current losses were further analyzed when the generator sleeve conductivity was changed. The worst range of the sleeve conductivity was also given, in which the rotor eddy-current losses were the largest. Additionally, the increase of the sleeve permeability could reduce the main magnetic circuit reluctance and improve the operating point of permanent magnets. On the other hand, it can increase the pole-to-pole flux leakage dramatically. So, the generator performance should be analyzed by considering the two factors when the rotor-sleeve permeability was different.

High-speed permanent-magnet generators (HSPMGs) are common and important power generation equipment used in distributed generation systems. A 100-kW-level HSPMG is investigated in this paper, and its cooling system is optimized through electromagnetic-fluid-thermal analysis. First, the 2-D electromagnetic field of the machine is calculated by using the time-stepping finite element method, and the electromagnetic performance and loss distributions (heat sources) are determined, particularly the eddy loss of the rotor sleeve. Then, a thermal analysis model of the fluid for the HSPMG is established. Through numerical calculating, the whole region 3-D temperature distribution in the HSPMG is obtained, in which the influence of temperature on material properties is considered. Considering the variations of heat transfer abilities of the cooling medium, the temperatures in machines with different cooling structures are comparatively analyzed, and new cooling grooves with variable cross sections are proposed, which make the temperatures in the machine lower and more evenly distributed. The obtained conclusions may provide useful reference for the optimal design and research of HSPMGs.

The rotor temperature rise of high voltage line-start solid rotor permanent magnet synchronous motors (HVLSSR-PMSMs) may be too high while operating, which properly causes thermal demagnetization for permanent magnets. Therefore, it is necessary to perform the thermal investigation on HVLSSR-PMSM. In this article, a 315-kW, 6-kV HVLSSR-PMSM with the air-cooled hybrid ventilation system is studied in the view of thermal phase. The losses, obtained from the electromagnetic analyses, are applied to the thermal investigation as the distributed heat sources. Whereas, both the mathematical and the geometrical models are proposed for the three-dimensional (3-D) fluid-thermal coupled investigation, from which the fluid velocity and the temperature in motor different components are determined. Whereas, with the hybrid ventilation system, temperatures in motor different components reduce, obviously comparing with those in motor with the original cooling system. The experimental investigations are performed on prototypes in both cases, which verify the calculation results and approve the effectiveness of the proposed hybrid air cooling system as well.

Permanent magnet motors are widely used in the driving system of electric vehicles because of their high power density and small size. However, the permanent magnet motor is prone to demagnetization due to the complex operating environment of electric vehicles and characteristics of permanent magnet motors. To ensure the normal operation of vehicles, the demagnetization fault diagnosis of permanent magnets should develop. In this study, the thermal behavior of a permanent magnet motor under local demagnetization fault is discussed. Results show that the demagnetization of permanent magnets has a significant effect on the temperature of the motor; thus, the temperature is added into input signals of the permanent magnet demagnetization fault diagnosis. The healthy state of the permanent magnet is predicted by the back propagation (BP) neural network to realize the demagnetization fault diagnosis. First, the demagnetization test platform is built to test the performance of the motor, and the current, torque, and temperature of the motor are measured according to different demagnetization degrees. Second, the demagnetization simulation model of the motor is established by the finite-element method, and the air gap magnetic field, loss, and temperature of the motor are analyzed. Lastly, the temperature, current, speed, and torque signals are selected as input signals of the neural network model, and the demagnetization rate of the rotor is taking as the output signal. The neural network prediction model is established and trained, and the good generalization ability is obtained.