Search

In this paper, taking a high-speed permanent magnet generator (HSPMG) as an example, the unbalanced load limit of HSPMG is studied based on the analysis of the electromagnetic and temperature fields of the generator. The influences of different degrees of unbalance currents on the losses of the generator are studied, and the influence mechanisms of unbalance currents on the losses of the rotor sleeve and permanent magnet are revealed. Based on the theory of fluid dynamics and heat transfer, the temperature field distribution of HSPMG under the unbalanced load condition is studied, and the non-linear relation between the current unbalance and the temperature field of HSPMG is determined. Finally, the load unbalance resistant limit of HSPMG is determined. These conclusions can provide a reference for determining the unbalanced load limit of HSPMG. It is also helpful for improving the reliability of HSPMG under abnormal working conditions.

A power converter is very necessary in the system of high-speed permanent magnet generators (HSPMG), since the frequency of the output electrical energy is generally hundreds of Hertz or even more than 1000 Hz. However, the converter with switches in fast on–off transitions will have some effects on the generator and, therewith, some current harmonics will be also induced in the device. Taking a 117 kW 60 000 r/min HSPMG as an example, the harmonics in this generator were analyzed. And then, the voltage harmonic content, the current harmonic content, and the current total harmonic distortion could be obtained. In addition, stator core losses and rotor eddy current losses were analyzed comparatively, and the influence of the converter on the generator power factor was further studied. Based on the 3-D coupling field between fluid and temperature, the temperature distributions were obtained when the generator was connected to different loads, and the influence of the rectifier on the generator temperature field could be obtained, which was also compared with the test data.

A new approach has been proposed to evaluate the influence of the transverse edge effect of high-temperature superconducting (HTS) linear induction motor (LIM) in this paper. Taking a 3.5 kW single-sided HTS LIM for an example, the cross-flux density distributions were analyzed by analytical method. Based on results mentioned above, a new transverse coefficient was proposed to evaluate the influence of the transverse edge effect on the cross-flux density distribution. The influences of the motor configurations and parameters on the transverse coefficient were also investigated. The 3-D finite-element method was adopted to verify the accuracy of the presented analytical method.

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.

In a high-speed permanent-magnet generator (HSPMG), an alloy sleeve is often used to prevent damage to rotor magnets caused by the large rotational centrifugal forces. However, eddy-current losses appearing in the sleeve increase the generator working temperature, which may reduce the generator performance and even cause thermal demagnetization of the magnets. Thus, a sleeve scheme designed with low eddy current losses is necessary, and a rotor structure with copper plating is presented in this paper. The two-dimensional mathematical model of a 117 kW, 60 000 rpm HSPMG is established, and the electromagnetic field in the generator is calculated using the finite element method. The results show the effectiveness of the copper plating in reducing the eddy current losses in the rotor, and the influences of the sleeve thickness and the copper layer thickness on rotor eddy current losses are analyzed. Using the fluid-thermal coupling method, the temperature distribution of the generator with different copper layer thicknesses is comparatively analyzed based on the theories of fluid mechanics and heat transfer. The relationship between the temperature and the copper layer thickness is obtained, and finally the temperature of the permanent magnets, which is the part most seriously affected by the temperature, is given with different copper layer thicknesses. The obtained conclusions may provide useful reference for the design and research of HSPMG.

With the development of the high-temperature superconducting material, the high-temperature superconducting machine becomes the very important research direction in the electrical machine domain. It integrates the advantages of high-power density, small machine size, and zero resistance of the superconducting windings. In this paper, taking an axial-radial flux-type high-temperature superconducting permanent-magnet synchronous motor (ARFTHTSPMSM) as an example, based on the investigations about the configuration characteristics and the operation principles of such machine, the mathematical model for the 3-D transient electromagnetic field was established. The magnetic field in this motor was analyzed by using the time-stepping finite-element method. In addition, the distribution characteristics of the magnetic flux in the air gap and ferromagnetic bridge were discussed, and then, the variations of the air-gap flux density, ferromagnetic bridge flux density, and non-load back electromotive force were analyzed when the motor is operating at different axial magnetic motive force. Both the theoretical analysis results and the experimental data indicate the notable advantage of adjustable excitation in such machine. Finally, based on the aforementioned analysis, the rotor eddy current losses were calculated, and their distribution characteristics were studied when the motor is operating at the starting process and the steady state, respectively. The obtained conclusions may provide useful reference for the design and research on the ARFTHTSPMSM.