Electromagnetic Field Computation And Operating Characteristic Analysis For A Permanent Magnet-Inductor Hybrid Excitation Generator

Compared with electrical excitation generator, Permanent Magnet (PM)generator has many favorable features, like simple structure, reliable operation, noexcitation loss, et al. However, the drawback of the output voltage fluctuation withload or speed variations limits the further application of the PM generator. Thevirtues of hybrid excitation generator include not only small volume, highefficiency like PM generator, but also adjustable output voltage like electricalexcitation generator. In recent years, hybrid excitation generator has rapidlydeveloped. Permanent Magnet-Induction Hybrid Excitation Generator (PM-IHEG)has many excellent qualities, such as simple structure, independent magneticcircuits of the PM and inductor sections, and no electrical brush. However, thePM-IHEG is a new electrical machine with complex magnetic circuit. The designand calculation of the PM-IHEG is special. At present, the research on thePM-IHEG is few and the theory system about PM-IHEG is immature. In this thesis,a PM-IHEG is put into focus, and the problems of electromagnetic fieldcomputation, inductance computation, operation performances analysis, losses andtemperature field computations have been studied deeply.Electromagnetic field computations of the PM and inductor sections areperformed by 2-D and 3-D Finite Element Method (FEM). The magneticdistribution regularities of the two sections are obtained. Aimed at 3-D FEMcomplex computation, a 2-D equivalent model of the inductor section has been built.The influence of the rotor tooth and slot shape on the air-gap magnetic field of theinductor section is analyzed. The results show that the waveform of the air-gap fluxdensity of inductor section and the output voltage adjustment range of thePM-IHEG can be improved by optimizing the rotor shape. The magnetic fieldcoupling between the PM and inductor sections is analyzed by 3-D FEM. Theresults show that the magnetic flux coupling between them is quite slight, and thetwo sections can be computed and analyzed independently.The winding inductance of the PM-IHEG are computed by 2-D and 3-D FEMand the influence of the armature current, excitation current and structure parameteron the winding inductance is studied. The results show that by the action of the armature current, the self-inductance varies two periods within an electrical periodwhen the current is small and it varies one period when the current is large.Furthermore, the variation of self-induction is similar to that of PM machine underthe condition of 0A or strengthened excitation current. The fluctuating range ofself-induction reduces with the increase of armature current under the condition ofweakened excitation current. Based on the calculated winding inductance, a circuitsimulation model which can consider the time-varying winding inductance is builtto calculate the PM-IHEG external characteristics. The results show that thismethod can not only dramatically reduce the calculation time, but also effectivelyimprove the calculation precision of the external characteristic. The influence of theaxial length of the inductor section on the external characteristic of the PM-IHEG isanalyzed and the optimizing axial length of the inductor section is discovered.The PM-IHEG losses are computed and analyzed deeply. The influence of thedc biased magnetic field on the stator core loss is considered while computing thecore loss of the inductor section. The armature winding copper loss of thePM-IHEG with a rectifier load and three-phase balanced load is computed,respectively. The results show that the armature winding copper loss with a rectifierload is larger than that with a three-phase balanced load under the condition of thesame output power. The rotor eddy loss of the PM-IHEG is calculated by FEM andthe influencing factors of the rotor eddy are analyzed. The rotor friction loss of thePM-IHEG is computed by analytical method and FEM. The results show that theslotted rotor friction loss increases significantly. The experimental results confirmthe correctness of the computation and analysis of the losses.The transient temperature field of the PM-IHEG is calculated by 3-D FEM.The influences of excitation current, machine speed, and load on the temperaturefield are analyzed. The results show that the PM-IHEG temperature field along theaxial direction varies violently owing to the special structure. The steady-statetemperature rise of the PM-IHEG with a rectifier load is higher than that with athree-phase balanced load under the condition of the same output power. Theexperiments confirm the correctness of the calculated result of temperature field.