Study On Key Technique In Hybrid Excitation Wind Turbine Generator

The hybrid excitation generators have different structures with traditional electric excitation synchronous machine and permanent magnet synchronous generator, so it's worthy to be promoted and applicated.The hybrid excitation generators have the advantages of which the volume are small, the structure are simple and the magnetic adjustment is convenient like the PMSG.. But the capacity is much low for most hybrid excitation generators. The large volume can arise long time-consuming for three-dimensional field calculation when this large capacity generator is designed. Simultaneously, low harmonics can rise eddy current loss of permanent, so high temperature may lead to demagnetize. Furthermore, the pole shoes structure are appicated on the rotor, so the existence of magnet slots can reduce the mechanical strength of rotor pole. The key technical problems of the PMSG in design are researched in this paper. The main contents are as follows:Firstly, the structure and principle of the PMSG is introduced. The calculation method on the equivalent two-dimensional axial length of the PMSG is proposed by analyzing kinds of magnetic circuits of the machine at no-load. The curve of correction factor of the equivalent axial length is obtained by calculating the two-dimensional field under different sections, and the three-dimensional field of two kinds of PMSG is analyzed. The calculation method on the equivalent axial length has been verified by the no-load EMF test of the 10kw generator.Secondly, the reason of producing eddy current losses in permanent magnet is analyzed, and the speed and frequency of the air-gap harmonic magnetic field relative to the stator and rotor has been summed up. The factors affecting permanent magnet eddy current loss calculated by using FEM method have been researched. The magnetic vector potential wave, the density wave of eddy current and the distribution of eddy current are obtained. The air-gap harmonic magnetic field under the state of no-load and load has been calculated. The harmonics of the prototype under the sate of load has been analyzed and the eddy current loss on the fundamental current has been calculated. Simultaneously, the motor temperature rising test has been done. It has been summed up that air-gap length, the chamfering of PM in different ways and different pole structures of rotor has a impact on eddy current losses.Finally, the force of the rotor pole is analyzed and calculated. The impact of permanent magnet slot position changes and changes in the length of the magnetic barrier on the magnetic pole strength is analyzed by the software of ANSYS, and the length of the magnetic barrier impact on the radial magnetic flux leakage factor also by the software of ANSOFT. Therefore, it provides a guideline for the motor design.