The Demagnetization Analysis Of Direct-Driven Permanent-Magnet Synchronous Generator In The Wind Power Generation System

In all of the exploited renewable energy, the wind power generation is most widely used, because of its mature technology development condition and commercial prospect. While the PM-motors are widely put into use, the demagnetization of permanent magnetic (PM) materials has been an important issue for researchers. Based on the existing analysis, the thesis discusses the demagnetization risk in a MW level surface mounted PMSM in several aspects.Firstly the thesis analyses the reasons for the demagnetization in PM. From every aspect of causing irreversible demagnetization to PM, combining with the demagnetization in PM in actual situation, the research emphasis and the flowchart is summarized in how to analyze the demagnetization risk in PM.The surface mounted PMSM is modeling in Ansoft Maxwell software. The performances of PMSM including no-load and some sudden short-circuit are analyzed. Through theoretical analysis and simulation results to check, this thesis obtains the different initial conditions to get the maximize armature current in different fault conditions. Combined with demagnetization curve of permanent magnetic materials at maximum operating temperature 150℃, the most worst demagnetized field distribution under the maximum armature current is analyzed and flux density distribution covered the surface is obtained. From the flux density distribution curve, the partial demagnetization can be studied and the lowest demagnetization operating point is calculated at 0.267 T, higher than the knee point. So the irreversible demagnetization will not happen in this PMSM, and the rationality of the design of motor is to be proved. Meanwhile some shape designs are discussed to improve the ability of resistance to the irreversible demagnetization.Finally, the thesis analyses the eddy current and its influence to PMSM. The eddy-current loss in PM made by space harmonic is calculated and it increases the temperature of PM; and then damping effect of the eddy current is discussed in the transient process. Using of the result of the three-phase short-circuit current and the graphic method, the ultra-transient reactance is calculated and the Leakage resistance of damping winding is obtained, to provide research basis for accurate transient model of PMSM.