Research On The Surface-mounted PMSM Demagnetized By The Influence Of Short Circuit Winding Fault

With the widespread using of PMSM in recent years,the requirement made by people for safe operation to PMSM is growing. Nowadays, PMSM is developing to some aspects such as higher powerful, higher efficiencial, higher performance and microminiaturize and so on. The environment of operation is more and more complicated than before, should be given more emphases on several fault operation. Detecting potential accident earlier, decreasing the chance of accident, cutting down the cost of maintenance and economic loss, enhancing ability to monitor and analyze the fault of motor that will be a very important research subject to ensure the safe and reliable operation of PMSM.Although the material NdFeB is extensively used in PMSM because of its high magnetic energy product and without strategic materials, the thermo stability of NdFeB is bad and coercive force with the feature of negative temperature coefficient which will make the NdFeB-PMSM be different from traditional motor when there is happening short circuit windding fault. Specially, the transient current which made by short circuit fault will demagnetize the permanent magnet partially, at last the motor will be broken down.Now some scholars just take the stationary short circuit process demagnetizes the permanent magnet entiretily and check the distribution of magnetic whether it is below inflection point with some excess as the mainly means into account when they prevent from the demagnetizing fault, the result may not be correct because the transient short circuit current will be more powerful to demagnetize the permanent magnet than the stationary short circuit current, and the permanent magnet will be demagnetized partially, not entirely. So it's very easy to be an over or insufficient preventing problem.To ensure the safe operation of PMSM and eliminate potential safety hazard earlier, we need more efficient method and means to detect the demagnetization of permanent magnet. Exacting the character parameter and learning about the operation behaviour of demagnetzing PMSM that will be the precondition to on-line monitor and diagnose the fault motor. So the Finite Element Method will be applied in this paper to find out how the transient process of four kinds of short circuit demagnetizes the PMSM, and extracts and studies the wave and different times harmonic of no load Back-emf and Flux-linkage which are varying regularly, and then go on analyzing the performance of different kinds of demagnetzing motor which is operating with full load.Firstly, this thesis briefly introduces the basic structure and principle of PMSM, then illustrates the character of permanent material and four kinds of short circuit winding model briefly. Secondly, feature of the basic Electromagnetic Fields theory and the Finite Element Method are introduced briefly, the Finite Element model of PMSM is established with the software Ansoft which is used in the electromagnetic field for simulation and calculation, the different operating conditions such as no load and rated load of normal PMSM is simulated to calculate relative operation parameter. Thirdly, the transient process of four kinds of short circuit fault is simulated to demagnetize the permanent magnet and extracting the characterization of Back-emf and Flux-linkage waves and relative FFT parameter when the PMSM appears vary degrees demagnetization. Last but not least, on the basis of the demagnetizing model, this thesis simulates different demagnetizing degrees PMSM which is operated in motor and generator with rated load demagnetizing fault, and discusses whether the permanent magnet will appear new demagnetizing area.The result shows that extracting and analyzing the wave and different times harmonic of no load Back-emf and Flux-linkage that will be an evidence to judge the types of different short circuit fault and the demagnetizating level of permanent magnet. Observing the representation of demagnetizing PMSM which operated with full load that will be used to compensate for the on-line monitor theory of PMSM.