自起动永磁同步电动机非正常运行工况下退磁磁场分析

Analysis of demagnetization field of line-start permanent magnet synchronous motor under abnormal operation conditions

为了研究自起动永磁同步电机非正常运行工况下的退磁磁场对永磁体的影响,建立了计及不可逆退磁的自起动永磁同步电动机时步有限元模型,计算分析了包括失步、三相短路和重合闸3种非正常运行工况,得到3种工况下永磁体各单元不可逆退磁情况。结果表明过大负载导致永磁电机失步振荡,相对转子旋转的定子磁场造成永磁体单元的计算矫顽力下降,产生不可逆退磁;三相短路导致永磁电机停转,停转过程中短路去磁电流产生的退磁磁场使得永磁体磁密降低,且负载系数越小,永磁体受退磁磁场作用时间越长,越容易发生不可逆退磁;重合闸存在过渡过程,且过渡过程持续时间和暂态冲击电流大小受重合闸时刻开关两端电压差的幅值影响,电压差越大,则冲击电流越大,且过渡过程持续时间越长,永磁体经历退磁磁场时间越长,不可逆退磁越严重。

To research the influence of the demagnetization field on the permanent magnet of line-start permanent magnet synchronous motor （LSPMSM） under the abnormal operation conditions, the time- stepping finite element model of LSPMSM, which took the irreversible demagnetization effect into ac- count, was established to calculate and analyze the three abnormal operation conditions including out of step, three-phase short circuit and reclosing, and the irreversible demagnetization situations of each per- manent magnet element under the three abnormal operation conditions were gained. Results show that the excess load causes the permanent magnet motor out of step and shock, and then the stator magnetic field which rotates relatively to the rotor causes the effective coercivity of the permanent magnet element re- duced, and irreversible demagnetization occurred. The three-phase short circuit condition leads to the stall of the permanent magnet motor. During the stop process, the demagnetization field caused by the short-circuit currents results in the lower flux density of the permanent magnets, and the action time of the demagnetization field is longer when the load is smaller, which makes the permanent magnets more prone to be demagnetized. There is a transition state during the reclosing process, and the transition time and the transient inrushing current amplitude are affected by the switch voltage at the moment of reclosing. When a reclosing is performed with the larger switch voltage, the transient inrushing current is larger and the transition time is longer; the time the permanent magnet endure the demagnetization field is therefore longer, and then the irreversible demagnetization is severer.