集总参数热路结合温度场和流场的电机永磁体温升分析方法
Lumped parameter thermal circuit method combined with temperature field and flow field analyses for temperature predictions of permanent magnets in motors

烧结钕铁硼永磁体电导率高，永磁体内涡流有导致永磁体热失磁的风险，因而电机永磁体的温升分析非常重要。该文提出一种基于集总参数热路的永磁体温升分析方法，用有限元法分析定子温度场得到定子等效热路参数，用计算流体动力学方法分析定子开槽下的气隙热阻。应用该方法分析了一台30 kW 4极电机的永磁体温度，与红外测温结果相比，在永磁体涡流损耗较大的脉宽调制（PWM）电压激励的情况下，永磁体与定子外圆温度差的计算值与实验测量值相差小于3.7%。采用该方法能较准确地根据电机定子外圆温度预测电机转子永磁体温度。
Abstract：Sintered Nd-Fe-B permanent magnets (PM) have high electrical conductivity, but eddy currents in the PMs may cause thermal demagnetization, so the temperatures of the PMs in motors must be known. A lumped parameter thermal circuit method is presented in this paper to predict the temperature rise in the PMs using an equivalent thermal circuit for the stator obtained by a temperature field analysis, and the air gap thermal resistance obtained by a computational fluid dynamics analysis including the stator slot opening. The PM temperature of a 30-kW 4-pole motor is analyzed by this method. The predictions compare well with measurement by an infrared sensor for a pulse width modulation (PWM) voltage excitation case with significant eddy current losses in the PM with less than 3.7% error in the temperature difference between the PM and the outer stator surface. The PM temperature in the motor can be well predicted by this method from the temperature of the outer stator surface.