变频供电条件下感应电机空载铁耗分布特点及其精细化分析

No-Load Iron Loss Distribution Characteristics and Its Fine Analysis for Inverter-Fed Induction Motors

变频供电条件下电源谐波与电机内部谐波共同作用下损耗产生机理及分布特点更为复杂,使得电机铁耗准确计算及精细化分析对于高效变频电机设计至关重要。以一台5.5 k W变频感应电机为例,分析了变频供电时电机定转子主要位置磁密变化情况;为了准确计算铁耗,提出一种损耗系数随磁密幅值和频率变化的两项式分段变系数铁耗模型,该模型在经典两项式常系数铁耗模型基础上引入两个附加磁密项,用于考虑非线性特性及谐波磁场对磁滞和涡流损耗的影响;进一步利用该模型对变频供电时电机铁耗进行了精细化分析,揭示了定转子铁心磁滞和涡流损耗的分布规律,并获得了谐波磁场在定转子铁心产生附加铁耗的变化特点。通过对不同电压及开关频率下的空载铁耗进行实测对比,验证了文中模型及分析结果正确性。文中研究成果可为高效变频电机设计提供重要理论支撑。

Due to the coaction of supply harmonics and harmonic fields inside the motors, the mechanism and distribution characteristics of iron losses become more complicated when an induction motor is supplied with an inverter. Therefore accurate prediction and fine analysis of iron loss are very important at the design stage of high-efficiency inverter-fed induction motors. This paper firstly analyzed the variation of flux density in the typical positions of stator and rotor core for a 5.5 k W inverter-fed induction motor. In order to predict the iron losses accurately, this paper presented a two-term piecewise iron loss model with variable parameters which are determined by the amplitude and frequency of flux density. Meanwhile, considering the influence of the nonlinearity of magnetic material and harmonic fields on hysteresis and eddy current losses, two additional flux density terms were introduced to the classical two-term iron loss model. With this model, the iron loss of inverter-fed induction motor was studied, the distribution regularity of hysteresis loss and eddy current loss in stator and rotor core was revealed, and the characteristics of additional iron loss caused by harmonic fields were also acquired. By the comparison of predicted and measured no-load iron loss under different supply voltages and switching frequencies, the proposed model and analysis results were validated. The achievement presented in this paper provides important theoretical support for the design of high-efficiency inverter-fed induction motors.