分数槽绕组永磁电机低空载反电势谐波设计

Low spatial back electromotive force harmonics designfor fractional-slot winding permanent-magnet motor

分数槽绕组永磁电机因其独特的优点而被广泛应用,其中最显著的优点是空载反电势波形正弦高,这不仅有助于提升电机系统的控制性能,而且能够有效降低电机运行时的转矩脉动和损耗,提升电机品质。首先,对比分析了整数槽绕组和分数槽绕组永磁电机的结构特点和磁路特征。然后,基于绕组函数和气隙磁密函数,推导了永磁电机空载反电势的一般表达式,并从空间谐波角度出发,揭示了分数槽绕组结构改善永磁电机空载反电势波形的内在影响机制。优化设计一台24槽8极整数槽绕组永磁电机和一台27槽8极分数槽绕组永磁电机来验证理论分析结果,对比分析了两台电机的绕组因数谐波与气隙磁密谐波、空载反电势和转矩性能。研究表明,空载反电势第k次谐波由kpr(pr为永磁体极对数)阶次的空载气隙磁密谐波与v=kpr阶次的绕组因数谐波产生,同阶次绕组因数谐波与空载气隙磁密谐波数量越多,空载反电势谐波含量亦越多。最后,研制了27槽8极分数槽绕组永磁电机样机并进行了部分实验,测试了电机的空载反电势波形、相电流和转矩等性能,并与有限元预测结果进行比较,以验证理论分析与有限元预测的正确性。

Fractional-slot winding permanent magnet motors(PM)are widely applied due to their unique advantages,with the most notable being their high-quality sinusoidal no-load back electromotive force(EMF)waveform.This characteristic not only enhances the control performance of the motor system but also significantly reduces torque ripple and operational losses,thus improving overall motor quality.Firstly,a comparative analysis of the structural characteristics and magnetic circuit features of integer-slot and fractional-slot winding PM motors was conducted.Next,based on winding functions and air-gap flux density functions,a general expression for the no-load back-EMF of permanent magnet motors was derived.From the perspective of spatial harmonics,the intrinsic impact of the fractional-slot win-ding structure on optimizing the no-load back EMF waveform of PM motors is elucidated.To validate the theoretical analysis,an optimized design of a 24-slot 8-pole integer-slot winding PM motor and a 27-slot 8-pole fractional-slot winding PM motor is performed.The winding factor harmonics,air-gap flux density harmonics,no-load back EMF,and torque performance of both motors were comparatively analyzed. The findings indicate that the k-th harmonic of the no-load back EMF is generated by the no-load air gap magnetic density harmonic of the order kpr-th (where pr is the number of PM pole pairs) and the winding factor harmonic of the order v=kpr. The presence of more harmonics of the same order in the winding factor and air-gap flux density increases the harmonic content in the no-load back EMF. Finally, a prototype of the 27-slot 8-pole fractional-slot winding PM motor was developed and partially tested, measuring the motor′s no-load back-EMF waveform, phase current, and torque performance. These experimental results were compared with finite element predictions to confirm the accuracy of both the theoretical analysis and the finite element simulations.