一种基于波形等效原则的永磁电机空载反电动势在线测量方法研究

永磁电机的空载反电动势是电机设计的重要指标，综合反映了电机的电磁性能。一台永磁电机在设计完成时，其额定转速下的空载反电动势的大小是确定的。但随着电机投入运行，由于工作环境的温度、机械或是化学变化，可能会使得永磁体发生退磁问题，进而影响电机的工作性能。传统的反电动势测量方法均为离线测量，具有诸多不便性。本文根据实际的工程需要，提出一种在线测量永磁电机反电动势的方法，并设计样机验证了理论的有效性。通过捕获电机在任意转速断电后一个电周期内的反电动势波形，利用波形等效思想得到等效正弦波，并进一步推算出永磁电机在额定转速下的反电动势。将其与空载反电动势设计值进行对比，即可对当下永磁体的磁性能做出快速评估，为电机的故障维护和长期稳定运行提供技术保障。

Research on On-Line Measurement Method of No-Load Back EMF of Permanent Magnet Synchronous Motor Based on Waveform Equivalence Principle

The no-load back EMF of permanent magnet motor is an important index of motor design, which reflects the electrical and magnetic performance of the motor comprehensively. When a permanent magnet motor is designed, the no-load back EMF at its rated speed is determined. However, as the motor is put into operation, the demagnetization of the permanent magnet may occur due to the temperature, mechanical or chemical changes of the working environment, which will affect the working performance of the motor. The traditional back EMF measurement methods are off-line measurement, which has many inconveniences. According to the actual engineering needs, this paper proposes a method of on-line measurement of back EMF of permanent magnet motor, and designs a prototype to verify the effectiveness of the theory. By capturing the back EMF wave in an electric cycle after power off at any speed, the equivalent sine wave is obtained by using the principal of waveform equivalence, and the back EMF of permanent magnet motor at rated speed is further calculated. Compared with the design value of no-load back EMF, the magnetic properties of the current permanent magnet can be quickly evaluated, which provides technical guarantee for fault maintenance and long-term stable operation of permanent magnet motor.