Answer: In the case of variable frequency speed regulation, the magnetic circuit of the motor changes with a large range of operating frequency fX. It is very easy to seriously saturate the magnetic circuit of the motor, resulting in severe distortion of the excitation current waveform and high peak value. Peak current. Therefore, the frequency and voltage should be changed in proportion, that is, the frequency of the inverter is controlled while changing the frequency, so that the magnetic flux of the motor is kept constant to avoid the occurrence of weak magnetic and magnetic saturation.