The electromagnetic torque of any motor is the result of the interaction of current and flux. The current is not allowed to exceed the rated value, otherwise it will cause the motor to heat up. Therefore, if the magnetic flux is reduced, the electromagnetic torque must also be reduced, resulting in a decrease in the load carrying capacity.
It can be seen from the formula E=4.44*K*F*N*Φ that in the variable frequency speed regulation, the magnetic circuit of the motor changes with a large range of operating frequency fX, which is extremely easy to make the magnetic circuit of the motor serious. Saturation causes the waveform of the field current to be severely distorted, resulting in a spike with a very high 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. This type of control is mostly used for energy-saving inverters such as fans and pumps.