The torque of the asynchronous motor is generated by the interaction between the magnetic flux of the motor and the current flowing in the rotor. At the rated frequency, if the voltage is constant and only the frequency is reduced, the magnetic flux will be too large and the magnetic circuit will be saturated. will burn the motor. Therefore, the frequency and the voltage should be changed proportionally, that is, the output voltage of the inverter should be controlled while the frequency is being changed, so that the magnetic flux of the motor is kept constant, and the phenomenon of field weakening and magnetic saturation is avoided. This control method is mostly used in energy-saving inverters for fans and pumps.
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