When the asynchronous motor is rated for operation, when the slip ratio S is close to 0, the slip is small, no power is small, and the power factor is high.
When the inverter starts the motor, the output frequency is low, so that the asynchronous motor slip can be guaranteed within the rated slip range, so the motor is always working in the high power factor state.
Therefore, it can be said that the inverter changes the output frequency and controls the slip of the asynchronous motor within the rated slip range, thus ensuring high operating power factor of the motor.
If the ratio of the output frequency f of the inverter to the output voltage U is constant, the motor flux Φ is a constant value, that is, the field current (NIo) remains unchanged.
Excitation current (NIo) decreases only when the motor flux Φ decreases
Therefore, the main way to increase the power factor of the inverter is to control the slip rate of the asynchronous motor.
When the asynchronous motor is in the big horse-drawn car, the frequency converter can adjust the frequency-to-pressure ratio, reduce the magnetic flux Φ of the motor, reduce the reactive current, and improve the power factor.
Therefore, simply speaking, the conclusion of "low frequency, low output voltage, small reactive current" is wrong, lowering the frequency, lowering the voltage, but the frequency-to-pressure ratio is constant, which is to ensure that the motor core flux Φ is constant, equal to the motor design magnetic Through Φ, that is, the magnetic flux Φ at the power frequency
When the big horse car is used, the motor flux Φ can be reduced, that is, the value of the frequency-to-pressure ratio is changed, that is, at the same frequency, the voltage is appropriately reduced, and the field current is lowered.
Reduce the frequency, reduce the voltage, do not reduce the magnetic flux Φ, the excitation current does not change, the reactive power remains unchanged
Change the frequency-to-pressure ratio, reduce the motor flux Φ, reduce the excitation current, reduce the reactive power, and improve the power factor
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