The rotation speed of the rotor is the same as that of the stator, which is called a synchronous motor. If not consistent, it is called an asynchronous motor.
Differences between ordinary and variable frequency motors.
Firstly, it should be clarified that ordinary motors cannot be used as variable frequency motors. Ordinary motors are designed based on constant frequency and voltage, and cannot fully meet the requirements of variable frequency speed regulation, therefore they cannot be used as variable frequency motors.
The impact of frequency converters on motors mainly lies in their efficiency and temperature rise.
The frequency converter can generate varying degrees of harmonic voltage and current during operation, causing the motor to operate under non sinusoidal voltage and current. High order harmonics inside can cause an increase in stator copper loss, rotor copper loss, iron loss, and additional losses of the motor.
The most significant one is the rotor copper loss, which will cause additional heating, reduce efficiency, and output power of the motor. The temperature rise of ordinary motors generally increases by 10-20%.
The carrier frequency of the frequency converter ranges from several thousand hertz to more than ten thousand hertz, causing the stator winding of the motor to withstand a high voltage rise rate, which is equivalent to applying a steep impulse voltage to the motor, causing the insulation between turns of the motor to withstand a more severe test.
When ordinary motors are powered by frequency converters, the vibration and noise caused by electromagnetic, mechanical, ventilation and other factors become more complex.
The various harmonics contained in the variable frequency power supply interfere with the inherent spatial harmonics of the electromagnetic part of the motor, forming various electromagnetic excitation forces and increasing noise.
Due to the wide operating frequency range and large speed variation range of electric motors, it is difficult to avoid the natural vibration frequency of various structural components of the motor due to the frequency of various electromagnetic force waves.
When the frequency of the power supply is low, the losses caused by higher harmonics in the power supply are relatively large; Secondly, when the speed of the variable motor decreases, the cooling air volume decreases proportionally to the third power of the speed, resulting in the inability of the motor to dissipate heat and a sharp increase in temperature rise, making it difficult to achieve constant torque output.
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