What is the difference between a variable frequency motor and a normal motor?

The variable frequency motor is a general term for the motor driven by the inverter. The variable frequency motor is an organic combination of the motor and the frequency converter, and the speed and torque of the motor are controllable. Ordinary motor speed and torque are fixed. The variable frequency motor can be arbitrarily adjusted within its speed regulation range, and the motor will not be damaged. Generally, most of the domestically produced ordinary motors can only operate under AC380V/50HZ conditions. Ordinary motors can be used for frequency reduction or upsampling, but the range Not too big, otherwise the motor will heat up or burn out.


The efficiency and temperature rise of the motor under variable frequency drive, the efficiency of the variable frequency motor will be about 10% higher, and the temperature rise will be about 20% smaller, especially in the low frequency region of vector control or direct torque control.

The cooling fan in the ordinary fan uses the same line as the fan movement, and the two of the inverter fans are separated. Therefore, when the inverter frequency is too low, it may burn out due to overheating. Ordinary motors are designed according to the frequency of the mains and the corresponding power, and can only operate stably under rated conditions. The variable frequency motor is different. The variable frequency motor has to overcome the overheating and vibration at low frequency, so the inverter motor is better in design than the ordinary motor.

Variable frequency motors are superior to ordinary motors for occasions requiring frequent start, frequent speed regulation, and frequent braking.

The stability and service life of the two are different, and the variable frequency motor is more energy efficient, and its use range is wider. The heat dissipation system of the variable frequency motor is more powerful; the variable frequency motor enhances the slot insulation. First, the insulation material is strengthened. First, the thickness of the slot insulation is increased to increase the level of high frequency voltage. At the same time, the variable frequency motor increases the electromagnetic load. The working point of the ordinary motor is basically at the magnetic saturation inflection point. If it is used for frequency conversion, it is easy to saturate and generate a high excitation current, and the variable frequency motor increases the electromagnetic load during design, making the magnetic circuit difficult to saturate.


The problem of the insulation strength of the motor. Since the variable frequency motor is designed for inverter drive, it can withstand large du/dt, so the insulation strength of the variable frequency motor is high. Especially in the DTC control mode, the insulation strength of the motor is a big test.

Because the frequency conversion motor has to bear the high frequency magnetic field, the insulation level is higher than that of the ordinary motor. In principle, the ordinary motor can not be driven by the frequency converter, but in practice, in order to save money, the ordinary motor is used in many occasions requiring speed regulation. Instead of the variable frequency motor, the speed regulation accuracy of the ordinary motor is not high, and it is often done in the energy-saving transformation of the fan and the pump. When using a normal motor instead of a variable frequency motor, the chopper frequency of the inverter should be as low as possible to reduce the insulation damage of the motor at high frequencies.


The main difference is that the variable frequency motor has additional heat dissipation (using a separate axial fan forced air), which is much better than ordinary AC asynchronous motors in low frequency, DC braking and some special applications. In summary, compared to ordinary motors, the price of variable frequency motors is not much more expensive, but the advantages are obvious. The variable frequency motor adopts the AC speed regulation mode of “special frequency induction induction motor + inverter”, which makes the mechanical automation degree and production efficiency greatly improve the miniaturization and increase the comfort of the equipment.

Reprinted from the network