What is the difference between variable frequency motor and ordinary motor

Update:13 Apr 2022
Summary:The efficiency and temperature rise of the motor are driven by variable frequency, and the efficiency of the variable fr...
The efficiency and temperature rise of the motor are driven by variable frequency, and the efficiency of the variable frequency motor will be about 10% higher, while 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 core, but the two in the variable frequency fan are separate. Therefore, when the frequency conversion of ordinary fans 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 run stably under the rated conditions. The variable frequency motor is different. The variable frequency motor has to overcome the overheating and vibration at low frequency, so the design of the variable frequency motor is better than that of the ordinary motor.
Frequency conversion motors are better than ordinary motors for occasions requiring frequent starting, frequent speed regulation, and frequent braking.
The stability and service life of the two are different, and the frequency conversion motor is more power-saving, and its use range is wider. The heat dissipation system of the frequency conversion motor is stronger; the frequency conversion motor has strengthened the slot insulation, one is to strengthen the insulating material, and the other is to increase the thickness of the slot insulation to improve the level of high frequency voltage. At the same time, the frequency conversion motor increases the electromagnetic load. The operating point of ordinary motors is basically at the inflection point of magnetic saturation. If they are used for frequency conversion, they are easy to saturate and generate higher excitation current. However, when the frequency conversion motor is designed, the electromagnetic load is increased, so that the magnetic circuit is not easily saturated.
Dielectric strength of the motor. Since the frequency conversion motor is specially designed for the frequency converter drive, it can withstand a large du/dt, so the insulation strength of the frequency conversion motor is higher. Especially in the DTC control mode, the insulation strength of the motor is a big test.
Inverter motors have to withstand high-frequency magnetic fields, so the insulation level is higher than that of ordinary motors. In principle, ordinary motors cannot be driven by inverters, but in practice, in order to save money, ordinary motors are used in many occasions where speed regulation is required. It replaces the variable frequency motor, but the speed regulation accuracy of the ordinary motor is not high, and it is often done in the energy-saving transformation of fans and pumps. When replacing the variable frequency motor with an ordinary motor, the frequency of the frequency converter is as low as possible to reduce the insulation damage to the motor by high frequency.
The main difference is that the variable frequency motor has additional heat dissipation (using an independent axial fan for forced ventilation), and the heat dissipation in low frequency, DC braking and some special applications is much better than that of ordinary AC asynchronous motors. In conclusion, compared with ordinary motors, the price of variable frequency motors is not much more expensive, but the advantages are obvious. The frequency conversion motor adopts the AC speed regulation method of "special frequency conversion induction motor + frequency converter", which greatly improves the degree of mechanical automation and production efficiency, and greatly improves the miniaturization of the equipment and the comfort.