The Difference Between Asynchronous Motor and VFD Electric Motor

As we all know, VFD electric motor is a kind of asynchronous motor, and it is also known that asynchronous motor can be controlled by frequency converter. So the question is, if an ordinary asynchronous motor supports to be driven by a frequency converter, is it equal to a VFD electric motor? Certainly not. What is the difference between asynchronous motor and vfd for synchronous motor?

Ⅰ. The difference between asynchronous motor and VFD electric motor

We all know that the ordinary asynchronous motor can only operate under the condition of AC380V / 50Hz and can work under the standard sine wave. Its basic feature is that the rotor winding does not need to be connected with other power sources, and the stator current is directly taken from the AC power system; Compared with other motors, asynchronous motor has the advantages of simple structure, convenient manufacture, use and maintenance, high operation reliability, light weight and low cost. Some people say that VFD electric motor is just an asynchronous motor with a frequency converter, which can work anyway. According to their working principle, it seems right to say so. In fact, it is not. The index design of the VFD compatible motor is different from that of ordinary asynchronous motor.

The influence of frequency converter on motor:

1. The efficiency and temperature rise of motor;

2. Insulation strength of motor;

3. Harmonic electromagnetic noise and vibration;

4. Adaptability of motor to frequent starting and braking;

5. Cooling problems at low speeds. Only by overcoming these problems can we work normally. In order to have a VFD electric motor with higher performance, people should make the motor have better working effect under the influence of the frequency converter, overcome many problems and control the working state of the motor through the output of the frequency converter.

In the structural design, due to the high impulse voltage of the winding, it is necessary to strengthen the ground insulation and turn insulation strength. In terms of motor vibration and noise, the rigidity of motor components and the whole shall be considered to avoid resonance with each force wave. The main motor cooling fan with independent motor drive shall be used for heat dissipation. In the electromagnetic design, the stator resistance shall be reduced, that is, the fundamental copper consumption shall be reduced to make up for the increase of copper consumption caused by high-order harmonics. In order to suppress the high-order harmonics in the current, the inductance of the motor shall be appropriately increased to ensure impedance matching within the whole speed regulation range. Only by doing this can we meet the rigid requirements of the VFD electric motor.

Ⅱ. Select asynchronous motor and VFD electric motor as required

Asynchronous motor and variable frequency motor have their own characteristics. In order to select the motor more reasonably, it should be based on a series of conditions such as working mode and actual working environment. Because the mechanical structure and electrical parameter design of VFD electric motor are different from asynchronous motor. According to the more demanding working methods and requirements, VFD electric motor is more competent, and the cost is also higher.