Introduction to VFD (Variable-frequency Drive)

1. Motor selection

First, the power of the motor should be selected based on the average power and maximum power required when the load is moving, converted to the motor shaft side (there may be reduction devices such as reducers and pulleys), and the overload capacity of the motor should also be considered. Motor manufacturers can provide the torque characteristic curve of the motor, and the motor characteristics will change at different temperatures.

By the way: The selection sequence is of course to select the motor first and then select the VFD (Variable-frequency Drive) based on the motor, because the ultimate goal of control is not the VFD (Variable-frequency Drive) or the motor, but the mechanical load.

2. Selection of VFD (Variable-frequency Drive)

The first thing that should be emphasized is that the selection should be based on current. For general loads, VFD (Variable-frequency Drive) can be selected based on the rated current of the motor, that is, the rated current of the VFD (Variable-frequency Drive) (i.e., the maximum continuous operating current under normal circumstances) can be greater than the rated current of the motor. However, the occurrence of extreme conditions must be considered. Therefore, the VFD (Variable-frequency Drive) also needs to be able to provide short-term overload current. (Note: The current of the motor is determined by the mechanical load) VFD (Variable-frequency Drive) has an overload current curve, which is an inverse time limit curve, describing the relationship between overload current and time. This is why VFD (Variable-frequency Drive) manufacturers often say that the overload capacity can reach 150% rated current for 2 seconds and 180% rated current for 2 seconds. This is actually a curve. Therefore, as long as the current curve of the motor is within the overload current curve of VFD (Variable-frequency Drive), it is the correct selection. This is why sometimes the VFD (Variable-frequency Drive) power is 1 or 2 gears greater than the motor power (such as lifting applications), and sometimes the low-power VFD (Variable-frequency Drive) can still drive high-power motors (such as conveyor belts) )s reason.

Another thing that must be noted: in abnormal environments, such as high altitude, high ambient temperature (for example, greater than 50 degrees and less than 60 degrees), side-by-side installation (some VFDs (Variable-frequency Drives) are installed side-by-side without derating, and some require Derating is determined based on the VFD (Variable-frequency Drive) design), etc., the derating of the VFD (Variable-frequency Drive) must be considered. This information can be provided by VFD (Variable-frequency Drive) manufacturers.

The result is: the rated power of the VFD (Variable-frequency Drive) may be greater than the motor power or less than the motor power. In fact, the selection of the VFD (Variable-frequency Drive) is also determined based on the mechanical load.

Conclusion: The final basis for VFD (Variable-frequency Drive) selection is that the current curve of the VFD (Variable-frequency Drive) includes the current curve of the mechanical load.

3. Y-type motor and variable frequency motor

The Y-type motor should be an ordinary asynchronous motor (I am under the impression, not sure).

The fundamental function of VFD (Variable-frequency Drive) is to change the power frequency, thereby changing the motor speed. Therefore, theoretically, no matter what kind of motor it is, as long as the speed can be adjusted by changing the frequency, VFD (Variable-frequency Drive) can be used.

Variable frequency motors have a special design and are more suitable for variable frequency use.

Therefore, it is not a so-called variable frequency motor that has an independent fan.

When using VFD (Variable-frequency Drive) control for ordinary asynchronous motors, you need to pay attention to the following:

1. At low frequencies (generally less than 25hz), since the motor uses a coaxial fan, the heat dissipation effect will be poor at low speeds. After the motor heats up, the torque characteristics will become soft, resulting in unstable speed, large current and other problems.

2. At high frequencies (generally greater than 50hz), it depends on whether the motor can withstand problems caused by high speeds, such as bearing heating and poor dynamic balance.

3. There are still many questions that I can’t think of.

From this point of view, VFD (Variable-frequency Drive) controls ordinary asynchronous motors, depending on the working requirements of the motor. Of course, if the motor does not run at low or high frequency for a long time, it is no problem to use VFD (Variable-frequency Drive) control. This application can be found everywhere.