With the continuous development of power electronic technology, variable frequency speed regulation has become the mainstream way of AC motor speed regulation. Frequency converter (hereinafter referred to as -VFD) is widely used in industrial and civil control fields due to its excellent speed regulation performance and significant energy saving effect.
As we all know, the thyristor in each brand of VFD is in a high-speed switching state. Continuous on-off will generate continuous interference current, accompanied by a large amount of radiation, harmonics and other electrical pollution, which will interfere with engineering, cause the failure of the measurement and control system, and seriously damage the system. stability, and even the VFD itself will be disturbed to cause "bootstrap" speed regulation failure.
After a VFDstart command is issued at a certain location, the motor does not run. The frequency source for viewing the VFD is provided by an external 4-20mA. After giving the VFD4-20mA signal, the monitoring panel shows that the frequency is 0.00, and the output of the VFD is measured with a multimeter, but there is no output. Connect a capacitor in parallel with the output end of the VFD, start it again, and the device will return to normal. This indicates that the signal source is disturbed.
This kind of interference belongs to the interference of VFD to external equipment.
Now that VFD has been widely used, it will encounter many interference problems, such as the interference event in the above case. It is an important topic to analyze and study the methods of interference suppression. No matter what kind of interference, high-order harmonics are the cause of much interference in VFDs. Therefore, when installing and using the VFD, it is necessary to take anti-interference measures for the control loop, and do the correct anti-interference measures to ensure the reliable operation of the engineering system.