The voltage waveform output by the frequency converter is only similar to a sine wave, but it is by no means a true sine wave. Its waveform contains a large number of harmonic components.
As is well known, high-order harmonics increase the output current of frequency converters, causing motor windings to heat up, generating vibration and noise, accelerating insulation aging, and potentially damaging the motor. At the same time, harmonics of various frequencies emit different levels of radio interference into space, which may cause malfunctions in other electromechanical equipment.
Therefore, when installing a frequency converter, it is necessary to comprehensively consider the distances between the central control room, the frequency converter, and the motor in order to minimize the impact of harmonics and improve the stability of control.
#Definition of Distance#
1. Short distance: The distance between the frequency converter and the motor is ≤20m;
2. Medium distance: The distance between the frequency converter and the motor is >20m and ≤100m;
3. Long distance: The distance between the frequency converter and the motor is >100m;
#Industrial application scenarios#
1. Short distance: The inverter and the motor can be directly connected;
2. Medium distance: The inverter and the motor can be directly connected; however, the carrier frequency of the inverter needs to be adjusted to reduce harmonics and interference.
3. Long distance: The inverter and the motor can be directly connected. Not only is it necessary to adjust the carrier frequency of the inverter to reduce harmonics and interference, but it is also necessary to install an output AC reactor.
#In a highly automated factory#
In highly automated factories, all equipment needs to be monitored and controlled in a central control room. Therefore, the signals from the frequency converter system also need to be sent to the central control room.
1. Close proximity: This refers to the inverter being installed in the central control room. The control panel and inverter can be directly connected, controlled via 0-5/10V voltage signals and some switching signals. However, the electromagnetic radiation from the inverter's high-frequency switching signals can interfere with weak current control signals. Therefore, placing the inverter in the central control room is not necessarily aesthetically pleasing or neat.
2. Medium distance: This refers to a distance between the frequency converter and the central control room. A 4-20mA current signal and some switching signals can be used for control connection. If the distance is even greater, RS485 serial communication can be used for connection.
3. Long distance: This refers to a distance greater than 100m between the frequency converter and the central control room. In this case, a communication intermediate relay can be used to achieve a distance of 1km; if the distance is even greater, fiber optic connectors are required, with a maximum range of 23km.
Using communication cables for connection, multi-level drive control systems can be easily constructed to meet requirements such as master/slave and synchronous control. Connecting to currently popular fieldbus systems will significantly improve data conversion rates. Extending the distance between the central control room and the inverter cabinet helps to shorten the distance between the inverter and the motor, allowing for a more rational layout to improve system performance.
