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.
(one) Definition of distance:
1. 1. Short distance: The distance between the inverter and the motor is ≤20m; 2. Medium distance: The distance between the inverter and the motor is >20m and ≤100m; 3. Long distance: The distance between the inverter and the motor is >100m;
(ii) 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, but 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, but not only does the carrier frequency of the inverter need to be adjusted to reduce harmonics and interference, an output AC reactor also needs to be installed.
(III) In highly automated factories:
In highly automated factories, all equipment needs to be monitored and controlled from a central control room. Therefore, the signals from the frequency converter system must also be sent to the central control room. 1. Short distance: If the frequency converter is installed in the central control room, the control panel and the frequency converter can be directly connected, controlled via 0-5/10V voltage signals and some switching signals. However, the electromagnetic radiation from the frequency converter's high-frequency switching signals can interfere with weak current control signals, so it's not always aesthetically pleasing to place the frequency converter in the central control room. 2. Medium distance: If the frequency converter is farther from 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 . 3. Long distance: If the distance between the frequency converter and the central control room is greater than 100m , a communication relay can be used to achieve a distance of 1km . For even greater distances, fiber optic connectors are needed, 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.
