The voltage waveform output by the frequency converter is similar to a sine wave, but it is by no means a true sine wave. The waveform contains a large number of harmonic components. In particular, high - order harmonics can increase the output current of the frequency converter, causing the motor windings to heat up, generate vibration and noise, accelerate the aging of the insulation, and may even damage the motor. At the same time, harmonics of various frequencies will emit radio interference of different levels into space, which may lead to the misoperation of other electromechanical equipment.

  Therefore, when installing a frequency converter, it is necessary to comprehensively consider the distances among the central control room, the frequency converter, and the motor to minimize the impact of harmonics and improve the stability of control.

  (1) 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.

  (2) Industrial application scenarios:

  1. Short - distance: The frequency converter and the motor can be directly connected.

  2. Medium - distance: The frequency converter and the motor can be directly connected, but the carrier frequency of the frequency converter needs to be adjusted to reduce harmonics and interference.

  3. Long - distance: The frequency converter and the motor can be directly connected. Not only does the carrier frequency of the frequency converter need to be adjusted to reduce harmonics and interference, but an output AC reactor also needs to be installed. 【Frequency converter supporting equipment】

  (3) In highly automated factories:

  In highly automated factories, all equipment needs to be monitored and controlled in the central control room. Therefore, the signals of the frequency converter system also need to be sent to the central control room.

  1. Short - distance: That is, if the frequency converter is installed in the central control room. The console and the frequency converter can be directly connected and controlled through 0 - 5/10V voltage signals and some switch - quantity signals. However, the electromagnetic radiation of the high - frequency switching signals of the frequency converter will interfere with the weak - current control signals. Therefore, it is not necessary to place the frequency converter in the central control room just for the sake of aesthetics and neatness.

  2. Medium - distance: That is, if the frequency converter is a bit farther from the central control room, 4 - 20mA current signals and some switch - quantities can be used for control connection. If the distance is even farther, the RS485 serial communication method can be used for connection.

  3. Long - distance: That is, the distance between the frequency converter and the central control room is greater than 100m. At this time, a communication intermediate relay can be used to reach a distance of 1km. If it needs to be farther, an optical fiber connector needs to be used, and the maximum distance can reach 23km.

  Using communication cables for connection can easily form a multi - stage drive control system, thus meeting the requirements of master/slave and synchronous control. Connecting with the currently popular field - bus system will greatly increase the data conversion rate. Extending the distance between the central control room and the frequency converter cabinet is conducive to shortening the distance between the frequency converter and the motor, so as to improve the system performance with a more reasonable layout.