As the inverter output voltage waveform is similar to a sine wave, but never a true sine wave. Its waveform contains a large number of harmonic components, especially the high harmonics will make the inverter output current increase, resulting in motor winding heating, vibration and noise, accelerate insulation aging, and may even damage the motor; at the same time, a variety of frequency harmonics will be launched into the space of the different procedures of radio interference, therefore, may lead to other electromechanical equipment malfunction.
Therefore, when installing the frequency converter, it is necessary to comprehensively consider the distance between the central control room, the frequency converter and the motor in order to minimize the influence of harmonics and improve the stability of control.
(i) Definition of distance:
1, close distance: the distance between the inverter and the motor ≤ 20 m;.
2, in the distance: the distance between the inverter and the motor > 20m, and ≤ 100m.
3, long-distance range: frequency converter and the distance between the motor > 100m.
(ii) industrial use site occasions:
1, Near distance: the frequency converter and motor can be directly connected to each other.
2, in the distance: inverter and motor can be directly connected between, however, need to adjust the carrier frequency of the inverter to reduce harmonics and interference.
3, long distance: inverter and motor can be directly connected between, not only need to adjust the frequency converter carrier frequency to reduce harmonics and interference, but also need to add the output AC reactor.
(iii) In highly automated factories:
In highly automated factories, all equipment needs to be monitored and controlled in the central control room. Therefore, the signal of the inverter system should also be sent to the central control room.
1, proximity: that is, if the inverter is installed in the center control room. Between the console and the frequency converter, it can be directly connected, through the 0-5/10V voltage signal and some switching signals for control. However, the inverter's high-frequency switching signals of electromagnetic radiation on the weak control signals will produce some interference, so it is not necessarily beautiful and neat, put the inverter in the center control room.
2, in the distance: that is, the frequency converter and the center control room is far away, you can use the 4-20mA current signal and some switching for control connection; if the distance is farther away, you can use RS485 serial communication to connect; 3, long distance: that is, the frequency converter and the center control room is far away, you can use the 4-20mA current signal and some switching for control connection; if the distance is farther away, you can use RS485 serial communication to connect.
3, long distance: that is, the distance between the inverter and the central control room is greater than 100 m. At this time, you can use the communication intermediate relay to reach a distance of 1km; if you want to go farther, you need to use the fiber optic connector, the farthest you can reach 23km.
The use of communication cable connection, can easily constitute a multi-stage drive control system, so as to achieve the master/slave and synchronous control and other requirements. Connection with the currently popular fieldbus system will enable the data conversion rate to be greatly increased. The extension of the distance between the center control room and the inverter cabinet is conducive to shortening the distance from the inverter to the motor in order to improve system performance with a more reasonable layout.