The voltage waveform output by the motor inverter may look similar to a sine wave, but it is not a true sine wave. The waveform contains a large number of harmonic components, especially high-order harmonics, which will increase the output current of the motor inverter, causing the motor windings to heat up, produce vibration and noise, accelerate insulation aging, and even damage the motor. Simultaneously, the various frequencies of harmonics can emit diverse radio interference signals into space. Consequently, this may lead to malfunctions in other electromechanical equipment.
Therefore, during the installation of an motor inverter, it is necessary to comprehensively consider the distance between the central control room, the inverter, and the motor to minimize the impact of harmonics and, as a result, enhance control stability.
(1) Definition of distance:
1. Close distance: the distance between the motor inverter and the motor is ≤20m;
2. Medium distance: the distance between the motor inverter and the motor is >20m and ≤100m;
3. Long distance: the distance between the motor inverter and the motor is >100m;
(2) Industrial use site occasions:
1. Close distance: The motor inverter and the motor can be directly connected;
2. Medium distance: The motor inverter and the motor can be connected directly, but the carrier frequency of the inverter needs to be adjusted to reduce harmonics and interference;
3. Long distance: The motor inverter and the motor can be directly connected. Not only does the carrier frequency of the inverter need to be adjusted to reduce harmonics and interference, but also an output AC reactor needs to be installed.
(3) In a highly automated factory:
In a highly automated factory, all equipment needs to be monitored and controlled in a central control room. Therefore, the signal of the motor inverter system must also be sent to the central control room.
1. Close distance: That is, If the motor inverter is installed in the central control room, the console and the motor inverter can be directly connected and controlled using 0-5/10V voltage signals and some switching signals. However, the electromagnetic radiation of the high-frequency switching signal of the motor inverter will cause some interference to the weak current control signal, so it does not have to be beautiful and neat, and the motor inverter must be placed in the central control room.
2. Medium distance: That is, if the distance between the motor inverter and the central control room is farther, the 4-20mA current signal and some switching values can be used for control connection; if the distance is further, the RS485 serial communication method can be used for the connection.
3. Long distance: That is, the distance between the motor inverter and the central control room is greater than 100m.
Cable modeling using pi-elements
At this time, the communication intermediate relay can be used to reach a distance of 1km; if it is further, an optical fiber connector needs to be used, which can reach up to 23km.
By utilizing communication cables for connection, it becomes feasible to establish a multi-level drive control system, thereby fulfilling master/slave and synchronous control requirements. Moreover, connecting with the current popular Fieldbus system will greatly increase the data conversion rate. The extension of the distance between the central control room and the inverter cabinet is conducive to shortening the distance between the motor inverter and the motor, ultimately improving system performance with a more reasonable layout.
