1. Use software anti-disturbance method
In detail, the carrier frequency of the inverter is lowered through the human-machine interface of the inverter to an appropriate scale. If this method does not work, then the following hardware anti-disturbance method can only be adopted.
2. Carry out correct grounding
After a detailed investigation on the site, we can see that the grounding situation on the site is not ideal. The correct grounding can not only be used by the system to press external disturbances, but also reduce the disturbance of the equipment itself to the outside world, which is a useful way to solve the disturbance of the inverter. In detail, it is necessary to do the following:
(1) It is necessary to ground the main circuit terminal PE (E, G) of the inverter, which can be grounded with the motor of the inverter, but cannot be co-ground with other equipment, and it is necessary to drive the grounding pile alone, and the connection address should be as far away as possible from the connection address of the weak current equipment. Together, the cross-sectional area of the inverter grounding wire should not be less than 4mm2, and the length should be controlled within 20m.
(2) In the ground wire of other mechanical and electrical equipment, the protective grounding and the working grounding should be separated from the grounding electrode and merged into the electrical connection address of the distribution cabinet. The shielding ground of the control signal and the shielding ground of the main circuit wire should also be separated from the grounding electrode and the electrical connection address of the distribution cabinet after being imported.
3. Shielding the source of disturbance
Blocking the source of the disturbance is a very useful way to control the disturbance. Usually the inverter itself is shielded with an iron shell, which can prevent its electromagnetic disturbance from leaking, but the output line of the inverter is better to be shielded with a steel pipe, especially when controlling the inverter with an external signal (output 4-20mA signal from the controller), the control signal line is required to be as short as possible (generally within 20m), and it is necessary to choose a shielded twisted pair cable, and completely separate from the main electrical road (AC380) and the control line (AC220V). In addition, the circuits of electronic sensitive equipment in the system also require the selection of shielded twisted pairs, especially pressure signals. And all the signal lines in the system must not be placed in the same pipe or trunking as the main power road and control line. In order for the shield to be useful, the shield must be reliably grounded.
4. Reasonable wiring
The details are:
(1) The power line and signal line of the equipment should be as far away as possible from the input and output lines of the inverter.
(2) The power line and signal line of other equipment should be prevented from being parallel to the input and output lines of the inverter.
If the above methods are still not effective, then continue with the following methods:
5. Interference barrier
The so-called disturbance blocking refers to the isolation of the disturbance source from the part that is susceptible to disturbance from the circuit so that they do not have electrical contact. Usually between the power supply and the amplifier circuit such as the controller and the transmitter, the barrier transformer is selected on the power line to avoid conduction disturbance, and the power barrier transformer can be used to apply noise barrier transformer.
6. Set the filter in the system line
The function of the equipment filter is to conduct the disturbance signal from the inverter through the power line to the power supply and the motor. In order to reduce electromagnetic noise and loss, an output filter can be set on the output side of the inverter; In order to reduce the disturbance to the power supply, an input filter can be set on the input side of the inverter. If there are sensitive electronic devices such as controllers and transmitters in the line, a power noise filter can be installed on the power line of the equipment to avoid conducted disturbance. Filters can be divided into the following according to the different application positions:
(1) Input filter
There are usually two kinds:
a. Line filter: It is mainly composed of inductance coils, which weaken the harmonic current with higher frequency by increasing the impedance of the line at high frequency.
b. Radiation filter: It is mainly composed of high-frequency capacitors, which will absorb harmonic components with high frequency points and radiant energy.
(2) The output filter is also composed of an inductance coil
It can usefully weaken the higher harmonic component of the output current. In addition to the effect of anti-turbulence, it also reduces the additional torque caused by the harmonic current generated by the higher harmonics in the motor. Regarding the anti-disturbance method at the output end of the inverter, it is necessary to pay attention to the following aspects:
a. The output end of the inverter is not allowed to access the capacitor, so as to avoid the occurrence of a large peak charge (or discharge) current at the moment of power tube on-on (shutdown), which will endanger the power tube;
b. When the output filter is composed of LC circuits, it is necessary to connect the side of the capacitor in the filter with the motor side.
7. Select reactors
In the input current of the inverter, the harmonic components with lower frequencies (5th harmonic, 7th harmonic, 11th harmonic, 13th harmonic, etc.) account for a very high proportion, in addition to the normal operation of other equipment, but also because they consume a lot of reactive power, so that the power element of the line is greatly reduced. Serial insertion of reactors into the input circuit is a useful way to press the lower harmonic current. Depending on the wiring position, there are two main types:
(1) Communication reactor
It is connected in series between the power supply and the input side of the inverter. Its primary functions are:
a. By pressing the harmonic current, the power element is increased to (0.75-0.85);
b. Weaken the impact of the inrush current in the input circuit on the inverter;
c. Weaken the influence of power supply voltage imbalance.
(2) DC reactor
It is connected in series between the rectifier bridge and the filter capacitor. Its function is relatively simple, that is, to weaken the higher harmonic component in the input current. However, it is more useful than the communication reactor in improving the power element, up to 0.95, and has the advantages of simple structure and small size.
Therefore, the anti-disturbance method of the inverter mainly includes the installation of communication reactors and filters in the inlet part of the inverter, the selection of shielded cables for the incoming and outgoing lines, and the shielding layer of all cables is grounded together with the protective ground of the reactor, filter, inverter and motor, and the connection address is separated from other connection addresses, insisting on sufficient distance. Together, the signal cable and the power cable of the inverter should not be placed in parallel.
In addition, in order to prevent the inverter from disturbing the signal and control loop, it is necessary to use a separate barrier power supply for the controller, exterior and industrial computer.
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