1According to the basic principles of electromagnetism, the formation of electromagnetic interference must have three elements: electromagnetic interference sources, electromagnetic interference pathways, and systems sensitive to electromagnetic interference. To prevent interference, hardware anti-jamming and software anti-jamming can be used. Among them, hardware anti-jamming is the most basic and most important anti-jamming measure. Generally, it starts from both resistance and attenuation to suppress interference.
Its overall principle is to suppress and eliminate the interference source, cut off the coupling channel to the system, and reduce the system interference signal. The sensitivity. Specific measures can be used in engineering isolation, filtering, shielding, grounding and other methods.
1. Proper grounding
Through the site’s specific investigation, we can see that the site’s grounding situation is not ideal. Correct grounding can be the most effective way to solve the inverter interference by effectively suppressing external interference and reducing the interference of the device itself to the outside world. Specifically, it is to do the following:
(1) The main circuit terminal PE (E, G) of the inverter must be grounded. The grounding can be shared with the motor carried by the inverter, but it cannot share ground with other devices. It must be grounded separately and connected. The location should be as far away as possible from the grounding point of weak equipment. At the same time, the cross-sectional area of the grounding conductor of the inverter shall not be less than 4mm2, and the length shall be controlled within 20m.
(2) In the ground wire of other electromechanical equipment, the protective earthing and working earthing should be separately set up for the grounding pole, and finally imported into the electrical grounding point of the power distribution cabinet. The shield ground of the control signal and the shield ground of the main circuit conductor shall also be separately provided with the ground electrode, and finally be imported into the electrical grounding point of the distribution cabinet.
2. Mask interference sources
Masking interference sources is a very effective way to suppress interference. Normally, the inverter itself is shielded by a steel shell, which can prevent its electromagnetic interference from leaking. However, the output cable of the inverter is preferably shielded by steel pipe, especially when the inverter is controlled by an external signal (outputs 4~20mA signal from the controller). It is required that the control signal line be as short as possible (generally within 20m), and shielded twisted pairs must be used, and completely separated from the main circuit line (AC380) and the control line (AC220V). In addition, shielded twisted pairs, especially pressure signals, are also required for the electronic sensitive equipment circuits in the system. And all signal lines in the system must not be placed in the same pipe or slot in the main circuit and control lines. For the shielding to be effective, the shield must be reliably grounded.
3. Reasonable wiring
(1) The power and signal cables of the equipment should be as far away as possible from the input and output cables of the inverter.
(2) The power lines and signal lines of other equipment should be avoided parallel to the input and output lines of the inverter.
If you still cannot work after taking the above measures, continue the following:
4, interference isolation
The so-called interference isolation means that the interference source is isolated from the vulnerable parts of the circuit so that they do not have electrical connections. An isolation transformer is usually used between the power supply and the amplifier circuit such as the controller and the transmitter to avoid conduction interference. The power isolation transformer can use a noise isolation transformer.
5, set the filter in the system line
The function of the equipment filter is to suppress the interference signal from the inverter through the power line to conduct interference to the power supply and the motor. In order to reduce electromagnetic noise and losses, an output filter can be set on the output side of the inverter; to reduce interference with the power supply, an input filter can be set on the input side of the inverter. If there are sensitive electronic devices in the circuit such as controllers and transmitters, a power noise filter can be set on the power line of the device to avoid conducting interference.
6, using reactors
The proportion of the harmonic components with lower frequency in the input current of the inverter (5th harmonic, 7th harmonic, 11th harmonic, 13th harmonic, etc.) is very high, and they may interfere with other In addition to the normal operation of the equipment, because they consume a large amount of reactive power, the power factor of the line is greatly reduced. Series reactors in the input circuit are effective ways to suppress lower harmonic currents.
Therefore, the anti-jamming measures of the inverter mainly include the installation of AC reactors and filters in the incoming line of the inverter, shielded cables for incoming and outgoing cables, shields of all cables, reactors, filters, inverters and motors. The protective ground is commonly grounded, and the grounding point is separated from other grounding points to maintain a sufficient distance. At the same time, the power cables of signal cables and frequency converters should not be arranged in parallel.
In addition, in order to prevent the frequency converter from interfering with the signal and the control loop, it is necessary to use a separate isolated power supply for the controller, the instrument, and the industrial control computer.