Análisis en profundidad de las interferencias electromagnéticas de los convertidores de frecuencia

  The electromagnetic interference of the inverter has a serious impact on the stability and reliability of the factory automation system, which is manifested in the following aspects:

        Pollution of power supply system: The nonlinear equivalent load of the DC-AC inverter of the inverter will pollute the power supply system of the factory, resulting in the distortion of the voltage waveform and affecting the normal operation of other equipment.

        Measurement and control system inaccuracy and failure: The electromagnetic interference of the inverter may interfere with the normal operation of the measurement and control system, resulting in inaccurate measurement data and failure of the control system.

        Damage to the stability of the large system: The electromagnetic interference of the inverter may destroy the stability of the entire automation system, resulting in the normal operation of the production line and even causing safety accidents.

        Inverter self-failure: Under severe electromagnetic interference, the inverter may be interfered with by itself, causing “bootstrapping” speed regulation failure.

四、the anti-interference measures of electromagnetic interference of frequency converter

        In order to solve the problem of electromagnetic interference of the frequency converter, the following anti-interference measures can be taken:

        Single-point grounding: The inverter should be grounded at a single point, preferably with a short and thick wire. The ground resistance should be less than 100Ω to absorb surge interference. At the same time, the E end of the inverter should be connected to the shell of the control cabinet and the motor, and be connected to the safe ground.

        Shielding interference sources: Shielding interference sources is an effective way to suppress interference. The inverter itself is shielded with an iron shell to prevent leakage of electromagnetic interference. The output line of the inverter is best shielded with a steel pipe, especially when the inverter is controlled by an external signal, the control signal line is required to be as short as possible, and the shielded twisted pair must be used, and it must be completely separated from the main power line and the control line. Shielded twisted pair cables are also required for the circuits of electronic sensitive equipment in the system.

        Reasonable wiring: 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. The power and signal lines of other equipment should not be parallel to the input and output lines of the inverter. In the electric control cabinet equipped with the inverter, the power line and the signal line should be separated from the pipe and route, and the metal hose should be well grounded.

        Install filters: Installing filters at the input and output ends of the inverter can suppress the interference signal from the inverter through the power line to the power supply and motor. The input filter is mainly composed of an inductor coil, which can attenuate the harmonic currents with higher frequencies. The output filter suppresses interference at the output of the inverter.

        Use reactor: In the input current of the inverter, the harmonic component with lower frequency accounts for a high proportion. These harmonic components may interfere with the normal operation of other equipment and consume a large amount of reactive power, so that the power factor of the line is greatly reduced. Serial insertion of reactors into the input circuit is an effective way to suppress lower harmonic currents. The AC reactor can suppress the harmonic current, improve the power factor, and weaken the impact of the inrush current in the input circuit on the inverter. DC reactors can weaken the higher harmonic components in the input current.

        Adjust the carrier frequency: Appropriately reducing the carrier frequency of the inverter can reduce electromagnetic interference, but the electromagnetic noise will increase accordingly. Therefore, it is necessary to adjust the carrier frequency according to the actual situation to achieve the best anti-interference effect.

        Isolate the interference source: isolate the interference source from the circuit and the part that is susceptible to interference, so that they do not have electrical contact. Isolation transformers are typically used on the power lines between the power supply and amplifier circuits such as controllers and transmitters to avoid conduction interference.

        Other measures: For high-frequency and high-power DC welding machines, they should be kept away from the inverter and keep a good grounding. The on-off contact of the electromagnet should be equipped with an RC surge absorber. For the contactor installed in the same electrical cabinet as the inverter, it is necessary to choose products with low noise and good arc extinguishing effect, and if necessary, an RC surge absorber should be installed. The impedance of the power supply should be low, so as to avoid the instantaneous mutation of the input voltage of the inverter caused by the start and stop of hundreds of kilowatts of electrical appliances nearby. The phase voltage of the power supply should be balanced, so as not to cause the inverter to work in an under-voltage or over-voltage state.       

Conclusion

        With the rapid development of industrial automation, the use of inverters is becoming more and more common, and the electromagnetic interference problems of inverters will also encounter a lot. Many end-users often don’t know how to solve this problem when they encounter it. Through the introduction of this article, it is hoped that readers can have an in-depth understanding of the source, propagation mode, impact and corresponding anti-interference measures of inverter electromagnetic interference, and provide some references and ideas for solving the problem of inverter electromagnetic interference.