Dc converter
As the electric power electronics and control the development of technology, frequency converter and variable frequency speed regulation has been widely applied to industrial control each domain, such as variable frequency speed regulation in the water supply, air conditioning equipment, process control, elevator, machine tool, the application of frequency converter, the widely used also brought cannot ignore the interference problems. This interference in the power supply and other performance of electrical equipment of the frequency converter interference and frequency converter running higher harmonic generation when to power grid and the surrounding equipment interference two aspects. If a frequency converter to the interference problems solve bad, not only inverter system can't reliable operation, will also affect its neighboring other electronic and electrical equipment to work properly. Therefore, frequency converter application system of interference problems much theory and engineering application industry wide attention. Combined with the practice, mainly discusses the inverter and the interference of speed regulation system and its control method.

2 inverter system's main interference
2.1 outside of the frequency converter to interference
(1) nonlinear electric equipment in frequency converter of interference
Because all sorts of rectifier equipment, ac/dc exchange equipment, electronic voltage adjustment equipment, lighting equipment and so on the application of the nonlinear load, the load in the grid harmonics source of be, that power grid voltage, current produce waveform distortion. Figure 1 shows the thyristor commutation cause distortion.

Figure 1 thyristor commutation cause distortion

The inverter power supply, from contaminated by the exchange network of interference, if not dealt with, the electric grid noise will through the grid inverter power supply circuit interference. The power supply, the interference of frequency converter mainly over-voltage, voltage, instantaneous power lost; Surge, drop; Peak voltage pulse; Radio frequency interference. Second, through the common mode interferences inverter control signal lines will also interfere with the normal work of the frequency converter.
(2) compensation capacitor of input and cut out in frequency converter of interference
Many customers in the use of substation on the compensation of capacitance method to improve the power factor compensation capacitor, in input and cut out of the transient process, the network voltage there may be very high peak value, as shown in figure 2 shows, the result is may make of the frequency converter because of bearing of the high milena voltage and breakdown.

Figure 2 compensation capacitor input voltage distortion when

2.2 outside the frequency converter interference
Frequency converter is also nonlinear load of power grid, which causes the same power network of harmonic other electronic, electrical equipment harmonic generation interference. In addition, inverter adopts SPWM technology, when its work in switching mode and high speed switching, produce the large amount of coupling noise, including nets of other electronic, electrical equipment is an electromagnetic interference sources.
(1) the input current waveform
Ac-dc-ac pressed a frequency converter to the input side is rectifier and filter circuit in the power supply line, only on both ends of the capacitor voltage ul than dc voltage when the ud agent, rectifier bridge is only found in charging electric current. So charge current always appear in the power supply voltage amplitude values, a discontinuous near shock wave form, as shown in figure 3 a) below. It has a strong higher harmonic composition, of which 5 times harmonic and seven times a harmonic component, as shown in figure 3 b) as shown.

Figure 3 of the input current harmonic wave and its analysis

Figure 4 output voltage and current of the wave

(2) the output voltage and current of the wave
The frequency converter is used mostly SPWM inverter bridge technology, the output voltage of empty for according to the distribution of the law than the sine wave, the output of rectangular series of voltage and current power spectrum is discrete, and carry a switch frequency of the corresponding higher harmonic group, as shown in figure 4 a) below. Its high carrier frequency and field control switch device of high speed switching (dv/dt can reach 1 kv/u s above) caused by the radiated interference is serious.

3 the transmission way of electromagnetic interference
Frequency converter can produce power larger harmonic, the system other equipment interference sex is stronger. The interference channels and general electromagnetic interference, as a way of electromagnetic radiation, circuit coupling, inductive coupling [1], we are as follows. Analysis
3.1 electromagnetic radiation
For grid inverter is a nonlinear load, which causes to access the same power grid harmonics other electronic, electrical equipment harmonic generation interference. When the inverter metal shell with a crack or hole, the radiation intensity and interfering signal wavelength, when with the size of the hole the wavelength of the electromagnetic wave to, can form interference sources around to radiation. And radiation field of metal objects may also form secondary radiation. Also, frequency converter of external radiation will interfere with the normal work of the frequency converter.
3.2 circuit coupling
The electromagnetic interference except for the wires connected to it to the outside, but also through the launch impedance coupling or ground loop coupling, would interfere with signals into other circuits. More typical is the transmission way of the: connect the low voltage network since the industrial frequency converter, the interference caused by signal along in medium voltage distribution transformer, and other network along the distribution transformers and ultimately into low voltage distribution network to make civil pick from the electrical equipment of the civil power distribution bus become the victims of the remote.
3.3 induction coupling
When the inverter input or output circuit and other equipment circuit very close, higher harmonic frequency converter signals can be through the inspiration to other equipment of the coupling way to go. One current signal mainly electromagnetic induction, voltage transmission jamming signal of electrostatic induction main transmission.

4 anti-electromagnetism interference measures and the matters needing attention
To prevent interference, can use hardware and software anti-interference measures. Among them, the hardware anti-interference is the most basic and the most important anti-disturbance measures the general rule is suppression and eliminate interference sources, to cut off the interference on system, reduce the system of the coupling channels to the sensitivity of the jamming signal from the "fight" and "and" two aspects to take measures to restrain the interference [2].
4.1 the correct installation, reasonable wiring
Inverter to the installation environment request is higher. General inverter to use manual environment temperature, ventilation, humidity, altitude to have specific provision. The following several aspects of the installation process requirement note:
(1) ensure that all the equipment control cabinet grounding is good, should use short, thick grounding line (had better use a conductor or flat metal nets, because of its high frequency low impedance in when) connected to the public ground. According to the national standard, the grounding resistance should be less than 4 ohm. In addition to control and frequency converter of equipment (such as PLC and pid control instrument)