Frequency Converters and Their Impact on Electrical Systems
Frequency converters, based on semiconductors, operate on the principle of converting nonlinear components with relay properties. When these elements switch, it leads to wave-like changes in current or voltage, causing distortions over a wide range of frequencies. Such cases are particularly noticeable in converters, as many key components are switched there.
Causes of Electromagnetic Interference
Rapid changes in electric current and voltage in key components are the main cause of noise generation. The distortion spectrum varies depending on the maximum values of current and voltage in the electrical circuit, as well as the conversion speed of conductivity. In radio electronic equipment, interference most often enters through wiring since distortions mainly arise from sources of interference or due to distributed capacitance that separates the source of distortions from the conductors. Interference can be transmitted through the common resistance of the circuit, power sources and their resistance, as well as under the influence of external electromagnetic fields.
Methods to Reduce Interference
To eliminate interference during installation, the following methods are used:
- - separating the control circuit from the power circuit;
- - crossing circuits is done only at an angle of ninety degrees;
- - conductors of the power circuit are chosen to be of minimal length;
- - three-phase circuit wiring is done in a single bundle;
- - separating circuits with alternating and direct current;
- - wires for highly sensitive devices are made as twisted pairs;
Means of Protection Against Electromagnetic Interference
The main means of protection against electromagnetic waves are:
- Shielding – a screen made of aluminum or copper foil is installed around the source of interference, which limits the spread of electric fields due to the metal casing. The effectiveness of the screen heavily depends on the quality of its grounding.
- Electromagnetic Shield – used for protection against high-frequency fields, operates on the principle of reflecting electromagnetic interference, and has a bulky construction.
- Magnetostatic Shield – designed to protect and reduce magnetic fields, consists of magnetic material, but is less effective due to the influence of eddy currents.
Filters for Reducing Distortions
Another means of protection against interference and distortions is filters. H-shaped filters are the most popular, used in medium power circuits. Depending on the component base, filters at different frequencies demonstrate varying effectiveness. Filters for protecting against interference should be developed at the early stages of creating converters.