Description
In commonly used frequency converters, the high frequency of current changes and the high steepness of current pulses induced by commutation of very fast power semiconductor devices cause, as in the input circuits of converters, a number of unfavorable phenomena in the converter circuit - cable connections - motor.
The short switching times of IGBT transistors of the order 100 ns and the steepness of the square wave at the output of the inverter between 3 and 10 KV / μs cause the occurrence of high-frequency currents in cable connections.
In longer connections, the inverter - motor, high-frequency currents cause surges that significantly exceed the rated voltage of the drive. In cables, overvoltages cause micro-perforations and the process of insulation destruction. In motors, high-frequency currents and associated parasitic capacitances cause mechanical stresses in the windings and, as a result, damage to the insulation. There is an increase in noise in the engine and the associated additional losses. Mechanical corrosion occurs in the mechanical parts of the engine. Unfavorable effects of noise emission occur most often in older engine constructions. In engines explicitly provided by the manufacturer for supplying from frequency converters, these phenomena are less critical
A high du / dt value in the drive voltage can cause a resonance effect. The resonance voltage is applied to the drive voltage. Momentary voltage increase up to twice the rated value is usually recorded from the engine side.
 | The effect of the du / dt filter is to limit the steepness of the impulse waveforms in the line voltage and to limit the negative effects of disturbing currents. Du / dt filters suppress the asymmetric component of the fault current. The current-compensated choke limits the overvoltage at the output of the frequency inverter. By suppressing the asymmetric component of the fault current, we significantly reduce electromagnetic interference in the frequency range from 1 to 30 MHz. The du / dt filters have a low leakage flux, so they can be installed near electronic devices. The limiting steepness of occurring overvoltages is effective for short cable lengths (up to 50 m) and modulation frequencies of converters above 2,5 kHz. |
CNW 933 - sinusoidal output filters
 | Sinusoidal filters are a combination of inductance and capacitance. They shape the impulse waveforms at the output of the frequency inverter modulated by a specific frequency into a sinusoidal waveform devoid of practically interfering surges. The phase current has a sinusoidal waveform, therefore the loss balance and the operating conditions of asynchronous motors supplied from converters with sinusoidal filters at the output are analogous to those of the industrial network. The discomfort that should be taken into account when using sinusoidal filters are the losses generated in the filter. Sinusoidal filters should be used for cable lengths above 100m, and shielded cables can be omitted. |
