Harmonic current emissions through bridge rectifiers and damping measures

Answer:
Controllers use uncontrolled diode bridge rectifiers (B6) for DC-bus voltage generation. If the DC-bus capacity is recharged at maximum mains voltage, there will – depending on the internal resistance of the system - occur higher current peaks. These current peaks cause a non-sinusoidal current flow in the supply cable. If the controllers are operated with the corresponding mains chokes, the current flow time for DC-bus capacity charging will be extended and, at the same time, the current peak will be reduced. In this way, the current characteristic will be closer to a sine wave and contain less harmonics. The effective current is reduced by approx. 30 %.

The harmonic current emissions lead to voltage distortions at the system impedance at the medium voltage level. The intensity of the voltage distortions is determined by the ratio between rated mains power and controller power.

The voltage distortion can be reduced by:

For detailed information on system current harmonics and damping measures, please see the attachment.