PFC chokes are made of a metal powder core with one main winding and an auxiliary winding if needed.
Area of application:
Limitation of harmonics of nonlinear loads connected to the AC mains, such as primary SMPS's and frequency converters. Since it is required by law more and more power factor correction (PFC) controllers are used.
Conventional SMPS's and frequency converters take their energy from the AC mains. The AC mains is rectified and fed into a DC intermediate circuit, by which the switching circuits are supplied. This results in an irregular current consumption from the mains, since current only flows if the mains voltage exceeds the voltage of the intermediate circuit plus the breakdown voltage of the rectifier. This non-sinusoidal current consumption generates strong harmonics in the mains and decreases the efficiency of other devices by increasing parasitic losses.
PFC controllers work basically like SMPS's or frequency converters.
They can be placed before the nonlinear load where they act as step-up converters to generate a sinusoidal current consumption from the AC mains.
They also can be placed parallel to the AC mains supply of several nonlinear loads where they actively compensate the harmonics generated by the nonlinear loads. For this reason, PFC controllers return current to the mains for specific phase angles in order to restore a sinusoidal current curve at the mains terminal.
Due to reversal of the current direction higher core loss and thus heat occurs in the PFC controller storage choke. This requires cores with low loss. A secondary auxiliary winding is optional.
MS: low cost material
MP: lowest loss material
HF: material with best L = f(IDC)