A combined buck and boost power-factor-controller for three-phase input

Power factor controllers presented in the past are mostly either boost-type (with high output voltage) or buck-type (with low output voltage). An alternate solution is a combination of a buck and a boost stage, giving important advantages at high input voltage: favourable output voltage, e.g. 400 V; wide input voltage range; and no additional inrush limiter necessary. For three-phase input, it is possible to use three single phase units connected each to two phases (line-to-line). Since the busses have different voltages to ground, it is not possible to connect them. Therefore it is necessary to use DC/DC converters with load sharing to get equal input currents. The control is simple: a conventional PFC-controller is augmented by an additional current loop and a circuit which switches between the two stages.<
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