Telefonaktiebolaget Lm Ericsson (Publ)

Tadeus Wolpert

Mats Karlsson

An electric supply system comprising two or more phases (R S T ), one rectifier ( ) for each phase, the second primary terminals of said rectifiers ( ) being interconnected, also comprises an Artificial Neutral Point (ANP) creating means (A ) for creating an artificial neutral point (NA ) in the electric supply system, connected in parallel with said rectifiers. The ANP means (A ) short-circuits the zero sequence voltage component of the system but does not affect the positive and negative sequence components. The ANP means (A ) includes magnetic components of such a kind that the vector sum of the phase voltages is zero. According to a first embodiment, the ANP means (A ) comprises one transformer ( ) for each phase, the primary winding of each transformer connected to the respective phase (R S T ) in a star configuration, the secondary windings serially connected and the interconnection point of the primary windings forming an artificial neutral point.

Stable artificial neutral point in a three phase network of single phase rectifiers

A smoothing filter for a rectifier (LR) includes a series inductance (L) and a parallel capacitance (C). Because the capacitive voltage drop (V.sub.c) is in counterphase relative to the inductive voltage drop (V.sub.c) there is found on the series inductance (L) a point (K) where the voltage drop towards earth is zero for a given frequency (fg). The load (Z) on the rectifier is connected to this point (K) in order to achieve high attenuation the fundamental harmonic of the ripple voltage at this frequency.

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Bandhagen, Sweden

Tadeus Wolpert