Method and device to compensate for an asymmetrical DC bias current in a power transformer connected to a high voltage converter

摘要

A method and a device to compensate for an asymmetrical DC bias current in a multi-phase transformer. The transformer is connected between an AC power system and an AC/DC or DC/AC high voltage converter. For each phase of the AC side of the transformer a current quantity is determined. The current quantity reflects the time dependent behavior of the magnetizing current in the phase. Time intervals in the current quantity are determined during which the current quantity reaches a positive or a negative maximum, respectively. A DC magnetizing quantity is determined from a difference between the amplitude of the positive maximum and the amplitude of the negative maximum. An asymmetrical quantity is determined from a difference between the amplitudes of the positive and/or negative maxima of at least two of the phases and a control signal is generated from the asymmetrical quantity and provided to a control device of the converter in order to adjust the generation of the AC or DC voltage in the particular phase of the converter which corresponds to the phase of the AC side of the transformer.