DC-bias in the magnetic flux is a common challenge for transformer-connected converters. Typically, in isolated switched-mode converters, it is generated by a DC current flowing through one or more windings of the transformer. This bias can increase the core losses of the transformer and saturate the transformer core, which deteriorates the performance of the transformer and can even cause the malfunction of the converter. Conventional methods for DC-bias mitigation require expensive measurement circuitry and/or impair the performance of the converter. This paper presents a novel DC-bias detection and mitigation strategy for a three-phase transformer-connected converter. It detects a DC-bias current through the transformer from the presence of a switching-frequency harmonic component in the DC-link current. The proposed scheme can be implemented in a wide range of transformer-connected converters to detect and mitigate the DC-bias current without requiring expensive measurement circuitry. Experimental measurements are conducted to validate the theoretical analysis and effectiveness of the detection and mitigation strategy.
