DC-Bias Current Detection and Mitigation for a Three-Phase Transformer-Connected Converter through DC-Link Measurement

DC-bias of the magnetic flux is a common challenge for transformer-connected converters, leading to increased losses and potential converter malfunction. This paper presents a novel strategy to detect and mitigate DC-bias currents through the transformer. It detects DC-bias currents from the presence of a switching-frequency harmonic component in the DC-link current and successively regulates it to zero. Stability analysis demonstrates the robustness of the proposed method against phase errors in the current measurement circuit. Experimental measurements are conducted to validate both the theoretical analysis and effectiveness of the detection and mitigation method.