Common-Mode Noise Suppression in Isolated DC-DC Converters Based on Coupled Inductor Rectifier

Abstract

The electromagnetic interference (EMI) filter is essential for industrial products to comply with EMI standards. It can reduce the EMI noise, which may cause harmful effects on other electronic devices or human health. However, the EMI filter typically occupies a large volume, around one-third of the entire power supply volume, leading to a deterioration in power density. Among previous studies, the winding cancellation method is an attractive approach for reducing the volume of EMI filter. It can reduce the common-mode (CM) noise by canceling the CM voltages of the transformer without requiring shielding layers. However, the winding cancellation method is only applicable to specific topologies. Particularly, in topologies with an output inductor, the implementation of winding cancellation method requires additional components such as reset windings or capacitors. Therefore, this article proposes a novel coupled inductor rectifier that enables the winding cancellation method without any additional components. The proposed rectifier ensures that the voltages generated at the primary and secondary nodes of the transformer have the same dv/dt directions. Consequently, the CM voltages of the transformer cancel each other, leading to the significant mitigation of CM noise. Furthermore, the proposed rectifier can be implemented simply by replacing the existing output inductor with a coupled inductor. It does not require additional components and has the same circuit characteristics as conventional converters. Finally, the proposed rectifier can be extended to different converter topologies with an output inductor. As a result, the proposed rectifier can achieve high power density by reducing the volume of EMI filter. To verify the performance of the proposed rectifier, laboratory prototypes of forward and asymmetric half-bridge converters were built and tested. The proposed prototypes reduced CM noise by 9.7 and 15.4 dB, respectively, compared to conventional prototypes through winding cancellation. Consequently, the volume of EMI filter in the proposed prototypes was reduced by 55.7% and 75.9%, respectively.