IPOS Two-Stage Isolated Bidirectional DC/DC Converter With Low Common-Mode Noise

Two-stage isolated bidirectional DC/DC converter with LLC-DCX cascaded with Buck converter is suitable for wide voltage range applications. Multiple converters with input parallel output series (IPOS) connection can further extend the output voltage range and power rating of the system. However, conventional series connection of the synchronous rectifiers of the Buck converters will exacerbate common- mode (CM) noise. This paper analyzes the CM noise characteristics and reveals the mechanism which worsens the CM noise of the converter. The loss of the stable reference ground for the CM noise source due to the series connection of the synchronous rectifiers is the reason. To reduce the additional CM noise induced by the IPOS connection, the impedance balance method with modified coupled inductor is presented. Furthermore, an improved topology is proposed by modifying the position of the filter inductor. Modeling and analysis indicate that the CM noise is reduced by providing a stable reference ground for each noise source with the modified topology. Effectiveness and feasibility of the proposed method are verified with experimental results.