Common-Mode Noise Characterization and Reduction for Isolated PWM DC-DC Converters With Stacked-Rectifiers

Isolated pulsewidth modulation (PWM) dc–dc converters with stacked rectifiers have been widely employed in various high and/or wide output voltage applications. However, the series-connection of two high-frequency rectifiers on the secondary side will seriously deteriorate the common mode noise characteristics of the converter. The inherent mechanism by which the series connection of high frequency rectifiers leads to higher common-mode noise is revealed in this article. From the perspective of equivalent noise sources, it is pointed out that the lack of a fixed reference potential for the noise source is the key to the coupling effect of stacked rectifiers. To decouple the cross-effect between the stacked rectifiers, improved output rectifier circuit is proposed, and a new family of isolated PWM dc–dc converters with stacked rectifiers are derived. Different optimization strategies are developed based on the specific rectifier configurations. A full-bridge dc–dc converter with stacked full-bridge rectifier is taken as an example to be analyzed in detail and demonstrate the principle of the proposed solution. The proposed method is further extended and applied to a dual-input buck converter for PV optimizer to address the leakage current issue as well. Experimental results are provided to verify the feasibility and effectiveness of the proposed method.