Stabilization of Cascaded DC/DC Converters via Adaptive Series-Virtual-Impedance Control of the Load Converter

It has been shown recently that a cascaded dc/dc converter system can be stabilized via amplitude compensation (SAC) or phase compensation (SPC) for the input impedance of the load converter. In this letter, it is shown that the cascaded system when adopting the SAC is unconditionally stable but conditionally stable when adopting the SPC, that is, SAC is more stable than SPC. Then, the comparison is carried out for the parallel-virtual-impedance (PVI) and series-virtual-impedance (SVI) control strategies that are adopted to implement the SAC, and it is found that only the SVI control strategy can achieve the SAC for the whole load and input voltage range of the load converter without limitation. Therefore, SVI is in general better than PVI when realizing SAC. Following on this, an adaptive mechanism is introduced to improve the traditional SVI control strategy so that the load converter can be stably connected to different source converters such as
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input filters and traditional dc/dc converters. Finally, a load converter cascaded with three different source converters is fabricated to validate the effectiveness of the proposed adaptive SVI control strategy.