Decentralized voltage sharing control strategy for fully modular input-series output-series high-voltage system

Input-series and output-series (ISOS) system connection of dc-dc converters is very suitable for high input-voltage and high output-voltage applications. Input voltage sharing and output voltage sharing of the constituent modules among the ISOS system must be ensured. This paper proposes a novel distributed voltage sharing control strategy featuring high modularity. In order to ensure proper sharing of input and output voltages, the input voltage sensing signal is added to reference voltage for each module, resulting in the positive output voltage gradient regulation characteristic of ISOS system, moreover, a system output voltage calibration loop is introduced to improve the system output voltage regulation. The proposed control strategy can effectively improve the modularity and reliability of ISOS system. An ISOS system prototype consisting of three two-transistor forward converter modules is tested in the lab and the experimental results verify the effectiveness of the proposed control strategy.