Decentralized Voltage-Sharing Control Strategy for Fully Modular Input-Series–Output-Series System With Improved Voltage Regulation

Input-series-output-series (ISOS) system connection of dc-dc converters is 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 decentralized voltage-sharing control strategy, which has the advantages of full modularity and high reliability, and each module is controlled independently without any control communication with other modules. In order to ensure proper sharing of input and output voltages, the input voltage sensing signal is added to the reference voltage for each module, resulting in the positive output voltage gradient regulation characteristic of the ISOS system; moreover, a system output voltage shifting loop is introduced to improve the system voltage regulation. The proposed control strategy can effectively improve the modularity and reliability of the ISOS system. An ISOS system prototype consisting of three two-transistor forward converter modules is tested in the laboratory, and the experimental results verify the effectiveness of the control strategy.