Control Strategy For Input-series Output-independent DC-DC Converter With Voltage Sharing

In medium and high input voltage applications, DC-DC converter faces high voltage stress. As a result, ordinary power electronic devices can’t meet the demands of circuit performance. In DC-DC converter’s auxiliary power, the switching device also faces high voltage stress. If Input-Series Output-Independent(ISOI) converter is used in auxiliary power as well as dispersing voltage control into each module, it can both decrease the overvoltage and satisfy the demand of system modularization. ISOI converter input voltage is unbalanced, which needs input voltage sharing control strategy to guarantee the system works regularly.The paper presents the structure of the DC-DC converter’s system and analyzes the relations among input voltage and output voltage of each module, then puts forward control strategy for input voltage sharing, which is evaluated by discussing the validity of control loop and anti-interference ability under different load and input disturbance. Design two modules DC-DC ISOI converter for convenience of study, then determine Buck as the topology of main circuit and Flyback as the topology of auxiliary power, which both have input voltage sharing control. Simulating analysis of two modules ISOI converter of Flyback can prove that structure of ISOI is reasonable and control strategy for voltage sharing is useful.In order to design and analyze system better, the small-signal modeling is set up. The two modules ISOI converter modeling generates from extension of Buck modeling by state space method. The gathered control to input and output voltage transfer function can provide theoretical base for design of compensate net, which can improve the stability and dynamic response capability of the system. Make the same work like the main convert for auxiliary power circuit which works in DCM and CPM, considering its role at start and no-load state of system.Design the main circuit and auxiliary power circuit and its control circuit as well as compensate circuit according to requirements. Based on the theoretical analysis and design plan, build the two modules ISOI converter whose input voltage is 400 V and output voltage is 50 V, proving that voltage control strategy is effective in dynamic and static state in different loading capacity and voltage fluctuation as well as different device parameters.