Study On Input Voltage Sharing Control Strategies For High-Reliability Input-Series Systems

With the rapid development of power electronics technology, the development orientations of switching-mode power supply are high frequency, modularity and integration. Several series-parallel power conversion systems can be made by connecting multiple standardized high-frequency converter modules in series or parallel at the input and output sides. The major advantage of the series-parallel power conversion system is that the difficulty, cost and cycle of the development of power electronics system can be reduced, and the redundancy and the reliability of power electronics system can be improved. In order to ensure the proper operation of series-parallel power conversion systems, the basic objective is to ensure voltage sharing and current sharing among the constituent modules. This dissertation is dedicated to the input-series system include input-series output-parallel (ISOP) and input-series output-series (ISOS) systems, where the DC/DC converters are taken as the basic modules.The main parts of this dissertation are as follows:1. The first part focuses on the research of input voltage sharing control strategy of input-series system without interconnection lines, where ISOP system is taken as example. The the disadvantages of existing control strategies of input-series system are analysed. It can be concluded that common interconnection part exists resulting in lower reliability and lower modularity of system. Therefore, a novel input voltage sharing control strategy without interconnection lines of input-series system is proposed. The detail theoretical analysis and simulation verification of the proposed control strategy are carried on. The control strategy not only ensures the input voltage sharing of ISOP system, but also avoids the mutual connection among modules, thus truly realizing the modularity design and improving the reliability of input-series system. 2. The second part, taking ISOS system an example, as for the poor output voltage regulation of proposed input voltage sharing control strategy of input-series system without interconnection lines, proposes an improved input voltage sharing control strategy of input-series system without interconnection lines. The improved control strategy not only ensures the input voltage sharing of ISOS system, but also improves the output voltage regulation performance greatly. Moreover, the output voltage shifting loop without adding interconnection lines has no influence on the modularity and the reliability of ISOS system.3. In the third part three two-transistor forward converter modules are designed and the input-series system prototype consisting of three two-transistor forward converter modules are fabricated. Finally, the two proposed control strategy including input voltage sharing control strategy of input-series system without interconnection lines and improved input voltage sharing control strategy of input-series system without interconnection lines are conducted in the lab, respectively.