Research On Modular And Combined DC-DC Converter

Power electronics system integration is seen as an important development trend in power electronics technique nowadays. Research on modular and combined DC-DC converters is one of the most important projects in the power electronic system integration.To overcome the disadvantages of the large input and output current ripple fluctuation,high voltage stresses of the secondary-side diodes,large losses of the power devices,high electromagnetic interference etc in the single power converter of high voltage area, modular and combined DC-DC converters with naturally input (output) voltage and output(input) current sharing are studied in this paper. The main advantages of the modular power converters include: low voltage and current stresses of the power devices; significant improvement in reliability by introducing desired level of redundancy; standardization of components leading to reduction in manufacturing cost and developing time; power systems can be easily reconfigured to support varying input-output specifications; and higher efficiency and power density of the overall system, especially with interleaving control methods.The advantages of the two types of the input-parallel and output-series and one type of the input-series and output-parallel modular DC-DC converter are verified by a plenty of experimental research work. The system power level is enlarged by the parallel structure of each modular at the input-end (or output-end), and the voltage level is enlarged by the series structure of each modular at the output-end (input-end). As a single-unit of the modular combined converters, Full-bridge converters are main research objects chosen to discover the characteristics of the input-parallel and output-series as well as that of the input-series and output-parallel modular DC-DC converters, and the research conclusions can be extended and applied to the circuit structures of the half-bridge,forward,push-pull and so on. The interleaving control techniques and constant duty cycle strategies are adopted to achieve better performance of the system.In this paper, firstly the full-bridge modular DC-DC converters connected in input-parallel and output-series symmetrically are studied, and the research conclusions exhibit the following advantages: low voltage stresses in transformer secondary side diodes; low current stresses of the power devices; output voltage sharing; input current sharing; small volume of input and output filter. Secondly the Full-Bridge modular DC-DC converters connected in input-parallel and output-series dissymmetrical are studied, and the research conclusions exhibit the following advantages: small number of inductors; fast dynamic response time and low losses of the system besides that in the full-bridge modular DC-DC converters connected in input-parallel and output-series symmetrically. Thirdly the Full-Bridge modular DC-DC converters connected in input-series and output-parallel are studied, and the research conclusions exhibit the following advantages: the simplicity of the control strategy; low voltage stresses in transformer primary side MOSFET; input voltage sharing; output current sharing; small volume of input and output filter.A reduced-order system model and responding control method using the equivalent energy contribution is presented to alleviate the hardness of designing controller resulting from the complicated modular combined system.The effect on the system quality brought about by the parameter difference existing in the components of each modular is studied to verify the practicality of the scheme.Some research results of this paper are obtained from an aeronautical static converter and a modular uninterrupted power supply (UPS).