| In applications such as spacecraft power supply system,rail transit converter,high voltage self-supplying power source,and medium voltage dc distribution,medium and high dc voltage brings great challenges to semiconductor device selection,system insulation and reliability.The input-series combined converter can effectively reduce the voltage/current stress of devices,reduce the difficulty of system development and improve the system reliability by connecting the input side of multiple power modules in series and the output side in series,parallel or independent.The basic module is the key component of the input series combined DC/DC converter.Its voltage/current level,conversion efficiency,power density and voltage regulation ability directly determine the electrical properties and performance of the input series combined DC/DC converter.However,when the range of medium and high voltage dc bus and load voltage is wide,the cascaded basic modules need to process the output power twice,which makes the combined converter inefficient.Moreover,the standardized power supply module can not directly constitute the input series combined converter,so it is necessary to rebuild the sub-module or introduce a special voltage sharing compensator,which makes the system design complex and the development cycle long.In addition,in the case of high-voltage dc bus,the number of low-voltage isolated basic modules will increase significantly,which will increase the number of transformers with high insulation stress,increase the volume and quality of the system,and reduce the reliability.Therefore,in this thesis,the basic module,building block method and structure optimization of input series combined converter will be deeply studied,aiming at realizing the power conversion from medium and high voltage dc bus to medium and low voltage load with high efficiency,high reliability and flexibility.In view of the low efficiency of cascaded basic modules,and the complex structure of high-efficiency isolated quasi-single-stage modules,this thesis proposes an input-indirect-parallel output-series partial power processing module by analyzing the construction method of quasi-single-stage circuits.By adding an auxiliary winding,not only the voltage stress of the devices in the adjustment stage is reduced,but also most of the power is converted through an unregulated dc transformer with high efficiency and high power density,and a small part of the power is processed by two stages,thus improving the conversion efficiency of the input series converter and reducing the complexity of the system structure.Aiming at the problem that the input series combined system composed of standardized power modules cannot run stably,and the existing methods require sub-module reconstruction or the introduction of a dedicated voltage sharing loop,which leads to complex system design,and long research and development cycle,this thesis analyzes the reason why the input series combined system composed of two modules cannot achieve input voltage sharing,and puts forward a method of coupling inductive sharing module with open loop control in parallel with the input side of two standardized power modules.This method inherits the high dynamic output response of the standardized power module,realizes the input series combination of two standardized power modules,avoids the design of power topology and input voltage sharing compensator,and simplifies the design links of input series converter in the medium and low voltage dc applications.To further improve the flexibility of multi-module input series combination,this thesis discusses and proposes a building block construction method for input series combined converter.The open loop voltage sharing modules are used to form a chain structure to deal with the tiny unbalanced power between the sub-modules,which realizes the stable operation of the combined converter while simultaneously having the expansion function of multiple modules.The proposed method can directly select and assemble standardized power modules as device-level devices,thereby significantly improving the flexibility of constructing the input series combined DC/DC converter in the medium and high voltage applications.In view of the problem that the input series combined system composed of low-voltage dc converter under the high-voltage bus has a large number of transformers with high insulation stress,large volume and mass,and low reliability,the structure of the input series combined converter with multi-terminal high-voltage arm is optimized,and a topology consisting of multiple half bridge modules in series with three terminal high-voltage arm is proposed.Through the collaborative design of boost inductor and transformer magnetizing inductance,soft switching of all half bridge sub-modules and rectifier is realized,which effectively improves the system efficiency.In addition,the proposed dual circulant modulation method realizes the self equalization of the half bridge sub-module capacitor voltages under various modulation coefficient,avoids the complex sampling and sorting algorithm,and expands the application range of circulant modulation.The high-voltage dc module has a simple single stack and centralized isolation transformer structure.As the basic module of the input series combined converter,it will significantly reduce the number of high insulation stress transformers and improve the reliability of combined converter. |
