Research Of SiC Modules Based DC-DC Converter For Electric Locomotive Auxiliary System

With the rapid development of power electronics technology,the auxiliary power system in electric locomotive is progressing towards more compact,light and effective.DC-DC converters are essential components for DC-DC-AC type auxiliary power system in electric locomotives.Their further development has encountered challenges in terms of weight,volume and efficiecncy.However,the high voltage stress and loss of switching devices make it difficult to improve switching frequency and reduce size of passive components of the adopted chopper circuit in existing auxiliary power system,thus limiting the improvement of efficiency and power density.Recently,silicon carbide(Si C)devices have been widely used in railway vehicles and realized further enhancement of auxiliary power system,showing good application prospect.Therefore,this thesis analyzes a switched capacitor based resonant converter(SCRC),with using Si C devices to achieve higher efficiency and compact design,and evaluate the application prospect of SCRC in auxiliary power system.Based on the operation principle of SCRC,the analysis of the current ringing during switching process was focused on,and an optimized switching patterns was proposed.In addition,the influence of circuit parasitics on SCRC output performance was analyzed based on the equivalent model.In order to meet the voltage conversion requirements of different type of auxiliary power systems,the universal equivalent model of expanded n-SCRC has been developed as well.Results show that the output voltage of SCRC not only changed with the input voltage variation and load mutation,but also be influenced by the device characteristic parameters.Therefore,the optimized output control is necessary to meet the practical demand.Therefore,the phase shift control is introduced to improve SCRC voltage regulating ability.On the basis of detailed analysis and state tracjectories,the mathematical models between phase shift time and steady-state variables have been deduced,and then the influence of circuit parasitics was analyzed as well.By considering the dead time effect and device parasitic capacitance,the soft switching conditions were discussed.Based on analyzing small signal model and transfer function,the optimized output control strategy was proposed to enhance the output adjusting ability.Results show that SCRC is flexible to deal with the voltage variation and load mutation with high efficiency by using the soft-switching technique.The experimental prototype employing Si C devices has been designed and constructed to verify theoretical analysis.Results show that SCRC realized the expected voltage conversion with good adjusting ability.Compared with the existing hybrid Si C based SCRC prototype,the adoption of Si C devices helped achieve compact design and higher efficiency by using soft-switching technique.Therefore,Si C-SCRC shows good application prospect in the auxiliary power system of electric locomotive.