Analysis And Control Of New Traction System Based On Power Electronic Transformer

The high-speed railway has become a beautiful card representing the achievements of science and technology innovation in China's rapid economic development in recent years.The technical innovation of the high-speed EMU is an important help for the further development of high-speed railway.The development of the next-generation high-speed EMUs has become a hot area for researchers at home and abroad,and the traction drive system has become one of the research hotspots as part of the core of EMUs.The large size,heavy weight and concentration of traditional traction transformers limit the further development of high-speed EMUs.How to overcome the shortcomings in the current traction drive systems is important for EMUs to move toward faster,more efficient and more comfortable.In this context,the article proposes a new type of traction system main circuit based on power electronic transformers.Based on the mathematical model and operating principle,this article analyzes and controls the main circuit.The specific work is as follows:Firstly,by introducing the main topological structural formulas of current power electronic transformers,the main forms and characteristics of single-stage PET,two-stage PET,and three-stage PET are summarized.By comparing and discussing the advantages and disadvantages of each,the advantages and disadvantages of both the multi-winding common core and the single-winding independent core existing in the IF transformer are summarized.Based on this and combined with a certain technical background,a new type of traction system main circuit is proposed,and the main circuit structure is established.Secondly,the two parts of the input rectification stage and intermediate DC isolation stage are analyzed as the key points.For the input rectification stage,based on the mathematical model and operation principle of a single-phase voltage-type PWM rectifier,the mathematical model and operation principle of the output cascaded H-bridge rectification stage are generalized.For the intermediate DC isolation stage part,the dual active bridge DAB is studied and the average switching function mathematical model and the small signal mathematical model are determined respectively,and the virtual direct power control strategy(VDPC)and the direct power The results of the simulation analysis of the feed control(DPC)obtained the DAB output response dynamic characteristics of the two control methods.Finally,the factors that affect the voltage balance of the cascaded H-bridge on the input side are analyzed.The inconsistent capacitance at the output side of the rectification,the difference in the connected load,and the modulation algorithm are the main factors causing the voltage imbalance.The cascaded H-bridge on the input side is determined to be in communication with the control principle of a single-phase PWM rectifier under balanced conditions,and double-closed-loop control is used for simulation verification.For unbalanced conditions,voltage balance control based on voltage equalization compensation is proposed and verified by simulation.