Research On Optimal Control Of Double Bridge Series Resonant Converters In Locomotive Power Electronic Transformer

In order to realize the weight reduction and high power density of high-speed trains,on-board power electronic transformers have become the vital branch of a new generation of high-speed trains that replace power frequency transformers.The power electronic transformer is composed of a single-phase H-bridge rectifier and a bidirectional DC-DC converters.The high-frequency DC-DC converters are equipped as the load of its single-phase rectifier and the power supply of the traction inverter on the motor side,which face the external operating environment such as the output voltage ripple of the front rectifier as well as the sudden load change caused by the acceleration and deceleration of the motor.The high efficiency is essential.Meanwhile,with the application of wide band-gap devices such as silicon carbide and gallium nitride,the breakdown voltage and power range of devices have increased.The topologies have gradually developed toward high reliability and simplification.So selection of DC-DC topologies and enhancement of corresponding control method are beneficial to the requirements of high density,light weight,and high reliability.Firstly,the current research about the structures and characteristics of bidirectional DC-DC topologies are analyzed in this topic.Based on the topological structure,the research contents of modeling and control algorithm are comprehensively illustrated.The bidirectional series resonant converter is selected and through comparison with the traditional dual active full-bridge DC-DC converter.Secondly,the steady-state characteristics and efficiency of the converter are influenced by the output voltage fluctuation and the peak current of the resonant inductor.From the perspective of output voltage ripple suppression and resonant current optimization,current stress optimization are applied.The model predictive voltage control method and the optimal virtual direct power control method are applied to the bidirectional series resonant converter to improve the dynamic response speed.PI-free control and robustness can be achieved separately and the settling time can be shortened under different conditions.Finally,a full-bridge bidirectional DC-DC experimental platform based on SiC MOSFETs is established.The dynamic control algorithm and steady-state optimal control method are verified respectively.In addition,the performance and advantages of the control method are analyzed and explained in detail.