Research On Three-phase Dual Active Bridge Converter For DC Solid State Transformer

In order to solve the problem of energy shortage,China vigorously develops clean energy.Distributed energy and energy storage technologies have been vigorously developed.DC transmission has become a hotspot in research.DC solid-state transformer is the core device of DC grids.so the research on DC solid-state transformer has a very important theoretical significance and application value.The three-phase dual active bridge converter has the advantages of electrical isolation,bidirectional energy flow,high single-machine power,high power density,and small filter capacitance.It is widely used in the field of DC solid-state transformers.This paper takes three-phase dual active bridge converter as the research object,and studies it from the aspects of theoretical derivation,simulation analysis and experimental verification.This paper first summarizes the domestic and foreign research status of DC solidstate transformers,comparatively analyzes the advantages and disadvantages of several typical DC solid-state transformer topologies,and then selects a two-level three-phase dual active bridge converter topology based on YY connection for research,Analyze its basic working principle,and get the power,current and other transmission characteristics of three-phase DAB converter under phase shift control.Then,the soft-switching behavior of the three-phase DAB converter is analyzed,and the range of the softswitching behavior of the three-phase dual active bridge converter under ideal conditions is obtained.Then use the space state averaging method to model the three-phase DAB converter with small signals,and derive the transfer function between its output voltage and input voltage and phase shift angle.Then use MATALAB / simulink to build a three-phase DAB simulation model,and perform open / closed loop simulation analysis and verification of its control method.The simulation results are consistent with the theoretical analysis.Finally,the output capacity of the three-phase DAB converter is studied,the impact of the dead zone on its transmission power is analyzed,and the ability of the three-phase DAB converter to transmit power,output voltage,and current is obtained.Then,the construction process of 15 k W three-phase dual active bridge converter engineering prototype is introduced in detail,which is divided into four parts: power circuit,drive circuit,control circuit and sampling conditioning circuit.In the design of power circuits,the design basis and design method of auxiliary inductors are proposed based on the influencing factors such as return power,current stress,and current effective value.Finally,the three-phase dual active bridge converter prototype is tested and verified.First,the three-phase DAB converter with passive load is experimentally verified,and the method of slow start of the three-phase DAB converter duty cycle is proposed,which reduces the startup The inrush current of the process makes the converter start smoothly.Then with the active load,the bidirectional power transmission capability of the threephase DAB converter was experimentally verified.Finally,the parameter design method of auxiliary inductance proposed in this paper is experimentally verified,and the efficiency curves of the prototype under different auxiliary inductances are obtained.