Research On Dual Phase-shift Controlled Bidirectional Dual-Active-Bridge DC-DC Converter

The shortage of traditional fossil energy has led to the extensive research and application of new energy technology.Photovoltaic(PV)power systems,wind power systems,and electrical vehicles are the key technology,currently.Due to the inherent unstable characteristics of PV and wind power,energy storage systems with high power density and bidirectional power flow capability are needed to buffer and regulate the peak power.Feeding back the kinetic energy to batteries and super capacitors when braking is beneficial to make better use of electrical energy,which will increase the endurance range.These applications need high-power-density DC/DC converters with bidirectional power flow capability as power flow devices.Dual-active-bridge isolated bidirectional DC/DC converters have the advantages of bidirectional power flow capability,high power density and ease of realizing softswitching which helps increasing the efficiency.They are widely used in numerous applications.However,the traditional control strategy of DAB-IBDC is single-phaseshift(SPS)control,which has its limitations.When the voltage amplitude of the two sides of the converter do not match,the current stress of the switches and the circulating power become much bigger,and the soft-switch range decreases,resulting in significant efficiency decrease.Hence,modifying the traditional control method to improve the performance and increase the voltage conversion range has a vital significance.In this thesis,the operation principles of the converter in SPS and DPS control are introduced.The power transfer and current stress characterizations under different control methods are derived.The soft-switching processes,requirements and ZVS range are analyzed.Theoretical analysis and comparisons of the two control methods indicate that the DPS control is more flexible and has the advantage of reducing current stress,easier to achieve soft-switching.On the basis of the theoretical analysis,the minimum peak current optimized control strategy is derived,and the small signal model is built.Simulation results validated the outstanding effect of reducing the current stress of the proposed control strategy.At last,a 400 W prototype based on TMS320F28069 microcontroller is developed.The detailed hardware design procedures including main circuits,driving circuits,sample circuits,control and protection circuits are provided.The software design procedures are briefly introduced.The control loop of the converter is compensated using classical control theory.The transfer function of the compensator with its discrete difference equation are acquired via bode diagram.Experimental results verified the correctness of the theoretical analyses and the rationality of the prototype design.