Research On Design And Control Strategy Of Three-level Dual Active Bridge DC-DC Converter

Dual Active Bridge DC-DC Converter(Dual Active Bridge DC-DC Converter)has the advantages of high power density,two-way energy transmission,electrical isolation,diversified control methods and easy realization of soft switching.Widely concerned,it is also widely used in DC power grids,electric locomotive traction systems and charging and discharging and energy storage systems.In addition,dual active bridge DC-DC converters are also the core part of power electronic transformers.Compared with traditional transformers,power electronic transformers can not only realize the functions of voltage conversion and energy transmission,but also adjust output voltage and current,improve power quality,and enhance system stability.The three-level dual active bridge DC-DC converter adds a clamp to the structure of the two-level dual active bridge DC-DC converter,so that the switching voltage stress is reduced to half of the DC side input voltage,which can effectively meet the withstand voltage Demand,more suitable for high power and high voltage applications.This thesis takes the diode-clamped three-level dual active bridge DC-DC converter as the research object.First,it introduces the working principle of the traditional single-phase shift control method and the switching mode of the converter,and deduces that the converter is in steady state.The transmission power characteristics,soft switching range,inductor current stress characteristics and return power characteristics at time.Through simulation,it is found that under the traditional single-phaseshift control method,the converter cannot realize the zero-voltage turn-on of the secondary side switch at light load,the return power and the large inductor current stress and other problems.In order to achieve soft switching of all switches on the primary and secondary sides of the converter in the full power range and reduce the return power and inductor current stress of the converter,this paper analyzes the working principle of single-sided dual phase shift control and the working characteristics of the converter,and finds that Under this control method,the converter can also achieve zero-voltage turn-on of the secondary side switch at light load.Based on the single-sided dual phase shift control,the inductor current stress optimization control and the return power optimization control are proposed,and the optimization function is established with the inductor current stress and the return power of the converter as the optimization objectives.It is found through simulation that under the optimized control method,the return power of the converter in the full power range and the inductor current stress under heavy load can be effectively reduced.However,under the single-sided dual-phase-shifted return power optimization control method,the inductor current stress is relatively large when the converter is under light load.In order to solve the problem of the large inductor current stress of the converter under light load,this paper analyzes the working principle of double-sided double phase shift control and the working characteristics of the converter.Based on the double-sided double phase shift,the inductor current stress is proposed.The optimization control and the return power optimization control respectively establish the optimization function with the inductor current stress and the return power as the optimization targets.It is found through simulation that the inductor current stress optimization control method can further reduce the inductor current stress of the converter,and the return power optimization control method can reduce the inductor current stress of the converter under light load.Finally,the design plan of the converter is introduced in detail,including the selection of the main components of the main circuit,the calculation and design of the parameters of the high-frequency transformer and the resonant inductor,the design of the drive,sampling,protection and DSP control circuit,etc.An experimental platform for a three-level dual-active bridge DC-DC converter based on DSP28335 is built.The experiment verifies that the proposed single-phase converter can reduce the inductor current stress and return power of the converter and improve the power transmission efficiency of the converter.The optimized control of the side double phase shift and the optimized control of the double side double phase shift have good optimization effects,and it also verifies that the optimization effect of the double side double phase shift optimization control is more significant.