Average Current Optimization Based Operation Mode Smooth Switching Strategy For DAB

With the widespread use of clean energy,dual active bridge converters(DAB)are getting more and more attention.It has high efficiency,two-way flow of energy,soft switching,electrical isolation,etc.,so it is widely used in solid state transformers,electric vehicles,energy routers and uninterruptible power supplies.Therefore,this paper proposes a new optimized modulation strategy and a new closed-loop control strategy based on DAB as the converter topology.In this paper,the modulation modes,soft switching characteristics and power characteristics of single phase shift control,extended phase shift control and triple phase shift control are analyzed in detail.The average value of the inductor current is derived in the extended phase shift mode,and a mathematical model of power transmission,voltage gain,and average current is established.In order to reduce the average current of the inductor,reduce the on-state loss of the power switch,and improve the transmission efficiency of the converter,this paper analyzes the average current of the inductor under different modes based on extended phase shift control,and obtains the optimal inductor average current control curve,which is in the traditional DAB.Based on this,a rectified average current o ptimized modulation strategy is proposed.The control strategy obtains the control mode of the inner phase-shift angle by extended phase shift control.In order to ensure that the converter maintains the lowest rectified average current at different power and voltage gains.The control strategy proposed in this paper effectively reduces the on-state loss of the power switch and improves the transfer efficiency of the converter.In this paper,small-signal modeling of DAB is carried out,and a traditional PI closed-loop regulator is built.After theoretical analysis,it is concluded that the transmission power is fluctuating when the inner phase-shift angle is abrupt.Therefore,a closed-loop control strategy of the external phase-shift angle compensation is proposed.When designing the closed-loop control strategy,this paper first analyzes the relationship between transmission power,the inner phase-shift angle and the external phase-shift angle.Then,the compensation angle of the external phase-shift when the inner phase-shift angle is abrupt is determined.It ensures that the working mode is smoothly switched of DAB.Finally,a 1.5kW experimental prototype was built,and the correctness of the theoretical analysis and the feasibility of the closed-loop control strategy were verified by experiments.