Study On Efficiency And Dynamic Performance Optimization Methods For Dual-active-bridge DC-DC Converters

Small and lightweight design is one of the main development trends and key technologies of modern high-speed trains.In order to achieve lightweight design of high-speed trains,power electronic traction transformer(PETT)has become a key equipment for the new generation of high-speed trains.Thus,based on the application background of PETT,this paper mainly focuses the dual-active-bridge(DAB)dc-dc converters,which is one core component of PETT.Firstly,a state space average model of the output voltage for single DAB converter under single phase-shift(SPS)modulation is established,and the discrete model of the output voltage is deduced.A model feedforward control method based on SPS modulation is proposed to improve dynamic response of the output voltage under the input voltage fluctuation and load disturbance conditions.And parameters sensitivity analysis of the model feedforward controller is presented.Furthermore,the design of control parameters and the stability of the control system are analyzed based on the small signal modelling of the DAB converter.Experimental results show that the proposed control method has excellent dynamic performance and weak parameters dependence.Then,in order to improve the efficiency and dynamic performance of the DAB converter simultaneously,a multi-objective optimization method based on extended phase-shift(EPS)modulation is studied.This method analyses and improves the power model and current stress model of the DAB converter under EPS modulation comprehensively,and further combines Lagrange multiplier method and direct power control to improve efficiency and dynamic performance.Experimental results show that the proposed control method can improve the efficiency and dynamic performance of the DAB converter,simultaneously.Subsequently,aiming at the output-parallelled DAB converters in PETT,the influence of the control method for the cascaded H-bridge(CHB)converter on the output-parallelled DAB converters is analyzed,and its mechanism is revealed: when the intermediate dc-side voltage balance is realized by the CHB converter,the output-parallelled DAB converters are equivalent to the input-independent-output-parallelled connection;when the CHB converter does not adopt the intermediate dc-side voltage balance method,the output-parallelled DAB converters are equivalent to the input-series-output-parallelled connection.Furthermore,a model feed-forward control method with power self-balancing based on dual phase-shift(DPS)modulation is proposed for the input-independent-output-parallelled DAB converters to achieve the transferring power balance,efficiency optimization and the dynamicperformance improvement under the input voltage fluctuation and load disturbance conditions.Experimental results show that the proposed control method can improve efficiency and dynamic performance,and achieve the transferring power balance among each DAB module.Finally,in order to achieve multiple performance optimizations of output parallelled DAB converters and take the current quality in ac side of CHB converter into account,a multi-module optimized power balance method for input-series-output-parallelled DAB converters is proposed.By introducing virtual power and defining dynamic power components,the efficiency and dynamic performance of the DAB converter can be improved,and the transferring power balance over the whole power range is achieved.Meanwhile,the control structure of this method is simple,which greatly reduces the computational burden of the controller and facilitates the modularization promotion.Experiments show that the proposed control method can improve the efficiency and dynamic performance,achieve the intermediate dc-side voltage balance and transferring power balance of each module,and improve the quality of ac current.