Research On Optimal Control Strategy Of Dual Active Bridge Converter Considering Dead-time Effect

Once the excessive consumption of energy contributed to the global energy shortage and environmental pollution,the development and utilization of clean energy such as wind power and solar energy has become the effective way to solve the problem of energy and environmental problems at present.A large number of distributed power sources,such as wind power and photovoltaic,improve the power structure of China’s power industry,but also make the power quality and reliability of traditional AC distribution network face unprecedented impact and challenge.Compared with traditional AC power distribution network,DC power distribution network has incomparable advantages in transmission capacity,power supply efficiency,power supply reliability,high efficiency and consumption of distributed power supply,and has become an important development direction of the power industry in the future.This dissertation focuses on Dual Active Bridge(DAB)converter widely used in DC distribution networks.Aiming at the problem of non-negligible dead-time effect during operation,this dissertation respectively based on Single Phase Shift(SPS)control and Double Phase Shift(DPS)control,the influence mechanism of dead-time effect on its operation characteristics is analyzed in detail,and the current stress optimization and soft-starting control strategy of its Zero Voltage Switch(ZVS)operation are studied.The main work and innovations are as follows:(1)The operation mechanism of DAB converter considering dead-time effect is analyzed,and the transmitted power model and soft switching range of DAB converter under SPS control are revised.Dead-time effect is an unavoidable problem in the operation of DAB converter,especially in the case of high frequency and high power,but it is ignored in the traditional phase-shift control.Aiming at the most commonly used SPS control of DAB converter,this dissertation analyzes the operation characteristics of DAB converter in detail through switching mode.Based on this,the traditional mathematical model of DAB converter under SPS control is modified by introducing the ratio of dead time.The soft switching range of DAB converter under different ratio of dead time is described.The operation characteristics of DAB converter before and after considering dead-time effect are compared and analyzed,and the influence of dead-time ratio on transmitted power model and soft switching range of DAB converter is summarized.(2)An optimal control strategy for minimum current stress of DAB converter considering dead zone effect is proposed,which can reduce current stress and realize soft switching in full power range.Soft switching and current stress optimization are important ways to improve the operation efficiency of DAB converter.However,the traditional soft switching and current stress optimization strategies based on DPS control do not consider the dead zone effect,and are prone to failure in the low power section.To solve this problem,based on the traditional DPS control,this dissertation analyzes the operation characteristics of DAB converter under the influence of dead zone effect in detail,establishes an accurate mathematical model of DAB converter with full ZVS operation mode including dead zone ratio,and describes the soft switching range under different dead zone ratio.The optimal solution of current stress of DAB converter under different transmission power in full ZVS operation is derived.Compared with SPS control,the proposed optimal control strategy has lower current stress in the full power range.(3)A soft-starting control strategy of DAB converter considering dead-time effect is proposed to realize smooth transition between different stages in the starting process.Soft-starting is an important step before DAB converter are put into normal operation.Direct start or traditional soft-starting control strategy without considering dead-time effect will lead to inrush current or voltage sag,resulting in protection misoperation and startup failure.Based on this,this dissertation analyzes the causes of shock current,DC bias and voltage sag in the process of starting,considers the influence of dead-time effect,establishes the mathematical relationship between the transmission power and the ratio of dead time in the process of starting,and analyzes the influence of deadtime effect on the soft-starting process.The mechanism of transient DC bias and voltage sag during switching between two stages is revealed,and a soft-starting control strategy based on phase-shift ratio compensation is proposed to achieve smooth transition in soft-starting process.