Research On Performance Optimization Of Dual Active Bridge And Voltage Sharing Control Of Its Series-Parallel System

Dual Active Bridge(DAB)DC-DC converter are widely used in micro-grids,energy routers and other medium-to high-power applications due to their advantages such as higher power density,bidirectional energy transfer capability,and ease of modular design.But on the one hand,when the input voltage and output voltage ratio does not match,single-phase modulation will cause the soft switching range to be reduced,the reactive power will increase and the efficiency will be reduced.To solve this problem,on the basis of bidirectional dual phase shift modulation,this paper proposes An optimized control strategy for reactive power and soft switching;on the other hand,in high power applications,multiple DAB converters need to be connected in series and parallel to expand their transmission capacity.However,the existing voltage sharing control strategy cannot balance reliability and output voltage characteristics under wide input voltage.In response to this problem,this paper proposes a modular input voltage sharing control strategy based on secondary voltage regulation.The main research work and innovation of the thesis are as follows:1)The paper introduces the DAB converter under single-phase modulation,analyzes and discusses its working principle,reactive power generation mechanism and conditions for achieving soft switching,derive the relationship between the voltage conversion ratio and the reactive power,soft switching realization conditions.When the input voltage does not match the output voltage conversion ratio,single-phase modulation will cause the soft switching range to decrease and the reactive power to increase.2)Under the condition that the input voltage and output voltage ratio does not match,the single-phase modulation will cause the soft switching range to decrease and the reactive power to increase.An optimized control strategy for reactive power and soft switching is proposed.On the basis of bidirectional dual phase shift modulation,all operating modes of power forward transmission are optimized to obtain smaller reactive power and a wider soft switching range.Studies have shown that compared to single phase shift and unoptimized bidirectional dual phase shift modulation,The optimized control strategy mentioned can effectively reduce the reactive power and expand the soft switching range.3)Corresponding to the series-parallel dual active bridge DC-DC converter used in high-power occasions,the average circuit model and decoupling control strategy is derived.Based on this,the principles of centralized and decentralized control strategies are analyzed and discussed.The contradiction between the reliability and the output voltage characteristics of the existing voltage-sharing control strategy under a wide input voltage is described.4)Aiming at the problem that the existing voltage-sharing control cannot balance the reliability and output voltage characteristics due to the different degree of dependence on communication under wide input voltage,a modular voltage-sharing control strategy based on secondary voltage regulation is proposed.Based on the decentralized control strategy,the control strategy adjusts the voltage sharing command value to achieve better output voltage characteristics.Research shows that the proposed control strategy can take into account both reliability and output voltage characteristics.5)Two sets of series and parallel experimental systems consisting of two 5k W dual active bridge DC-DC converters were built.Through this experimental platform,the optimized control strategies for reactive power and soft switching,and the modular input voltage sharing control strategy based on secondary voltage regulation were verified.experimental results Verifies the effectiveness of the control strategy.