Research On Improved DAB Control Strategy For Dual Active Bridge In Modular Cascaded Solid State Transformer

With the rapid development of domestic and global economy,the demand of energy has increased greatly.The problem of traditional fossil fuel and environmental pollution is becoming more and more serious.The development and utilization of new energy has become an urgent problem to solve.Renewable energy,such as photovoltaic solar energy,wind energy,tidal energy,has become a main research direction.Grid generation of distributed energy will exert an influence on the power grid and even affect the stability of power grid because of its uncontrollability.How to build a stable'energy router' to connect distributed new energy and large power grid has become a main research topic.Solid state transformer(SST),which can not only support the distributed generation,storage and plug and play of controllable loads,but also effectively manage the power dispatch and fault isolation,has become an ideal choice for future energy routers.However,the current control mode of solid state transformer still has the problem of low efficiency and high switching current stress.The paper optimizes the control method and analyses the selection of control methods under different conditions.First of all,the paper analyzed main circuit topology and the key control technology of solid state transformer briefly,that is,the paper analyses advantages and functions of modular cascaded SST which is proposed by the center of FREEDM.In order to improve the voltage and power levels and reduce the voltage and current stress of a single module,the topology integrates a number of low-voltage modules of rectifier stage and DAB stage by series parallel combination,The main circuit parameters are designed according to the requirements of power and voltage level.Secondly,control strategies of different stages are analyzed.The rectifier stage takes the common duty ratio based on virtual d-q transform SPWM control and DAB stage takes voltage of positive negative feedback following control.At last,the paper builds small signal models and designs control parameters according to the models.Then,two dual-phase-shift controls are introduced aimed at the larger backflow power problem of DAB stage.The paper analyzes its working principle and establishes a mathematical model of power transmission and backflow power.With the goal of the least reflux power,backflow power of two dual-phase-shift controls optimization are analyzed respectively.On this basis,backflow power and current stress of two dual-phase-shift controls which take optimal backflow power control are compared respectively,their advantages and disadvantages are analyzed and the optimum phase selection method is acquired to adapt to different requirements.Finally,the experimental platform is built to verify the feasibility and effectiveness of the above control strategy...