Research On Control Strategy Based On Modular Cascaded Solid State Transformer

With the development of science and technology under the national policy,and the electric energy that is closely related to people is very important,the demand for electricity is increasing.Nowadays in view of the above factors,with the expansion of the scale of the power grid,the traditional transformers are becoming more and more to meet the needs difficultly.Solid state transformer is a kind of new device,which combines the advantages of high frequency transformers and power electronics technology.It is able to keep the circuit running at unity power factor,such as transformation of energy,voltage change,electrical isolation and plug and play.Hence,solid state transformer has the potential to solve many new problems in modern power system,and it is of great significance to improve the quality of power grid and to build digital power grid and green power grid.Based on the basic idea of solid state transformer,this dissertation each part of the module cascade SST is analyzed and designed.In this dissertation,a double closed loop control scheme is proposed,which is combined with the internal model control method.That is to say,the two degrees of freedom internal model control strategy is adopted in the outer voltage loop,and the internal model decoupling control scheme is applied to design the system in the current inner loop.The current has fast tracking performance,which can make the input voltage and current have the same phase,the low distortion factor of output voltage is realized,and the power quality is good.Firstly,the research background and development status of solid-state transformer are described.Compared with the traditional transformers,many advantages of solid state transformer variable pressure are obtained.The basic ideas of the topology and running time of the solid state transformer are introduced and analyzed.Then we analyze the operation characteristics of the three parts of the module cascaded SST,including the input stage,the middle isolation stage and the low voltage output stage,and the mathematical modelling was established.Secondly,the proposed control strategy is designed for the module cascade SST system,and the control block diagram of various control strategies is given.At last,the simulation system of module cascade SST is built under the environment of Matlab/Simulink to verify the simulation experiment.In view of the above mentioned above,the basic ideas,mathematical models,modulation strategies and control strategies of modular cascaded SST are analyzed and designed in detail.The simulation results show that the proposed control strategy makes the system achieve the desired control effect.