| With the continuous development of distributed power generation system,the structure of modern power system is undergoing complex changes,and more small distributed power sources are directly connected to the DC transmission network.As the key equipment connecting distributed power supply and DC power grid,DC power electronic converter has been widely used for its advantages of electrical isolation,high transmission efficiency and easy control.The output voltage of distributed power system to converter fluctuates greatly with the change of external environment.Therefore,dc power electronic transformers need to adapt to a wider range of voltage changes to maintain the advantages of high efficiency transmission.The multilevel DC power electronic transformer is widely used in the scenarios with large voltage changes because of its significant reduction of voltage waveform distortion rate and current stress of inductance current.In this paper,a new T-type and dual-transformer DC converter is proposed based on topology reconstruction and efficiency optimization control,which is suitable for wide-voltage operation scenarios.It is called a new type wide voltage gain DC converter based on T-type half-bridge and dual-transformer.The converter has the characteristics of wide voltage gain,low voltage and current stress of power device and simple control principle.Firstly,the topology is divided into three different working modes based on the fact that the integral of the absolute pressure difference between the two ends of the equivalent inductor is proportional to the loss.During operation,it can be reasonably selected according to the different ratio of input voltage and output voltage.Based on this,the trigger principle of five-level voltage on primary side and two-level voltage on secondary side is given.Fourier series is used to decompose the primary and secondary voltage into the superposition of fundamental and harmonic components,which is finally transformed into the superposition of fundamental and third harmonic components respectively,so as to deduce the power transmission expression of this topology.Then,the overall control method of the novel wide voltage gain DC converter is studied,including efficiency optimization control method,mode switching control method and their coordination relationship.Based on the voltage vector diagram at both ends of transformer equivalent inductance,the optimal condition is given,and a new three-d OF optimal control idea is obtained.Combined with the topological characteristics and the three-Dof control principle,the general process of optimal design is sorted out.For the process of mode switching frequent switching and switching smoothness problem,design application switching with hysteresis characteristics,the switching program is executed at the zero point of current crossing when transformer switching is involved,effectively avoid the jitter of the input voltage in the critical switching point and when switching transformer current overshoot phenomenon,ensure the smooth operation process.Finally,a simulation model of the topology was built in Plecs software,the selection basis of experimental parameters was given,and simulation experiments were set up to verify the different performance of the control method.It includes simulation verification of anti-shake characteristics,switching smoothness and overall control,which effectively proves the correctness of the proposed control principle.At the same time,in order to further verify the practical feasibility of the topology and more directly verify its efficiency advantages,a 1kW experimental platform was built in this paper to verify the working principle of the topology and its efficiency advantages compared with the T-type half-bridge DC converter topology.It includes working mode experiment verification,mathematical model experiment verification and efficiency comparison experiment verification,which proves the practical value of the proposed topology. |
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