Research Of Push-pull Power Electronic Transformer

As an important component of the smart grid, the power electronic transformer(PET) has many advantages, such as high controllability, small volume, light on weight, and strong reliability. It has been more and more concerned in recent years. Comparing to the traditional electrical transformer, PET is a new kind of power transmission device, and it combines the high-frequency transformer with the power electronic technologies. This paper mainly considers the power electronic transformer. Based on the characteristics of PET, a new kind of power electronic transformer – push-pull power electronic transformer is proposed, and its main properties are explored.Firstly, this paper introduces the concept and fundamental principle of power electronic transformer. Depending on the existence of internal DC part, PET could be categorized as two types, AC-AC PET and AC-DC-AC PET. Each of the type both has its own typical structure. The most typical structure of AC-AC PET is the matrix converter PET, which has many advantages, such as high power density, compact structure and high efficiency. The most typical structure of AC-DC-AC PET is the PET with PWM rectifier and SPWM inverter. Because of the existence of internal DC part, this kind of structure has higher circuit controllability and more flexible power factor. So, generally it could meet the actual demand of application better.Based on the analysis of push-pull circuit and its features, this paper combines push-pull circuit with power electronic transformer, and puts forward a new-style push-pull PET. Depending on the existence of internal DC part, push-pull PET could also be categorized as AC-AC push-pull PET and AC-DC-AC push-pull PET. Each of the type has its own typical structure and operating principle. Comparing to the typical PET topology, the structure of push-pull PET is briefer, and the required number of semiconductor devices could be reduced by 50 percent, so it leads to the decrease of cost and volume. By the construction of simulation model, the simulation analysis of these two new types of push-pull PET could be conducted. The result indicates that these two types of push-pull PET could achieve the similar or better power factors by briefer circuit topologies.In order to achieve the better overall power factor, this paper puts forward the circuit structure of impedance transformer, and also analyzes its basic topology and control strategy. Impedance transformer could effectively help overall circuit to promote its power factor, and also make the control methods more abundant. Based on this fact, impedance transformer could be combined with push-pull PET, to propose a new type of PET, the push-pull PET with impedance transformer. And then, the analysis of its circuit structure, basic principle, and advantages in practical application could be conducted. Meanwhile, the simulation analysis of this improved push-pull PET could be conducted by the construction of simulation model. The result indicates that the push-pull PET with impedance transformer has the advantages of both impedance transformer and push-pull circuit. It not only has the briefer and more efficient structure, but also could achieve the excellent overall power factor. So the push-pull PET with impedance transformer has a high value for further research.