Design And Research Of Single-phase Electronic Power Transformer

Electronic Power Transformer(EPT)is a new type of intelligent transformer which can realize the transmission and adjustment of electric power quality through combining power electronic converter with high frequency transformer.Compared with the traditional oil-immersed power transformers,EPT has many advantages,for example: no matter how input stage power quality changes or how output stage current changes,the output voltage is always sine wave;through setting the input stage reasonably,no matter how output stage current changes,the input current is always been sine wave and makes the power factor approximately equal to 1.And the input stage of EPT includes ac input port and dc input port,it can be effectively connected to the distributed generation system.Therefore,conducting the research about EPT deeply has very important practical significance.Firstly,this paper makes a brief summarization about the current situation and the development of EPT and makes analysis about several typical circuit topological structures.After summarizing the advantages and disadvantages of these topological structures,this paper decides to make a deep study on single phase EPT which is based on level 3 topology structure.Input stage consists of single-phase PWM rectifier circuit,and the paper analyses working principle,mathematical model and control strategy of the circuit in detail.Intermediate isolation stage consists of full bridge phase shift circuit with clamp diode,and the paper makes a theoretical analysis about circuit topological structure and the period of working mode.Output stage consists of single-phase inverter circuit and LC filter circuit,and the paper makes a theoretical analysis about the circuit working principle,mathematical model and control strategy.After finishing all levels analysis of EPT circuit,this paper uses Matlab/Simulink software to conduct a series of simulation experiments which conclude of steady-state experiment,voltage drop experiment,harmonic experiment and load switching experiment.The simulation results prove that EPT not only has the function of voltage level transformation and electrical isolation,but also has the function of adjusting the power quality.After finishing the simulation experiments,this paper builds the hardware circuit of the EPT.The intermediate isolation stage circuit uses UCC3895 chip and peripheral circuit to realize,the output stage circuit uses DSP chip and peripheral circuit to build the hardware circuit.The other work includes the switch tube model selection,rectifier diode model selection,the design of high-frequency transformer,the design of LC filter,auxiliary power supply design,the design of drive circuit and protect circuit,the design of the DSP program.After finishing building the hardware circuit,this paper conducts the electrical test.Experiment result verifies the situation of the EPT working in steady state.