Research On DC Transformer Topology And Its Control Method Based On DC Distribution Network

Compared to AC distribution network,The DC distribution network is superior to the AC power distribution network in the aspects of power capacity,controllability and power quality.DC transformer is an important unit in DC distribution network,its level of development seriously affects the development level of the whole DC distribution network,it is the key factor for the rapid development of DC distribution network.In numerous DC transformer topologies,input series output parallel(ISOP)structure,with its modular design,simple control strategy,control of each module is relatively independent,can withstand high voltage characteristics,has very high practical value for the DC power distribution network.At the same time LLC resonant converter can effectively solve the leakage inductance of the transformer leakage inductance,peak voltage,switching loss of pipe ZVS and reduce the switch,thus can realize the energy transmission efficiency and high power density.In this thesis,the ISOP structure DC transformer based on LLC resonant converter module is studied.The main research work is as follows:1?The main circuit of DC transformer based on DC distribution network is studied.The LLC resonant converter is selected as its unit module,analyzed the working principle and the DC gain characteristics,focusing on the study of LLC resonant converter harmonic analysis method of parameter design method and simulation combination.2?The steady state mathematical model of DC transformer main circuit based on DC distribution network is established,the input voltage and output current sharing characteristics are analyzed,and the loss characteristics of the system are analyzed.3?The small signal mathematical model is established,according to the mathematical model,the paper makes a comparative study on the system of equal pressure and current sharing,the inherent relationship between the input voltage and the output current sharing is analyzed,the advantages and disadvantages of the double loop control and the three loop control strategy are copared.Finally,the control strategy of the DC transformer is proposed.4?According to the rated parameters of DC distribution network,a 10kV/400V DC transformer system is designed,the system parameters are designed,including the number of cascaded modules,the selection of switching devices and the selection of the working frequency of the transformer,the parameters of the resonant network are optimized,and the input capacitance and the output capacitance are determined.5?According to the design parameters,the system simulation model is built on the MATLAB/SIMULINK platform,the simulation analysis of the system at the rated condition,the load,the voltage fluctuation under the condition of stable operation,and the pressure of the system,the stability of the output voltage and the input and output current sharing performance is proved.The simulation results show that the system has good stability in the face of sudden load change and net voltage fluctuation,and the output voltage is stable.