Design Of Three Port DC-DC Converter For Low Voltage DC Distribution Network

With the introduction of the national “Carbon Peaking Action Plan Before 2030” and the“14th Five-Year plan” industrial green and low-carbon development plan,the transformation of the power industry has released huge opportunities and potentials.The DC distribution network can well coordinate the contradiction between distributed power and grid access,fully develop the value and benefits of distributed energy,and become a new direction for the development of the power industry.However,the current traditional DC-DC converters have problems such as single topology structure and low power density,which can only complete one-way transmission of energy,which makes the distributed energy cannot be fully utilized.For the problem of distributed energy transfer,this thesis is based on a three-port DC-DC converter for low-voltage DC distribution network to realize energy transfer between DC distribution network,distributed energy and low-voltage load.Three-port converter can not only charge the distributed energy and low-voltage load,but also feed back the distributed energy to the DC power grid.Thesis research work are as follows:Firstly,the energy transfer modes of the three-port DC-DC converter is introduced.Combined with the converter topology and energy transfer mode,a simplified equivalent model of the converter is established.The frequency characteristics and voltage gain characteristics of the converter are studied,and the effects of the excitation inductance to primary resonance inductance ratio parameter k and the quality factor Q on the voltage gain characteristics of the converter are discussed.On this basis,the resonant cavity design of the converter is based on the optimal selection of parameters k and Q so that the converter can meet the voltage gain requirements in both forward and reverse operation.The simulation results under different loads verify the reasonableness of the resonant cavity components selection.Secondly,the core material is selected as 0.15 mm ultra-thin silicon steel sheet,and the magnetic properties of ultra-thin silicon steel are measured by using a single silicon steel sheet test system.Based on the test results of magnetic characteristics of ultra-thin silicon steel sheet,a 20 k VA three-winding medium frequency transformer is optimally designed with the objective of minimizing losses using the area product AP method.On this basis,the loss of medium frequency transformer is studied and the electromagnetic and temperature rise verification is completed.Thirdly,the electromagnetic and thermal two-way coupling finite element simulation of the three-winding medium frequency transformer based on the magnetic characteristics of ultrathin silicon steel sheet is carried out,and the loss distribution and magnetic field distribution in the core of the medium frequency transformer are obtained through the electromagnetic simulation;the temperature distribution of the core at no-load and the temperature distribution of the winding under rated load are obtained through the electromagnetic and thermal bidirectional coupling simulation,which verifies the correctness of the design scheme.Finally,a prototype three-winding medium frequency transformer is fabricated and no-load tests are completed.The excitation current,hysteresis loop,magnetization curve and core loss curve of the medium frequency transformer are obtained respectively when the medium voltage side and the low voltage side are excited.The experimental platform of 20 k W three-port DCDC converter is built,and on this basis,experimental studies are conducted under different loads to verify the feasibility of ultra-thin silicon steel wafers for high-power,medium frequency convert applications.