Research On Bidirectional DC-DC Converter Based On Multi-winding Transformer

With the development of new energy distributed microgrid,especially the increasing proportion of photovoltaic power generation in the power grid,vigorously developing distributed energy storage system is one of the more feasible options to deal with the volatility of new energy power generation.Nowadays,the voltage between the DC bus and the energy storage system is not uniform,and the multi winding converter has a wider working voltage range and application scenarios.Therefore,it is necessary to deeply study its working characteristics.In this paper,a bi-directional DC-DC converter based on multi winding transformer is built under the background of 750V DC bus.The ZVS soft switch on the high voltage side and zero current soft switch on the low voltage side are realized through a unique control strategy,which reduces the switching loss,reduces the high-frequency interference during operation and improves the stability of operation.Firstly,the working principle and characteristics of traditional DAB converter and traditional LLC resonant converter are briefly introduced,and the control strategy and working mode of bidirectional zero current switching DC-DC converter are explained and deduced.Then two improved control methods are introduced,that is,the control of restraining the influence of junction capacitance oscillation and the improvement of ZVS control based on pulse front control.Then,the soft switching characteristics and power transmission characteristics are analyzed.Then,aiming at the application scenario under 750V DC bus in DC microgrid,a multi winding transformer and corresponding full bridge circuit are added on the basis of bidirectional zero current switching DC-DC converter,and a multi winding DC-DC converter is built.Its control strategy adds independent current control and voltage sharing control on the basis of bidirectional zero current switching control.In the parameter design,according to the working principle of the converter,the theoretical analysis is carried out around the main parameter transformation ratio N and external inductance value L of the converter from the two aspects of optimizing current stress and optimizing loss,the corresponding relationship between transformation ratio N and inductance value L is obtained,the function image of transformation ratio N and current peak i _Hpeak and i _Lpeak at high and low voltage side is drawn,and the function image between transformation ratio N and loss P’_off under rated current is drawn,Finally,a reasonable parameter range is selected according to theoretical analysis and image rendering.Finally,the main parameters of the circuit topology are determined,the software and hardware of the converter are designed,and a 2k W three winding Bidirectional DC-DC converter experimental platform is built.The basic working principle,two control improvements and multi winding voltage sharing control proposed in this paper are verified by experiments,which are consistent with the theory and simulation.