Optimization Of A Resonant Converter With Modular Rectifier Structure And Its Medium Frequency Transformer Design

Compared with traditional AC power grids,DC power grids have greater current-carrying capacity,higher efficiency,and faster dynamic response.In addition,renewable energy sources,energy storage devices,and electronic loads can be connected to DC power grids directly without rectifier or inverter,which can reduce costs and losses.As the core equipment of the DC power grid,DC transformer,which realizes the interconnection and active control between different levels of DC power grids,has an important impact on the reliability,stability and efficiency of the DC power grid.This paper studies the control and efficiency optimization of a DC transformer topology(Resonant converter with Modular Rectifier structure,RMR),and designs and manufactures its core component medium frequency transformer(MFT).In terms of RMR converter control,a closed-loop control based on bisection method is proposed,which can adjust frequency and pulse width simultaneously,so that RMR converter always works in the critical mode with high efficiency in a wide voltage range.The design procedure of bisection method controlling frequency and PI closed loop control adjusting the phase shift pulse width is described in detail.The feasibility of this control method is verified by experiments on a 300V/1200 V 8k W RMR prototype.The experimental results show that the RMR prototype can always work in critical mode after adopting this control method,and it has good dynamic performance.In addition,by optimizing the resonance parameters,the efficiency of the prototype is increased by about 2.5% under heavy load.In terms of the design of medium frequency transformer,firstly,referring to the insulation standards of traditional transformers,the bobbin is designed based on finite element simulation to meet the insulation requirements;secondly,the transformer core loss and copper loss are calculated,and the number of turns is selected with the goal of minimizing the total loss of the transformer.A 30 k VA MFT prototype is built,and insulation test,transformer loss measurement and parasitic capacitance measurement are carried out.This prototype passes the IEEE Std.C57.12.01 insulation standard,and works well in the RMR prototype;under the rated voltage and current,the measured copper loss and core loss are 117.9W and 72.4W respectively.