Research On The Power Banlance Control Of Paralled Operated Dual-active-bridge DC-DC Converters

Power electronic transformer with high density,fault isolation and high efficiency has been regarded as one of the most popular technologies in the high-speed train and the power distribution system.In addition,the power electronic transformer can be employed as harmonic filtering and reactive power compensating equipments in AC grid,and this converter is regared as the key device in future renewable system and energy management system.This paper focuses on the input-independent-output-parallel full-bridge isolated DC-DC converters,which is a part of the power electronic transformer.In power electronic transformers,the circuit parameters mismatch or the input voltage difference of these DC-DC converter cells will lead to the unbalanced power sharing among them,which may result overcurrent through power semiconductor devices,and even damage power devices.Thus,in order to avoid the power unbalance among these DC-DC converter cells,it is necessary to design a power balance control scheme of the output-parallel DC-DC converters to face with the unbalance power caused by the different circuit parameters and the unequal input voltages of DC-DC converter cells.Firstly,on the basis of direct power control,a power balance control scheme with single-phase-shift mode is proposed in this paper.And then,when the the converter system is in large output power range,some DC-DC converters cells will run in full load condition,so the over power working analysis is also presented in this paper to meet this condition.Finally,the proposed power balance control method is tested and verified on a hardware-in-loop?HIL?emulational platform with RT-LAB simulator and TMS320F28335.Simulational results show that the adopted power balance control scheme can guarantee the balanced power sharing among the output-parallel DC-DC converter cells when the circuit parameters are mismatched or the input voltages are not the same.In addition,when a part of DC-DC converter cells reach the full load condtion,this converter system can also achieve rapid dynamic performance.And when there exists fluctuation ripples in the input voltages,the proposed method can reduce the output voltage ripple.Moreover,in order to boost efficiency of the input-independent-output-parallel full-bridge isolated DC-DC converters,according to the idea of direct power control,a power balance control scheme with extended-phase-shift mode is proposed in this paper.Finally,the proposed power balance control method is tested and verified on a HIL simulational platform.Finally,these proposed methods are tested and verified on a small-scale experimental platform with FPGA₆SLX45 and TMS320F28335.Experimental results show that the adopted power balance control schemes can guarantee the balanced power sharing among the output-parallel DC-DC converter cells.Moreover,this converter system can also achieve perfect dynamic performance with the adopted power control schemes.And when the input voltages are much higher than the output voltage,the output-parallel DC-DC converter system can achive smaller current stress and higher efficiency obviously by the direct power balance control scheme with extended-phase-shift control.