A DAB DC-DC Converter With Soft Switching Current As Setted Value Over The Full Load Range

With the popularization of new energy power generation,dual active bridge bi-directional DC-DC converter(DAB)has been widely studied by scholars.The converter is applied to the energy storage device and the DC bus in the micro grid,electric vehicles,uninterruptible power supply(UPS)and so on.At present,the goal of the research is to improve the converter efficiency,improve the power density,expand the soft switching range,increase the input voltage range,etc.In order to make all the switches of the converter to achieve actual ZVS in light condition,and reduce the conduction losses due to the reflux power during heavy load conditions,this paper proposes a new hybrid control scheme,using the topology of improved dual active bridge converter based on three winding center tapped transformer.A small inductance is added between the partial capacitor and secondary side of the transformer.Using constant frequency double PWM phase-shift(TPS)control during light load condition,the worst soft switching current and the phase shift between secondary side bridge shows a linear relationship.With the micro voltage phase difference betweent the center tapped inductor both ends,helping the most difficult switching legs to achieve actual ZVS with the setted current value;The phase shift of secondary side bridge decreases to 0 when the load is heavy,using variable frequency Extended phase-shift control(EPS).By using switching frequency and phase angle decoupling control,The switch tube of most difficult to achieve actual ZVS can still turn on and off at a pre setted current value.So the worst switching legs can achieve actual ZVS through a new hybrid control scheme during the full load range.On the one hand,the scheme ensures the actual ZVS of all the switches,on the other hand,the reactive power flow is minimized,reducing the conduction loss of the converter without complex mathematical models.This paper studies the scheme of traditional EPS control first,analysis the switching environment of the internal mode and the reactive power flow problems of the external mode.Taking the MOSFET parasitical output capacitance effect to the soft switching process into account.The parasitic output capacitors of one bridge arm switches is fully charge and discharged by the reverse current is defined actual ZVS condition.Through putting forward a new hybrid control scheme,optimization soft switching environment at light load condition,putting the theoretical soft switching into actual ZVS condition;Optimization the reactive power flow problems due to the excessive large soft switching current during heavy load condition.Finally,a 1.5k W experimental platform is built to verify the correctness and validity of the theoretical analysis.