Research On Compound Resonant DAB Converter Based On LLC

In the field of DC power supply,high efficiency DC chopper conversion circuit is needed to ensure the stable DC power supply.Bidirectional DC-DC converter is the key link of energy conversion.It is widely used in hybrid electric vehicles,battery energy storage,super capacitor charging,UPS uninterruptible power supply system,solar power generation and other new energy fields.The symmetry LLC resonant converter has become a research hotspot because of its good soft switching performance.This paper studies the symmetry LLC-DAB resonant converter to analyze the topology,performance,power characteristics and voltage gain as well as the exact angle range of the soft switch.Firstly,the working state of each phase is determined under the single phase shift control condition,and the external phase Angle is directly determined by the compound power solution method to control the transmitted power and voltage gain.Through the normalized resonant current calculation,each resonant parameter is simplified,and the guiding conclusion is obtained.The boundary range of hard and soft switches is determined,and the full-load soft switch is realized when M≠1.However,due to the influence of resonant inductance and capacitance,the range of single-phase shift soft switch is small.Then you compute the peak current and you get the functionI_{pea k.}=f（M,Q,φ）.Through the combination control of voltage gain,quality factor and phase shift Angle,the current stress of switch tube can be reduced,so as to reduce the loss.Then,when the extended phase shift control analysis is in M≠1,the range of the full-load soft switch is larger than that of the single phase shift,and it greatly reduces the resonant current peak value.Compared with the condition Q=0.6,the extended phase shift current stress is reduced from 73.17A to10.61A,which increases the power transmission efficiency.Summarizing the above two phase shifting methods,this paper then proposes an optimal control method based on the dual phase shifting control of introducing the internal phase shift angle and introducing the external phase shift angle on the primary side of the high voltage side to ensure that the converter operates at the minimum current stress when all the primary and secondary switching tubes achieve the ZVS turn-on soft switching condition within a certain power range.The resonant current is used to increase the range of the soft switch,and the peak current of the primary and secondary sides is reduced by the combination of the optimal double phase-shifting Angle,so as to achieve higher power transmission efficiency of the resonant converter.The symmetric LLC-DAB converter transmits energy under different power and different loads,so that the output voltage at the load end is maintained at 50V.However,when the load rate is 0.6,it can only realize the secondary side ZVS.When the load rate is not less than 0.6,both the primary and secondary sides of the converter can realize the ZVS open soft switch.It can be used in a wider range of resonant converters with more complex topology.Finally,by experimental verification,in order to ensure the stable output of 24 v dc voltage,input the 48 v or 44 v dc voltage,under the condition of using single phase and double phase-shift control mode,whether it’s full,partly filled,and under no load,can realize the former vice edge ZVSon,validation of dual phase shift in the implementation of soft switch is compared under the condition of single phase shift and reduce the current stress.In full load condition,48V input condition,single phase-shifted primary resonant current is 2.918A,but double phase-shifted primary resonant current is 1.821A;At 44V input,single phase shift is 1.75A,double phase shift is 1.669A.In the first mode,when the inwardly shifted phase Angle is greater than the outwwardly shifted phase Angle,the input range of soft switching voltage is realized from 44V to 48V.In the second mode,when the inwardly shifted phase Angle is smaller than the outwwardly shifted phase Angle,the input range of the soft switching voltage is realized from 41V to 44V,and the first mode is verified to achieve a larger soft switching range.