Current-Sharing Control Technology Forinterleaved LLC-DCX

High efficiency,high frequency,and high power density are the main trends in DC/DC converter application.Compared with PWM type topology,due to the nature soft switching feature,the resonant converter have many advantages,such as higher efficiency,higher operation frequency,and higher power density.As compared with other resonant topologies,LLC resonant converter can achieve zero voltage switching(ZVS)of the primary switches and zero current switching(ZCS)of secondary rectifier diodes in the whole load range.Thus,it is widely used in the high frequency switching field.The LLC-DCX(DC Transformer)maintains the constant DC gain,instead of stabilizing the output voltage by regulating switching frequency.Therefore,LLC-DCX can get higher power density and efficiency.However,the single LLC converter,including LLC-DCX,has to employ the larger output capacitance because of the large output current ripple,and it is not suitable for high power and high power density application.Compared with the single power module,the multi-module paralleling technology can achieve the higher output power while ensuring high operation efficiency.Therefore,the interleaved LLC-DCX can greatly increase power density,expand capacity and reduce output current ripple.However,in practice case,the component parameter tolerance between the parallelled modules is inevitable.The tolerance not only leads to the output current mismatch of each module,but also reduce the reliability of the total parallelled system.Therefore,the current sharing technology becomes very important for the paralleled system.In order to solve the above problems,the current sharing strategy are proposed for the half bridge and full bridge topology,respectively.Taking the reason of current unbalance as the starting point in this thesis,the interleaved LLC resonant converter is studied firstly.The effect of the parameter error of resonant components on the DC gain is discussed theoretically.The research results show that under different resonant element parameter condition,the output current of interleaved LLC-DCX is unbalanced.Moreover,the larger the resonant element parameter,the smaller the output current is.The simulation results are given to verify the validity of the theoretical analysis on reason of current unbalance.Secondly,to solve the current unbalance issue of the interleaved half-bridge LLC-DCX,the Bidirectional-Switch structure is imposed to half-bridge LLC resonant converter.Furthermore,the Bidirectional-Switch based current sharing scheme is proposed.Accordingly,the modulation scheme for the Bidirectional-Switches is discussed in detail,and the operation principle of the converter is introduced.The results indicate that LLC-DCX has the boost characteristic when the secondary switches turning on at the same time.This scheme is able to regulate DC gain through the PWM control method.A 400 W two-phase interleaved LLC-DCX laboratory prototype is built to verify the feasibility and demonstrate the advantages of the proposed solution.Experimental results show that the proposed current sharing strategy can reduce the output current mismatch from 20% to 5% when the resonant inductance,capacitance,and magnetic inductance increase 10%.Finally,it goes without saying that the problem of current unbalance also occurs in interleaved full-bridge LLC-DCX.Therefore,the phase-shift current sharing control strategy is applied to the interleaved LLC-DCX.The relationship between the phase-shift angle and DC gain is derived.Similarly,A 400 W two-phase interleaved LLC-DCX prototype is built to demonstrate the feasibility of the proposed solution.The experimental results show that the current sharing error can be reduced to 5% from 10% with the proposed current sharing scheme.