Research On Hybrid Control Strategy Of Full Bridge LLC Resonant Converter Based On Multivariable

LLC resonant converter plays an important role in many fields,such as rechargeable battery equipment,LED drive power supply and communication power supply,etc.In terms of topology,it has the advantages of zero voltage switching of the primary side switch tube and zero current switching of the secondary side diode through resonance,which can reduce the loss of the converter.By replacing resonant inductance with leakage inductance,the volume can be reduced and the power density of switching power supply can be improved.However,it still has the problems of narrow input voltage range,wide frequency adjustment range under wide input conditions,and large loss when outputting large current.In this dissertation,the control strategy of full-bridge LLC resonant converter is investigated in detail.The traditional control method of single variable has a single control mode and drawbacks;the mode switching point of the variable mode control method is inaccurate,in order to solve the above problems,this paper proposes a multi-variable hybrid control strategy with three variables of frequency,duty ratio and phase shift angle to achieve high efficiency of the converter with wide input range.For the accurate analysis of switching mode of full-bridge LLC resonant converter,the time domain analysis method is used in this paper to obtain the complete time domain equation and gain characteristic equation,the relationship between variables is revealed.In view of the inaccuracy of the fundamental wave analysis method,the error of the fundamental wave analysis method is analyzed,the gain curve of the time-domain analysis is analyzed,the gain characteristic curve is modified,and the parameter design is optimized,which has a certain guiding effect on the design of LLC resonant converter.In order to improve the efficiency of the converter,this dissertation proposes an optimal efficiency model from the perspective of the loss of the converter,choose the minimum peak value of the resonant inductor current as the target function,the variable relationship under different gain and different load conditions is analyzed,and the variable relationship under the optimal efficiency model is obtained.The detailed design flow of the control scheme is given,and the control of the converter is achieved under the goal of minimum loss,and the optimized control scheme is obtained by combining with the actual converter control.The simulation and experimental platform were designed and the experiment verified that the proposed control strategy could realize the wide input voltage range of the converter,it is verified that the proposed control strategy can effectively reduce the resonant cavity inductance peak current through the converter running in modes with gain greater than 1 and less than 1,the efficiency of the converter is compared between the pulse frequency modulation method and the proposed control strategy,and it is verified that the proposed multi-variable hybrid control strategy can effectively improve the efficiency of the converter.