Study Of LCC Resonant Converter With High Efficiency And Fast Response

With increasing requirements on the efficiency and volume of power electronic converters,resonant converters have been widely considered and applied due to their features of high density,high working efficiency and low Electromagnetic interference(EMI).As a three-component resonant converter,the LCC resonant converter combines the advantages of series resonant converter and parallel resonant converter,and also retains no-load voltage regulation capacity and light load circulation loss while switching frequency variation range is narrow.The LCC resonant converter is a promising dc-dc converter.Firstly,based on the problems of traditional frequency conversion modulation and fixed frequency modulation of LCC resonant converter,this paper uses a PWM-PFM hybrid modulation strategy.When the input voltage or output load of the LCC resonant converter changes,the switching frequency and conduction angle willed be changed at the same time to achieve the purpose of output voltage stabilization.The secondary rectifying circuit is designed by synchronous rectifying technology to improve the efficiency of the converter on the basis of hybrid modulation strategy.The fundamental wave approximation method is used to model and analyze the PWM-PFM hybrid modulation LCC resonant converter,and its steady-state working model is derived to guide the parameter design.The results show that compared with the traditional variable frequency and fixed frequency LCC resonant converter,the PWM-PFM hybrid modulation can achieve a wider soft switching range within a narrower switching frequency range,which improves the working efficiency of the converterand reduces the design difficulty.Time-domain simulation and experimental results verify the theoretical analysis.Secondly,to improve the transient performance,the charge control technique is applied to LCC resonant.This paper analyzes the working principle of the charge-controlled LCC resonant converter,and establishes its steady-state operating model through the extended fundamental wave approximation method.The small signal models are established using the describing function method,and the corresponding control-to-output transfer function and loop gain expression are obtained.Frequency domain simulation verify the theoretical modeling.The results indicate that the charge-controlled LCC resonant converter has faster input and load transient response speed than the single-voltage control technology,and the charge control method can significantly reduce the overshoot of the input transient.Simulation and experiment verify the theoretical analysis.Finally,in view of the large load transient overshoot of the charge-controlled LCC resonant converter,in order to comprehensively improve the load transient response performance of the converter,an improved charge-controlled LCC resonant converter with superposition output filter capacitor current is proposed.By adding output filter capacitor current in to the outer voltage loop of charge control technology,new output information is introduced into the control loop to further improve the load dynamic characteristics of the converter.The small signal model of the improved charge-controlled LCC resonant converter is established by using the describing function method,and compared with the charge-controlled method.The results show that the improved charge-controlled LCC resonant converter with superposition output filter capacitor current can reduce the overshoot of the load transient response without affecting the input and load transient response speed,and also reduce the output voltage turbulence,improve the output voltage stabilization accuracy of the converter.Experimental results verify the correctness of the theoretical analysis.