Research On Control Strategy Of Constant Current Output For LCC Resonant Converter

Traditional hard switching converter has high switching loss and low efficiency.In order to make the converter work reliably,it is necessary to use a larger transformer and radiator,which are difficult to meet the requirements of miniaturization and high power density of electronic products.Because of its soft-switching characteristics,resonant converter has the advantages of high efficiency,low electromagnetic interference and low voltage or current stress.Therefore,it has been widely used in the fields of LED driver,constant current charging equipment and distributed power supply.It can be predicted that resonant converters with soft switching characteristics will gradually replace traditional hard switching converters.Because of many advantages of soft-switching resonant converter,a new design method of constant-current LCC resonant converter is proposed in this paper.The calculation formula of components parameters is deduced in detail,and a 96 W experimental prototype is made for experimental verification.The main tasks completed in this paper include:(1)In terms of basic knowledge,this paper first introduces the causes of switching losses in hard switching converters,and analyses the working principles of zero voltage switching(ZVS)and zero current switching(ZCS),the two soft switching modes,as well as the control methods of realizing soft switching.(2)Then,the voltage gain formula and current gain formula of LLC resonant converter and LCC resonant converter are analyzed and deduced,and their gain curves are drawn according to their gain formula.By analyzing and comparing the voltage gain curve and current gain curve of LLC resonant converter and LCC resonant converter,it is concluded that LCC resonant converter is more suitable for constant current output.The characteristics are as follows: in the constant current output state,the switching frequency range of LCC converter is smaller than that of LLC converter when the load changes.(3)The first harmonic equation of the main signal of the resonator is obtained by the first harmonic analysis method,and the AC equivalent circuit of the LCC resonant converter with constant current output is deduced.According to the AC equivalent circuit,the calculation formula of the parameters of the important components of the converter is deduced.The main point of the design is that the common points on the current gain curve family are regarded as the rated operating points of the converter,which simplifies the calculation method of the resonant cavity,and analyses the influence of the empirical parameters on the performance of the converter.(4)According to the input and output conditions,the parameters of resonant cavity elements and transformer are calculated in detail by the method proposed in this paper.The manufacturing method of transformer and resonant inductance is pointed out.A 96 W LCC constant current converter experimental prototype is developed.(5)The switching frequency,peak current of resonant cavity loop,switching frequency change caused by load change and converter efficiency of the prototype are measured.The measured values are in agreement with the calculated values,which proves the correctness and feasibility of the design method proposed in this paper.