Research On Control Strategy Of Input Parallel Output Series LCC Converter

With the development of laser technology,X-ray technique,radar technology,medical device technology,electrostatic precipitator technology,voltage level,power level,dependability and power density of DC-DC converter have a higher demand.However,Traditional non-modular DC-DC converters have the disadvantages of large input and output current ripple fluctuation,large voltage stresses,losses of the power devices,high electromagnetic interference,and other defects,which resulting difficult to improve in voltage levels and power levels.Modular DC-DC converter,through the combination of series and parallel can effectively reduce the voltage and current stress for semiconductor switching devices,improve system reliability,and unit module converter design is simple,thereby reducing system development costs and shorten the development cycle.This paper focuses on the input-parallel output-series(IPOS)modular converter system,the main research contents are as follows:First,this paper analyzes the working principle and switch states of modular converters,gives the mathematical description and circuit characteristics of the resonant converter in DCM mode and designs the resonance parameters of the unit converter.This paper analyzes the modulation of the LCC converter,resulting in a constant pulse width PFM adapted to LCC resonant converter.Secondly,the overall structure of the n-module IPOS converter system is designed,and the working principle and characteristics of the system are analyzed.The stability of the IPOS converter system is analyzed.It is deduced that the system can realize the natural current sharing at the input side as long as voltage sharing at the output side,and the influence of the different resonance parameters of each unit module on the output voltage sharing of the system is analyzed.Thirdly,by analyzing the traditional PFM and PT techniques,this paper presents a new pulse sequence control technology and presents the system output voltage control strategy,voltage sharing control strategy,interleaving control strategy.Based on the above theory,the control strategy of multi-module IPOS converter system is designed.Finally,this paper designs a experimental prototype of IPOS converter system with two unit modules.The test results show that IPOS converter system can achieve soft switchfor both light load and full load,the relative error for voltage sharing control is less than 2%between converter modules,the relative error for output voltage control is less than 1%when the system works in steady state,the recovery time of the system to steady state is less than 0.8s after sudden change of the load.Experimental results verify that the control strategy proposed in this paper and the new pulse sequence control technology make the IPOS converter system realize the interleaved control among multiple modules,system output voltage control and voltage sharing control,at the same time,still able to achieve a good soft switch.The correctness of this paper study is verified.