Research On Partially Power Regulated LLC Resonant Converter

The data center power supply adopts the high-voltage DC bus architecture to supply power,which can reduce the number of energy conversion stages,improve the voltage level,and reduce line loss,which is of great significance for achieving "carbon peaking" and "carbon neutrality".The HVDC bus architecture requires a DC/DC converter for power conversion.While completing voltage conversion,the DC/DC converter needs to have the function of voltage regulation,and try to improve the efficiency of power conversion and power transmission density.In this thesis,a partially power regulated LLC resonant converter is studied,which has achieved the purpose of voltage conversion and high efficiency.In view of the current situation that when the LLC resonant converter uses pulse frequency modulation technology to adjust the voltage gain,the switching frequency deviates from the resonant frequency and it is difficult to obtain the best performance.This thesis introduces a full bridge PWM converter at the input end of the LLC resonant converter,in which the LLC resonant converter undertakes most of the power transmission and the PWM converter transmits a small part of the power to realize the regulation of the output voltage.The converter operates at the resonant frequency point,which can make full use of the soft switching characteristics of the LLC resonant converter,which has the characteristics of high efficiency,high energy transmission density and small size of magnetic components at high-frequency switching frequency;Using the excellent control performance of PWM converters,the constant frequency and phase shift control method is used to control part of the transmitted power and achieve the regulation of the output voltage.Firstly,this thesis analyzes in detail the working principle,control method,and circuit characteristics of a partially power regulated LLC resonant converter.According to the structure of series input and parallel output,the relationship between the phase shift angle of the converter and the voltage gain is derived.According to the operating indicators of the converter,the parameters are designed to ensure that the converter can not only meet the requirements of transmission power and voltage gain,but also realize the soft switching of the primary side switch tube to ensure high-efficiency operation.The software and hardware design of the experimental platform has been completed.The theoretical analysis and topology validity of the circuit are verified by simulation using PSIM software.Finally,an experimental prototype of a partially power regulated LLC resonant converter with an input voltage of 380-420 V,output voltage of 240 V,and a full load power of 2k W was built.Stable operation and load disturbance closed-loop experiments were conducted.The efficiency curves under different input voltages and different output powers were tested and plotted.The maximum efficiency of the converter can reach97.5%,and the efficiency is greater than 90% under different loads.Experiments have verified the rationality of the circuit working principle,the effectiveness of software and hardware design,and the efficiency of the converter.