Research On Topology And Control Characteristics Of High Frequency LCC Resonant Converter

With the increasing proportion of renewable energy in the power system,wind power generation and photovoltaic power generation have become the development trend of future energy.Although the type of power system is still dominated by AC system,the current trend of AC to DC development and the increasing proportion of power electronic equipment in the power grid make it an urgent problem to improve energy efficiency.Photovoltaic power generation module components generate direct current and relatively low voltage.Before effectively supplying power to the load,a direct current converter needs to be used to improve and stabilize the output voltage of the components.Due to the intermittence of photovoltaic resources,the output voltage varies with weather conditions,so the ideal converter should have fast response and stable output under different conditions.Therefore,it is very important to control and adjust the output voltage.With the increasing power demand,the converter will maintain a very high input current.This high current will bring many design challenges to the existing topology,such as high element current stress and power loss,complex and expensive magnetic element design,high input current ripple,etc.In order to meet these challenges,a new type of switching device and high frequency magnetic element are needed.Silicon carbide(SiC)power devices have much lower gate capacitance than silicon devices,and their on-state resistance is similar to silicon devices,which makes it very suitable for high frequency operation in switching converters,thus having significant advantages in power density,cost and system volume.MnZn ferrite core has many advantages:high resistivity,very low eddy current loss,wide working frequency range,suitable for working environment with frequency range from 1kHz-1 GHz.The objective of this thesis is to study the topology and control characteristics of high frequency LCC resonant converter based on SiC.Aiming at the problems existing in LCC resonant converter under frequency conversion control,such as easy loss of soft switch,large heavy load resonant current,complex selection of resonant parameters and difficulty in transformer fabrication,a parameter optimization design method of high frequency and high efficiency LCC resonant converter with wide output range is proposed.By using the improved fundamental analysis method,the relationship curves between resonance parameters and conduction angle,input impedance angle and switching frequency are obtained,so as to select resonance parameters.In the selection of the magnetic core structure,a partially staggered structure is used to increase the coupling between the primary and secondary sides,reduce parasitic capacitance and leakage inductance,and reduce losses.The design process of the plane transformer can be used to guide the actual design of transformers with different specifications.The proposed converter has the characteristics of wide output voltage,low voltage stress and soft switching,so it is suitable for high frequency,wide output and high-power situations.Finally,simulation was performed in PSIM to verify the operation of the circuit and support design analysis.A prototype with 400V - 800V output and 500W output power was built.The maximum efficiency can reach 96%at full load,and the overall high efficiency is further improved.The experimental results and theoretical analysis has a good consistency,proposed the resonant converter is verified the correctness of the theoretical analysis and parameter design.