Study On Full-bridge LLC Resonant Parallel High-power Digital Pulsed MIG Welding Power Supply System

With the improvement of its equipment and the innovation of its technology,welding technology is widely applied in important fields such as automobile,railway,and ship.Switching power supply,as the core of welding power supply equipment,is one of the important research trend of contemporary welding industry.At present,most welding power supplies in the market work under the traditional pulse width modulation(PWM)control mode,which means the switching devices work in the hard-switching state,resulting in serious switching loss and limiting the improvement of power supply efficiency.Additionally,it brings with large di/dt and du/dt,leading to serious electromagnetic pollution.And most of the rest welding power supplies adopt a phase-shifting soft-switching topology,which has defects such as loss of duty ratio on the secondary side,and loss of ZVS under low load condition.In order to improve the current condition of welding power supply,a full-bridge LLC resonant parallel high-power digital welding power supply system is designed,which is used for pulsed metal inert gas welding(MIG),and its principle and application are studied.Firstly,the working principle of pulsed MIG welding,the working characteristic of welding power supply and welding characteristic of aluminum alloy,are analyzed.Based on the analysis,the main circuit structure scheme of multi-module parallel and the control system scheme of CAN bus communication technology based on ARM chip STM32F103RBT6 are proposed for pulsed MIG welding power system.The working principle and process of the full-bridge LLC resonant converter are described,and its advantages and features are highlighted.And the working states and working modes of the full-bridge LLC resonant converter are further analyzed,especially the possible working modes of the converter at different welding stages are determined,and the characteristics are analyzed.The main circuit of the full-bridge LLC resonant converter is designed.According to the requirement of pulsed MIG welding power supply system,the parameters of main circuit components are calculated and selected.The simulation model of the resonant converter is established by computer.Through the simulation experiment,the main circuit designed is verified to meet the requirements of different loads and gains in the welding process,and the working mode changes of LLC main circuit in the welding process are explored to verify the feasibility of the main circuit.The software design of the control system is completed,which realizing pulse frequency modulation(PFM)control signal output and anti-windup closed-loop PI control,and realizeing welding timing control and fault protection of the pulsed MIG welding power supply system.Switching control of pulsed current is realized through real-time transfer instruction by CAN communication.Simulated load test and welding process experiment are carried out for the developed full-bridge LLC resonant parallel high-power digital pulsed MIG welding power supply system.The results showed that,the full-bridge LLC resonant converter is proved to be able to work in the default ideal working state and working mode and achieve the ideal conversion efficiency.The full digital control of welding sequence is achieved.Moreover,the welding process is stable and the welding beam is well formed,indicating the feasibility of the full-bridge LLC resonant parallel high-power digital pulsed MIG welding power supply system.