Development And Application Of Variable Polarity Transistor Spot Welding Power Supply Based On Dual MCU Contro

Resistance welding has the advantages of high efficiency,low cost,easy integration and automation,and is a common welding method for power lithium battery pack.With the rapid development of new energy vehicle industry,there is a huge demand for resistance welding of lithium battery,which also puts forward higher requirements for welding quality and consistency of battery pack.The traditional resistance welding process of lithium battery has many problems,such as low efficiency,single power control mode and insufficient output stability.Therefore,it is necessary to design a new transistor spot welding power supply with high load persistence,multiple control modes and high stability.Aiming at improving welding efficiency and welding joint quality,this paper carries out in-depth research on the main circuit design,control system development and load characteristics analysis of power supply.Firstly,the main circuit topology of capacitor energy storage power supply based on inverter converter and dual-phase chopper technology was designed,and a highperformance digital control system based on dual-MCU controller was developed.Prototype trial production and performance test were completed.The prototype can realize the rapid charge and discharge control of the capacitor group,the working frequency is 100 k Hz,the rated output current is 4 k A,the load duration is more than 5%,with constant current,constant voltage,constant power and mixed control and other control modes,can achieve double pulse unipolar and variable polarity output,high current rise speed,short polarity switch time.Then,based on the power of the developed prototype structures,welding test platform,the orthogonal experimental study on the influence law of process parameters on the tensile strength of joints,constant voltage,constant current and constant power control mode of the optimal process parameters,the single polarity output mode power control mode of the welding joint performance and the influence law of process fusion nuclear growth.The welded joints with similar tensile strength,surface morphology and core size can be obtained under constant current,constant pressure and constant power modes,and the physical characteristics of joint formation process are similar.However,the welding process energy consumption under constant pressure control mode is far less than that under constant current and constant power mode.Finally,the influence of unipolar output and variable polar output on welding joint forming consistency was studied by comparing the unipolar output and variable polar output on welding quality.In unipolar mode,the consistency of solder joints is poor due to the polarity effect of materials,and the size of the weld core of the positive electrode is obviously larger than that of the negative electrode.The variable polarity mode can balance the heat of the two solder joints by pulse output alternately,which can overcome the polarity effect and obtain the welding core with good consistency.In variable polarity mode,cooling time has great influence on solder joint quality.Reasonable cooling time plays an important role in improving solder joint quality.