Research On Control Strategy Of Inverter Spot Welding Power Supply

As a very common welding process,resistance spot welding is widely used in electrical,aerospace,mechanical manufacturing and other occasions.In recent years,with the rapid development of China’s manufacturing industry,welding equipment is also moving towards automation and intelligence.Welding current not only has a direct impact on the welding process,but also one of the key parameters to analyze the quality of spot welding.Therefore,it is very important to control the constant current output of inverter spot welding power supply.Traditional PID control requires the controlled object to have an accurate mathematical model,and once the control parameters are set,they cannot be modified online.Resistance spot welding is a nonlinear and time-varying process affected by many factors.Therefore,it is difficult to achieve the ideal control effect of welding current by using a single PID control.In addition,in the long-time discharge process,among the mainstream products in the market,the grid side voltage and current of the inverter spot welding power supply based on three-phase diode rectification are different phases,which makes the power factor of the power supply low,and will inject certain reactive power and harmonics into the power grid,reducing the power quality.In addition,due to the uncontrollability of the diode,the rectified bus voltage is uncontrollable,which will affect the subsequent inverter circuit,thus reducing the control accuracy of the welding current.Therefore,it is necessary to improve the three-phase rectifier module in the power supply.Aiming at controlling the bus voltage stability and maintaining the constant current output of the power supply,this paper deeply studies the three-phase PWM rectifier and the intelligent constant current algorithm based on particle swarm optimization fuzzy PI.Firstly,the overall structure framework of inverter spot welding power supply system is constructed,and the three-phase PWM rectifier in the main circuit is studied.Compared with the three-phase diode rectifier,the superiority and feasibility of the power supply based on three-phase PWM rectifier are verified by Simulink simulation under the condition of constant power supply parameters.By using voltage and current double closed-loop control and PWM control,the power supply can operate under the unit power factor and maintain the stability of bus voltage.Then,the constant current control strategy of inverter spot welding power supply is studied,and the design of fuzzy controller and the preparation of particle swarm optimization(PSO)algorithm are completed.The simulation results show that compared with the single PI algorithm,the control scheme combining PSO and fuzzy PI has better control effect on the welding current,and the oscillation amplitude of the output welding current is smaller and more stable;The hardware of the power supply is designed,including the design of the main circuit and control circuit.The hardware part of the power control system takes the high-performance dual core TMS320F28335 DSP as the core,and designs the sampling circuit,IGBT driving circuit,protection circuit and RS485 communication circuit;Complete the software design and debugging of the power control system,including the main program,PWM generation,AD sampling,constant current algorithm,welding process,fault interruption and other subroutines.Finally,the power supply test platform is built and the related circuits are tested to verify the rationality of the hardware circuit design of the control system.4KA constant current welding tests were carried out on 304 stainless steel,iron and 6061 aluminum alloy respectively.The results show that although the welding resistance changes nonlinearly with time during the welding process,the power supply output current can still follow the given current,so as to maintain the constant current output during the welding process.And the control precision of the power supply is high and the response speed is fast.The experimental results also prove that the particle swarm optimization fuzzy PI constant current algorithm has certain application value.Figure [69] Table [9] Reference [68]...