Development Of Power Supply For Mobile Flash Rail Welding Machine

Rail flash welding machines currently mostly use diesel generator sets as the power supply for welding machines,while mobile flash welding systems use single-phase power supplies.The working characteristics of welding machines are the drastic changes of low voltage,high current and high power load.Diesel generators are often used Overload operation is required,which has a great loss on diesel generators.Aiming at the power supply problem of the welding machine,the solution of super capacitor and battery as the energy storage device is proposed to supply power to the flash welding machine through DC / DC rectification and DC / AC inversion,focusing on the research of converter and inverter control strategy.The method of adding load current feedforward solves the problem of voltage instability during sudden load changes to improve the dynamic response capability of the entire control system.After a comparative study of the topological structures of various commonly used bidirectional converters and inverters,in order to ensure that the power supply can work stably under high power conditions,it is determined that the DC side adopts a bidirectional staggered parallel DC / DC converter structure.A single-phase full-bridge inverter structure is used on the side.After making corresponding explanations on the working principles and modulation methods of the two,combined with the overall main circuit topology,a system-level control strategy for the power supply of the welding machine is proposed,and the three working conditions of standby,charging and discharging are analyzed in detail.During the working process,charging and discharging are the main working modes of the power source of the welding machine.Under the working state of charging and discharging,the mathematical models of the DC / DC converter structure with two-way interleaved parallel connection are established respectively,in which the charging mode is Buck mode and the discharging mode is Boost mode.Based on the analysis of the mathematical model,the control strategies under two modes are designed.The charging mode uses a single-current loop constant-current voltage-limiting charging method to charge the supercapacitor from the battery.In order to improve the dynamic response capability in the discharge mode,it is proposed to add the load current feedforward on the basis of the traditional double closed loop.At the same time,in order to eliminate the effect of the double frequency on the feedforward value,the SOGI algorithm is used as a digital band rejection filter for the double frequency To eliminate.The single-phase full-bridge inverter only works in the discharge mode.After the analysis of the mathematical model,the double closed-loop control strategy is adopted for control.In order to improve the control speed and control accuracy,a load current feedforward control strategy is introduced.The inverter controller compares and analyzes the three controllers PI,PR,and quasi-PR.The voltage loop selects the quasi-PR controller with the best control effect,and the current loop selects the P controller with simple structure.According to the requirements of the actual rail welding machine,the hardware design of the filter module,the withstand voltage of the switch and the control circuit of the main circuit of the welding machine is designed by hardware,and the correctness of the parameters is verified by open loop simulation.Using Typhoon to build a power supply semi-physical simulation platform,the overall system-level control strategy and the control strategies of each part are simulated to verify the feasibility of the control strategy.