斩波式中频点焊电源的PLC控制系统

PLC control system of chopped mode medium frequency spot welding source

设计的斩波式中频点焊电源主电路由一对反向串联的IGBT及其保护电路组成,两个IGBT在设定的占空比通断信号控制下轮流导通,从而实现了焊接变压器次级交流斩波波形的输出,线路简单、工作稳定可靠。以S7-200PLC为核心,设计开发了电源及焊接过程控制系统。其中,斩波控制信号由基于TL494的PWM信号发生电路产生,该电路还可对斩波电压进行闭环控制实现网压补偿。空载调试结果表明,PLC控制系统的软、硬件设计合理,能够控制主电路按照设定的占空比输出理想的斩波电压波形。从输出波形可以看出,该电源可获得较高的调节精度及连续稳定的能量输出,理想焊接工艺性更理想。

The designed main circuit of chopped mode medium frequency spot welding source is composed of one pair of inverse opposing IGBTs and protective circuit.The two IGBTs conduct in turn under the control of switching signal whose duty cycle is presetted,which could lead the output of welding transformer secondary AC chopping waveform.The main circuit is simple and works stably and reliably.The control system of power supply and welding process is developed based on S7-200PLC.The chopping signal which controls the two IGBTs to take turns conduction is generated by PWM signal generating circuit based on TIA94,besides,this circuit could play the roleof closed loop control on chopped voltage to realize voltage auto-compensating.Finally,the whole system is debugged in the case of welding transformer no-load, and the experiment result shows that the hardware and software of control system are designed reasonably, which could control the main circuit to output ideal chopped voltage waveform with pre-set duty cycle.As can be seen from the output waveform that this power supply could obtain higher regulation accuracy and more continuous energy output compared with the general spot welding source,therefore,it has a more ideal welding process.