变极性TIG焊电弧燃烧稳定性与恒占空比控制

电流换向的快速性和稳定性是影响变极性TIG焊接电弧燃烧稳定性的关键因素，尤其是在小电流变极性TIG焊时，极易出现熄弧和电弧燃烧不稳定问题. 对电流换向期间的电压/电流波形深入分析发现，一次逆变采用基于PID的电流反馈控制获得恒流输出时，在电流换向结束后易产生焊接电流回调现象，小电流焊接时甚至降至零，从而导致电弧熄灭，这与PID控制中的di/dt项密切相关. 提出了一次逆变在电流换向期间采用恒占空比控制新方法. 结果表明，该方法可有效提高换向电流的响应速度，防止换向后的电流回调或超调，增强了变极性电流换向过程的稳定性.

Arc burning stability of variable polarity TIG welding and control with constant duty cycle

The rapidity and stability of current commutation are the key factors that influence the arc burning stability of variable polarity TIG welding. Especially, arc extinguishing and burning instability occur easily when the variable polarity TIG welding is performed under low current value. The waveforms of voltage and current during the current commutation process were deeply analyzed. It was found that the phenomenon of current declination occurred easily after the current commutation process and even arc extinguished welding with low current when the current feedback control based on PID was applied in the primary inverter to obtain constant current output, which was closely relative to the term of di/dt within the PID control. In this paper, a new control method with constant duty cycle was proposed and adopted in the primary inverter during the current commutation process. The experimental results showed that this method improved the response speed of commutation current effectively and prevented the declination or overshoot of current after commutation, which enhanced the stability of current commutation process for the variable polarity TIG welding.