【作者】 傅强；

【导师】 薛松柏；

【作者基本信息】 南京航空航天大学 ， 材料加工工程， 2013， 博士

【摘要】 随着薄板和超薄板焊接技术在汽车、集装箱等企业中大量应用，对焊接过程提出了低热输入的要求。短路过渡变极性控制是一种新型的低热输入焊接方法，日益受到关注。然而这种方法尚处于发展的初期阶段，国外参考资料少，国内研究目前还处于起步阶段。因此，对短路过渡的控制及能量分配原理进行深入研究，提出理想的变极性控制方案，并研制出焊接系统平台，是目前焊接技术发展的一个重要课题。为了满足低热输入短路过渡的变极性控制，本文设计了双芯DSP控制的焊接电源系统，由主电路、控制电路和送丝系统三部分组成。双芯分别负责控制电路和送丝系统，两者通过CAN总线进行通信。主电路结构采用二次逆变结构，一次逆变采用全桥双零软开关逆变器，通过PWM控制获得焊接过程中所需的能量；二次逆变采用带耦合电感的半桥逆变结构，实现电流的极性变换，达到低热输入的目的。控制系统以DSP为核心，实现整个系统的时序控制，采用数字PID算法，实现PWM控制的数字化。采用了固定点采样的数值处理方法和整周期协调控制的策略，保证了控制的精度和稳定性。针对传统的软开关逆变电源无法满足700W以下的低功率输出的问题，创造性地提出“两级连续PWM控制方法”，使逆变电源能在全桥和半桥两种工作方式下切换，解决软开关逆变电源小功率输出的问题，从而真正实现低热输入。数字化送丝系统是数字化焊接电源的重要组成部分，其性能的好坏直接影响整个系统的精度及焊接过程稳定性，因此提高送丝系统的稳态精度和快速响应性是焊接过程中不可回避的问题。本文设计了受限单极式可逆PWM调速电路，控制芯片采用DSP，通过CAN总线与焊接电源的控制系统进行通信。通过采样电流断续时的电枢感应电压，采用数字PI方法调节PWM占空比，维持电枢感应电压恒定，从而保证送丝电机转速恒定。采用模糊PI控制技术在线整定PI参数，可提高送丝系统的动态性能。试验表明，送丝系统的静态和动态性能均高于一般的电枢电压负反馈控制，能够完美地实现送丝稳定性。提出基于弧压负反馈的变速送丝系统来解决分段恒流控制引起的弧长不稳定的问题。该系统采用双闭环模糊PI控制，内环采用感应电压负反馈的模糊控制，提高送丝速度的稳定性和快速响应性；外环采用电弧电压负反馈，调节送丝速度，保证弧长的稳定性。试验证明，该方法还能实现恒弧长、等熔深的控制。通过对短路过渡过程中熔滴受力情况的分析，提出一种波形控制方法，在短路初期降低电流减小瞬时飞溅，在短路末期液桥爆断之前迅速降低电流，使熔滴在表面张力的作用下稳定过渡。在燃弧期间采用大恒流+小恒流控制，可精确控制燃弧能量、改善焊缝成形。通过对DCEP和DCEN时焊丝和工件的热作用分析，提出了一种变极性控制方法：在短路末期实现DCEP→DCEN，不影响熔滴过渡和电弧稳定性；在燃弧初期采用DCEN实现焊丝的快速熔化、减小熔池冲击、提高熔敷效率；在燃弧后期DCEN→DCEP，对熔滴进行整形，便于熔滴过渡。提出一种电流控制方法，可避免燃弧后期极性变换时的熄弧问题，在电流过零前施加较大的燃弧脉冲，保证电流换向的顺利进行。提出一种短路限流加慢送丝的引弧方法，提高了引弧成功率。在分析短路过渡电弧物理特性的基础上，利用Matlab/Simulink工具建立了GMAW焊接电源-电弧系统动态仿真模型。功率变换单元以实际应用电路和器件为原型，所建模型能实现固定臂的零电流开关、移动臂的零电压开关。通过移动臂占空比的调节，验证了软开关逆变电路存在最小输出功率的问题，采用“两级连续PWM控制方法”可以降低功率输出。数字控制单元能根据电弧电压和电流信号实时计算主电路IGBT的驱动信号，实现分段恒流控制，使焊接电流与给定的波控信号具有很好的一致性。短路负载单元考虑了短路期间的熔滴动态变化过程，包括燃弧时弧长变化模型和液桥电路模型。仿真波形与试验结果基本一致，证明所建的系统仿真模型是正确的。在自制的变极性GMAW焊接电源平台上，进行了大量的试验研究。试验结果证明变极性短路过渡焊接方法是一种低热输入的焊接方法。同时论文还针对该方法焊接过程中各种参数大小对能量分配的实际影响作用进行相关试验研究，并得出了相应的规律。更多还原

【Abstract】 Wide application of sheet metal and ultra thin sheet metal welding technology in car, containerand other manufacturing leads to the requirements of low heat input during welding process.Short-circuit transfer control of variable polarity is a novel low heat input welding method, which hasbeen drawing more and more attention. However, this method is still in the initial stage ofdevelopment. Additionally, there is little foreign reference, and domestic research is still in its infancy.Therefore, studying control and energy distribution principle of short-circuit transfer in-depth,proposing ideal control schemes and developing a welding system platform are important topics in thedevelopment of welding technology.In order to realize the low heat input and short-circuit transfer control of variable polarity,dual-chip DSP controlled welding power supply system was introduced in this paper, which wascomposed of three parts, the main circuit, control circuit and wire-feeding system. Dual chips wererespectively responsible for the control circuit and the wire-feeding system, both communicating viaCAN bus. The two-stage inverter structure was adopted in main circuit. Full-Bridge Zero Voltage andZero Current (FB-ZVZC) soft-switching inverter was applied to the first inverter, which obtained therequired energy during welding process by PWM control. The half-bridge inverter structure withcoupled inductor was applied to the second inverter to realize current polarity transformation so that itcan achieve the purpose of low heat input. Control system based on DSP as the chip of the entiresystem timing control, used digital PID algorithm to digitized PWM control. Use numerical method offixed point sampling and full cycle control strategy to ensure the control precision and stability. Tosolve the problem that traditional soft-switching inverter cannot output low power below700W, thetwo-stage continuous control of PWM was creatively put forward to enable inverter switch betweenfull-bridge and half-bridge, thereby the problem caused by low power output of soft-switchinginverter can be solved and low heat input can be realized.The digital wire-feeding system is an important part of the digital welding power supply system,whose performance directly affect the accuracy and stability of the welding process. Therebyincreasing the steady-state accuracy and fast response of wire-feeding system is an inevitable issueduring the welding process. A limited unipolar reversible speed control circuit was designed in thispaper. Control chip adopted DSP and communicated with welding power control system throughCAN bus. According to the armature induction voltage sampling when current was zero, digital PImethod was used to adjust the PWM duty cycle to maintain the armature induced voltage constant, thus to ensure a constant wire-feeding motor speed. It used fuzzy PI control technology for onlinetuning of PI parameters to improve dynamic performance of wire-feeding system. Tests showed thatthis system can feed wire stably and its static and dynamic performance is better than that of thearmature voltage negative feedback control system. Variable speed wire-feeding system based on arcvoltage negative feedback was proposed to solve the problem of arc instability caused by sectionalconstant current control. This system used double-loop fuzzy PI control. The inner loop adoptedinduced voltage negative feedback fuzzy control to improve the stability of wire-feeding speed andthe ability of fast response. The outer loop adopted arc voltage negative feedback to adjustwire-feeding speed and ensure the stability of the arc length. Tests proved that this method canachieve constant arc length and equal penetration depth control.Basing on the force analysis of molten droplets during short circuit transfer process, a waveformcontrol method was adopted, that reducing current to eliminate the instantaneous splash in initial shortcircuit period and reducing current quickly before liquid bridge blasting off in the final period of shortcircuit. In arcing period the peak current and the background current was adopted to control arcenergy precisely and improve the weld formation. Basing on thermal effect analysis of the wire andthe work piece during DCEP and DCEN period, a variable polarity control method was adopted thatemploying DCEP to DCEP at the end of the short-circuit phase to ensure the stability of arc andmolten droplet transition, employing DCEN in the early of arcing for rapid melting of welding wire,less molten pool impact and high deposition efficiency, and employing DCEN to DCEP later in thearcing period to facilitate the droplet transition through shaping the drop. A current control methodwas proposed in order to avoid arc-quenching triggered by polarity reversal later in the arcing period.And large arc pulse was applied before the current through zero to ensure the smooth progress of thecurrent commutation. In addition, an arc method consisting of short-circuits current limiting and slowwire-feeding was adopted to improve the success rate of arc ignition.Basing on the analysis of the physical characteristics of short arc transition, a GMAW weldingpower-arc system dynamic simulation model was created by Matlab/Simulink. Power conversionunit used practical application circuits and devices as the prototype. This model was able to achieve afixed arm zero-current switching, zero-voltage switching of moving arm. Adjusted the duty of movingarm to verify the presence of the issue that soft-switching inverter circuit had minimum power output."Two-stage continuous PWM control method” could reduce the power output of the system. Digitalcontrol unit could realize real-time computing main circuit IGBT drive signal according to the arcvoltage and current signals to achieve sectional constant current control. So that the welding currentand the given wave control signal had a good consistency. Short circuit load cell took the droplet dynamic process into account during short period, which included the model of arc length changesand the liquid bridge circuit model during arcing period. Simulation waveforms were consistent withthe experimental results, which proved that the system simulation model was correct.After a lot of experimental researches carried out in a homemade variable polarity the GMAWwelding power platform, it was proved that this variable polarity short circuit welding method is a lowheat input welding method. The paper also elaborated on the experimental research relating to theeffect of various parameters on the energy allocation by using this method. The corresponding lawwas drawn in this paper as well.更多还原