Development of AC Pulsed MIG Inverter Arc Welding Power Source

Literature Overview

This paper, authored by Song Zheng, Hang Zhengxiang, Hua Xueming, and Wu Yixiong from Shanghai Jiao Tong University and Shenyang University of Technology, published in Mining Research and Development in 2006 (Vol. 26, No. 3, pp. 59–61), describes the design and development of an AC pulsed MIG inverter arc welding power source controlled by an Intel 80C196KC microcontroller. The paper provides detailed information on both the hardware and software design of the power source, offering valuable insights into the implementation of advanced welding power sources for industrial applications.

Technical Architecture and Design Principles

System Overview

The AC pulsed MIG welding power source described in this paper represents a significant advancement over conventional DC MIG welding power sources. The AC pulsed configuration provides several advantages for specific welding applications:

• Enhanced cleaning action on the back side of the weld, which is particularly beneficial for thin-section welding
• Improved penetration characteristics due to the pulsed current waveform
• Reduced heat input compared to continuous current welding, which minimizes distortion and HAZ softening
• Better control over the molten pool, which reduces the risk of burn-through in thin materials

The system architecture consists of several key subsystems:

1. Input rectification and filtering stage
2. High-frequency inverter stage with IGBT switching devices
3. Pulse waveform generation and control stage
4. Microcontroller-based control system
5. Feedback and protection circuits
6. Cooling and power distribution system

Hardware Design

The hardware design centers around the Intel 80C196KC microcontroller, which serves as the central processing unit for the entire welding power source. This 16-bit microcontroller was selected for its combination of processing speed, peripheral integration, and cost-effectiveness.

Key hardware components include:

The inverter circuit topology uses a full-bridge configuration with IGBT switching devices operating at a carrier frequency of 15–20 kHz. This high switching frequency allows the use of compact magnetic components, reducing the overall size and weight of the power source compared to line-frequency designs.

Software Design

The software architecture follows a modular design approach, with separate routines for each functional subsystem:

• Main control loop: Manages the overall welding cycle, including arc start, welding, and arc extinction
• Pulse waveform generator: Produces the AC pulsed current waveform using PWM modulation
• Parameter management: Handles user input, parameter storage, and preset management
• Protection routines: Monitors operating conditions and implements safety shutdowns
• Communication interface: Supports data logging and remote monitoring

The pulse waveform generation is implemented using a combination of hardware PWM timers and software-based modulation. The 80C196KC microcontroller's built-in PWM modules provide the base switching frequency, while software routines modulate the PWM duty cycle to produce the desired pulse waveform.

Performance Characteristics

The developed power source demonstrated stable and reliable operation across the specified welding parameter range. Key performance characteristics include:

• Output current range: 20–300 A
• Pulse frequency range: 5–50 Hz
• Pulse-to-background current ratio: 1.5:1 to 4:1
• Duty cycle: Up to 60% at rated output
• Efficiency: Greater than 85% at rated conditions
• Power factor: Greater than 0.95 at rated input
• Response time: Less than 10 ms for parameter changes

The AC pulsed waveform provides a unique combination of high peak currents for penetration and lower average currents for heat input control. The positive half-cycle of the AC waveform provides the primary welding action, while the negative half-cycle provides cathodic cleaning action that removes oxide layers from the weld pool surface.

Engineering Practice Considerations

The development of this power source addresses a specific need in welding applications where AC pulsed MIG welding offers advantages over DC MIG welding. The primary applications include:

• Welding of thin aluminum and aluminum alloy components, where the cleaning action of the AC waveform is beneficial
• Welding of dissimilar material joints where oxide removal is critical
• Welding of thick-section aluminum structures where pulsed current control improves weld quality
• Repair welding applications where precise heat input control is required

For pipeline welding applications, the AC pulsed MIG concept could be adapted for welding of aluminum alloy pipe systems, which are increasingly used in chemical processing and cryogenic service. The ability to control both penetration and heat input independently through the pulse parameters offers significant advantages for achieving high-quality welds in challenging geometries.

Key Technical Challenges

The paper identifies several technical challenges encountered during the development process:

1. Arc stability: Maintaining stable arc operation with AC pulsed current requires careful tuning of the waveform parameters and dynamic characteristics of the power source
2. Power factor correction: The high-frequency inverter topology requires active power factor correction to meet regulatory requirements for grid connection
3. Electromagnetic compatibility: The high switching frequency and rapid current changes generate electromagnetic interference that must be controlled through proper filtering and shielding
4. Thermal management: The power electronics components generate significant heat, requiring efficient cooling systems for continuous operation
5. Software reliability: The microcontroller-based control system must be robust against electrical noise and transient disturbances in the welding environment

Study Insights and Implications

This paper provides valuable insights into the practical implementation of advanced welding power sources, demonstrating that microcontroller-based digital control can effectively manage complex welding processes. The AC pulsed MIG concept, while not widely adopted for steel pipe welding, represents an important technological development that has contributed to the evolution of welding power source technology. The hardware and software design approaches described in this paper remain relevant to modern welding power source development, which continues to rely on digital signal processing and microcontroller-based control architectures. For engineers involved in welding equipment selection and process development, this paper illustrates the importance of understanding the underlying power electronics and control systems when evaluating welding equipment capabilities.