Study Note on IGBT Dual Inverter Square Wave AC TIG Welder

Literature Overview

This paper by Liu Guiqiu, Hang Zhengxiang, and Wang Hui, published in Power Electronics in 1997, presents the design and implementation of an IGBT-based dual inverter square wave AC TIG welder. The research was conducted at Shenyang University of Technology. The paper introduces the basic structure and operating principles of the main circuit, proposes methods for constant current characteristics through primary inverter current negative feedback and threshold composite control, and describes a secondary inverter arc striking method.

Core Technical Points

Dual Inverter Architecture

The dual inverter configuration is a key innovation that enables square wave AC output for TIG welding. The system consists of:

• Primary inverter: Converts DC input to high-frequency AC, enabling precise control of the welding current waveform.
• Secondary inverter: Shapes the current waveform into square wave AC, providing the balanced electrode cleaning and melting action required for AC TIG welding.

This architecture overcomes the limitations of traditional transformer-based AC TIG welders, which have limited dynamic response and poor controllability.

Control Methods

The constant current characteristic is essential for stable welding, particularly when the arc length varies due to workpiece surface irregularities or operator technique. The negative feedback loop continuously adjusts the inverter output to maintain the set current value.

Performance Characteristics

The experimental results demonstrate that the welder achieves stable welding of aluminum alloys under the following conditions:

• No-load voltage: 45 V
• Welding current: ≥ 15 A

These parameters indicate a practical, compact welding system suitable for aluminum alloy fabrication.

Engineering Practice Implications

For aluminum alloy pipe and fitting welding, particularly in the aerospace and automotive industries:

• AC balance control: The square wave AC output provides independent control of the positive and negative half-cycles, allowing optimization of the cleaning and melting phases.
• Dynamic response: The IGBT-based inverter offers significantly faster dynamic response compared to transformer-based systems, enabling better arc stability during travel.
• Portability: The compact design of the inverter-based welder improves portability and operator ergonomics.

Key Questions and Reflections

The paper does not extensively discuss the effects of the square wave frequency and duty cycle on weld quality. In practice, these parameters significantly influence the arc cleaning effect, weld penetration, and spatter formation. A systematic investigation of these parameters would be valuable for process optimization.

Another reflection: the study focuses on aluminum alloys, but the system architecture could potentially be applied to other materials requiring AC TIG welding, such as magnesium alloys or certain titanium alloys. The adaptability of the control methods to different material systems is an important consideration.

Reference Value and Outlook

This research represents an early application of IGBT technology to AC TIG welding, demonstrating the feasibility of inverter-based AC welding systems. The control methods described provide a foundation for the development of more advanced welding power sources. Modern IGBT-based AC TIG welders have evolved significantly from this design, incorporating digital signal processing, advanced control algorithms, and integrated sensing systems. However, the fundamental concepts presented in this paper remain relevant and continue to inform the design of contemporary welding equipment.