Design of Inverter AC TIG Control Circuit with Dual Inverter Topology

Literature Overview

The paper by Chang Yunlong, Sun Jinggang, Wang Dianlong, and Song Wenqing from the School of Materials Science and Engineering at Shenyang University of Technology, published in the "Journal of Shenyang University of Technology" (Vol. 26, No. 4, 2004, pp. 385-388), presents the design of a novel dual-inverter IGBT AC TIG control circuit. This circuit comprises a primary inverter and a secondary inverter control circuit, achieving current closed-loop control, frequency and duty ratio adjustment, and multiple control functions. The paper provides a detailed analysis of the control circuit operating principles and experimental validation demonstrating the simplicity and versatility of the design.

Technical Background and Circuit Architecture

AC TIG welding is essential for welding aluminum and its alloys, where the alternating current provides cathodic cleaning action on the oxide layer while maintaining an acceptable heat balance between the electrode and the workpiece. The design of AC TIG power sources has evolved significantly from traditional transformer-based systems to modern inverter-based designs, which offer advantages in terms of size, weight, efficiency, and control flexibility.

The dual-inverter topology described in this paper represents an advanced approach to AC TIG power source design. The architecture consists of:

1. Primary inverter control circuit: Drives the half-bridge main circuit and implements current closed-loop control.
2. Secondary inverter control circuit: Regulates current frequency and duty ratio to meet various welding process requirements.

Operating Principles and Control Strategy

The control circuit operates on the principle of high-frequency switching using IGBT (Insulated Gate Bipolar Transistor) devices. The primary inverter converts the DC input voltage into a high-frequency AC waveform, while the secondary inverter further shapes the output waveform to achieve the desired welding characteristics.

The current closed-loop control in the primary inverter ensures that the welding current remains stable despite variations in arc voltage and load conditions. This is achieved through real-time feedback of the welding current, comparison with a reference value, and adjustment of the IGBT switching pattern to maintain the desired current level.

The secondary inverter provides additional control flexibility by independently adjusting the frequency and duty ratio of the AC output. This capability allows the operator to optimize the welding parameters for different aluminum alloy compositions, joint configurations, and welding positions. For example:

• Higher frequency: Produces a more stable arc with reduced noise and improved cleaning action.
• Lower frequency: May be preferred for thicker sections where deeper penetration is required.
• Duty ratio adjustment: Controls the balance between the cleaning half-cycle and the welding half-cycle, which is critical for aluminum welding where oxide removal and heat input must be balanced.

Experimental Validation and Performance Characteristics

The experimental results presented in the paper demonstrate several key performance characteristics of the dual-inverter AC TIG control circuit:

1. Simplicity of structure: The circuit design avoids complex analog components, relying instead on digital control signals and IGBT switching, which simplifies manufacturing and maintenance.
2. Convenient parameter adjustment: The frequency and duty ratio can be adjusted electronically, allowing rapid optimization of welding parameters without mechanical modifications.
3. Multiple control functions: The circuit supports various welding modes, including constant current, constant voltage, and pulsed AC TIG, providing versatility for different welding applications.

The experimental validation likely involved testing the power source with various aluminum alloy plates, measuring arc stability, penetration depth, and weld bead appearance. The results would have confirmed the effectiveness of the dual-inverter approach in achieving stable AC TIG welding with the desired parameter ranges.

Engineering Practice and Design Considerations

For engineers designing or selecting AC TIG power sources for aluminum welding applications, this paper highlights several important design considerations:

• IGBT selection: The IGBT devices must be rated for the required voltage and current levels, with adequate thermal management to ensure reliable operation under continuous duty cycles.
• Gate driver design: The IGBT gate drivers must provide sufficient drive current and voltage to ensure fast switching and minimize switching losses.
• Control algorithm: The closed-loop current control algorithm must respond quickly to arc disturbances while maintaining stability.
• Safety considerations: The high-frequency switching generates electromagnetic interference (EMI) that must be filtered to comply with regulatory standards.

The dual-inverter topology offers a significant advantage over single-inverter designs in terms of control flexibility. By separating the primary and secondary inverter functions, the circuit can independently optimize the main power conversion and the output waveform shaping, resulting in superior welding performance.

From a manufacturing perspective, the simplicity of the control circuit translates into lower production costs and easier maintenance. The use of standard IGBT modules and digital control components reduces the reliance on specialized analog components, improving supply chain reliability and reducing spare parts inventory requirements.

This paper represents a significant contribution to the field of welding power source design, demonstrating the application of modern power electronics to improve AC TIG welding performance. The dual-inverter approach provides a robust and flexible platform for aluminum welding applications, and the design principles described can be adapted for other welding processes and power source types. For engineering teams involved in welding equipment development, the detailed circuit analysis and experimental validation presented in this paper provide a valuable reference for designing next-generation inverter-based welding power sources with enhanced control capabilities and improved welding quality.