IGBT Dual-Inverter Square Wave AC TIG Welder

Literature Overview

This 1997 publication from Shenyang University of Technology and Liaoyang Petrochemical College describes the development of an IGBT-based dual-inverter square wave AC TIG welder. The work represents a significant advancement in power electronics applied to welding, introducing solid-state switching technology to AC TIG welding applications that previously relied on transformer-based or cycloconverter-based power sources.

Core Technical Content

The dual-inverter topology employs two independent inverter circuits operating in complementary phases to generate a controlled square wave AC output. This architecture provides precise control over both the positive (electrode positive) and negative (electrode negative) half-cycles of the AC waveform, which is critical for AC TIG welding of aluminum, magnesium, and their alloys.

Key technical parameters:

Parameter	Specification	Significance
Output current	20-300 A	Range for thin to thick sections
Frequency	50-200 Hz	Controls arc stability and cleaning action
Balancing ratio	30-70% positive/negative	Controls penetration vs. cleaning
Switching frequency	20-50 kHz	Determines waveform quality
IGBT voltage rating	600-1200 V	System voltage capability
Duty cycle	Up to 100%	Continuous operation capability

Technical Interpretation

The square wave AC waveform differs fundamentally from the traditional sinusoidal AC output. In a sinusoidal AC TIG welder, the current gradually passes through zero, causing arc extinction and reignition at each half-cycle transition. This results in arc instability, particularly at lower frequencies, and limits the minimum practical welding current.

The square wave topology eliminates the zero-current crossing problem by maintaining substantial current throughout both half-cycles. The current transitions between positive and negative values occur at controlled switching instants, with the arc maintained through the transition by the inductive energy stored in the circuit. This results in:

Stable arc at lower frequencies - enabling better control of the cleaning action
Independent control of positive and negative half-cycles - optimizing penetration and cathodic cleaning separately
Reduced spatter - stable arc reduces metal transfer irregularities
Improved weld quality - consistent arc characteristics throughout the weld

Application to Cladding and Dissimilar Metal Welding

While AC TIG welding is primarily associated with aluminum and magnesium welding, the technology has relevance to cladding applications involving:

Aluminum alloy cladding on steel substrates for thermal management applications
Dissimilar metal joints between aluminum and steel in automotive and aerospace applications
Repair welding of aluminum components in chemical processing equipment

The square wave AC capability allows engineers to optimize the welding process for dissimilar metal joints by adjusting the balancing ratio to control heat distribution between the two metals. For aluminum-to-steel cladding, a higher negative half-cycle proportion provides deeper penetration into the aluminum while maintaining adequate cleaning action on the oxide surface.

Power Electronics Architecture

The dual-inverter system architecture:

Component	Function	Technology
Input rectifier	AC to DC conversion	Diode bridge or PFC rectifier
DC link capacitor	Energy storage, voltage stabilization	Film or electrolytic
Inverter 1	Generates positive half-cycle	IGBT bridge
Inverter 2	Generates negative half-cycle	IGBT bridge
Output transformer	Voltage step-down, isolation	High-frequency design
Current sensing	Feedback for control	Rogowski coil or shunt

Performance Advantages

Compared to traditional AC TIG power sources:

Performance Metric	Traditional AC	IGBT Square Wave AC	Improvement
Minimum stable current	30-50 A	10-20 A	50-75% reduction
Frequency range	50-100 Hz	50-200 Hz	Extended range
Balancing control	Limited	Precise (±2%)	Significant improvement
Arc stability	Moderate	Excellent	Qualitative improvement
Efficiency	70-80%	85-92%	10-15% improvement
Weight	Heavy	Lightweight	40-60% reduction

Study Insights and Implications

This research demonstrated that solid-state power electronics could provide superior performance compared to traditional welding power sources. For cladding engineers, the implications include:

Improved process control - precise current waveform control enables optimization of penetration depth and dilution in cladding applications
Enhanced flexibility - the ability to switch between DC and AC modes within the same power source facilitates multi-material cladding operations
Reduced equipment footprint - lighter, more compact power sources enable field applications and mobile cladding operations
Energy efficiency - reduced power consumption lowers operating costs for large-scale cladding programs

The work also established the technical foundation for subsequent developments in inverter welding technology that now dominate the welding equipment market. Engineers involved in cladding process development should understand the capabilities of modern inverter power sources to fully exploit their potential for process optimization.