Development of a New Inverter TIG Welding Power Source

Literature Overview and Technical Context

The 1993 study by Yang Lijun, Hu Shengsun, Zhao Jiarui, Sun Dong, and Lu Dengping from Tianjin University, published in Welding Technology, represents an important contribution to the development of inverter-based TIG welding power sources. This work was conducted during a critical period of transition from conventional transformer-based welding power sources to modern inverter technology. The research addresses the design, implementation, and performance evaluation of a novel inverter TIG power source that incorporates advanced control strategies for improved welding quality.

Technical Background and Design Philosophy

Conventional TIG welding power sources based on transformer or generator technology suffer from several inherent limitations: large size and weight, low power factor, limited dynamic response, and inability to provide sophisticated control over welding parameters. The development of inverter technology, based on high-frequency switching of semiconductor devices, offers a pathway to overcome these limitations while enabling advanced control features.

The design philosophy of the new inverter TIG power source was guided by several key objectives:

Compact size and light weight: Achieving a power density significantly higher than conventional sources
High dynamic response: Rapid adjustment of welding current to respond to arc length changes and other disturbances
Precise current control: Fine adjustment of welding parameters for improved weld quality
High power factor: Minimization of reactive power consumption from the mains supply
Versatility: Capability to support multiple welding modes including DC, AC, and pulsed operation

Circuit Topology and Key Components

The inverter TIG power source developed in this study employs a full-bridge inverter topology with insulated gate bipolar transistor (IGBT) switches operating at a switching frequency of 20-40 kHz. The main circuit consists of the following stages:

Stage	Function	Key Components
Input rectification	Convert AC mains to DC	Diode bridge rectifier
DC bus	Energy storage and smoothing	Capacitor bank, 400-600 V DC
Inverter	High-frequency AC generation	Full-bridge IGBT inverter
Output transformer	Voltage transformation and isolation	High-frequency transformer
Output rectification	Convert high-frequency AC to welding DC	Thyristor or diode rectifier
Control system	Parameter regulation and mode selection	Microprocessor-based controller

The switching frequency of 20-40 kHz was selected as a compromise between transformer size (higher frequency allows smaller transformers) and switching losses (lower frequency reduces IGBT losses). The IGBT devices were selected for their favorable balance of switching speed, voltage blocking capability, and current handling capacity.

Control Strategy and Performance Characteristics

The control system of the inverter TIG power source implements a closed-loop current regulation scheme with a sampling rate of 10 kHz. The welding current is measured using a current transformer and compared with a reference setpoint generated by the operator through a potentiometer or digital interface. The error signal is processed by a proportional-integral (PI) controller that generates the gate drive signals for the IGBT switches.

The power source offers three welding modes:

DC mode: For welding of steel, titanium, and other materials where cathode cleaning is not required
AC mode: For welding of aluminum and magnesium alloys, with adjustable negative-to-positive time ratio
Pulsed mode: For advanced applications requiring precise heat input control, with independent adjustment of base current, peak current, pulse frequency, and duty cycle

Performance Comparison with Conventional Sources

The study provided a detailed comparison of the inverter TIG power source with conventional transformer-based sources:

Parameter	Inverter Source	Conventional Source	Improvement
Weight	15 kg	60-80 kg	75-80% reduction
Power factor	>0.95	0.5-0.7	35-45% improvement
Current regulation time	<10 ms	50-100 ms	5-10x faster
Current step size	1 A	10-20 A	10-20x finer
Duty cycle at rated current	100%	60-80%	20-40% improvement
Efficiency	85-90%	75-80%	10-15% improvement

The superior dynamic response of the inverter source is particularly important for TIG welding applications where maintaining a stable arc length is critical to weld quality. The rapid current regulation capability allows the power source to compensate for minor arc length variations that inevitably occur during manual welding, resulting in more consistent weld bead geometry and reduced defect rates.

Engineering Implications for Cladding and Overlay Applications

The development of this inverter TIG power source has significant implications for the cladding and overlay welding field. The precise current control capability enables better control over the dilution ratio in overlay welding, which is a critical parameter that directly affects the corrosion resistance and wear resistance of the cladding layer. The pulsed welding mode offers additional flexibility by allowing the operator to control the heat input on a cycle-by-cycle basis, which can be used to minimize dilution while maintaining adequate fusion.

For bimetallic pressure vessel fabrication, the compact size and high duty cycle of the inverter source make it particularly suitable for field welding applications where access is limited and power supply capacity may be constrained. The high power factor reduces the load on the mains supply, which is important when multiple welding stations are operated simultaneously.

The study also highlights the importance of power source development in enabling new welding process capabilities. As welding technology advances, the power source must evolve in parallel to provide the control precision and flexibility required. The inverter TIG power source represents a foundation upon which more advanced control strategies, such as adaptive control and expert system integration, can be built.