CLADDING TECHNOLOGY SHANXI CO., LTDControl of IGBT Inverter Pulse TIG Welding Machine Using 80C196KC Microcontroller
Literature Overview
The paper by Liao Guohua from Changsha Railway Institute, published in Mining Research and Development in 2000, describes the implementation of IGBT inverter pulse TIG welding machine control using the Motorola 80C196KC microcontroller. This work represents a significant advancement in welding power supply technology, transitioning from conventional SCR-based inverters to IGBT-based inverters with microcontroller-based control, which enabled precise pulse current control essential for high-quality welds.
Technical Background
Pulse TIG welding uses a periodic variation of welding current between a peak value and a background value. This pulsed current mode offers several advantages over continuous DC TIG: improved penetration control, reduced heat input, better bead appearance, and the ability to weld thinner materials without burn-through. The pulse frequency, peak current, background current, and pulse duration ratio (duty cycle) are all controllable parameters that affect weld quality.
The transition from SCR (Silicon Controlled Rectifier) to IGBT (Insulated Gate Bipolar Transistor) inverter technology was a major advancement in welding power supply design. IGBTs offer faster switching speeds, higher efficiency, lighter weight, and better controllability compared to SCRs. However, IGBT-based inverters require sophisticated control algorithms to manage the switching, current regulation, and pulse waveform generation.
80C196KC Microcontroller Architecture
The Motorola 80C196KC is a 16-bit microcontroller with integrated peripherals including timers, ADC, PWM generators, and communication interfaces. Its features make it well-suited for real-time control of power electronics systems. The microcontroller handles several critical functions in the welding power supply:
| Function | Implementation | Purpose |
|---|---|---|
| PWM Generation | Hardware PWM module | Controls IGBT switching for current regulation |
| ADC Sampling | 8-channel ADC | Monitors welding current, voltage, and auxiliary signals |
| Timer Interrupts | Programmable timers | Generates pulse waveform timing |
| Operator Interface | Serial/parallel ports | Controls parameter setting and display |
| Protection Logic | Interrupt routines | Handles overcurrent, overvoltage, and fault conditions |
The 80C196KC operates at clock frequencies of up to 16 MHz, providing sufficient processing speed for real-time control of IGBT switching at frequencies of several kHz. The integrated PWM generators allow hardware-assisted pulse generation, reducing software overhead and ensuring precise timing.
Pulse TIG Current Waveform Control
The pulse current waveform in TIG welding is characterized by several parameters: peak current (I_peak), background current (I_background), pulse frequency (f_pulse), peak current duration (t_peak), and background current duration (t_background). The duty cycle is defined as the ratio of peak current duration to the total pulse period.
The microcontroller generates the pulse waveform by programming timer interrupts to switch between peak and background current states. The IGBT inverter converts DC input voltage to high-frequency AC, which is then rectified to produce the desired welding current. The current regulation loop uses feedback from a current sensor to adjust the PWM duty cycle of the IGBTs, maintaining the target current at each phase of the pulse waveform.
Typical pulse parameters for thin-sheet welding include: I_peak of 100–200 A, I_background of 20–50 A, f_pulse of 1–10 Hz, and duty cycle of 30–70%. The peak current provides penetration, while the background current maintains arc stability and prevents arc extinction.
Control Algorithm and Implementation
The control algorithm implemented in the 80C196KC involves several layers: a current regulation loop that operates at the IGBT switching frequency (several kHz), a pulse waveform generator that operates at the pulse frequency (1–10 Hz), and a parameter management layer that handles operator inputs and system configuration.
The current regulation loop uses a proportional-integral (PI) controller to minimize the error between the measured welding current and the reference current. The PI controller output adjusts the PWM duty cycle of the IGBTs. The pulse waveform generator sets the reference current at each phase of the pulse cycle. The parameter management layer stores and retrieves welding parameters from non-volatile memory and handles operator interface functions.
Engineering Practice and Reliability Considerations
The reliability of the welding power supply is critical for production welding operations. The 80C196KC-based control system must incorporate robust protection features including: overcurrent protection to prevent IGBT damage, overvoltage protection on the DC bus, arc monitoring to detect arc loss, and thermal protection for the power electronics. The microcontroller's interrupt system allows rapid response to fault conditions, typically within microseconds, which is essential for protecting expensive IGBT devices.
The use of a microcontroller also enables advanced features such as current profiling (ramping current at start and end of weld), automatic arc starting, and parameter storage for different welding applications. These features improve weld quality and operator productivity.
Study Insights and Implications
This paper documents an important technological transition in welding power supply design. The use of the 80C196KC microcontroller for IGBT inverter control represents a practical implementation of digital control in power electronics, enabling features that were not possible with analog control systems. For engineers involved in welding equipment design and selection, this work demonstrates the importance of understanding power electronics fundamentals and microcontroller-based control systems.
The pulse TIG welding technology described here has direct applications in cladding and overlay welding, where precise heat input control is essential for managing dilution and microstructure. The ability to program pulse parameters allows operators to optimize the welding process for specific overlay applications, balancing deposition rate, penetration, and dilution control. The principles of digital control described in this paper continue to underpin modern welding power supplies, which now use more advanced microprocessors and digital signal processors (DSPs) for even more sophisticated control algorithms.