Zhuojin Pipe Fitting Co., LtdPulse MIG Welder Control System Based on 80C196KC Microcontroller
Literature Overview
This paper by Chen Kexuan, Li Shuhui, Zhang Shiqin, and Chen Xiang from Lanzhou University of Technology (2012, Journal of Electric Welder, Vol. 42, No. 3, pp. 39-43) describes the design and implementation of a pulse MIG welder control system based on the 80C196KC microcontroller. The system integrates A/D conversion, PI control, timing control, fault handling, parameter presetting, parameter display, PWM generation, and data acquisition. The IGBT power stage is driven by the SG3525 PWM chip and EXB841 IGBT gate driver, while wire feed speed is controlled via a MOSFET-based switching power supply.
Core Technical Architecture
The control system architecture is designed around the 80C196KC, a 16-bit single-chip microcomputer from Intel (now NXP). The microcontroller serves as the central processing unit, coordinating all welding functions through a combination of hardware and software control loops.
System Functional Blocks
| Functional Block | Implementation | Purpose |
|---|---|---|
| A/D Conversion | 80C196KC internal ADC | Sample welding current and voltage |
| PI Control | Discrete incremental PI algorithm | Regulate welding current |
| Timing Control | Microcontroller timer | Control pulse width, frequency, and sequence |
| Fault Handling | Microcontroller interrupt routines | Detect and respond to abnormal conditions |
| Parameter Presetting | Microcontroller memory | Store and retrieve welding parameters |
| Parameter Display | Microcontroller I/O | Display current parameters to operator |
| PWM Generation | SG3525 chip | Generate gate drive signals for IGBT |
| Wire Feed Control | MOSFET switching supply | Regulate wire feed motor speed |
| IGBT Drive | EXB841 driver | Provide isolated gate drive for IGBT |
PI Control Algorithm
The system employs a discrete incremental PI control algorithm, which is particularly suited for microcontroller implementation. The algorithm computes the change in control output at each sampling instant based on the error between the measured current and the reference current:
- Proportional term: Responds to the current error magnitude
- Integral term: Eliminates steady-state error by accumulating past errors
- Incremental form: Only the change in output is computed, reducing computational load and memory requirements
The PI output is converted to a PWM duty cycle via a D/A converter, which modulates the IGBT switching. This closed-loop control ensures that the welding current remains constant despite variations in arc length, wire diameter, and other process disturbances.
Process Analysis and Performance Evaluation
The authors tested the welder's static and dynamic characteristics to verify performance:
Static Characteristics
The static characteristics refer to the welder's ability to maintain a constant welding current under steady-state conditions. The PI controller should minimise the steady-state error between the reference current and the actual welding current.
Dynamic Characteristics
The dynamic characteristics refer to the welder's response to sudden changes in welding conditions, such as:
- Changes in arc length due to wire feed variations
- Changes in wire diameter or composition
- Transient conditions during welding start and stop
The PI controller should provide a fast response with minimal overshoot and oscillation.
Test Results Summary
| Performance Metric | Result | Assessment |
|---|---|---|
| Static current accuracy | Within ±2% of set value | Good |
| Dynamic response time | <50 ms | Acceptable |
| Current ripple | Low | Good for stable arc |
| Wire feed speed regulation | Stable | Good |
| Fault detection | Reliable | Good |
| Overall performance | Meets design objectives | Successful |
Engineering Practice Implications
The design described in this paper represents a practical approach to welding power source control using a cost-effective microcontroller. Several aspects are particularly relevant to production engineers:
- Cost-effectiveness: The 80C196KC and SG3525 are relatively inexpensive components, making this design suitable for mid-range welding equipment.
- Scalability: The modular architecture allows for easy addition of features such as network connectivity, data logging, and advanced process control.
- Reliability: The discrete PI algorithm and hardware-based PWM generation provide robust control without relying on complex software.
Limitations and Considerations
While the design is successful, several limitations should be noted:
- The 80C196KC is an older microcontroller with limited processing power compared to modern 32-bit MCUs.
- The discrete PI algorithm, while effective, may not be optimal for all welding applications—adaptive or fuzzy control could provide better performance for dynamic welding conditions.
- The system lacks advanced features such as arc sensing for seam tracking, which would be required for fully automated welding applications.
Study Insights and Reflections
This study demonstrates the practical application of microcontroller-based control in welding power sources. The key insight is that a well-designed control algorithm, combined with appropriate hardware selection, can achieve good welding performance without requiring expensive or complex components. For engineers designing welding equipment, this paper serves as a useful reference for control system architecture and PI tuning strategies.
The use of the discrete incremental PI algorithm is particularly noteworthy, as it is a computationally efficient approach that is well-suited to microcontroller implementation. The algorithm's ability to minimise steady-state error while maintaining a fast dynamic response is essential for achieving stable welding performance.