Research On The Digital Control Of Welding Inverter

The development of welding process research, welding automation and welding flexible manufacturing system (W-FMS) has raised an ever-increasing requirement for precisely controlled and flexible welding power source. Welding inverter that works at the frequency between 20k to 100 kHz not only has a much less volume and weight, its output inductance value is also very small which means more rapid current or voltage transition, a better fundamental of precise control. But because analog circuit is widely adopted in welding inverter control, the control precision in output amplitude value is little enhanced, needless to say the control flexibility. So the research presented here is concentrating on digital control of welding inverter, aiming at enhancing control precision and flexibility.Because digital control is much different from analogy control adopted in traditional welding inverter, we begin our research with the characters of digital control. Fortunately from 1960s as the development of computer and communication science, digital signal processing and digital control technique have been greatly developed. So we just have to investigate the differences between digital control and analog control considering the characters of welding inverter, design the digital control strategy, optimize the control parameters and get a digital controller to meet the need of welding inverter application. It is also the process to find a new way of welding inverter control system design. At first we established an AC small-signal model of welding inverter and designed a digital controller on the basis of analyzing a typic analog welding control circuit. With this digital controller, we also predicted the control effect by theory analyse.As a kind of mathematical analytic model, AC small-signal model is very important to guide the digital control system design. But it cannot get a precise prediction for the control effect because of the too much predigestion of practical physical procedure during the model establishment, neither can it describe the fixed-point computations exactly. After the AC small-signal model, we establish a Matlab model for welding inverter including the fixed-point digital control system. With this Matlab model we simulate the working processes of welding inverter and digital controller, predicted the control precision and effect. Welding inverter externalcharacteristic and dynamic characteristic including the loading resistance mutation and current given value step change are also simulated and analyzed in this dissertation oHow to establish the digital control system is the key technology to realize digital control of welding inverter. We developed a duplex CPU digital control system using ADSP-2181 and C167CR and succeeded in constant-current control on the basis of the survey of digital control application in welding inverter, the DSP technology and the embedded system application. As it is the first time that we use these two microcontrollers in welding inverter control in China, their hardware characters and software developing tools are also introduced here for future reference.After debugging of the digital control system, we program a constant-current control software and make a power load experiment including external characteristic and dynamic characteristic tests on the almost the same conditions as that of simulation of Matlab model. The experimental results were analyzed and compared with that of simulation. The power experiment proved that the simulation results are exact and the digital welding inverter developed by us accords with the design requirements and can meet the need of welding process.