Research Of DSP Control System On AC Inverter Resistance Spot Welding Power Supply

Compared with the traditional resistance welding power supply, DC inverter typeresistance welding power supply has good process performance and dynamic response,welding output can be controlled precisely and quality of welding spot is better. For the pastfew years, it is getting more and more important and has become one of the maindevelopment directions. The single-phase AC resistance welder is the most widely usedresistance welding equipments, which provides alternating current that is similar to thesine-wave. This kind of welder may easily occur splash on the workpiece and its heating isnot continuous. This article has designed a DSP controller of AC inverter resistance spotwelding power supply in order to enhance the welding performance of AC resistance welder.AC inverter resistance welder provides AC square-wave current, which can reduce the currentzero-acrossing time and splash, and its heating is more continuous. It has no secondaryrectification, thus there is no problems caused by secondary rectification, such as the highprice and the difficulties of manufacturing. It will have a good development prospect.This project has designed a DSP controller that can control a AC inverter resistancespot welding power supply whose power is2.5kVA. The main circuit consists of IGBT fullbridge inverter structure and welding transformer. The control system takes DSP as thecontrolling core, including circuits of information detection, PWM output, human-computerinteraction, I/O interface, fault detection and the corresponding software. The control systemuses PWM control technology, which can achieve output current in a wide range ofcontinuous regulation by adjusting the welding transformer primary voltage. Control systemhas three feedback control modes, constant current, constant voltage and constant power.Each control mode has five kinds of frequency to select. Because the frequency of modulationwave is20kHz, the system can realize more feedback adjustment in a half cycle to improvethe control precision and the process adaptability.According to the design scheme, the PCB board of control circuit has been made and thecontrol system of inverter AC resistance spot welding power supply has been debuggedsuccessfully. PI parameters have been set to realize the three feedback control modes. The output wave of power supply is more stable and similar to the AC square wave. The data ofcurrent wave in different kinds of frequency has been collected and compare to thepower-frequency resistance welder. It turns out that the inverter AC resistance spot weldingpower supply has the advantages as follows, the quick current zero-crossing and without stay,the smaller ripple wave, the various output wave and so on. The control system has a moreoutstanding performance than that of the power-frequency resistance welder. Theperformance of the control system is excellent and could help improve the performance of theAC resistance welder.