Research On The Control System Of Variable Polarity Power Source For Submerged Arc Welding

Variable polarity submerged arc welding (VPSAW) power source is a special square wave AC power source, which frequency, time, current value of direct current electrode negative (DCEN) and direct current electrode positive (DCEP) of welding current can be adjusted respectively and independently, the arc force, heat distribution relationships, heat input to base metal, the penetration and weld formation of two sides can be controlled. Variable polarity submerged arc welding power source both have a DC power source in the welding speed, penetration depth and other aspects of the advantages, also have AC power source in the deposition rate, anti-magnetic blow and other areas of the advantages, in order to effectively solve the DC submerged arc welding and the AC submerged arc welding shortcomings, and shortage of analog control system.In this paper, VPSAW power source inverter main circuit is consists of two stages, and in the first stage a full-bridge zero-voltage switching pulse-width-modulation (FB-ZVS-PWM) inverter is adopted, a half-bridge inverter is used in second stage.Based on the employed main circuit topology of the VPSAW power source, a digital and analog hybrid control system was designed, employing the PIC16F877A as the core, this system includes the design of external characteristics control circuit, the design of driver circuits, the design of hardware and software, and slso the design of the human-machine interface.The first stage main inverter circuit under the control of the control circuit to achieve the main circuit switching mode to reduce switching losses of the main circuit, and avoid the phenomenon of the duty cycle loss when the main circuit at light loads generated, increase reliability and stability of the circuit system.Tests of variable polarity SAW power source control system have been conducted, and related waveforms from the tests have been analyzed. Results of the tests show that the designed control system can achieve the current ripple setting of the positive and negative half-wave, at the same time the setting signals of the first inverter are strictly synchronous with the drive signals of the secondary inverter in the frequency and the cycle, and achieves that five parameters of the welding current can be adjusted respectively and independently. The keyboard used combining with the LCD enables the welding current of the power source parameters can be set, the function of choice and the exchange of information can be done for the clients and the control system.