Control model and software flow of main circuit for 3-phase low frequency welder

The working principle and process of the main circuit for 3-phase low frequency welder were discussed. After analyzing the conducting and shutting process of the six silicon-controlled rectifiers (SCR) with changing the pilot angle, the reliable phase-shift range of pilot angle was obtained, within which the main circuit can work steadily. Based on the above studies, the current-percentage-control mathematic model and voltage-compensation mathematic model were set up respectively, and the software flow of control system for main circuit was designed. A control system was made according to the control model and method in this study, and it was tested for controlling a 600 kW 3-phase low frequency welder. The welding experiment showed that, one of the SCRs will not shut normally when the current-percentage is up to 80%, which proved that the last conducted SCR is difficult to shut when the pilot angle is less than the power angle.