Choice of control function in magnetically-coupled full bridge DC-DC power controller for arc welding: A Practical Approach

In a full bridge DC-DC converter (FBDC) the transformer is a major component for controlled power delivery to secondary side isolated DC loads. Its excitation characteristics is nonlinear and it suffers from a serious problem called magnetic saturation. The power loss in it and also in power switching devices connected at its primary are calculated based on the assumption that the DC flux in core is considered zero. Inverter topology often influences the parametric design of transformer. This article elaborates, with detailed practical validation, that the transformer could influence on choice of suitable control function and its gain values. For that, two popular control functions i.e., proportional plus integral (PI) and second order sliding mode control (SOSMC) would be elaborated here. The approach of controller design for PI and SOSMC is different. Collective approach of gain selection in PI results conservative values of its two gains. On the other hand, two gains in SOSMC are purely based on worst-case process behavior, value of each gain is large. For compatibility study of both control functions in FBDC, nonlinear, extremely dynamic, wide range and diverse arc welding process would be considered as load. Experimental results suggests that SOSMC generates superior control performance in terms of robustness features and control response. Still, as this article further establishes with requisite practical validations, that non-linear magnetic circuit could act as a hindrance for effective utilization of capacity of FBDC based on high-gain fractional order SOSMC function.