A novel digital controller for 12-pulse back-to-back AC/DC converters in nuclear fusion experiments

This paper presents a novel digital controller purposely developed for nuclear fusion power supply systems and a MATLAB/Simulink model to simulate its behavior. Nuclear fusion experiments, as ITER, JT-60SA, FAST and DTT, require high current AC/DC converters, typically implemented in 4-quadrant 12-pulse back-to-back configurations, able to follow a desired current profile (scenario). With respect to a classic PID controller, the new digital controller features: a simple and robust feedback loop control of current by using two digital PID-based current controllers, an adapted and flexible direct control of the circulating current, good accuracy and stability during the current circulation to avoid dangerous oscillations, faster dynamic response, sequential control, variable firing angle limits, lower reactive power and reduced harmonic distortion. The controller and the developed simulation models were used to design and analyze the power supply systems for JT-60SA, an international fusion research project that is under construction with the joint contribution of Japanese and European researchers. The JT-60SA converters are designed to supply a DC current up to ±20 kA with an accuracy of ±1%.