Adaptive control systems for line-commutated converters

Most of the magnets of the particle accelerators at CERN are driven by high-current power supplies which are built with line-commutated or thyristorized AC to DC converters. To this application, the power converters are usually included in a double feedback control loop intended to establish a high-precision trapezoidal-like current waveform in the inductive load. The precision required for the magnet current is typically 100 ppm. The dynamics and precision of the magnet current strongly depend on the loop compensation achieved. The correct tuning of the system demands an accurate assessment of the load because it is included in the forward path of the current loop. Normally, the set-up of each power converter attached to a given magnet, requires a manual adjustment of the current loop. However, in some cases non-linear current-related effects or thermal dependence of the load prevent an optimum compensation. In addition, the manual adjustment is a time-consuming task. In this work an efficient adaptive control scheme is presented which avoids manual tuning of the feedback system and compensates for load variations.