Direct digital control of a superconducting magnet

A microcomputer-based controller and its input/output interfaces have been developed for an inductor-converter unit (IC unit) which consists of a six-pulse Graetz-type converter and a solenoidal superconducting magnet (SM). The SM current is feedback-controlled through the following operations: detection of the SM current, comparison with the reference input for generation of the error signal, determination of the firing angle by the digital operation of compensation, and generation of the trigger pulses. The algorithms for digital compensation have been studied by experiments as well as computer simulations. Proportional-integral-derivative (PID), first-order exponential response with transport delay (Dahlin algorithm), and finite time settling control (FTSC) algorithms have been simulated and experimented by using the IC unit. Accurate agreements between the results of simulations and experiments have been obtained for the PID and Dahlin algorithms. The FTSC algorithm has shown the best response of the three methods.