Optimization of an on-line function generation

A particular example of process control is the analog function generator of the CERN proton synchrotron. For magnet field correction, some magnets have to follow reference currents synchronous with the pulses of the synchrotron. Depending on the dynamic behaviour of the magnet system to be controlled, the output current will show a somewhat distorted image of the reference current used as input. An on-line computer strategy has been designed to compensate the distortions: i.e. to adjust the input function at successive pulses in such a way that the output current follows the reference as closely as required. However, the identification of such a system is not carried out because it is difficult and singular in any case. Modifications cannot be computed directly, but will result from an iterative strategy: the closed-loop adaptive control is based on a maximization procedure, requiring little memory and no gradient information. The algorithm is a variant of the optimization method called extended sequential search. (12 refs).