Digitally-controlled optimum current tracking scheme of two-paralleled high-power PWM amplifier for magnetic resonance imaging

This paper presents a two paralleled bridge power conversion circuit using switch-mode power current tracking technique in order to generate a gradient magnetic field in the magnetic resonance imaging (MRI) system. This power amplifier is connected in parallel with the conventional 4-switch type full-bridge PWM power conversion circuit using IGBTs at their inputs/outputs in order to realize further high-power density. A digital optimal control scheme for PWM power conversion circuit requires minimization of the current ripple and improvement of dynamic response characteristics of the current in the gradient coils (GCs). It is proposed in this paper that a unique current tracking control scheme can achieve the research objective. This power amplifier can be easily used in the advanced MRI because the output current waves are not restricted to ramped-square waves and can assume any arbitrary wave forms. It is proved that the proposed technique will highly enlarge the diagnostic target and improve the image quality of MRI.