Advanced digital control scheme of two-paralleled bridge type current tracking power conversion amplifier for magnetic resonance imaging

This paper presents a two parallel bridge PWM power conversion circuit for the switch-mode gradient power current tracking amplifiers for the gradient coil in the magnetic resonance imaging (MRI) systems. This power amplifying processor is connected in parallel with the conventional 4-switch type full-bridge power circuits using IGBTs at their inputs/outputs in order to realize further high-power density. A unique digital control scheme for PWM power conversion, which requires minimized ripple and improved rise/fall response characteristics of the current in the gradient coils (GCs), is proposed and described here. This power processor as an overall system is completely suited to the power amplifier for advanced MRI applications because the output current waves are not restricted to ramped-square waves and can assume any arbitrary waveform. It is expected that the proposed techniques will highly enlarge the diagnostic target and improve the image quality of MRI.