A unique digital control scheme of multiple bridges power conversion circuit for advanced magnetic resonance imaging

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