Digital controlled MOSFET gradient amplifier for magnetic resonance imaging

This paper presents a digital controlled gradient amplifier for magnetic resonance imaging that is composed of an H-bridge of power MOSFETs with the voltage and current ratings of 150V/240A. An output filter is designed for both differential and common modes that can be decoupled in the circuit model. A digital tracking control algorithm, including a full-state feedback and a feed-forward loop, is proposed with an additional nonlinear PI to eliminate the tracking error. The common-mode dv/dt can be attenuated by simply keeping the common-mode input constant. To ease the requirements for the accuracy of both the state variable sensors and the A/D samplings, a simple PI is applied instead of the tracking control during the steady period of the output current. Simulations and experiments are carried out to demonstrate the performances of the amplifier.