Multiple-bridge PWM current-regulated power amplifier for magnetic resonance imaging system and its feasible digital control implementation

This paper presents a four-paralleled full-bridge-type PWM current controlled power amplifier using IGBTs in order to generate high speed gradient magnetic fields for magnetic resonance imaging system (MRI) and its unique parallel processing digital control scheme based on a phase-lead compensator by a reference delay and a load model feedforward in addition to a dead time compensator. The maximum output voltage of the current controlled power amplifier is 600 VDC and its maximum current is 400 A for inductive loads. The observed waveforms in its experiment are illustrated to demonstrate the effectiveness of the four-paralleled full-bridge power amplifier topology and its unique control scheme.