Shuji Watanabe

Power conversion PWM amplifier with two paralleled four quadrant chopper for MRI gradient coil magnetic field current tracking implementation

This paper presents a two-paralleled PWM amplifier using switch-mode power current tracking technique in order to generate a gradient magnetic field in the magnetic resonance imaging (MRI) system. This circuit has 8-IGBTs at their inputs/outputs so as to realize further high-power density. A digital control scheme is adopted to minimize the current ripple and improve its control response in the gradient coils (GCs). It is proved that the proposed technique will highly enlarge the diagnostic target and improve the image quality of MRI.

Analysis on a PWM power conversion amplifier with IGBT macro model to generate gradient magnetic fields in MRI systems

This paper presents a two-paralleled PWM amplifier using switch-mode power current tracking technique in order to generate a gradient magnetic field in the magnetic resonance imaging (MRI) system. This circuit has 8-IGBTs at their inputs/outputs so as to realize further high-power density. A digital control scheme can minimize the current ripple and improve its control response in the gradient coils (GCs). It is proved that the proposed technique will highly enlarge the diagnostic target and improve the image quality of MRI.

DSP-based high precision current tracking control of gradient coil in two-paralleled PWM amplifiers for MRI systems

This paper presents a two-paralleled PWM amplifier using the switch-mode power current tracking technique in order to generate a gradient magnetic field in a magnetic resonance imaging (MRI) system. This circuit has 8-IGBTs at their inputs/outputs so as to realize further high-power density. A digital control scheme can minimize the current ripple and improve its control response in the gradient coils (GCs). It is proved that the proposed technique will highly enlarge the diagnostic target and improve the image quality of MRI.

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.

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.

Development of digital optimum predictive control implementation for gradient magnetic field current controller in MRI system

This paper presents a digital control scheme for a four-quadrant high frequency PWM chopper type power conversion amplifier. It is the gradient magnetic field current pattern generator which is designed for medical use MRI. The main research objective of this paper is to propose the current control implementation in gradient magnetic coil (GC), which is driven by a high frequency PWM DC-DC converter system with a four-quadrant output scheme. The current pattern required for GC should follow up in accordance with any desired current pattern. In this current amplifier system, the current servo controller employs the optimum type-1 predictive control strategy, which has the advantages for the multiple input voltage and output current. The dynamic and steady state performances of the current PWM amplifier are described and evaluated on the basis of simulation analysis.