High-frequency ZVS PWM power amplifier for magnetic-field current tracking control scheme and its design considerations

In order to minimize switching losses and stresses, reduce EMI and RFI noises, and realize snubberless configuration, the soft-switched PWM power conversion circuits and systems using new power semiconductor devices have attracted special interest. The authors have proposed a novel topology with auxiliary transformer-assisted quasi-resonant commutated pole (TQRCP) circuit which can operate under a principle of zero-voltage switching (ZVS) transition without initial resonant current control loop. In this paper, the high-frequency ZVS-PWM power amplifier which incorporates auxiliary TQRCP circuits into the bridge legs is newly developed for the magnetic-field current tracking control system. The control implementation for achieving a precise magnetic-field current tracking realization with low ripple factor is introduced into the switched-mode PWM power amplifier and its design considerations are described for an efficient generation of gradient-magnetic-fields in magnetic resonance imaging (MRI) machines. It is expected that this technique will improve the image quality of MRI machines