Takanobu Hatakeyama

Resonant PWM inverter linked DC-DC convertor using parasitic impedances of high-voltage transformer and its applications to X-ray generator

A description is given of a resonant DC-DC converter that uses both the leakage inductances and stray winding capacitances of a high-voltage transformer as LC resonant components and the input capacitance of high-voltage cables as a smoothing DC capacitor. The converter incorporates a pulsewidth-modulated (PWM) control based on a high-frequency inverter at constant frequency to adjust output over a wide range of loads, Its application to an X-ray generator power supply system is reported. A computer-aided state-variable analysis of the circuit is presented. Experimental results using a prototype transformer are given, covering output voltage control characteristics, maximum output power, and converter output waveforms in the X-ray generator.<<ETX>>

Feasible characteristic evaluations of resonant tank PWM inverter-linked DC-DC high-power converters for medical-use high-voltage application

The main purpose of this study is to describe the particular characteristic features and inherent benefits of series, parallel and series-parallel resonant tank inverter-fed DC-DC power converters with a high-voltage high-frequency transformer link for medical-use X-ray high-voltage power generators from a practical application viewpoint, along with a specially-designed high-voltage transformer and its dynamic circuit modeling considering iron and copper loss resistances. An effective method to take advantage of the harmful parasitic resonant circuit parameters of the high-voltage high-frequency transformers which are used in three typical resonant tank circuit topologies and their output voltage performances in both the steady and dynamic-states are comparatively discussed. The dynamic and steady-state characteristics of these resonant power converters are evaluated on the basis of computer simulation results under the conditions of wide allowable load ranges used in actual X-ray high-voltage DC power generators.<<ETX>>

High-frequency parallel resonant converter for X-ray generator utilizing parasitic circuit constants of high voltage-transformer and -cables

The authors describe a resonant PWM (pulse-width-modulated) inverter-linked DC-DC converter which uses the high-voltage transformer parasitic LC circuit parameters as resonant components and the high-voltage cable input capacitance as smoothing filter. Theoretical results obtained by computer-aided simulation and experimental results obtained by a test circuit including prototype transformers are illustrated and discussed from a practical point of view. The phase-shift PWM control for adjusting the DC output voltage of the resonant converter is presented. One of the advantages of this converter is minimization of circuit components; this kind of circuit topology can minimize the size and weight of power supply systems and can be applied to the filament heating circuit connected to the cathode of the X-ray tube.<<ETX>>

Comparative performance evaluations of high-voltage transformer parasitic parameter resonant inverter-linked high-power DC-DC converter with phase-shifted PWM scheme

The main purpose of this study is to analyse the inherent characteristic features and salient benefits of series, parallel, series and parallel tank inverter-fed DC-DC power converters for medical-use X-ray high-voltage generators from a practical viewpoint. The method to make the most of the harmful parasitic circuit parameters of specially-designed high-voltage transformers used in three typical resonant tank topologies is discussed on the basis of simulated results over wide load ranges.<<ETX>>

Resonant PWM inverter linked d.c.-d.c. power converter utilizing parasitic circuit constants of high-voltage transformer and cables

Abstract A state-of-the-art resonant d.c.-d.c. converter using new power transistors has been incorporated into an X-ray generator applicable to multidiverse X-ray apparatus. This converter consists of a resonant inverter to convert the d.c. voltage to a high-frequency a.c. voltage. It incorporates a high-voltage transformer to boost the inverter output voltage corresponding to a set value, together with a high-voltage rectifier. In practice, the high-voltage transformer includes inherently parasitic impedances such as a magnetizing inductance and leakage inductances, together with stray capacitances which exist between the layers of the secondary windings. This paper is mainly concerned with a resonant high-frequency inverter linked d.c.-d.c. converter which is able to utilize effectively the transformer parasitic impedances as resonant circuit parameters as well as the input capacitance of high-voltage cables as a smoothing capacitor.

Parallel operation of four‐switch full‐bridge power amplifiers and a unique digital control scheme for advanced magnetic resonance imaging

In recent years, magnetic resonance imaging (MRI) systems have been in demand to diagnose moving parts in the human body such as the heart or the blood in angiography, where images should be taken in milliseconds instead of minutes. Gradient power amplifiers, which are small but vital components for advanced MRI, require higher output power capacity as well as faster rise/fall dynamic response characteristics under a variety of specified current reference signals. This paper presents a novel switch-mode gradient power amplifier using IGBTs which are connected in parallel to a conventional four-switch full-bridge power conversion circuit at their inputs/outputs in order to realize a higher power density. To satisfy the design specifications, which require minimized ripple and improved rise/fall dynamic response characteristics of the current in the gradient coil, a unique digital control scheme based on an optimal type 1 servo system is proposed and described in detail. The effectiveness of the above is discussed and evaluated through computer-aided analysis. It is expected that the proposed techniques will greatly expand the diagnostic targets and improve the image quality of MRI.