M. Nakaoka

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>>

The state-of-the-art phase-shifted ZVS-PWM series and parallel resonant DC-DC power converters using internal parasitic circuit components and new digital control

The authors present two circuit topologies for constant-frequency phase-shifted pulse-width-modulated (PWM) resonant full-bridge inverter-type DC-DC high-power converters with a single high-frequency high-voltage (HFHV) transformer AC link, which effectively make the best of parasitic circuit components existing in the HFHV transformer and HV cable. Two resonant circuit topologies are introduced which are concerned with series and parallel-loaded resonant (SPR) tank type and multiresonant (MR) type composed of SPR tank and two zero voltage switched (ZVS) quasi-resonant poles. These converter characteristics are evaluated in terms of computer-aided analytical and experimental results. Real-time direct digital signal processing based model control strategies for two resonant converters treated here have been implemented to improve transient and steady-state operating performance for an X-ray high-power generator in industrial and medical applications.<<ETX>>

Saturable reactor assisted soft-switching technique in PWM DC-DC converters

A family of saturable-reactor-assisted soft switching pulse-width-modulated (PWM) DC-DC power converters is presented. It uses saturable reactors to achieve efficient soft switching in a wide load range, from no-load to full-load, with no substantial increase in conduction losses. An approximate analysis and key experimental results are presented. In addition, a summary of voltage conversion ratios and voltage and current stresses for this family of converters is provided.<<ETX>>

A new conceptional PWM DC-DC converter with zero-voltage switching incorporating non-controlled saturable reactors

A constant-frequency, phase-shifted-mode, PWM (pulse-width-modulated) DC-DC power converter is described which incorporates two-stage inverters with high-frequency transformer links and saturable reactors as nonlinear elements. The proposed converter performs efficient zero-voltage switching over a large load range (no limitation for load range) and a wide voltage regulation range. Its steady-state characteristics are evaluated and discussed on the basis of computer simulation and experimental results. The experiments were carried out with a 0.5 kW 500 kHz breadboard, and power conversion efficiency of more than 88% was obtained.<<ETX>>

New soft-switching phase-shifted PWM high-frequency inverter-linked cycloconverter incorporating voltage-clamped quasi-resonant technique

A sinewave CVCF power conversion conditioning system (PCS) based on a high-frequency (HF)-isolated AC-link cycloconversion circuit using soft-switching phase-shifted PWM (PSM) and instantaneous voltage regulation schemes is presented. This advanced circuit topology of voltage-clamped quasi-resonant (QR) switch concept, which comprises two-cascaded power conversion stages operating under the principle of zero-voltage switching (ZVS), is introduced in order to minimize switching losses, device stresses, and EMI noise, and to remove a complicated HFAC snubber. A considerable improvement in power-density output performance and power conversion efficiency is achieved employing HF-link soft-switched cycloinversion concept. Its working principle is described, including the control processing strategy. A voltage-clamped QR sinewave PSM HFAC-inverter is analyzed under load-dependent current-source model and its approximate circuit design approach is discussed theoretically. The computer-aided simulation and experimental results are illustrated and evaluated for uninterruptible power supply (UPS) and utility line-interfaced power supply systems.<<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>>

High-frequency inverter with phase-shifted PWM and load-adaptive PFM control strategy for industrial induction-heating

The authors describe a control scheme incorporated in the voltage-fed full-bridge series resonant high-frequency inverter using static induction high power transistors (SITs), which is based on a load-adaptive variable frequency modulated phase-shift PWM (pulse-width modulation) control strategy. The operating principle of the load-adaptive variable frequency PWM series resonant inverter system with a new control scheme is described along with its operating characteristics in steady state. The 20 kW-200 kHz prototype inverter system suitable for induction heating in industry is demonstrated, including a specially designed power transformer. SIT stacks with a water cooling system, and a building-block assembly for high-power use. Experimental results and simulation results are presented. Finally, an improved variable frequency PWM series resonant inverter topology incorporating partially inserted capacitive lossless snubbers is proposed for soft switching and compared with the inverter mentioned above.<<ETX>>

Zero-voltage soft-switched PDM three phase AC-DC active power converter operating at unity power factor and sinewave line current

This paper is concerned with a newly improved version of the pulse density modulation (PDM) three-phase AC-DC converter including an active clamped resonant DC link (ACRDCL) and its digital signal processor (DSP) control strategy to achieve a unity power factor correction and sinewave line current shaping. The operating principle of the zero-voltage soft-switched three-phase AC-DC converter using ACRDCL under the control scheme of an instantaneous space voltage vector-based clamping-voltage distributed PDM (modified-PDM) scheme to improve its control response and operating performances is illustrated. Performance evaluations are discussed using simulation and experimental results, and a comparison with the conventional PDM converter is given. The experimental results of this active converter are shown from a practical point of view. Finally, the utility-interfaced ACRDCL double-converter system operating under the DSP controlled modified-PDM strategy is illustrated and evaluated by using simulation results under inductive load conditions.<<ETX>>

Overlapping commutation-mode analysis of a high-frequency inverter

This paper describes the steady-state operating analysis and performance evaluation of a high-frequency inverter for high-intensity ultrasonic power supply. The high-frequency inverter using reverse-conducting thyristors (abbreviated RTh type inverter) is analysed with an R–C load model of the ultrasonic transducer System. The steady-state characteristics and circuit operation, in which the overlapping commutcation-mode is considered, are quantitatively discussed and compared with those of a basic series-capacitor-commutated inverter (abbreviated basic type inverter). The necessary data for circuit design of the power supply are also presented.