Junming Sun

Feasible development of soft-switched SIT inverter with load-adaptive frequency-tracking control scheme for induction heating

This paper describes the latest feasible developments of a voltage-source-type series-capacitor-commutated load-resonant high-frequency bridge inverter using static induction transistors (SITs) for industrial induction-heating and melting applications. A load-adaptive variable-frequency tuned controller, composed of a phase-locked loop integrated circuit (PLLIC) device, a pulse amplitude modulation (PAM) power controller employing a phase-controlled AC/DC converter, and protective control schemes for overvoltage and/or overcurrent generation, is also demonstrated for this series resonant inverter. In addition to these, a short-circuit test of a high-power SIT incorporated into the bridge leg high-frequency series resonant inverter is carried out from a practical point of view and evaluated, in order to obtain important design data considering reliable switching characteristics of large-capacity SITs and to realize cost-effective protective circuits for SITs.

Series resonant high-voltage ZCS-PFM DC-DC converter for medical power electronics

In general, high-voltage DC power supplies employing a variety of high-frequency inverters are implemented for constant value control schemes. In particular, their good transient and steady-state performances cannot be achieved under wide load variations involved in a medical-use X ray tube drive high voltage generator ranging from 20 kV to 150 kV in the output voltage and from 0.5 mA to 1250 mA, respectively. A high-voltage power supply designed for X ray power generator applications is considered, which uses series resonant inverter-linked multistage DC voltage multiplier instead of a conventional high voltage diode module rectifier connected to the second-side of a high-voltage transformer, a constant on-time/variable frequency control scheme of this converter operating at zero-current switching modes is described. Introducing the capacitor-diode based multistage voltage multiplier, the secondary turn numbers and stray capacitance of the high-voltage high-frequency transformer as well as the rectifier diode voltage ratings can be greatly reduced. It is proven that the proposed converter control scheme of the 2 step frequency selected switching is more effective for improving output voltage responses. A series resonant high-frequency transformer-linked voltage-multiplying rectifier is evaluated for any ray high-voltage generator on the basis of simulation analysis and observed data in experiment.

Series resonant high-voltage PFM DC-DC converter with voltage multiplier based a two-step frequency switching control for medical-use X ray power generator

In general, high-voltage DC power supplies employing a variety of high-frequency inverters are implemented for constant value control schemes. In particular, their good transient and steady-state performances can not be achieved under wide load variations for a medical-use high voltage X ray generator ranging from 20 kV to 150 kV in the output voltage and from 0.5 mA to 1250 mA, respectively. A high-voltage DC power supply designed for X ray power generator applications is considered, which uses series resonant inverter-linked multistage DC voltage multiplier instead of conventional high voltage diode module rectifier connected to the secondary-side of a high-voltage transformer. A constant on-time/variable frequency control scheme of this converter operating at zero-current soft switching mode is described. Introducing the capacitor-diode cascaded multistage voltage multiplier, the secondary turn numbers, and secondary-side stray capacitance of the high-voltage high-frequency transformer as well as the rectifier diode voltage ratings can be greatly reduced. It is proven that the proposed converter control scheme of the 2 step changed frequency selection switching is more effective for improving output voltage responses. A series resonant high-frequency transformer-linked voltage-multiplying rectifier is evaluated for an X ray high voltage generator on the basis of simulation analysis and observed data in experiment.

Zero voltage soft-commutation PWM DC-DC converter with saturable reactor switch-cascaded diode rectifier

An improved single-ended push-pull (SEPP) half-bridge type zero-voltage soft-switching pulse width modulation (ZVS-PWM) DC-DC power converter is presented in this paper, which makes use of a saturable reactor-assisted lossless capacitor type zero voltage soft-switching method. The SEPP power converter with a high-frequency forward and flyback hybrid transformer link has some advantages such as lowered switching and conduction losses, soft-switching transition operation over a wide load range, constant frequency PWM regulation and minimized Electro Magnetic Interference (EMI) as well as Radio Frequency Interference (RFI) noises. Its operating principle is illustrated and its periodic steady-state circuit analysis is implemented. In order to demonstrate the remarkable effectiveness of this converters characteristics, feasibility experiments are conducted with a 150 W/200 kHz prototype of a high-frequency link ZVS-PWM DC-DC converter using power MOSFETs with an ultrafast soft-recovery diode.

Repetitive learning control system of phase-shifted PWM DC-DC converter using high-frequency high-voltage transformer parasitic resonant components

This paper presents a digital repetitive learning control scheme to realize quick response of output voltage for a medical-use X-ray power generator incorporating a converter fed by a phase-shifted PWM IGBT inverter which makes the most of high-frequency high-voltage transformer parasitic resonance. The effectiveness of the digital control scheme for this sort of X-ray power generator is confirmed through simulation analysis and experimental results.

Novel digital control topology of a high power resonant DC-DC converter for X-ray high-voltage applications

This paper describes a 32-bit RISC processor-based digital feedback control scheme for a series-parallel resonant high power DC-DC converter using its high-voltage transformer parasitic LC circuit components which is applied to a medical use X-ray high-voltage generator. In the converter system, I-PD feedback control algorithm with a nonlinear compensator for steady-state voltage regulation characteristics and an input voltage fluctuation compensator are presented in this paper. A practical estimation procedure to obtain the adequate I-PD gains specified by logarithmic interpolation from some regulation points is established under conditions of extremely wide load ranges as the medical use X-ray high-voltage generator. High speed processing hardware for the digital feedback control scheme with 20 kHz sampling frequency are also discussed as well as programming guidelines. Finally, the performances of this application-specific converter and the effectiveness of the proposed gain parameter estimation procedure of the I-PD compensator are demonstrated on the basis of experimental results.

High-voltage transformer parasitic resonant PWM DC-DC high-power converters and their performance evaluations

The main purpose of this study is to describe some particular characteristic features and inherent benefits of series, parallel and series-parallel resonant tank inverter-fed DC-DC converters for medical-use X-ray high-voltage generators from a practical viewpoint. The method to treat the parasitic resonant circuit parameters of the high-voltage high-frequency transformer used in three typical resonant tank topologies is discussed on the basis of some simulation results, and the simulation results are also verified by experiments.

Transformer parasitic high-frequency inverter-fed DC-DC converter for medical-use X-ray power generator and its digital control

This paper describes a 32-bit RISC processor-based digital feedback control scheme for a series-parallel resonant high power DC-DC converter using its high-voltage transformer parasitic LC circuit components which is applied to medical use X-ray high-voltage generator. In this converter system, the I-PD feedback control algorithm with a nonlinear compensator for steady-state voltage regulation characteristics and an input voltage fluctuation compensator are presented. A practical estimation procedure to obtain the adequate I-PD gains specified by logarithmic interpolation from some regulation points is established under conditions of extremely wide load ranges for the medical X-ray high-voltage generator. The high speed processing hardware for the digital feedback control scheme with 20 kHz sampling frequency is also discussed, as well as the programming guidelines. Finally, the performance of this application-specific converter and the effectiveness of the proposed gain parameter estimation procedure of the I-PD compensator are demonstrated on the basis of experimental results.

Comparative transient and steady-state performances of three resonant PWM inverter-controlled DC-DC converters using high-voltage transformer and cable parasitic circuit components

The main purpose of this study is to describe some particular characteristic features and inherent benefits of series, parallel and series-parallel resonant tank inverter-fed DC-DC converters for a medical-use X-ray high-voltage generator from a practical viewpoint. The method to treat the parasitic resonant circuit parameters of the high-voltage high-frequency transformer used in three typical resonant tank topologies is discussed on the basis of some simulation results, and the simulation results are also verified by experiments.

High-frequency high-voltage transformer parasitic resonant DC-DC converter and its repetitive learning control system

This paper presents a digital repetitive learning control scheme to realize quick response of output voltage for a medical-use X-ray power generator incorporating a power converter fed by a phase-shifted PWM IGBT inverter which makes the most of the high-frequency high-voltage transformer parasitic resonance. The effectiveness of a digital control scheme for this sort of X-ray power generator is confirmed through simulation analysis and experimental results.