Fu-Sheng Tsai

Constant-frequency clamped-mode resonant converters

Two novel Clamped-Mode Resonant Converters are proposed which operate at a constant frequency while retaining many desired features of conventional series- and parallel-resonant converters. State-plane analysis techniques are employed to identify all possible operating modes of clamped-mode series-resonant converter and define their mode boundaries. The control-to-output characteristics are derived that specifies the regions for natura; and forced commutation The predicted operating modes are verified using a prototype circuit.

Voltage and current stress reduction in single-stage power factor correction AC/DC converters with bulk capacitor voltage feedback

Single-stage power factor correction (PFC) AC/DC converters integrate a boost-derived input current shaper (ICS) with a flyback or forward DC/DC converter in one single stage. The ICS can be operated in either discontinuous current mode (DCM) or continuous current mode (CCM), while the flyback or forward DC/DC converter is operated in CCM. Almost all single-stage PFC AC/DC converters suffer from high bulk capacitor voltage stress and extra switch current stress. The bulk capacitor voltage feedback with a coupled winding structure is widely used to reduce both the voltage and current stresses in practical single-stage PFC AC/DC converters. This paper presents a detailed analysis of the bulk capacitor voltage feedback, including the relationship between bulk capacitor voltage, input current harmonics, voltage feedback ratio, and load condition. The maximum bulk capacitor voltage appears when the DC/DC converter operates at the boundary between CCM and DCM. This paper also reveals that only the voltage feedback ratio determines the input current harmonics under DCM ICS and CCM DC/DC operation. The theoretical prediction of the bulk capacitor voltage as well as the predicted input harmonic contents is verified experimentally on a 60 W AC/DC converter with universal-line input.

Constant-frequency, clamped-mode resonant converters

Two novel Clamped-Mode Resonant Converters are proposed which operate at a constant frequency while retaining many desired features of conventional series- and parallel-resonant converters. State-plane analysis techniques are employed to identify all possible operating modes of clamped-mode series-resonant converter and define their mode boundaries. The control-to-output characteristics are derived that specifies the regions for natura; and forced commutation The predicted operating modes are verified using a prototype circuit.

High-frequency AC power distribution in Space Station

A utility-type, 20-kHz, AC power distribution system for the space station employing resonant power-conversion techniques is presented. The system converts raw DC voltage from photovoltaic cells or three-phase, low-frequency AC voltage from a solar dynamic generator into a regulated, 20-G kHz AC voltage for distribution among various loads. Operations of the components of the system such as driver inverter, DC receiver, bidirectional receiver, and three-phase AC receiver are discussed. EASY5 computer modeling and simulations were performed to study the local and global performance of the system. Simulation results show that the system has fast response and good transient behavior. The AC bus voltage is effectively regulated using the phase-control scheme, which is demonstrated with both line and load variations. The feasibility of paralleling the outputs of driver modules is illustrated with the driver modules synchronized and sharing a common feedback loop. A high-frequency, sinusoidal AC voltage is generated in the three-phase, AC input case, when the driver modules are phased 120 degrees away from one another and their outputs are connected in series. >

Design optimization of an off-line input harmonic current corrected flyback converter

Characterization of bulk capacitor voltage stress in a single-switch, input harmonic current corrected flyback converter is presented. A design procedure for optimizing such a converter design by limiting the bulk capacitor voltage stress, maintaining high efficiency while complying with IEC 1000-3-2 class D input harmonic current requirements is introduced. A 60 W universal input, 5 V at 12 A power supply designed following the procedure was built, and the theoretical prediction of bulk capacitor voltage as well as the predicted input harmonic contents are verified experimentally.

State-Plane Analysis of Clamped-Mode Parallel-Resonant Converter

A novel constant-frequency, clamped-mode parallel-resonant converter is proposed and analyzed. Employing graphical state-plane techniques, five circuit operating modes together with their operating regions are defined, regions for natural and forced commutation are specified, and the dc control-to-output characteristics are derived. The predicted operating modes are experimentally verified using a 105kHz prototype circuit.12

A Novel Control for Bidirectional Power Flow of a Parallel Resonant Converter

A new control parameter is proposed to achieve output regulation and bidirectional power flow of a parallel-resonant converter which employs a controlled output rectifier. The control parameter, ¿ angle, is defined as the displacement angle between the firing of the inverter switches and their corresponding rectifier switches. Employing ¿ angle control, the control-to-output characteristics of the converter are shown to be load independent. Closed-form expressions for the steady-state operation are derived. Desired operating regions are analytically defined such that all inverter switches are naturally commutated and output rectifier switches are line commutated.