David Ki-Wai Cheng

Steady-state analysis of an interleaved boost converter with coupled inductors

Boost converters are widely used as power-factor corrected preregulators. In high-power applications, interleaved operation of two or more boost converters has been proposed to increase the output power and to reduce the output ripple. A major design criterion then is to ensure equal current sharing among the parallel converters. In this paper, a converter consisting of two interleaved and intercoupled boost converter cells is proposed and investigated. The boost converter cells have very good current sharing characteristics even in the presence of relatively large duty cycle mismatch. In addition, it can be designed to have small input current ripple and zero boost-rectifier reverse-recovery loss. The operating principle, steady-state analysis, and comparison with the conventional boost converter are presented. Simulation and experimental results are also given.

A single-switch continuous-conduction-mode boost converter with reduced reverse-recovery and switching losses

A single-switch continuous-conduction-mode boost converter with reduced reverse-recovery and switching losses is proposed. By utilizing the leakage inductances of a pair of coupled inductors and two additional rectifiers, the turn-off rates (di/dt) of the boost output rectifier and the additional rectifiers are slowed down to reduce the reverse-recovery loss. The boost power transistor is also operated under a low-voltage turn-on condition to reduce the switching loss. Experimental results are presented to confirm the theoretical analysis and the performance of the proposed converter.

Interleaved three-phase forward converter using integrated transformer

An interleaved three-phase forward converter using an integrated transformer is proposed in this paper. This type of converter has the attractive features of flexible voltage conversion ratio, high output current (due to the parallel connection of outputs), near-zero output-current ripple (due to the output-current-ripple cancellation), fast transient response (due to the small effective output-filtering inductance), and is particularly suitable for high-output-current and low-output-voltage applications such as telecommunication and computer systems. The integrated transformer of the proposed converter consists of three step-down transformers on a single magnetic core. The z-parameter (gyrator) model and the equivalent-circuit model of the integrated transformer are derived. Based on the equivalent-circuit model, the principle of operation of the proposed converter is explained. The analysis and design criteria of the basic circuit, the operation of the regenerative LC snubber circuit, the simulation, and experimental verification are also described.

Simple approximations of the DC flux influence on the core loss power electronic ferrites and their use in design of magnetic components

The effect of DC flux on the core loss is examined for the practical range of power and frequency. Relevant core loss equations are derived and applied to an optimization algorithm to determine the minimum core loss at a given ratio of s (DC flux density to AC peak flux density). It has been found that the curves of hysteresis loss density versus the ratio of s exhibit a peak at a critical ratio. Below or above this critical ratio, the loss density decreases drastically. On the other hand, the curves of eddy-current loss density versus the ratio of s exhibits a minimum point at a critical ratio. Below or above this critical ratio, the loss density increases gradually.

Simulation and design of integrated magnetics for power converters

We introduce a method to use z parameters to model the interface between an electric circuit and a magnetic component. With this model, the electrical equivalent circuit of any complex integrated magnetic component can be developed easily. We describe the simulation and design of integrated magnetics using a z-parameter two-port network model. We use a single-switch regulator with power-factor-correction and a single integrated magnetic component as an example to demonstrate the practical applications of integrated magnetics in modern power converters. For the same example, we analyze the problem of uneven magnetic flux density in an integrated magnetic component and propose a possible solution to the problem.

A new approach to the modeling of converters for SPICE simulation

An approach to the modeling of DC-DC converters for SPICE simulation is developed in which the average current in the energy-storage inductor is first simulated in a SPICE subcircuit for both the continuous and discontinuous modes of operation. The inductor current is then weighted and redistributed to related branches of the circuit to simulate the average input and output currents of the converter. Based on this technique, various converter models, including that of the Cuk converter with coupled inductors, which are valid for both continuous and discontinuous modes of operation, are developed. >

Design, modeling, and analysis of integrated magnetics for power converters

Some guidelines on the synthesis of integrated magnetics are introduced. Potential problems of integrated magnetics are identified. PSpice models are developed for computer-aided analysis and design purposes. A boost-flyback SSIPP (single-stage isolated power-factor-corrected power supply) with regenerative clamping is used as an example circuit to verify the application and performance of integrated magnetics.

A current-sharing interface circuit with new current-sharing technique

This paper proposes a current-sharing (CS) circuit for parallel power modules. The interface circuit enables the outputs of independent and nonidentical power modules to equally share the load current in a fault-tolerant oring-connection power supply system. No CS interconnections among the power modules are required. In the proposed interface circuit, the output currents of the parallel power modules are sensed by measuring the inductor voltage drops and controlled in a hysteresis manner. A practical CS interface circuit is implemented. The experimental results are in good agreement with the theoretical analyses.

A new approach to the analysis and design of integrated magnetics

The electrical equivalent circuits of electric-magnetic interfaces, inductors, and transformers are introduced. The analysis and design of integrated magnetics using these electrical equivalent circuits is described. The uneven flux density problem of integrated magnetics is studied. A possible solution to the problem is proposed. A boost-flyback SSIPP (single-stage isolated power-factor-corrected power supply) with regenerative clamping is used as an example to verify the application and performance of integrated magnetics.

Media noise, nonlinear distortions, and thermal stability in high density recording

Low media noise and high thermal stability are required to achieve high density magnetic recording. Reduction of magnetic grain size is required in order to minimize transition jitter. However, very small grains become unstable and spontaneously reverse their magnetization due to thermal fluctuations. Future high density (>20 Gbit/in/sup 2/) recording systems are likely to operate in a media noise dominated environment and could exhibit a certain amount of signal decay. Recording performance degradation caused by media noise and thermal decay is evaluated. Density-dependent amplitude decay is caused by the presence of demagnetization fields and results in increasing level of nonlinear distortions and overwrite degradation. Magnetization decay is accompanied by changes in media noise in an unstable media as determined by the relative contributions of the transition and particulate noises. Experimental measurements suggest, that channel bit error rate degradation in an unstable medium is determined by signal and noise evolution, as well as by pattern-dependent distortions.