Showing papers by "Khai D. T. Ngo published in 1995"
TL;DR: In this article, a hybrid pulsewidth modulation (HPWM) method was proposed, which requires only two of the four switches in a full-bridge inverter to be pulsewidth-modulated at high frequency, thus reducing the switching losses in the other two switches.
Abstract: This paper presents the "hybrid pulsewidth modulation" (HPWM) method which requires only two of the four switches in a full-bridge inverter to be pulsewidth-modulated at high frequency, thus significantly reducing the switching losses in the other two switches. For triangular carriers, HPWM has the same frequency spectrum and switching losses as the conventional unipolar PWM (UPWM). A low-frequency model for a fast-switching HPWM full-bridge inverter with high-quality output is described, and is substantiated by experimental data. >
142 citations
05 Mar 1995
TL;DR: In this article, the design issues concerning the construction of planar windings for modern magnetic components are presented, along with some practical methods to achieve low winding resistances, and three representative pattern types are explored, namely, the circular, rectangular, and spiral patterns.
Abstract: Design issues concerning the construction of planar windings for modern magnetic components are presented, along with some practical methods to achieve low winding resistances. Three representative pattern types are explored, namely, the circular, rectangular, and spiral patterns. Equations for predicting the resistances are developed for windings with constant- and variable-width turns. Resistance measurement of a sample winding design is presented and compared with analytical prediction. >
41 citations
TL;DR: In this paper, the suitability of the sandwiched-winding matrix HF power transformer for low-profile applications from the loss standpoint was evaluated and it was shown that the core loss can be adequately characterized by approximating the matrix transformer as a collection of identical uncoupled elements.
Abstract: This paper assesses the suitability of the sandwiched-winding matrix HF power transformer for low-profile applications from the loss standpoint. Finite-element simulations and experiments suggest that the core loss can be adequately characterized by approximating the matrix transformer as a collection of identical uncoupled elements. Thus, a matrix transformer with a large number of elements may have higher core loss than a conventional (tall) transformer, and more core loss than winding loss. Eddy-current analysis reveals that the interconnects which parallel the elements incur a significant fraction of the winding loss. Thus, load distribution is recommended to eliminate the paralleling interconnects in matrix transformers. >
37 citations
18 Jun 1995
TL;DR: In this article, the configuration of the Hammerstein model, which includes a nonlinear static block followed by a linear dynamic block, is applied to model the dynamics of the insulated gate bipolar transistor (IGBT).
Abstract: The configuration of the Hammerstein model, which includes a nonlinear static block followed by a linear dynamic block, is applied to model the dynamics of the insulated gate bipolar transistor (IGBT). Using least-squares methods, the parameters in the proposed behavioral model can be extracted from the electrical measurements of physical devices or from the circuit simulations of physics-based models. In this work, a physics-based IGBT model is used for extracting the model parameters and for comparison. This Hammerstein-like model structure of the behavioral model gives satisfactory simulation results for various test circuits in terms of efficiency and accuracy. >
30 citations
TL;DR: In this article, two operating modes have been identified for a matrix inductor/transformer made by weaving conductors through the holes perforated in a flat magnetic plate, which is analyzed to assess its suitability for low-profile power converters.
Abstract: Two operating modes have been identified for a matrix inductor/transformer made by weaving conductors through the holes perforated in a flat magnetic plate. The Mode-1 perforated-plate matrix transformer (M1PPMT) is analyzed to assess its suitability for low-profile power converters. Analysis and finite-element simulation suggest that this type of transformer may be approximated as a collection of weakly coupled "toroidal" cores. Thus, it is possible to derive closed-form expressions relating typical performance parameters, such as magnetizing inductance and losses, to the hole radius, identified as a meaningful design parameter. High peak flux density around the holes appears to be a problem. Nevertheless, it is possible to design a 100 W M1PPMT with acceptable magnetizing inductance, efficiency, and power density. >
8 citations
TL;DR: An analytical approach to model the inductance of the perforated-plate matrix inductor/transformer (M2PPMI) is presented in this article, which is guided by finite-element simulation, and has been verified experimentally.
Abstract: As the Mode-1 perforated-plate matrix transformer/inductor (M1PPMT), the Mode-2 perforated-plate matrix inductor/transformer (M2PPMI) is attractive for the construction of low-profile inductors and transformers for switched-mode power converters. Finite-element simulation suggests that the M2PPMI may be approximated as weakly coupled "U-cores". Conventional inductance formulae for U-cores, however, can underestimate the inductance of the M2PPMI by as much as 50%, the error source being the magnetic material in the winding windows. An analytical approach to model the inductance of the M2PPMI is presented here. The approach is guided by finite-element simulation, and has been verified experimentally. It suggests design guidelines for practical applications of perforated-plate magnetic devices. >