A unified analysis of PWM converters in discontinuous modes

Three discontinuous operating modes of PWM (pulsewidth modulated) converters are considered: the discontinuous inductor current mode (DICM), the discontinuous capacitor voltage mode (DCVM), and a previously unidentified mode called the discontinuous quasi-resonant mode (DQRM). DC and small-signal AC analyses are applicable to all basic PWM converter topologies. Any particular topology is taken into account via its DC conversion ratio in the continuous conduction mode. The small-signal model is of the same order as the state-space averaged model for the continuous mode, and it offers improved predictions of the low-frequency dynamics of PWM converters in the discontinuous modes. It is shown that converters in discontinuous modes exhibit lossless damping similar to the effect of the current-mode programming     

Non-stationary thermal model of indoor transformer stations

The paper presents a thermal model of an indoor transformer station. The model includes generation of heat and its transfer from the transformer active parts to the surrounding air, natural air ventilation through ventilation holes, and convection and conduction transfer of heat through room parts. All parameters of the model are discussed and the procedure, based on measurements, for the determination of natural air ventilation parameters is described. The model is tested using measurements on a typical indoor 10 kV/0.4 kV transformer station. The results of the proposed thermal model and those of a simplified approach from Standards are compared. Received: 24 July 2001/Accepted: 20 November 2001     

Modeling and simulation of power electronic converters

This paper reviews some of the major approaches to modeling and simulation in power electronics, and provides references that can serve as a starting point for the extensive literature on the subject. The major focus of the paper is on averaged models of various kinds, but sampled-data models are also introduced. The importance of hierarchical modeling and simulation is emphasized     

Design of the clamped-current high-power-factor boost rectifier

This paper examines a high-power-factor boost rectifier where the peak switch current is clamped at a constant value during the input voltage line cycle. Optimum parameter values are derived to minimize the harmonic distortion in the input current. Advantages of the clamped-current control include overall simplicity, relatively low inductive energy storage and component stresses, and a fixed operating frequency. Results are experimentally verified on a 1.3 kW prototype featuring high efficiency and high power factor over a wide load range     

Online calibration of MOSFET on-state resistance for precise current sensing

An approach for online current sensing calibration is presented where an auxiliary switch and a precision sense resistor are connected in parallel with a main power switch to achieve accuracy comparable to the sense resistor method, together with the advantage of essentially no additional power loss. The proposed current-sensing circuit and the calibration methods are particularly well suited for digital controller implementations where the required control and calibration functions can be easily accomplished. Experimental results with a digitally controlled 1.5-V 15-A synchronous buck converter demonstrate functionality of the online calibration approach, showing a significant improvement in accuracy over voltage sensing across the power MOSFET on-resistance.     

A new algorithm for simulation of power electronic systems usingpiecewise-linear device models

This paper describes a new algorithm for simulation of power electronic systems. Piecewise-linear (PWL) approximation is used to model nonlinear components, including switching devices, nonlinear reactive components, and nonlinear control circuitry. A representation of PWL elements is constructed such that a constant system matrix is obtained, regardless of the states of PWL elements. An efficient method for state determination is proposed, which is capable of resolving difficulties caused by discontinuous characteristics of PWL elements. The resulting simulation algorithm is quite general, requires no prior knowledge of the circuit operation, is void of convergence problems, and yields relatively short simulation times on desktop PC machines     

An ESD test reduction method for complex devices

We define rules to reduce the ESD test complexity for chips with large pin count. These rules exploit the structural similarity in the pad-ring and have a long history of use without bad experiences. Using these rules an automated software tool can be developed for reduced ESD test generation.     

Switched-capacitor DC/DC converters with resonant gate drive

In this paper, we examine how switched-capacitor (SC) converters can be used in low-voltage low-power DC/DC applications with power management. Analysis of losses is presented to facilitate SC converter design and optimization. A resonant gate drive is proposed to reduce switching losses and simplify control of switches in SC converters. A closed-loop controller is designed to enable and disable oscillations of the resonant gate drive so that the output DC voltage is well regulated down to zero load and so that high efficiency is maintained for a very wide range of loads. Results are experimentally verified on two low-power (0.2 and 5 W) five-one step-down converters with regulated 3 Vdc output and efficiency greater than 80% in a 100-1 load range     

Dead-zone digital controllers for improved dynamic response of low harmonic rectifiers

This paper introduces a simple digital control method that enables fast regulation of the output voltage in low harmonic rectifiers with power factor correction (PFC). The method is based on the use of an insensitive region, i.e., "dead-zone," in analog-to-digital conversion, for elimination of the output capacitor voltage ripple in the feedback loop. The dead-zone can either be fixed and larger than the maximum ripple magnitude, or it can be dynamically adjusted in accordance with the output load. Simple implementations of these two dead-zone controllers are shown on an experimental completely digitally controlled 250-W boost PFC operating at 200-kHz switching frequency. The experimental results show that this control method results in low current harmonics and improved load transient responses, which are significantly faster than in low-harmonic rectifiers with conventional low-bandwidth voltage-loop controllers.