Integration of an Active Filter and a Single-Phase AC/DC Converter with Reduced Capacitance Requirement and Component Count

Existing methods of incorporating an active filter into an AC/DC converter for eliminating electrolytic capacitors usually require extra power switches. This inevitably leads to an increased system cost and degraded energy efficiency. In this paper, a concept of active-filter integration for single-phase AC/DC converters is reported. The resultant converters can provide simultaneous functions of power factor correction, DC voltage regulation, and active power decoupling for mitigating the low-frequency DC voltage ripple, without an electrolytic capacitor and extra power switch. To complement the operation, two closed-loop voltage-ripple-based reference generation methods are developed for controlling the energy storage components to achieve active power decoupling. Both simulation and experiment have confirmed the eligibility of the proposed concept and control methods in a 210-W rectification system comprising an H-bridge converter with a half-bridge active filter. Interestingly, the end converters (Type I and Type II) can be readily available using a conventional H-bridge converter with minor hardware modification. A stable DC output with merely 1.1% ripple is realized with two 50-μF film capacitors. For the same ripple performance, a 900-μF capacitor is required in conventional converters without an active filter. Moreover, it is found out that the active-filter integration concept might even improve the efficiency performance of the end converters as compared with the original AC/DC converter without integration

Self-Configurable Current-Mirror Circuit With Short-Circuit and Open-Circuit Fault Tolerance for Balancing Parallel Light-Emitting Diode (LED) String Currents

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An evolutionary Monte Carlo algorithm for identifying short adjacent repeats in multiple sequences

Evolutionary Monte Carlo (EMC) algorithm is an effective and powerful method to sample complicated distributions. Short adjacent repeats identification problem (SARIP), i.e., searching for the common sequence pattern in multiple DNA sequences, is considered as one of the key challenges in the field of bioinformatics. A recently proposed Markov chain Monte Carlo (MCMC) algorithm has demonstrated its effectiveness in solving SARIP. However, high computation time and inevitable local optima hinder its wide application. In this paper, we apply EMC to parallelize the MCMC algorithm to solve SARIP. Our proposed EMC scheme is implemented on a parallel platform and the simulation results show that, compared with the conventional MCMC algorithm, EMC not only improves the quality of final solution but also reduces the computation time. ©2010 IEEE.published_or_final_versionThe 2010 IEEE International Conference on Bioinformatics and Biomedicine (BIBM), Hong Kong, China, 18-21 December 2010. In Proceedings of BIBM, 2010, p. 643-64

A new noncontact method for the prediction of both internal thermal resistance and junction temperature of white light-emitting diodes

Although critical to the lifetime of LED, the junction temperature of LED cannot be measured easily. Based on the general photoelectrothermal theory for LED systems, the coefficient for the reduction of luminous efficacy with junction temperature is first related to the characteristic temperature of the LED. Then, a noncontact method for estimating the internal junction temperature T j and junction-case thermal resistance R jc of LED from the external power and luminous flux measurements is presented and verified practically. Since these external measurements can be obtained easily, the proposal provides a simple tool for checking T j in new LED system designs without using expensive or sophisticated thermal monitoring equipment for the LED junctions. The proposed method has been checked with measurements on LED devices from three different brands with both constant and nonconstant R jc. The theoretical predictions are found to be highly consistent with practical measurements. © 2011 IEEE.published_or_final_versio

Novel self-configurable current-mirror techniques for reducing current imbalance in parallel Light-Emitting Diode (LED) strings

Traditional current-mirror methods require one fixed current reference for controlling other current source or sources. In this paper, a new self-configurable current-mirror method that can dynamically determine the best current branch as the current reference in order to ensure good balance of all parallel current sources is proposed. The operating principle involves a dynamic and self-configurable transistor-based current-balancing circuit that can be operated in saturation or linear mode. In either operating mode, good current balance or sharing among all parallel-connected current sources can be guaranteed. The novel current-balancing circuit does not require a separate power supply for powering their control circuits. The proposal is a modular one that can be expanded to any number of parallel current sources. Its principle has been successfully applied to current balancing of parallel LED strings. © 2011 IEEE.published_or_final_versio

Direct AC/DC Rectifier With Mitigated Low-Frequency Ripple Through Inductor-Current Waveform Control

In a rectification system with unity power factor, the input power consists of a dc and a double-line frequency power component. Traditionally, an electrolytic capacitor (E-Cap) is used to buffer the double-line frequency power such that the dc output presents a small voltage ripple. The use of E-Cap significantly limits the lifetime of the rectifier system. In this paper, a differential ac/dc rectifier based on the use of an inductor-current waveform control methodology is proposed such that a single-stage direct ac/dc rectification without the need of an E-Cap for buffering the double-line frequency power, and a front-stage diode rectifier circuit can be achieved. The feasibility of the proposal has been practically confirmed in an experimental prototype.published_or_final_versio

Direct AC/DC rectifier with mitigated low-frequency ripple through waveform control

In a rectification system with unity power factor, the input power consists of a DC and a double-line frequency power component. Traditionally, an electrolytic capacitor (E-Cap) is used to buffer the double-line frequency power such that the DC output presents a small voltage ripple. The use of E-Cap significantly limits the lifetime of the rectifier system. In this paper, a differential AC/DC rectifier based on the use of an inductor-current waveform control methodology is proposed. The proposed configuration achieves single-stage direct AC/DC rectification without the needs of a front-stage diode rectifier circuit, an input EMI filter, and an E-Cap for buffering the double-line frequency power. The feasibility of the proposal has been practically confirmed in an experimental prototype. © IEEE.published_or_final_versio

Power Flow Analysis and Critical Design Issues of Retrofit Light-Emitting Diode (LED) Light Bulb

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A review and classification of LED ballasts

This paper presents a review on existing ballasts for light-emitting diodes (LED) with considerations to their compliance to regulations, technological challenges, and on meeting various application requirements. All existing LED ballasts, including those proposed in recent literature, have been appropriately classified and systematically organized for the discussion. The dissemination of this information and its understanding is helpful for future R&D pursuits in this area. © 2013 IEEE.published_or_final_versio