A review on flicker-free ac-dc LED drivers for single-phase and three-phase ac power grids

Light-Emitting Diodes (LEDs) are coming strongly into the lighting market due to their advantages over conventional lighting solutions: energy efficient, controllable in both light and color, long lifetime, lack of a warm-up period and high power density. Some of these advantages will make LED light sources to be more than just a lightbulb, being able to transmit data, control light color, hue and intensity or even detect people in indoor environments. Nevertheless, these advantages attributed to LED capabilities are, in reality, achieved thanks to the LED driver. The present work reviews the current stateof- the-art strategies to drive LEDs from ac power grids with special emphasis into removing the most limiting component from the point of view of the lifetime, which is the electrolytic capacitor, while achieving a flicker-free performance of the light output of the LED driver. Moreover, it focuses on analyzing the required regulations, challenges and applicability of LED drivers in both single-phase and three-phase ac power gridsTrabajo apoyado en parte por el Gobierno español en virtud del Proyecto MINECO-17-DPI2016-75760-R, por el Principado de Asturias bajo la subvención BP14-142 de Severo Ochoa y el Proyecto GRUPIN2018 JAVIER SEBASTIAN, y en parte por el Fondo Europeo de Desarrollo Regional (FEDER

A flicker-free electrolytic capacitor-less AC-DC LED driver

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A Survey, Classification and Critical Review of Light-Emitting Diode Drivers

Based on a survey on over 1400 commercial LED drivers and a literature review, a range of LED driver topologies are classified according to their applications, power ratings, performance and their energy storage and regulatory requirements. Both passive and active LED drivers are included in the review and their advantages and disadvantages are discussed. This paper also presents an overall view on the technical and cost aspects of the LED technology, which is useful to both researchers and engineers in the lighting industry. Some general guidelines for selecting driver topologies are included to aid design engineers to make appropriate choices.published_or_final_versio

Multi-cell three phase ac-dc driver for HB-LED lighting applications

High Brightness Light-Emitting Diodes (HB-LEDs) are becoming omnipresent across all aspects of illumination products, due to their incredible characteristics: efficiency, reliability, long lifetime, controllability, etc. This paper proposes power conversion topologies to drive medium to high power HB-LEDs in three phase power grids when these connection is available. For that reason, an evaluation of several drivers for medium to high power HB-LEDs in three-phase power grids is done. Moreover, a new topology is proposed which complies with IEC 1000-3-2 Class C requirements, achieves high Power Factor (PF), low Total Harmonic Distortion (THD), as well as, the capability to have a flicker free behaviour while disposing of the bulk capacitor and having galvanic isolation. The HB-LED driver is based on a modular approach with several cells working together with their inputs connected to the three-phase network and their outputs connected in parallel generating a dc output. Each one of these cells is a DC-DC converter operating as a Loss Free Resistor (LFR). In order to validate the concept a prototype has been built by the use of flyback converters operating in Discontinuous Conduction Mode (DCM). Furthermore, it operates in the full range of the European three-phase line voltage, which varies between 380V and 420V, and it supplies an output voltage of 48V with maximum power of 90

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

A Single-Stage LED Driver Based on ZCDS Class-E Current-Driven Rectifier as a PFC for Street-Lighting Applications

This paper presents a light-emitting diode (LED) driver for street-lighting applications that uses a resonant rectifier as a power-factor corrector (PFC). The PFC semistage is based on a zero-current and zero-derivative-switching (ZCDS) Class-E current-driven rectifier, and the LED driver semistage is based on a zero-voltage-switching (ZVS) Class-D LLC resonant converter that is integrated into a single-stage topology. To increase the conduction angle of the bridge-rectifier diodes current and to decrease the current harmonics that are injected in the utility line, the ZCDS Class-E rectifier is placed between the bridge-rectifier and a dc-link capacitor. The ZCDS Class-E rectifieris driven by a high-frequency current source, which is obtained from a square-wave output voltage of the ZVS Class-D LLC resonant converter using a matching network. Additionally, the proposed converter has a soft-switching characteristic that reduces switching losses and switching noise. A prototype for a 150-W LED street light has been developed and tested to evaluate the performance of the proposed approach. The proposed LED driver had a high efficiency (>91%), a high PF (>0.99), and a low total harmonic distortion (THD i <; 8%) under variation of the utility-line input voltage from 180 to 250 V rms . These experimental results demonstrate the feasibility of the proposed LED scheme

Modular three-phase ac-dc LED driver based on summing the light output of each phase

IEEE Applied Power Electronics Conference and Exposition, San Antonio, (Estados Unidos de Norteamérica), marzo de 2018This work proposes the driving of high power Light-Emitting Diodes (LEDs) luminaires in three phase power grids using each phase to drive an independent LED load. The driving is done by means of a boost converter in charge of controlling the current across its LED load. Moreover, each boost converter needs to achieve Power Factor Correction (PFC) to comply with IEC 61000-3-2 Class C requirements. Hence, achieving unity Power Factor (PF) and low Total Harmonic Distortion (THD). Taking advantage of the light properties, the output of the LED driver will be the sum of the light of each of the phases. Therefore, a theoretical study will be carried out to observe the feasibility of removing the electrolytic capacitor while guaranteeing a flicker free behaviour of the LED luminaire, even if the current of each string is pulsating at twice the mains frequency. In order to validate the study, a prototype has been built comprised of three PFC boost converters disposing of their electrolytic capacitors. The designed prototype operates in the full range of the European three-phase line voltage, which varies between 380 V and 420 V, and it supplies an output light of 42.000 lm at a maximum power of 300 W while achieving an electrical efficiency of 97.5

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

High-efficiency asymmetrical half-bridge converter without electrolytic capacitor for low-output-voltage AC-DC LED drivers

Due to their high reliability and luminous efficacy, high-brightness light-emitting diodes are being widely used in lighting applications, and therefore, their power supplies are required to have also high reliability and efficiency. A very common approach for achieving this in ac-dc applications is using a two-stage topology. The power factor corrector boost converter operating in the boundary conduction mode is a very common converter used as first stage. It is normally designed without electrolytic capacitors, improving reliability but also increasing the low-frequency ripple of the output voltage. The asymmetrical half-bridge (AHB) is a perfect option for the second stage as it has very high efficiency, it operates at constant switching frequency, and its output filter is small (i.e., it can be also easily implemented without electrolytic capacitors). Moreover, the AHB is an excellent candidate for self-driven synchronous rectification (SD-SR) as its transformer does not have dead times. However, the standard configuration of the SD-SR must be modified in this case in order to deal with the transformer voltage variations due to the input voltage ripple and, more important, due to the LED dimming state. This modification is presented in this paper. Another important issue regarding the AHB is that its closed-loop controller cannot be very fast and it cannot easily cancel the previously mentioned low-frequency ripple. In this paper, a feed-forward technique, specifically designed to overcome this problem, is also presented. The experimental results obtained with a 60-W topology show that efficiency of the AHB may be very high (94.5%), while the inherent control problems related to the AHB can be overcome by the proposed feed-forward techniqueThis work has been supported by Spanish Government under projects RUE-10-CSD2009-00046 FEDER Funds and MICINN10-DPI2010-21110-C02-01 and by company AEG Power Solutions B.V. under project FUO-EM-002-1

A sustained increase of input current distortion in active input current shapers to eliminate electrolytic capacitor for designing ac to dc HB-LED drivers for retrofit lamps applications

Nowadays, the solid-sate lighting technology evolution has changed traditional solutions in lighting. High-Brightness Light–Emitting Diodes (HB-LEDs) have become very attractive light sources due to their excellent characteristics: high efficiency, high life-time and low maintenance. It is evident that HB-LED drivers must be durable and efficient to achieve these advantages. Moreover, for replacing incandescent bulbs, the ac-dc HB-LED driver must be low cost and comply with international regulations (i.e. injection of low frequency harmonics into the mains). Traditionally, authors have focused its efforts on increasing efficiency. All these solutions obviate the elimination of traditional electrolytic capacitor of ac to dc converters, highlighting that this is the price to pay for a very low-cost solution. This paper presents a new proposal to design a simple and low-cost ac to dc HB-LED driver for retrofit lamps without electrolytic capacitor. The proposed solution comes from a very well-known technique used in the past: Active Input Current Shapers (AICS), but in this case without electrolytic capacitor. If the electrolytic capacitor of an AICS is removed, then low frequency ripple arises in its intermediate dc bus, increasing the distortion of the line input which already has appreciable distortion. However, the increase of distortion is very slight. Also, the low frequency ripple is not transferred to the output due to the high output dynamic response of AICS, avoiding flickering. This paper presents a theoretical analysis that guarantees a trade of between compliance with international regulations and the use of other capacitor technologies different from the electrolytic one. Finally, a 24W experimental prototype has been built and tested in order to validate the theoretical results presented in this digestSpanish Ministry of Education and Science under Project MINECO-13-DPI2013-47176- C2-2-R, by Government of the Principality of Asturias under the Project FC-15-GRUPIN14-143 and by European Regional Development Fund (ERDF) grant