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Author

Shu Wang

Bio: Shu Wang is an academic researcher from Nanjing University. The author has contributed to research in topics: Harmonics & Capacitor. The author has an hindex of 2, co-authored 2 publications receiving 403 citations.

Papers
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Journal ArticleDOI
Shu Wang1, Xinbo Ruan1, Kai Yao1, Siew-Chong Tan, Yang Yang1, Zhihong Ye 
16 Dec 2011
TL;DR: In this paper, a flick-free electrolytic capacitor-less single-phase ac-dc driver for LED lighting is proposed, which consists of an electrolytic capacitive-less PFC converter and a bidirectional converter, which serves to absorb the ac component of the pulsating current of the PFC converters.
Abstract: The electrolytic capacitor is the key component that limits the operating lifetime of LED drivers. If an ac-dc LED driver with power factor correction (PFC) control is allowed to output a pulsating current for driving the LEDs, the electrolytic capacitor will no longer be required. However, this pulsating current will introduce light flicker that varies at twice the power line frequency. In this paper, a configuration of flicker-free electrolytic capacitor-less single-phase ac-dc driver for LED lighting is proposed. The configuration comprises an electrolytic capacitor-less PFC converter and a bidirectional converter, which serves to absorb the ac component of the pulsating current of the PFC converter, leaving only a dc component to drive the LEDs. The output filter capacitor of the bidirectional converter is intentionally designed to have a large voltage ripple, thus its capacitance can be greatly reduced. Consequently, film capacitors can be used instead of electrolytic capacitors, leading to the realization of a flicker-free ac-dc LED driver that has a long lifetime. The proposed solution is generally applicable to all single-phase PFC converters. A prototype with 48-V, 0.7-A output is constructed and tested. Experimental results are presented to verify the effectiveness of the flick-free electrolytic capacitor-less ac-dc LED driver.

366 citations

Journal ArticleDOI
TL;DR: In this article, the relationship between the peak-to-average ratio and the injected harmonics is discussed, and the optimum injected third and fifth harmonics to minimize the peak to average ratio are obtained, while ensuring that the input power factor is higher than 0.9 to meet the regulatory requirement such as ENERGY STAR.
Abstract: The lifetime of an ac-dc LED driver can be increased by eliminating the electrolytic capacitor. Unfortunately, it results in pulsation with twice the line frequency in the driving current. Injection of the third and fifth harmonics into the input current can reduce the peak-to-average ratio of the driving current, which is beneficial for reliable operation of the LEDs. This letter discusses the relationship between the peak-to-average ratio and the injected harmonics, and the optimum injected third and fifth harmonics to minimize the peak-to-average ratio are obtained, while ensuring that the input power factor is higher than 0.9 to meet the regulatory requirement such as the ENERGY STAR. This optimum injected current harmonics is verified by a flyback-based electrolytic capacitor-less LED driver with 25 V, 0.35 A output.

100 citations

DOI
08 Jul 2022
TL;DR: In this paper , the authors quantitatively analyzes the relationship between the sharing of negative current and sensitive node VUF suppression and proposes a distributed control strategy that can share unbalanced power among VCM and CCM inverters accurately and suppress sensitive nodes VUF effectively.
Abstract: With the large-scale access of distributed generation in the distribution network, operation control of the distribution network faces new challenges. Unbalanced distortion has emerged as one of the critical power quality problems for the distribution network, which has escalated especially due to the high application of unbalanced loads. This paper first quantitatively analyzes the relationship between the sharing of negative current and sensitive node VUF suppression and proposes a distributed control strategy that can share unbalanced power among VCM and CCM inverters accurately and suppress sensitive node VUF effectively. The strategy does not need to know the line parameters and is robust to load changes. Finally, the proposed method is verified through the simulation results based on MATLAB/Simulink.
Journal ArticleDOI
TL;DR: In this paper , a distributed control strategy that facilitates an effective suppression of output voltage and grid-connected current, with accurate unbalanced/harmonic power sharing, is proposed, which is independent of line parameters and robust to load changes.
Abstract: In the contemporary distribution network, unbalanced and harmonic distortions have been considered some major power quality problems, which have escalated especially due to the high penetration of unbalanced and nonlinear loads. This study first analyzes the dispute around the distortion restraint and grid-connected unbalanced/harmonic current suppression quantitatively and proposes a distributed control strategy that facilitates an effective suppression of output voltage and grid-connected current, with accurate unbalanced/harmonic power sharing. Compared with the majority of existing studies only addressing the voltage-controlled mode (VCM) inverters, our scheme can also be applied to current-controlled mode (CCM) inverters without adding additional current regulation loops. The proposed control strategy is independent of line parameters and robust to load changes. The corresponding small-signal dynamic model is constructed to analyze the system stability and the controller hardware-in-the-loop simulations aid in determining the outcome of the proposed strategy.

Cited by
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Journal ArticleDOI
TL;DR: In this paper, a thorough study for different power decoupling techniques in single-phase microinverters for grid-tie PV applications is presented, compared and scrutinized in scope of the size of decoupled capacitor, efficiency, and control complexity.
Abstract: The reliability of the microinverter is a very important feature that will determine the reliability of the ac-module photovoltaic (PV) system. Recently, many topologies and techniques have been proposed to improve its reliability. This paper presents a thorough study for different power decoupling techniques in single-phase microinverters for grid-tie PV applications. These power decoupling techniques are categorized into three groups in terms of the decoupling capacitor locations: 1) PV-side decoupling; 2) dc-link decoupling; and 3) ac-side decoupling. Various techniques and topologies are presented, compared, and scrutinized in scope of the size of decoupling capacitor, efficiency, and control complexity. Also, a systematic performance comparison is presented for potential power decoupling topologies and techniques.

458 citations

Journal ArticleDOI
Yao Sun1, Yonglu Liu1, Mei Su1, Wenjing Xiong1, Jian Yang1 
TL;DR: In this paper, the authors provide a comprehensive review of active power decoupling circuit topologies and their development laws from the view of the dual principle, switch sharing, and differential connection.
Abstract: Active power decoupling methods are developed to deal with the inherent ripple power at twice the grid frequency in single-phase systems generally by adding active switches and energy storage units. They have obtained a wide range of applications, such as photovoltaic (PV) systems, light-emitting diodes (LEDs) drivers, fuel cell (FC) power systems, and electric vehicle (EV) battery chargers, etc. This paper provides a comprehensive review of active power decoupling circuit topologies. They are categorized into two groups in terms of the structure characteristics: independent and dependent decoupling circuit topologies. The former operates independently with the original converter, and the latter, however, shares the power semiconductor devices with the original converter partially and even completely. The development laws for the active power decoupling topologies are revealed from the view of “duality principle,” “switches sharing,” and “differential connection.” In addition, the exceptions and special cases are also briefly introduced. This paper is targeted to help researchers, engineers, and designers to construct some new decoupling circuit topologies and properly select existing ones according to the specific application.

395 citations

Journal ArticleDOI
TL;DR: 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 as discussed by the authors.
Abstract: 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.

210 citations

Journal ArticleDOI
TL;DR: In this paper, the authors present a literature overview of power decoupling in single-phase applications and present the best reference on this topic, which can be implemented as series or parallel with respect to the ac, dc or link side.
Abstract: This paper presents a literature overview of all techniques proposed until the submission of this paper in terms of mitigating power oscillation in single-phase applications. This pulsating energy is the major factor for increasing the size of passive components and power losses in the converter and can be responsible for losses or malfunctioning of the dc sources. Reduction of power ripple at twice the fundamental frequency is one of the key elements to increase power converter density without lack of dc stiffness. Pulsation reduction is achieved by incorporating control techniques or auxiliary circuitries with energy storage capability in reactive elements to avoid this oscillating power to propagate through the converter, creating what is called as single-phase power decoupling. The topologies are divided as: rectifiers, inverters, and bidirectional. Among them, it is possible to classify as isolated and nonisolated converters. The energy storage method may be classify as: capacitive and inductive. For the power decoupling technique, it is convenient to divide as control and topology. The power decoupling technique may be implemented as series or parallel with respect to the ac, dc or link side. This paper represents the best reference on this topic.

165 citations

Journal ArticleDOI
TL;DR: Benefits and disadvantages of different LED drivers are discussed and a detailed technology review is presented which is good for researchers and engineers to make right choices in design and selection of LED drivers.
Abstract: Light-emitting diode (LEDs) have a promising prospect because of its outstanding advantages: 1) long lifetime, 2) environmentally friendly, 3) flexibility of color mixing, 4) high illumination efficiency, etc. Based on the electrical characteristics of LEDs, a constant current driver is needed to support the LED working performance. With the wide applications of LEDs, many new technologies are presented. In this paper, advantages and disadvantages of different LED drivers are discussed. A detailed technology review is presented which is good for researchers and engineers to make right choices in design and selection of LED drivers.

164 citations