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.

A Review of LED Drivers and Related Technologies

The main function of the dc–dc converter in a grid-connected photovoltaic (PV) system is to regulate the terminal voltage of the PV arrays to ensure delivering the maximum power to the grid. The purpose of this paper is to design and practically implement a robust continuous-time model predictive control (CTMPC) for a dc–dc boost converter, feeding a three-phase inverter of a grid-connected PV system to regulate the PV output voltage. In CTMPC, the system behavior is predicted based on Taylor series expansion, raising concerns about the prediction accuracy in the presence of parametric uncertainty and unknown external disturbances. To overcome this drawback, a disturbance observer is designed and combined with CTMPC to enhance the steady-state performance in the presence of model uncertainty and unknown disturbance such as the PV current, which varies nonlinearly with the operating point. An interesting feature is that the composite controller reduces to a conventional PI controller plus a predictive term that allows further improvement of the dynamic performance over the whole operating range. The effectiveness of the proposed controller was tested numerically and validated experimentally with the consideration of the grid-connected PV inverter system and its controller.

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A Robust Continuous-Time MPC of a DC–DC Boost Converter Interfaced With a Grid-Connected Photovoltaic System

Critical conduction mode (CRM) boost power factor (PF) correction converter features zero-current turn-on for the switch and no reverse recovery in diode, which is suitable for low-to-medium power applications. However, the switching frequency varies in a line cycle, and the wide variation range of the switching frequency is different under different input voltage and load conditions. This makes the conducted electromagnetic interference (EMI) spectra appearing great differences and complicates the design of EMI filter. In this paper, based on the expression of the switching frequency for traditional CRM control strategy, a variable on-time control strategy is proposed, and the implementation circuit is designed to realize a fixed switching frequency in a half-line cycle. The proposed strategy also achieves a lower output voltage ripple and a lower peak current for the power components. In spite of the PF decrease, the input current harmonic values are much lower than the IEC 61000-3-2 Class D limits. A 120 W prototype has been fabricated and tested in the laboratory and the experimental results are presented to verify the effectiveness of the proposed method.

Critical Conduction Mode Boost PFC Converter With Fixed Switching Frequency Control

This article introduces two general ways to derive single-phase bridgeless power factor correction (PFC) topologies and then, 15 accessible bridgeless topologies are derived based on the configuration of different basic types of dc–dc converter cells. Although the majority of the topologies have been previously proposed, other possible research points are reviewed. Besides, a consistent component sizing procedure with electric, thermal, and cost models is applied to conduct the performance benchmarking of these PFC topologies in terms of power loss, volume, and cost. Three boost-type PFC topologies are chosen as examples to demonstrate the procedure and the corresponding benchmarking results with both theoretical analyses and experimental verification. Finally, mission profiles of one specific application are introduced to show the material cost payback period of adopting one modified bridgeless boost topology instead of conventional one in different scenarios.

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Single-Phase Bridgeless PFC Topology Derivation and Performance Benchmarking

Due to the global environmental issues and energy crisis, the injection of renewable energy sources (RESs) into the power system is continuously increasing. As the interface between RESs and power grid, grid-tied inverters using MOSFET switches, without traditional line frequency transformers, show some potential advantages, in terms of low cost, high efficiency, and lightweight and small size. Among several proposed configurations, the Aalborg inverter was proposed as a new family of high efficiency MOSFET-switch-based hybrid source inverters. For a conventional “half bridge” type Aalborg inverter, due to the imbalance of two independent dc sources, the input dc energies may not be fully utilized, which may reduce the efficiency of whole system. In order to extract the maximum energy from two independent dc sources, a coupled-inductor-based “half bridge” type Aalborg inverter is proposed in this paper. The principle of operation is presented and demonstrated through equivalent circuits. The effectiveness of a new energy balancing technique has been validated through simulations and experiments on a 110 V/ 500 W prototype.

Coupled-Inductor-Based Aalborg Inverter With Input DC Energy Regulation

Compared with constant duty cycle-controlled discontinuous conduction mode (DCM) boost power factor (PF) correction (PFC) converter, constant duty cycle-controlled quadratic DCM–DCM boost PFC converter features with much lower second-order line frequency output voltage ripple, and however, it suffers from low PF. To increase PF of quadratic DCM–DCM boost PFC converter, a variable duty cycle control technique for quadratic DCM–DCM boost PFC converter is presented in this paper. An approximation equivalent for the variable duty cycle is employed to simplify the implementation circuit. The corresponding expressions of PF and output voltage ripple are analyzed. For input voltage range of 100–240 Vac, quadratic DCM–DCM boost PFC converter with variable duty cycle control benefits with very high PF, and tradeoff between PF and output voltage ripple of this converter is analyzed. Experimental results from 100-W prototypes are given to verify the theoretical analysis.

Variable Duty Cycle Control for Quadratic Boost PFC Converter

Compared with conventional power factor correction topologies, although dual-converter cell-based bridgeless topologies usually have higher efficiency, most of them suffer from high component counts. Thus, this article proposes general topology simplification methods for these topologies. Besides, several selected converter cells are exemplified to show the specific topology simplification processes, and the performance of the resultant simplified topologies is reviewed. Meanwhile, based on the same design specifications, in order to provide an unbiased quantitative topology comparison in terms of power loss, cost, and volume, this article introduces a consistent component database-based design procedure with electrical, thermal, and cost models. As case studies, the conventional and two selected bridgeless buck–boost-type topologies are compared by following the design procedure. The comparison results are analyzed to provide a reference for topology selection. Three prototypes are built and tested to verify the theoretical analysis.

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Bridgeless PFC Topology Simplification and Design for Performance Benchmarking

This paper proposes a unity power factor (PF) bridgeless buck-boost power factor correction (PFC) converter to minimize conduction losses caused by the diode bridge. Moreover, compared to the conventional buck-boost PFC converter, the proposed converter has lower voltage stresses across switches, which further improves the overall efficiency of the proposed converter, especially when it operates in the light load conditions. Operation modes with inductors working in the discontinuous conduction mode (DCM) are given in detail, and comparative analysis is conducted to show the proposed converter performance regarding the PF, component stresses, and output ripple. The proposed and conventional converter prototypes with load range of 20∼100 W are built and tested. The obtained results verify merits and theoretical predictions of the proposed.

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Efficiency Enhancement of Bridgeless Buck-Boost PFC Converter with Unity PF and DC Split to Reduce Voltage Stresses

We propose a lithography-free wide-angle polarization-insensitive ultra-broadband absorber by using three pairs of tungsten (W) and calcium fluoride (CaF2) films. The simulation results show that the absorptivity is larger than 0.9 with normal incidence in the wavelength range from 400 nm to 1529 nm. By adding a pair of CaF2-W films, we can get a broader absorption bandwidth with absorptivity larger than 0.9 over the wavelength of 400-1639 nm. In addition, the absorption performance is insensitive to the polarization and angle of incidence. The electric field distributions at the absorption peaks show that the absorption is originated from the destructive interference between the reflection waves from the top and bottom interfaces of the multilayer CaF2-W films. Furthermore, the ultra-broad bandwidth is attributed to the anti-reflection effect from the increased effective refractive index from top to down of the proposed absorber. Such physical mechanism of broadening bandwidth based on anti-reflection effect provides a new idea for the design of broadband absorber. Meanwhile, this broadband absorber is a good candidate for potential applications such as detection and energy harvesting.

Zhengge Chen

Papers

Single-Phase Bridgeless PFC Topology Derivation and Performance Benchmarking

Variable Duty Cycle Control for Quadratic Boost PFC Converter

Bridgeless PFC Topology Simplification and Design for Performance Benchmarking

Efficiency Enhancement of Bridgeless Buck-Boost PFC Converter with Unity PF and DC Split to Reduce Voltage Stresses

Lithography-free wide-angle polarization-independent ultra-broadband absorber based on anti-reflection effect.