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Conventional boost power factor correction (PFC) converter is only suitable for two-stage power conversion system due to its high output voltage. Inherent step-up characteristic limits its applications in single-stage low voltage output. In this article, a boost-type single-stage step-down resonant PFC converter, which combines a boost PFC converter and a resonant switched capacitor network by using one active switch, is proposed and analyzed. Similar to conventional boost PFC converter, the proposed converter can achieve unity power factor and low input current ripple in universal-input applications. Moreover, the proposed converter can achieve step-down voltage conversion. Furthermore, high-efficiency is realized due to single-stage power conversion. The proposed converter is studied in terms of operation principle, voltage gain, power factor analysis, and key circuit parameters design. Finally, a 70-W prototype with 96.05% peak efficiency is built to verify the theoretical analysis results. [ABSTRACT FROM AUTHOR]

Conventional buck power factor correction (PFC) converter has the disadvantage of high harmonic currents, which limits its applications. In this article, a buck type single-switch integrated PFC converter is presented and analyzed. It is composed of buck and flyback PFC converters by using only one active switch, which benefits from simple control. The buck and flyback PFC converters are input-parallel and output-parallel connected. With critical conduction mode constant on time control, the effect of dead zone of buck input current is eliminated by flyback unit. Therefore, the input harmonic currents of the proposed converters can easily meet IEC61000-3-2 Class C limits. With the advantages of buck and flyback PFC converters, the proposed converter can achieve high efficiency and low total harmonic distortion in universal-input applications. Simplified steady-state analysis and design considerations are introduced in this article. Finally, a 96-W prototype with 94.5% peak efficiency is built to verify the analysis results. [ABSTRACT FROM AUTHOR]

An integrated buck–boost–buck-type single-switch multistring resonant light-emitting diode (LED) driver is proposed and analyzed. It combines buck–boost and buck converters to achieve passive current balancing and power factor correction. With this circuit configuration, the proposed LED driver employs only one low-side connection active switch, resulting in a very simple control requirement involving one closed-loop controller for regulating one output current. Other output currents can be balanced automatically by resonant capacitor and storage capacitors, making the control strategy economical. In addition, high efficiency is achieved due to single-stage power conversion. Taking three-string LED driver as an example, the proposed buck–boost–buck-type single-switch LED driver is studied in terms of operating principle, current balancing principle, power factor (PF) analysis, voltage gain, and key circuit parameter design. Finally, an 84-W high-PF three-string LED driver prototype with 94.3% peak efficiency is built to verify the analytical results. [ABSTRACT FROM AUTHOR]

A flicker-free single switch multi-string LED driver with high power factor and current balancing is proposed and analyzed. It combines a pre-stage boost PFC converter and multiple second-stage buck dc–dc converters by a single active switch and multiple dc-link capacitors. With the proposed circuit configuration of multiple dc-link capacitors, the output current of each LED string can be balanced. Therefore, by controlling the output current of one LED string, the output currents of other LED strings can be controlled via current balancing of dc-link capacitors. The effect of the ripple of dc-link voltage on each output can be eliminated by fast voltage mode control loop. Therefore, flicker-free low ripple current for each LED string is achieved. With small voltage ripple across dc-link capacitors, the turn on time of active switch is almost constant in a half line cycle. Therefore, power factor correction can be achieved with inductor current of pre-stage operating in discontinuous conduction mode (DCM). Finally, prototypes of dual-string LED driver with 90–135 Vac input and 175–265 Vac input for 47 W output power are built to verify the studied results. [ABSTRACT FROM AUTHOR]

MR16 lighting system with a high-frequency step-down electronic transformer is widely used in commercial lighting. In this paper, a single-switch quadratic boost light emitting diode (LED) driver compatible with electronic transformers for the MR16 lighting system is proposed and analyzed. It combines a prestage boost power factor correction (PFC) converter and a second-stage boost dc–dc converter with a single switch. The effect of the dc link voltage ripple of the prestage boost PFC converter on the output of the second-stage boost dc–dc converter is eliminated by a fast voltage mode control loop of a second-stage circuit. Therefore, flicker-free low ripple LED current is achieved. With a small dc link voltage ripple of prestage, the turn-on time of the active switch is almost constant in a half-line cycle. Therefore, PFC can be achieved with inductor current of prestage operating in a discontinuous conduction mode. With small input capacitance, the proposed LED driver presents a good compatibility performance with different kinds of electronic transformers. Furthermore, the proposed LED driver needs only one active switch and one control loop, which makes circuit volume small and low cost. Finally, a 4 W LED driver for a small-size MR16 lighting system is provided to verify the studied results. [ABSTRACT FROM AUTHOR]

A novel high-efficiency resonant light emitting diode (LED) backlight driver with passive current balancing and dimming is proposed and analyzed in this paper. The proposed LED driver achieves uniform brightness of each LED string by the charge balance of the resonant capacitor, which benefits from high efficiency. By controlling the output current of one LED string, the output currents of other LED strings can be controlled via current balancing of resonant capacitors, which makes its control simple. The proposed LED driver uses only one active switch, which decreases circuit volume and simplifies the control. Furthermore, a wide load range can be achieved by controlling the turn-on duty ratio of the single power switch of the LED driver with a fixed frequency. Finally, a prototype of a high-dimming-ratio small-size three-string LED driver is provided to verify the studied results. [ABSTRACT FROM PUBLISHER]

A resonant single-stage single-switch four-output LED driver with high power factor and passive current balancing is proposed. By controlling one output current, the other output currents of four-output LED driver can be controlled via passive current balancing, which makes its control simple. When magnetizing inductor current operates in critical conduction mode, unity power factor is achieved. The proposed LED driver uses only one active switch and one magnetic component, thus it benefits from low cost, small volume, and light weight. Moreover, high-efficiency performance is achieved due to single-stage power conversion and soft-switching characteristics. The characteristics of the proposed LED driver are studied in this paper and experimental results of two 110-W four-output isolated LED drivers are provided to verify the studied results. [ABSTRACT FROM AUTHOR]

A single-inductor dual-output (SIDO) buck–boost power factor correction (PFC) converter operating in critical conduction mode is proposed in this paper. By multiplexing a single inductor, each output of the SIDO buck–boost converter can be regulated independently. Compared with a conventional two-stage multiple-output converter, the SIDO buck–boost PFC converter benefits from significant overall cost saving, small size, and light weight. Moreover, the efficiency of the SIDO buck–boost PFC converter can be improved due to single-stage power conversion. The control strategy and characteristics of the proposed converter are analyzed. The efficiency, power factor, total harmonic distortion, and output accuracy are verified using the experimental results. [ABSTRACT FROM PUBLISHER]

Slow load transient performance, potential cross-regulation, and low efficiency are the major drawbacks for pseudocontinuous conduction mode single-inductor dual-output (SIDO) dc–dc converters. To overcome these drawbacks, this article proposes a voltage-ripple (VR)-based dynamic freewheeling (DF) control technique for hybrid conduction mode (HCM) SIDO buck converter. With the employment of VR controller, the proposed control technique improves the load transient performance significantly. As the fast recovery during load transition, the cross-regulation is minimized. Additionally, due to the DF controller, the freewheel current value automatically updates in each switching period, which can improve the efficiency of the HCM SIDO buck converter, especially under the light load conditions. Finally, the proposed converter has been verified through experimental results. The transient response time on 0.5 A load change takes only 1–2 switching periods. No observable cross- regulation is found and maximum efficiency of 92.03% is achieved. Finally, the experimental waveforms are presented to verify the theoretical research. [ABSTRACT FROM AUTHOR]

By the powder metallurgy, as well as subsequent forging and annealing processes, a series of W-3Re-HfC (WRH) composites were fabricated successively. Microstructure and performance of WRH composites were investigated comparatively. It is found that the sintered, forged and annealed WRH composites are consistently made up of W-Re matrix, HfO 2 and HfC second phase particles. The larger HfO 2 particle is derived from the oxidation of HfH 2 powder, playing an important role in purifying grain boundary and refining grain of matrix. The smaller HfC particle inside W-Re grains has a dispersion reinforcement effect. The forged WRH composites can obtain the highest relative density (99.9%), the micro-hardness (534.1 HV) and ultimate tensile strength (758 MPa), which is ascribed to the refinement of grains and dispersion strengthening. Although the performance of annealed WRH composites has a slight drop, an excellent interfacial matching between second phase particles and W-Re matrix can be produced, which facilitates to gain a better interfacial strength and homogenized microstructure. • Composites are composed of W-Re matrix, HfO 2 and HfC second phase particles. • The HfO 2 particle can effectively purify and pin the grain boundary. • Composites after forging can obtain superior micro-hardness and tensile strength. • Composites annealed at 1700 °C can yield an excellent interface strength. [ABSTRACT FROM AUTHOR]

A high‐efficiency multi‐string LED driver based on constant current bus with time‐multiplexing control scheme is proposed and analysed. Each LED string is connected to the constant current bus, which is provided by the output of a front‐end high‐efficiency converter. The current of each LED string can be independently controlled by the turn on duty ratio of its time‐multiplexing switch. A capacitor is connected to the current bus to provide a current flowing path for constant bus current when none of the LED string is connected to the current bus. It needs only one output filter capacitor, which makes circuit volume small and cost low. Finally, a 7.2 W two‐string LED driver is provided to verify the studied results. [ABSTRACT FROM AUTHOR]

A resonant two‐string LED driver with power factor correction and passive current sharing is proposed. By controlling one output current, the other output current of the two‐string LED driver can be controlled via passive current sharing, which makes its control simple. The proposed converter uses only one active switch and one magnetic component with single‐stage power conversion, thus it benefits from low cost, small volume, light weight and high efficiency. The proposed converter is studied and experimental results of a 75 W two‐string LED driver are provided to verify the studied results. [ABSTRACT FROM AUTHOR]

Due to the input current dead zones, the buck power factor correction converter has to set a fixed output voltage for a tradeoff between the total harmonic distortion (THD ${_\mathit{i}}$) and efficiency. Thus, many converter-cell integrated buck-type converters have been proposed to eliminate the dead zones, which unfortunately deteriorate efficiency due to the extra components.This article proposes a group of bridgeless buck-type integrated topologies. Then, a dead-zone-free bridgeless buck-type topology with a wide output voltage range is targeted for further study. The studied converter operates in the buck+flyback mode and can automatically change to flyback mode when the dead zones occur, which only requires a simple control. Moreover, an integrated transformer based on an E-E core is investigated to reduce cost and volume. The bridgeless operation modes are introduced, followed by the PF and THD ${_\mathit{i}}$ analysis to optimize its performance. Prototypes are built and tested, which confirm the effectiveness of the converter and the integrated magnetic. [ABSTRACT FROM AUTHOR]

• Six PCFT columns with internal energy dissipation bars were cyclically tested. • UHPC bedding layer and steel tube can ensure the larger ductility of PCFT columns. • The effects of initial PT force and ED bars on PCFT columns are identified. • The PCFT column is a minimal-damage precast structure with superior seismic behavior. In this paper, a promising construction option, which combines the concrete filled steel tubular (CFT) column and the self-centering rocking system, is introduced and its seismic behavior is experimentally investigated. In this hybrid system, named as post-tensioned concrete filled steel tubular (PCFT) column, the unbonded post-tensioned (PT) tendons and energy dissipation (ED) devices are employed to provide recentering and ED properties, respectively. The steel tube acts as a protective jacket, stay-in-place formwork, and transverse reinforcement. Six PCFT columns with different amounts of initial PT force and ED bars were tested. All columns failed due to the fracture of ED bars and the crushing of mortar bed which though was cast from ultra-high performance concrete (UHPC). The column shafts of specimens suffered little damage after testing. The amount of ED bars greatly affected the self-centering capacity and ED capacity of the PCFT columns when the ratio of ED bars was less than 1.2%. Beyond this ratio, its effect was negligible. Additionally, increasing initial PT force made only a little difference to the load-carrying capacity but significantly enhanced the self-centering capacity of the column. [ABSTRACT FROM AUTHOR]

• A novel cold-formed thin-walled steel beam-column joint entirely using self-tapping screws. • Influence of different connection modes on static load carrying effect. • Seismic behavior of H-section beam-square steel column joints connected by self-tapping screws. • The calculation method for yielding moment strength based on the improved component method. This paper proposes a novel thin-walled steel beam-column joint entirely using self-tapping screws. Compared to bolted and welded connections, its advantages of easy construction, low precision requirements, and fast construction are suitable for low-rise steel structures. Four full-scale H-section beam-square steel column joints connected by self-tapping screws were tested and the force transfer mechanism was investigated. Three of the specimens were loaded monotonically at the beam ends. The effects of the L-shaped connecting plate thickness and the arrangement of stiffening ribs on the bending performance of the joints are analyzed. Monotonic loading tests have demonstrated that the increased thickness and the arrangement of stiffening ribs enhance the common forces in the clusters of self-tapping screws, thereby increasing the bending stiffness of the joints. One of the specimens was tested with cyclic loads. The cyclic loading test revealed that the hysteretic curve of the self-tapping screws connection is relatively full, with high energy dissipation capacity and low degradation of strength and stiffness. Finally, the improved component method proposed the calculation method of bending resistance of self-tapping connection joints. The calculation accuracy is within 10 %, which can be used as a reference for the design of bending resistance. [ABSTRACT FROM AUTHOR]

In this article, a minimum-copper-loss fault-tolerant control scheme is proposed for open-phase fault and open-switch fault of dual three-phase permanent magnet synchronous motor (DT-PMSM) drives. Both the winding configurations of isolated neutral points and connected neutral points are studied in this article. In conventional minimum-copper-loss fault-tolerant control schemes, the constraints of sinusoidal phase currents result in insufficient copper-loss reduction. Different from them, the current references with the theoretically lowest copper losses are first derived and applied for different fault cases of DT-PMSM drives without using any unnecessary constraints in the proposed fault-tolerant control scheme. Thus, all phase currents in the proposed minimum-copper-loss fault-tolerant control scheme are optimized to be nonsinusoidal waveforms. Besides, the copper losses are further reduced by fully utilizing the remaining healthy switch in the faulty inverter leg for the open-switch fault of DT-PMSM drives with the proposed scheme. It has been theoretically and experimentally proved that the proposed fault-tolerant control scheme can reduce copper losses than all existing fault-tolerant schemes for both open-phase fault and open-switch fault in typical two-level voltage-source-inverter-fed DT-PMSM drives. [ABSTRACT FROM AUTHOR]

A flicker‐free transformerless light emitting diode (LED) driving circuit based on a quadratic buck power factor correction (PFC) converter is proposed. It combines a cascaded input buck PFC converter and an output buck dc–dc converter with a single switch. The proposed LED driving circuit can not only achieve high PFC to comply with the EN61000‐3‐2 standard and low output voltage without a high step‐down transformer, but also reduces second‐order line frequency current ripple flowing through the LED to eliminate light flicker of the LED. Experimental results of a 7 W prototype are presented to verify the analysis results of the proposed converter. [ABSTRACT FROM AUTHOR]

Based on outlier detection algorithms, a feasible quantification method for supraharmonic emission signals is presented. It is designed to tackle the requirements of high-resolution and low data volume simultaneously in the frequency domain. The proposed method was developed from the skewed distribution data model and the self-tuning parameters of density-based spatial clustering of applications with noise (DBSCAN) algorithm. Specifically, the data distribution of the supraharmonic band was analyzed first by the Jarque–Bera test. The threshold was determined based on the distribution model to filter out noise. Subsequently, the DBSCAN clustering algorithm parameters were adjusted automatically, according to the k-dist curve slope variation and the dichotomy parameter seeking algorithm, followed by the clustering. The supraharmonic emission points were analyzed as outliers. Finally, simulated and experimental data were applied to verify the effectiveness of the proposed method. On the basis of the detection results, a spectrum with the same resolution as the original spectrum was obtained. The amount of data declined by more than three orders of magnitude compared to the original spectrum. The presented method will benefit the analysis of quantification for the amplitude and frequency of supraharmonic emissions. [ABSTRACT FROM AUTHOR]