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Porous photonic structures have greatly advanced large‐scale radiative cooling application owing to its satisfying optical properties, easy‐designation, and low cost. However, current reported porous radiative cooling materials mainly focuses on uniform or random pore distribution structure, which failed to achieve precise spectrum control for sunlight and mid‐infrared light, thereby weakening the radiative cooling performance. Herein, gradient structural porous metamaterials (GSPMs) are proposed and successfully constructed for maximizing cooling effectiveness based on step‐by‐step freeze‐casting technology. The designed GSPMs with gradient micro‐nano porous structure can wide‐range scatter entire solar spectrum while possess gradual refractive index transition to increase air‐medium interface absorption at mid‐infrared regions. Notably, solar reflectivity and mid‐infrared emissivity of GSPMs reach 97.3% and 97.6%, achieving maxinum cooling temperature of 8.7 °C and net cooling power of 94.1 W m−2, presenting a higher cooling effect than random porous materials. Moreover, GSPMs enable achieve compatibility with color aesthetic and cooling superiorities due to selective spectra response behavior, as well as can be applied in building materials, realizing efficient energy saving and CO2 emission reduction. This work proposed gradient porous structure can achieve highly efficient daytime radiative cooling, offering new possibilities in the structure design of next‐generation porous radiative cooling materials. [ABSTRACT FROM AUTHOR]

This document discusses the increasing demand for high-efficient isolated DC/DC converters in renewable energy applications. It presents seventeen papers that cover various topics such as reducing switch count and current balancing, addressing voltage ringing issues, solving current unbalance problems, and optimizing converter design. The papers provide experimental results and propose innovative methods to improve the efficiency and performance of DC/DC converters in renewable energy applications. The document also includes three research papers related to power converters, including one on a prototype for NanoGrid applications, one on a new DC-DC bipolar resonance converter, and one on enhancing the stability of a DCMG cluster. The text also includes acknowledgments and biographies of the guest editors. [Extracted from the article]

LLC resonant converters are widely adopted in many different industrial applications due to their high efficiency operation. To further improve LLC resonant converters' efficiency, the secondary unregulated diode rectifier is replaced by the synchronous rectifier (SR). In many applications, LLC converter is designed to operate at resonant frequency to maximize the system efficiency and act as a DC transformer (DCX). The SR driving signal is set as the same as the primary driving signal to work in an open‐loop mode. However, the resonant frequency will deviate due to the tolerance, working environment, and ageing effect of circuit components, which will lead to the degradation of the system efficiency and output voltage variation. Unfortunately, most of the existing techniques cannot be simply adopted in SR LLC DCX. Therefore, an adaptive SR driving strategy that can compensate the circuit components' variations is necessary for SR LLC DCX. Inan adaptive SR strategy based on the constant voltage gain characteristic at resonant frequency point is proposed. The proposed strategy is applicable for all different scenarios with easy implementation and low cost. [ABSTRACT FROM AUTHOR]

Mixing of reagents in microfluidics is critical, and currently, the focus is on Newtonian fluids, but these reagents are often viscoelastic fluids. In this study, a micromixer containing a conductive cylinder is proposed based on the principle of induced charge electro-osmosis (ICEO). The Oldroyd-B constitutive model was chosen to characterize the flow properties of viscoelastic fluids, and the Poisson–Boltzmann model was used to describe the ion distribution in the electrolyte. The impact of the elasticity number (El) of viscoelastic fluids on the mixing efficiency, velocity, and vortex in the micromixer was studied. The results show that the mixing efficiency is only 55.41% when El = 0 (Newtonian fluid), and the mixing efficiency reaches 99.08% when El = 50. As El increases from 0 to 50, the cross-sectional average velocity at 50 μm from the micromixer exit decreases from 160 to 26.1 μm/s. Furthermore, the vortices around the conductive plate generated by the ICEO phenomenon begin to fluctuate at El = 7. [ABSTRACT FROM AUTHOR]

Defoliation, often induced by herbivores, and soil microbiomes are recognized as key drivers of plant diversity and productivity in grasslands. However, lack of experiments simultaneously manipulating defoliation and soil microbial diversity has constrained our understanding of how these two factors interactively influence both above‐ground and below‐ground net primary productivity (ANPP and BNPP).We employed a soil filtering approach to create the gradient of soil microbial diversity and removal of above‐ground biomass by clipping to simulate defoliation effect from herbivores. Our goal was to investigate how soil microbial diversity affected both ANPP and BNPP under the stress of defoliation.We found that defoliation and soil microbial diversity loss decreased the ANPP and BNPP of the plant community, and Medicago falcata (legume) was more responsive to these treatments than Leymus chinensis (grass) and Artemisia frigida (forb). ANPP was positively correlated with soil microbial richness only when plants suffered defoliation. By contrast, BNPP showed a closer relationship with soil fungal richness than bacteria, and defoliation enhanced this relationship. The structural equation model (SEM) showed that defoliation indirectly regulated ANPP by affecting plant P content, while soil bacterial diversity loss decreased the ANPP through altering plant P and fungal diversity loss directly decreased BNPP. The LEfSe and linear regression analysis revealed that the biomarkers of bacteria (e.g. Actinobacteria, Xanthobacteraceae) and fungi (e.g. Ascomycota, Glomerales) significantly contributed to the variation of ANPP and BNPP under defoliation treatment respectively. Defoliation enhanced phosphorus acquisition by soil microorganisms, further strengthening the microbial regulation of plant productivity.Overall, we provide novel insights on how defoliation enhances the positive effects of soil microbial diversity on above‐ and below‐ground net primary productivity. Our findings highlight that soil microorganisms associated with phosphorus cycling are mobilized to play a more active role in promoting productivity after defoliation. It may provide a new perspective on how to better utilize the role of soil microorganisms in grazed or managed grasslands. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Micromixers have important applications in lab-on-a-chip, biomanufacturing, and chemical engineering. In this study, a micromixer with a conductive barrier plate based on the induced charge electro-osmosis is proposed. The Oldroyd-B constitutive model was chosen to characterize the flow characteristics of viscoelastic fluids, and the Poisson–Boltzmann model was used to characterize the electrokinetic properties. The effects of the installation of the conductive plate, the concentration of the polymer, and the shape of the conductive plate on the mixing were studied based on the finite volume method. The mixing efficiency of the viscoelastic fluids is 78.3% when a non-conductive plate is placed in the micromixer. However, placing a conductive plate increases the mixing efficiency to 89.8%. As the polymer concentration increases, the mixing efficiency increases, which is attributed to the elastic instability. As the curvature of the conductive plate increases from 0° to 360°, the mixing efficiency of the Newtonian fluid increases by 2.82%, while that of the polyacrylamide solutions at concentrations of 100 and 250 ppm increases by 5.31% and 1.97%, respectively. [ABSTRACT FROM AUTHOR]

With the growing adoption of wide bandgap devices in power electronic applications, current sensor design for switching current measurement has become more important. The demands for high accuracy, high bandwidth, low cost, compact size, and galvanic isolation pose significant design challenges. The conventional modeling approach for bandwidth analysis of current transformer sensors assumes that the magnetizing inductance remains constant, which does not always hold true in high-frequency operations. This can result in inaccurate bandwidth estimation and affect the overall performance of the current sensor. To address this limitation, this paper provides a comprehensive analysis of nonlinear modeling and bandwidth, considering the varying magnetizing inductance in a wide frequency range. A precise and straightforward arctangent-based fitting algorithm was proposed to accurately emulate the nonlinear feature, and the fitting results were compared with the magnetic core's datasheet to confirm its accuracy. This approach contributes to more accurate bandwidth prediction in field applications. In addition, the droop phenomenon of the current transformer and saturation effects are analyzed in detail. For high-voltage applications, different insulation methods are compared and an optimized insulation process is proposed. Finally, the design process is experimentally validated. The bandwidth of the proposed current transformer is around 100 MHz and the cost is around $20, making it a low-cost and high-bandwidth solution for switching current measurements in power electronic applications. [ABSTRACT FROM AUTHOR]

The performance of the provincial cable television (CATV) industry in China has become one of the main points of interest as competition in this market intensifies and policy making gradually moves from the central to the provincial level with the introduction of Internet Protocol Television (IPTV) and Over the Top (OTT). The CATV industry has two different vertically integrated activities: program production and service transmitting. In this paper, we develop a dynamic framework to describe an integrated system aiming to reflect the operation process of the CATV industry. Considering the service transmitting division further affects the program production division in the following period, this paper proposes a multi-period two-stage DEA model with feedback structures between service transmitting stage in the current period and program production stage in the next period to evaluate the relative performance. Detailed empirical results are presented from a panel data set of Chinese CATV industry from 2010 to 2019, covering two Five-Year Plans. [ABSTRACT FROM AUTHOR]

Enhancing the micro-channel flow mixing is always a difficult problem. In this study, a micromixer based on induced charge electro-osmosis is proposed. A T-shaped micromixer, which has a chamber with conductive surfaces in the channel, is chosen. Due to the electro-osmotic effect of the induced charge, the induced potential is generated on the conductive surface. The Oldroyd-B constitutive model is chosen to characterize the flow characteristics of polyacrylamide solution, and an open-source solver named rheoTool based on the finite-volume method is used. The effect of the chamber shape, the chamber size, the conductive edge numbers in the chamber, and the applied electric intensity on the mixing efficiency are investigated. The results show that the micromixer with conductive edges in the chamber has better mixing effect because of the vortices. At the same time, compared with other shapes, the micromixer with diamond chamber has the best mixing effect, and the mixing efficiency reaches 79.51%. In addition, the mixing efficiency of one conductive edge in the diamond chamber is 4.39% higher than that of the two conductive edges chamber. It is found that increasing the chamber size will improve the mixing efficiency, and the mixing efficiency increased by 12.76% with the increase in chamber size. On the other hand, when increasing the electric field intensity from 100 to 200 V/cm, the mixing efficiency will decrease. [ABSTRACT FROM AUTHOR]

Shoot and root litter are two major sources of soil organic carbon, and their decomposition is a crucial nutrient cycling process in the ecosystem. Altitude and land use could affect litter decomposition by changing the environment in mountain grassland ecosystems. However, few studies have investigated the effects of land use on litter decomposition in different altitudes. We examined how land-use type (mowing vs. grazing) affected shoot and root litter decomposition of a dominant grass (Bromus inermis) in mountain grasslands with two different altitudes in northwest China. Litterbags with 6 g of shoot or root were fixed in the plots to decompose for one year. The mass loss rate of the litter, and the environmental attributes related to decomposition, were measured. Litter decomposed faster in mowing than grazing plots, resulting from the higher plant cover and soil moisture but lower bulk density, which might promote soil microbial activities. Increased altitude promoted litter decomposition, and was positively correlated with soil moisture, soil organic carbon (SOC), and β-xylosidase activity. Our results highlight the diverse influences of land-use type on litter decomposition in different altitudes. The positive effects of mowing on shoot decomposition were stronger in lower than higher altitude compared to grazing due to the stronger responses of the plant (e.g., litter and aboveground biomass) and soil (e.g., soil moisture, soil bulk density, and SOC). Soil nutrients (e.g., SOC and soil total nitrogen) seemed to play essential roles in root decomposition, which was increased in mowing plots at lower altitude and vice versa at higher altitude. Therefore, grazing significantly decreased root mass loss at higher altitude, but slightly increased at lower altitude compared to mowing. Our results indicated that the land use might variously regulate the innate differences of the plant and edaphic conditions along an altitude gradient, exerting complex impacts in litter decomposition and further influencing carbon and nutrient cycling in mountain grasslands. [ABSTRACT FROM AUTHOR]

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In order to further improve the efficiency of dual-active-bridge (DAB) converter, a hybrid five-variable modulation scheme with minimal root mean square (rms) current is proposed in this article, which combines the traditional phase-shift and pulsewidth modulation schemes. By adopting the proposed optimal scheme, a wider zero-voltage switching (ZVS) operation range and lower rms current level are achieved simultaneously when compared with other modulation schemes, which significantly improves the efficiency of the DAB converter. Moreover, for the complexity of the proposed modulation scheme with five variables, the Fourier decomposition based analytical expressions are derived for the converter and a generalized performance analysis results are presented. Besides, in order to avoid the analysis error, especially at light-load condition, the optimization strategy takes the rms current as the optimal objective, which includes the eight harmonic component of the inductor current rather than just considers the fundamental component. And an offline particle swarm optimization algorithm is introduced to acquire the optimal operating points for the whole power range. To substantiate the effectiveness of the proposed modulation scheme, a comprehensive comparison among related works in terms of the rms value and ZVS range were carried out under various operation condition. Finally, a 1.2 kW experimental platform was built and the highest experimental efficiency under the proposed modulation scheme reaches 96.8%. [ABSTRACT FROM AUTHOR]

Light-emitting diodes (LEDs) are widely used in street lighting, landscape lighting, liquid crystal display (LCD) backlighting, healthcare, etc. As an important part of LED lighting products, LED driver plays a vital role in maintenance costs reduction, energy saving and lifetime prolongation. In this paper, a single-stage LED driver is proposed, which is integrated by a totem-pole bridgeless power factor correction (PFC) unit and several modular LCL-T resonant rectifiers. The totem-pole bridgeless PFC unit and the LCL-T resonant rectifiers are integrated by sharing switches, which can simplify the circuit and reduce the system cost. The output current can be regulated by applying the variable inductor control. Constant duty cycle and fixed switching frequency operation can be achieved as well. The operating principle and the performance of the proposed converter are analyzed in this paper. In addition, a precise parameter design method is proposed by considering the high-order harmonics. At last, an experimental prototype is established to validate the proposed parameter design and variable inductor control method. [ABSTRACT FROM AUTHOR]

Although LLC converters are attractive in industrial applications due to its advantages of soft switching, high efficiency, and simple control, in wide voltage gain range applications, large switching frequency operating range is required, which may cause the loss of soft switching operation and existence of control instability issue. In this article, a novel LLC converter with two LLC resonant tanks is proposed. The proposed converter has three operation modes, namely, dual full-bridge operation mode, full-bridge operation mode, and half-bridge operation mode, which can cover the high voltage gain range, medium voltage gain range, and low voltage gain range operations, respectively. The operational principles of the proposed converter are presented, and brief design considerations are discussed. A 250 W experimental prototype with six times input voltage range (50–300 V) was built to validate the theoretical analysis of the proposed converter. Comparisons among different LLC topologies for wide voltage gain range applications are made. [ABSTRACT FROM AUTHOR]

Hold-up time operation is a crucial requirement for distributed power systems and server power supplies. LLC resonant converter is widely used in these applications due to its high efficiency and power density characteristics. Conventional pulse frequency modulation (PFM)-controlled inductor-inductor-capacitor (LLC) resonant converter requires a wide switching frequency operation range to satisfy the hold-up requirement. In this article, a novel control scheme is proposed for stacked structure LLC resonant converter. During the normal operation, the frequency doubler modulation strategy is adopted to reduce the switching loss and driving loss, and the output is regulated by PFM. During the hold-up time operation, the pulsewidth modulation is adopted to increase the system voltage gain, where the switching frequency is fixed during this operation stage. For the proposed converter, the resonant tank parameters are designed at the nominal operation point, and the only design consideration for the magnetizing inductor is the zero-voltage switching for primary switches. Therefore, compared with PFM-LLC, both the switching frequency operating range and the circulating current are reduced, and high efficiency feature is obtained. Finally, a 100-W experimental prototype with input voltage range of 160–340 V was built to validate the advantages of the proposed converter. [ABSTRACT FROM AUTHOR]

Gallium nitride (GaN) devices are widely used due to their excellent performance when integrated into power electronics applications. However, owing to their low parasitic parameters and fast switching speed, they are more prone to instability than the silicon devices. The sustained oscillation discussed in this article is one of the instability problems, which may result in overshoot or even more serious device breakdown; thus, it is pretty necessary to suppress it effectively in practical applications. It is the first time to adopt an RC snubber to suppress the sustained oscillation in this article, which is very simple and cheap but effective. First, the sustained oscillation modeling based on a double pulse circuit is carried out. Then, the RC region is established quantitatively according to the root locus analysis results, which makes up for the defects of these qualitative methods before. Furthermore, it is first found that the sustained oscillation can be fully suppressed due to the existence of dipoles. Finally, the oscillation suppression effect within the RC region is compared with that outside the region by the simulation and experimental results, which are consistent with the theoretical analysis. Additionally, the possible negative influence of the added RC snubber is also discussed in this article, which shows that it has a little impact on the switching speed and energy loss, while the sustained oscillation is well suppressed. [ABSTRACT FROM AUTHOR]

National Basketball Association (NBA) is one of the four major sports leagues in North America. The performance evaluation of NBA teams is an important reference for team managers. However, non-homogeneity issues exist on both inputs and outputs sides for NBA teams evaluations. For example, some teams do not have "high-level" players as inputs and some teams are not qualified to play in the playoffs with respect to "wins in the playoffs" as an output. The current paper extends the existing non-homogeneous DEA method to address the non-homogeneous structure of NBA teams in performance evaluation by splitting NBA teams into types of homogeneous sub-units. The sub-unit, in this paper, consists of empirical input subset and output subset which satisfies both atomic property and maximum property. In addition, our method yields a unique efficiency decomposition of sub-units of NBA teams in 2018–2019 season without the need for imposing any additional conditions which are needed in some prior relative researches. As a result, detailed performance improvement directions for all teams can be provided. [ABSTRACT FROM AUTHOR]

LLC resonant converters have been widely used in many different industrial applications. Analysis and design methodologies have great effect on the converter performance. Accordingly, a complete step-by-step optimal design methodology based on time-domain analysis has been proposed for an LLC resonant converter in this article. The proposed design methodology is implemented under the worst operation condition, and the following considerations are included to obtain the suitable design area: operation mode; voltage stress for resonant capacitor; zero voltage switching operation for primary switches; and resonant tank root-mean-square current. Then, by finding all possible design candidates and comparing them based on the power loss model, the optimized design candidate can be found. Compared with the existing design methodologies, the proposed one has the advantages of high accuracy and small computation requirement, which makes it application in industry possible. Finally, a 192-W experimental prototype was built to validate the effectiveness of the proposed design methodology. In addition, a MATLAB graphical user interference program was built based on the proposed design methodology to visualize and facilitate the design process for engineers. [ABSTRACT FROM AUTHOR]

Unregulated LLC resonant converters operating at resonant frequency have been adopted in numerous applications due to its high efficiency characteristic. However, in practice, resonant frequency operation cannot always be guaranteed due to the tolerances and variations of circuit parameters. Therefore, in this brief, a simple resonant frequency tracking method based on the transformer secondary voltage is proposed. When LLC converter operating in the below resonant frequency region, the ratio of the average transformer secondary voltage and output voltage is less than unity, while the ratio is unity at resonant frequency. By adopting this characteristic, the resonant frequency tracking is achieved by comparing the calculated voltage ratio and unity, then the switching frequency is adjusted to track the resonant frequency. To reduce the sampling circuit complexity, the rectified transformer secondary voltage is sensed, and the voltage ratio becomes 0.5 at resonant frequency. The effectiveness of the proposed resonant frequency tracking method has been experimentally validated under different scenarios. [ABSTRACT FROM AUTHOR]

Asymmetric duty modulation (ADM), as a recently proposed modulation scheme, provides new chance to improve the performance of dual active bridge (DAB) converter. On this basis, an optimal ADM (OADM) scheme is proposed in this article to minimize the inductor peak-to-peak current over the whole voltage and power range. First, the DAB converter adopting ADM scheme is analyzed in frequency-domain and time-domain, and four operating modes are established. Then, the minimum peak-to-peak inductor current for each operating mode is obtained under Karush–Kuhn–Tucker condition, and the corresponding optimal closed-loop control with low calculation complexity is derived. Then, the key values and features of the OADM scheme are compared with recent state of the art, mainly including the inductor root mean square current and soft-switching performance. Finally, an experimental prototype was built to validate the efficiency enhancement of the converter by adopting the proposed OADM scheme. [ABSTRACT FROM AUTHOR]

In this article, an efficiency-oriented hybrid duty modulation (HDM) scheme is proposed for the dual active bridge (DAB) converter that can reduce the inductor root-mean-square (rms) current and extend the switch soft-switching range. First, a complete description of the combination forms of different modulation schemes is presented considering the allocation of the zero-voltage portion. A unified description for these combination forms is obtained in the frequency domain. Second, the symmetric–symmetric duty modulation (SSDM) scheme and asymmetric–symmetric duty modulation (A2SDM) scheme are established to minimize the inductor rms current by considering its fundamental component. Third, the characteristics of SSDM, A2SDM, and the traditional phase shift modulation schemes are compared from several aspects, mainly including the inductor rms current and the soft-switching performance. Furthermore, the loss breakdown analysis results for the three modulation schemes are presented and compared. According to these results, the HDM scheme is proposed to improve the overall efficiency of the DAB converter. Finally, an experimental prototype was built with a peak efficiency of 97%, which validates the effectiveness of the proposed modulation scheme. [ABSTRACT FROM AUTHOR]

The cascaded H-bridge (CHB) inverter is one of the most attractive multilevel topologies for renewable energy applications. Due to the fact that CHB inverters employ a large number of components, they suffer from a higher probability of fault, which reduces the system reliability. A fault-tolerant operation for a CHB inverter is described in this article. New features ensure reliable and robust operation of the converter in the event of a fault. The proposed strategy uses an additional cross-coupled CHB (X-CHB) unit in companion with the existing CHB units to support the output voltage and ensure continuity of operation in the event of an open/short-circuit fault. The operation of the proposed X-CHB inverter is described in detail. Simulation and experimental verification of the proposed concept are demonstrated using a seven-level CHB. Both simulation and experimental results confirm the fault-tolerant operation of the X-CHB for a battery energy storage system in case of switch faults. [ABSTRACT FROM AUTHOR]

A conventional pulse frequency modulation (PFM) controlled LLC resonant converter requires a wide switching frequency operating range to regulate the output voltage. There are some disadvantages of PFM LLC resonant converters: (i) the design and optimisation of magnetic components and gate driver circuitry are challenging; (ii) due to the variable switching frequency operating range, electro‐magnetic interference performance of the converter is degraded; (iii) efficiency degradation; (iv) inability to achieve independent control in multiple‐output applications. To address the above‐mentioned problems and achieve fixed switching frequency operation, a variable magnetising inductance control (VMIC) strategy is proposed. In the proposed VMIC control strategy, the operating switching frequency of the primary switch is fixed and the duty cycle remains constant at 0.5. At the resonant frequency operating point, the output voltage is independent of both the magnetising inductance and load. In addition, the zero current turn‐off operation of the secondary rectifier requires that the switching frequency be designed below the resonant frequency. The operational principles and design considerations of the LLC resonant converter with VMIC are presented. Experimental results from a 200 W prototype are presented to validate the theoretical analysis and the effectiveness of the proposed VMIC control strategy. [ABSTRACT FROM AUTHOR]

In wide voltage range applications, traditional LLC converters suffer from the following issues: (i) to cover a wide voltage gain operating range, the required switching frequency range is also large, which challenges the design and optimisation of magnetic components, gate driver circuitry, and electro-magnetic interference filter; (ii) a small magnetising inductance is preferred in wide voltage gain range application, which leads to the increase of circuit circulating current and corresponding conduction loss; (iii) passive elements are determined based on the minimum switching frequency, so bulky passive elements are required to satisfy the required operation range. To solve these problems, in this study, a full-bridge LLC (FBLLC) resonant converter with two operation modes, namely full-bridge operation and frequency doubler operation, is proposed for wide voltage gain range application. The FBLLC converter discussed in this study can be designed in half of the input voltage range when compared with the conventional method, so smaller switching frequency operating range and higher efficiency operation are guaranteed. In addition, the smooth mode transition is achieved by introducing switching frequency feedforward control and small output voltage overshoot or undershoot is observed. A 150 W experimental prototype was built to validate the theoretical analysis. [ABSTRACT FROM AUTHOR]

In order to realize power flow control among photovoltaic (PV) panel port, battery port, and load port in the distributed photovoltaic power generation system, integrated three-port dc–dc converters (TPCs) are widely adopted. The objective of this article is to provide a comprehensive, comparative, and insightful analysis and overview of these TPCs. First, based on the power transmission and control requirements of the system, five topological structures of three-port dc–dc conversion system (TPCS) composed of two or three two-port dc–dc converters are presented. And the five structures are comparatively analyzed. Second, based on these topological structures, and combing with the basic two-port dc–dc converters, three groups of typical TPCs with different galvanic isolation requirements are derived, respectively, by sharing switches, combining branches, etc., And comprehensive analysis, comparisons, and reviews of these TPCs with different structures of each isolation type are presented with tables and figures. Finally, the comparison results of the three isolation groups are summarized, which leads to a guidance for the selection of TPCs in different applications, and then some suggestions for the future research on TPCs are given. [ABSTRACT FROM AUTHOR]

In this article, based on the LLC resonant converter fundamental harmonic analysis model, the modulation strategies for LLC resonant converter can be categorized into the following three groups: 1) input voltage fundamental harmonic modulation; 2) resonant tank elements modulation; and 3) secondary equivalent impedance modulation. Operational principles and control diagrams for different modulation strategies are given. Comprehensive comparisons between these modulation strategies in terms of topology complexity, control complexity, and voltage gain range are presented with respect to the same system specifications. The advantages and disadvantages for each modulation strategy are summarized to provide guidance for engineers when analyzing and designing an LLC resonant converter. The hybrid modulation strategies are categorized into different groups based on the specific applications. Brief introductions of these hybrid modulation strategies are presented. Future trends regarding the modulation strategies of LLC resonant converters are presented. [ABSTRACT FROM AUTHOR]

In this letter, a magnetically controlled single-stage ac–dc converter is proposed for low-power application which has the following features. First, single-stage operation is achieved by sharing switches between LLC resonant converter and totem-pole bridgeless power factor corrector (PFC) converter. Second, the power factor correction function is inherently achieved by designing the PFC converter to operate in discontinuous conduction mode. Third, the dc-link voltage is almost constant. Fourth, fixed switching frequency and duty cycle can be implemented for the switches, which simplifies the magnetic component and driver circuit design. Fifth, the LLC resonant converter is designed to operate at series resonant frequency, the highest efficiency operating point, so the converter can always achieve the maximum efficiency operation. Meanwhile, at this operating point, the converter output voltage is independent of the load so that it is functioning as a dc transformer; and finally, soft switching for all semiconductors is achieved. A 75-W experimental prototype is built to validate the proposed magnetically controlled single-stage ac–dc converter [ABSTRACT FROM AUTHOR]