Secondary Switches Research Articles

A Novel SVM Strategy to Reduce Current Stress of High-Frequency Link Matrix Converter

High-frequency link matrix converter (HFLMC) can directly realize DC/AC conversion without intermediate energy storage components, reduce the power conversion stage, and improve efficiency and power density. With the conventional space vector modulation strategy, the secondary side voltage of the high-frequency transformer presents an asymmetric trapezoidal wave, which leads to the DC magnetic bias phenomenon and increases the current stress in secondary side switches. This paper proposes a novel SVM strategy for HFLMC. It optimizes the space vector distribution, makes secondary side voltage periodic and symmetric, and reduces the switching actions. The current stress is reduced, and the converter's efficiency is improved. Simulation and experiment results verify the advantages of the proposed modulation strategy.

Effective Design Methodology of CLLC Resonant Converter Based on the Minimal Area Product of High-Frequency Transformer

In DC microgrids, CLLC topology is commonly applied for battery integration. It provides galvanic separation, the ability to integrate a high-frequency transformer into the resonance circuit, and the ability to operate in a wide range of voltage. Moreover, it assures zero voltage switching conditions for all switches and zero current switching conditions for secondary side switches, which enables obtaining high efficiency. This paper presents a clear and effective approach to design a methodology for a CLLC DC/DC converter, especially a resonant tank. High-frequency transformer is fully integrated in a resonant tank. Its size is minimal and based on area product parameter Ap. An equivalent scheme for first harmonic approximation analysis is presented with inclusion of parasitic elements. Based on it, the analytical formulas are provided, which enable graphical determination of working characteristics. It was proved that the model increases the accuracy of the results. The conditions of ZVS and maximal magnetizing inductance are established, including parasitic capacitances of secondary side switches and transformer parasitic capacitances. Based on the proposed design methodology, as the proof of concept, a small-power prototype with a GaN transistor was built operating at 364 kHz. Converter losses were determined through analytical expressions and compared with the experimental and simulation results.

Interleaved Boost-Integrated LC Series Resonant Converter With Frequency-Free Designed Transformer for Wide Voltage Range Applications

This paper presents a novel interleaved boost integrated LC series resonant converter with two output rectification modes, which are voltage-doubler rectifier mode and voltage-quadrupler rectifier mode with constant output voltage for wide input voltage range applications. Due to the symmetrical configuration of the rectifier, the voltage stress of switches and diodes on the secondary side are only half of the output voltage. With the proposed pulse frequency modulation, the maximum magnetic flux density <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B_m</i> of high frequency transformer is only related with the resonant frequency rather than the switching frequency. Hence, the transformer can be frequency-free designed. The zero-voltage-switching of the primary switches and zero-current-switching of the secondary switches and diodes are achieved, respectively. Moreover, the design procedure for some key parameters is presented. Finally, a 470 W prototype with a switching frequency range from 50 kHz to 140 kHz is built to verify the operation principles of the proposed converter and modulation.

The evolution of wireless mobile networks and the future 5G mobile technology for sustainability.

In this paper, our study focused on the framework of big data-driven and mobile optimization. We will study the significant points of 5G and previous mobile networks, and mostly we have a look at past mobile technologies. After that, we will focus on the future 5G Mobile Technology. We will make an essential reference to the architecture of the 5G Mobile Network. We will see the two OSI levels (network level and Internet Protocol (IP)). The purpose of IP is to ensure adequate control data (in IP header) for proper routing of IP packets belonging to specific application connections or sessions between client and server applications somewhere on the Internet. Also, we mention the primary points of 5G. The device-based architectures, the millimeter-wave, the massive multiple inputs - multiple outputs, the smarter devices, and the manual support for machine-to-machine communication.Finally, in this paper, we will see how much faster will be the future 5G mobile network and services can support. Those services, including experience at speeds of at least 1 Gbps or higher, 10 Gbps data transfer, zero secondary switches, enormous capacity, and reduce power consumption, are the areas of 5G network we see in this study.

Backward Step-Up Control Strategy for Bidirectional LLC Resonant Converter

An LLC resonant converter has the advantages of simple structure and soft switching. It can enable bidirectional power transmission, but it is difficult to realize a normalized gain greater than one under backward mode (backward step-up mode). Cascaded dc/dc converters or topological changes can solve this problem, but additional switches and components are required and losses are added. Without changing the LLC resonant converter’s basic topology, this paper proposes a variable duty-cycle control strategy of primary side switches for backward step-up mode. Using variable duty-cycle control, the LC resonant tank can be charged, and then the backward step-up mode can be realized. Soft switching characteristics of some primary side switches and all secondary side switches are guaranteed. In this study, the working principle of an LLC resonant converter under bidirectional control strategy was analyzed, and the backward step-up control was analyzed in detail. The voltage gain and the boundary of continuous conduction mode (CCM) and discontinuous conduction mode (DCM) were derived. A synchronous rectification method related to the backward step-up control is proposed. The control strategy was verified by experiments.

Single-Stage Isolated AC-AC Converter Without Commutation Problem

A single-stage isolated ac–ac converter without the commutation problem is proposed. The proposed converter has the step-up/down function dependence on the phase shift control which provides zero-voltage switching zero-voltage switching (ZVS) for all switches in rated condition. Also, the commutation paths of the secondary side switches are provided for any switching case by adding a single capacitor; originally, a filter capacitor is used for the switching mode power supply input, and in this case, this filter capacitor also solves the primary-side commutation problem. The ZVS and solving the commutation problem increase the power efficiency and reliability. The proposed converter achieves high power quality with a simple control algorithm. A 1 kW/ 220 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub> prototype is implemented to verify the theoretical analysis and performance of the proposed converter. The California energy commission efficiency is 97.3%, the total harmonic distortion (THD) of the input current is 2.45% at full load, and the THD of the output voltage is 1.07% at full load.

Generalized State-Plane Analysis of Bidirectional CLLC Resonant Converter

The <i>CLLC</i> resonant converter is a promising candidate for high efficient, bidirectional power transfer applications, such as vehicle-to-grid on-board charger and hybrid vehicle dc&#x2013;dc converter. Nevertheless, the analysis of <i>CLLC</i> still remains challenging because of its complex multiresonant nature and several storage elements. In this article, a circuit analysis method based on change of variables is presented that maps the state-space equations into two decoupled sets of equations. The analyses are carried out in two state-plane coordinate systems, then the results are mapped onto the original region. The proposed method is then used to thoroughly analyze the <i>CLLC</i> resonant converter operating in the continuous conduction mode (CCM). The voltage and current stresses of components, zero voltage switching condition, output voltage gain, output characteristic diagram, and mode boundary of CCM&#x002F; discontinuous conduction mode are then obtained. The accuracy of the proposed approach is verified by the experiments on a 3 kW bidirectional <i>CLLC</i> resonant converter with GaN transistors as the primary and secondary side switches. The results confirm the accuracy of the proposed state-plane analysis of the <i>CLLC</i> resonant converter operating in either direction of power transferring.

A High-Efficiency High-Power-Density On-Board Low-Voltage DC–DC Converter for Electric Vehicles Application

The on-board low-voltage dc-dc converter (LDC) in electric vehicles (EVs) is used to connect the high-voltage battery with the low-voltage auxiliary system. With the advancement of auxiliary equipment in EVs, the output current of the LDC can be hundreds of amperes, which will cause high-conduction loss and severe thermal concern. In this article, a high-efficiency high-power-density on-board LDC is presented. To reduce current stress and improve efficiency, three-phase interleaved LLC dc-dc converters are paralleled to provide 270 A load current. Synchronous rectifier is used to reduce secondary conduction loss. zero-voltage-switching (ZVS) turn-on of primary switches and ZCS turn-off of secondary switches are achieved, thus switching loss can be reduced significantly. Moreover, phase-shedding technology is used to improve light load efficiency. Switch-controlled capacitor (SCC) technology is used to achieve accurate load current sharing among the three phases, which protects the devices against high-current stress, reduces the conduction loss, and improves the reliability of the system. As SCC switches achieve ZVS turn-on and turn-off by its nature, the loss of the SCC circuit is of less concern with regard to the rated output power. In addition, GaN HEMTs are used in the primary side to improve the power density and eventually help achieving light weight. A 3.8-kW (14 V/270 A) LDC prototype is developed and tested. Experimental results show good current balancing among the three phases. A peak efficiency of 96.7% at 140 A load and a full load efficiency of 95.8% are achieved with 3 kW/L power density and 1.5 kg weight.

Xylem vessel-specific SND5 and its homologs regulate secondary wall biosynthesis through activating secondary wall NAC binding elements.

Secondary cell wall biosynthesis has been shown to be regulated by a suite of transcription factors. Here, we identified a new xylem vessel-specific NAC domain transcription factor, secondary wall-associated NAC domain protein5 (SND5), in Arabidopsis thaliana and studied its role in regulating secondary wall biosynthesis. We showed that the expression of SND5 and its close homolog, SND4/ANAC075, was specifically associated with secondary wall-containing cells and dominant repression of their functions severely reduced secondary wall thickening in these cells. Overexpression of SND4/5 as well as their homologs SND2/3 fused with the activation domain of the viral protein VP16 led to ectopic secondary wall deposition in cells that are normally parenchymatous. SND2/3/4/5 regulated the expression of the same downstream target genes as do the secondary wall NAC master switches (SWNs) by binding to and activating the secondary wall NAC binding elements (SNBEs). Furthermore, we demonstrated that the poplar (Populus trichocarpa) orthologs of SND2/3/4/5 also activated SNBEs and regulated secondary wall biosynthesis during wood formation. Together, these findings indicate that SND2/3/4/5 and their poplar orthologs regulate the expression of secondary wall-associated genes through activating SNBEs and they are positioned at an upper level in the SWN-mediated transcriptional network.

A Soft-Switching Double-Input Micro-Inverter

In this article, a new high step-up soft-switched double-input micro-inverter is introduced, which is proper for low-power applications. This inverter is composed of a forward resonant inverter and two series boost converters that are coupled electrically and apply five switches. The input powers are controlled separately using the duty-cycle of input switches, and if one of the inputs is omitted, the operation of the inverter is not interrupted. The energy is transmitted to the output and provides soft-switching conditions without any auxiliary switch. Secondary side switches are controlled at low frequency to control the direction of current in each half-cycle of the output voltage. The proposed inverter is analyzed, and design considerations and soft-switching range are discussed. Also, the schematic of the control circuit is presented. The proposed inverter is implemented to supply a 100-W load, and experimental results are presented to justify the theoretical analysis.

Modelling and optimisation of a dual‐control MHz‐level CLLC converter with minimised power losses in battery charging applications

In this study, a novel ‘ f − φ ’ dual-control modulation is proposed for the MHz-level CLLC converters in battery charging applications. Phase shift between the primary and secondary switches is utilised as an additional control variable to effectively reduce the power losses, especially in light- and medium-load conditions. Compared to other state of the art, a more generalised theoretical model is developed to characterise the converter with higher accuracy based on extended harmonic approximation. Furthermore, a numerical algorithm is utilised to thoroughly examine the converter performance under various operating conditions and systematically search for the optimised design parameters under the proposed modulation scheme. The modelling and optimisation are verified by simulation on a 3.3 kW onboard charger design for electric vehicles, which shows an estimated efficiency enhancement between 1 and 4%. Finally, a laboratory prototype has been developed using gallium nitride semiconductor devices, at the resonant frequency of 1 MHz. The converter measured efficiencies are 96.4, 96.2 and 94% for the selected heavy, medium- and light-load conditions, respectively. This system would allow insights into the practical implementation and evaluation of utilising wide bandgap semiconductors to achieve both high power density and enhanced efficiency for emerging power electronic systems.

An Improved Modulation Scheme of Active Commutated Current-Fed Bidirectional dc/dc Converter

Active commutated or naturally clamped techniques have emerged as a new solution to achieve wide range soft-switching and eliminate the necessity of active clamping circuit of current-fed bidirectional dc/dc converter. Multiple typical modulation schemes have been proposed, which include single phase-shift (SPS) modulation, dual phase-shift (DPS) modulation, and discontinuous current SPS (DCSPS) modulation. DCSPS provides the lowest circulating current compared with prior two modulations, but it suffers from the problem of resonance and high peak current at partial loads. This article proposes a DCDPS modulation based on the existing modulations. The duty cycles of the two legs on the high-voltage side are controlled to be unsymmetrical to solve the current resonance problem in DCSPS. Extra phase shift is introduced to achieve much lower circulating current at wide range load conditions. Zero current switching (ZCS) of primary switches and zero voltage switching (ZVS) of secondary switches can be achieved over wide input range and wide load range. A 250-W laboratory converter prototype has been built. Experimental results are presented to validate the analysis and design.

Interleaved Active Clamp Forward Converter With Extended Operating Duty Ratio by Adopting Additional Series-Connected Secondary Windings for Wide Input and High Current Output Applications

This paper presents a new interleaved active clamp forward converter for low and wide input, and high current output applications. In the proposed converter, the operating duty ratio can be extended over 0.5 due to the additional powering path resulting from additional series-connected secondary windings from each transformer. As a result, the proposed converter can be designed with large transformer turns ratio. Thus, since the proposed converter can reduce not only the primary RMS current but also switch turn- off current, it can achieve high efficiency. Moreover, since all secondary switches can operate without floating gate drivers, the proposed converter can maintain simple structure and low complexity of gate driving circuits in the secondary side. The validity of this proposed converter is verified by the experimental results from 36V–72 V input and 12 V/500 W output for the dc/dc prototype.

Peak Current Control of Multichannel LED Driver With Selective Dimming

A novel selective dimming method of the output channels of a multichannel LED driver is proposed in this paper. This LED driver comprises a front-end ac-dc boost power factor correction converter followed by symmetric half-bridge isolated nonresonant dc-dc converter and symmetric voltage-multiplier rectifier with purely capacitive output filters. By controlling the duty ratios of the secondary side switches, which are strategically placed at the output voltage-multiplier-based rectifiers, the average LED current and hence the brightness of individual channels are controlled. Moreover, a unique primary side peak current control is implemented to control the peak currents of LEDs during pulsewidth modulation dimming, which prevents electromigration-related fast aging of the LEDs. This driver also has the advantages of high power (>120 W) operation capabilities, and high efficiency (>94%) with primary side switches zero voltage switching turning on and secondary side rectifier diodes zero current switching turning off. A detailed analysis and design procedure of the proposed converter is presented. To validate the analysis, an industry-standard 150 W prototype is developed, which is digitally controlled by a cost-effective non-DSP microcontroller. The experimental results are in perfect agreement with the claims. A comparison for universal ac input and isolated LED drivers with selective dimming is displayed.

Adaptive delay control for synchronous rectification phase‐shifted full bridge converter with GaN HEMT

An adaptive delay control method for a phase-shifted full bridge converter with a synchronous rectifier is presented. With this control, the delay time between primary and secondary switches can be optimised to reduce dead time, according to output power. Moreover, due to the poor third quadrant conduction of gallium nitride (GaN) high-electron-mobility transistors (HEMTs), the dead time needs to be optimised to utilise the benefits of a GaN HEMT. The experimental results with a 500 W prototype show that the efficiency can be improved by 0.7% with the proposed control.

High-Frequency Soft-Switching PWM DC-DC Converter with Active Output Rectifier Operating as a Current Source for Arc Welding Applications

This paper introduces a high-frequency soft-switching pulse-width modulation DC-DC power converter with secondary active rectifier tested as a DC current source for arc welding applications. The soft-switching DC-DC converter consists of a high-frequency full-bridge inverter, high-frequency power transformer, and a controlled output rectifier with new secondary energy recovery turn-off snubber. Circulating currents in the converter are reduced by using active rectifier, and RMS values of the currents in primary and secondary switches are decreased by utilizing a novel control algorithm. The experimental results of a 4.5 kW DC-DC converter working at switching frequency of 100 kHz are presented.

Modified LLC resonant converter with secondary paralleled bidirectional switch for applications with hold‐up time requirement

For applications with hold-up time requirement, the conventional LLC converter requires a small magnetising inductance L m to provide enough output voltage gain under the hold-up operation. However, it deteriorates the efficiency in normal operation. Different from the conventional one, the proposed converter has a bidirectional switch paralleled with the secondary winding of the transformer. In normal operation, the secondary bidirectional switch remains off, and the proposed converter works around the resonant frequency f r as the conventional one. While during the hold-up time, the converter provides sufficient output voltage gain with phase-shift control between primary and secondary switches. However, its output voltage gain is mainly determined by the phase shift angle φ and the normalised load p on but not the L m . Then it can have a larger L m than the conventional LLC converter, decreasing primary conduction and turn-off losses, and improving the efficiency in normal operation. A 200 V/420 W prototype was built, and experimental results show that the efficiency can be improved by 1% compared with the conventional LLC converter in normal operation, which has verified the effectiveness of the proposed solution.

Cytosol-Localized UDP-Xylose Synthases Provide the Major Source of UDP-Xylose for the Biosynthesis of Xylan and Xyloglucan.

Xylan and xyloglucan are the two major cell wall hemicelluloses in plants, and their biosynthesis requires a steady supply of the sugar donor, UDP-xylose. UDP-xylose is synthesized through conversion of UDP-glucuronic acid (UDP-GlcA) by the activities of UDP-xylose synthase (UXS). There exist six UXS genes in the Arabidopsis thaliana genome; three of them (UXS1, UXS2 and UXS4) encode Golgi-localized enzymes and the other three (UXS3, UXS5 and UXS6) encode cytosol-localized enzymes. In this report, we investigated the contributions of these UXS genes in supplying UDP-xylose for the biosynthesis of xylan and xyloglucan. Expression analyses revealed that the six UXS genes exhibited distinct and overlapping expression patterns in different cell types of stems, root-hypocotyls and young seedlings, and that the relative enzymatic activity of UXS in the cytosol was 17 times higher than that in the Golgi. Among the six UXS genes, UXS3, UXS5 and UXS6 showed the highest expression in stems and were expressed predominantly in xylem cells and interfascicular fibers. Their predominant expression in secondary wall-forming cells was consistent with the finding that the expression of UXS3, UXS5 and UXS6 was directly activated by the secondary wall NAC master switches. Although simultaneous mutations of UXS1, UXS2 and UXS4 did not cause any apparent effects on plant growth and xylan biosynthesis, simultaneous down-regulation/mutations of UXS3, UXS5 and UXS6 led to a drastic reduction in secondary wall thickening, a severe deformation of xylem vessels, a significant decrease in xylan content without an apparent reduction in its chain length and an absence of GlcA side chains in xylan, which are reminiscent of the phenotypes of some known xylan-deficient mutants. Moreover, Immunolocalization with two xyloglucan monoclonal antibodies, LM15 and LM25, revealed a significant reduction in the amount of xylogulcan in the primary walls. These results demonstrate that the cytosol-localized UXS3, UXS5 and UXS6 play a predominant role in the supply of UDP-xylose for the biosynthesis of xylan and xyloglucan.

Visualizing the formation of an RNA folding intermediate through a fast highly modular secondary structure switch.

Intermediates play important roles in RNA folding but can be difficult to characterize when short-lived or not significantly populated. By combining 15N relaxation dispersion NMR with chemical probing, we visualized a fast (kex=k1+k−1≈423 s−1) secondary structural switch directed towards a low-populated (∼3%) partially folded intermediate in tertiary folding of the P5abc subdomain of the ‘Tetrahymena' group I intron ribozyme. The secondary structure switch changes the base-pairing register across the P5c hairpin, creating a native-like structure, and occurs at rates of more than two orders of magnitude faster than tertiary folding. The switch occurs robustly in the absence of tertiary interactions, Mg2+ or even when the hairpin is excised from the three-way junction. Fast, highly modular secondary structural switches may be quite common during RNA tertiary folding where they may help smoothen the folding landscape by allowing folding to proceed efficiently via additional pathways.

ZVZCS PWM DC-DC Converter with Controlled Secondary Rectifier for ARC Welding

A zero-voltage, zero-current switching (ZVZCS) PWM DC-DC power converter with secondary active rectifier tested as a dc current source for arc welding is described in this paper. The soft switching DC-DC converter consists of high frequency inverter, high frequency power transformer and controlled output rectifier with new secondary energy recovery turn-off snubber. Circulating current in the converter is reduced by using active rectifier and rms value of the current in secondary switches is decreased by utilizing a novel control algorithm. The experimental results of a 4.5 kW DC-DC converter working at switching frequency of 100 kHz are presented.