Enhancement of thermal rectification by asymmetry engineering of thermal conductivity and geometric structure for multi-segment thermal rectifier

Thermal rectification is an exotic thermal transport phenomenon,an analog to electrical rectification,in which heat flux along one direction is larger than that in the other direction and is of significant interest in electronic device applications.However,achieving high thermal rectification efficiency or rectification ratio is still a scientific challenge.In this work,we performed a systematic simulation of thermal rectification by considering both efforts of thermal conductivity asymmetry and geometrical asymmetry in a multi-segment thermal rectifier.It is found that the high asymmetry of thermal conductivity and the asymmetry of the geometric structure of multi-segment thermal rectifiers can significantly enhance the thermal rectification,and the combination of both thermal conductivity asymmetry and geometrical asymmetry can further improve thermal rectification efficiency.This work suggests a possible way for improving thermal rectification devices by asymmetry engineering.

High-Efficiency Rectifier for Wireless Energy Harvesting Based on Double Branch Structure

A rectifier circuit for wireless energy harvesting(WEH) with a wide input power range is proposed in this paper. We build up accurate models of the diodes to improve the accuracy of the design of the rectifier. Due to the nonlinear characteristics of the diodes, a new band-stop structure is introduced to reduce the imaginary part impedance and suppress harmonics. A novel structure with double branches and an optimized λ/4 microstrip line is proposed to realize the power division ratio adjustment by the input power automatically. The proposed two branches can satisfy the two cases with input power of-20 dBm to 0 dBm and 0 dBm to 15 dBm, respectively. Here, dBm = 10 log(P mW), and P represents power. An impedance compression network(ICN) is correspondingly designed to maintain the input impedance stability over the wide input power range. A rectifier that works at 2.45 GHz is implemented. The measured results show that the highest efficiency can reach 51.5% at the output power of 0 dBm and higher than 40% at the input power of-5 dBm to 12 dBm.

Varifolds的某些Rectifiability特征

该文证明下面的定理:设一Varifold V具有特征0<lim_(r→0)(μV(Cr(x)))/(r^n)<∞,那么,V是Rectifiable的.另外,该文还给出了一个Varifold的结构表示定理.

A Fractional Order Fast Repetitive Control Paradigm of Vienna Rectifier for Power Quality Improvement

Due to attractive features,including high efficiency,low device stress,and ability to boost voltage,a Vienna rectifier is commonly employed as a battery charger in an electric vehicle(EV).However,the 6k±1 harmonics in the acside current of the Vienna rectifier deteriorate theTHDof the ac current,thus lowering the power factor.Therefore,the current closed-loop for suppressing 6k±1 harmonics is essential tomeet the desired total harmonic distortion(THD).Fast repetitive control(FRC)is generally adopted;however,the deviation of power grid frequency causes delay link in the six frequency fast repetitive control to become non-integer and the tracking performance to deteriorate.This paper presents the detailed parameter design and calculation of fractional order fast repetitive controller(FOFRC)for the non-integer delay link.The finite polynomial approximates the non-integer delay link through the Lagrange interpolation method.By comparing the frequency characteristics of traditional repetitive control,the effectiveness of the FOFRC strategy is verified.Finally,simulation and experiment validate the steadystate performance and harmonics suppression ability of FOFRC.

Enhancement of holding voltage by a modified low-voltage trigger silicon-controlled rectifier structure for electrostatic discharge protection

A novel structure of low-voltage trigger silicon-controlled rectifiers(LVTSCRs) with low trigger voltage and high holding voltage is proposed for electrostatic discharge(ESD) protection. The proposed ESD protection device possesses an ESD implant and a floating structure. This improvement enhances the current discharge capability of the gate-grounded NMOS and weakens the current gain of the silicon-controlled rectifier current path. According to the simulation results, the proposed device retains a low trigger voltage characteristic of LVTSCRs and simultaneously increases the holding voltage to 5.53 V, providing an effective way to meet the ESD protection requirement of the 5 V CMOS process.

A Hybrid Five-Level Single-Phase Rectifier with Low Common-Mode Voltage

Rectifiers with high efficiency and high power density are crucial to the stable and efficient power supply of 5G communication base stations,which deserves in-depth investigation.In general,there are two key problems to be addressed:supporting both alternating current(AC)and direct current(DC)input,and minimizing the common-mode voltage as well as leakage current for safety reasons.In this paper,a hybrid five-level single-phase rectifier is proposed.A five-level topology is adopted in the upper arm,and a half-bridge diode topology is adopted in the lower arm.A dual closed-loop control strategy and a flying capacitor voltage regulation method are designed accordingly so that the compatibility of both AC and DC input is realized with low common voltage and small passive devices.Simulation and experimental results demonstrate the effectiveness and performance of the proposed rectifier.

Study on Various Rectifiers for Fan-Filter Units

The face velocities of the high efficiency particulate air filters and the ultra low penetration airfilters in fan filter units (FFUs) have large relative standard deviation and turbulivity. It seriously affects the unidirectivity of the flow in the unidirectional flow clean zone and cleanroom. The cross contamination in this kind of unidirectional flow area is hardly controlled. It is significant to find optional method for keeping the face velocity uniformity of FFU and reducing the face velocity turbulivity of FFU, furthermore, to keep the cleanliness level under FFUs. The normal and easy method is to add flow rectifiers under filters. FFUs with various flow rectifiers have been tested. The uniformity and turbulivity of facevelocity under the FFU are presented in this paper. The influence of the facevelocity uniformity and turbulivity on the contamination boundary of the unidirectional flow is studiedas well.

Rectifier Configurations Based on Harmonic Injecting and Counteracting Principle

On the basis of detailed analysis of a novel harmonic counteracting method which can be used to effectively compensate the supply line harmonic currents of a passive single phase diode bridge rectifier, this paper presents two simpler single phase diode bridge rectifier configurations and their alternatives which can achieve low supply line current THD(total harmonic distortion) too. Moreover, this paper also proposes a few passive hamonic counteracting networks for multi single phase rectifiers which are connected in parallel.

Enhanced gated-diode-triggered silicon-controlled rectifier for robust electrostatic discharge (ESD) protection applications

A robust electron device called the enhanced gated-diode-triggered silicon-controlled rectifier (EGDTSCR) for electrostatic discharge (ESD) protection applications has been proposed and implemented in a 0.18-μm 5-V/24-V BCD process. The proposed EGDTSCR is constructed by adding two gated diodes into a conventional ESD device called the modified lateral silicon-controlled rectifier (MLSCR). With the shunting effect of the surface gated diode path, the proposed EGDTSCR, with a width of 50 μm, exhibits a higher failure current (i.e., 3.82 A) as well as a higher holding voltage (i.e., 10.21 V) than the MLSCR.

Rectifiable空间中的基数不变量

讨论了Rectifiable空间G中以下几个基数不变量:(1)A是G的U-离散子集当且仅当A的闭包是U-离散的;(2)nω(G)≤ib(G)χ(G);(3)若U是e在G中的开邻域,则存在G的子集A且||A≤c(G)使得G=(AU)U;(4)ω(G)=nω(G)χ(G).这些结果推广了拓扑群中的相应结果 .

Coordinate control strategy for stability operation of offshore wind farm integrated with Diode-rectifier HVDC

Due to low investment cost and high reliability,a new scheme called DR-HVDC(Diode Rectifier based HVDC)transmission was recently proposed for grid integration of large offshore wind farms.However,in this scheme,the application of conventional control strategies for stability operation face several challenges due to the uncontrollability of the DR.In this paper,a coordinated control strategy of offshore wind farms using the DR-HVDC transmission technology to connect with the onshore grid,is investigated.A novel coordinated control strategy for DR-HVDC is proposed based on the analysis of the DC current control ability of the full-bridge-based modular multilevel converter(FB-MMC)at the onshore station and the input and output characteristics of the diode rectifier at the offshore.Considering the characteristics of operation stability and decoupling between reactive power and active power,a simplified design based on double-loop droop control for offshore AC voltage is proposed after power flow and voltage–current(I–V)characteristics of the offshore wind farm being analyzed.Furthermore,the impact of onshore AC fault to offshore wind farm is analyzed,and a fast fault detection and protection strategy without relying on communication is proposed.Case studies carried out by PSCAD/EMTDC verify the effectiveness of the proposed control strategy for the start up,power fluctuation,and onshore and offshore fault conditions.

Application of Single-to-Single Phase Matrix Conversion in Conventional Rectifier-Inverter

The principle of single to single phase matrix electric power conversioin is further studied and the conversioin switch function is introduced into conventional rectifier inverter, thus a general character of the two conversion techniques is discovered. It is characteristic of the switch functiion to follow mains voltage distortion and mains frequency drift. By utilizing the merit, unidirectional switch duty rations of the inverter follow the variation of DC link voltage automatically, thus the size of DC link electrolytic capacitor can be reduced considerably, bringing about improved mains side power factor. Corresponding topologies and theoretical and theoretical derivations are given, and so are the simulation results, based on which it is confirmed that the single to single phase matrix conversion technique is potentially useful in large scale production, and the introduction of switch function can yield good economic returns.

Experimental and numerical analyses of high voltage 4H-SiC junction barrier Schottky rectifiers with linearly graded field limiting ring

This paper describes the successful fabrication of 4H-SiC junction barrier Schottky （JBS） rectifiers with a linearly graded field limiting ring （LG-FLR）. Linearly variable ring spacings for the FLR termination are applied to improve the blocking voltage by reducing the peak surface electric field at the edge termination region, which acts like a variable lateral doping profile resulting in a gradual field distribution. The experimental results demonstrate a breakdown voltage of 5 kV at the reverse leakage current density of 2 mA/cm2 （about 80% of the theoretical value）. Detailed numerical simulations show that the proposed termination structure provides a uniform electric field profile compared to the conventional FLR termi- nation, which is responsible for 45% improvement in the reverse blocking voltage despite a 3.7% longer total termination length.

A Nonlinear Control Strategy for Vienna Rectifier Under Unbalanced Input Voltage

The Vienna rectifier with unbalanced input voltage and load transient is analyzed.A nonlinear control strategy for Vienna rectifier under unbalanced input is proposed.From the view of positive and negative sequence components,the proposed nonlinear control strategy suppresses the twice frequency ripple and guarantees the dynamic response characteristic at the same time.Thanks to the proposed nonlinear control strategy,the DC bus capacitor can be reduced a lot since the voltage ripple and drop can be suppressed.A 10 kW Vienna rectifier is built to verify the proposed control strategy.After applying the proposed nonlinear control strategy,the voltage ripple is only7 V and decreases over 75%over the traditional PI control when the unbalanced degree is 20%.The voltage drop can be reduced about 80%than former control strategy which is helpful to reduce the DC bus capacitor and achieve higher power density.The volume of the capacitor can be reduced by 83.3%with the new control method.

Trapezoid mesa trench metal-oxide semiconductor barrier Schottky rectifier:an improved Schottky rectifier with better reverse characteristics

An improved structure of Schottky rectifier, called a trapezoid mesa trench metal oxide semiconductor （MOS） barrier Schottky rectifier （TM-TMBS）, is proposed and studied by two-dimensional numerical simulations. Both forward and especially better reverse I-V characteristics, including lower leakage current and higher breakdown voltage, are demonstrated by comparing our proposed TM-TMBS with a regular trench MOS barrier Schottky rectifier （TMBS） as well as a conventional planar Schottky barrier diode rectifier. Optimized device parameters corresponding to the requirement for high breakdown voltage are given. With optimized parameters, TM-TMBS attains a breakdown voltage of 186 V, which is 6.3% larger than that of the optimized TMBS, and a leakage current of 4.3×10^-6 A/cm2, which is 26% smaller than that of the optimized TMBS. The relationship between optimized breakdown voltage and some device parameters is studied. Explanations and design rules are given according to this relationship.

Stability Mechanisms of Gas Bubbles Subject to Ultrasonic Field during the Rectified Diffusion in Liquids

The spherical oscillation of a gas bubble in liquids is important to growth in liquids during rectified diffusions( e. g., the onset of the sonoluminescence and the enhancement of sonochemical reactions). The present paper numerically shows stability maps( divided into four zones),in which gas bubbles maintain the linearly spherical oscillation without nonlinear disturbance of rectified diffusions within a large range of bubble radius. The critical pressures of spherical and diffusional oscillations are two decisive indexes determining the stability status. Specifically,the stability boundaries and influential factors( including acoustic parameters and gas concentration in liquids) were discussed and analyzed. The results show that the variations of gas concentration and acoustic parameters dramatically changed the stable status of the gas bubbles. The gas bubble maintained stable status when external parameters and gas concentration were set between the two critical values properly. The cases of high-frequency and low-frequency limits were also introduced at the end of the whole paper.

Numerical and experimental study of the mesa configuration in high-voltage 4H–SiC PiN rectifiers

The effect of the mesa configuration on the reverse breakdown characteristic of a SiC PiN rectifier for high-voltage applications is analyzed in this study.Three geometrical parameters,i.e.,mesa height,mesa angle and mesa bottom corner,are investigated by numerical simulation.The simulation results show that a deep mesa height,a small mesa angle and a smooth mesa bottom（without sub-trench） could contribute to a high breakdown voltage due to a smooth and uniform surface electric field distribution.Moreover,an optimized mesa structure without sub-trench（mesa height of 2.2 μm and mesa angle of 20°） is experimentally demonstrated.A maximum reverse blocking voltage of 4 kV and a forward voltage drop of 3.7 V at 100 A/cm^2 are obtained from the fabricated diode with a 30-μm thick N^- epi-layer,corresponding to 85% of the ideal parallel-plane value.The blocking characteristic as a function of the JTE dose is also discussed for the PiN rectifiers with and without interface charge.

Study of a double epi-layers SiC junction barrier Schottky rectifiers embedded P layer in the drift region

This paper proposes a double epi-layers 4H-SiC junction barrier Schottky rectifier （JBSR） with embedded P layer （EPL） in the drift region. The structure is characterized by the P-type layer formed in the n-type drift layer by epitaxial overgrowth process. The electric field and potential distribution are changed due to the buried P-layer, resulting in a high breakdown voltage （BV） and low specific on-resistance （Ron,sp）. The influences of device parameters, such as the depth of the embedded P＋ regions, the space between them and the doping concentration of the drift region, etc., on BV and Ron,sp are investigated by simulations, which provides a particularly useful guideline for the optimal design of the device. The results indicate that BV is increased by 48.5% and Baliga＇s figure of merit （BFOM） is increased by 67.9% compared to a conventional 4H-SiC JBSR.

Differential Effects of d, l-Sotalol and d-Sotalol on Isoproterenol-Increased Delayed Rectifier Outward Potassium Current in Guinea Pig Single Ventricular Myocytes

The aim of this study was to compare the effects of d, l-Sotalol and dSotalol on the delayed rectifier K+ outward current in the presence of isoproterenol at different concentrations. Time-dependent delayed rectifier K+ outward currents were measured in isolated guinea pig single myocytes using the whole-cell configuration of the patch-clamp technique. Currents were measured in response to 300 ms depolarizing pulses from a holding potential of -40 mV in three experimental protocols [control, isoproterenol (10^(9)mol/L - 10^(-6) mol/L ), and isoproterenol (10^(-9)mol/L - 10^(-6)mol/L ) plus either d, l-Sotalol (10^(-4) mol/L) or d-Sotalol (10^(-4) mol/L)]. IK tail currents were measured upon repolarization to -40 mV. It was found that Ik was significantly amplified in the presence. of isoproterenol (10^(-9) mol/L- 10^(-6) mol/L) plus d-Sotalol. At 10-8 mol/L isoproterenol, Ik was increased by 92. 7%±17. 1 % (P<0. 05) and 54. 3 %±13. 4 % after d-Sotalol addition (P<0. 05). In contrast, d, l-Sotalol completely conteracted the increase of iK by isoproterenol (<10^(-8) mol/L), and compared to control, Ic was decreased by 35. 6 % ±8. 1% at 10^(-8) mol/L isoproterenol plus d, l-Sotalol (P<0. 05). It is concluded that the β-adrenergic blocking property of d, l-Sotalol but not that of dSotalol maintains the delayed rectifier K+ outward current blockade in the presence of isoproterenol in guinea pig myocytes. This might contribute to a superior antiarrhythmic efficacy as compared to d-Sotalol.

Structure-dependent behaviors of diode-triggered silicon controlled rectifier under electrostatic discharge stress

The comprehensive understanding of the structure-dependent electrostatic discharge behaviors in a conventional diode-triggered silicon controlled rectifier （DTSCR） is presented in this paper. Combined with the device simulation, a mathematical model is built to get a more in-depth insight into this phenomenon. The theoretical studies are verified by the transmission-line-pulsing （TLP） test results of the modified DTSCR structure, which is realized in a 65-nm complementary metal-oxide-semiconductor （CMOS） process. The detailed analysis of the physical mechanism is used to provide predictions as the DTSCR-based protection scheme is required. In addition, a method is also presented to achieve the tradeoff between the leakage and trigger voltage in DTSCR.