Coordinated Control of Voltage Balancers for the Regulation of Unbalanced Voltage in a Multi-Node Bipolar DC Distribution Network

In a bipolar DC distribution network, the unbalanced load resistance, line resistance and renewable energy source will cause an unbalanced current for each node of the neutral line and lead to its unbalanced voltage. This is a unique power quality problem of bipolar DC distribution networks, which will increase the power loss in the network and lead to overcurrent protection of the neutral line in serious cases. A voltage balancer can be adopted to suppress the unbalanced voltage and current. However, the existing literature does not consider the consistent application of multiple voltage balancers in a multi-node bipolar DC distribution network. This paper creatively proposes a consensus control topology combining primary control and secondary control in a radial multi-node bipolar DC distribution network with voltage balancers. In this paper, the formulas for the positive and negative current and duty cycle of a bipolar DC distribution network with voltage balancers are derived, and improved voltage balancer modeling based on a consensus algorithm is built. The radial multi-node bipolar DC distribution network is established in MATLAB/Simulink. The simulation results compare the consensus control with the traditional droop control and verify the effectiveness of the new control structure with voltage balancers.

Effect of low-load resistance training with different degrees of blood flow restriction in patients with knee osteoarthritis: study protocol for a randomized trial

Background Knee osteoarthritis (KOA) is a common degenerative disease that causes pain, functional impairment, and reduced quality of life. Resistance training is considered as an effective approach to reduce the risk of muscle weakness in patients with KOA. Blood flow restriction (BFR) with low-load resistance training has better clinical outcomes than low-load resistance training alone. However, the degree of BFR which works more effectively with low-load resistance training has not been determined. The purpose of this study is to evaluate the effectiveness of different degrees of BFR with low-load resistance training in patients with KOA on pain, self-reported function, physical function performance, muscle strength, muscle thickness, and quality of life. Methods This is a study protocol for a randomized, controlled trial with blinded participants. One hundred individuals will be indiscriminately assigned into the following groups: two training groups with a BFR at 40% and 80% limb occlusion pressure (LOP), a training group without BFR, and a health education group. The three intervention groups will perform strength training for the quadriceps muscles twice a week for 12 weeks, while the health education group will attend sessions once a week for 12 weeks. The primary outcome is pain. The secondary outcomes include self-reported function, physical function performance, muscle strength of the knee extensors, muscle mass of the quadriceps, quality of life, and adverse events. Intention-to-treat analysis will be conducted for individuals who withdraw during the trial. Discussion Previous studies have shown that BFR with low-load resistance training is more effective than low-load resistance training alone; however, a high degree of BFR may cause discomfort during training. If a 40% LOP for BFR could produce similar clinical outcomes as an 80% LOP for BFR, resistance training with a low degree of BFR can be chosen for patients with KOA who are unbearable for a high degree of BFR. Trial registration Chinese Clinical Trial Registry ChiCTR2000037859 (http://www.chictr.org.cn/edit.aspx?pid=59956&htm=4). Registered on 2 September 2020

Experimental and Numerical Study on the Winged Pile-Soil Interaction under Lateral Loads

Increasing the cross-sectional area of piles leads to an increase in the lateral bearing resistance and reduces displacements near ground level. This increase compensates for the reduction in soil stiffness at the seabed level. Installing wings near the mudline level is one approach for increasing the area of the pile in mudline level. This research paper discusses a number of small-scale laboratory models and FEM models to study the benefit of adding wings on the variation of bearing capacity of laterally pile loaded embedded in sandy soil. To determine the advantages of adding wings to the pile, four embedded ratios (4, 6, 8, 10) were used to model both flexible and rigid pile types with various wing numbers and dimensions. The results revealed that adding wings to the pile improves lateral load resistance and greatly reduces lateral deflection. So, to achieve better resistance, wings must be linked with the pile shaft perpendicular to the lateral load applied nearer the top of the pile head. Increasing the number of wings results in a large increase in lateral pile capacity. The ultimate lateral applied load is proportional to the rise in relative density at the same (L/D) ratio.

Load & Resistance Factors Calibration for Front Covered Caisson Breakwater

Calibration of load-resistance factors for the limit state design of front covered caisson breakwaters were presented. Reliability analysis of the breakwaters which are constructed in Korean coast was conducted. Then, partial safety factors and load-resistance factors were sequentially calculated according to target reliability index. Load resistance factors were optimized to give one set of factor for limit state design of breakwater. The breakwaters were redesigned by using the optimal load resistance factor and verified whether reliability indices larger than the target value. Finally, load-resistance factors were compared with foreign country’s code for verification.

A High-Efficiency Self-Synchronous RF–DC Rectifier Based on Time-Reversal Duality for Wireless Power Transfer Applications

An RF–DC rectifier is an important part in a wireless power transfer system. Diode-based rectifiers are widely used in low-power harvesting scenarios, and for high power, a transistor based on the time-reversal duality was proposed. This paper presents a high-efficiency self-synchronous RF–DC rectifier based on a waveform-guided design method and an improved rectification model of a commercial GaN device. The main contributions of this paper are that (1) an improved transistor model with correct reverse bias is built for accurate rectifier simulation, and (2) a new design method of self-synchronous RF–DC rectifier is proposed: as soon as the operating mode of the rectifier, input power, and DC load are set, matching and coupling network can be calculated directly based on waveform-guided method, thus design and adjustment process of a conventional power amplifier (PA) due to the duality between a PA and a rectifier would no longer be required. A 5.8 GHz self-synchronous RF–DC rectifier is designed for validation, and the optimum RF–DC conversion efficiency is 68% with 12 W input power as well as 19.9 V output DC potential with 50 Ω load resistance. The proposed rectifier is suitable for high input power rectification applications of wireless power transfer.

Layer Adhesion Test of Additively Manufactured Pins: A Shear Test

Additive Manufacturing (AM) became a popular engineering solution not only for Rapid Prototyping (RP) as a part of product development but as an effective solution for producing complex geometries as fully functional components. Even the modern engineering tools, such as the different simulation software, have a shape optimization solution especially for parts created by AM. To extend the application of these methods in this work, the failure properties of the 3D-printed parts have been investigated via shear test measurements. The layer adhesion can be calculated based on the results, which can be used later for further numerical modeling. In conclusion, it can be stated that the layer formation and the structure of the infill have a great influence on the mechanical properties. The layers formed following the conventional zig-zag infill style show a random failure, and the layers created via extruded concentric circles show more predictable load resistance.

Compact and High-Efficiency Rectenna for Wireless Power-Harvesting Applications

A compact, single-layer microstrip rectenna for dedicated far-field RF wireless power-harvesting applications is presented. The proposed rectenna circuit configurations including multiband triple L-Arms patch antenna with diamond slot ground are designed to resonate at 10, 13, 17, and 26 GHz with 10 dB impedance bandwidths of 0.67, 0.8, 2.45, and 4.3 GHz, respectively. Two rectifier designs have been fabricated and compared, a half wave rectifier with a shunted Schottky diode and a voltage doubler rectifier. The measured and simulated maximum conversion efficiencies of the rectifier using the shunted diode half-wave rectifier are 41%, and 34%, respectively, for 300 Ω load resistance, whereas they amount to 50% and 43%, respectively, for voltage doubler rectifier with 650 Ω load resistance. Compared to the shunted rectifier circuit, it is significant to note that the voltage doubler rectifier circuit has higher efficiency. Both rectifier’s circuits presented are tuned for a center frequency of 10 GHz and implemented using 0.81 mm thick Rogers (RO4003c) substrate. The overall size of the antenna is 16.5 × 16.5 mm2, and the shunted rectifier is only 13.3 × 8.2 mm2 and 19.7 × 7.4 mm2 for the voltage doubler rectifier. The antenna is designed and simulated using the CST Microwave Studio Suite (Computer Simulation Technology), while the complete rectenna is simulated using Agilent’s ADS tool with good agreement for both simulation and measurements.

Influence of cenosphere on CAI strength of glass epoxy laminate

Under controlled lab settings, two distinct laminates, one containing cenosphere and the other with neat resin, were evaluated for impact using a Fractovis impact machine, compression testing, and compression after impact tests (CAI) with a Tinus Olsen UTM. The GFRP laminates were made by hand lay-up method with 16 layers of glass fiber in 4.7±0.2 mm thickness and combined with epoxy resin reinforced Cenospheres at concentrations of 1, 3 and 5 wt. %, according to ASTM specifications. The dominant failure mode controlling the specimen's compression ultimate load resistance, and other failure modes of impacted specimens such like fiber pull-out and debonding, were found to be the effects of delamination using coupled acoustic emission (AE) monitoring and compression tests. On specimens with a 3 wt. % filler additive, there was a noticeable increase in strength. Both impacted and non-impacted samples exhibited significant compression ultimate load resistances, with the 3 wt. % filler impregnated specimen having the maximum.

GRAPHICAL METHOD FOR DETERMINATION OF MQ-SERIES GAS SENSOR CIRCUIT PARAMETERS FOR A STAND-ALONE GAS ALARM SYSTEM

Background: MQ-series gas sensors belong to the metal oxide semiconductor (MOS) family of sensors that can sense the presence of many gases. These sensors find their application in gas alarm systems as key components. While necessary sensor circuit output voltage value for alarm point in a stand-alone gas alarm system is desirable, but what exact combination of the sensor circuit parameters is required? Hitherto, the determination of these circuit parameters has not been given much attention in the research community. Aim: the purpose of this work is to explore a structured graphical approach of determination of MQ series gas sensor circuit parameters for a stand-alone gas alarm system that yields desired sensor circuit output voltage value for the alarm point; the main objective of the study was to develop mathematical model equations that relate the: (i) sensor resistance (RS) with the gas concentration (x) and the sensor resistance at standard calibration concentration of the sensor base gas in the clean air (Ro) and (ii) sensor circuit output voltage (VRL), load resistance (RL) and sensor resistance (RS). It is expected from the model equations developed that graphical correlations of the sensor circuits parameters will be generated. Using these graphs for a particular case of an MQ-4 gas sensor under the influence of LPG, the parameters that yield desired sensor circuit output voltage of 2V for 1000 ppm of LPG alarm point will be determined. Methods: Model equations were developed for the sensor dynamics, and based on these model equations, graphs for the determination of required sensor parameters were plotted for a case of MQ-4 gas sensor response to LPG. Results and Discussion: The results yielded optimal values for R_O,R_S and R_L of 20 kΩ, 30 kΩ and 20 kΩ respectively, for alarm settings of 1000 ppm and a desired sensor circuit output voltage of 2 V. Based on determined parameters, the calibration equation for determination of best concentration value for a given value of emulated LPG concentration was developed. Using the method proposed in this study makes the process of determining the MQ-series gas sensor circuit parameters less cumbersome as their value can easily be obtained from the resulting graphs. Conclusions: a structured graphical approach for determination of MQ-series gas sensor circuit parameters for alarm points in a stand-alone gas alarm system showed that using MQ-4 gas sensor and LPG as the target gas, and for a sensor circuit output voltage of 2 V for alarm point at 1000 ppm of LPG, the corresponding value of R_O, R_S and R_L obtained were 20 kΩ, 30 kΩ, and 20 kΩ respectively. Hence, a structured graphical approach is suitable for determining MQ series gas sensor circuit parameters for a stand-alone gas alarm system under the influence of its associated gases.

A Multi-Mode Broadband Vibration Energy Harvester Based on MEMS 3D Coils

This paper presents an electromagnetic vibration energy harvester utilizing 3D MEMS coils and multi-mode structure to improve the output power and broaden the frequency band. We fabricated and assembled the prototype, with a pair of 3D coils fabricated by lithography, silicon etching, silicon direct bonding and copper electroplating, et al., which are compatible with CMOS processes. The numerical simulation was conducted to analysis the vibration modes of the spring-mass system, which revealed the multi-mode mechanism of serpentine springs. We also tested the output power-frequency curves for different load and excitation acceleration to investigate the optimal load resistance and the influence of excitation. The test results showed that the proposed prototype can generate 1.2μW power under 992Hz for 1g acceleration with a half-power bandwidth of 65Hz, which are higher than some recent published data, proving the superiority of proposed structure.