Passive Load Research Articles

Mechanical Response Analysis for an Active–Passive Pile Adjacent to Surcharge Load

Due to the complexity of pile–soil interaction, there is little research on active–passive piles that bear the pile-top load transmitted from the superstructure and the pile shaft load caused by the lateral soil movement around the pile simultaneously. The purpose of this study is to analyze the displacement and internal force of active–passive piles. Most of the pile design codes in China use the elastic resistance method to describe the relationship between the lateral soil resistance and the horizontal displacement of the pile, but this is not accurate enough to analyze the internal force and deformation of the pile when the pile displacement is large. For this case, the passive load on the pile shaft caused by the adjacent surcharge load can be described in stages, and the p–y curve method can be used to express the relationship between the lateral soil resistance and the horizontal displacement of the pile. Additionally, taking both the active load (vertical force, horizontal force, and bending moment on the pile top) and the passive load into account, the deflection differential equation of the pile shaft is herein established, and a corresponding finite difference method program is implemented to obtain the calculations pursuant to the equation. The correctness of the analysis method and program was verified by two test cases. The results show that our calculation method can effectively judge the flow state of the soil around piles and accurately reflect the nonlinear characteristics of pile-soil interaction. Moreover, the influence depth of the pile displacement under the passive pile condition caused by the adjacent load is significantly greater than that under active pile condition, and the maximum pile-bending moment appears near the interface of soft and hard soil layer.

Performance analysis on parallel operation of multimode droop controller doubly fed induction generator based wind energy conversion system with Other wind unit, solar units, loads and facts device

Due to their numerous advantages, wind turbines with changeable speed power production systems are increasingly being used. This study proposes the architecture and specifications of an induction turbine-generating wind system, as well as a PI controller-based DC voltage link regulator and optimal torque control system. The suggested control technique as stated in this paper allows the system to function in grid-linked mode as well as the islanded mode and also in parallel with other power generation units, loads, FACTS devices, etc. This paper involves the analysis of different test cases in grid-connected mode as well as an islanded mode with a PV generation unit, passive loads, induction motor loads, and other wind energy generation systems. The paper also includes an analysis of the response of the system with the switching on and off of the other units. MATLAB 2013a thereby validates the system findings and analysis.

Flare folding wing tips for static and gust loads alleviation

The Passive gust load alleviation device can effectively simplify the control system by relying on the adaptive deformation of the structure. This research examines the influence of using folding wingtips during flight as a means of reducing static loads and gusty loads. Effects of hinge direction, wing-tip weight, stiffness and wing-tip centre of gravity on static and gust alleviation performance has been examined. The results show that the flare folding wing-tip can significantly reduce the static load and gust load of the aircraft. In a static aeroelastic trim analysis, a folding wingtip can increase span by 25% without increasing the wing root bending moment and decrease the trim angle of attack by 0.14°. In the gust response analysis, the maximum bending moment of wing root can be decrease by nearly 50% compared with the fixed wing-tip, only 17% higher than the baseline model without a wing-tip.

Flexible and Low-Cost Emulation of Control Behaviors for Testing and Teaching of AC Microgrid

The fast development of distributed generations enables the microgrid a popular solution for the construction of the modern power grid, where the control behaviors of power electronics converters play a crucial role. Under this scenario, the emulation of microgrid control behaviors is becoming an emerging need for the testing and teaching of the AC microgrid. However, conventional approaches, such as the dynamic simulation test and the Power-Hardware-In-Loop, are still costly or bulky to flexibly recreate the correct characteristics of microgrid including different layers of controls and the interactions among multiple converters. The dynamic simulation test is bulky and costly to emulate various types of control behaviors since all physical components in the test system may need to be adjusted. The high cost of Power-Hardware-In-Loop is mainly caused by the high-performance real-time simulator and power amplifier. In this paper, a novel emulation system is proposed for the testing of the AC microgrid. A low-cost circuit configuration, which includes two face-to-face connected DC–AC converters and some passive loads, is introduced with the possibility of flexibly emulating most of the typical control schemes in an AC microgrid. In addition, a user interface for the real-time operation and measurement of the hardware platform is introduced on a host computer to further facilitate the testing process. Finally, various control schemes in microgrids, including the voltage control, current control, droop control, and secondary control, are validated in the experiment setup based on the proposed emulation approach.

Assessment and enhancement control for small‐signal voltage stability of VSC‐HVDC systems supplying passive industrial loads

AbstractThis paper presents a comprehensive assessment for the small‐signal voltage stability of voltage source converter (VSC)‐HVDC systems supplying industrial loads represented by the induction motors (IMs) and provides a stability enhancement control for the VSCs. First, the steady‐state voltage stability is analysed to seek the factors that affect the existence of the stable equilibrium point. Then, the small‐signal voltage stability analysis is performed based on the developed linear model. Eigenvalue analysis is carried out to capture the critical factors that induce instability phenomena correlative to the system voltage. It demonstrates that decreasing either the proportional gain K of the VSC's PI controller or the electrical distance between the VSC and IM is detrimental to voltage stability. Next, the enhancement control strategy is elaborated. It adopts virtual reactance and virtual admittance control for the VSC to improve the voltage control capability. Finally, the effectiveness and robustness of the proposed enhancement control are validated via time‐domain simulations in a multi‐IM system supplied by VSC‐HVDC.

Aging-robust amplifier composed of p-type low voltage OTFT and organic semiconductor load

This paper proposes an amplifier circuit design suitable for low-voltage organic thin-film transistors (OTFTs). To overcome the issues common to low-voltage OTFTs, such as the yield, degradation, and performance differences between p-type and n-type TFTs, we design the circuit based on an inverter comprising only p-type transistors. The optimal bias voltage for the amplifier stage is provided through a bias circuit. The transistor performance degradation is compensated for by sharing the gate bias voltage (i.e. the main cause of degradation) between the bias and amplifier stages. In addition, an organic semiconductor is used as a passive load of the amplifier to reduce the area and failure probability. Test chip measurements demonstrate that the organic material operates as a resistor. The gain and cut-off frequencies of the proposed amplifier circuit can be adjusted by changing the size of the dinaphtho[2,3-b:2’,3’-f]thieno[3,2-b]-thiophene resistor, providing a maximum gain of 27 dB. The proposed circuit can operate continuously for over 100 min without significant characteristic changes. The operation of the bias circuit, when applied to a differential amplifier design, is also verified. The differential amplifier achieves a maximum common-mode rejection ratio of 25 dB.

Novel High Power Pulsed Mode Operation of Commercial Continuous-Wave Magnetron

In this article, for the first time, we proposed and studied the operation of industrial 1 kW continuous-wave (CW) S-band magnetrons in a high-power pulsed mode. It turns out that these devices in standard version have a superior pulsed performance: range of stable regulation of pulse power with high efficiency up to 8 kW, pulse duration from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.3~\mu \text{s}$ </tex-math></inline-formula> to continuous mode, and repetition rate of at least 1 MHz. The possibility of forming sequences of paired pulses with an adjustable time shift from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1~\mu \text{s}$ </tex-math></inline-formula> has been demonstrated. The parameters are provided both in the free-running and injection-locking modes. A specialized high-voltage pulse power supply (PPS) with adjustable parameters was designed for measurements. On a passive resistive load, the PPS provides output high voltage of 4.0–5.2 kV, output current up to 3 A in pulse and 0.5 A in average mode, pulse duration from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.1~\mu \text{s}$ </tex-math></inline-formula> , pulse edges less than 0.1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> , and repetition rate up to 1 MHz. The effect of limiting the pulsed microwave power by emission current was detected for the first time. The investigated CW magnetrons in pulsed mode can be used in microwave technology, accelerator equipment, and for research purposes.

The effect of external loads and biological sex on coupling variability during load carriage

BackgroundLoad carriage is a fundamental requirement for military personnel that commonly results in lower-limb injuries. Coupling variability represents a potential injury mechanism for such repetitive tasks and its unknown whether external loads and biological sex affect coupling variability during load carriage. Research questionIs there a sex-by-load interaction during load carriage at self-selected walking speeds? MethodsTwenty-six participants (13 males, 13 females) completed three 10-minute treadmill-based trials wearing body-borne external load (0 %BM, 20 %BM, and 40 %BM) at load-specific self-selected walking speeds. A Vicon motion capture system tracked markers with a lower-body direct-kinematic model calculating sagittal-plane segment kinematics of the thigh, shank, and foot across 19 strides. Continuous relative phase standard deviation (CRPv) provided a measure of coupling variability for each coupling angle (Thigh-Shank and Shank-Foot). The CRPv for each load and sex was compared using statistical parametric mapping repeated measures ANOVA and paired t tests. ResultsSignificant sex-by-load interactions were reported for the Thigh-Shank coupling. Males demonstrated no significant load differences in CRPv, however, females displayed significantly higher CRPv in the 40 %BM than the 0 %BM condition. A significant main effect of load was observed in the Shank-Foot coupling, with the 40 %BM having significantly greater CRPv than the other load conditions. SignificanceBoth biological sex and external loads significantly affected CRPv during load carriage at self-selected walking speeds. Females demonstrated greater CRPv at the heavier loads, suggesting that the perturbation from the heavier mass increases coupling variability, which may also be amplified by a greater total passive load due to their relatively higher adipose tissue compared to males. The consistent CRPv in males suggests that higher relative loads may be required to change coupling variability. Collectively, these results suggest that external load affects the coupling variability of males and females differently, providing potential for injury screening and monitoring programs.

Informed Prosumer Aggregator Bidding Strategy via Incorporating Distribution Grid Outage Risk Predictions

FERC Order 2222 paves the way for aggregated distributed energy resources (DERs) participation in the wholesale electricity market. A particular DER assumed to be widely available in the future is the distributed prosumer (DP), also called virtual power plant (VPP), which may host PV generation, and stationary and mobile battery energy storage systems, in addition to the on-site passive load. DP aggregation and participation in the day-ahead market ancillary service products (ASPs) require managing uncertainties associated with load consumption and photovoltaic generation, electric vehicle (EV) scheduling, market-clearance prices, etc. Outages in the distribution grid may distort these energy-limited resources from their optimal operating point, potentially impacting their ability to deliver the committed ASPs in real-time. To address these challenges, first, we develop a machine learning algorithm to predict the risk of outages in distribution feeders. Next, we incorporate the distribution feeder State of Risk (SoR) predictions with the bidding model of the DP aggregator to provide an informed decision-making tool for optimal participation in the energy and ASP markets. The simulation results demonstrate the efficacy and scalability of the proposed model in improving the aggregator profitability and preventing penalties for the inability to deliver ASPs due to unexpected energy capacity limits of DP assets.

Radially Extended 3D Birdcage Antenna for MRI With Loop-Type Legs and Connection to the Shield

A novel radially extended 3D birdcage (BC) coil antenna was designed, simulated, and optimized for a cylindrical dielectric phantom at 4.7 T. The 3D birdcage consists of a classical birdcage with additional protrusions toward the inside and connections to the shield. To overcome the huge computational burden of the optimization process using the particle swarm optimization (PSO) method, an in-house method of moment (MoM) code exploiting the symmetry of the structure has been developed. The code produces open-circuit embedded element patterns and makes use of a Schur complement to analyze the effects of passive loads, in the presence of a phantom. The simulation results have been verified with the use of commercial software. The proposed 3D BC coil showed a 34 % improvement in the homogeneity of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> and a 37 % reduction in the peak specific absorption rate (SAR), compared with a conventional BC coil.

Enhancing active reconfigurable intelligent surface

A Reconfigurable Intelligent Surface (RIS) panel comprises many independent Reflective Elements (REs). One possible way to implement an RIS is to use a binary passive load impedance connected to an antenna element to achieve the modulation of reflected radio waves. Each RE reflects incoming waves (incident signal) by using on/off modulation between two passive loads and adjusting its phase using a Phase Shifter (PS). However, this modulation process reduces the amplitude of the reflected output signal to less than unity. Therefore, recent RIS works have employed Reflection Amplifiers (RAs) to compensate for the losses incurred during the modulation process. However, these systems only improve the reflection coefficient for a single modulation state, resulting in suboptimal RE efficacy. Thus, this paper proposes a strategy for optimising RE by continuously activating the RA regardless of the switching load state. The performance of the proposed scheme is evaluated in two scenarios: (1) In the first scenario (Sc1), the RA only operates to compensate for high-impedance loads, and (2) in the second scenario (Sc2), the RA runs continuously regardless of the RE loads. To benchmark the performance of Sc1 and Sc2, various metrics are compared, including signal-to-noise ratio, insertion loss, noise figure, communication range, and power-added efficiency. Numerical examples are provided to demonstrate the effectiveness of the proposed scheme. It is found that the proposed system in Sc2 leads to better overall performance compared to Sc1 due to the increased gain of the RIS reflection.

Flow-Induced Dynamic Behavior of Head-Cover Bolts in a Prototype Pump-Turbine during Load Rejection

In order to ensure stable grid operatiFon and improve power quality, active or passive load rejection of pumped storage power stations (PSPS) inevitably occurs from time to time. The rapid closing of the guide vanes will cause drastic changes in pressure pulsations in the flow channel of the pump-turbine (PT) unit. The high-level pressure pulsations during load rejection transfer to the entire flow passage of the PT unit and generate strong vibrations on the head-cover and the connecting bolts. In this study, the 1D/3D joint simulation of the pipeline in a pumped storage power station and the turbine flow channels including the flow domains of the runner, crown chamber, band chamber, upper and lower labyrinths and pressure balance tubes is carried out first. Then, by applying the calculated pressure loads on the head-cover, stay vanes and bottom ring of the PT unit, the flow-induced dynamic behavior of the structures including the head-cover bolts is analyzed in detail. The results demonstrate that pressure loads on head-cover bolts change dramatically during the load rejection process. The flow-induced deformation of the inner head-cover during the load rejection is larger than that of other structures, and the flow-induced displacement and stress of different head-cover bolts are not uniform. The achieved conclusions in this study can be a useful reference for the design and operation of head-cover bolts for other PT units and high-head Francis turbine units.

Application of Aeroelastic Tailoring for Load Alleviation on a Flying Demonstrator Wing

This article presents the application of aeroelastic tailoring in the design of wings for a flying demonstrator, as well as the validation of the design methodology with flight test results. The investigations were performed in the FLEXOP project (Flutter Free Flight Envelope Expansion for Economical Performance Improvement), funded under the Horizon 2020 framework. This project aimed at the validation of methods and tools for active flutter control, as well as at the demonstration of the potential of passive load alleviation through composite tailoring. The technologies were to be demonstrated by the design, manufacturing and flight testing of an unmanned aerial vehicle of approximately 7 m wingspan. This article addresses the work towards the load alleviation goals. The design of the primary load-carrying wing-box in this task is performed using a joint DLR–TU Delft optimization strategy. Two sets of wings are designed in order to demonstrate the potential benefits of aeroelastic tailoring—first, a reference wing in which the laminates of the wing-box members are restricted to balanced and symmetric laminates; second, a tailored wing in which the laminates are allowed to be unbalanced, hence allowing for the shear–extension and bending–torsion couplings essential for aeroelastic tailoring. Both designs are numerically optimized, then manufactured and extensively tested to validate and improve the simulation models corresponding to the wing designs. Flight tests are performed, the results of which form the basis for the validation of the applied aeroelastic tailoring approach presented in the article.

Study on mechanical properties of wind turbine blades with bend-twist coupling effect

Bend-twist coupling (BTC), a method of passive load alleviation for turbine blade, has a significant influence on blade mechanical properties. The coupling behavior between bending and twisting motions stems from the material anisotropy in blade laminate or from the unique blade geometry such as sweep, deflection, and pre-bending. The material-based approach is employed in this research to determine influence regularity of BTC design on blade mechanical properties. To begin with, the blade property analysis tool PreComp that integrates a shear flow method with the classical laminate theory is adopted to compute the cross-sectional stiffnesses of the blades with different degree of BTC effect. Next, the bend-twist coupling coefficients for the BTC blades with different fiber orientation are calculated. Finally, the remaining mechanical properties including static performance, modal characteristics and buckling limits for different BTC blades are determined by the finite element method and the influence of changes in the degree of BTC effect on all these mechanical properties is further evaluated. The results show that the BTC effect markedly influences the different mechanical properties of the blade in different patterns. The 20° BTC blade has the highest BTC coefficient and the edgewise BTC coefficient at 100 m is 2.5 times higher than the flapwise BTC coefficient, while the maximum value of the torsional modal frequency of 3.8429 Hz and the greatest critical buckling load of 4328.1 kN corresponds to the 10° BTC blade and the 15° BTC blade respectively.

Frontal plane ankle stiffness increases with axial load independent of muscle activity

Ankle sprains are the most common musculoskeletal injury, typically resulting from excessive inversion of the ankle. One way to prevent excessive inversion and maintain ankle stability is to generate a stiffness that is sufficient to resist externally imposed rotations. Frontal-plane ankle stiffness increases as participants place more weight on their ankle, but whether this effect is due to muscle activation or axial loading of the ankle is unknown. Identifying whether and to what extent axial loading affects ankle stiffness is important in understanding what role the passive mechanics of the ankle joint play in maintaining its stability. The objective of this study was to determine the effect of passive axial load on frontal-plane ankle stiffness. We had subjects seated in a chair as an axial load was applied to the ankle ranging from 10% to 50% body weight. Small rotational perturbations were applied to the ankle in the frontal plane to estimate stiffness. We found a significant, linear, 3-fold increase in ankle stiffness with axial load from the range of 0% body weight to 50% body weight. This increase could not be due to muscle activity as we observed no significant axial-load-dependent change in any of the recorded muscle activations. These results demonstrate that axial loading is a significant contributor to maintaining frontal-plane ankle stability, and that disruptions to the mechanism mediating this sensitivity of stiffness to axial loading may result in pathological cases of ankle instability.

Slow-Scale Bifurcation in Three-Level T-Type Inverter With Passive Memristive Load

Slow-Scale Bifurcation in Three-Level T-Type Inverter With Passive Memristive Load

Short-Circuit Fault Detection and Isolation Using Filter Capacitor Current Signature in Low-Voltage DC Microgrid Applications

This article describes a novel short-circuit (SC) fault detection approach to protect the low-voltage dc microgrid (LV-DCMG). The SC faults are the most common fault in the dc power system and can cause severe hazards if not isolated. Since a DCMG is a capacitor-dominated grid, the proposed scheme utilizes these filter capacitor current dynamics. An LV-DCMG system is considered for building the application to realize the proposed fault detection scheme. Active sources such as solar photovoltaic and battery are connected to the passive loads through a dc-dc converter, dc cable, and solid-state relays. The proposed method considers an average of the capacitor current as a detection parameter. An iteration-based isolation configuration is also suggested for a zonal type of distributed network. Furthermore, a selection procedure of the thresholds is also presented in detail. The validity of the proposed approach is verified through both digital simulation studies and DSP-based experimental studies. The proposed approach is capable of detecting both low and high impedance faults.

Optimal Control Strategy of Back-to-Back Converter Based on AC/DC Voltage Source Converter

The back-to-back converter is a converter system composed of two voltage source converters (VSC). Because VSC can regulate the output of active and reactive power, the back-to-back converter has a good dynamic and static performance. However, not all passive loads are three-phase symmetrical. The existing control strategy may lead to asymmetric output voltage when back-to-back converter is used to supply unbalance load. Usually, an inner loop d/q decoupling controller, a constant DC voltage controller of the rectifier side, and a constant AC voltage controller of the inverter side are established. In this article, in order to improve the rectifier side, fuzzy online self-tuning is used to increase PI parameters on the outer voltage loop. PI control is replaced by PR control on the inner current loop. The improved rectifier control can reduce the overshoot and the output of harmonics. For the inverter side, the three-phase voltage will be imbalanced. Therefore, using PR control, which can track a sinusoidal signal without steady-state error, the control strategy of inverter is changed into “outer loop constant voltage and PR control-inner loop current d/q decoupling control.” This strategy can solve the unbalance problem of three-phase AC output. The simulation results show that the control strategy can solve the problem of asymmetric output voltage of the inverter side effectively.

Thirteen-Level Multilevel Inverter Structure Having Single DC Source and Reduced Device Count

This article proposes a single dc source-based hybrid three-phase thirteen-level inverter suitable for medium voltage applications. The multilevel structure is composed of a three-level T-type neutral point clamped (NPC), half-bridge, and three-level Flying capacitor converter with optimal switch count and high dc bus voltage utilization as high as 0.63 times the dc-link voltage. This requires a special attention to a novel capacitor balancing method using redundant switching states in order to operate at any power factor under grid-connected mode. A unified common-mode voltage is injected in the carrier based pulse width modulation (PWM) technique to maintain the voltage balance in dc-link capacitors as well as floating capacitors. Simulation results are presented under different operating conditions that include unity power factor operation with passive load as well as grid-connected inverter mode. The performance of the proposed multilevel inverter in the grid-connected mode is also validated with experimental results using a lab prototype.

Life cycle assessment (LCA) of precast concrete blocks utilizing ground granulated blast furnace slag.

Concrete paving block (CPB) has become a popular construction material for pavements subjected to passive loads (parking, toll plazas, gas stations, and street pavements). Due to the short time in the production of CPB, the concrete block industry has experienced tremendous growth over the past decade. In this scenario, the environmental distress cannot be ignored due to the increased extraction of raw materials (fossil fuels, limestone, river sand, and crushed aggregates) in the manufacturing of CPB. The sustainability issues demand the utilization of eco-friendly materials instead of natural ones to minimize the abiotic depletion caused by the construction industry. This study investigates the technical and environmental performance of CPB production incorporating an eco-friendly mineral admixture, i.e., ground granulated blast furnace slag (GGBS), as a cement replacement material. The optimum level of GGBS was decided based on the required engineering performance and minimal environmental impact. For the determination of the engineering performance of CPB, several parameters were considered such as compressive strength (CS), impact toughness (IT), and water absorption (WA). The environmental impact of Global Warming Potential (GWP) was assessed based on a cradle-to-gate LCA analysis. The results suggested that maximum mechanical performance and minimum GWP can be simultaneously achieved at 5-10% replacement of cement with GGBS, while to satisfy the minimum strength requirement, CPB can be prepared using 25% GGBS as a replacement for cement that accounts for 17% lower GWP than that of the conventional CPB manufacturing.