Ramp Changes Research Articles

Novel bio-inspired memetic salp swarm algorithm and application to MPPT for PV systems considering partial shading condition

This paper proposes a novel bio-inspired optimization method named memetic salp swarm algorithm (MSSA). It is developed by extending the original salp swarm algorithm (SSA) with multiple independent salp chains, thus it can implement a wider exploration and a deeper exploitation under the memetic computing framework. In order to enhance the convergence stability, a virtual population based regroup operation is used for the global coordination between different salp chains. Due to partial shading condition (PSC) and fast time-varying weather conditions, photovoltaic (PV) systems may not be able to generate the global maximum power. Hence, MSSA is applied for an effective and efficient maximum power point tracking (MPPT) of PV systems under PSC. To evaluate the MPPT performance of the proposed algorithm, four case studies are undertaken using Matlab/Simulink, e.g., start-up test, step change of solar irradiation, ramp change of solar irradiation and temperature, and field atmospheric data of Hong Kong. The obtained PV system responses are compared to that of eight existing MPPT algorithms, such as incremental conductance (INC), genetic algorithm (GA), particle swarm optimization (PSO), artificial bees colony (ABC), cuckoo search algorithm (CSA), grey wolf optimizer (GWO), SSA, and teaching-learning-based optimization (TLBO), respectively. Simulation results demonstrate that the output energy generated by MSSA in Spring in HongKong is 118.57%, 100.73%, 100.96%, 100.87%, 101.35%, 100.36%, 100.81%, and 100.22% to that of INC, GA, PSO, ABC, CSA, GWO, SSA, and TLBO, respectively. Lastly, a hardware-in-the-loop (HIL) experiment using dSpace platform is undertaken to further validate the implementation feasibility of MSSA.

Ultrafast Rectifier for Variable-Frequency Applications

In this paper, an ultrafast active rectifier is presented for variable-frequency applications. Three-phase ac-dc converters (rectifiers) are extensively implemented in motor-drives, wind turbines, electric vehicles, and aircraft's power systems. In some technologies, e.g., more electric aircraft and drones, power systems may employ variable-frequency generators for higher efficiency and reliability indices. The proposed ultrafast rectifier is equipped by a step-ahead predictive control scheme, an instantaneous phase-locked loop (PLL), and a module of six SiC MOSFETs. The control scheme regulates the dc voltage and maintains unity power factor with an extremely low total harmonic distortion in the input currents. The instantaneous PLL, applicable only for three-phase systems, is integrated to the proposed variable-frequency control scheme in order to minimize the error in the power factor. The step-ahead predictive scheme and instantaneous PLL combination provides fast and smooth dynamic responses under rapid frequency transients. Experimental results are presented using a laboratory-scale SiC-based MOSFET 115VLL/270Vdc rectifier, and the performance of the proposed controller is compared with a classical power factor correction controller in the presence of frequency ramp and step changes. The experimental results demonstrate a superior dynamic performance of the proposed ultrafast active rectifier.

Performance comparison of different maximum power point trackers for photovoltaic system under fast varying of environmental conditions

Knowing that a large number of MPPT (maximum power point tracking) techniques exist so far and that each technique has its own advantages and disadvantages. Therefore, an appropriate examination of these techniques is indispensable to facilitate the selection of one of the more appropriate ones for a given application. This document provides a summary of these MPPT algorithms. Among them, four commonly used are examined and compared using five evaluation criteria. Perturb and observe (PO), incremental conductance (IC), sliding mode (SM), and fuzzy logic (FL) control are selected for this study and tested under a rapid change of illumination. A combined step and ramp changes in solar illumination is used to assess the effectiveness of the chosen MPPTs. The simulations of the PV system are performed by Simulink tools of MATLAB software. The results conclude that the fuzzy logic controller is the best MPP (maximum power point) tracker due to the absence of steady-state oscillations and its average efficiency of 98%. Second place belongs to the slide mode control which is the fastest and has small fluctuations. In addition, the best MPPT is successfully tested for a change in temperature and load.

Lateral dynamics of a SUV on deformable surfaces by system identification. Part I. Identification experiment

The paper presents a study on lateral dynamics of a 1.6 tonne Sport Utility Vehicle SUV on deformable surfaces performed by means of system identification method. The first part of this study describes an identification experiment, methods and procedures. The identification experiment, in which steering wheel rotation was an input and vehicle motion in the lateral direction was an output has been conducted on three different surfaces: a loess and a sandy soil and on wet snow. The vehicle used for the experiment was equipped with a steering robot to apply repeatable excitations and a high precision Digital Global Positioning System DGPS system to gather dynamic response of the test vehicle, physical measures of the resulting motion: lateral acceleration, yaw rate and vehicle side slip angle. The vehicle was driven with a constant speed of 10km/h. The steering robot input sine wave excitation at 0.5, 1.0 and 2.5 Hz, as well as ramp change (or trapezoidal) excitation with steering wheel rate of 100, 500 and 1500deg/s. It was concluded the methods applied in the field tests were informative and in the sense of the system identification method.

An improved perturb-and-observe based MPPT method for PV systems under varying irradiation levels

The present paper studies thoroughly the performance of the classical perturb-and-observe (P&O) method under fast-changing solar irradiation, including increase or decrease of the irradiation level with small or large steps, when the initial operating point lies to the right or left of the MPP. In sixteen case studies of sudden variation of solar irradiation, the classical P&O method fails to track MPP properly in four cases. The classical P&O tracker does not work properly under a ramp change of irradiation level. A modified P&O-based-MPP tracking method is proposed and tested under step and ramp changes of irradiation irrespective of the value and direction of the perturbation in irradiation level and the location of the initial operating point. The proposed method succeeds in capturing the MPP under a ramp or slow change of irradiation level. The proposed method tracks correctly the MPP in the above-mentioned case studies and shows better performance in tracking speed, steady state efficiency, dynamic efficiency and tracking accuracy when compared with the classical P&O method and other modified methods reported in the literature.

A machine learning approach to targeted balance rehabilitation in people with Parkinson's disease using a sparse sensor set.

Clinical Balance Assessments Often Rely On Functional Tasks As A Proxy For Balance (E.G., Timed Up And Go). In Contrast, Analyses Of Balance In Research Settings Incorporate Quantitative Biomechanical Measurements (E.G., Whole-Body Angular Momentum, H) Using Motion Capture Techniques. Fully Instrumenting Patients In The Clinic Is Not Feasible, And Thus It Is Desirable To Estimate Biomechanical Quantities Related To Balance From Measurements Taken From A Subset Of The Body Segments. Machine Learning Algorithms Are Well-Suited For This Type Of Low- To High-Dimensional Mapping. Thus, Our Objective Was To Develop And Validate An Artificial Neural Network For Estimating Contributions To H From 12 Body Segments Using Only Five Inertial Measurement Units. The Network Was Trained, Tested And Validated On Data From Five Able-Bodied Individuals Performing Forty Trials Each Of A Circuit Involving Complex Walking Tasks, Including Stairs, Ramp, And Direction Changes. The Network Was Also Separately Tested On Four Trials Of An Individual With Parkinson'S Disease Walking On The Circuit. The Output Of The Network Was Strongly Correlated With The Segment Contributions To H In Both Able-Bodied (R= 0.997) And Parkinson'S Disease (R= (0.998) Subjects. The Estimated Values Also Had Low Error Relative To The Signal Magnitude, With The Largest Mean ± SD Rootmean-Squared Errors Of 8.04 ± 1.76% Peak Signal Magnitude In Able-Bodied Individuals And 7.96 ± 0.91% In The Individual With Parkinson'S Disease. These Promising Results Establish The Feasibility Of Using A Sparse Set Of Inertial Measurement Units To Provide Quantitative Data To Clinicians For Targeted Balance Rehabilitation Across Different Patients.

Mitigation of Current Distortion in a Three-Phase Microinverter With Phase Skipping Using a Synchronous Sampling DC-Link Voltage Control

To improve light load efficiency, a three-phase photovoltaic (PV)-based microinverter may operate in single-phase, two-phase or three-phase mode depending on the available input power. Therefore, its dc-link capacitor may be subjected to large peak-to-peak voltage ripple when operating in phase skipping mode. This paper determines the minimum value of the dc-link capacitor by allowing the maximum acceptable voltage ripple on the dc link. This allows for the use of film capacitors instead of electrolytic capacitors in order to improve the microinverter reliability. Unfortunately, higher dc-link voltage ripple introduces harmonic distortion on the inverter output current waveform if it is not compensated for by the dc-link voltage controller. This paper proposes a simple synchronous control method to regulate the dc-link voltage with the presence of large voltage ripple. The dc-link voltage controller is synchronized with the phase-locked loop and samples the average value of dc-link voltage without introducing unwanted harmonics into the voltage sense path. Experimental results were obtained from a 300-W three-phase half-bridge microinverter prototype to verify the proposed dc-link voltage control performance. Inverter output current total harmonic distortion of 1.6% was achieved even though the dc-link peak-to-peak voltage ripple reached as high as 87 V with 219-V split dc-link voltage. Dynamic response is fast enough to easily track the most extreme ramp change in input PV power.

Effect of input parameters intensity and duration on dynamic performance of MED-TVC plant

Multi-Effect-Desalination (MED) may be exposed to fluctuations (disturbances) in input parameters during operation. Therefore, there is a requirement to analyze the transient behavior of such MED systems. In this work, a dynamic model is developed and used to examine the effect of abrupt and ramp changes in the main operational parameters on the plant behavior and performance. The results show that the disturbance intensity variation has a major role in the desalination plant behavior. For the current MED-TVC configuration, it is recommended to limit the reduction in the seawater cooling flow rate to under 12% of the designed steady-state value to avoid dry out in the evaporators. A reduction in the motive steam flow rate and cooling seawater temperature of more than 20% and 35% of the nominal operating values, respectively, may lead to flooding in the evaporators and a complete plant shutdown. On the other hand, the disturbance period has a minimal effect on plant performance if it avoids the critical values of the disturbance intensity that can cause plant shutdown. Simultaneous combinations of two different disturbances with opposing effects result in a modest effect on the plant operation and they can be used to control and mitigate the flooding/drying effects of the disturbances. For simultaneous combinations of disturbances with similar effect, the plant needs an accurate control system to avoid an operational shutdown.

Transient performance of MED processes with different feed configurations

Four different configurations of Multi-Effect-Desalination (MED): backward feed (BF), forward feed (FF), parallel feed (PF) and parallel/cross feed (PCF) are modeled in steady and dynamic operation to examine the behavior of these configurations under transient operation. Adding thermal vapor compressor (TVC) unit with the last effect of parallel/cross configuration is also studied and compared to the other configurations to show the advantage of this type of integration. The transient operation is achieved by applying ramp changes (disturbances) in the main input parameters that include steam flow rate at the heat source and cooling seawater temperature and flow rate at the heat sink. Steady state results indicate that parallel/cross feed has a relatively better performance characteristic than the other feed configurations regarding Gain Output Ratio (GOR) and specific heat consumption (SHC). Adding TVC unit to the parallel/cross feed achieves the lowest water production cost. Dynamic results show that MED-TVC with parallel/cross feed has the fastest response while backward feed and forward feed have the slower response to the applied disturbances. In the case of heat source disturbance, MED plants operating in the backward feed arrangement may be exposed to shut down due to the significant increase in brine level for the first effect. The MED-TVC process is susceptible to the heat sink disturbances compared to the PCF and other configurations. Also, changes in input parameters lead to the highest reduction in GOR for the MED-TVC process compared to the different configurations, especially for cooling seawater temperature. The highest reduction in brine level occurs in MED-TVC for a disturbance in the cooling seawater flow rate and may lead to MED-TVC evaporator drying condition. Hence, MED-TVC will require a reliable control system to avoid this type of plant operational disturbance.

Numerical investigation of over expanded flow behavior in a single expansion ramp nozzle

The single expansion ramp nozzle is severely over-expanded when the vehicle is at low speed, which hinders its ability to provide optimal configurations for combined cycle engines. The over-expansion leads to flow separation as a result of shock wave/boundary-layer interaction. Flow separation, and the presence of shocks themselves, result in a performance loss in the single expansion ramp nozzle, leading to reduced thrust and increased pressure losses. In the present work, the unsteady two dimensional compressible flow in an over expanded single expansion ramp nozzle has been investigated using finite volume code. To achieve this purpose, the Reynolds stress turbulence model and full multigrid initialization, in addition to the Smirnov's method for examining the errors accumulation, have been employed and the results are compared with available experimental data. The results show that the numerical code is capable of predicting the experimental data with high accuracy. Afterward, the effect of discontinuity jump in wall temperature as well as the length of straight ramp on flow behavior have been studied. It is concluded that variations in wall temperature and length of straight ramp change the shock wave boundary layer interaction, shock structure, shock strength as well as the distance between Lambda shocks.

Obtaining Performance of Type-3 Phase-Locked Loop Without Compromising the Benefits of Type-2 Control System

A phase-locked loop (PLL) is a closed-loop feedback control system that estimates the frequency as well as phase of an input signal. The most commonly deployed synchronization method in three-phase applications is a type-2 synchronous reference frame PLL. With pre/in-loop selective harmonic filtering stage, type-2 PLLs can obtain good detection speed, decent stability margins, and better disturbance rejection. However, it suffers from the finite steady-state phase error during ramp change in input signal frequency. To tackle this challenge type-3 PLLs have been developed recently, either by adding a feed-forward path to the PLL structure, or by using a second-order controller as the loop filter. However, recent analysis carried out of type-3 PLLs show that they aggravate stability problem and compromise the performance in terms of detection speed and disturbance rejection. A new concept of synchronization is proposed in this paper that obtains the performance of type-3 PLL but retains all the advantages associated with type-2 PLL. Extensive experimental results are provided to validate the proposed work.

Dynamic modeling and simulations of the behavior of a fixed‐bed reactor‐exchanger used for CO2 methanation

A multidimensional heterogeneous and dynamic model of a fixed‐bed heat exchanger reactor used for CO2 methanation has been developed in this work that is based on mass, energy and momentum balances in the gas phase and mass and energy balances for the catalyst phase. The dynamic behavior of this reactor is simulated for transient variations in inlet gas temperature, cooling temperature, gas inlet flow rate, and outlet pressure. Simulation results showed that wrong‐way behaviors can occur for any abrupt temperature changes. Conversely, temperature ramp changes enable to attenuate and even fade the wrong‐way behavior. Traveling hot spots appear only when the change of an operating condition shifts the reactor from an ignited steady state to a non‐ignited one. Inlet gas flow rate variations reveal overshoots and undershoots of the reactor maximum temperature. © 2017 American Institute of Chemical Engineers AIChE J, 64: 468–480, 2018

Single-molecule spectroscopy of LHCSR1 protein dynamics identifies two distinct states responsible for multi-timescale photosynthetic photoprotection.

In oxygenic photosynthesis, light harvesting is regulated to safely dissipate excess energy and prevent the formation of harmful photoproducts. Regulation is known to be necessary for fitness, but the molecular mechanisms are not understood. One challenge has been that ensemble experiments average over active and dissipative behaviours, preventing identification of distinct states. Here, we use single-molecule spectroscopy to uncover the photoprotective states and dynamics of the light-harvesting complex stress-related 1 (LHCSR1) protein, which is responsible for dissipation in green algae and moss. We discover the existence of two dissipative states. We find that one of these states is activated by pH and the other by carotenoid composition, and that distinct protein dynamics regulate these states. Together, these two states enable the organism to respond to two types of intermittency in solar intensity-step changes (clouds and shadows) and ramp changes (sunrise), respectively. Our findings reveal key control mechanisms underlying photoprotective dissipation, with implications for increasing biomass yields and developing robust solar energy devices.

Simulation of Lift Tab/Ramp Contact During Load/Unload

The lift tab/ramp interface in a hard-disk drive is investigated during load/unload. The von Mises stress on the ramp and the lift tab is determined as a function of the ramp profile, the friction coefficient, and the lateral motion of the lift tab. A step function like stress increase was observed, where the slope of the ramp changes discontinuously. A large reduction in stress can be obtained if the slope discontinuity is eliminated. Comparing simulation results with experimental wear results, we observe that maximum wear debris generation occurs at the location of largest maximum von Mises stress.

Numerical and experimental investigations of transient behaviour of compact plate fin heat exchanger

In this paper, models for the transient simulation of a 2 stream plate fin heat exchanger (PFHE) with offset strip fins (OSF) have been formulated based on unsteady mass and energy conservation equations. The behaviour of a PFHE during start up, cool down and during a ramp change in the inlet temperature of one of the fluids have been studied with the help of these models. Initially, a simplified model considering constant helium properties is developed. This model is further evolved to take into account the temperature dependence of helium properties in the cryogenic temperature domain, along with axial heat conduction (AHC) and thermal capacity of the metal separating plate. Computer codes based on the models have been developed to simulate PFHE behaviour. Experiments at room temperature have been carried out for code validation. It has been found that the model based on constant helium properties is sufficient to predict behaviour of the heat exchanger under room temperature conditions.

Modeling of the mechanobiological adaptation in muscular arteries

Abstract The growth and remodeling of arteries, as controlled by the local stress state and the sensory input from the endothelial cells of the artery wall, is given a novel theoretical framework incorporating the active behavior of vascular smooth muscle. We show that local sensory input maps uniquely to the ratio between a target arterial wall cross-section area corresponding to homeostatic conditions and the current arterial wall area. A growth law is formulated by taking the production rates of individual constituents of the arterial wall to be functions of this target-to-current wall area ratio. We find that a minimum active stress response of vascular smooth muscle is necessary to achieve stable adaptation of the artery wall to dynamic flow conditions. With a sufficient active stress alteration in response to stretch, stable growth toward a homeostatic state can be observed for finite step changes or ramp changes in the transmural pressure or the flow rate.

Partial Shading Detection and Smooth Maximum Power Point Tracking of PV Arrays Under PSC

One of the most important issues in the operation of a photovoltaic (PV) system is extracting maximum power from the PV array, especially in partial shading condition (PSC). Under PSC, P–V characteristic of PV arrays will have multiple peak points, only one of which is global maximum. Conventional maximum power point tracking (MPPT) methods are not able to extract maximum power in this condition. In this paper, a novel two-stage MPPT method is presented to overcome this drawback. In the first stage, a method is proposed to determine the occurrence of PSC, and in the second stage, using a new algorithm that is based on ramp change of the duty cycle and continuous sampling from the P–V characteristic of the array, global maximum power point (MPP) of array is reached. Perturb and observe algorithm is then re-activated to trace small changes of the new MPP. Open-loop operation of the proposed method makes its implementation cheap and simple. The method is robust in the face of changing environmental conditions and array characteristics, and has minimum negative impact on the connected power system. Simulations in Matlab/Simulink and experimental results validate the performance of the proposed methods.

Development of an Analytical Unsteady Model for Wind Turbine Aerodynamic Response to Linear Pitch Changes

A simple unsteady blade element analysis is used to account for the effect of the trailing wake on the induced velocity of a wind turbine rotor undergoing fast changes in pitch angle. At sufficiently high tip speed ratio, the equation describing the thrust of the element reduces to a first order, nonlinear Riccti's equation which is solved in a closed form for a ramp change in pitch followed by a constant pitch. Finite tip speed ratio results in a first order, nonlinear Abel's equation. The unsteady aerodynamic forces on the NREL VI wind turbine are analyzed at different pitch rates and tip speed ratio, and it is found that the overshoot in the forces increases as the tip speed ratio and/or the pitch angle increase. The analytical solution of the Riccati's equation and numerical solution of Abel's equation gave very similar results at high tip speed ratio but the solutions differ as the tip speed ratio reduces, partly because the Abel's equation was found to magnify the error of assuming linear lift at low tip speed ratio. The unsteady tangential induction factor is expressed in the form of first order differential equation with the time constant estimated using Jowkowsky's vortex model and it was found that it is negligible for large tip speed ratio operation.

Global statistical maps of extreme‐event magnetic observatory 1 min first differences in horizontal intensity

AbstractAnalysis is made of the long‐term statistics of three different measures of ground level, storm time geomagnetic activity: instantaneous 1 min first differences in horizontal intensity ΔBh, the root‐mean‐square of 10 consecutive 1 min differences S, and the ramp change R over 10 min. Geomagnetic latitude maps of the cumulative exceedances of these three quantities are constructed, giving the threshold (nT/min) for which activity within a 24 h period can be expected to occur once per year, decade, and century. Specifically, at geomagnetic 55°, we estimate once‐per‐century ΔBh, S, and R exceedances and a site‐to‐site, proportional, 1 standard deviation range [1 σ, lower and upper] to be, respectively, 1000, [690, 1450]; 500, [350, 720]; and 200, [140, 280] nT/min. At 40°, we estimate once‐per‐century ΔBh, S, and R exceedances and 1 σ values to be 200, [140, 290]; 100, [70, 140]; and 40, [30, 60] nT/min.

Modelling and control for eliminating flux oscillations in generation IV high temperature gas cooled reactor

The core power distribution in the advanced high temperature prismatic reactor (AHTPR 625) belonging to the high temperature gas cooled reactor family is controlled using the constrained receding-horizon control algorithm. The outputs from each region of the reactor core are used as the inputs of the system. The reactor model is based on the two-point-coupled xenon oscillation model. It utilises the nonlinear xenon and iodine balance equations along with the one-group, one-dimensional neutron diffusion equation including feedback with a power coefficient. Axially, the reactor core is divided into two regions. Each region has one input and one output. These regions are coupled with each other. The proposed control method demonstrates very fast response to input flux change in the form of a step and ramp change without any residual flux oscillations between the regions of the reactor core. The constrained receding-horizon control problem involves solving an optimisation problem for finite future samples and obtaining the control with few samples. Among the few constrained control samples only the first one is applied and the process to solve the optimisation problem is repeated again.