Inertia In Order Research Articles

INFLUENCE OF THE SYNTHETIC INERTIA REGULATOR ON FREQUENCY CHANGES OF ELECTRIC POWER SYSTEMS IN TRANSIENT MODES

The article is devoted to the use of wind power plants as sources of synthetic inertia in order to increase the stability margins and damping frequency fluctuations. The purpose of this study is to establish the possibility of using the synthetic inertia controller of wind turbines to reduce the amplitudes of frequency fluctuations in transient conditions. One consequence of integrating a large number of wind farms is to reduce the amount of kinetic energy (inertia) available to operate the system. If the system inertia becomes too low, it can compromise frequency stability when large generating units fail. The smaller the moment of inertia in the system, the greater the frequency fluctuations occur after the active power balance is disturbed. A regulator of synthetic inertia of a wind power plant has been obtained, which makes it possible to reduce frequency dips during transient conditions. Recommendations are made regarding the choice of gain factors for the inertia controller. A control model for wind turbines with a synthetic inertia controller is presented. On the example of a test circuit of an electric power system, modeling of disturbances in the form of a load surge and a short circuit was carried out. As a result, the characteristics of the change in the frequency of the electric power system in the absence and presence of a wind power plant are given.

Enabling flexible CHP operation for grid support by exploiting the DHN thermal inertia

As a result of the increased penetration of intermittent renewable energy sources, Combined Heat and Power (CHP) units are being looked upon as one of the sources that might provide for the ever growing need for electrical flexibility. However, CHP units are often considered as must-run units on the grid for their main purpose is generally to cover the heat demand of an adjoining District Heating Network (DHN). This paper demonstrates how a CHP–DHN system may be used as a frequency reserve without excessively compromising the lifetime of the CHP, using either a specific storage tank or the DHN’s thermal inertia in order to compensate for the resulting heat imbalance. In the latter case, it is shown that a buffer tank, although smaller than a specific Thermal Energy Storage (TES), is required due to restrictions for acceptable DHN temperature gradients. In both approaches, the size of the tank has been mapped out considering frequency reserve’s duration and capacity. The results show that a simplistic static model of the DHN is sufficient for the design of a specific TES, while a detailed dynamic simulation is required when the DHN is used as storage, to prevent overestimating the flexibility of the CHP–DHN system. This research could be used to assess the potential for improving CHP–DHN systems flexibility, using them as frequency reserves, and to design the required storage or buffer tanks.

The scaling of rotor inertia under dynamic inflow conditions

Rotor moment of inertia significantly influences the performance of rotating systems, such as wind and tidal turbines, when operating in unsteady environments. However, rotor moment of inertia in itself does not fully define the unsteady behaviour of such rotating systems without taking flow inertia, e.g. the gust acceleration, into consideration. We therefore introduce a normalized inertia number (I∗), which relates the influence of rotor moment of inertia relative to the flow inertia in order to characterize the dynamic response of a generic-rotor system. Experiments are performed in a towing-tank facility using three geometrically-identical rotor models with weighted tips so as to investigate the influence of I∗ on the rotor’s ability to adapt to changing inflow conditions. Gust profiles with four gust durations were tested, ranging from slow quasi-steady operation to rapid disturbances. Rotors operating with sufficiently low I∗ are found to produce higher normalized power during the fastest tested gust when compared to the quasi-steady operation. For instance, the power output of the rotor model with (I∗=3.2×10−3) is, at its maximum, 30% higher during the fastest gust versus quasi-steady operation. However, by increasing I∗ on the same rotor model to 8.7×10−3, by decreasing the flow inertia, the rotor model produced, at maximum, only 19% higher power output. Therefore, we are able to show that our normalization I∗ is a reasonable way to determine the dynamic performance of a rotating system during a gust.

Heterogeneous Inertia Estimation for Power Systems with High Penetration of Converter-Interfaced Generation

The increasing and fast deployment of distributed generation is posing challenges to the operation and control of power systems due to the resulting reduction in the overall system rotational inertia and damping. Therefore, it becomes quite crucial for the transmission system operator to monitor the varying system inertia and damping in order to take proper actions to maintain the system stability. This paper presents an inertia estimation algorithm for low-inertia systems to estimate the inertia (both mechanical and virtual) and damping of systems with mixed generation resources and/or the resource itself. Moreover, the effect of high penetration of distributed energy resources and the resulting heterogeneous distribution of inertia on the overall system inertia estimation is investigated. A comprehensive set of case studies and scenarios of the IEEE 39-bus system provides results to demonstrate the performance of the proposed estimator.

Dynamic Inchworm Crawling: Performance Analysis and Optimization of a Three-Link Robot

Inchworm crawling allows for both quasistatic and dynamic gaits at a wide range of actuation frequencies. This locomotion mechanism is common in nonskeletal animals and exploited extensively in the bio-inspired field of soft robotics. In this work we develop and simulate the hybrid dynamic crawling of a three-link robot, with passive frictional contacts. We fabricate and experimentally test such robot under periodic inputs of joints’ angles, with good agreement to the theoretical predictions. This allows to comprehend and exploit the effects of inertia in order to find optimal performance in inputs’ parameters. A simple criterion of robustness to uncertainties in friction is proposed. Tuning the inputs according to this criterion improves the robustness of low-frequency actuation, while increasing the frequency allows for gaits with both high advancement velocity and robustness. Finally, the advantages of uneven mass distribution are studied. Time-scaling technique is introduced to shape inputs that achieve similar effect without reassembling the robot. A machine-learning based optimization is applied to these inputs to further improve the robot's performance in traveling distance.

Surmounting potential barriers: Hydrodynamic memory hedges against thermal fluctuations in particle transport.

Recently, trapped-particle experiments have probed the instantaneous velocity of Brownian motion revealing that, at early times, hydrodynamic history forces dominate Stokes damping. In these experiments, nonuniform particle motion is well described by the Basset-Boussinesq-Oseen (BBO) equation, which captures the unsteady Basset history force at a low Reynolds number. Building off of these results, earlier we showed that, at low temperature, BBO particles could exploit fluid inertia in order to overcome potential barriers (generically modeled as a tilted washboard), while its Langevin counter-part could not. Here, we explore the behavior of neutrally buoyant BBO particles at finite temperature for moderate Stokes damping. Remarkably, we find that the transport of particles injected into a bumpy potential with sufficiently high barriers can be completely quenched at intermediate temperatures, whereas itinerancy may be possible above and below that temperature window. This effect is present for both Langevin and BBO dynamics, though these occur over drastically different temperature ranges. Furthermore, hydrodynamic memory mitigates these effects by sustaining initial particle momentum, even in the difficult intermediate temperature regime.

Inflation targeting, disinflation, and debt traps in Argentina

This paper highlights the role of external indebtedness and the presence of inflationary inertia in order to assess the effectiveness and sustainability of inflation targeting during disinflation episodes. As the recent Argentinian experience illustrates, a sluggish inflation rate and a significant current-account deficit may make the stabilization process difficult. To illustrate the point, we build a model that shows that, when inflation adjusts fast, the target may be achieved without building too much external debt. But if inflation adjusts slowly, an excessive build-up of external debt could lead to an increase in the risk premium, a sudden shortage of foreign exchange, and the eventual collapse of the inflation-targeting regime.

Inflation targeting, disinflation, and debt traps in Argentina

This paper highlights the role of external indebtedness and the presence of inflationary inertia in order to assess the effectiveness and sustainability of inflation targeting during disinflation episodes. As the recent Argentinian experience illustrates, a sluggish inflation rate and a significant current-account deficit may make the stabilization process difficult. To illustrate the point, we build a model that shows that, when inflation adjusts fast, the target may be achieved without building too much external debt. But if inflation adjusts slowly, an excessive build-up of external debt could lead to an increase in the risk premium, a sudden shortage of foreign exchange, and the eventual collapse of the inflation-targeting regime.

Multifunctional Remotely Actuated 3-DOF Supernumerary Robotic Arm Based on Magnetorheological Clutches and Hydrostatic Transmission Lines

Supernumerary robotic limbs (SRL) are wearable extra limbs intended to help humans perform physical tasks beyond conventional capabilities in domestic and industrial applications. However, unique design challenges are associated with SRLs as they are mounted on the human body. SRLs must 1) be lightweight to avoid burdening the user, 2) be fast enough to compensate for human unpredictable motions, 3) be strong enough to accomplish a multitude of tasks, 4) have high force-bandwidth and good backdrivability to control interaction forces between the user and the environment. This letter studies the potential of a remotely actuated 3-DOF supernumerary robotic arm equipped with a 3 fingers soft gripper, both powered by magnetorheological (MR) clutches and hydrostatic transmission lines. The tethered configuration allows the power-unit to be located on the ground, which minimizes the remote mass (4.2 kg) on the user. MR clutches minimize the actuation inertia in order to provide fast dynamics and good backdrivability. An experimental open-loop force-bandwidth of 18 Hz is obtained at each joint and the maximal speed reached by the device end-effector is 3.4 m/s, which is sufficient for compensating human motions. In addition, the two first joints provide 35 Nm and the third joint provides 29 Nm, which is strong enough to hold manual industrial tools. Finally, the SRL is put in real practical situations, as fruit and vegetables picking, painting, tools holding and badminton playing. The capability of the proposed MR-Hydrostatic SRL to perform successfully various tasks with high speed and smoothness suggests a strong potential of SRLs to become future commonly used devices.

Accurate angle estimation based on moment for multirotation computation imaging.

In a multirotation computation imaging system, the fidelity of the reconstructed result is limited by the accuracy of the estimated rotation angles. Here, an accurate angle detection method using image moment is proposed to estimate angles of diffraction images. The second moment of a digital image is adopted as the rotational inertia in order to estimate angles of diffraction images. Compared with previous versions based on Radon/Hough transform, it has higher accuracy and is simultaneously time-saving, which is verified in both simulation and experiment. The angle error of moment method is narrowed down within 0.1°, or even less, and it also can perform well in sample diversity or when slightly out of focus.

Stability and control of power grids with diluted network topology.

We consider sparse random networks of Kuramoto phase oscillators with inertia in order to mimic and investigate the dynamics emerging in high-voltage power grids. The corresponding natural frequencies are assumed to be bimodally Gaussian distributed, thus modeling the distribution of both power generators and consumers, which must be in balance. Our main focus is on the theoretical analysis of the linear stability of the frequency-synchronized state, which is necessary for the stable operation of power grids and the control of unstable synchronous states. We demonstrate by numerical simulations that unstable frequency-synchronized states can be stabilized by feedback control. Further, we extend our study to include stochastic temporal power fluctuations and discuss the interplay of topological disorder and Gaussian white noise for various model configurations and finally demonstrate that our control scheme also works well under the influence of noise. Results for synthetic Erdös-Renyi random networks with low average connectivity and with symmetric or asymmetric bimodal frequency distributions are compared with those obtained by considering a real power grid topology, namely, the grid of Italy.

Performance and Loss Analysis of Squirrel Cage Induction Machine Based Flywheel Energy Storage System

Flywheel energy storage systems (FESS) are one of the earliest forms of energy storage technologies with several benefits of long service time, high power density, low maintenance, and insensitivity to environmental conditions being important areas of research in recent years. This paper focusses on the electrical machine and power electronics, an important part of a flywheel system, the electrical machine rotating with the flywheel inertia in order to perform charge-discharge cycles. The type of machine used in the electrical drive plays an important role in the characteristics governing electrical losses as well as standby losses. Permanent magnet synchronous machine (PMSM) and induction machines (IM) are the two most common types of electric machines used in FESS applications where the latter has negligible standby losses due to its lower rotor magnetic field until energised by the stator. This paper describes research in which the operational and standby losses of a squirrel-cage induction machine-based flywheel storage system (SCIM-FESS) are modelled as a system developed in MATLAB/Simulink environment inclusive of the control system for the power electronics converters. Using the proposed control algorithm and in-depth analysis of the system losses, a detailed assessment of the dynamic performance of the SCIM-FESS is performed for different states of charging, discharging, and standby modes. The results of the analysis show that, in presence of system losses including aerodynamic and bearing friction losses, the SCIM-FESS has satisfactory characteristics in energy regulation and dynamic response during load torque variations. The compliance of FESS and its conversion between the generating and motoring mode within milliseconds show the responsiveness of the proposed control system.

Construct Validity, Test-Retest Reliability, and Repeatability of Performance Variables Using a Flywheel Resistance Training Device.

Bollinger, LM, Brantley, JT, Tarlton, JK, Baker, PA, Seay, RF, and Abel, MG. Construct validity, test-retest reliability, and repeatability of performance variables using a flywheel resistance training device. J Strength Cond Res 34(11): 3149-3156, 2020-Power production is highly associated with physical performance; however, the ability to quantitatively measure power output during resistance exercise is lacking. The purpose of this study was to determine the validity and test-retest reliability of flywheel-based performance testing. Twelve young, resistance trained subjects completed 2 bouts of resistance exercise using a flywheel resistance training device (Exxentric kbox 4 Pro). Each session consisted of 3 sets of 3 exercise (bent-over row, Romanian deadlift, and biceps curl) with varying moments of inertia (0.050, 0.075, and 0.100 kg·m, respectively) in random order. Each set consisted of 5 maximal effort repetitions with 3-minute recovery between sets. Average power, peak concentric and eccentric power, average force, average speed, and total work for each set were recorded. Regression analysis revealed a near-perfect relationship between measured and predicted power, force, and work at given workloads. Pearson's r between trials 1 and 2 revealed good (≥0.70) to excellent (≥0.90) test-retest reliability for all outcomes with the exception of peak eccentric power for biceps curls (r = 0.69), which narrowly missed the cutoff for acceptable reliability. Bland-Altman plots revealed small (approximately 5-15%), but statistically significant bias between the 2 trials for some measures. Coefficient of repeatability for all outcomes was relatively high, indicating poor repeatability. Flywheel-based performance testing provides valid data. However, reliability varies between individual lifts and specific outcomes. Given the poor repeatability between trials, it is likely that subjects who are unaccustomed to this modality may require multiple testing sessions or a thorough familiarization period to ensure accurate measures of power, force, speed, and work during flywheel-based performance testing.

Soybean oil-based nanoemulsion systems in absence and presence of curcumin: Molecular dynamics simulation approach

Curcumin is the most bioactive compound of turmeric (Curcuma longa) plant, which has a wide range of beneficial biological and pharmacological activities, including antioxidants, anti-inflammatory, and anti-cancer agents. The application of curcumin is limited due to low solubility and low bioavailability. Today, the use of nanotechnology in curcumin formulations has been considered to improve the performance of curcumin. Particularly nanoemulsions can be used as agents of increasing penetration in the pharmaceutical and food industries. Despite the extensive empirical research on nano-curcumin, the behavior and formation of the curcumin nanoemulsion have not been theoretically investigated. Molecular dynamics Simulation of nanoemulsion systems is performed to have a better understanding of molecular behavior. Here, the simulation was performed on the base on the ratios obtained in experimental work, and by reviewing the trajectory, the variety of assemblies was determined at different times. This study revealed that molecular assemblies formed in the absence and presence of curcumin have different size and arrangement. The Variety of assemblies was studied after reaching to the constant number of assemblies in the equilibrium. The average radius of gyrations was estimated for assemblies composed of more than three molecules in the curcumin nanoemulsion system and the effective radius of the different assemblies was determined based on the related relationship. The size of particles was determined to be in the range of 2–6.3 nm. The size of particles were determined to be in the range of 2–6.3 nm. The necessary information was gained by analyzing the average ratio of the principal moments of inertia in order to determine the shape of the assemblies and it was found that the assemblies have almost spherical and prolate spheroid shapes. Particle size and shape results were in good agreement with experimental results. The arrangement of various assemblies showed that all molecules except curcumin were placed into the assemblies in the way that hydrophobic and hydrophilic parts were located inside and at the surface of the assemblies, respectively. While curcumin selected surface in all assemblies.

Model predictive control of a thermally activated building system to improve energy management of an experimental building: Part I—Modeling and measurements

A simple way to reduce energy consumption is to minimize heating use during unoccupied periods. This implies the possibility of adjusting the room temperature setpoint. However, systems with a large thermal capacity cannot follow sudden setpoint changes because of their thermal inertia. A model predictive control (MPC) allows the harnessing of this inertia in order to reduce heating costs and improve comfort. This advanced control technique is based on disturbances anticipation (occupation, weather conditions) and requires a model of the system which has to be controlled. Therefore, the use of such controller needs a reliable model that describes well the dynamics of the room on upcoming days. This paper presents a method for the selection of the model (type, level of complexity) to be implemented in a MPC controller to anticipate the control of a long time response floor heating system on a real building. The demonstration room and embedded systems serving as experimental support are presented. Short measurement periods are carried out to identify the model parameter values minimizing the gap between model output and measurement. Gray-box models based on electrical analogy and state-space representation are proposed. They are constructed from physical knowledge and then identified by choosing the most appropriate measurement series. A sensitivity analysis method (Morris) is used to improve the quality of the identified model which satisfies control criteria with two specific validation measurement series. In a complementary paper, the predictive controller integrating the selected model is compared to more conventional management strategies in simulation and on-site with the experimental building.

Free Vibrations of Uniform Timoshenko Beams on Pasternak Foundation Using Coupled Displacement Field Method

Abstract Complex structures used in various engineering applications are made up of simple structural members like beams, plates and shells. The fundamental frequency is absolutely essential in determining the response of these structural elements subjected to the dynamic loads. However, for short beams, one has to consider the effect of shear deformation and rotary inertia in order to evaluate their fundamental linear frequencies. In this paper, the authors developed a Coupled Displacement Field method where the number of undetermined coefficients 2n existing in the classical Rayleigh-Ritz method are reduced to n, which significantly simplifies the procedure to obtain the analytical solution. This is accomplished by using a coupling equation derived from the static equilibrium of the shear flexible structural element. In this paper, the free vibration behaviour in terms of slenderness ratio and foundation parameters have been derived for the most practically used shear flexible uniform Timoshenko Hinged-Hinged, Clamped-Clamped beams resting on Pasternak foundation. The findings obtained by the present Coupled Displacement Field Method are compared with the existing literature wherever possible and the agreement is good.

Shaft Torque Limiting Control Using Shaft Torque Compensator for Two-Inertia Elastic System With Backlash

This paper aims to present a solution for torsional vibration suppression and shaft torque limitation simultaneously in servo system with backlash. The existence of backlash, which would make conventional notch filter invalid, will aggravate the mechanical vibration and bring the risk of unsafety to the system. In order to solve that problem, a novel shaft torque compensator is proposed, which would make the system similar to a rigid system with one inertia. What is more, this compensator can limit shaft torque as expected, making the system relatively safe under any situation with different load inertias and torques. The limiting control is based on the adaptive online identification of load inertia in order to improve robustness of the system and ensure not only the accuracy, but also the arbitrariness of shaft torque limit. Simulation and experimental results are presented to illustrate the favorable behavior of the drive with the robust shaft torque compensator.

The Role of the Thermal Mass in nZEB with different Energy Systems

European and Italian standards establish high levels of energy performance of buildings that have to be designed considering their energy balance near zero. To achieve this goal, the reduction of energy demand, attainable by improving energy efficiency of the construction, and the use of renewable energy available both on site and off site are effective solutions to be applied. In particular, in buildings that use energy produced from renewable sources, due to their unstable and unpredictable nature, having the right strategy to compensate the variations is essential. A technical solution reevaluated as a consequence of passive design principles, is to provide an adequate thermal inertia in order to store energy when it is offered and to use it when the source is not available. In these cases, the ability of construction elements to retain heat becomes fundamental as they contribute to maintain internal comfort conditions. This paper aims to investigate how various types of heating and cooling systems, based on different modes of heat transfer, are able to interact differently with the thermal mass of the building, producing a different level of its activation. The investigation considers a case study used to carry out dynamic simulation by means of DesignBuilder which is a user interface of EnergyPlus. The model consists of a building with elementary geometry and a single thermal zone, delimited by walls with outside thermal insulation and a heat accumulation layer inside. The variation of the internal temperature by using different types of conditioning system is analyzed in order to individuate the technology that takes the greatest advantages from the thermal mass.

Dynamic isotropy in 6-DOF kinematically constrained platforms by three elastic nodal joints

The principle of kinematic design has a wide range of applications e.g. from optical mirror mounts to parallel robots. Despite the importance of dynamic isotropy in the optimization of dynamic performance, a thorough analysis of dynamic isotropy in different kinematic arrangements has not yet been addressed in the literature. Dynamic isotropy, leading to equal eigenfrequencies, is a powerful optimization measure. In this paper, we present fully-parametric solutions for obtaining dynamic isotropy in general 3D platforms kinematically constrained by three elastic nodal joints in 6 DOFs. It is analytically shown that there exist two possible kinematic arrangements which are described by 3-2-1 and 2-2-2 kinematic node spaces. Both kinematic arrangements are studied with respect to their Jacobian formulation, Jacobian singularity and stiffness decoupling. It is proven that decoupling of stiffness matrices and accordingly dynamic isotropy for both kinematic arrangements are possible. Subsequently, conditions concerning geometry, stiffness and inertia in order to obtain dynamic isotropy are parametrically established. Finally, it is numerically demonstrated that the presented formulation is general enough even for being directly used, as a novel and efficient approach, in order to design dynamically isotropic 6-6 Gough–Stewart platforms (6-6 hexapods).

A novel approach for prediction of a repulsive force in a haptic manipulator: experimental verification with different trajectories

This paper proposes a novel technique for predicting a repulsive force in a haptic interface. The goal of many haptic systems is to reflect a desired repulsive force to an operator. However, there is no way of describing a repulsive force mathematically. This means that the force-reflection performance of haptic systems cannot be simulated at the design process. Even though reflecting a repulsive force to an operator is the purpose of the systems, many haptic systems have been designed without knowing how an operator perceives a repulsive force during manipulation. Such design process unavoidably entails a lot of trials and errors and increases development time and costs. Here we show that the repulsive force can be predicted by establishing an optimal controller. 1-Degree of freedom lever system is designed with light and heavy inertia in order to reflect inertial variation. The dynamics of the system is derived and an optimal controller is established based on the system dynamics. The optimal controller predicts the repulsive forces under three different position trajectories. After manufacturing the lever system, actual repulsive force data is collected under the same position trajectories. The predicted repulsive forces are then compared with the actual repulsive forces. To demonstrate the effectiveness of the proposed method, a correlation coefficient between the predicted repulsive force and the actual one is presented. In addition, the mean value and standard deviation of the force error are provided. After showing that a repulsive force can be predicted by an optimal controller, a steering-wheel simulator is designed and manufactured to show that the proposed method is applicable to a haptic system’s design as well.