Excitation System Research Articles

Complex-valued derivative propagation method with adaptive moving grids for electronic nonadiabatic dynamics

The coupled complex quantum Hamilton–Jacobi equations in the diabatic representation are solved on adaptive moving grids for electronic nonadiabatic dynamics. Substitution of the wave functions in exponential form into the coupled time-dependent Schrödinger equations yields the coupled complex quantum Hamilton–Jacobi equations. Analytic equations of motion are derived for the spatial derivatives of the complex action functions for both surfaces. The equations of motion for the complex actions and their spatial derivatives are converted into the arbitrary Lagrangian–Eulerian frame, allowing us to have many ways to choose the velocities for the moving points. The grid points can be specified to move along with the probability fluid. In contrast, choosing the boundary grid points to follow Lagrangian trajectories and forcing the internal grid points to be equally spaced at each time step, we obtain a moving structured grid of uniform spacing during the wave packet evolution. Several examples are presented to illustrate main features of the adaptive grid method, including a single avoided crossing system, a dual avoided crossing system, an ultrashort laser pulse excitation system, and a three-dimensional nonadiabatic system. Accurate computational results demonstrate that the adaptive grid method provides an alternative way to study electronic nonadiabatic dynamics.

A novel virtual synchronous machine implementation and verification of its effectiveness to mitigate renewable generation connection issues at weak transmission grid locations

AbstractLarge‐scale penetration of renewable resource based generation will displace conventional synchronous machine‐based power generation. This will lower the overall system inertia and will result in lower short circuit levels at point of connection (POC) of renewable resources. Renewable resources such as wind and solar photovoltaic (PV) are interfaced to the power system via power electronic inverters. Operation of inverter‐based equipment under low inertia and low short circuit conditions is challenging. Specific challenges include fault recovery response, unstable oscillatory interactions, and impact on torsional oscillations of thermal generating units. In this paper, the effectiveness of inverters, controlled as a virtual synchronous machine (VSM), to overcome some of these issues is investigated. A battery energy storage system (BESS) inverter is controlled as a VSM. The input signals provided to the BESS inverter are derived from solving the time domain equations of a synchronous machine. The response of exciter, governor, and power system stabilizer (PSS) are also included in the VSM strategy. The dynamic characteristics of the proposed VSM are verified using a single machine infinite bus (SMIB) test model. The effectiveness of the proposed VSM approach to mitigate specific technical challenges is verified by performing dynamic response studies on two test systems. The two test systems represent selected regions of practical power systems with high renewable penetration. The VSM response is compared with a conventional synchronous machine response in all test cases, to demonstrate the close correlation of dynamic response. The simulation results demonstrate that the VSM's response is as expected and is capable of mitigating stability‐related issues due to low system inertia and low short circuit strength.

Bistable nerve conduction

It has been demonstrated experimentally that slow and fast conduction waves with distinct conduction velocities can occur in the same nerve system depending on the strength or the form of the stimulus, which give rise to two modes of nerve functions. However, the mechanisms remain to be elucidated. In this study, we use computer simulations of the cable equation with modified Hodgkin-Huxley kinetics and analytical solutions of a simplified model to show that stimulus-dependent slow and fast waves recapitulating the experimental observations can occur in the cable, which are the two stable conduction states of a bistable conduction behavior. The bistable conduction is caused by a positive feedback loop of the wavefront upstroke speed, mediated by the sodium channel inactivation properties. Although the occurrence of bistable conduction only requires the presence of the sodium current, adding a calcium current to the model further promotes bistable conduction by potentiating the slow wave. We also show that the bistable conduction is robust, occurring for sodium and calcium activation thresholds well within the experimentally determined ones of the known sodium and calcium channel families. Since bistable conduction can occur in the cable equation of Hodgkin-Huxley kinetics with a single inward current, i.e., the sodium current, it can be a generic mechanism applicable to stimulus-dependent fast and slow conduction not only in the nerve systems but also in other electrically excitable systems, such as cardiac muscles.

Nonlinear analysis of forced mechanical systemswith internal resonance using spectral submanifolds, Part I: Periodic response and forced response curve

We show how spectral submanifold theory can be used to construct reduced-order models for harmonically excited mechanical systems with internal resonances. Efficient calculations of periodic and quasi-periodic responses with the reduced-order models are discussed in this paper and its companion, Part II, respectively. The dimension of a reduced-order model is determined by the number of modes involved in the internal resonance, independently of the dimension of the full system. The periodic responses of the full system are obtained as equilibria of the reduced-order model on spectral submanifolds. The forced response curve of periodic orbits then becomes a manifold of equilibria, which can be easily extracted using parameter continuation. To demonstrate the effectiveness and efficiency of the reduction, we compute the forced response curves of several high-dimensional nonlinear mechanical systems, including the finite-element models of a von Kármán beam and a plate.

Research on the Brushless Excitation System with Linear Current Amplifier Characteristics

In terms of improving the dynamic response characteristics of brushless AC synchronous generators, the concept of integrated design of AC exciter and rotating rectifier and their electromagnetic characteristics are studied, and the conditions and judgment methods for determining their operating modes are obtained in theoretical design and simulation design, pointing out that when the brushless excitation system operates in or is close to mode III, i.e., the rectifier always has three or four diodes in each operating cycle. The linear current amplifier characteristics can be basically achieved when the brushless excitation system is operated in mode III or is close to mode III, i.e., the rectifier always has three or four diodes alternating in each operating cycle. The impact of the key parameters of the AC exciter at different rotational speeds and temperatures on the characteristics of the linear current amplifier was explored, and an engineering prototype was manufactured. The related test verified the correctness of the concept of integrated electromagnetic design and simulation calculation. This study provides an engineered design method for enhancing the dynamic response properties of the brushless AC synchronous generators.

Negative Damping Mechanism Analysis of Power System Stabilizer Based on Damping Torque

Power system stabilizer plays an important role in suppressing the low frequency oscillations, but a PSS with poorly tuned parameters may produce negative damping and aggravate the system oscillation. The purpose of this paper is to study the mechanism of damping of a PSS in multi machine system and to analyze whether the PSS has produced negative damping. This paper adopts Park model for analysis. According to the concepts of complex frequency and generalized phasor, the correlation between the damping torque phasor and the real part of the complex eigenvalue is studied. With the auxiliary of Park equivalent circuits, the damping torque provided by the excitation system is separated from the electrical torque phasor. Then, the damping torque coefficient of the PSS is defined as an indicator of the damp effect of the stabilizer. Finally, the simulation results of single machine infinite bus system and 4-machine system demonstrate the validation of the proposed method for evaluating the damping effect of PSS on the system.

Development and Characteristic Investigation of a Multidimensional Discrete Magnetostrictive Actuator

Active combustion control (ACC) has been proved to be an effective method for the suppression of pressure oscillation in aero engine combustion chambers, which will seriously endanger flight safety of aircrafts. However, the actuators for ACC need to work with a bandwidth of 1000 Hz, a stroke up to submillimeter level and a high power density simultaneously. Existing electromagnetic actuators, or smart material actuators, are still unable to meet these requirements at the same time. To address this issue, in this article, a multidimensional discrete magnetostrictive actuator (MDMA) was developed by adopting the multidimensional discrete configuration. In order to obtain large output displacement while maintaining the characteristics of high bandwidth and high power density of magnetostrictive materials, tubular and cylindrical magnetostrictive rods are nested axially and radially through sleeves to form a discrete magnetostrictive stack; independent excitation coils and permanent magnet rings are integrated axially to form a discrete electromagnetic excitation system. Then, a magnetic equivalent circuit (MEC) model was developed to analyze the magnetic field distribution characteristic of MDMA components. Next, a multiphysics comprehensive dynamic model was established to describe the complex dynamic properties of multidimensional discrete structures. Subsequently, a prototype of the MDMA was fabricated, which is only 56 mm in diameter and only 71.5 mm high. Experimental results indicate that, the proposed MDMA reaches a stoke of 100 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m, and the working bandwidth can exceed 1000 Hz. Furthermore, closed-loop control tests were conducted and the results showed that the MDMA can effectively track sinusoidal references of different amplitudes under low frequency with a feedback PID controller.

Improvement of power grid stability and load distribution using diesel excitation controller

One of the requirements for controlling hybrid power systems is designing an appropriate excitation system, flexibility, protection, and coordination of all components to improve system stability. In this paper, various types of equipment simulated in the linear form and non-linear models are connected to the power supply. In the same direction, while presenting a new controller for the diesel generator excitation system and a filter used to purify and attenuate current harmonics is reported on the stability of a grid-independent system. Finally, the variation of the mode for the voltage and power of the system has been confirmed at the time of error and complete system stability. Also, the important indicators in the analysis are obtained in the lowest values, which can be seen from the controlled harmonics of the system of this data. In addition, the variation of the mode for the voltage and power of the system has been confirmed and the important indicators in the analysis are obtained in the lowest values.

Effect of Atomic-Temperature Dependence of the Electron-Phonon Coupling in Two-Temperature Model.

Ultrafast laser irradiation of metals can often be described theoretically with the two-temperature model. The energy exchange between the excited electronic system and the atomic one is governed by the electron–phonon coupling parameter. The electron–phonon coupling depends on both, the electronic and the atomic temperature. We analyze the effect of the dependence of the electron–phonon coupling parameter on the atomic temperature in ruthenium, gold, and palladium. It is shown that the dependence on the atomic temperature induces nonlinear behavior, in which a higher initial electronic temperature leads to faster electron–phonon equilibration. Analysis of the experimental measurements of the transient thermoreflectance of the laser-irradiated ruthenium thin film allows us to draw some, albeit indirect, conclusions about the limits of the applicability of the different coupling parametrizations.

A new dual-ferrite–assisted hybrid reluctance machine with two-stage excitation for starter generator application

Reluctance machines with DC field coil in stator are a competitive candidate for starter generation application, due to the elimination of rare-earth permanent magnet (PM), robust structures, and controllable excitation. However, due to the poor excitation ability of DC field coils, the torque density is disadvantageous. Moreover, with the increase in the DC field current, it is exposed to the risk of extra DC saturation in stator teeth. As a consequence, the torque density and efficiency are both constrained. To solve the aforementioned problems, based on the comprehensive consideration of production cost and torque performance, this study proposed a novel type of hybrid reluctance machine with dual-ferrite–assisted in stator slots. The inner-layer ferrite PM is magnetized tangentially, which can effectively achieve the DC-saturation–relieving effect, while the outer-layer ferrite PM is magnetized radially to increase the machine torque density through the flux modulation effect. Based on finite element analysis, the machine torque density and efficiency can be improved by 20 and 5%, respectively. Furthermore, to simplify the excitation system of the DC terminal, a two-stage excitation method is proposed by splitting some turns of armature winding to feed DC field winding with passive rectifier. No power switching devices are needed for the excitation system in this way, making the system highly robust. The effectiveness of the proposed design is verified by time-stepping finite element analysis.

Impact of local timescales in a cellular automata model of excitable media

A cellular automata system known as the Greenberg-Hastings cellular automata (GHCA), with cyclic and excitable individual dynamics, provides a useful paradigm for modeling emergent phenomena in an excitable medium. Most past studies of GHCA have investigated the asymptotic dynamics of the system, assuming fixed extents for the active and passive dynamical phases. This study is a systematic investigation of the relationship between the dynamical properties of individual cells of a small system implementing excitable dynamics, and the emergent system wide asymptotic state. The impact of the temporal extents of individual dynamical phases (τa, τp), on the probability of persistence P(τa,τp), defined as the fraction of initial configurations which sustain spatiotemporal oscillations asymptotically, is examined for each unique configuration of the system. The main result obtained is that the probability of persistence P(τa, τp) assumes a characteristic sigmoidal form, as the dynamical behaviour of the system transitions from absolute quiescence to persistent spatiotemporal oscillations, with respect to the parameters (τa, τp). A plot of the numerical findings in the (τa, τp) space provides a consolidated view of their impact on the emergent behaviour of the system. In conclusion, some implications of the methods and results presented in this work, to the study of emergent phenomena in excitable systems, are discussed.

Manifestation of Sharia-based credit in its realization fulfilling needs using a credit system

Sharia credit is the provision of money based on a loan agreement or agreement between the lender and the recipient. The recipient must return the money within the agreed timeframe in exchange for profit sharing. This article aims to analyze and explain the description of Sharia credit, distinguish Sharia credit from conventional credit, and the effectiveness of Sharia credit in Indonesia. Sharia credit is a product of Sharia-based financial institutions in which all transactions are exempt from laws violating religion's provisions. The most fundamental difference between Islamic credit and conventional credit is in the remuneration system. Established credit uses interest rates, while Islamic credit uses a profit-sharing system based on an agreement. The results of writing this article show that Sharia credit is more down-to-earth than conventional credit with all the advantages possessed by Sharia credit. It does not apply an exciting system but implements a profit-sharing or &lt;em&gt;mudharabah&lt;/em&gt; system. Through the profit-sharing system, Islamic credit is hoped to improve the economy by providing financing to those in need without violating Islamic religious rules.

The vibration isolation characteristics of torsion bar spring with negative stiffness structure

Nonlinear stiffness systems are an effective way to achieve low frequency vibration isolation. To improve the support capacity and ride comfort of nonlinear stiffness systems, this paper proposes a quasi-zero stiffness (QZS) vibration isolator composed of the torsion bar spring and negative stiffness structure (NSS) and investigates its vibration isolation characteristics. The influence of the system parameters on the static nonlinear stiffness peculiarities of the vibration isolator is delved. The motion equation of the isolator under the harmonic excitation from the base can be expressed as Helmholtz–Duffing equation due to an offset distance from zero stiffness point to the equilibrium position. The primary resonance response of the QZS system is approximately analytically predicted by Harmonic Balance Method (HBM). The absolute acceleration transmissibility of the QZS system considering the effect of excitation amplitude and system parameters is investigated and compared with the equivalent linear system to evaluate the isolation performance of the nonlinear system. Then, the numerical simulation is investigated and good agreement with theoretical analysis. The validity of the proposed model is verified by finite element method (FEM) and an experiment. Based on the numerical simulation and experiment results, the proposed nonlinear system possesses a better vibration isolation performance of heavy equipment in the low-frequency region.

An Ultrafast Self‐Polarization Effect in Barium Titanate Filled Poly(Vinylidene Fluoride) Composite Film Enabled by Self‐Charge Excitation Triboelectric Nanogenerator

AbstractAlthough charge excitation is an effective approach to achieve high charge density for triboelectric nanogenerators (TENGs), high output charge is limited by air‐breakdown. Due to capacitor structure, there are two ways to reduce the influence of air‐breakdown in TENG: decrease in thickness and increase in permittivity of dielectric film. Obviously, the increase in permittivity is more reliable in applications. Herein, a double‐layer TENG shared with one floating metal electrode is proposed, on which charge is injected by a self‐excitation circuit. An ultrafast self‐polarization effect is found in two barium titanate filled poly(vinylidene fluoride) composite films in the TENG by high electrical field produced from the floating electrode. According to comparison and analysis, the speed of polarization to saturation of dielectric composite films in self‐charge excitation approach is ≈3 times faster than that of external‐charge excitation. Optimization of various parameters is investigated to enhance the output performance of the TENG. A large output charge density of 1.67 mC m–2 is achieved in the atmosphere with 40% relative humidity due to self‐polarization effect of the dielectric composite film. This study provides insights into understanding the polarized behavior of molecules in dielectrics and further optimizing the output performance of TENGs in self‐charge excitation systems.

Spike propagation in a nanolaser-based optoelectronic neuron

With the recent development of artificial intelligence and deep neural networks, alternatives to the Von Neumann architecture are in demand to run these algorithms efficiently in terms of speed, power and component size. In this theoretical study, a neuromorphic, optoelectronic nanopillar metal-cavity consisting of a resonant tunneling diode (RTD) and a nanolaser diode (LD) is demonstrated as an excitable pulse generator. With the proper configuration, the RTD behaves as an excitable system while the LD translates its electronic output into optical pulses, which can be interpreted as bits of information. The optical pulses are characterized in terms of their width, amplitude, response delay, distortion and jitter times. Finally, two RTD-LD units are integrated via a photodetector and their feasibility to generate and propagate optical pulses is demonstrated. Given its low energy consumption per pulse and high spiking rate, this device has potential applications as building blocks in neuromorphic processors and spiking neural networks.

Small‐disturbance stability of a concentrating solar power collecting system with multiple synchronous generators

This paper examines the small-disturbance stability in planning a concentrating solar power collecting system (CSPCS) with multiple concentrating solar power (CSP) generation plants, which are modelled as synchronous generators (SGs). The examination indicates that an oscillation mode of the CSPCS gradually moves to the right half of complex plane when the planned number of the CSP generation plants increases. Such oscillatory instability is different with the low-frequency electromechanical power oscillations (LEPOs) in a conventional multi-machine power system, because the unstable oscillation mode is associated with the excitation systems, rather than the electromechanical dynamics of the SGs. Analysis is carried out in the paper to explain why the instability risk found in the planning is associated with the excitation systems instead of electromechanical dynamics of the SGs. The analysis helps to understand the finding made in the planning. Furthermore, rules are proposed to adjust the gain of feedback loop of the excitation systems to eliminate the risk of oscillatory instability. This suggests that the parameters’ setting of excitation systems recommended by the IEEE standard may need to be modified to accommodate the planning of CSPCS. Tests are presented to demonstrate and evaluate the analysis and conclusions made.

Digital Twin Development of a Dynamic Hardware Emulator

The increasing deployment of new technologies to contribute to the decarbonization of power systems is imposing new challenges in terms of system dynamics and stability. To deal with different operating and control issues in this sense, and support actual needs, advanced tools and solutions are required. Therefore, this paper presents a digital twin of a dynamic hardware emulator that can be used for controller hardware in the loop (CHIL) testing and is based on a small-scale laboratory system. To build the simulation model, the parameters of involved synchronous machines, excitation systems, prime movers and transmission lines have been identified and then compared to laboratory measurements to assess the accuracy of the digital twin. Static and dynamic accuracy have been investigated and an overall good accuracy can be shown with the help of quantification of errors. Furthermore, a case study is presented where the digital twin was used to design a controller to damp inter-area oscillations with the help of wide area measurements. This controller was then implemented and tested within the dynamic hardware emulator in the laboratory.

Structural Optimization Design of Rotary Loose Coupler

The loose coupling transformer, the core component of the rotary wireless excitation system, has a large leakage inductance due to the existence of a large gap, and the coupling coefficient cannot be effectively improved, thus limiting the improvement of the system efficiency. In order to solve this problem, firstly, the equivalent modeling and leakage inductance analysis of the rotary loosely coupled transformer are carried out, and the improved design is carried out according to the defects of common windings, and an improved shaft rotary coupler is proposed. The feasibility of this optimized structure was determined using Ansys/Maxwell simulation analysis software. The S-S resonance compensation scheme is designed, and the co-simulation with Simplorer and Maxwell is used to compare the coupling coefficient and transmission efficiency of the loosely coupled transformer before and after the improvement under the condition of large air gap, and the rationality of the proposed scheme is verified.

Spontaneous emission of a moving atom in a waveguide of rectangular cross section

We study the spontaneous emission (SE) of an excited nonrelativistic two-level system (TLS) interacting with the vacuum in a waveguide of rectangular cross section. All TLS’s transitions and the center-of-mass motion of the TLS are taken into account. The SE rate and the carried frequency of the emitted photon for the TLS initially being at rest are obtained, it is found that in the first order of the mass M, the frequency of the emitted photon is smaller than the transition frequency of the TLS and the SE rate is smaller than the SE rate Γ f of the TLS fixed in the same waveguide. The SE rate for the TLS initially being moving is obtained in the second order of the mass M. The SE rate is smaller than Γ f but it is dependent not only on the atomic mass but also on the initial momentum. The carried frequency of the emitted photon is decreased when it travels along the direction of the initial momentum, whereas it is increased when it travels in the opposite direction of the initial momentum.

SELF-STARTING OF SYNCHRONOUS MOTORS WITH COMPENSATION INERTION OF THE EXCITATION CONTOUR

The actual scientific problem is solved in the work, which consists in the development, theoretical and experimental researches of devices for self - starting of synchronous motors with compensation of inertia of excitation circuit. The aim of the work is to increase the reliability of the self-starting mode of synchronous motors of responsible mechanisms to maintain the continuity of complex technological processes. In the event of natural disasters and natural disasters, power outages can cause long-term disruptions of technological processes, large material losses, and in some cases fires and explosions, which can lead to human casualties and significant economic damage.&#x0D; Under these conditions, the mode of restarting synchronous motors must be used to power the responsible electric drives of mechanisms, such as mine fans, water pumping stations.&#x0D; To limit the dynamic loads, it is necessary to have the smallest possible value of e.r.s. stator SD in order to limit the switching current, which can be achieved by using various methods and means of extinguishing the field, increasing the time of introduction of automatic re-inclusion or automatic inclusion of the reserve. The calculated dependences of the self-starting modes of SD when extinguishing the magnetic field due to the inclusion of capacitive energy storage devices are obtained. The developed device for self-starting of SD with a capacity of 1000 kW of the drive unit of the pump unit with ENE was implemented at the pumping station of the Dnieper Metallurgical Plant. The efficiency of the developed device does not depend on the presence of voltage that supplies the excitation system in the self-starting mode. The use of ENE in the excitation circuit provides compensation for the inertia of the OZ and increase the input coin and intensive quenching of the magnetic field. The developed devices provide reliable self-starting of synchronous electric drives of mechanisms with continuous technological processes regardless of the presence of voltage in the power supply system of the exciter.