Stable Synchronization Research Articles

Transient Synchronization Stability Improvement Control Strategy for Grid-Connected VSC Under Symmetrical Grid Fault

Under grid fault, the grid-connected voltage source converters (VSCs) have the risk of transient synchronization instability during low voltage ride through. Based on the equivalent rotor swing equation of VSC, this letter proposes an improved transient synchronization stability control strategy, which improves the existence of equilibrium points and transient synchronization behaviors of the VSC system. Thus, the transient synchronization stability of grid-connected VSC can be significantly enhanced. The simulation and experimental results demonstrate the validity of the proposed strategy.

Dynamic analysis of delayed neural networks: Event-triggered impulsive Halanay inequality approach

This paper proposes a generalized impulsive Halanay inequality from the impulsive control standpoints, where the impulse action is event-triggered. Namely, the control task is executed when an external event generated by the state-dependent event-triggered mechanism (ETM) is activated, rather than at a fixed time. It is shown that under the proposed event-triggered impulsive control (ETIC) strategy, the solution of the underlying inequality is guaranteed to converge to zero asymptotically. Moreover, the key point is the introduction of monitoring value to ensure a positive minimum inter-execution time, which exactly assists ETIC with reducing the pressure of information transmission. Then, the generalized impulsive Halanay inequality with appropriate ETIC scheme is utilized to the analysis of delayed neural networks (DNNs). In particular, some synchronization and asymptotic stability criteria of DNNs are derived, where the design of impulsive controller is based on ETIC strategy. At last, some numerical examples are provided to illustrate the validity of the obtained results.

The relationship between stability of interpersonal coordination and inter-brain EEG synchronization during anti-phase tapping

Inter-brain synchronization is enhanced when individuals perform rhythmic interpersonal coordination tasks, such as playing instruments in music ensembles. Experimentally, synchronization has been shown to correlate with the performance of joint tapping tasks. However, it is unclear whether inter-brain synchronization is related to the stability of interpersonal coordination represented as the standard deviation of relative phase (SDRP). In this study, we simultaneously recorded electroencephalograms of two paired individuals during anti-phase tapping in three interactive tapping conditions: slow (reference inter-tap interval [ITI]: 0.5 s), fast (reference ITI: 0.25 s), and free (preferred ITI), and pseudo tapping where each participant tapped according to the metronome sounds without interaction. We calculated the inter-brain synchronization between pairs of six regions of interest (ROI): frontal, central, left/right temporal, parietal, and occipital regions. During the fast tapping, the inter-brain synchronization significantly increased in multiple ROI pairs including temporoparietal junction in comparison to pseudo tapping. Synchronization between the central and left-temporal regions was positively correlated with SDRP in the theta in the fast condition. These results demonstrate that inter-brain synchronization occurs when task requirements are high and increases with the instability of the coordination.

Oscillation suppression and chimera states in time-varying networks.

Complex network theory has offered a powerful platform for the study of several natural dynamic scenarios, based on the synergy between the interaction topology and the dynamics of its constituents. With research in network theory being developed so fast, it has become extremely necessary to move from simple network topologies to more sophisticated and realistic descriptions of the connectivity patterns. In this context, there is a significant amount of recent works that have emerged with enormous evidence establishing the time-varying nature of the connections among the constituents in a large number of physical, biological, and social systems. The recent review article by Ghosh et al. [Phys. Rep. 949, 1-63 (2022)] demonstrates the significance of the analysis of collective dynamics arising in temporal networks. Specifically, the authors put forward a detailed excerpt of results on the origin and stability of synchronization in time-varying networked systems. However, among the complex collective dynamical behaviors, the study of the phenomenon of oscillation suppression and that of other diverse aspects of synchronization are also considered to be central to our perception of the dynamical processes over networks. Through this review, we discuss the principal findings from the research studies dedicated to the exploration of the two collective states, namely, oscillation suppression and chimera on top of time-varying networks of both static and mobile nodes. We delineate how temporality in interactions can suppress oscillation and induce chimeric patterns in networked dynamical systems, from effective analytical approaches to computational aspects, which is described while addressing these two phenomena. We further sketch promising directions for future research on these emerging collective behaviors in time-varying networks.

Current-Limiting Virtual Synchronous Control and Stability Analysis Considering DC-Link Dynamics Under Normal and Faulty Grid Conditions

An improved nonlinear virtual synchronous control for three-phase grid-connected inverters, that can maintain a reliable operation under both normal and faulty grid conditions, i.e. balanced grid voltage sags, is proposed. The proposed controller can ensure a desired RMS current limitation at all times, provide virtual inertia and damping via the DC-link voltage and AC system frequency coupling, and realize the desired real and reactive power regulation without requiring accurate knowledge of the system parameters. Opposed to the conventional methods that use saturated PI controllers with or without anti-windup techniques to limit the reference value of the inverter current, the proposed controller includes a nonlinear bounded integrator, which limits the actual value (instead of the reference) of the inverter RMS current and leads to a fast system recovery even after significant grid voltage sags. The closed-loop stability of entire system is rigorously proven using nonlinear singular perturbation theory. Moreover, analytic conditions for the controller parameter selection to guarantee the stability of entire inverter system with the DC-link dynamics are provided. To prove the effectiveness of proposed controller and its superior performance compared to the traditional approaches, extensive Matlab/Simulink-based simulations are performed, followed by Typhoon-HIL hardware-in-the loop implementation using a TI microcontroller.

Predicting basin stability of power grids using graph neural networks

The prediction of dynamical stability of power grids becomes more important and challenging with increasing shares of renewable energy sources due to their decentralized structure, reduced inertia and volatility. We investigate the feasibility of applying graph neural networks (GNN) to predict dynamic stability of synchronisation in complex power grids using the single-node basin stability (SNBS) as a measure. To do so, we generate two synthetic datasets for grids with 20 and 100 nodes respectively and estimate SNBS using Monte-Carlo sampling. Those datasets are used to train and evaluate the performance of eight different GNN-models. All models use the full graph without simplifications as input and predict SNBS in a nodal-regression-setup. We show that SNBS can be predicted in general and the performance significantly changes using different GNN-models. Furthermore, we observe interesting transfer capabilities of our approach: GNN-models trained on smaller grids can directly be applied on larger grids without the need of retraining.

Synchronization implementation of two eccentric rotors actuated with swung and fixed motors

In a vibrating screen machinery, two eccentric rotors (ERs) are actuated by swung and fixed motors. When the working efficiency of vibrating screens is the highest, the motion trajectory of the vibrating body is an ellipse. However, to implement elliptical trajectory, the ideal synchronization between the two ERs must be needed. Hence, the self-synchronous theory and synchronous control method for the vibrating screen machinery are explored. First, the mathematic model of the vibration system is deduced based on Lagrange equation; then, the synchronous condition and stability criterion are inferred from averaged small parameter method. In addition, the synchronization controllers, related to speed and phase of the ERs, are designed by with sliding mode control (SMC), and the master–slave control strategy is applied to design the control structure. Meanwhile, the stability performance of the controllers is demonstrated by Lyapunov theory and Hurwitz condition. Finally, computer simulations are implemented to validate the theoretical reliability of self-synchronization and synchronous control. The simulation results show that the system can be self-synchronized, but the ideal synchronization is difficult to achieve when the two ERs are self-synchronously rotated, which leads to non-ideal dynamic characteristics; nevertheless, the ideal synchronization can be implemented by the proposed synchronous control method.

Transient synchronization stability analysis of PLL-based VSC using Lyapunov’s direct method

Direct method has been a promising development for decades due to its interpretability. This paper presents the transient energy function based on the Lyapunov’s direct method to quantitatively assess the synchronization stability for PLL-based voltage source converter (VSC). First, the reduced order model of VSC is built, with the consideration of the impact of the outer-loop control system on the dynamic synchronization process of the phase-locked loop (PLL). Then the motion equation of PLL-based VSC considering the interaction between the outer-loop control and PLL control is derived. Furthermore, the equal area criterion (EAC) method is employed to exhibit the synchronization instability mechanism of PLL-based VSC. Next, the transient energy function on the basis of the motion equation is proposed by the first integral method considering the outer-loop control, and the critical energy value is determined by the controlling unstable equilibrium point (UEP) method. Based on the grid-connected equivalent circuit of multiple-VSCs system, the transient energy function for multi-VSCs system is further proposed. Finally, the VSC-Infinite bus system is used as the test system to investigate the effectiveness and advantage of the proposed transient energy function.

Stability of multiple attractors in the unidirectionally coupled circular networks of limit cycle oscillators

The network structure plays a significant role in the system dynamics. In this work, we study the dynamic behaviors of a circular network of the coupled Landau–Stuart oscillators which interact unidirectionally with forward d nearest neighbors. Based on the method of linear stability analysis of existing attractor(s), we then theoretically and numerically investigate the stabilities of the stationary state together with different splay states, and in particular the global synchronization (or sync). Compared with the bidirectional topological approach, our analysis shows that d has a vital impact on the synchronous frequency and stability of global sync, i.e., dc∝N23, but the global sync is much harder to achieve. All the analytic findings are validated by numerical simulations.

Pattern formation in a thermosensitive neural network

Pattern formation and synchronization stability in the network are dependent on cooperation between nodes and the local kinetics as well. Temperature has a significant effect on the membrane potential by regulating the channel conductance and excitability of neurons. Thermistor is a smart sensor and its resistance value changes with temperature. A nonlinear circuit composed of thermistors is effective to detect the changes in surroundings temperature. In this paper, a temperature-induced pattern formation in a two-dimensional regular lattice network composed of thermosensitive neurons is studied. Numerical simulations are performed to research the effect of parameters (coupling amplitude) and temperature spatial gradient distribution of neural network on pattern formation and synchronization stability. The bifurcation analysis of the membrane potential reveals the conversion in electrical activity and pattern selection. The results show that neural membrane potential can present distinct firing patterns with the change of temperature. The electrical synapse coupling between neurons promotes effective signals propagation in the network. It is found that the collective dynamic behavior of the network is changed by taming the coupling intensity. The Hamilton energy is estimated to predict the mode selection in neural activities. The energy can be ordered in the network under the temperature gradient distribution. Our results confirm that electrical synapse coupling and temperature spatial gradient distribution can be controlled to affect the neural activities in nervous system.

Algebraic theory of quantum synchronization and limit cycles under dissipation

Synchronization is a phenomenon where interacting particles lock their motion and display non-trivial dynamics. Despite intense efforts studying synchronization in systems without clear classical limits, no comprehensive theory has been found. We develop such a general theory based on novel necessary and sufficient algebraic criteria for persistently oscillating eigenmodes (limit cycles) of time-independent quantum master equations. We show these eigenmodes must be quantum coherent and give an exact analytical solution for all such dynamics in terms of a dynamical symmetry algebra. Using our theory, we study both stable synchronization and metastable/transient synchronization. We use our theory to fully characterise spontaneous synchronization of autonomous systems. Moreover, we give compact algebraic criteria that may be used to prove absence of synchronization. We demonstrate synchronization in several systems relevant for various fermionic cold atom experiments.

Focusing on transient chaos

Recent advances in the field of complex, transiently chaotic dynamics are reviewed, based on the results published in the focus issue of J. Phys. Complex. on this topic. One group of achievements concerns network dynamics where transient features are intimately related to the degree and stability of synchronization, as well as to the network topology. A plethora of various applications of transient chaos are described, ranging from the collective motion of active particles, through the operation of power grids, cardiac arrhythmias, and magnetohydrodynamical dynamos, to the use of machine learning to predict time evolutions. Nontraditional forms of transient chaos are also explored, such as the temporal change of the chaoticity in the transients (called doubly transient chaos), as well as transients in systems subjected to parameter drift, the paradigm of which is climate change.

Synchronization Instability of Inverter-Based Generation During Asymmetrical Grid Faults

The transient stability of traditional power systems is concerned with the ability of generators to stay synchronized with the positive-sequence voltage of the network, whether for symmetrical or asymmetrical faults. In contrast, both positive- and negative-sequence synchronizations should be of concern for inverter-based generation (IBG) under asymmetrical faults. This is because the latest grid codes stipulate that IBG should inject dual-sequence current when riding through asymmetrical faults. Currently, much less is known about the synchronization stability during asymmetrical faults. This significantly differs from the positive-sequence synchronization alone because the coupled dual-sequence synchronization is involved. This paper aims to fill this gap. Considering the sequence coupling under asymmetrical faults, the dual-sequence synchronization model of IBG is developed. Based on the model, the conditions that steady-state equilibrium points should follow are identified. The conditions throw light on the possible types of synchronization instability, including the positive-sequence dominated instability and the negative-sequence dominated one. For different types of instability, the dominant factors are analyzed quantitatively, which are reflected by the limit on the current injection amplitude. Exceeding the limit will lead to the loss of both positive- and negative-sequence synchronizations. The model and the analysis are verified by simulations and hardware-in-the-loop experiments.

Interpersonal motor synchronization in children

<p id=C9>Interpersonal motor synchronization refers to the simultaneous and consistent actions of an individual toward others in the process of social interaction. It is like a social glue that can promote more pro-social behaviors in children. This paper focuses on the interpersonal motor synchronization in children, explores the development trajectory of childrens interpersonal motor synchronization and its influencing factors through literature review. In particular, the paper discussed the atypical interpersonal motor synchronization among a specific group of children, namely those with autism. <p id=C10>Although humans have acquired certain form of rhythm perception ability in early infancy, it takes six to seven years to synchronize rhythm and movement perfectly. The accuracy and stability of the interpersonal motor synchronization in children improve as they grow. In the development process, childrens synchronization performance is affected by two major aspects. The first factor is that in the context of the laboratory, children’s synchronization performance is affected by their motor effectors (finger, head, feet, etc.), rhythmic stimulation types (such as visual stimulation, auditory stimulation), and synchronization objects (such as robots, adults, and children). The second factor is that children’s synchronization performance is restricted by cognitive factors, including time perception, motor planning, and motor execution. That is, in the process of interpersonal motor synchronization, children need to obtain cues from the environment and peers to form rhythm perception and time perception; in addition, they also need to plan their own actions, and at the same time anticipate the results of their own actions; At the same time, monitor the other partys behavioral responses, and adjust their own movement and rhythm perception accordingly to the synchronization of both parties, so as to better keep pace with others. Therefore, if an individual wants to achieve good synchronization performance, he must have a good time perception and rhythm perception ability, being able to expect the consequences of his own actions in advance, minimize motor noise during the motor execution and perform accordingly to the synchronization of both parties. <p id=C11>The core symptoms of autistic children are social interaction defects and communication disorders. The interpersonal motor synchronization of this group shows atypical characteristics, that is, the level of spontaneous synchronization is lower and the synchronization performance is worse. The defect of time processing and the abnormality of the movement system may be the potential restricting factors of the difficulty of interpersonal movement synchronization in this group. To clarify the similarities and differences in the interpersonal motor synchronization between autistic children and typical children not only can help us understand the development trajectory of childrens interpersonal movement synchronization but also inspire the practical application and intervention effect of interpersonal motor synchronization in autistic children. <p id=C12>Future research needs to further explore the following issues: (1) The influence of motor ability on the interpersonal motor synchronization in children; (2) The influence of interpersonal and non-interpersonal factors on the synchronized movement among autistic children; (3) Explore the reason behind high failure rate of interpersonal motor synchronization interventions in the autistic group.

Intralayer and interlayer synchronization in multiplex network with higher-order interactions.

Recent developments in complex systems have witnessed that many real-world scenarios, successfully represented as networks, are not always restricted to binary interactions but often include higher-order interactions among the nodes. These beyond pairwise interactions are preferably modeled by hypergraphs, where hyperedges represent higher-order interactions between a set of nodes. In this work, we consider a multiplex network where the intralayer connections are represented by hypergraphs, called the multiplex hypergraph. The hypergraph is constructed by mapping the maximal cliques of a scale-free network to hyperedges of suitable sizes. We investigate the intralayer and interlayer synchronizations of such multiplex structures. Our study unveils that the intralayer synchronization appreciably enhances when a higher-order structure is taken into consideration in spite of only pairwise connections. We derive the necessary condition for stable synchronization states by the master stability function approach, which perfectly agrees with the numerical results. We also explore the robustness of interlayer synchronization and find that for the multiplex structures with many-body interaction, the interlayer synchronization is more persistent than the multiplex networks with solely pairwise interaction.

EU’S NEW APPROACH TO THE STRATEGY CENTRAL ASIA – AFGHANISTAN

The article examines new aspects of the EU’s strategy towards Afghanistan – Central Asia aimed at stabilizing the region as a whole. New elements of the EU’s strategy towards Central Asia are connected with the EU desire to modernize it with the aim to assure synchronous stabilization of Afghanistan and the states of Central Asia in the context of negative repercussions of the Afghan crisis. The article underlines the view of some experts that Central Asia and Afghanistan have common interests in maintaining security and stability in the region as well as in developing mutually advantageous cooperation covering both Central Asia and Afghanistan. Based on these premises the EU tries to integrate Afghanistan into political dialogue between EU and Central Asia as well as into EU’s regional projects. In this context the EU considers as a matter of priority a transition to a trilateral model of political and economic cooperation in the format EU – Central Asia – Afghanistan on the basis of regional connectivity. According to the author, stabilization of Afghanistan and Central Asia will be heavily dependent on the ability of the EU as the largest western donor to Afghanistan to revive the Afghan economy in a speedy manner and to provide effective development assistance for post conflict reconstruction of the country. Special attention was devoted to research on EU’s policy on humanitarian assistance to Afghanistan in the context of reducing challenges to the EU’ security stemming from potential largescale irregular migration, terrorism and narcotraffic. The article envisages that the EU further development assistance to Afghanistan would be more related to the concept of the EU’s strategic autonomy.

A novel method for synchronization stability enhancement of grid connected converters based on equal area criterion

Penetration of inverter-based distributed energy (DG) resources into power grid has notably risen in recent years. Hence, new grid code standards require DGs to remain connected to the main grid even during faults and inject a certain amount of reactive power. However, in weak grids and during severe voltage faults, converters may fail to maintain their synchronization with the main grid. A main cause for this synchronization instability is the improper operation of synchronization unit which is phase locked loop (PLL). In literature, imitating the transient stability analysis of synchronous generators, swing equation and Equal Area Criterion (EAC) are applied to study the synchronization of grid-connected converters. In this paper, a new method based on EAC and swing equation is proposed to keep the damping coefficient in the swing equation positive, and consequently increase the maximum buffer area in EAC. Hence, the synchronization stability of voltage source converters (VSCs) connected to weak grids is enhanced. When the fault is detected, the proposed technique simply adds a certain gain of frequency deviation to the PLL and does not need any additional information of grid changes. The simulation results in MATLAB verify the viability of the proposed controller.

Stability analysis of intralayer synchronization in time-varying multilayer networks with generic coupling functions.

The stability analysis of synchronization patterns on generalized network structures is of immense importance nowadays. In this article, we scrutinize the stability of intralayer synchronous state in temporal multilayer hypernetworks, where each dynamic units in a layer communicate with others through various independent time-varying connection mechanisms. Here, dynamical units within and between layers may be interconnected through arbitrary generic coupling functions. We show that intralayer synchronous state exists as an invariant solution. Using fast-switching stability criteria, we derive the condition for stable coherent state in terms of associated time-averaged network structure, and in some instances we are able to separate the transverse subspace optimally. Using simultaneous block diagonalization of coupling matrices, we derive the synchronization stability condition without considering time-averaged network structure. Finally, we verify our analytically derived results through a series of numerical simulations on synthetic and real-world neuronal networked systems.

Hamilton-Based Stability Criterion and Attraction Region Estimation for Grid-Tied Inverters Under Large-Signal Disturbances

As the crucial interface of renewable energy integration, the stable operation of power converters under grid faults and external disturbances has become much more important. However, synchronization instability of grid-tied inverters has been found caused by the phase-locked loop (PLL) under some critical operating conditions, such as the grid voltage sag, current surge, and transmission line faults. Due to the strong nonlinearity, transient stability analysis of inverters with PLL becomes much more complicated under large-signal perturbations and weak grid conditions. In this article, the large-signal synchronization stability of grid-tied inverters is investigated from the energy perspective. Based on the structural resemblance between the PLL and synchronous generator, the energy function is constructed to establish a port-Hamiltonian model for the grid-tied inverter. For the nonlinear inverter system, an explicit Hamilton-based stability criterion is developed for grid-tied converters according to the concept of dissipativity and LaSalle&#x2019;s theorem. Moreover, the analytical stability boundary is acquired based on the proposed stability criterion and attraction region estimation, covering both controller parameters and grid parameters. To verify the effectiveness of the proposed analysis approach, extensive simulation and experimental results are presented. Compared with the conventional large-signal methods, the proposed Hamilton-based approach has explicit physical meaning and high accuracy.

Hopf bifurcation in the study of synchronous motor stability

&#x0D; &#x0D; &#x0D; In this document the dynamic model of the synchronous motor is presented, which has a typical structure of Lienard-type systems, the theory of dynamic systems is used, especially bifurcations, in this case, Hopf’s, which will be applied to the described model, to show the variations in the balance points of the system by taking the voltage of the bus to which it is connected as a variable parameter.&#x0D; &#x0D; &#x0D;