Loss Of Synchronization Research Articles

A transient stability enhancement framework based on rapid fault-type identification for virtual synchronous generators

The virtual synchronous generator (VSG) control, widely used for voltage source inverters, is prone to the loss of synchronization (LOS) under large disturbances such as grid voltage sags. Despite the significant amount of research that has been conducted on the transient stability of VSGs, the existing conclusions on the influence of virtual inertia under different fault conditions remain controversial. In this paper, the conflicting effect of virtual inertia on VSG transient stability under different severities of grid voltage sag is comprehensively investigated. Faults, like grid voltage sags, are classified into two types in this paper: transient tolerable faults and transient intolerable faults. Moreover, a unified control framework for rapid fault-type identification and transient stability improvement is proposed. The Learning vector quantization (LVQ) neural networks are used to distinguish fault types within 5 ms. Based on the fault-type identification results, the proposed control strategies are applied to enhance the transient stability of VSG. Finally, simulations and control-hardware-in-loop experimental validations are carried out to demonstrate the effectiveness of the proposed framework.

Alleviation and control of chaotic oscillations in SMIB power systems using a modified-Whale optimization-based battery-STATCOM

BackgroundChaotic oscillations within the power system give rise to instability. While these oscillations may not have an immediate impact on the synchrony of the machine, they stimulate one of the oscillation modes, ultimately leading to voltage collapse and a loss of synchronism. ObjectiveThis paper introduces a modified Whale Optimization Algorithm (WOA)-based Battery-STATCOM (Static Synchronous Compensator) as a solution to mitigate chaotic oscillations within a Single Machine Infinite Bus (SMIB) system. MethodologyAn adaptable controller is implemented to manage the gate signal within the Battery-STATCOM. The AC-DC currents of this controller are optimally governed by two distinct WOA-tuned Proportional-Integral (PI) controllers. The battery storage unit serves as a robust voltage source, with the intelligent controller maintaining the DC-link voltage at the desired level. Test CasesAdditional disturbances, such as gradual variations in reference voltage and electromagnetic torque, are introduced to exacerbate chaotic oscillations. This is done to assess the controller's real-world performance under adverse conditions. Results and ConclusionUnder zero damping conditions, rotor parameters, including rise time, settling time, peak time, and overshoot, initially remain undefined due to uncontrolled oscillations. However, once the Battery-STATCOM is applied, these parameters are defined and achieve values (in seconds) of 0.90, 6.21, 1.71, and 21.10, respectively. After further optimization through the proposed modified WOA optimizer, the parameters reach values of 0.25, 1.01, 0.89, and 1.78, respectively. These results underscore the effectiveness of the proposed metaheuristic controller in suppressing overall chaotic oscillations within the power system.

Analysis of Power System Transient Stability of the Nigerian 330-kV Electricity Grid

Faults on power system are inevitable and can occur at any time resulting into transient instability. Transient instability can cause loss of synchronism and possible damage to power equipment and consumer loads. Therefore, this study analyzed the transient stability (TS) of the Nigerian 330-kV, 34-bus power network. Power flow and swing equations describing the system steady and transient states were respectively analyzed using Newton-Rahpson and Runge-Kutta, fourth order numerical techniques to provide linear solution due to their non-linearity. Simulations were done and swing curves for different fault conditions obtained. The critical clearing time at which the simulated faults were cleared was determined. The results of load flow analyses revealed that buses 6, 10, 13, 14, and 17 with respective voltage magnitude of 0.937, 0.921, 0.938, 0.829 and 0.780 per unit violated voltage tolerance limit of 0.95 to 1.05 p.u. The system total active and reactive power losses were 57.62 MW and -70.62 MVar respectively. The obtained swing curve showed that for fault on bus 11 [line 9-11] generators 2, 3 and 7 lost synchronism after 1.0 s but other generators retained their stability. Similarly, for fault on bus 13 [line 10-14] generators 3 and 7 lost synchronism but other generators retained stability after 0.4 s. These results indicate that faults occurrence on generating stations of power system is unavoidable, but the clearance time must be short (few seconds) to avert total system collapse and loss of synchronism.

ANALYSIS OF RWANDA’S GRID POINT OF STABILITY LOSS

E Electricity stability is the key component in ensuring reliable power supply which is a major hurdle in most developing countries. Power angle being part of grid stability pillars, this work sought to theoretically and numerically investigate the maximum power angle variation that the power system in Rwanda could experience while maintaining transient stability at an acceptable range beyond which generators lose synchronism affecting overall system stability. A steady state and dynamic stability assessment of the lightly loaded Rwandan grid is conducted using PSS/E while MATLAB is used to obtain input values for calculating the system stability power angle. This involved collecting actual network parameters, creating an accurate model of the entire Rwandan grid and validating the model simulation results using regularly metered values at various critical busbars of the network. Results from the study show that a sudden drop in load of 11 MW and 6 MVAr leads to a variation of power angle of the largest power plant by 23o triggering transient stability problems leading to loss of synchronism. Both calculated and simulation results show that, a sudden power angle variation of between 23o to 23.5o at the swing bus power plant, causes the monitored generating units to trip triggering a long-term instability. This was done while also interrogating possible mitigation measures based on the developed and validated model. Based on the system status, the study revealed that the grid point of stability can be determined through simulation using software and to further obtain optimum stability, installation of active devices such as shunt reactors helps the grid to counter sudden variation of power angle due to line and load tripping. B

Controlled Power System Separation Using Generator PMU Data and System Kinetic Energy

With the growing number of severe system disturbances and blackouts around the world, controlled system separation is becoming an increasingly important system integrity protection scheme (SIPS) to save the electric power system from a complete or partial disintegration. A successful controlled splitting approach should at least tackle the following two well-known and interrelated problems: "when to split?" and "where to split?". Multiple previous publications consider these problems separately, and even those pursuing a combined approach propose solutions with limited applicability. In this paper, we are proposing a novel PMU-based detector of loss of synchronism that utilizes generator rotor angles and speeds to promptly detect rotor angle instabilities over a wide area. Moreover, we are showing how our loss of synchronism detection principle can be coupled with the known controlled splitting techniques to form an integrated defense scheme against unintentional loss of synchronism. The performance of this wide-area SIPS is demonstrated on the IEEE 39-bus test power system for various types of unstable conditions.

Modeling the effects of climate change on the population dynamics of mosquitoes that are vectors of infectious diseases

We incorporate almost periodic functions in a mosquito model to take into account a loss of synchronicity in the population dynamics of mosquitoes due to climate change. The model takes into account the skip oviposition strategy that is associated with the mosquitoes that are vectors of infectious diseases as dengue, malaria and leishmaniasis. We prove existence and uniqueness of a stable almost periodic solution for some conditions over the parameters of the model. Numerical simulations are performed using values estimated for the life cycle of Aedes albopictus gathered in literature. The results show that the vector population can be underestimated or overestimated if an almost periodic dynamics is approximated by a periodic dynamics. Therefore, using an almost seasonal model can be more adequate to design breeding habitat-targeted mosquito control strategies when seasonal drivers are modeled since climate-mediated shifts can induce a loss of periodicity in environmental drivers.

Control of Grid-Forming VSCs: A Perspective of Adaptive Fast/Slow Internal Voltage Source

Grid-forming (GFM) capability requirements are increasingly imposed on grid-connected voltage-source converters (VSCs). Under large grid disturbances, GFM-VSCs need to remain stable while providing GFM services. Yet, such objectives, as pointed out in this paper, inherently lead to conflicting requirements on the dynamics of internal voltage source (IVS) of GFM-VSCs, i.e., the fast IVS dynamics is needed to avoid the loss of synchronism with the grid, whereas the slow IVS dynamics is preferred for maintaining GFM capability. To tackle this challenge, an adaptive fast/slow IVS control is proposed, which switches GFM-VSC between fast and slow IVS dynamics based on system needs. The proposed method enhances the transient stability of GFM-VSC, whilst maximizing its capability of providing GFM service. Further, the approach is robust to different grid strengths and different types of grid disturbances. The experimental results verify the theoretical findings and the effectiveness of the proposed control method.

EEG phase synchronization during absence seizures.

Absence seizures-generalized rhythmic spike-and-wave discharges (SWDs) are the defining property of childhood (CAE) and juvenile (JAE) absence epilepsies. Such seizures are the most compelling examples of pathological neuronal hypersynchrony. All the absence detection algorithms proposed so far have been derived from the properties of individual SWDs. In this work, we investigate EEG phase synchronization in patients with CAE/JAE and healthy subjects to explore the possibility of using the wavelet phase synchronization index to detect seizures and quantify their disorganization (fragmentation). The overlap of the ictal and interictal probability density functions was high enough to preclude effective seizure detection based solely on changes in EEG synchronization. We used a machine learning classifier with the phase synchronization index (calculated for 1 s data segments with 0.5 s overlap) and the normalized amplitude as features to detect generalized SWDs. Using 19 channels (10-20 setup), we identified 99.2% of absences. However, the overlap of the segments classified as ictal with seizures was only 83%. The analysis showed that seizures were disorganized in approximately half of the 65 subjects. On average, generalized SWDs lasted about 80% of the duration of abnormal EEG activity. The disruption of the ictal rhythm can manifest itself as the disappearance of epileptic spikes (with high-amplitude delta waves persisting), transient cessation of epileptic discharges, or loss of global synchronization. The detector can analyze a real-time data stream. Its performance is good for a six-channel setup (Fp1, Fp2, F7, F8, O1, O2), which can be implemented as an unobtrusive EEG headband. False detections are rare for controls and young adults (0.03% and 0.02%, respectively). In patients, they are more frequent (0.5%), but in approximately 82% cases, classification errors are caused by short epileptiform discharges. Most importantly, the proposed detector can be applied to parts of EEG with abnormal EEG activity to quantitatively determine seizure fragmentation. This property is important because a previous study reported that the probability of disorganized discharges is eight times higher in JAE than in CAE. Future research must establish whether seizure properties (frequency, length, fragmentation, etc.) and clinical characteristics can help distinguish CAE and JAE.

Stabilizing the Operation Modes of a Modern Multi-Machine Power System after Large Disturbances

Operational experience has shown that the tuning of stabilization channels of automatic excitation controllers (AEC) adopted in the UES of Russia improves steady-state stability in the power system both for long power lines and through weak connections, as well as in the event of small fluctuations in parameters. However, situations may occur in a multi-machine power system during transients after large disturbances and loss of synchronism between generators with large power fluctuations when the adopted (standard) tuning does not provide rapid suppression of these fluctuations. In an emergency situation, a prolonged transient with large power fluctuations can cause a local damage to evolve into a system accident. The article describes a method for stabilizing the operation modes in a multi-machine power system, according to which it is proposed to produce stabilizing AEC signals based on the difference of deviations between the shaft rotation frequency of each unit and the voltage frequency on the power plant busbars. Such signals will contribute to fast synchronization of generators with respect to one another and prevent power overflows between them during oscillations. In addition, with the stabilizing signals formed in this way, there will be no need for repeatedly retuning the AEC in the course of power system development and as changes are made in the electrical network structure; moreover, a widespread introduction of the proposed approach will significantly reduce the risk of torsional vibration of the turbine unit shaft. The results of the discussion of the proposed stabilization method by the UES Scientific and Technical Council are presented.

A non-PMU-based WAN protection scheme for swing detection and stability enhancement in power systems

This paper presents a scheme for power swing detection and stability assessment for multi-machine power systems in addition to a brief survey on that topic. The scheme adopts smart grid perception. It is an asynchronous scheme that uses the rate of change of the angle of the generator bus voltage instead of synchronously estimating the absolute rotor angle value for stability assessment. Therefore, it does not require phasor measurement units (PMUs). Instead, it uses commercially available intelligent electronic devices (IEDs). It introduces a new application of the multicast Generic Object Oriented Substation Event (GOOSE) protocol or its routable version (R-GOOSE) to reflect the disturbance in the power grid on the transmission pattern of data packets over the grid data network. In this scheme, the angle change information is transmitted in the form of GOOSE packets simultaneously from the IEDs that readily measure the angles of the affected generators. On the other hand, the detecting device identifies the stability status of each affected generator. The proposed scheme is validated by simulating disturbances on the IEEE 39-bus system. The results show that the scheme can discriminate between stable and unstable swings. In addition, the loss of synchronism of the unstable generator is predicted ahead of its occurrence by enough time to take an appropriate action.

Synchronization Stability Enhancement of Grid-Following Converter Under Inductive Power Grid

The loss of synchronization (LOS) is a main issue for dynamic behavior of grid-following converter (GFC) under inductive power grid. This letter reveals the underlying mechanism of insufficient damping or even negative damping during grid disturbance, and analyzes how the initial speed of angle-difference between PLL output and grid voltage affects the synchronization stability. Then a synchronization stability enhancement scheme to add a positive damping and a reverse angular frequency during transient process is proposed in this letter.

The ECCANDE Project: Design, Field Implementation, and Operation of a Special Protection Scheme Based on Synchronized Phasor Measurements

This paper presents the ECCANDE project, one of the first Special Protection Schemes (SPS) conceived to rely on the structure of a Wide-Area Monitoring, Protection, and Control System (WAMPACS) and currently operating in a real, large-sized power system. This project was developed and implemented to enable the interconnection between the Argentinean and Paraguayan bulk power transmission systems, which involves and directly affects two of the largest hydropower plants in the world (the Itaipu and Yacyreta power plants). Building this WAMPACS-based SPS took more than a decade of work performed by multiple teams, involving modeling, planning studies, design, manufacturing, real-time hardware-in-the-loop (HIL) simulation for equipment testing, implementation, commissioning, field tests and evaluation of daily operation. The paper describes how system stability problems (detected during the initial studies for the interconnection) made it clear that the ECCANDE SPS had to be a WAMPACS-based one, and how its architecture and logic functions were conceived to deal with these problems. The results of HIL real-time simulations and a main field test show that the ECCANDE SPS enabled the interconnection, successfully protecting against the loss of synchronism between the Itaipu and Yacyreta power plants before the system separation.

FEM-based optimal design and testing of synchronous magnetic coupling for aerospace Starter/Generator applications

Improvements in high energy density rare-earth permanent magnets make it innovative to develop magnetic couplings for Starter/Generator applications in the light of more electric aircraft to ensure magnetically insulated contactless power transmission between decoupled shafts for safe operation. Although there are essential studies on magnetic couplings in the literature, especially those for aerospace Starter/Generator structures are rarely encountered. However, methodologies considering system constraints and examining design parameters of couplings are in demand. In response to such a need, this paper proposes the novel design of highly reliable synchronous radial magnetic couplings with torque requirements of 6 and 12 N·m to isolate Starter/Generator and piston engine shafts in model aircraft. The preliminary volume is obtained analytically. Simulations are executed by optimetric approaches in Ansys Maxwell 2D. Optimisation techniques are compared in Maxwell 3D to get the final shape. The retaining sleeve of 0.5 mm is suggested. Loss of synchronisation in the event of the piston shaft failure or exceeding the maximum torque of the coupling is also examined. The torque fluctuation at load changes is 0.1%. Performance tests are conducted on the direct dynamic test bench. Absolute error margin is 37% for the Virtual Work method, 13% for 2D FEM and 6% for 3D FEM. The coupling efficiency is 93.8% at the maximum operating speed and the critical angle, and 96.9% at the minimum torque angle and the minimum operating speed.

PROPORTIONAL INTEGRAL QUASI RESONANT CONTROLLER FOR ZERO-SEQUENCE CIRCULATING CURRENT AND RIPPLES SUPPRESSION IN PARALLEL THREE-PHASE PWM RECTIFIERS

Parallel three-phase pulse with modulation (PWM) rectifiers with common sc and ac buses are widely used in power systems due to their many advantages such as flexibility, sinusoidal grid currents, lower switching frequency, and good reliability. However, this topology suffers from zero-sequence circulating current (ZSCC) generated by numerous reasons including filters inductors unbalanced, unequal dead time, and losses of synchronism between the control of each rectifier, which will distort the ac-side currents and increase power losses. This paper proposes both an adjusted space vector pulse width modulated (ASVPWM) method and proportional integral quasi resonant controller (PIQRC) method not only to force the ZSCC to be zero but also to reduce its ripples, which results in low frequency harmonic components in the ac side currents. This twofold objective can be achieved by adjusting the zero-vector duty ratios of ASVPWM to suppress the ZSCC and by using PIQRC to mitigate its predominant harmonics. Finally, the superiority and efficiency of the proposed control method in terms of ZSCC suppression and current ripple reduction are verified through comparative analysis with the conventional ZSCC-PI controller.

Preventing loss of synchronism of droop-based grid-forming converters during frequency excursions

This short communication addresses the risk of synchronisation loss during frequency excursions for droop-based grid-forming converters when active power limitations are considered. The synchronising capability of this control approach is based on the converter’s active power exchange, which is used to generate the internal frequency of the converter control. The power available in the resource or converter ratings can impact the synchronising capability during frequency deviations. The analysis is restricted to droop-based grid-forming converters, but it could be extended to other active-power-based synchronising methods. A droop-based control is proposed to extend the operation frequency range of grid-forming converters. The performance of the suggested method is also compared to alternative ones presented in the literature. Finally, the proposed control is validated in the IEEE 9-bus system with different VSC penetration levels through EMT simulations developed in PSCAD.

Finite Element Method-Based Optimisation of Magnetic Coupler Design for Safe Operation of Hybrid UAVs

The integration of compact concepts and advances in permanent-magnet technology improve the safety, usability, endurance, and simplicity of unmanned aerial vehicles (UAVs) while also providing long-term operation without maintenance and larger air gap use. These developments have revealed the demand for the use of magnetic couplers to magnetically isolate aircraft engines and starter-generator shafts, allowing contactless torque transmission. This paper explores the design aspects of an active cylindrical-type magnetic coupler based on finite element analyses to achieve an optimum model for hybrid UAVs using a piston engine. The novel model is parameterised in Ansys Maxwell for optimetric solutions, including magnetostatics and transients. The criteria of material selection, coupler types, and topologies are discussed. The Torque-Speed bench is set up for dynamic and static tests. The highest torque density is obtained in the 10-pole configuration with an embrace of 0.98. In addition, the loss of synchronisation caused by the piston engine shaft locking and misalignment in the case of bearing problems is also examined. The magnetic coupler efficiency is above 94% at the maximum speed. The error margin of the numerical simulations is 8% for the Maxwell 2D and 4.5% for 3D. Correction coefficients of 1.2 for the Maxwell 2D and 1.1 for 3D are proposed.

Analysis of transient stability of generator groups in the future power system

Transient stability is an essential property of electrical power systems. It describes the ability of the system to maintain synchronous operation of all generators. Classically, transient stability of individual generators is analyzed based on possible loss of synchronism after near short-circuit faults. In contrast, this paper considers transient stability of generator groups as a potential instability phenomenon in future grid scenarios. We investigate and analyze relevant factors of influence and countermeasures and modeling aspects to consider when studying the phenomenon. Based thereon we discuss the effectiveness of possible countermeasures. The main focus of this paper is to provide a better understanding of the underlying dependencies within the power system and their impact on the stability itself.

Early impairments of visually-driven neuronal ensemble dynamics in the rTg4510 tauopathy mouse model

Tau protein pathology is a hallmark of many neurodegenerative diseases, including Alzheimer's Disease or frontotemporal dementia. Synaptic dysfunction and abnormal visual evoked potentials have been reported in murine models of tauopathy, but little is known about the state of the network activity on a single neuronal level prior to brain atrophy. In the present study, oscillatory rhythms and single-cell calcium activity of primary visual cortex pyramidal neuron population were investigated in basal and light evoked states in the rTg4510 tauopathy mouse model prior to neurodegeneration. We found a decrease in their responsivity and overall activity which was insensitive to GABAergic modulation. Despite an enhancement of basal state coactivation of cortical pyramidal neurons, a loss of input-output synchronicity was observed. Dysfunction of cortical pyramidal function was also reflected in a reduction of basal theta oscillations and enhanced susceptibility to a sub-convulsive dose of pentylenetetrazol in rTg4510 mice. Our results unveil impairments in visual cortical pyramidal neuron processing and define aberrant oscillations as biomarker candidates in early stages of neurodegenerative tauopathies.

Special issue on “Optimal design and operation of energy systems”

Special issue on “Optimal design and operation of energy systems”

Indirect adaptive fuzzy finite time synergetic control for power systems

Introduction. Budget constraints in a world ravenous for electrical power have led utility companies to operate generating stations with full power and sometimes at the limit of stability. In such drastic conditions the occurrence of any contingency or disturbance may lead to a critical situation starting with poorly damped oscillations followed by loss of synchronism and power system instability. In the past decades, the utilization of supplementary excitation control signals for improving power system stability has received much attention. Power system stabilizers (PSS) are used to generate supplementary control signals for the excitation system in order to damp low-frequency oscillations caused by load disturbances or short-circuit faults. Problem. Adaptive power system stabilizers have been proposed to adequately deal with a wide range of operating conditions, but they suffer from the major drawback of requiring parameter model identification, state observation and on-line feedback gain computation. Power systems are nonlinear systems, with configurations and parameters that fluctuate with time that which require a fully nonlinear model and an adaptive control scheme for a practical operating environment. A new nonlinear adaptive fuzzy approach based on synergetic control theory which has been developed for nonlinear power system stabilizers to overcome above mentioned problems. Aim. Synergetic control theory has been successfully applied in the design of power system stabilizers is a most promising robust control technique relying on the same principle of invariance found in sliding mode control, but without its chattering drawback. In most of its applications, synergetic control law was designed based on an asymptotic stability analysis and the system trajectories evolve to a specified attractor reaching the equilibrium in an infinite time. In this paper an indirect finite time adaptive fuzzy synergetic power system stabilizer for damping local and inter-area modes of oscillations for power systems is presented. Methodology. The proposed controller design is based on an adaptive fuzzy control combining a synergetic control theory with a finite-time attractor and Lyapunov synthesis. Enhancing existing adaptive fuzzy synergetic power system stabilizer, where fuzzy systems are used to approximate unknown system dynamics and robust synergetic control for only providing asymptotic stability of the closed-loop system, the proposed technique procures finite time convergence property in the derivation of the continuous synergetic control law. Analytical proofs for finite time convergence are presented confirming that the proposed adaptive scheme can guarantee that system signals are bounded and finite time stability obtained. Results. The performance of the proposed stabilizer is evaluated for a single machine infinite bus system and for a multi machine power system under different type of disturbances. Simulation results are compared to those obtained with a conventional adaptive fuzzy synergetic controller.