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Inverter‐dependent renewable energy sources are being integrated into the grid, raising several stability‐related difficulties. This is because these renewable sources have less inertia than synchronous generators. Since the power grid's overall inertia has improved, the introduction of virtual synchronous generators (VSG) has gained much attention. A robust microgrid system requires an effortless transition from grid‐connected to autonomous mode. This can be easily achieved with the help of VSGs. The angle, frequency, and magnitude of the grid voltage needed for synchronization have traditionally been determined by phase‐locked‐loop (PLL). The virtual synchronizing torque and voltage‐based synchronization controller for simple switching between islanding and grid‐connected modes are presented in this study. The proposed method requires no additional controller to identify the unwanted islanding situations because the operating mode can be identified with the help of synchronizing torque. The proposed method does not need to shift to different control algorithms while changing between grid connection and stand‐alone modes. The effectiveness of the suggested controller is established by comparing the experimental prototype of the VSG incorporating the proposed controller to the existing synchronization methods. [ABSTRACT FROM AUTHOR]

There are many effective techniques for virtual inertia emulation in DC microgrids that can help DC bus voltage stability through power exchange with virtual inertia injection. But one of the vexingly complicated challenges in virtual inertia emulation is the connection of unbalanced loads on the AC side of a DC microgrid. Unbalanced AC loads connected to a DC microgrid may cause severe fluctuations in DC bus voltage and battery power, as well as distorting AC side voltage. The need to solve this issue is very important because it can be a threat to the microgrid DC bus voltage stability and feed sensitive loads. One effective method to mimic the real inertia feature and dampen the unfavourable unbalanced conditions is to employ a virtual synchronous generator (VSG) equipped with a decoupled double synchronous reference frame (DDSRF) approach. The DDSRF can extract positive and negative components with high precision and create pure DC signals for the control system to improve accuracy and controllability. Hence, this paper investigates a combination of a VSG structure enhanced with a DDSRF technique to attenuate the fluctuations of DC bus voltage, battery power, and AC-side voltage caused by an unbalanced AC load in an islanded DC microgrid. The simulation results confirm that the unbalanced loads connected to the AC side of the microgrid are destructive for DC bus voltage, battery power, and also create voltage imbalances for AC loads. Furthermore, the proposed DDSRF-based VSG control system that has been implemented on the AC side of the microgrid can strongly dampen the fluctuations on the DC bus, battery, and AC loads. [ABSTRACT FROM AUTHOR]

The highly uncertain and uncontrollable power output of renewable energy sources (RES), when integrated into power systems at high penetration levels, reduces system inertia and introduces uncertain changes in system structure, parameters, and frequency response characteristics. This renders traditional frequency regulation analysis methods and frequency response models inapplicable, lacking a generalized model to describe renewable energy's participation in frequency regulation. Thus, this paper proposes a method where RES utilize suitable means to reduce load, thereby contributing to frequency regulation. Furthermore, employing Virtual Synchronous Machine (VSM) technology, these renewable energy units emulate the inertia and droop characteristics of Synchronous Generators (SG), enabling their equivalent modeling alongside traditional generators within a single-machine aggregate model. An SFR (System Frequency Response) model integrating renewable energy's frequency regulation has been established. This model enables the analysis of the relationships between the system's equivalent droop coefficient and the frequency nadir, nadir time, and quasi-steady-state point. Furthermore, the required equivalent droop coefficients are proposed for various sending-end system capacities and operating conditions. Finally, the model's validity and accuracy are confirmed through a modified WSCC 4-machine 10-bus system, offering theoretical underpinnings for stable system operation and optimized operational planning. [ABSTRACT FROM AUTHOR]

This paper explores an integration of virtual synchronous generators into voltage source converter–based VSC‐HVDC systems to enhance grid stability and performance. VSGs emulate the inertia and damping characteristics of traditional synchronous generators, thereby providing essential frequency support and improving transient stability during disturbances. The study focuses on design considerations, control strategies, and the impact of VSG incorporation on system dynamics. Through detailed simulations and analyses, it is demonstrated that VSGs can significantly reduce the rate of change of frequency during transient events, thus enhancing the overall robustness and reliability of VSC‐HVDC systems. In addition, the practical challenges of implementing VSG‐based control are addressed, and solutions are proposed to optimize system integration and performance. [ABSTRACT FROM AUTHOR]

As renewable energy sources become more integrated into the power grid, traditional virtual synchronous generator (VSG) control strategies have become inadequate for the current low-damping, low-inertia power systems. Therefore, this paper proposes a VSG inertia and damping adaptive control method based on multi-agent deep deterministic policy gradient (MADDPG). The paper first introduces the working principles of virtual synchronous generators and establishes a corresponding VSG model. Based on this model, the influence of variations in virtual inertia (J) and damping (D) coefficients on fluctuations in active power output is examined, defining the action space for J and D. The proposed method is mainly divided into two phases: "centralized training and decentralized execution". In the centralized training phase, each agent's critic network shares global observation and action information to guide the actor network in policy optimization. In the decentralized execution phase, agents observe frequency deviations and the rate at which angular frequency changes, using reinforcement learning algorithms to adjust the virtual inertia J and damping coefficient D in real time. Finally, the effectiveness of the proposed MADDPG control strategy is validated through comparison with adaptive control and DDPG control methods. [ABSTRACT FROM AUTHOR]

This paper reviews the possible contributions of Hybrid Power Plants (HPPs) to support weak grids while maintaining the desired system stability. Moving towards a converter-dominant power system with less inherent inertia and distant connections to the nearest synchronous generator, frequency and voltage controls are becoming more critical to ensure the stability of the weak grid. In this regard, state-of-the-art literature is reviewed for frequency and voltage controllers in single-technology power plants, like wind and solar power plants. The contribution of this paper lies in providing a clear overview of available literature in terms of frequency and voltage control stages, regardless of the utilized control method. On the other hand, focus has been put on the increased utilization of HPPs to provide more flexibility, increased availability, and reduced variability through the combination of various sources, i.e., wind, solar, and storage. Furthermore, investigating the specific capabilities and challenges of HPPs, this review shows that very little literature has been conducted on voltage control using HPPs. Finally, the aspect of relevance of HPPs is discussed in the control and stability of modern power systems. [ABSTRACT FROM AUTHOR]

An axial field hybrid excitation synchronous generator (AF-HESG) is proposed for an independent power supply system, and its electromagnetic performance is studied in this paper. The distinguishing feature of the proposed generator is the addition of static magnetic bridges at both ends to place the field windings and the use of a sloping surface to increase the additional air-gap cross-sectional area. The advantage of the structure is that it achieves brushless excitation and improves the flux-regulation range. The structure and magnetic circuit characteristics are introduced in detail. Theoretical analysis of the flux-regulation principle is conducted by studying the relationship between field magnetomotive force, rotor reluctance, and air-gap flux density. Quantitative calculation is performed using a magnetomotive force (MMF)-specific permeance model, and the influence of the main parameters on the air-gap flux density and flux-regulation range is analyzed. Subsequently, magnetic field, no-load, and load characteristics are investigated through three-dimensional finite element analysis. The loss distribution is analyzed, and the temperature of the generator under rated conditions is simulated. Finally, a 30 kW, 1500 r/min prototype is developed and tested. The test results show good flux-regulation capability and stable voltage output performance of the proposed generator. [ABSTRACT FROM AUTHOR]

As renewable energy integration scales up, power systems increasingly depend on sources interfaced through power electronic converters, which lack rotating mass and substantially diminish system inertia. This reduction in inertia, coupled with the complex and diverse control strategies governing power electronics, presents significant challenges in accurately assessing the equivalent inertia levels within modern power systems. This paper introduces an online method for estimating the inertia time constant of power nodes, grounded in the node power flow equation, to address these challenges. The approach begins by deriving the rotor motion equation for synchronous generators and defining the inertia time constant of power nodes through an analysis of the power flow equations. Real-time frequency and voltage phasor data are collected from system nodes using phasor measurement units. The frequency state of the power equipment is then characterized using a divider formula, and the equivalent reactance between the power equipment and the node is further derived through the node power flow equation. This enables the real-time estimation of the equivalent inertia time constant for power nodes within the system. The effectiveness of the proposed method is demonstrated through simulations on the WSCC9 system, confirming its applicability for real-time system analysis. [ABSTRACT FROM AUTHOR]

Grid-forming virtual synchronous generator (GFVSG) can improve the voltage regulation ability and frequency stability of power grid, but it has the problem of grid connected active power dynamic oscillation similar to that of traditional synchronous generator under the conditions of internal disturbance of active power command and external disturbance of power network frequency. To solve this problem, the grid connected active power closed loop equivalent control model of the grid connected system for grid-forming virtual synchronous generator is established, and the reasons for the dynamic oscillation of the grid connected active power of grid-forming virtual synchronous generator under the disturbance of internal active power command and external power network frequency are analyzed in this study. An improved grid-forming virtual synchronous generator control method based on loop reconstruction mechanism (LRM-GFVSG) is proposed, and the corresponding parameter design method is given in detail. Finally, the MATLAB simulation platform as well as experimental platform of 100 kV·A GFVSG grid connected system are established, then the feasibility and superiority of the improved LRM-GFVSG control method in suppressing the dynamic oscillation of the grid connected active power of grid-forming virtual synchronous generator are verified by the simulation and experimental comparison results. Simulation and experimental comparison results show that the grid connected active power closed loop control system of GFVSG is upgraded to a second order oscillation control system due to the introduction of virtual inertia control. Therefore, the grid connected active power and output frequency of the grid connected system of grid-forming virtual synchronous generator are prone to dynamic oscillation and overshoot under the disturbance of internal active power command and external power network frequency. Although increasing the value of the virtual damping parameter of grid-forming virtual synchronous generator can improve the ability to suppress the dynamic oscillation and overshoot of the grid connected active power as well as its output frequency, the steady-state deviation of the grid connected active power is introduced. Compared with grid-forming virtual synchronous generator, the existing grid-forming virtual synchronous generator control method based on feedforward compensation (FFC-GFVSG) as well as the existing grid-forming virtual synchronous generator control method based on feedback compensation (FBC-GFVSG), on the one hand, under the simulation and experimental test conditions where the active power instruction jumps from 20 kW to 60 kW, the improved control method of LRM-GFVSG can improve the transient damping characteristics of the grid tied system, and realize the effective suppression of the dynamic oscillation and overshooting of the grid connected active power as well as its output frequency, and the grid connected active power has a faster dynamic response speed. On the other hand, under the simulation and experimental test conditions where the frequency of the power grid jumps from 50 Hz to 49.95 Hz, the improved control method of LRM-GFVSG can improve the transient damping characteristics of the grid tied system, effectively suppress the dynamic oscillation and overshoot in the grid connected active power as well as its output frequency, and eliminate the steady state deviation of the grid connected active power when the power network frequency deviates from the rated frequency. [ABSTRACT FROM AUTHOR]

The voltage control of synchronous generators, particularly under varying load conditions, remains a significant and complex challenge in the field of engineering. Although various control methods have been implemented for automatic voltage regulator (AVR) systems to control the terminal voltage of synchronous generators, the PID-based control method continues to be one of the most basic and widely used approaches. Determining the optimal values for the Kp, Ki, and Kd values is essential to ensuring efficient and rapid performance in a PID controller. This study presents PLC-based PID controller tuning using an adaptive artificial bee colony–fuzzy logic (aABC-FL) approach for voltage control in a micro-hydro power plant installed as an experimental setup. The real-time control and monitoring of the system was conducted using an S7-1200 programmable logic controller (PLC) integrated with a totally integrated automation (TIA) portal interface and a SCADA screen. The aABC-Fuzzy design was developed using the MATLAB/Simulink platform, with PLC-MATLAB communication established through OPC UA and the KEPServerEX interface. The results obtained from experiments conducted under different load conditions showed that the proposed aABC-FL PID significantly minimized settling time and overshoot compared to the classical PLC-PID. Additionally, the proposed method not only provided a good dynamic response but also proved to be robust and reliable for real physical AVR systems. [ABSTRACT FROM AUTHOR]

Building a high-proportion renewable energy power system is a key measure to address the challenges of the energy revolution and climate change. However, current high-proportion renewable energy systems face issues of frequency instability and voltage fluctuations. To address these challenges, this paper proposes a novel topology for a stator free speed regulating wind turbine generation system. The stator free speed regulating machine connects a gearbox and a synchronous generator, forming a flexible drive chain that increases system inertia and enhances frequency stability in high-proportion renewable energy power systems. The synchronous generator at the end of the drive chain can be directly connected to the grid without the converter, thanks to the speed regulation provided by the stator free speed regulating machine, thus avoiding harmonic pollution caused by power electronic devices in traditional wind turbines, enhancing the reactive power support capability, and improving voltage stability in high-proportion renewable energy systems. Given that the proposed stator free speed regulating machine consists solely of a rotating inner and outer rotor without a stator, traditional motor control strategies are not applicable. Therefore, this paper focuses on developing control strategies for the stator free speed regulating machine, employing a dual closed-loop PI control strategy with an outer loop for speed and an inner loop for current, based on flux orientation of the outer rotor. Simulation experiments will validate the feasibility of the proposed stator free speed regulating wind turbine generation system topology and the effectiveness of the control strategy. [ABSTRACT FROM AUTHOR]

Compared with the grid-following (GFL)-converter-interfaced generations (CIG), the power-controlled static synchronous machine (PCSSM) can realize voltage and frequency control through the power tracking function, which has the potential to improve the transient stability of the power system. However, the evolution trend of transient stability of power systems with integrated power-controlled static synchronous machine is still unknown. This paper studies the transient stability characteristic of power systems after replacing synchronous generators (SGs) with the PCSSM. The PCSSM and GFL-CIG are integrated into the New England IEEE 39-bus test system, respectively. Firstly, we compare the transient stability of the PCSSM-integrated system with the GFL-CIG-integrated system by changing Converter-interfaced generation's integration proportions and locations. Then, the impact of equivalent inertia coefficient J and damping coefficient D on the transient stability of the PCSSM-integrated system is analyzed. Finally, the advantages of PCSSM compared to GFL-CIG are compared and summarized. [ABSTRACT FROM AUTHOR]

To keep pace with the construction of the new‐type power system, virtual synchronous generator control, as a classical method of virtual inertia control, has been widely adopted due to its electromechanical characteristics similar to synchronous generator. However, the introduction of rotor motion equations leads to low‐frequency oscillation issues in virtual synchronous generator units similar to synchronous machines. To address this challenge, this paper constructs the Phillips‐Heffron model of the virtual synchronous generator grid‐connected system and analyses the mechanism of low‐frequency oscillation in virtual synchronous generator through the damping torque method. Subsequently, a virtual dual‐input power system stabilizer is proposed by drawing inspiration from the design principles of the traditional dual‐input power system stabilizer to suppress low‐frequency oscillations in the power system. The structure of the virtual dual‐input power system stabilizer is provided, and the phase compensation method is used to optimize the parameters of the virtual dual‐input power system stabilizer. Finally, the effectiveness of the proposed virtual dual‐input power system stabilizer is verified by simulation comparison. [ABSTRACT FROM AUTHOR]

With the share of renewable generation increasing, considerable synchronous generators have been displaced. This trend results in the decline of system inertia and thus raises the frequency secure issue. Concurrently, electric vehicles (EVs) proliferate. Numerous EVs hold a huge potential of frequency regulation in case of contingency as EVs are able to achieve primary frequency responses (PFRs) via vehicle to grid chargers. However, the value of frequency responses from aggregated EVs has not fully exploited. This paper, proposes a chance constrained scheduling model incorporating the ability of PFRs from aggregated EVs. The proposed model characterizes uncertainties associated PFR capacities from aggregated EVs and wind power forecast errors by the Wasserstein‐metric ambiguity sets, which do not rely on distributional assumption, and then formulates uncertainties‐related constraints as distributionally robust (DR) chance constraints. These DR chance constraints are reformulated as tractable linear programs. Consequently, the proposed model leads to a mixed‐integer linear program. Numerical results on a modified IEEE 39‐bus system show that incorporating PFR from EVs can reduce total costs from $4,540,396 to $4,431,233, which is reduced by 2.4%. The proposed model also achieves better reliability compared to traditional methods, demonstrating the distributionally robust optimization in enhancing electricity scheduling and rising renewable integration. [ABSTRACT FROM AUTHOR]

The mechanism of oscillations that occur in the system connected to renewable energy sources is complex, generally including negative damping oscillation, limit induced oscillation etc. Combining with the dynamic characteristics of the low‐dimensional system after limit working, this paper analyses the mechanism of a type of limit induced oscillation that occurs when the output of the DC voltage outer loop continuously touches the limit for single‐machine infinite‐bus system of permanent magnet synchronous generator with positive damping under a large disturbance. Specific study as follows: firstly, a non‐smooth state space model of single‐machine infinite‐bus system of permanent magnet synchronous generator with nonlinear state limit (clarified as a Filippov system) is established. Secondly, the small disturbance characteristics of the system are analysed when the limit does not work. Thirdly, the piecewise dynamic description of the system is analysed with the limit working, and the reason that the final contraction of the system to an eight‐dimensional manifold is explained based on mathematical derivation and physical characteristics. Finally, the characteristics of equilibrium point of the system in a low‐dimensional manifold are analysed when the limit continuously working, revealing that the existence of a pair of conjugate unstable eigenvalues in the low‐dimensional system is the reason of system oscillation. [ABSTRACT FROM AUTHOR]

In the classical differential‐algebraic equations (DAEs) framework for the traditional power system stability analysis, synchronous generators are depicted by differential equations and network by algebraic equations under the quasi‐steady‐state assumption. Differently, in the power‐electronic‐dominated power system (PEDPS), the dynamics of transmission lines of network for fully differential equations should be considered, due to the rapid response of converters' controls, for example, the alternating current controls. This poses a great challenge for the cognition, modeling, and analysis of the PEDPS. In this article, a nonlinear DAE model framework for the PEDPS is established with differential equations for the source nodes and algebraic equations for the dynamical electrical network, by generalizing the application scenarios of Kron reduction. The internal and terminal voltages of source nodes of converters are chosen as ports of nodes and network. Namely, the internal and terminal voltages of source nodes work as their output and input, respectively, whereas they work as the input and output of the algebraic network, respectively. The impact of dynamical network becomes clear, namely, it serves as a (linear) voltage divider and generates the terminal voltage based on the internal voltage of the sources simultaneously. By keeping only useful independent state variables, all differential equations for the transmission lines can be transferred to algebraic equations. With this simple model, the roles of both nodes and network become apparent, and it enhances the understanding of the PEDPS dynamics. On the other hand, broad simulations are conducted and compared to verify the proposed DAE framework for the PEDPS. As all independent variables have been kept in the model, it is found that they show the same computational accuracy, but better efficiency in computational time, compared to the electromagnetic‐transient simulation results. [ABSTRACT FROM AUTHOR]

In this study, we establish a fractional‐order direct drive permanent magnet synchronous wind turbines (DPMSG) model defined by Caputo based on the fractional calculus theory to overcome the singularity and limitations of integer‐order DPMSG models. The path and characteristics of the DPMSG system entering the bifurcation and chaos caused by the internal parameter changes and external disturbances were analyzed. First, we established a nonlinear fractional‐order mathematical model of a DPMSG system. Second, a bifurcation diagram was drawn using the maximum algorithm, and the path to chaos of the system at different orders was analyzed by combining its chaotic phase portrait and temporal sequence diagram. Subsequently, the impact of variations in the system order on the chaotic features of the original system was analyzed. The internal parameter adjustments of the system and changes in the system stability under external disturbances and other external excitations were analyzed. The influence of the system on its bifurcation phenomenon and chaotic behavior under multidimensional orders was determined, and it was observed that its path into chaos was opened by period‐doubling bifurcation. Lastly, the dual‐parameter stability domain of the system order corresponding to the internal parameters of the system was obtained by determining the parameter conditions for the critical stability of the system. [ABSTRACT FROM AUTHOR]

As the application of renewable energy sources continues to increase, the virtual synchronous generator (VSG) has been proposed and received widespread attention. In China, new energy stations are typically situated at the transmission end of LCC‐HVDC lines. A failure in DC commutation can lead to overvoltage at the DC transmission end, thus posing a significant risk of disconnection from the grid due to the occurrence of overvoltage. Compared to when low‐voltage occur, it was discovered that, during overvoltage, VSGs face difficulties in rapidly attaining the preset power and transient instability. These issues can significantly impact the voltage support capability of the VSG. To address these concerns, an enhanced control strategy has been proposed. The control strategy sets reasonable power reference values, leveraging the advantage of fast voltage response in VSG by matching its voltage with virtual impedance. This ensures that the power rapidly reaches the designated reference value while reducing fluctuations in power angle. The transient power‐angle stability is validated using the energy function method. This approach enhances the reactive power absorbed by VSG, thereby mitigating transient overvoltage. Finally, simulation results from PSCAD/EMTDC validate the rationale and effectiveness of the control strategy. [ABSTRACT FROM AUTHOR]

Numerous High‐Voltage Direct Current (HVDC) interconnections in a bipolar configuration are currently in the design phase and set to become operational in the next decade. In the meantime, the shift from Synchronous Generators (SGs) to converter‐interfaced units is raising concerns over the stability of power systems. Grid‐Forming (GFM) control in converters, as opposed to Grid‐Following (GFL) mode, is anticipated to replicate, to some extent, the stabilizing behaviour of SGs. An open research question is whether mimicking the behaviour of SGs with GFM converters would, in turn, induce sub‐synchronous oscillations similar to those present in power systems dominated by SGs. This paper investigates sub‐synchronous interactions between converters and asynchronous AC systems at the terminals of a bipolar HVDC connection. A modal analysis based on a state‐space approach reveals the participation of converters as well as the influence of control modes and system parameters on these low‐frequency oscillations. Time‐domain simulations of a non‐linear model in EMTP software support the findings of the modal analysis. [ABSTRACT FROM AUTHOR]

Recently, owing to the high penetration of renewable power generations, random access to dynamical loads and wide application of power-electronic devices, the modern power systems exhibit new features such as high dynamics, low inertia and weak voltage and frequency support. As a powerful tool in revealing the dynamical evolution of the modern power systems, the dynamic state estimation (DSE) scheme gains a surge of research enthusiasms. Note that in actual power systems, various styles of power generations and mixed measurements generated by the supervisory control and data acquisition (SCADA) system and the phasor measurement unit (PMU) pose higher demands on the DSE. In addition, the measurements with anomalies such as gross errors, outliers and incomplete information are often encountered due to the unreliable measurement facilities, constrained communication resources and cyber-threats. Such anomalies, if not tactfully handled, would largely impair the DSE performance. In this paper, a systematic and timely review with respect to DSE for power systems is provided. First, several typical models for power systems include quasi-steady model, synchronous-generator-based multi-machine model and renewable power generation model are introduced. Then the measurement facilities of power systems and their features as well as the measurements with anomalies are reviewed, respectively. Subsequently, the DSE schemes are recalled and discussed from the perspectives of framework, methodology, anomaly-resistant ability and application, respectively. Finally, some possible future research topics are outlined for the DSE of power systems. [ABSTRACT FROM AUTHOR]

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The 2022 energy crisis highlighted the dependence of the Europe electricity sector on imported natural gas and the need to accelerate the adoption of renewables to the power system. However, operating a reliable power system with high share of renewables might require curtailing some renewables and activating conventional generators not scheduled in the day-ahead markets to ensure system reliability. These actions can result in environmental impacts, higher system costs and welfare impacts for customers. We use a novel high-granularity data from the Spanish power system for the period 2019–2022 to estimate the effects of these actions and forecast future impact of implementing ambitious targets of the European Gas Reduction Plan. We show that reliance on conventional generators will sharply increase with the addition of renewables. However, higher electricity consumption reduces the negative welfare impacts of integrating renewables. Until renewables and storage technologies advance further, conventional generators are needed for reliable operation of the systems. [ABSTRACT FROM AUTHOR]

This paper investigates a novel control strategy that enables hybrid excitation permanent magnet synchronous generator (HPMSG) to track the optimal extracted power of the modern wind turbine type (NASA-NSF). The proposed control mathematical model is based on two cases of variable speed—Maximum Power Point Tracking (MPPT) and variable speed—Constant Power Point Tracking (CPPT). The later one is specified for wind gust and higher than rated wind speed withstanding operation. The HPMSG generator quantitative performance characteristics are presented and validated through simulation for both steady and dynamics states. Simulation results prove the capability of the generator to operate correctly under load and speed variation over both MPPT and CPPT. The output voltage stays, in both cases, within the much lower limits that imposed by maximum values. [ABSTRACT FROM AUTHOR]

The virtual synchronous generator (VSG) technology has been proposed to address the problem of system frequency and active power oscillation caused by grid-connected new energy power sources. However, the traditional voltage-current double-closed-loop control used in VSG has the disadvantages of poor disturbance immunity and insufficient dynamic response. In light of the issues above, a virtual synchronous generator voltage outer-loop control strategy based on improved linear autonomous disturbance rejection control (ILADRC) is put forth for consideration. Firstly, an improved first-order linear self-immunity control structure is established for the characteristics of the voltage outer loop; then, the effects of two key control parameters-observer bandwidth ω0 and controller bandwidth ωc on the control system are analyzed, and the key parameters of ILADRC are optimally tuned online using improved gray wolf optimizer-radial basis function (IGWO-RBF) neural network. A simulation model is developed using MATLAB to simulate, analyze, and compare the method introduced in this paper. Simulations are performed with the traditional control strategy for comparison, and the results demonstrate that the proposed control method offers superior anti-interference performance. It effectively addresses power and frequency oscillation issues and enhances the stability of the VSG during grid-connected operation. [ABSTRACT FROM AUTHOR]

Faulty synchronizations of synchronous generators can cause significant detrimental effects, primarily due to a large current and high electromagnetic torque. These effects not only impact the generator but they can also extend to the prime mover and the step-up transformer. Furthermore, such events can trigger disturbances in the power system, potentially leading to system collapse if not promptly cleared. Although the autosynchronizers and synchro-check technologies are well established in the industry, faulty synchronizations, such as those caused by incorrect wiring during maintenance or commissioning operations, can go undetected by these systems. Existing protections do not allow for the detection of faulty synchronizations in a timely manner. This paper presents novel protection methods specifically designed for this issue: one based on instantaneous current value and the other on the instantaneous current-derivative value. These schemes are activated exclusively during the synchronizations process, allowing for faster fault detection compared to existing methods, thereby reducing the duration of harmful electrical and mechanical stresses after a faulty synchronization. The effectiveness of the proposed schemes has been validated through computer simulations of a 362 MVA turbo-generator from a thermal power plant and also through experimental tests on a 5 kVA synchronous generator using a specialized laboratory synchronization test bench, yielding promising results. [ABSTRACT FROM AUTHOR]

Grid-forming wind turbines (GFM-WTs) based on virtual synchronous control can support the voltage and frequency of power system by emulating the synchronous generator. The dynamic characteristics of a GFM-WT decided by virtual synchronous control, dq-axis voltage, and current control is significant for small-signal stability analysis. This paper builds a small-signal model of a GFM-WT in active power control (APC) and DC voltage control (DVC) timescale from the perspective of internal voltage. The proposed model describes how the magnitude and phase of the internal voltage are excited by the unbalanced active and reactive power when small disturbances occur. Interactions in different control loops can be identified by the reduced order model. We verify the accuracy of the proposed model in APC and DVC timescales by time domain simulations based on MATLAB/Simulink. Case studies show how the control parameters interact with each other in the two timescales. [ABSTRACT FROM AUTHOR]

With the increasing integration of distributed energy resources into modern power systems, virtual synchronous generators (VSGs) have been a promising approach to imitate the inertial response of synchronous generators, thereby enhancing microgrid stability in a dynamic state. When many VSGs are integrated into microgrids, the dynamic characteristics of the system become increasingly complex. Current studies typically assume that different VSGs are connected to a common coupling point, focusing on analyzing the interaction characteristics, which may overlook the widely distributed line impedances in microgrids with distance between different facilities. This may lead to incomplete understanding of the interaction dynamics when VSGs are distributed over long feeder lines. Therefore, this paper proposes and investigates a multi-node, multi-VSG model incorporating line impedances among different nodes, establishing transfer function models for multi-node load disturbances and the frequency responses of individual VSGs. The study explores the dynamic response characteristics of VSGs under varying parameter influences and proposes principles for designing VSG port impedance and inertia parameters to optimize system dynamic frequency characteristics. The findings, validated through simulations in PSCAD v46, provide insights for enhancing the flexibility and reliability of grids incorporating VSGs. [ABSTRACT FROM AUTHOR]

As the integration of distributed generation units into the power grid continues to grow, the system becomes increasingly vulnerable to power fluctuations and potential failures, which significantly challenge grid stability. Virtual synchronous generators (VSGs) have emerged as a key technology to enhance grid stability by emulating the behavior of traditional synchronous generators. However, with multiple VSGs operating within independent microgrids, coordinating their control parameters becomes critical to ensuring stable and reliable operation. This article proposes an optimization method based on the gradient descent algorithm to fine‐tune the control parameters of multiple VSGs in independent microgrids. A small‐signal model for microgrids with multiple VSGs is developed to analyze the system's dynamic behavior under small disturbances. The proposed method optimizes VSG control parameters to improve the frequency and voltage dynamic response and enhance the overall system stability. The simulation results demonstrate that the proposed multi‐VSG control parameter optimization method significantly enhances the frequency and voltage dynamic response, as well as the stability of the independent microgrid under small disturbances, offering a practical solution for improving microgrid performance in real‐world applications. [ABSTRACT FROM AUTHOR]

Conventional inverter control methods reduce the grid inertia and are susceptible to parameter variations, resulting in a gradual weakening of grid stability. To address the above problems, an improved vector selection model predictive control strategy is proposed, with virtual synchronous generator technology to control the quasi‐Z‐source inverter. First, the influence of different operating states on the quasi‐Z‐source inverter state variables is analysed, and the established quasi‐Z‐source inverter‐virtual synchronous generator discrete‐time model predicts the input current, output capacitor voltage, and load current of the quasi‐Z‐source inverter network. Second, the inverter switching timing is analysed to establish the optimal switching vector set, and the optimal switching vector set is selected by defining the sub‐objective function, which reduces the average switching frequency of the system. Compared with the finite control set model predictive control, this strategy is to reduce the computation time of the system to obtain the optimal solution of the quasi‐Z‐source inverter, to improve the dynamic responsiveness of the system during the control process, and to improve the power quality. Finally, the effectiveness and correctness of the proposed algorithm are verified by experiments. [ABSTRACT FROM AUTHOR]

ABSTRACT The virtual synchronous generator (VSG)–based photovoltaic system is affected by the external environment and sudden changes in load, which can lead to deteriorations in dynamic characteristics of power and frequency and even system instability. To ensure the dynamic performance and stability of the system, it is necessary to adjust the inertia‐damping parameters in time. This paper proposes a new cooperative adaptive control strategy for VSG inertia and damping parameters by analyzing the output angular frequency change and angular frequency deviation during the dynamic process of the system. Segmental adaptation is based on the size of the perturbation. The parameter selection rule is improved to increase the sensitivity of the parameter adjustment, and the improved sign function is used to prevent the parameter overmodulation problem. Finally, the proposed strategy is verified to effectively improve the system response speed and antidisturbance ability by comparing it with the traditional strategy on the MATLAB/Simulink simulation platform. [ABSTRACT FROM AUTHOR]

Rotor interturn short circuit (RISC) fault is one of the most prevalent fault types in the non‐salient wound‐rotor synchronous generator (WRSG). In the paper, the theoretical mechanism of the RISC fault is studied in detail. Building upon this understanding, from the fault detection and harm consequences, the further work of this article includes proposing a RISC detection method and analyzing the influence of RISC on the insulation thermal damage. On the one hand, a new detection for RISC fault is first proposed based on the phase voltage. The proposed detection method innovatively allows for accurate determination of both the severity and location of RISC faults. On the other hand, the loss and the temperature of the stator core‐winding system are comprehensively investigated with varied RISC degrees and positions. The thermal responses of the winding insulation are obtained under the joint action of the external magnetic heat source and the internal electric heat source. The study identifies critical points of insulation vulnerability, particularly noting areas prone to noise and connection joints. This research contributes to the timely online identification of RISC faults and supports preventive maintenance strategies for protecting winding insulation. © 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

As inverter‐based resources like wind turbines increase, grid inertia and stability decrease. Optimal placement and control of energy storage systems can stablise low‐inertia grids. This paper investigates how optimal battery energy storage systems (BESS) enhance stability in low‐inertia grids after sudden generation loss. The sitting, sizing and control of BESS are determined simultaneously in each genetic algorithm (GA) population, then voltage and frequency stability is evaluated based on the network simulation. This continues until the optimal solution is found. A network based on Kundur's four‐machine system is modelled for the first study and two of the four synchronous generators (SGs) have been replaced with wind farms. Then, the production of the third SG has been decreased by 13%. According to the results, addition of wind farms causes the frequency drop below 49.6 Hz for more than 5 min, indicating instability. It is also demonstrated that with optimal control parameters and placement, a 60 MW BESS can alleviate the voltage and frequency fluctuations, leading to enhanced stability. This method has also been tested on the IEEE 39‐bus network, where the installation of a BESS with a capacity of 9 MVA could restore the frequency stability. [ABSTRACT FROM AUTHOR]

An increase in renewable energy generation in the microgrid can cause voltage oscillation problems. To address this issue, an equivalent circuit of the microgrid was established, including a synchronous generator, grid-connected inverter, and constant power load. Then, the impact of different renewable energy generation ratios, different direct current (DC) voltage loops, and phase-locked loop control bandwidths of the grid-connected inverter on microgrid stability were analyzed. The results indicate that an increase in the renewable energy generation ratio leads to a decrease in the stability margin of the microgrid. A microgrid stability improvement method involving the parallel connection of a virtual resistor with the grid-connected inverter was proposed. The resistance value of the virtual resistor was obtained through an adaptive algorithm. This method ensures the stable operation of the microgrid under different renewable energy generation ratios. [ABSTRACT FROM AUTHOR]

Protection of synchronous generators (SGs) against internal faults, such as stator earth fault (SEF) and turn‐to‐turn fault (TTF), is crucial for ensuring the stability and security of the power system. This paper presents a phase domain model for simulating SEF and TTF in SGs, requiring only nameplate data and avoiding the need for complex geometric data or lengthy simulations typical of FEM models. The stator winding is divided into three sections, allowing for the calculation of magnetic field distribution in both healthy and faulty conditions. The model is capable of simulating short‐circuit turns at various locations within the stator winding with high accuracy and speed. The dynamic response of the generator is also incorporated into the model. The model's accuracy is validated through comparison with results from multiphysics simulation software. Furthermore, this study addresses the limitations of conventional protection methods in detecting TTF and proposes a novel, simple, fast, and accurate protection logic that can be implemented in digital protection relays and is effective across a wide range of TTF scenarios. [ABSTRACT FROM AUTHOR]

With the large-scale integration of renewable energy into the grid, traditional short-circuit current (SCC) calculation methods for synchronous generators are no longer applicable to inverter-based non-synchronous machine sources (N-SMSs). Current SCC calculation methods for N-SMSs often use a single-machine multiplication method, which tends to overlook the internal variability of N-SMSs within power plants, leading to low calculation accuracy. To address this issue, this paper first derives an analytical expression for SCC in grid-connected inverters under low voltage ride through (LVRT) control strategies. Then, a single-machine steady-state SCC calculation model is proposed. Based on the classification of N-SMSs, a practical SCC calculation model for renewable power plants is introduced, balancing accuracy and computational speed. The feasibility of the model is validated through simulations. The proposed method enables simple calculations to obtain the steady-state voltage and SCC at the machine terminal, offering strong engineering practicality. [ABSTRACT FROM AUTHOR]

A polarity identification is very important for operation of transformers, measurement and protection equipment, where it is useful in analyzing of transformer connections and operation as well as testing of protective systems. Moreover, it's essential in assessment of power systems performance during both normal and abnormal operation. Ensuring the correct polarity of the primary and secondary windings in voltage and current transformers is of paramount importance for various measurement and protection schemes in power networks. This paper proposes a digital polarity detector and tester using correlation coefficients and nine polarity indices calculated for instrument transformer signals. In order to test the performance of the proposed polarity tester algorithm, MATLAB code is imported to the LABVIEW model, and the numerical data obtained from the synchronous generator terminals via instrument transformers are interfaced with the computer through the Data Acquisition Card (DAC). The experimental system consists of a motor-generator set supplying a three-phase inductive load with instrument transformers connected to measure each phase voltage and current. The obtained results for various operating conditions and different types of abnormal conditions prove that the suggested algorithm is accurate, reliable and applicable to smart grids and substation automation systems. It can be considered as an integrated system incorporated with digital fault recorders, relays and meters. [ABSTRACT FROM AUTHOR]

ABSTRACT Since the microgrid lacks inertia compared to the conventional grid with synchronous generators, the microgrid is unable to address the frequency change issues resulting from the integration of large‐scale distributed generation. Due to the ability to provide virtual inertia, generalized droop control (GDC) and virtual synchronous generator (VSG) control are considered effective solutions for improving frequency regulation. However, in response to external frequency disturbances, the grid‐connected inverters may experience a significant transient active power overshoot caused by GDC and VSG. In this paper, the GDC is used as the fundamental control architecture, and then the small signal models of the GDC and VSG are compared and analyzed under various disturbances. A reduced‐order method for the GDC model is proposed to simplify the analysis of GDC. Additionally, GDC adaptive inertia (GDCAI) and adaptive inertia for operation mode switching (AIOMS) are proposed to mitigate frequency fluctuations and improve active power response. The effectiveness of the two control strategies is verified by MATLAB/Simulink simulation and StarSim hardware‐in‐the‐loop (HIL) experiment. [ABSTRACT FROM AUTHOR]

This study aims to investigate the finite-time control problem for a class of strict-feedback time-delay nonlinear systems with unknown functions. The control design is based on a fast finite-time practical stability criterion. Unknown nonlinear functions can be estimated using the universal approximation performance of neural networks. Finite-time control design is performed using adaptive backstepping technology. By performing closed-loop stability analyses and choosing appropriate Lyapunov–Krasovskii functionals, all signals in a closed-loop system can be bounded within a finite time. Subsequently, the proposed control method can be applied for the excitation control of synchronous generators. The effectiveness of the proposed method is verified using a numerical model of a single-machine power system. [ABSTRACT FROM AUTHOR]

Cold energy generation is an important part of liquefied natural gas (LNG) cold energy cascade utilization, and existing studies lack a specific descriptive model for LNG cold energy transmission to the AC subgrid. Therefore, this paper proposes a descriptive model for the grid-connected process of cold energy generation at LNG stations. First, the expansion kinetic energy transfer of the intermediate work mass is derived and analyzed in the LNG unipolar Rankine cycle structure, the mathematical relationship between the turbine output mechanical power and the variation in the work mass flow rate and pressure is established, and the variations in the LNG heat exchanger temperature difference, seawater flow rate, and the turbine temperature difference in the cycle system are investigated. Secondly, based on the fifth-order equation of state of the synchronous generator, the expressions of its electromagnetic power, output AC frequency, and voltage were analyzed. Finally, the average equivalent models of the machine-side and grid-side converters are established using a direct-fed grid-connected structure, thus forming a descriptive model of the overall drive process. The ORC model is built in Aspen HYSIS to obtain the time series expression of the torque output of the turbine; based on the ORC output torque, the permanent magnet synchronous generator (PMGSG) as well as the direct-fed grid-connected structure are built in MATLAB/Simulink, and the active power and current outputs of the grid-following-type voltage vector control method and the grid-forming-type power-angle synchronous control method are also verified. [ABSTRACT FROM AUTHOR]

With the popularity of renewable energy sources, fault‐tolerant frequency stability of distributed generation systems has become a major challenge. This paper proposes an optimal frequency fault‐tolerant control method in the distributed generation system, utilizing adaptive dynamic programming combined with fuzzy critic estimation. First, based on the operational state of the system, a non‐linear dynamic model for the virtual synchronous generator is established. Then, considering the occurrence of actuator faults, the fault‐tolerant control problem is formulated as an optimal control problem, where a fault observer is designed to estimate the fault signals. Furthermore, the proposed adaptive dynamic programming method based on fuzzy critic estimation is employed to effectively solve the highly coupled nonlinear Hamilton–Jacobi–Bellman equation and ensure the state convergence of the system with uniform ultimate boundedness. The optimal fault‐tolerant control law ensures a bounded frequency error for the virtual synchronous generator system in the event of faults. Finally, the effectiveness of the optimal control method is verified by two sets of simulations. [ABSTRACT FROM AUTHOR]

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This paper introduces a novel real-time ANFIS controller, specifically designed for thermal synchronous generators, to mitigate the risks associated with cyber-physical attacks on power systems. The controller integrates the dynamic model of the turbine's thermomechanical components, such as the boiler and heat transfer processes, within the synchronous generator. In contrast to previous studies, this model is designed for practical implementation and addresses often-overlooked areas, including the interaction between electrical and thermomechanical components, real-time control responses to cyber-physical attacks, and the incorporation of economic considerations alongside technical performance. This study takes a comprehensive approach to filling these gaps. Under normal conditions, the proposed controller significantly improves the management of industrial turbines and governors, optimizing existing control systems with a particular focus on minimizing generation costs. However, its primary innovation is its ability to respond dynamically to local and inter-area power oscillations triggered by cyber-physical attacks. In such events, the controller efficiently manages the turbines and governors of synchronous generators, ensuring the stability and reliability of power systems. This approach introduces a cutting-edge thermo-electrical control strategy that integrates both electrical and thermomechanical dynamics of thermal synchronous generators. The novelty lies in its real-time control capability to counteract the effects of cyber-physical attacks, as well as its simultaneous consideration of economic optimization and technical performance for power system stability. Unlike traditional methods, this work offers an adaptive control system using ANFIS (Adaptive NeuroFuzzy Inference System), ensuring robust performance under dynamic conditions, including interarea oscillations and voltage deviations. To validate its effectiveness, the controller undergoes extensive simulation testing in MATLAB/Simulink, with performance comparisons against previous state-of-the-art methods. Benchmarking is also conducted using IEEE standard test systems, including the IEEE 9-bus and IEEE 39-bus networks, to highlight its superiority in protecting power systems. [ABSTRACT FROM AUTHOR]

This paper investigates fault detection in offshore wind permanent-magnet synchronous generators (PMSGs) for demagnetization and eccentricity faults (both static and dynamic) at various severity levels. The study utilizes a high-speed PMSG model on the National Renewable Energy Laboratory (NREL) 5 MW reference offshore wind turbine at the rated wind speed to simulate healthy and faulty conditions. An unsupervised convolutional autoencoder (CAE) model, trained on simulated signals from the generator in its healthy state, serves for anomaly detection. The main aim of the paper is to evaluate the possibility of fault detection by means of high-resolution electrical and electromagnetic signals, given that the typically low-resolution standard measurements used in supervisory control and data acquisition (SCADA) systems of wind turbines often impede the early detection of incipient failures. Signals analyzed include three-phase currents, induced shaft voltage, electromagnetic torque, and magnetic flux (air gap and stray) from different directions and positions. The performance of CAE models is compared across time and frequency domains. Results show that in the time domain, stator three-phase currents effectively detect faults. In the frequency domain, stray flux measurements, positioned at the top, bottom, and sides of the outside of the stator housing, demonstrate superior performance in fault detection and sensitivity to fault severity levels. In particular, radial components of stray flux can successfully distinguish between eccentricity and demagnetization. [ABSTRACT FROM AUTHOR]

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To address the issues of high current harmonic and power ripple in the traditional Finite Control Set Model Predictive Control (FCS-MPC) strategy for virtual synchronous generator system with quasi-Z-source inverter (qZSI-VSG), a double and triple-vector hybrid modulation model predictive control strategy is proposed. This strategy utilizes the inductor current sub-cost function to select the shootthrough state (ST state) or the non-shoot-through state (NST state). When NST state is selected, the voltage vector combinations in the double-vector and the triple-vector are initially established. Then, the voltage vector combinations are reduced from 18 groups to 6 groups by using the vector combination quick selection table. Subsequently, the duty cycle of each voltage vector is then determined based on the value of its cost function, and the voltage vector is re-synthesized. Finally, the predicted values of all control variables are calculated and substituted into the cost function for optimization. Experimental results show that the proposed strategy reduces 48.62% of current harmonic, 50% of active power ripple, and 25.53% of capacitor voltage ripple compared to the traditional strategy, which effectively improves the system control performance. [ABSTRACT FROM AUTHOR]

Abstract Protection of synchronous generators (SGs) against internal faults, such as stator earth fault (SEF) and turn‐to‐turn fault (TTF), is crucial for ensuring the stability and security of the power system. This paper presents a phase domain model for simulating SEF and TTF in SGs, requiring only nameplate data and avoiding the need for complex geometric data or lengthy simulations typical of FEM models. The stator winding is divided into three sections, allowing for the calculation of magnetic field distribution in both healthy and faulty conditions. The model is capable of simulating short‐circuit turns at various locations within the stator winding with high accuracy and speed. The dynamic response of the generator is also incorporated into the model. The model's accuracy is validated through comparison with results from multiphysics simulation software. Furthermore, this study addresses the limitations of conventional protection methods in detecting TTF and proposes a novel, simple, fast, and accurate protection logic that can be implemented in digital protection relays and is effective across a wide range of TTF scenarios.