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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]

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]

The increasing penetration of the distributed energy resources (DER) in the power grid, which, while having significant advantages, also pose significant challenges. The behaviors of DERs differ from those of synchronous generators, particularly in abnormal conditions. For this reason, the power grid enforces grid codes to ensure that DERs perform properly in different conditions. For instance, short circuit faults and unbalanced grid voltage are severe transient events that inverters need to be able to pass through without disconnecting from the grid. Furthermore, the inverters are required to support the grid voltage by regulating the active and reactive power injections. This article proposes a voltage support control scheme to support grid voltage during asymmetrical voltage drop by utilizing an optimization problem. In this optimization problem, the active and reactive powers injected into the grid will be obtained optimally by considering constraints such as instantaneous active and reactive power oscillation magnitudes and peak current limitation. To aid in this purpose, the corresponding mathematical formulations such as instantaneous active and reactive power oscillation magnitudes will be obtained by using the currents and voltages in stationary reference frame. The proposed scheme will be verified by simulating it in MATLAB/Simulink under three different scenarios and tested on a real‐time experimental Opal‐RT platform. [ABSTRACT FROM AUTHOR]

This paper proposes an improved expanding interior algorithm (EIA) to estimate the region of attraction (ROA) of power systems with wind power generation based on sum of squares (SOS) programming. An ordinary differential equation (ODE) model is derived for the doubly‐fed induction generator‐based wind turbine (DFIGWT), which is named as an enhanced synchronous‐generator‐mimicking (ESGM) model. The ESGM model bridges the gap between the requirement of an ODE model in ROA estimation and the conventional differential‐algebraic equation (DAE) model of the DFIGWT system. The ESGM model is able to accurately reflect the low frequency dynamics of the DFIGWT. Moreover, an improved EIA is designed to estimate the ROA based on SOS programming, which has higher efficiency than the existing ROA estimation algorithms based on SOS programming. It is able to adaptively search for the Lyapunov function and obtain an optimal estimation of the ROA in an iterative process. The accuracy and efficiency of this algorithm are verified in three test systems composed of DFIGWTs and synchronous generators (SGs). The morphological changes in the ROA of the test systems caused by the penetration of DFIGWT are examined. [ABSTRACT FROM AUTHOR]

With the increasing application of renewable energy sources (RESs), more and more grid‐connected voltage‐source converters (VSCs) in the grid need to operate in a "grid‐forming" manner. However, when large disturbances occur in the grid, grid‐connected converters may lose synchronization and cause the current to exceed set limits. To ensure the stable and safe operation of VSC during large disturbances and to improve the power supply capacity during voltage dips of RES, this paper proposes an emergency control method that takes into account the virtual synchronous generator (VSG) current limit and transient stability based on a large‐signal mathematical model of the VSG during fault and normal states. The method divides the operation area of the VSG into non‐emergency area and emergency area. If the operating point is in the non‐emergency region after a fault, only the active power reference value is changed to avoid current exceeding the limit and transient instability; if the operating point is in the emergency region, the current exceeding the limit and transient instability are avoided by changing the active power reference value and adding in the virtual impedance. Finally, the effectiveness of the proposed control strategy is verified by simulation. [ABSTRACT FROM AUTHOR]

The integration of the renewable energy sources (RESs) into the power grid, drives a significant transformation in the conventional power generation landscape. This transition from traditional synchronous generators to inverter based RESs introduces unique challenges in maintaining the grid frequency stability due to the reduced system inertia. The inherent stochastic nature of the RES power generation, load demand, and grid inertia includes further complexity in the assessment of frequency stability. Existing studies have limitations, including neglecting the stochastic nature of RES generation and load demand fluctuations, relying on limited metrics, and lacking a comprehensive day‐to‐day assessment. To address these shortcomings of the existing approaches, this paper introduces a novel methodology for assessing frequency stability in power grids with high RES penetration. It proposes three indices for evaluating grid frequency sensitivity, resiliency, and permissibility amidst varying RES integration. Utilizing a stochastic approach, the study incorporates uncertainties in RES generation and load demand, offering a comprehensive framework for day‐to‐day frequency stability analysis. Additionally, it presents a systematic method to ascertain the necessary inertial support for maintaining desired frequency reliability in RES‐dominated grids. The effectiveness of these methodologies is validated through a case study on a modified IEEE 39‐bus test system, demonstrating their applicability in ensuring reliable grid operation under high RES scenarios. [ABSTRACT FROM AUTHOR]

The integration of synchronous generators (SG) to the grid will present serious problems in some instances. The increase in fault current level is one of the most crucial issues, which causes miscoordination between directional over current relays (DOCRs), in addition to putting excessive pressure on the circuit breakers. This research uses the Fault Current Limiters (FCL) to restore coordination, without changing the settings of DOCRs, by reducing the level of fault current in the grid. The main goal of this research is to find the optimal size, location, and number of FCLs at the minimum cost and with the least operation time for the relays, using Jellyfish Search Optimisation (JSO) algorithm. This can be achieved through three different approaches. The first one is optimizing the location, number, and impedance size of the FCL by minimising a cost function. The second approach involves optimizing the backup relay operation time. A combination of the two previous approaches is used as the third approach. The outstanding feature of this research is that it considers the optimal location of DG and FCL while optimizing the operation times of DOCRs, which is a new framework. [ABSTRACT FROM AUTHOR]

This manuscript proposes a robust excitation control strategy for synchronous generators using backstepping theory and an artificial neural network with a radial basis function to improve power system performance during disturbances and parametric uncertainties. The artificial neural network is used to estimate unmeasurable quantities and unknown internal parameters of a recursive backstepping control. Lyapunov theory is used to carry out the stability analysis and to deduce the online adaptation laws of artificial neural network parameters (weights, centres and widths). To validate the performance of this approach, simulations are performed on an IEEE 9 bus multi‐machine power system. Different test results, compared with those of an existing non‐linear adaptive controller, confirm the high robustness of the proposed method against disturbances and uncertainties. [ABSTRACT FROM AUTHOR]

This paper demonstrates that the switching of one grid‐connected virtual synchronous generator (VSG) between two control modes, namely constant voltage control (CVC) and current limiting control (CLC) happens at the derived two switching lines. Based on the current limiting inequality, the traditional current‐switched model is transferred to the angle‐switched model proposed here, and the system can be studied as one switched dynamic system. Based on this model, the transient stability of VSG with controller limits is investigated. This is achieved by constructing Lyapunov functions for each subsystem and deriving the relationship between the values of Lyapunov functions constructed under different conditions at the switching moment. The stability of the system is ensured when the Lyapunov function of each subsystem presents a decreasing trend in two consecutive switching intervals. On this basis, the stability boundary of the switching system is derived. Further analysis shows that optimal adjustment of the saturation current angle can make the system reach the maximum stability boundary. Finally, the numerical simulations and experimental tests verify the correctness of the proposed analysis. [ABSTRACT FROM AUTHOR]

One of the common methods to detect Loss of Excitation (LOE) is the impedance‐based technique. But it is too slow, and may show incorrect performance when faced with power system disturbances like stable power swings (SPS). To improve the aforementioned problems, a new index is introduced based on the change of transient states of the synchronous generator which are estimated by Extended Kalman filter (EKF). The principal idea of the proposed method is that the angle between the transient voltage and q‐axis internal voltage phasor will be increasing during LOE events. Therefore, this angle and its derivative are used. Estimation of the internal variables of the generator is used to achieve the angle between transient voltage and internal voltage phasor. To evaluate the efficiency of this algorithm, numerous simulations are performed on various networks and in different operating conditions. The simulation results of the method demonstrate that this approach both reduces the detection time in most cases and improves its security in the encounter of the other disturbances. Experimentally, the performance of the proposed method is evaluated by using a 5 kVA laboratory generator. Experimental studies show that the presented algorithm performed correctly detects LOE and SPS conditions. [ABSTRACT FROM AUTHOR]

In the context of extremely uneven sources and loads in China, several large‐scale power transmission systems have been established. Affected by the small equivalent impedance of the system, the increase of negative sequence currents during open‐phase operation has seriously threatened the stable operation of synchronous generators. The necessity of negative sequence current suppression is particularly prominent. To address the above issues, this paper analyzes the feasible negative sequence suppression capacity of the grid‐connected inverter under the principle of positive sequence priority. Using the geometric analysis method to determine the optimal suppression capacity. The none‐phase‐locked loop (PLL) control method is used to improve the response speed and form the negative sequence current suppression strategy adapted to the open‐phase operation period. A simulation model was built in PSCAD to verify the effectiveness of the proposed strategy. The result shows that the suppression strategy has a faster response than the conventional PLL control. In scenarios with large negative sequence currents to be suppressed, a maximum suppression effect of approximately 63% can be achieved. Compared with the traditional suppression capacity selection, the strategy in this paper can reduce the residual of negative sequence current by about 10% at most. The negative sequence currents intruding into the generator can be effectively suppressed without additional devices. [ABSTRACT FROM AUTHOR]

This paper offers non‐linear control for enhancing the transient stability in power systems containing a photovoltaic (PV) and doubly fed induction generator (DFIG) by transient energy function (TEF) method and finite‐time observers. At first, the TEF method is utilized to enhance the transient stability in a power system containing a PV, DFIG, and synchronous generator (SG) by constructing a hybrid Lyapunov function. Then, the derivative terms in control are estimated with finite‐time observers. The main contribution of the research is the application of the TEF technique in the transient stability evaluation of a power system consisting of PV, SG, and DFIG. Another innovation of the research is the simultaneous control of DFIG and PV, whose uncertain parameters are estimated with the use of finite‐time observer. The proposed non‐linear control scheme is robust against changes in the configuration of the power system. In order to show the capability of this control scheme, time domain simulations are performed on the IEEE 9‐bus, and the NEW ENGLAND Standard 39‐Bus power system. Using the obtained result, some comparisons are made with the back‐stepping control scheme to clarify the superiority of the proposed method. The comparisons show that the proposed non‐linear control scheme can properly provide extra damping to reduce the first‐swing fluctuations in less time. The manuscript contains the new original results of the authors' research. In this article, to maintain and improve the transient stability, a new controller with simultaneous management of photovoltaic (PV) and doubly fed induction generator (DFIG) has been developed. The contributions of the paper are as follows. (1) The transient energy function (TEF) is obtained for the power system containing synchronous generator (SG) and DFIG. (2) The control laws are acquired with four PV and DFIG control variables. (3) The derivative parameters of the PV and DFIG controls by a finite‐time observer are estimated. [ABSTRACT FROM AUTHOR]

With the advancement of carbon peaking and carbon neutrality goals, microgrid clusters have attracted widespread attention due to their high stability and energy efficiency. This article proposes a scheduling architecture for microgrid clusters that integrates blockchain smart contracts, consensus mechanisms, and encryption technologies to address the issues of data trust, privacy protection, and security reliability in microgrid clusters. An economic adjustment model for microgrid clusters is constructed that combines economic and environmental objectives. Finally, based on the RPBFT (Rotating Proof of Believability) algorithm and group architecture of FISCO BCOS blockchain technology, an economic scheduling method for microgrid clusters is designed. The authors built a microgrid cluster model on the FISCO BCOS blockchain platform and conducted experiments on the effectiveness, economy, fault tolerance, and scalability of economic scheduling methods. The experimental results showed that the economic scheduling method proposed in this paper can effectively reduce the risk of nodes tampering with data in a microgrid cluster system, ensure the privacy of submicrogrids, and support the deployment of large‐scale microgrid clusters, the realization of multiparty collaborative autonomy and the stable, low‐carbon, economic operation of microgrid clusters. [ABSTRACT FROM AUTHOR]

The virtual synchronous generator (VSG) is a good solution for stabilizing the power system with high penetration of renewable energy. However, in case of serious unbalanced voltage disturbance/fault, the conventional VSG may lose voltage, inertia, and damping support characteristics to the grid and even can cause disconnection of renewable energy. This paper proposes an improved fault control strategy for VSG with the coordination of STATCOM. The proposed method can provide sufficient voltage support while keeping continuous system inertia and damping support under severe unbalanced fault. In the paper, an improved VSG and STATCOM control topology based on positive and negative sequence current control are first proposed so as to keep the damping and inertia support to grid during the grid fault. Secondly, the voltage support control method for the VSG with improved topology during unbalanced fault is introduced, which can achieve multiple control objectives, in terms of voltage support, current limitation, and active power output simultaneously. Then a coordination control scheme of improved VSG and STATCOM is developed so as to optimize the maximum control objectives in all possible scenarios, especially in the case of severe unbalanced fault. Finally, the effectiveness of the method is verified by using the MATLAB/SIMULINK simulation platform. [ABSTRACT FROM AUTHOR]

To handle the challenges attributed to the distributed generators, the protection system of distribution networks needs to be evolved. Recent protection schemes modify the standard characteristics of overcurrent relays, called non‐standard characteristics. These non‐standard characteristics are mostly case‐dependent and have limitations in solving the variety of protection challenges attributed to distributed generators. This paper analyses the performance of six voltage‐based non‐standard characteristics on photovoltaic distributed generators (PVDG) penetrated 3‐bus, 8‐bus, and IEEE 30‐bus distribution grid, as well as the 9‐bus Canadian radial distribution grid with synchronous distributed generator, wind turbine generator, and PVDG penetrations. Besides that, the optimum coordination of these non‐standard characteristics‐based overcurrent relays is a complex problem due to the involvement of additional controlling parameters. To find the best suitable method, a comparative analysis of the genetic algorithm, differential evolution, artificial bee colony, harmony search algorithm, firefly algorithm, cuckoo search algorithm and particle swarm optimization are performed for optimum relay coordination. The outcomes of the paper are thoroughly discussed for future research on non‐standard characteristics development. [ABSTRACT FROM AUTHOR]

Although inverter‐interfaced renewable energy sources (IIRESs) have great economic and environmental benefits, their fault current characteristics differ from those of synchronous generators. IIRESs also comply with modern grid code (GC) requirements for injecting reactive current to compensate for voltage drop during fault conditions. Moreover, the limits of renewable energy‐side fault current contribution and the phase angle difference between the local and infeed fault current from conventional sources lead to incorrect reactance estimation by the traditional distance relay at the IIRES substation and negatively affect relay dependability. As a result, the IIRES‐side distance protection is prone to incorrect operation. Furthermore, an improved relaying scheme is proposed to alleviate the adverse effects of IIRES on the reactance calculation. This research aims to improve the performance of the ground distance protection scheme in the case of a single‐phase to ground fault in zone one. The proposed method, with more than 99% accuracy, is solely dependent on the local information and, therefore, no communication link is required to implement the algorithm. Moreover, the algorithm is compatible with the existing pilot protection methods used in the industry. The simulation studies are modeled in the Digsilent Power Factory environment. [ABSTRACT FROM AUTHOR]

This paper investigates the dynamic interactions between large‐scale PV plants and nearby synchronous generators. To this end, a comprehensive model of a PV plant, including the PV arrays characteristic and their voltage controller, DC/DC converter, DC‐link dynamic, DC/AC inverter controllers, and output filter, is obtained. Then, the eigenvalues of the PV plant model are calculated, and it is revealed that the PV plant has a dynamic mode in the sub‐synchronous oscillations (SSOs) range. Furthermore, the modal analysis method is employed, and it is shown that the inductance of the DC/DC converter and the DC‐link capacitor significantly contribute to the PV sub‐synchronous mode. Also, it is shown that this mode oscillations penetrate the grid and increase the risk of sub‐synchronous resonance (SSR). Then, the mechanism of dynamic interactions between large‐scale PV plants and torsional modes of nearby synchronous generators is revealed. This paper also investigates the required conditions for these interactions and shows that solar irradiation level and the DC‐link capacitance are the essential factors that can intensify these interactions. [ABSTRACT FROM AUTHOR]

With the emergence of renewable energy sources (RESs), the power grid all over the world is going through a paradigm shift. The inverter based RESs are replacing the conventional rotating synchronous generators and this trend is expected to continue in coming years. Consequently, the grid strength is decreasing, which can pose significant challenges on the grid stability, especially during integration of IRESs. This paper presents a thorough analysis on the integration challenges of IRESs in weak grids. The paper also presents a comprehensive investigation on the impacts of factors, such as available fault level at the point of interconnection (POI), feeder length and grid nature on the POI voltage, and maximum allowable power injection by IRES. This is followed by maximum allowable IRES power injection sensitivity analysis to quantify the impacts of the aforementioned factors. The paper concludes with a thorough case study on the IEEE 39‐bus test system to numerically show the impact of diminishing grid strength on the integration of IRESs. [ABSTRACT FROM AUTHOR]

Permanent magnet synchronous generators (PMSGs) equipped with back‐to‐back grid‐forming converters have the ability to form a 100% renewable energy power grid. Black‐start is the key capability of grid‐forming converters when restoring the system from a blackout. It is necessary for a grid‐forming converter of the PMSG to operate in black‐start and grid‐connected active support modes. This paper investigates an improved damping adaptive grid‐forming (DA‐GFM) control method for PMSG wind turbines to suppress system frequency fluctuations and achieve a smooth black start. The proposed DA‐GFM control introduces the frequency variations and natural constant function to adaptively adjust its damping coefficient in the dynamic operating progress. The implementations and effects of the proposed DA‐GFM control method on the grid‐forming converter are theoretically evaluated. Additionally, the detailed black‐start operation process is completely studied through a microgrid system with two PMSG wind turbines and energy storages. Compared with the conventional grid‐forming control, the proposed control scheme can not only suppress frequency fluctuations better, but also achieve a smooth forming power grid process. Finally, experiment tests on a controller‐level hardware‐in‐the‐loop simulation platform are carried out to validate the proposed control strategy for achieving a smooth black start. [ABSTRACT FROM AUTHOR]

With the increasing proportion of renewable power generations in the power system, the power grid impedance may fluctuate greatly, and it is difficult for the virtual synchronous generator (VSG) with a single control structure to meet the stability requirements. Thus, the control principles of the two types of VSGs are compared to conclude that there are similarities in the control structure of the two VSGs. And the small signal models of the two types of VSGs are established to analyze the stability boundaries, coming to the conclusion that the stability region is complementary. Based on the conclusions, the paper puts forward the idea of switching operation modes: switch to the U‐VSG mode when the grid strength weakens and switch to the PQ‐VSG mode when greater, so that the inverter can keep stable in a wider range of grid strength. Therefore, the characterization method of the switching boundary with hysteresis properties is proposed. Then the improved recursive least squares (RLS) algorithm is introduced to identify the power grid impedance online without additional injected disturbance, based on which the adaptive multi‐mode smooth switching control strategy is proposed. Finally, the effectiveness of the analysis and the control strategy are verified by simulations. [ABSTRACT FROM AUTHOR]

Virtual synchronization control can be applied to DC/DC converter for enhanced inertia support by imitating the rotor dynamics of the synchronous generator (SG). However, efficient power sharing and robust operation ability cannot be guaranteed in a multiple parallel‐operated DC/DC converters system. This paper proposes the hierarchical control scheme to achieve higher efficiency and superior anti‐disturbance ability for multiple DC/DC converters with virtual synchronization‐based control. The primary control layer enables proportional power sharing by using improved virtual synchronization control for each DC/DC converter, which aims at eliminating the influence of line parameter mismatch among converters. The secondary control layer deals with DC voltage stability improvement through the extended disturbance‐observer‐based backstepping control with the consideration of external power fluctuation on the whole system. Two control levels are integrated as the hierarchical control architecture to realize different control objectives in different time scales, while only neighbouring communications and DC voltage information are needed among the system. Simulations on PSCAD/EMTDC are conducted and show that the load power is accurately and proportionally shared, while system oscillations are eliminated with the extended disturbance‐observer‐based backstepping control, which validates the advantages of the proposed hierarchical control scheme. [ABSTRACT FROM AUTHOR]

This paper expands the damping torque coefficient analysis (DTCA) for studying the small‐signal stability of permanent magnet synchronous generator (PMSG)‐based wind turbine (WT) under virtual synchronous generator (VSG) control with consideration of WT dynamics. Firstly, the typical VSG is implemented in the grid‐side voltage source converter (GSVSC), which enables selfsynchronization without phase‐locked loop (PLL). The maximum power point track (MPPT) algorithms are utilized to give the power reference for VSG. Then, the corresponding inertia and damping support can be provided by the kinetic energy of PMSG. Based on the established model, the DTCA is analytically conducted to not only reveal the key factors that influence the WT stability but also provide guidance for parameter tuning. As a result, it is important to find that the WT dynamics impair the damping and even lead to system instability. Moreover, the minimum value of VSG damping control parameter is analytically given to ensure the system stability under any load below the rated wind speed. Finally, the case studies considering one single PMSG connected to a large grid with and without inclusion of WT dynamics are performed and compared to demonstrate the accuracy of the proposed model and evaluate the applications of DTCA. [ABSTRACT FROM AUTHOR]

Stochastic renewable sources of energy have been causing changes in the structure and operation of power systems. High penetration of this type of generation results in decreased inertia of a power system, increased active power fluctuations, and a higher probability of false tripping of emergency control devices. Traditional algorithms of emergency control are not adaptable and flexible enough for systems with high penetration of renewables and flexible alternating current transmission systems. Integration and development of phasor measurement units make it possible to create adaptable emergency control systems, which would require minimal pre‐defined data. The purpose of this study is to develop an adaptable algorithm for turbine fast valving control synthesis and transient stability estimation for a generator. The suggested algorithm is based on the equal area criterion in the domain synchronous generator "torque–load angle". The measurements of the generator operation under consideration are used as the input data for the steam turbine fast valving control synthesis. Thus, the algorithm becomes adaptable because no pre‐defined parameters of a power system model are required. The suggested algorithm was tested on the power system model NE39bus using Matlab/Simulink. The efficiency of the suggested algorithm is verified and demonstrated. [ABSTRACT FROM AUTHOR]

The suppression of power grid frequency fluctuation, the inhibition of output active power oscillation, and the coupling of active and reactive power at the output of the virtual synchronous generator (VSG) are all investigated in this work. The connection between VSG output active power oscillation inhibition and grid frequency fluctuation suppression is explored, as well as the difficulties of achieving both power oscillation suppression and frequency fluctuation suppression for VSG at the same time. To overcome this problem, a control approach incorporating notch filter power feedforward decoupling and modifying virtual damping coefficient is presented, it is called power feedforward decoupling control (PFDC). The virtual resistance will worsen the P/Q coupling, whereas the virtual inductance will have no effect, according to the results of the P/Q coupling analysis. It can be demonstrated that the suggested solution does not jeopardize P/Q decoupling performance for VSG active power oscillation suppression and grid frequency fluctuation suppression. The understanding of VSG transient performance is deepened by the comprehensive investigation of the three issues. Finally, simulation is used to verify the soundness of the theoretical analysis and proposed strategy, while VSG’s transient performance is increased even more. [ABSTRACT FROM AUTHOR]

This paper presents an excitation controller design process for multimachine power systems with synchronous generators using an adaptive backstepping approach to ensure robust performance against parametric uncertainties as well as to improve the transient stability during large disturbances. In this work, electrical dynamics of synchronous generators are described using two‐axis models while excitations systems are represented as the IEEE Type II exciter which mainly captures electrical dynamics while swing equations are used to capture mechanical dynamics. The proposed adaptive backstepping control approach is then employed to derive the excitation control law. The proposed adaptive backstepping scheme uses all nonlinearities, which are mainly due to the interconnections and rotations of rotors in synchronous generators, within the dynamical models to improve the transient stability during severe disturbances. Furthermore, this excitation control scheme uses estimated values of parameters appearing in the dynamical models of power system which are estimated using adaptation laws based on real‐time measurements and hence, it provides robustness against parametric uncertainties. The theoretical stability of the proposed scheme is assessed using the Lyapunov stability theory, that is, by checking the negative definiteness or semi‐definiteness of the derivative of control Lyapunov functions (CLFs). Rigorous simulations are conducted on an IEEE 39‐bus 10‐machine test power system for evaluating the performance of the proposed scheme under different operating conditions. Simulation results clearly demonstrate the superiority of the adaptive backstepping excitation controller over existing nonlinear controllers including an existing adaptive backstepping excitation controller that is designed using the classical model of synchronous generators. [ABSTRACT FROM AUTHOR]

This paper offers novel non‐linear control of a doubly fed induction generator (DFIG) and unified power flow controller (UPFC) for transient stability increment with transient energy function (TEF) and sliding mode observer in a power system. First, the TEF technique is considered for the damping control in a power system with a synchronous generator (SG), DFIG, and UPFC, and then the controller time‐derivative signals are estimated by a second‐order sliding mode observer. The importance of the issue is in the employ of a complete UPFC model. Also, a one‐axis model is used for DFIG that is similar to the SG model. Another characteristic of the novel non‐linear technique is robust versus system topology changes and variable time delay of the control signals. To evaluate the performance of the novel non‐linear control method for increment transient stability, simulation studies are performed on a two‐machine connected to an infinite bus (TMIB), the IEEE 9‐bus, and the New England Standard 39‐bus power system. The results determine that the novel non‐linear control method decreases the first swing of fluctuations admissibly and enhancement stability margins considerably. [ABSTRACT FROM AUTHOR]

The model of synchronous generator (SG) plays an important role in the simulation of power system and planning of power grid. With the constant parameter practical model (CPPM), it is difficult to consider the time‐varying characteristic of the parameters affected by the complex non‐linear factors, such as the saturation, distortion, skin effect and various spatial harmonics; thus, it cannot guarantee the precision of the simulation. In this paper, a variable parameter practical model (VPPM) of SG is proposed by coupling the CPPM with the three‐dimensional parameter database and the parameter addressing model. The three‐dimensional parameter database containing the steady‐state, transient and sub‐transient reactances and time constants is established with the terminal voltage, active power and reactive power as the variables. The parameters of the VPPM are selected through linear inter‐polation according to the operating states of the generator. In order to verify the precision of the VPPM, a single‐machine infinite system and a real power system with 204 buses and 107 generators are simulated. The result indicates that the VPPM is more accurate than the CPPM, and the stability limit and damping ratio calculated by the VPPM are larger than that by the CPPM. The study can provide important support for the precise simulation of the power system. [ABSTRACT FROM AUTHOR]

Electrical Arc Furnaces (EAFs) consume time‐varying power. This causes mechanical torque variations in the nearby small scale synchronous generators (SSSGs) and reduces their life expectancy. In this paper, an appropriate EAF model is implemented and verified by using field measurements. Moreover, an actual distribution system to which an SSSG is connected to supply industrial loads including an EAF is investigated based on time‐domain simulation studies. To enhance dynamic performance of the SSSG adjacent to an EAF load, two novel approaches are presented in this paper. The first method is utilized for proper adjustment of governor controller parameters. Analytical and simulation‐based studies are accomplished to determine proper parameters of the SSSG conventional governor controller to mitigate the mechanical oscillations caused by EAF. These comprehensive investigations reveal that the governor PI controller proportional parameter should be adjusted as small as possible to mitigate the SSSG oscillations; while, the oscillations are fairly independent of integrator parameter. Besides, the integrator parameter should be set as high as possible to improve the SSSG dynamic performance. Moreover, a new modified SSSG governor controller including steady‐state and transient control loops is developed and a novel control strategy is proposed to enhance steady‐state and transient performance of SSSG. Finally, robustness and effectiveness of the proposed controller and its parameters are investigated using field measured EAF current signals for various transients. It should be noted that the proposed strategies of this paper can be also applied to similar cases where a nonlinear time varying load is connected to an SSSG. [ABSTRACT FROM AUTHOR]

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

Concerning the penetration of renewable energy resources into the power grid, investigation of the power system dynamics to meet the power demand and maintain stability has gathered momentum recently. On the other hand, evaluating the generator parameters in the distributed generation (DG) units as a subsystem of a large‐scale power grid is crucial for control and stability analysis purposes. To this aim, a simple and efficacious algorithm to identify the operational parameters of synchronous generators (SGs) in small hydro DGs is proposed here. The required data for the SG identification using the recommended approach is gathered during excitation system start‐up while the DG is disconnected from the grid. Using the proposed test procedure, the adverse impact of magnetic saturation on estimation results can be avoided. Furthermore, a straightforward parameter estimation (PE) procedure is established here to obtain the intended parameters from the recorded data. Finally, the proposed method was applied to a 10 MW hydro DG, and the results are discussed. [ABSTRACT FROM AUTHOR]

A new type of flexible excitation system (FES) is proposed by using fully‐controlled power electronic devices such as IGBTs to replace the half controlled devices in the conventional static excitation system, which has the merit of independent control of rotor angle and terminal voltage of the synchronous generator. This paper proposes nonlinear adaptive control (NAC) strategies for synchronous generator with FES in a single machine infinite bus system. External disturbances and the uncertainties of all parameters as well as modelling are defined as lumped perturbation terms and estimated by perturbation observers or state and perturbation observer. The estimated perturbation terms are used to compensate the real perturbations and achieve a model‐independent and robust NAC. Merits of the FES against the conventional static excitation system and effectiveness of the proposed NAC scheme against the accurate model based multi‐variable feedback linearisation control are verified via small‐signal stability analysis and simulation studies. The simulation results have shown that the proposed NAC can achieve superior control performance with less states feedback during a three‐phase short circuit and better robustness against parameter uncertainties, compared with linear control and multi‐variable feedback linearisation control. [ABSTRACT FROM AUTHOR]

To maintain synchronous operation of interconnected systems, it is necessary to keep balance between power generation and consumption. Faults may result in large oscillations in power flows and loss‐of‐synchronism between one generator and the rest of the power system. A correlation coefficient is a useful statistic that can be used to detect voltage, frequency or angular instabilities, and to determine an asynchronous process. Hence, it is a smart technique to predict the out‐of‐step event following fault situations. In this paper, the technique based on the auto/cross‐correlation and instantaneous powers is presented to identify sudden disturbances of various electrical signals in the case of asynchronous operation. To validate the method performance, a power network with real parameters is simulated on Alternative Transient Program (ATP) platform, and the algorithm is implemented in MATLAB software. Simulation studies reveal that the proposed scheme is able to detect the out‐of‐step conditions upon which the relay issues a trip signal, yet remains inactive under normal synchronized operating conditions. Thus, the out‐of‐step is declared before the second pole slipping occurs, and an instability time can be accurately assessed. Moreover, it can develop novel quadrilateral operating characteristics to discriminate between the synchronous and asynchronous operation of the AC generator. [ABSTRACT FROM AUTHOR]

In a high proportion of new energy grids or a 100% new energy source of power grid, the dynamic performance of PMSG under fault conditions is very important. However, the current small signal model lacks detailed and deep analysis of a permanent‐magnet synchronous generator (PMSG)‐based wind power generation under LVRT control. Here, a small signal model of a PMSG under pre‐fault, fault and after fault failure recovery stages are established. This paper employs linear analyses to characterize the dynamic performance of a PMSG‐based wind power generation system under LVRT control and practical generator characteristics. In particular, the conflict between frequency regulation and LVRT is discussed based on the constructed model. On this basis, the impact of dc‐link bandwidth on the system performance during failure recovery stage is discussed, and the active damping method is analysed to improve the performance of PMSG during failure and failure recovery stages. Finally, time‐domain simulations are utilized to verify the analyses and models discussed. The research results in this paper are helpful to promote and improve the performance of PMSG during LVRT conditions. [ABSTRACT FROM AUTHOR]

The increased penetration of large‐scale renewable energy resources results in the significant reduction of the system short‐circuit current (SCC) level, challenging current protection systems. In real‐time operation, several conventional synchronous generators are committed to maintaining the SCC level at a range that can be identified by the protection system. This limits the hosting capacity of renewable energy integration. This paper investigates the impacts of transmission switching (TS) and unit commitment (UC) on SCC magnitude and derives several linear expressions of SCC constraints for optimal control to restrain the SCC level to the desired range. Besides, an error compensation algorithm is developed to mitigate the linearization error. Numerical results carried out on the standard IEEE test systems show that the proposed method can effectively confine the SCC magnitude to the desired range while increasing the penetration of renewable energy. Comparison results with other methods highlight that the proposed method can achieve a higher level of renewable energy integration without violating SCC constraints. [ABSTRACT FROM AUTHOR]

A comprehensive dynamic model of a steam power plant, including turbine, governor, and boiler models, is proposed in this paper. The whole turbine‐boiler control strategies inter alia turbine following, boiler following, coordinated control, and sliding pressure control modes are also taken into account in the modelling procedure, making the integrated model adaptable for all the steam units. A novel multi‐stage algorithm is asserted in the other part of the paper to estimate the obtained model parameters using input‐output data from operational tests. Regarding the fact that the mechanical power as the turbine output and one of the synchronous generator (SG) inputs cannot be measured directly, an efficacious unknown input reconstruction (UIR) method is employed in this paper to determine the mechanical power from SG measured signals. The UIR observer in this method is obtained by solving a linear matrix inequality (LMI). Other parameters are identified by applying a Genetic Algorithm (GA) to the measurement data. Finally, the acquired model and parameters are validated by employing the recorded data from several tests, and the results are discussed. [ABSTRACT FROM AUTHOR]

The conventional impedance (Z)‐based relay which is the well‐known relay to preserve the power plant's synchronous generator (PPSG) against loss of field (LOF) accident may fail during some stable power swing (SPS); on the other hand, most of the previously introduced schemes may fail during the happening of hybrid events. In this paper to overcome the raised problems, a straightforward index is developed for reliable detection of the hybrid events, and it is combined with an AND‐logic cluster with the Z‐relay to avoid its spurious trip during SPS events. The reactive power (QSG) of the faulty PPSG is continuously decreased during LOF, while it oscillates under both SPS and hybrid events, leading to non‐detection of the hybrid event. Hence, using the integral operator and arithmetic mean value are suggested to eliminate the swinging variations of QSG as a Z‐relay blocking function (ZRBF). Thus, QSG decreases during both LOF and hybrid events and does not decrease under SPS events. Therefore, by combination of ZRBF with the Z‐relay, the PPSG is properly tripped out during the both LOF and hybrid events, and wrong tripping under SPS is reliably hindered. The reliable performance of developed scheme is completely approved thorough performed simulation studies. [ABSTRACT FROM AUTHOR]

Increasing penetration of renewable energy sources (RESs) into power systems has brought new challenges to guarantee transient voltage stability (TVS) of the system, due to complex and different characteristics of the RES compared with the synchronous generator. The related theories to the TVS for power systems with RES (PSRESs) are incomplete, and it is difficult to construct accurate physical model of the PSRES by using traditional TVS analysis method. Here a novel data mining‐based approach for extracting key factors that affect the TVS of a PSRES is put forward. The original Relief algorithm is modified to deal with the imbalance of sample size between stable and unstable samples of the practical data set and improve the calculation accuracy. Then, a data mining scheme based on the modified Relief algorithm is presented to acquire key factors affecting the TVS. With the proposed scheme, the influence degrees of different factors on the TVS can be evaluated quantitatively by their weighting values, and then the key factors as well as the influence patterns can be determined. Test results which are conducted on the modified IEEE‐39 test system with RESs are presented to demonstrate the accuracy and efficiency of the proposed method. [ABSTRACT FROM AUTHOR]

Power systems around the world are rapidly transitioning to much higher shares of inverter‐based resources (IBRs) with few synchronous generators remaining online. IBRs and synchronous generators have fundamentally different dynamic performance characteristics resulting in a difference in the overall power system dynamic performance. IBRs are generally more flexible and controllable than synchronous generators; however, at the same time they exhibit significantly more complex control systems. Furthermore, new and emerging capabilities are being developed progressively and in particular the so‐called grid‐forming inverters (GFM). GFM offer several new capabilities not previously possible with conventional grid‐following inverters (GFL). However, they are not well understood currently when applied in a mega scale and moving forward when they will likely take over the role synchronous generators have been performing for several decades as the workhorse of system security support. Key questions currently in the technical community include the extent to which GFM shall be similar or different to each of the synchronous machines and conventional GFL, and how various control strategies can assist in maximising the grid support capabilities sought and minimise or ideally eliminate any adverse impacts. The objective of this special issue is to provide insights into some of these unknowns. [ABSTRACT FROM AUTHOR]

In this study, a network mode energy (NME) method is used to analyse the low‐frequency oscillation (LFO) of a power system with a high penetration of a permanent magnet synchronous generator (PMSG). This method is also utilized to determine the dominant inter‐area oscillation path. NME comes from a network potential energy based on a small signal mode, which includes a generator internal node mode potential energy and a line mode potential energy (LMPE). The exchange process and distribution of NME in the power system containing the PMSG are studied by analysing the composition of LMPE. A sensitivity index is constructed to determine the state variables of the generator and the PMSG, which remarkably influences energy distribution. Then, the path characteristics of LFO are analysed. The dominant inter‐area oscillation paths and energy interaction of the system connecting to the PMSG are determined. The proposed NME can be calculated on the basis of measurement information, and network energy decomposition is carried out using the measured line mode oscillation index. The mechanism of PMSG participating in oscillation is revealed from the network perspective to provide a basis for network‐based regulation. The correctness analysis and simulation of a four‐machine two‐area system with the PMSG and the New England 10‐machine 39‐bus system with the PMSG are carried out. [ABSTRACT FROM AUTHOR]

Sub‐synchronous resonance (SSR) is a great danger to the stable and safe operation of the synchronous generator and power network. Detecting this condition in a fast and precise method is very important for power engineers. During the last decade, many methods have been proposed for SSR detection. The most famous of these methods use shaft speed analysis. On the other hand, it is noteworthy that SSR is a phenomenon that needs the use of both mechanical and electrical quantities for its analysis. Therefore, if both kinds of the signal are used, the protection system reliability can be enhanced significantly and its trip is more efficient and consistent. Subsequently, to enhance the precision and sensitivity of the SSR detection, this paper proposes the use of frequency analysis of the magnetic flux linkage of the generator as an electrical signal along with the shaft speed as a mechanical signal. The magnetic flux is a local index that is available at the relay location and does not require a communication channel to transmit. This index contains a lot of useful information about the performance of the machine. However, the main disadvantage of this index is its accessibility, which requires invasive sensors. [ABSTRACT FROM AUTHOR]

A protection scheme is proposed using alienation method derived from coherence model which is a backup protection method for the differential overcurrent protection of synchronous generators. This scheme which is realized by the computational technique based on the alienation coefficients estimated for generator voltage and current signals is considered to be mounted beside the main differential protection system, which operates in the cases that differential protection is unable to detect the internal faults. This novel protection algorithm operates by adjusting the alienation settings of the suggested relay that sends the trip signal to the three‐phase circuit breaker of the protected generator. In the proposed method, fault occurrences can be determined regardless of variations of terminal voltage and current in different working states of synchronous generator. This is done by designing new quadratic‐tripping characteristics based on alienation limits for the electrical signals. To demonstrate the proposed method, a motor‐synchronous generator set with built instrument transformers, for measuring voltage and current data at the generator terminals, are used. Extensive experimental investigations validate the functionality of this novel protection scheme under different abnormal, unbalance and operating conditions for the generator under test. [ABSTRACT FROM AUTHOR]

In this paper a novel method is proposed to estimate the rotor speed of synchronous generators in steady state and dynamic conditions using phasor measurement unit's data. This method uses the synchronous generator model to find the relationship between generator rotor speed and frequencies at different buses of the power system. The principles of the proposed method are first presented through a simple network consisting a generator connected to a transmission line. Afterward the general formulation is developed. To demonstrate the effectiveness of our method, IEEE 9‐bus and IEEE 39‐bus power systems are used as the benchmark systems. Different tests are carried out under three conditions including, normal condition, presence of measurement errors and uncertainty of the power system parameters. As well, the estimation results are compared with the results of other estimation methods. The results show the high accuracy of the proposed method in different conditions. [ABSTRACT FROM AUTHOR]

The authors propose a novel decentralised mixed algebraic and dynamic state observation method for multi-machine power systems with unknown inputs and equipped with phasor measurement units (PMUs). More specifically, they prove that for the third-order flux-decay model of a synchronous generator, the local PMU measurements provide enough information to reconstruct algebraically the load angle and quadrature-axis internal voltage. Due to the algebraic structure, a high numerical efficiency is achieved, which makes the method applicable to large-scale power systems. Also, they prove that the relative shaft speed can be globally estimated combining a classical immersion and invariance observer with – the recently introduced – dynamic regressor extension and mixing parameter estimator. This adaptive observer ensures global convergence under weak excitation assumptions that are verified in applications. The proposed method neither requires the measurement of exogenous input signals such as the field voltage and the mechanical torque nor the knowledge of mechanical subsystem parameters. [ABSTRACT FROM AUTHOR]

The first swing rotor angle stability is still an important stability challenge for modern power systems integrated with a large number of renewable energy-based sources, such as wind farms and solar-photovoltaic farms. Therefore, innovative strategies must be developed to exploit the full potential of doubly fed induction generators (DFIGs) to improve the first swing rotor angle stability in the system. This study presents a new active power logic (APL) controller for DFIGs which can reduce the active power during the fault and slowly recover it after the fault to allow synchronous generators to increase the electrical power during and after the fault; thus, enabling synchronous generators to improve the first swing rotor angle stability. The feasibility of the proposed control scheme is investigated via theoretical analysis and simulation studies. The reliability and voltage stability test system is used to demonstrate the effectiveness of the proposed scheme for local and remote faults and increased DFIG penetration conditions. The comparative results show that the proposed APL controller of the DFIG improves the first swing rotor angle stability, specifically when the DFIGs are located near the synchronous generators. [ABSTRACT FROM AUTHOR]

The present trend of inserting increasingly more solar photovoltaic (PV) sources into the electricity grid leads to a significant reduction in mechanical inertia. Inertia represents energy reserve in the grid, that inherently and instantaneously supports frequency stability. Therefore, recent studies have re-examined the frequency stability of the grid. Most of these consider scenarios where the participation from grid-following inverters remains relatively low. More importantly, these studies include an infinite bus in their analyses. The infinite bus acts as a very stiff voltage source which has a significantly stabilising influence, the more so as all control refers back to the infinite bus. Here, the frequency stability of a grid with significant generation from grid-tied PV inverters is considered without reference to an infinite bus. In the proposed simplified grid model, all the synchronous generators (SGs) are lumped as one large SG complete with classically operating controls. Similarly, all the PV generators are lumped as one large, quasi-instantaneous, non-linear power source. In this simplified network, the feasible operating region is identified using bifurcation techniques. It transpires that the stable operating region is bounded by a locus of Hopf bifurcations linked (inter-alia) to the fraction of power generated by grid-tied PV inverters. [ABSTRACT FROM AUTHOR]

This study presents a new index for fast and reliable protection of the synchronous generator (SG) against loss of field (LOF) incidence, focusing on the operation time, reliability in clustering LOF, power system disturbance (PSD), and practical application. To this end, all allowable electrical parameters at SG output are acquired and thoroughly analysed. Analytical analysis of the parameters indicates that reactive power (QSG) and load angle (δSG) parameters have better conditions to improve the mentioned factors. Hence, based on the δSG increment and QSG decrement during LOF events, a new index based on the ratio of deviations of the δSG over QSG (ΔδSG/ΔQSG) is proposed as a suitable criterion owing to remarkable fast sensitivity to LOF and PSD events. In the proposed algorithm, analysis of the events by the proposed ΔδSG/ΔQSG index is dependent on ΔVSG < 0 condition. Extensive simulation studies demonstrated that the proposed LOFPS is a straightforward method to immediately and securely distinguish between LOF and PSD events, and it also has minimum operation time than other methods. Moreover, numerical data affirmed the greater changes of the ΔδSG/ΔQSG index during LOF events than those in PSD events, giving rise to the easy clustering of both LOF/PSD events. [ABSTRACT FROM AUTHOR]

The ever-growing penetration of converter-interfaced distributed renewable energy sources (CI-DRES) in distribution networks, despite the undoubted advantages, has a profound impact on the traditional protection systems. The protection problem becomes even more complicated as the increase in the CI-DRES penetration level leads to the decommissioning of conventional power plants. Due to the limited current capability of CI-DRES, decommissioning of conventional units will lead to a transmission grid of significantly lower short-circuit level. This study proposes a novel protection philosophy for distribution grids of low short-circuit capacity and high CI-DRES penetration. According to the proposed approach, CI-DRES are controlled to actively participate in the fault-clearing procedure, supporting the short-circuit capacity, in an aggregated form, through the injection of controllable currents. Therefore, conventional overcurrent protection devices can be used, without any additional investments for a protection system upgrade. The CI-DRES fault contribution is based on their relative position to the fault, respecting technical and protection-malfunction constraints. In addition to the short-circuit level, the effect of the feeder parameters and the power factor of the injected fault current on the voltage recovery is also investigated. The proposed protection philosophy is validated via detailed simulations in DIgSILENT PowerFactory. [ABSTRACT FROM AUTHOR]

Nowadays, traditional synchronous generators are replaced by distributed renewable energy sources (DRESs), which are connected to the grid via power converters. This shift towards non-synchronous generation leads to low inertia power systems and affects considerably the frequency control procedure. To provide an inertial response and to enhance grid stability, DRESs can be equipped with fast discharging energy storage systems, such as ultracapacitors. This feature allows distribution system operators (DSOs) to provide an inertial response as ancillary service to transmission system operators (TSOs) by coordinating the operation of many DRESs. For this purpose, DSOs should develop tools to quantify and control the provision of inertial response. Towards this objective, in this study, two new methodologies are proposed. The first one aims to evaluate the maximum aggregated inertial capability of active distribution networks (ADNs). The second one aims to dispatch DRESs to provide specific, TSO-defined, inertial response with the minimum cost. Both methods are tested on a medium voltage grid. Several cases are examined highlighting the impact of different parameters, such as converter limitations, line congestions, on the inertial capability of ADNs. Results indicate that the proposed methods can fully exploit operational limits of ADNs and maximise their inertial capability. [ABSTRACT FROM AUTHOR]

As the penetration level of converter-based generators (CBGs) continues to grow in electric power systems, their impact on power system dynamics and control becomes increasingly significant. Maintaining a stable operation of the CBGs is becoming more and more critical. Since their controls and dynamic behaviour differ from synchronous generators, in this study, the transient stability mechanism of CBGs is analysed and the key influencing factors are identified and investigated. Moreover, a stability margin index, which can be obtained analytically, is proposed to identify potential transient stability issues of CBGs and can be used as a screening technique before conducting time-consuming electromagnetic simulation studies. This index can be used for both planning and operations studies and it outperforms the state-of-the-art index of short circuit ratio that is presently used to identify potential CBG instabilities due to weak grid scenarios. Dynamic simulations on a real power system model have been conducted to validate the accuracy and applicability of the proposed stability margin index. [ABSTRACT FROM AUTHOR]