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Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press 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.)

Most regions of the world have seen tremendous growth in distributed energy resources, especially photovoltaic (PV) generation. The penetration of PV generation into the power grid is high and hence it has a major impact in power system. The integration of solar PV plant into the power system has both negative as well as positive impacts on transient stability of the power system during faults. In this work, the proposed current amplitude limiting based Fault Ride Through (FRT) control algorithm is implemented in large scale power systems and enhancement of transient stability is also studied in terms of synchronous machine side and grid side parameters namely rotor speed deviation, load angle, relative rotor angle, active and reactive power. The transient stability of large-scale Grid Connected solar PV (GCPV) system is discussed in this article, when the system is incorporated with the proposed FRT control strategy. The large scale GCPV system is said to be stable, if the angular displacement between the machines in the system stays within predetermined limits. The parameters considered for transient analysis on the synchronous machine side are the rotor angle, rotor speed, and Critical Clearing Time. The proposed model is simulated in MATLAB Simulink and validated in 1 kW hardware setup of grid connected PV system which performs satisfactorily in terms of system parameters and transient stability improvement. [ABSTRACT FROM AUTHOR]

This paper proposes a critical clearing time (CCT) estimation method by the domain of attraction (DA) of a state-reduction model of power systems using sum of squares (SOS) programming. By exploiting the property of the Jacobian matrix and the structure of the boundary of the DA, it is found the DA of the state-reduction model and that of the full model of a power system are topological isomorphism. There are one-to-one correspondence relationships between the number of equilibrium points, the type of equilibrium points, and solutions of the two system models. Based on these findings, an expanding interior algorithm is proposed with SOS programming to estimate the DA of the state-reduction model. State trajectories of the full model can be transformed to those of the state-reduction model by orthogonal or equiradius projection. In this way, CCT of a grid fault is estimated with the DA of the state-reduction model. The calculational burden of SOS programming in the DA estimation using the state-reduction model is rather small compared with using the full model. Simulation results show the proposed expanding interior algorithm is able to provide a tight estimation of DA of power systems with higher accuracy and lower time costs.

Data-driven methods are widely recognized and generate conducive results for online transient stability assessment. However, the tedious and time-consuming process of sample collection is often overlooked. The functioning of power systems involves repetitive sample collection due to the constant variations occurring in the operation mode, thereby highlighting the importance of collection efficiency. As a means to achieve high sample collection efficiency following the operation mode change, we propose a novel instance-transfer method based on compression and matching strategy, which facilitates the direct acquisition of useful previous samples, used for creating the new sample base. Additionally, we present a hybrid model to ensure rationality in the process of sample similarity comparison and selection, where features of analytical modeling with special significance are introduced into data-driven methods. At the same time, a data-driven method can also be integrated in the hybrid model to achieve rapid error correction of analytical models, enabling fast and accurate post-disturbance transient stability assessment. As a paradigm, we consider a scheme for online critical clearing time estimation, where integrated extended equal area criterion and extreme learning machine are employed as analytical model part and data-driven error correction model part, respectively. Derived results validate the credible efficacy of the proposed method.

Nowadays, integration of large-scale wind farms (WFs) into power systems is experiencing rapid growth. As this rapid integration can affect transient stability significantly, employing doubly fed induction generator (DFIG)-based wind turbines, which have shown better behavior regarding system stability, has attracted much attention. This research contributes to the literature by investigating the transient stability of the power system with increasing penetration of DFIG-based WFs. In the proposed framework, the current-balance form is utilized for the network equations, and in this way, transient stability is performed using time-domain simulation. According to the simulation results, when the rate of wind power generation exceeds 0.7 per-unit, the increasing trend of the critical clearing time (CCT) is reversed and the CCT decreases greatly with the increased wind power penetration. In addition, the reactive power compensation by DFIG, the gearbox ratio, the power system strength, and DFIG parameters are comprehensively investigated as effective parameters on transient stability. Since the rated rotor speed of DFIG significantly impacts the electrical torque and machine currents, the reduction of the rated rotor speed due to the change of the gearbox ratio has been investigated as one of the effective factors to improve the transient stability. The simulation results demonstrate the effectiveness of the proposed approach in improving power system transient stability. [ABSTRACT FROM AUTHOR]

An adaptive neuro-fuzzy inference system (ANFIS) is a hybrid algorithm composed of fuzzy logic and an artificial neural network. It takes advantage of fuzzy logic and artificial neural networks to solve complex problems. For power transmission, several dynamic parameters are ignored for conventional transient stability assessment due to the complexity of the equations, and due to the long computational time required. Certainly, it is very difficult to do the real-time assessment of large power systems by considering dynamic impacts in detail. In this paper, an approach is required to increase the accuracy of results. Herein, a method, namely ANFIS, was found to overcome the limitations. All significant effects of dynamics can be taken into account; not only the machine model but also the turbine governor model, automatic voltage regulator (AVR) model, and load characteristic model are carefully considered. In addition, the model used for each generator unit is varied to achieve real conditions. The ANFIS output is the critical clearing time (CCT). CCT values are very important to be correctly predicted for the stability of power systems after clearing the faults. When the faults are cleared by opening the circuit breakers within the CCT values, the power systems are still stable. If the faults are cleared after the CCT values, the systems become unstable. The modified IEEE 9-bus and IEEE 39-bus systems are applied in the implementation of this study. The locations of faults and the levels of loads (except the power system topology changes) are varied for each simulation. The results from the ANFIS application indicate that ANFIS (considering the dynamic effects of the machine models, AVR system, turbine governors, and load characteristics) can predict CCT values with high accuracy. Moreover, when ANFIS results are compared to the artificial neural network (ANN) results, which are generally used, it can be seen that ANFIS results are better and take a lower time for training and testing processes than ANN. ANFIS can be adapted, improved, and implemented in real practice.

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press 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 Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press 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.)

Studying network stability requires determining the best critical clearing time (CCT) for the network after the fault has occurred. CCT is an essential issue for transient stability assessment (TSA) in the operation, security, and maintenance of an electrical power system. This paper proposes an algorithm to obtain CCT based on fuzzy logic (FL) under fault conditions, for a multi-machine power system. CCT was estimated using a two-step fuzzy logic algorithm: the first step is to calculate Δt, which represents the output of the FL, while maximum angle deviation (δmax) represents the input. The second step is to classify the system if it is a stable or unstable system, based on two inputs for FL, the first mechanical input power (Pm), the second average accelerations (Aav). The results of the proposed method were compared with the time domain simulation (TDS) method. The results showed the accuracy and speed of the estimation using the FL method, with an error rate not exceeding 5%, and reduced the performance time by about half the time. The proposed approach is tested on both IEEE-9 bus and IEEE-39 bus systems using simulation in MATLAB. [ABSTRACT FROM AUTHOR]

The electric power distribution scheme of a power plant should be analysed to prevent the occurrence of the slightest fault current and improve system reliability during the power production process. Protection relay settings installed on the electricity network should calculate the condition of the generator with various types of fault currents. Installation of relays that do not consider transient stability leads to generator instability even though the fault is eliminated. Therefore, it is necessary to calculate the stability limit while setting the overcurrent relay. However, a failure in the relay setting can occur if the inverse relay cannot protect against a high-impedance fault. Therefore, a method was proposed to determine the stability limit based on a short circuit without impedance and with an applied impedance, and the application of the method was demonstrated through existing settings and resetting conditions in simulation software. A modification relay setting prevented the loss of synchronisation of the generator during fault occurrence. The working time operation was integrated with the definite and inverse overcurrent relays in ANSI 50, 51, standard operating time of the relay, and critical clearing time of the generator. The type of fault used was a three-phase fault, with and without high-impedance. The calculation results demonstrated that this concept can be used to protect lines and generators during a short circuit current. [ABSTRACT FROM AUTHOR]

Accurate transient stability assessment (TSA) and effective preventive control are important for the stable operation of power systems. With the superiorities in precision and efficiency, data-driven methods are widely used in TSA nowadays. Data-driven TSA model can be adopted in the stability constraints of preventive control optimization, but existing methods are mostly iteration-based ones, which may result in low efficiency, sometimes even non-convergence. In this paper, an analytical representation method of data-driven transient stability constraint is proposed based on a non-parametric regression model built for TSA. Key feature extraction and dominant sample selection are proposed to reduce the scale of the TSA model, and bi-level linearization is applied to further modify it. Optimal preventive control model is then formulated as a mixed-integer linear program (MILP) problem with the linearized analytical data-driven transient stability constraint, which can be solved without iterations. An overall procedure of data-driven TSA and preventive control is finally developed. Case studies show that the proposed method has high accuracy in TSA and can achieve effective preventive control of power system with high efficiency.

Maintaining a stable operation of modern power systems, which are heavily loaded and strongly interconnected is a very complex task. This requires an optimal setting and coordination of protective relays considering the transient behavior of power systems. This paper proposes a new formulation of the optimal coordination of directional overcurrent relays (DOCRs) problem, considering power systems' transient stability and intelligent selection of non-standard characteristics. This problem is formulated as a mixed-integer optimization problem, taking into account non-standard relay characteristics and transient stability constraints, where the required power system parameters are calculated using Digsilent Power Factory Software. An enhanced version of a hybrid optimization method called: Hybrid Gravity Search Algorithm and Sequential Quadratic Programming (GSA-SQP), is proposed to solve the problem. The efficiency and performance of the proposed approach are validated on the 9-bus and 39-bus test systems considering various case studies. The obtained results show the efficiency of the proposed formulation to reduce the operating time of DOCRs with coordination and transient stability constraints satisfaction. [ABSTRACT FROM AUTHOR]

Transient stability analysis is a very important tool to deal with many behaviors of electrical power systems during and after being subjected to various disturbances. this paper propose a method for electrical power systems transient stability assessment using phase plane trajectories. A methodology for computing the critical stability conditions of generators is proposed. The critical conditions such as critical clearing time (CCT) and critical clearing angle (CCA) were obtained. The computation of CCA and CCT is curried out step by step using the characteristics of the faulted and postfault trajectories from given initial conditions until their intersection point. The angle and time values founded represent, by definition, the critical conditions of the system. The proposed algorithm can be used for complex models since it is based on solving systems of differential equations by iterative methods in the phase plane. The advantage provided by this method is it's accurate and small time consuming. To demonstrate the effectiveness of the proposed method, first, critical conditions calculation procedures are given, then the process used in judging power system stability is provided, finally, simulation results for various test cases of a single machine infinite bus (SMIB) system highlight the proposed methodology. [ABSTRACT FROM AUTHOR]

The assessment of transient stability of multi-machine power system, in a post-fault scenario, is a very challenging task due to highly non-linear nature of the system equations. In this work, the physical concept of maximum relative acceleration of a machine at a fault scenario is related with the boundary of stability region. This approach is extended to develop a quadratic Lyapunov function using singular perturbed modelling. Unlike the conventional energy function methods, this Lyapunov function candidate is a more general energy function and has a decaying nature around an equilibrium point. Moreover, with higher order corrections, an improved Lyapunov function candidate is presented with simulation results of power system examples. The decaying nature of Lyapunov function candidate remains similar even without higher order corrections. However, the relevance of inclusion of higher order corrections is brought out in the cases of faults occurring at other than generator buses. Also, the upper bound of singular perturbation parameter in the model is within allowable limits and ensures the accuracy of results. [ABSTRACT FROM AUTHOR]

Summary: Flywheel energy storage system (FESS) needs to be operated within its allowable speed range because it will be shut down outside this range. Furthermore, the power supplied/absorbed by FESS is constrained by the associated power electronic interface. This article proposes supervisory adaptive predictive control (APC) scheme for flywheel energy storage system to enhance power system transient stability while addressing the constraints mentioned earlier. The supervisory adaptive predictive controller gives a reference power command signal to the inner control loop of FESS while ensuring the operation of FESS within its regime of operation. The gains of the inner control loop are optimized by employing Genetic Algorithm (GA). The constraints on the state of charge of FESS and power rating of the associated converter are explicitly included in the adaptive predictive controller formulation, which is usually done in an ad hoc manner. The performance of the proposed control strategy is evaluated under four scenarios: a step wind disturbance, realistic wind profile, doubly fed induction generator (DFIG) outage, and a severe symmetrical fault condition on modified New York/New England 16 machine 68‐bus power system. The validity of the adaptive predictive control based flywheel energy storage system (APC based FESS) in improving transient stability of power system is verified by the simulation studies carried out in MATLAB/Simulink environment. [ABSTRACT FROM AUTHOR]

This paper deals with the transient stability of a grid-forming converter while embedding a current reference saturation strategy. The novelty of this work consists in investigating the impact of the current reference angle on the transient stability. In case of a balanced voltage sag, analytical formulas to estimate the critical clearing angle (CCA) and critical clearing time (CCT) while considering different values of the current reference angle are derived. It is demonstrated that the choice of this angle is constrained by the ability of the power converter to switch back to the voltage control mode. Based on that, its optimal value that enhances the transient stability and allows a switching from the saturated current control mode to the voltage control mode is calculated. Thereafter, the effectiveness of this optimal choice to guarantee the stability in case of a phase shift caused by a line re-closing event is verified. Time-domain simulations and experimental tests validate the correctness of the presented theoretical approaches. [ABSTRACT FROM AUTHOR]

The research on electromechanical transient stability of power systems is of great significance. Analyzing the parameters of the simulation system and its improved system with typical short-circuit faults, this paper studies the transient stability of power systems and its improvement. Firstly, based on the SIMULINK of MATLAB, a double-loop simulation with the single-machine-infinite-bus system is built. The simulation experiments of the system under the circumstances of three-phase short circuit and single-phase grounding short circuit faults are then carried out to analyze the parameters such as limit cutting time and voltage. Besides, this paper explores how the controllable series capacitor compensation device and reducing mechanical power output by prime mover improve the transient stability of the system. Experiments show that the stability after fault is under conditions where the fault is removed before the critical clearing time, which can increase the threshold to gain more response time for relay protection devices. Thus, the value of researching and improving system transient stability is proved.

A fault current limiter (FCL) is an economical option to limit the increased fault current levels, which may also improve the rotor angle stability. Previous studies on this topic mainly focused on the FCLs with quick recovery and concluded that the FCL improves the rotor angle stability. However, some commercially available FCLs have delayed recovery, which may pose different challenges and need to be studied. This paper studies the impact of a superconducting fault current limiter (SCFCL) with delayed recovery on transient rotor angle stability. This paper first develops an analytical understanding of the stability of a system with SCFCL using the equal area criterion. Later, time-domain simulations are employed to demonstrate the impacts of the SCFCL on the rotor angle stability of a single-machine infinite-bus system. The results show that the SCFCL with delayed recovery leads to rotor angle instability in some cases. • Identification of the adverse impact of SCFCL with delayed recovery on transient stability. • Transient stability assessment with different SCFCL technologies. • Transient stability assessment with different SCFCL parameters, locations, and fault types. [ABSTRACT FROM AUTHOR]

• This paper presents the mathematical model of the heterogenous three-machine system, considering the dynamics of the pre-fault, fault-on, and post-fault systems. • Based on the developed model, the critical clearing time is derived analytically for transient stability assessment. The method can deal with the nonlinearity between SG's rotor angle and VSC's PCC voltage phase. • Decreasing the active current component of VSCs has the potential to increase the maximum active power transmission capacity between the interconnected AC systems, so that the transient stability can be enhanced. • With the help of WAMS, the proposed enhancement control strategy achieves dynamic current modulation based on the angle difference between SGs and the PCC voltage phase of VSCs. • The proposed enhancement control strategy is adaptable to multimachine systems with the concept of COI. This paper analyzes the transient angle stability mechanism of interconnected AC power systems with voltage source converter (VSC) based generations and presents a stability improvement control strategy for the VSCs. Firstly, the mathematical model of the prototype AC system with both synchronous generator (SG) and VSC is developed, considering the dynamics of the pre-fault, fault-on, and post-fault systems. For the heterogenous three-machine system, the analytical method for the critical clearing time (CCT) is proposed for transient stability assessment. Then, the evolution of the transient stability margin of the AC system is studied, considering the impact of the VSCs. Under the conditions that VSCs can keep synchronism with the grid during the fault, reducing the active current of the VSCs benefits the transient angle stability of SGs. Based on the mechanism analysis, an enhancement control strategy is developed. It achieves active and reactive current modulation of the VSC using the frequency measurements of the critical SGs (CSGs) in the AC system. The proposed method devotes to boosting the electromagnetic power of CSGs during the entire transient process. Finally, time-domain simulations in PSCAD/EMTDC demonstrate the theoretical analysis. The effectiveness and robustness of the enhancement controller are further validated by the time-domain simulations in a 2-area interconnected system with 4 SGs and a modified New England 39-bus test system. [ABSTRACT FROM AUTHOR]