Power System Stability Problems Research Articles

A fast and high‐accurate commutation failure identification method for LCC‐HVDC system

AbstractCommutation failure (CF) is one of the most common issues in line‐commuted converter‐based high voltage direct current systems (LCC‐HVDC), leading to critical power system security and stability problems. Accurate and rapid identification of CF is crucial to prevent subsequent CF in HVDC systems. However, the existing CF identification methods are lack of the required accuracy and speed. The relationship between bridge arm current, commutation voltage, and trigger pulse based on the commutation progress mechanism after the AC fault is analysed in this paper. A novel CF identification method is presented, which utilises the CF identification factor, enabling fast and high‐accurate identification without relying on the value of the extinction angle. The proposed method offers a simpler and more efficient implementation in engineering practice. Finally, the effectiveness of the proposed method is verified in both the standard International Council on Large Electric systems HVDC model and the Hardware in Loop test using practical project parameters. The results demonstrate that the proposed method can accurately and fast identify CF.

Domain of Stability Characterization for Power Systems: A Novel Individual Invariance Method

In this paper, we approach the problem of stability in nonlinear systems through a new perspective that views them as a combination of individual artificial systems carefully chosen to simplify the complex structure of nonlinear systems. This is achieved by recasting nonlinear vector fields as an algebraic sum of individual vector fields for which artificial systems with known invariant sets or at least in forms that allow for tractable approximation of their invariant sets. This attempt to restructure nonlinear systems stands out in comparison to other previous attempts like Lure' systems or network based models as a purely mathematical structuring technique that transcends the physical constraints and dependencies within dynamical models and allows the user to creatively construct artificial systems with the sole focus on the overall stability. The theoretical foundation is provided for a theorem about individual invariance to relate the invariant sets of individual artificial systems to the invariant set of their original system in a way that significantly simplifies the task of approximating regions of attraction. Several examples are used to demonstrate this theorem and we also evaluate the use this theorem for the challenging power system stability problems in both AC and DC grids. The proposed method is successfully applied to the IEEE 39- bus New England system, and a DC converter with constant power load giving accurate and realistic estimations of the critical clearing time and stability regions in comparison to state of the art approaches.

A Comprehensive Review on the Modelling and Significance of Stability Indices in Power System Instability Problems

Many technological advancements in the modern era have made actual use of electrical power and the constrained operating of power systems within stability limits. Some expeditious load variations and rising power demands initiate complications in voltage stability and can put stress on performance, leading to voltage instability. Voltage Stability Indices can be used to perform voltage stability assessment. This review evaluates various VSIs based on mathematical derivations, assumptions, critical values, and methodology. VSIs determine the maximum loadability, voltage collapse proximity, stability margin, weak areas, and contingency ranking. Stability indices can also specify the optimal placing and sizing of Distributed Generators. Thus, VSIs play a vital role in power system voltage stability. This review is a comprehensive survey of various indices and analyses their accuracy in determining the instability of power systems. Voltage stability is a crucial concern in operating a reliable power system, and the systematic evaluation of voltage stability is essential in a power system. This review considered and analyzed 34 indices from 138 articles from the literature for their significant performance in various power system stability problems. Of 33 indices, were 22 derived from transmission line parameters, referred to as line indices, and 12 from bus and line parameters, referred to as bus indices.

Simulation of Secondary Frequency Modulation Process of Wind Power with Auxiliary of Flywheel Energy Storage

With the rapid increase in the proportion of wind power, the frequency stability problem of power system is becoming increasingly serious. Based on MATLAB/Simulink simulation, the role and effect of secondary frequency modulation assisted by Flywheel Energy Storage System (FESS) in regional power grid with certain wind power penetration rates are studied. First, the linear frequency control of the power system is used to establish the primary frequency modulation control model of FESS assisting wind power, and the frequency characteristics of FESS participating in primary frequency modulation are analyzed according to the transfer function. Then, in the case of step disturbance and continuous disturbance of load power, the frequency characteristics of a regional power grid are simulated and demonstrated through time domain simulation, and conclusions are drawn through comparison; a certain proportion of FESS can quickly respond to the frequency deviation signal. During secondary frequency modulation simulation, the maximum frequency deviation of the system is reduced by 57.1% and the frequency fluctuation range is reduced by 53.8%, effectively improving the frequency quality of the power grid.

Data-Driven Security and Stability Rule in High Renewable Penetrated Power System Operation

Power systems around the world are experiencing an energy revolution that substitutes fossil fuels with renewable energy. Such a transition poses two significant challenges: highly variable generators that add short-term and long-term difficulties for supply–demand balance, and a high proportion of convertor-based devices that may jeopardize power system security and stability. At the same time, machine learning techniques provide more opportunities to study the complex power system security and stability problems. This article summarizes the machine learning framework to embed security rules into power system operation optimization under high renewable energy penetration. First, we explore how high penetration renewable energy impacts power system security and stability. Then, we review how the complex security and stability boundary of power systems is modeled using various machine learning techniques. Finally, we show how the machine learning model is transformed into optimization constraints that can be embedded into the power system operation model. The framework is substantiated through case studies of practical power systems.

Nonlinear Stability of Complex Droop Control in Converter-Based Power Systems

In this letter, we study the nonlinear stability problem of converter-based power systems, where the converter dynamics are governed by a complex droop control. This complex droop control augments the well-known power-frequency (p-f) droop control, and it proves to be equivalent to the state-of-the-art dispatchable virtual oscillator control (dVOC). In this regard, it is recognized as a promising grid-forming solution to address the high penetration of converters in future power systems. In previous work, the global stability of dVOC (i.e., complex droop control) has been proven by prespecifying a nominal synchronous steady state. For a general case of non-nominal (i.e., drooped) synchronous steady states, however, the stability problem requires further investigation. In this letter, we provide parametric conditions under which a non-nominal synchronous steady state exists and the system is almost globally asymptotically stable with respect to this non-nominal synchronous steady state.

동해안 지역 재생에너지원 접속에 따른 과도안정도 여유 분석 및 발전제약 산정 연구

Increasing renewable energy resources can lead to critical stability problems in power systems. Specially in Korean power system, since the power generation complex is concentrated on the coast, there are constraints on transmitting to the load. If a connection of renewable energy resources near generator buses continues to grow, specially in the east cost, transient stability problems may arise due to shortage of transmission lines. Therefore, it is necessary to evaluate how much renewable energy access at each site can affect the power system by some stability index such as critical clearing time. This paper shows how to assess or calculate the margin of dynamic stability and verify the methodology through assessment of a practical power system. Based on the methodology, this paper analyzes the practical system and draws conclusions.

Neural Lyapunov Control for Power System Transient Stability: A Deep Learning-Based Approach

Power system control and transient stability analysis play essential roles in secure system operation. Control of power systems typically involves highly nonlinear and complex dynamics. Most of the existing works address such problems with additional assumptions in system dynamics, leading to a requirement for a complete and general solution. This paper, therefore, proposes a novel control framework for various power system control and stability problems leveraging a learning-based approach. The proposed framework includes a two-module structure that iteratively and jointly learns the candidate Lyapunov function and control law via deep neural networks in a learning module. Meanwhile, it guides the learning procedure towards valid results satisfying Lyapunov conditions in a falsification module. The introduced termination criteria ensure provable system stability. This control framework is verified through several studies handling different types of power system control problems. The results show that the proposed framework is generalizable and can simplify the control design for complex power systems with the stability guarantee and enlarged region of attraction.

Promising Grid-Forming VSC Control Schemes Toward Sustainable Power Systems: Comprehensive Review and Perspectives

Driven by environmental and economic aspects, the proliferation of renewable energy sources (RES) has been expanded in power systems worldwide. In this regard, the intermittent generation of such RESs (e.g., photovoltaic and wind farms) can cause several operational and stability problems in such low-inertia power systems. To handle these issues, great interest in the literature has been directed to develop feasible grid-forming voltage source converters (VSC) control schemes that have voltage/frequency regulatory functions. Accordingly, an inclusive review is presented in this paper for these promising grid-forming VSC control schemes which will be the backbone of sustainable converter-dominated power systems. Specifically, control structures, smart grid-support functionalities, stability issues, and fault current mitigations are compared considering the existing grid-forming VSC control schemes. Besides, the applications of grid-forming VSC along with their benefits and drawbacks are investigated for both isolated and bulk power systems. The evaluation aspects are also explored for assessing the performance of the existing VSC control schemes in the grid. Finally, the current challenges that face VSC in forthcoming applications and existing gaps are highlighted while corresponding perspectives for future research studies are defined for stable sustainable low-inertia power systems.

Cooperation of large-scale wind farm and battery storage in frequency control: An optimal Fuzzy-logic based controller

Grid integration of renewables and battery energy storage systems and its consequent synchronous machines retirement may drive power systems into low-inertia conditions with high risk of frequency instability which is associated with lack of sufficient inertia and primary frequency response previously supplied by synchronous machines. Therefore, there is a need to figure out alternative solutions to compensate the lack of system frequency dynamic supports in future renewable-dominated power systems. In this context, this paper aims to highlight wind farm capabilities, particularly doubly-fed induction generator (DFIG) and permanent magnet synchronous generator (PMSG), in system primary frequency control, similar to conventional synchronous units, while also investigates the synergy between the wind unit cooperation with large-scale battery storages. First, a novel dynamic model is presented which takes into account large-scale wind farms, as well as utility-scale batteries, equipped with frequency-sensitive active power reference scheme so as to control the system frequency violations following contingencies. The proposed frequency control model also includes power-electronics interface model, its associated control loops, and a novel Fuzzy-logic based controller. The proposed Fuzzy-logic based controller along with a wash-out filter allows combined wind-battery system to estimate the system active power mismatch, emerged from a contingency/trip, to determine the consequent frequency variations, and therefore to deliver fast frequency response in a robust and reliable way to arrest the mentioned frequency distortions. The proposed Fuzzy-based controller is then designed via optimizing its model parameters, including the membership function parameters, thereby improving its efficiency in frequency control provision as well as active power control. The optimization process is performed via a widely used artificial bee colony (ABC) algorithm while a multi-objective function is considered. The proposed frequency control model is then evaluated in the 14-generation low-inertia Australian test system with 30% wind penetration. This work tries to provide a deep insight on how to utilize wind farms for frequency support and how to wind-battery frequency response may positively interact with nearby converter-based resources, i.e., photovoltaic units. The proposed Fuzzy-based coordination approach for large-scale wind-battery units can be a potential solution to deal with frequency stability problems in future power systems with low-inertia conditions including multiple nearby converter-based resources.

Influence of water diversion system topologies and operation scenarios on the damping characteristics of hydropower units under ultra-low frequency oscillations

Ultra-low frequency oscillations are the typical dynamic stability problem of hydropower-dominated power systems. Hydraulic factors can directly affect hydropower unit damping, and related studies focus on the influence of hydraulic parameters on unit damping under a fixed operation situation, while ignoring the characteristics of water diversion system topologies (WDST) and diverse hydropower operation scenarios. In this paper, some simulation models of the hydro-turbine governing system (HTGS) with a variety of WDST are first established. Then, a damping calculation method based on phase diagrams is used to calculate the damping of overall system under different WDST and operation scenarios. The results show that the increase of the number of branch pipes in WDST will deteriorate the damping characteristics and setting a surge tank can effectively increase the damping. In addition, if there is a hydraulic connection between the unit integrated into a small power grid (SPG) and the unit integrated into a large power grid (LPG), the strong stability of the LPG will increase the damping of the unit integrated into SPG. Closing some units in multi-unit HTGS will improve damping characteristics of the running unit. Some measures to suppress ULFO are proposed from the perspective of design and stable operation.

A Bi-Level Control Strategy for PV-BES System Aiming at the Minimum Operation Cost of BES

With the increased penetration of the photovoltaic (PV) energy, the power system stability problem becomes an issue, as the output power of PV plants has unpredictable fluctuations. To maintain the power stability of the PV plants, battery energy storages (BESs) play an important role due to their fast and accurate response speed. However, it is challenging that the BES with multiple sub-modules responds well to the PV power fluctuations resulting from the various influence factors, such as defects, faults, and partial shading. Therefore, a bi-level control strategy is proposed in this paper, aiming at minimizing the operation cost of BES in maintaining power stability. The control strategy consists of the PV power fluctuations identification block and the mitigation block. In specific, the identification block can output the power fluctuation of a PV system by the PV power fluctuation identification technique. The technique is developed based on the characteristics of PV-string current under electrical faults and partial shading conditions. Meanwhile, the mitigation block can manage the multiple battery sub-modules with different regulation characteristics to meet the power fluctuations. At last, the promising results are obtained by MATLAB\Simulink with the coordinated operation of those two blocks, including the precise condition of the PV system and the optimal power output of each battery sub-module. Therefore, a comprehensive bi-level control strategy is developed to regulate the operation of battery sub-modules for PV-BES systems.

A New Design Method for Optimal Parameters Setting of PSSs and SVC Damping Controllers to Alleviate Power System Stability Problem

This paper presents an improved Teaching-Learning-Based Optimization (TLBO) for optimal tuning of power system stabilizers (PSSs) and static VAR compensator (SVC)-based controllers. The original TLBO is characterized by easy implementation and is mainly free of control parameters. Unfortunately, TLBO may suffer from population diversity losses in some cases, leading to local optimum and premature convergence. In this study, three approaches are considered for improving the original TLBO (i) randomness improvement, (ii) three new mutation strategies (iii) hyperchaotic perturbation strategy. In the first approach, all random numbers in the original TLBO are substituted by the hyperchaotic map sequence to boost exploration capability. In the second approach, three mutations are carried out to explore a new promising search space. The obtained solution is further improved in the third strategy by implementing a new perturbation equation. The proposed HTLBO was evaluated with 26 test functions. The obtained results show that HTLBO outperforms the TBLO algorithm and some state-of-the-art algorithms in robustness and accuracy in almost all experiments. Moreover, the efficacy of the proposed HTLBO is justified by involving it in the power system stability problem. The results consist of the Integral of Absolute Error (ITAE) and eigenvalue analysis of electromechanical modes demonstrate the superiority and the potential of the proposed HTLBO based PSSs and SVC controllers over a wide range of operating conditions. Besides, the advantage of the proposed coordination design controllers was confirmed by comparing them to PSSs and SVC tuned individually.

Reliability and Dynamic Performance Simulation Based on Relay Protection Summary

With the development of science and technology, national security and social life can not be separated from electricity every moment, and the safety of power grid is becoming more and more important. At present, the research on relay protection model in dynamic simulation of power system in China is still in the primary stage. Because the research is not deep enough, the control law of relay protection elements can not be well grasped. The failure can not be handled well. Therefore, in order to ensure the safe operation of the power system, we must first strengthen the grid structure of the power system, improve the elasticity coefficient, distribute the reserve capacity reasonably, strengthen the adjustment ability of the tie line between the major power grids, and improve the stable reserve of the power grid. In order to improve the authenticity and reliability of dynamic simulation, it is necessary to establish a set of relay protection models, which should be consistent with the actual relay protection. In this way, the stability problem in power system can be analyzed accurately to improve the reliability of power system. The relay protection model established in this paper reduces the complexity of modeling and can reflect the dynamic characteristics of power system after interference. It is of great significance to the analysis and research of power system.

Electric vehicle charging management using location-based incentives for reducing renewable energy curtailment considering the distribution system

There have recently been an increasing number of variable renewable energy curtailment cases to manage power system stability problems caused by the overproduction of variable renewable energy. Variable renewable energy curtailment can be a factor that hinders the development of the power industry by reducing the economic viability of variable renewable energy operators and the efficiency of energy use. In this study, an economic curtailment methodology using electric vehicles to mitigate energy waste and economic losses is proposed. Charging point operators participate in incentive-based demand response programs with their charging station loads under curtailment situations. A location-based incentive algorithm considering distribution system constraints is proposed to avoid distribution system congestion. A response model based on random arrival electric vehicles considering demand and price elasticity, time pressure, and charging pressure is developed. The proposed methodology is verified through case studies based on the environment of Jeju Island in Korea. The case study results show that the proposed methodology can use energy more economically and effectively than conventional variable renewable energy curtailment methodology.

Multi-objective Adaptive Evolutionary Algorithm to Enhance Voltage Stability in Power Systems

Problems with two or more conflicting objectives have been handled as needing a multi-objective approach in recent years. The solution for these types of problems is normally to satisfy the conflicting objectives simultaneously in order to find tradeoffs between different criteria. Optimization in power systems is an important example of how to tackle multi-objective problems since these systems have conflicting performance indicators and normally operate close to their constraints due to the continuous increase in demand. In this paper, a multi-objective approach is applied to the voltage stability problem in power systems by using an adaptive evolutionary algorithm. The proposed method regards examining the following stability indicators of power systems: the voltage profile, the total reactive power loss, and the voltage collapse margin as requiring a multi-objective approach. Several experiments were conducted in IEEE 14, 57, and 118 busbar systems by using the proposed method and other probabilistic and heuristic optimization methods. The results showed that the proposed adaptive evolutionary algorithm enhanced the voltage stability and outperformed the other methods, especially when the size of the power system increases.

Online inertia estimation for power systems with high penetration of RES using recursive parameters estimation

Low and time-changing inertia values due to the high percentage of renewable energy sources (RESs) can cause stability problems in power systems due to rapid frequency instabilities. Inertia monitoring will assist operators to apply suitable actions and more proper control methods to alleviate stability issues. Therefore, this paper proposes an online method to estimate the total inertia of a network using a recursive least-squares approach. The proposed method uses network measurements with a non-recursive system identification approach to initially estimate the network hypothesis model. Then, the recursive method is used together with time changing measurements to recursively estimate model parameters and extract online inertia estimates of the network. During the estimation, the method does not need to store previous data after each sample step; therefore, the computation burden is significantly reduced. More importantly, the technique incorporates the use of available electromechanical oscillation modes in the system, which are linked with system parameters, to determine the network inertia estimates. The applicability of the proposed method has been validated by numerical simulations of the IEEE 39-bus network and the aggregated New Zealand network with its actual inertia data.

Control of Photovoltaic Inverters for Transient and Voltage Stability Enhancement

The increasing number of megawatt-scale photovoltaic (PV) power plants and other large inverter-based power stations that are being added to the power system are leading to changes in the way the power grid is operated. In response to these changes, new grid code requirements establish that inverter-based power stations should not only remain connected to the grid during faulty conditions but, also provide dynamic support. This feature is referred in the literature to as momentary cessation operation. The few published studies about momentary cessation operation for PV power plants have not shed much light on the impact of these systems on the overall power system stability problem. As an attempt to address this issue, this paper proposes a control scheme for PV inverters that improves the transient stability of a synchronous generator connected to the grid. It is shown through the paper that the proposed control scheme makes the PV inverter's dc link capacitors absorb some of the kinetic energy stored in the synchronous machine during momentary cessation. Besides that, the proposed solution is also able to improve voltage stability through the injection of reactive power. Experimental and simulation results are presented in order to demonstrate the effectiveness of the proposed control scheme.

A Feasibility Solution of a Synchronous Generator for Optimisation of the System Power Stability using an Integrated Development Environment of Visual Basic Excel

Power systems are considered highly non-linear because the environment in which they operate keep changing and hence require iterative mathematical techniques to analyse them. Such changes have a resultant effect on the system`s stability. Fluctuations in parameters are experienced in loads across the networks of the system, generator`s outputs, network topology and other operating parameters. Practically, there is no analytical solution exists for solving the problem of stability. On the other hand, there are techniques available to obtain an acceptable approximate solution of such a problem, known as digital simulation. Runge-kutta method is one of these techniques which has been used broadly as it calculates every step in a sequence of sub-steps. The method relies on a complex mathematical modelling of the synchronous generator with the help of Park-Gorev`s transformation, for the sake of simplicity and intuitiveness the method is used to analyse and study the complex equations of the three-phase synchronous generator. Generally, the system is said to be stable if the opposing forces within it are balanced and at a perfect equilibrium. The aims of this research are to establish the effects of synchronous generator`s design and transient conditions upon power system stability with the help of Embedded Microsoft Excel Sheet based on Power System Stability Analysis (EMES-PSS), using the Runge-Kutta integration method. The study has proved that EMES-PSS can find the limits of Salient and Non-Salient machines stability when changing their essential parameters. The optimisation solutions of the power system stability problem can be achieved by using basic computational resources. The software can also be used on a number of modern tablets e.g., Apple`s tablets.

과도안정도와 미소신호안정도 관점에서 국내 전력계통의 임계관성계수 평가

The increase of inverter-based renewable energy sources reduces inertia constant of power systems and the loss of the system inertia may cause power system stability problems. To ensure a secure energy delivery system, these problems should be analyzed thoroughly from various perspectives about power system stability. This paper presents the estimation of the critical inertia of Korean power systems, which is the minimum amount of inertia required to maintain power system dynamic securities. The estimation has been made by gradually reducing the system inertia of Korean power systems and then by analyzing the change of dynamic securities in terms of transient and small signal stabilities. In the transient stability aspect, the decrease of critical clearing time(CCT) has been analyzed with four different reduced inertial models of Korean power systems. With the small signal stability perspective, the change of the system damping ratio has been studied. Based on the results from the stability studies, the critical inertia has been determined and it can be considered as the indirect limit of renewable energy shares in Korean power systems.