Power System Voltage Stability Research Articles

Power system harmonic analysis with real geomagnetically induced current from the 2003 halloween storm

It is well understood that geomagnetically induced currents (GICs) flow through the grounded neutrals of wye-connected transformers, generating harmonic currents that flow along frequency-dependent transmission lines. Harmonic currents affect protection systems and cause harmonic voltage drops that disturb power system voltage stability. In the literature, GICs are modelled as dc-currents for harmonic analysis. However, GICs are multi-frequency currents having both positive and negative polarities. Therefore, a representative harmonic analysis of power systems is only possible when GICs are modelled as multi-frequency AC currents. In this paper, the authors subjected a multi-machine power system model to real GICs from the 2003 halloween storm. Representative time intervals within the storm were selected, and a harmonic analysis of transmission line and generator stator currents was carried out. The results showed that the harmonic spectrum of currents fluctuated with a real GIC instead of reaching a steady state with a DC model for GIC. Moreover, harmonics induced on generator windings increase the risk of dynamic voltage and power system instability. The results confirm the susceptibility of power system generators to GICs and validate the use of synthetic GIC for modelling the effect of power system stability.

Improvement of voltage stability and loadability of power system employing the placement of unified power flow controller using artificial neural network

<span lang="EN-US">This paper proposes a voltage stability and loadability improvement model of power systems by incorporating the optimal placement of flexible alternating current transmission systems (FACTS) using an artificial neural network (ANN) called OPFANN. The key aspect of this model is to identify the weakest lines which having the most probability of voltage collapse utilized for placing FACTS devices. As installing a new power system network with rapidly increasing power demand cannot be possible, the operator usually operates the power system close to the stability limit. In this regard, continuous monitoring and improvement of system voltage stability and loadability of the existing system are vital issues for energy management systems nowadays. However, the proposed OPFANN introduces a more straightforward and faster scheme for voltage stability monitoring systems using ANN. Intelligent and reliable data samples have been designed to train the ANN based on two-line voltage stability indices (LVSI) techniques. Compared with other works, OPFANN effectively improves voltage stability and loadability at the load point by installing the unified power flow controller (UPFC) FACTS devices to the weakest lines. OPFANN can provide information on voltage collapse points using ANN and reduce the further computational cost of LVSI. Finally, OPFANN ensures faster and more secure operation of the power system.</span>

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.

Clustering Combined Multi-Objective Optimal Operation of Transmission Systems Considering Voltage Stability

In recent years, power systems have undergone major changes called energy transitions during which synchronous generators have been replaced with power electronics-based generation. Therefore, the voltage stability of power systems has become a major concern owing to the absence of synchronous generators. This study proposes multi-objective optimization using the non-dominated sorting genetic algorithm III to achieve optimal reactive power reserve procurement and improve the voltage stability of the overall system. These systematic approaches require high computational power and are unsuitable for the operational frameworks currently used for large-scale power systems. Previous works have rarely considered the local characteristics of reactive power or generation de-commitment with sufficient re-dispatch owing to greater renewable energy integration. We propose a framework for achieving systematic optimization by considering various objective functions while utilizing the regional aspect of reactive power via spectral clustering-based voltage control area (VCA) identification. The proposed method comprises systematic and regional approaches to optimizing systems for voltage stability improvement based on VCAs. The results demonstrate that the proposed method shows satisfactory performance. These results will be helpful for decision making for power system operations in harsher environments with more renewable energy.

A short-term voltage stability online assessment based on multi-layer perceptron learning

In this paper, a deep learning-based approach is used to analyze short-term voltage stability of power systems in order to completely learn the hidden timely dependencies from post fault behavior of the system. The direct measurements from the PMU, which did not require any significant amount of computation, have been used, and the results will be accurate. The proposed approach makes considerable use of a Multi-Layer Perceptron-based deep learning model in order to make the most accurate prediction feasible regarding the short-term voltage stability status. Rapid prediction of voltage stability allowed system operators sufficient time to take effective corrective action against large disturbances. In-depth offline simulations will be executed against various fault types, with the results being fed into the classifier as inputs. After the classifier has been trained using the results of the offline simulations, the online application will be applied to the test samples. The effectiveness of the suggested method will be evaluated based on the results of tests conducted on both small and large-scale test systems.

Analysis of overvoltage reactive power margin for future power systems with renewable energy generation

As modern power systems continue to adopt wide usage of Renewable Energy (RE) sources, the reliance on conventional generators is slowly reducing. Countries are adopting new energy policies to speed up the transition of future power systems to a fully renewable and clean system, and this is centered around the increase of RE penetration to reduce carbon emissions. However, it is expected that this transition will be met with stability issues due to the intermittent nature of REs and reduction of conventional generators. In recognition of these expected complications for the future systems, an analysis method is proposed in this paper to identify critical buses in terms of voltage stability for power systems with high RE penetration level. A new method that utilizes both modified continuation power flow and Q-V analysis to determine acceptable reactive power margins for each bus considering the intermittency of RE sources is presented in this study. This work is focused on the future Korea Power Systems with 16.05 GW of renewable energy. Considering different RE levels and loading conditions, several scenarios are studied to identify the voltage stability in the different Korea regions with a high penetration of RE. The resulting reactive power margins can be used to prevent overvoltage through the identification of weak and vulnerable buses for the future power systems.

Multi-task transient stability assessment of power system based on graph neural network with interpretable attribution analysis

Transient power angle stability analysis and voltage stability analysis are the key basis of power system security and stability control. The diversified operation modes of power system put forward higher requirements for real-time and topology generalization of transient stability assessment. Based on Convolution Neural Network (CNN) and Graph Attention Networks (GAT), this paper uses the wide-area transient response features to evaluate the transient angle stability and voltage stability of power system. Firstly, CNN is used to encode the temporal variation characteristics of transient features of electrical components in hidden layer space. Secondly, the encoded hidden layer features are mapped into graph data samples according to the spatial topological correlation of electrical components, so as to train and build a multi-task transient stability assessment model based on GAT. The model can adaptively capture the interaction relationship between encoded hidden layer features of topologically correlated components, and realizes real-time evaluation of transient angle stability and transient voltage stability by perceiving the temporal–spatial correlation of transient features. Finally, Shapley additive explanation (SHAP) method is used to explain the decision-making mechanism of the model and extract the key features that affect the transient stability, so as to enhance the ability of power grid operators to perceive the transient stability situation. The results of IEEE-39 system show that the transient stability assessment model has good accuracy and topology generalization, and the results of interpretable analysis are in line with the conclusions of traditional mechanism cognition, which helps to improve the credibility of the model results.

Multi-objective reactive power optimization strategy of power system considering large-scale renewable integration

To fully tap the abilities of renewables in reactive power optimization, this paper develops a detailed model for the power regulation capabilities of wind turbines and photovoltaic units and studies their impact on the power system’s operation. First, the power system model with renewables integration is established using AC power flow. The wind turbines and photovoltaic units are modeled in detail according to their topologies and operating characteristics, and then further simplified according to the feasible region. An improved DC power flow model is adopted to handle the non-linear characteristics of the power system. On this basis, a multi-objective reactive power optimization model is constructed to minimize the power generation cost, wind and solar power curtailment, and voltage offset. Finally, comparisons between two types of models in different scenarios are designed. Numerical simulations demonstrate that the participation of renewables in reactive power regulation can improve the operational economy and voltage stability of power systems.

A virtual synchronous generator control method for remote island power system considering dynamic voltage stability

Remote island power systems are difficult to install renewable energy sources (RES) because of the small system capacity and the large impact of intermittency of RES. Virtual synchronous generators (VSG) can equip inverters with the inertia of synchronous generators and can suppress frequency and voltage fluctuations. This paper proposes a VSG control method for dynamic voltage stability in remote island power systems. In conventional VSG control methods, the command of active and reactive power is determined by the Droop characteristics of frequency and transmission line voltage. However, the command are not based on dynamic voltage stability indices. Therefore, the compensation amount of active and reactive power is inappropriate. The proposed method determines the command of active and reactive power based on dynamic voltage stability indices. The dynamic voltage stability index considers the critical boundary index (CBI). The CBI is defined as the distance between the operating point of active and reactive power flowing through a transmission line and the stability limit curve calculated from the power flow between two bus lines. The proposed method improves dynamic voltage stability by determining power command so that the operating points of active and reactive power are closer to the origin direction. Simulation verification is performed for load increase and three-phase ground fault. In the three-phase ground-fault simulation, FRT requirements are considered to verify continued operation and the case of gate blocking. The conventional Droop control and the proposed method are compared for the case of continued operation with FRT requirements during load increase and ground fault. Simulation verification results show that the proposed method improves the dynamic voltage stability compared to the conventional method. Furthermore, it is shown that the proposed method is capable of stable continuous operation of the system even after a transmission line failure considering the FRT requirement.

Voltage stability assessment for solar photovoltaic penetration using Reactive Power–Voltage and Active Power–Voltage modal analysis

The assessment of voltage stability in a power system is crucial to ensure all buses in the network can maintain the desired voltage or avoid maximum loadability when subjected to load disturbance. Current research has tended to concentrate on developing new voltage stability assessment tools rather than identifying the best location for the penetration of solar photovoltaic (SP) generation in the network. This paper examines and evaluate the power systems voltage stability with increasing SP penetration levels by employing both the Active Power–Voltage (PV) and Reactive Power–Voltage (QV) modal analysis. The effect of load flow study by penetrating SP at the weakest and the strongest load bus has been investigated in this work. Furthermore, the analysis in this work was carried out in the modified Brunei Darussalam Department of Electrical Services (DES) power system. The main contribution of this paper is to assess and identify the best and worst locations for SP penetration in the simplified DES power system network in Brunei Darussalam using both the QV and PV modal analysis. The load flow results show that the penetration of SP generation is much better at the strongest bus due to it does not influence other load buses as compared to the least reliable bus in the network.

A Power System Reserve Configuration Solution That Satisfies the Frequency Stability Constraint Under the Given New Energy Index

Aiming at the problem of frequency stability and voltage stability of a new power system, this paper provides a new energy index method based on frequency stability constraints in the standby category of the new power system. Several concepts, such as maximum disturbance constraint and minimum reserve capacity, are proposed. Two constraints, power balance, and frequency constraint are set, and the factors to be considered, such as load frequency effect, security and control measure, demand-side response, and primary frequency change amplitude of each type of unit, are specified. Through analysis and study of regional data, the peak load of power grid new energy is a given index in a given scenario, according to the research of regional power grid in each category of a frequency modulation amplitude, the installed capacity is set to build a solution, to the problem of frequency stability caused by clean energy consumption, thus determine the ratio of each category of power output and heat capacity. Finally, according to the actual data of one regional power grid, the PSD-BPA power system simulation software is used to verify the effectiveness of the method.

Improvement of power system stability in wind connected generator by using PSAT

Voltage stability in power systems is a major problem that receives international attention. An open and free source piece of software, Power System Analysis Toolbox (PSAT) is used in this study to create a model of modified IEEE 14 bus system. Models of two recently created wind turbines—the Squirrel Cage Induction Generator (SCIG) and Doubly Fed Induction Generator (DFIG)—are connected to a modified IEEE 14 bus system. The stability of the power system is examined in this work in relation to the effects of Squirrel Cage Induction Generator (SCIG) and Doubly Fed Induction Generators (DFIG). Here, both DFIG and SCIG, which have variable speeds, are regarded as wind generators. In this work, a small signal stability investigation using SCIG and DFIG wind turbine systems was carried out on a modified IEEE 14 bus system. The results of their simulation were analysed.

The Impact of Serial Controllable FACTS Devices on Voltage Stability

As the world's population continues to grow, the demand for electricity is also increasing rapidly. Ensuring the quality of power supply, voltage stability, unity power factor, and minimizing power losses is essential for delivering power to every user end. In order to achieve this, compensation techniques are needed. This project focuses on Serial controllable Flexible AC Transmission Systems (FACTS) devices, such as Controllable Series Compensator (CSC) and Static Synchronous Series Compensator (SSSC), which have a significant impact on the voltage and power stability of an electric power system (EPS). The mathematical derivation of the voltage dependency of CSC and SSSC is extracted for the single-load infinitive-bus model (SLIB). New analytical equations are developed to compare the impact of CSC and SSSC on voltage stability in a five-bus system. The results of the analysis are expected to reveal that CSC has a crucial role to play in enhancing voltage stability, and its impact is greater than that of SSSC when considering equal CSC and SSSC MVA ratings. When it comes to voltage controllability, SSSC (Static synchronous series compensator) is superior to CSC (Controllable Series Compensator), especially in situations where there are having low voltages or having low loads.

Innovative AVR-LFC Design for a Multi-Area Power System Using Hybrid Fractional-Order PI and PIDD2 Controllers Based on Dandelion Optimizer

In this article, the problem of voltage and frequency stability in a hybrid multi-area power system including renewable energy sources (RES) and electric vehicles has been investigated. Fractional order systems have been used to design innovative controllers for both load frequency control (LFC) and automatic voltage regulator (AVR) based on the combination of fractional order proportional-integral and proportional-integral-derivative plus double derivative (FOPI–PIDD2). Here, the dandelion optimizer (DO) algorithm is used to optimize the proposed FOPI–PIDD2 controller to stabilize the voltage and frequency of the system. Finally, the results of simulations performed on MATLAB/Simulink show fast, stable, and robust performance based on sensitivity analysis, as well as the superiority of the proposed optimal control strategy in damping frequency fluctuations and active power, exchanged between areas when faced with step changes in load, the changes in the generation rate of units, and the uncertainties caused by the wide changes of dynamic values.

Optimal Placement and Size of SVC with Cost-Effective Function Using Genetic Algorithm for Voltage Profile Improvement in Renewable Integrated Power Systems

Given the concern for maintaining voltage stability in power systems integrated with renewable power systems due to a mismatch in generation and demand, there remains a need to invoke flexible alternating current transmission system (FACTS) devices in the distribution network. The present paper deals with identifying the locations of placement of a static var compensator in an experimental IEEE 14-bus system; the voltage drop in different buses in an IEEE 14-bus system is calculated by the standard formula. The total voltage drop in the network (TVDN) is also calculated as a reference. The ranking of buses in order of decreasing voltage drop is made, and the weak buses are identified as those showing the maximum or near-maximum voltage drop for the installation of a Static Var Compensator (SVC). The optimum usable size is calculated using a Genetic Algorithm approach to optimize the installation cost. After size optimization, installing a 2 MW solar generator is considered for the weak and most potential bus, which suffers from voltage drops or power loss. Based on the generator at the weakest bus, the total power loss in the network is calculated and compared with a similar method to assess the efficiency of the proposed model. Thus, the voltage stability enhancement problem is solved by applying a Genetic algorithm (GA) to optimize SVC size and using the Total Voltage Drop in Network (TVDN) method to identify weak buses in the systems. It is found that the performance of the proposed system is comparable with another existing system. It is further observed that a gain in power loss to 6.56% is achievable by adopting the proposed strategy, and the gain is better than the other system.

A Review on Power System Voltage Stability with Limitation of an On Load Tap Changing Transformer

Voltage stability of power systems reflects challenges to the power system operators due to its effect on the power systems components performances. Therefore, many solutions were invented in order to keep the systems within the voltage stability accepted limits. Because of the huge expansion of the power grids and the different loads natures on the grids, many techniques and solutions are used. The On Load Tap Changing Transformer (OLTC) was one of those techniques. In this paper, a review of past works that deal with the voltage stability limits, voltage stability improvement ways, OLTC types, the OLTC reverse action, and OLTC effect on voltage stability, in addition to several ways that make the OLTC work better. are discussed. The paper also sheds the light on the possible ways that may be employed to prevent the OLTC reverse action.

A Review on Power System Voltage Stability with Limitation of an On Load Tap Changing Transformer

A Review on Power System Voltage Stability with Limitation of an On Load Tap Changing Transformer

Novel Relative Slip Based Under-Voltage Load Shedding Protection Scheme to Mitigate FIDVR

Induction motors play a vital role in the voltage stability of power systems. This role would become more significant after clearing short-circuit faults in which the system voltage slowly recovers with a time delay referred to as fault-induced delayed voltage recovery (FIDVR). The FIDVR phenomenon can be classified into the stable and unstable types. To preserve network stability and reliability, the under-voltage load shedding (UVLS) protection schemes should i) be secure for the stable case and ii) quickly remove the disturbed loads for the unstable case. To do this, a new decentralized UVLS protection scheme against FIDVR events is proposed in this paper. A novel concept named relative slip, which is equal to the ratio of the motor slip to the critical one is developed. Using the proposed concept, the behavior of motor loads during stable and unstable regions can be discriminated. Since the proposed index can be exploited just by using the electrical signals, it can be simply implemented in the UVLS schemes without requiring any additional information and infrastructure. To evaluate the efficiency of the proposed method, multiple test systems are considered. Based on various simulation studies, the proposed UVLS scheme can superiorly preserve system voltage stability.

Coordinated voltage control for improved power system voltage stability by incorporating the reactive power reserve from wind farms

The absorption and output characteristics of reactive power of the doubly-fed induction generator (DFIG) greatly influence the voltage stability of PCC (Point of Common Coupling) where the wind farms are integrated into the bulk power grid. This study proposes a reactive power compensation strategy for coordinated voltage control (CVC) of PCC with large-scale wind farms to achieve the expected voltage quality of the power grid through a minimum amount of control actions in emergencies. To this end, the mechanism of reactive power and voltage control inside DFIG is first analyzed. Then, the concept of reactive power reserve (RPR) sensitivity concerning control actions is introduced and an index of voltage stability margin is proposed to evaluate and analyze the distance between the current operating point and the voltage collapse point by analyzing the relationship between reactive power reserve and voltage stability margin. In the event of an emergency, critical reactive power reserves are obtained to reduce the dimension and complexity of the control problem. The sensitivity of reactive power reserve and the control are formulated into a convex quadratic programming problem to optimize the control strategies for voltage stability. The proposed technology has been validated on the IEEE 39-bus system.

Static Voltage Stability Assessment of Ethiopian power System Using Normalized Active Power Margin Index

Voltage stability assessments, made so far on the Ethiopian electric power system (EEP), are limited both in number and in methodology. Here, in this paper the static voltage stability of the Ethiopian power system is investigated using an index called normalized active power margin. The methodology starts from determining Thevenin equivalent of a system as viewed from the load buses. The Thevenin equivalent parameters help to determine the load bus maximum active power transfer limit and to draw the PV relation curves. The approach avoids the time-consuming method of PV curve based maximum active power transfer determination, which requires large number of power flow computations. The resulting maximum active power transfer and current operating active power load are used for the index calculation. The index is tested using IEEE 30 bus system and produced results matching with other previously established indices. The index is capable of ranking vulnerability of load buses to voltage instability. Then, scenarios of heavy load and light load EEP cases, with and without system reactive power compensation, are investigated. Results reveal weakest buses are supplied from 66kV transmission lines, load bus 232 being the weakest of all. On the other hand, the most stable buses are supplied from 132 kV transmission lines, bus 149 being the most stable bus. PV curves drawn, also, reveal the improvement that come with reactive power compensation and with operating in light load condition.