Power System Voltage Stability Research Articles

Research on Applicability of the Practical Transient Voltage Stability Criterion Based on Voltage Magnitude and Sag Duration

Voltage sags threaten the transient voltage stability of power systems. To evaluate the transient voltage stability, practical criteria based on voltage magnitude and sag duration are widely used in practical engineering. However, the applicability of practical criteria needs to be studied. In this paper, in a single-load system, a theoretical derivation was first made to obtain the transient voltage stability boundary. Then, by studying the relationship between the practical criteria and the stability boundary, the application scope of the practical criteria was determined. The application scope described in this paper can guide operators to use the practical criteria correctly and avoid misjudgment of the transient voltage stability as much as possible. Finally, a case study based on PSCAD/EMTDC is presented, and the simulation results verified the conclusions proposed in this paper.

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.

Power System Voltage Stability analysis with Renewable power Integration

The purpose of this research is to find the loading limit of a power system before hitting voltage instability and to assess the margin to voltage instability of a system consisting of a wind farm. An index called Bus Apparent Power Difference Criterion (BSDC) is used to find maximum loadable point. The measure depends on the way that in the region of the voltage collapse no extra apparent power can be delivered to the affected bus. The analysis is performed combination of wind power injection at different wind speeds and line outages in the network. In the feasibility and siting studies of wind farms the steady state analysis with network contingencies give the utility or the developer a sense of network condition upon the injection of power in the network. However, the extent of voltage stability impacted due to load growth in the system is not assessed. The research paper makes way to assess the impact on voltage stability margin with obtaining the maximum loadable point of the system and assessing the best suited bus to integrate a wind farm into the system.

Investigation with UPFC-Fuel Cellof Steady and Transient Voltage Stability in Power Systems

Güç sistemlerinin sürekli ve geçici durum çalışmalarında Esnek AC İletim Sistemi (FACTS) cihazları tercih edilmektedir. FACTS cihazları içerisinde kontrol etme yeteneği en güçlü olan Birleştirilmiş Güç Akışı Kontrolü (UPFC)’dir. UPFC bara gerilimlerini reaktif güce bağlı olarak kontrol ederken, iletim hattını empedans ve akıma göre kontrol etmektedir. Bu çalışmada, Uluslararası Elektrik Elektronik Mühendisliği (IEEE) 14 baralı güç sisteminde UPFC’nin statik ve dinamik gerilim kararlılığı analizleri gerçekleştirilmiştir. Sürekli ve geçici durum için gerilim kararlılığı çalışma limitlerinin geliştirilmesi ve sistemin kararlı bölgede kalması için UPFC ile birlikte Enerji Depolama Sistemi (EDS) elemanlarından yakıt hücresi kullanılmıştır. UPFC-EDS ile sistemin gerilim-maksimum yüklenme parametre değerlerinin yanı sıra bara gerilim profilleri analiz edilmiştir. UPFC ile yakıt hücresinin birlikte kullanılması durumunda sistemin yüklenme parametre değerinin arttığı ve bara gerilim profillerinin iyileştiği görülmüştür.

Optimized Energy Storage System Configuration for Voltage Regulation of Distribution Network With PV Access

With the large-scale integration of renewable energy such as wind power and PV, it is necessary to maintain the voltage stability of power systems while increasing the use of intermittent renewable energy sources. The rapid development of energy storage technologies permits the deployment of energy storage systems (ESS) for voltage regulation support. This paper develops an ESS optimization method to estimate the optimal capacity and locations of distributed ESS supporting the voltage regulation of a distribution network. The electrical elements of the network integrated with PV and ESS are first modelled to simulate the voltage profile of the network. Then an improved multi-objective particle swarm optimization (PSO) algorithm is employed to minimise a weighted sum of the overall nodal voltage deviation from the nominal level across the network and across the time horizon and the energy capacity of ESS reflecting the associated investment. The improved PSO algorithm adaptively adjusts the inertia weight associated with each particle based on its distance from the best known particle of the population and introduces the cross-mutation operation for a small distance to avoid falling into local optimal solutions. Then the dynamic dense distance arrangement is taken to update the non-inferior solution set and indicate potential global optimal solutions so as to keep the scale and uniformity of the optimal Pareto solution set. To mitigate the impact of decision makers’ preference, the information entropy based technique for order of preference by similarity to ideal solution is used to select the optimal combination of the ESS access scheme and capacity from the Pareto solution set. The proposed ESS optimization method is tested based on the IEEE 24-bus system with additional imports from high-voltage power supply. The voltage profile of the network simulated without the ESS or with the random or optimized ESS placement is compared to illustrate the effectiveness of the optimized ESS in performing voltage regulation under normal operation and supporting emergency power supply during high-voltage transmission failures.

Voltage stability analysis of power systems with a large number of non-synchronous machine sources connected

Compared with synchronous generators, the steady-state and dynamic characteristics of non-synchronous machine sources represented by line commutated converters (LCC) and voltage source converters (VSC) are quite different. The voltage stability of power systems will be changed when a large number of non-synchronous machine sources (NSMS) are connected. The voltage stability of power systems with NSMSs connected is analyzed in this paper. Firstly, based on the relationship between the Jacobian matrix singularity and the small disturbance voltage stability (SDVS), the impact of NSMSs on the SDVS of active systems is analyzed. Secondly, whether there is a reasonable voltage solution in the transient process is taken as a large-disturbance voltage stability (LDVS) criterion, the impact of NSMSs on the LDVS of active systems is studied. Thirdly, for a special scenario where the VSC supplies power to a passive system, the requirements of the voltage stability on load types and VSC parameters are discussed. Finally, based on the Power System Simulator/Engineering (PSS/E), simulations are carried out in the Shanghai power system and a passive power system, and the theoretical analysis results are verified.

Improving Voltage Stability of Electrical Power System by Optimal Location of FACTS Devices Using an Evolutionary Method

In the present work, a new approach for improving voltage stability by optimal location of the Flexible AC Transmission Systems (FACTS) devices has been discussed. We used Genetic Algorithm (GA) as an optimization technique to search the good placements of different FACTS systems in great electrical networks and its contribution to enhance voltage stability. Various FACTS devices were used in our study such as SVC, TCSC, SSSC, STATCOM, TCVR, TCPST and UPFC. The search of optimal parameters of those devices has been also investigated. The method presented in the paper was tested by using Matlab/environment. In addition, the proposed method has been implemented and tested on various IEEE power systems; 14Bus, 57Bus, and 118Bus. The obtained results show the validity of the proposed method.

Island Power Systems With High Levels of Inverter-Based Resources: Stability and Reliability Challenges

As many island power systems seek to integrate high levels of renewable energy, they face new challenges on top of the existing difficulties of operating an isolated grid. With their drastically declining cost, variable renewables, such as wind and photovoltaics (PVs), are increasingly being integrated into island grids to reduce the use of imported fuels. These deployments of renewable energy are dominated by PV and wind generators, which bring unique challenges of their own. While the integration issues span numerous timescales (from microseconds to many months), this article focuses on reliability and stability challenges on short timescales (microseconds to seconds). In other words, we seek to answer (to the extent that it is currently known) how to ensure the frequency and voltage stability in an island power system with very high instantaneous levels of wind and PVs. And because island power systems are often among the first to reach these very high instantaneous levels of wind and PV generation, we note that they are forging a path for larger interconnected power systems to follow.

A simple method for estimating the effectiveness of reactive power‐based low‐voltage ride‐through support of the distributed energy resources

The increasing number of distributed energy resources (DERs) leads to the need for DER that can provide ancillary service, such as low-voltage ride-through (LVRT) voltage support. The support is made to improve the short-term voltage stability in power systems. Recently, DER LVRT voltage support through reactive power regulation are becoming common. Designing LVRT voltage support is highly influenced by the accuracy of the modelling and the data needed. However, in some cases, the required modelling can challenge the computational complexity, effort, and required data. Nevertheless, modelling the systems through an oversimplification may result in inaccuracies and hypothetical solution. Thus, the best compromise between model accuracy and simplicity will alleviate the problem. The study presents a methodology for estimating the effectiveness of the support. Unlike the commonly computer-assisted approach, such as the dynamic RMS simulation, the benefit of the methodology is on the computing process, which is much simpler since the dynamic DER modelling work is not needed, and the evaluation of the effectiveness can be achieved even when the grid information is incomplete. Its accuracy is validated against typical RMS simulation results obtained using PowerFactory DIgsilent software for well-characterised networks.

REACTIVE POWER ANALYSIS AT SOLAR POWER PLANT

Reactive power is essential to control the power system's voltage stability as the reactive power is directly proportional to the voltage. Hence, every new solar photovoltaic (PV) plant installed in the grid system must comply with the grid code requirements to ensure that the electricity supply remains stable and reliable. As the more penetration of PV plants, the electrical system will face some challenges related to reactive power control and voltage support. Thus, many countries including Malaysia have updated their grid codes to permit a smooth interaction between these new plants with the grid system. The inverter of PV solar connected to grid system are required to supply rated power output (MW) at point of common coupling (PCC) between the limits of 0.85 power factor lagging, and 0.95 leading follow to the Malaysian Grid Code (MGC) requirement. Hence, this research aims to design a controller for the PV inverter in Matlab/Simulink that able to absorb and supply the reactive power. Then, the comparison will execute between the simulation results and the MGC requirement. However, due to power loss in the system, the PV inverter controller may not comply with the reactive power capability as the MGC requirement. Thus, the PV system need to integrate with the capacitor bank as a reactive power compensator.

Voltage Stability of Power Systems with Renewable-Energy Inverter-Based Generators: A Review

The main purpose of developing microgrids (MGs) is to facilitate the integration of renewable energy sources (RESs) into the power grid. RESs are normally connected to the grid via power electronic inverters. As various types of RESs are increasingly being connected to the electrical power grid, power systems of the near future will have more inverter-based generators (IBGs) instead of synchronous machines. Since IBGs have significant differences in their characteristics compared to synchronous generators (SGs), particularly concerning their inertia and capability to provide reactive power, their impacts on the system dynamics are different compared to SGs. In particular, system stability analysis will require new approaches. As such, research is currently being conducted on the stability of power systems with the inclusion of IBGs. This review article is intended to be a preface to the Special Issue on Voltage Stability of Microgrids in Power Systems. It presents a comprehensive review of the literature on voltage stability of power systems with a relatively high percentage of IBGs in the generation mix of the system. As the research is developing rapidly in this field, it is understood that by the time that this article is published, and further in the future, there will be many more new developments in this area. Certainly, other articles in this special issue will highlight some other important aspects of the voltage stability of microgrids.

Data-Driven Short-Term Voltage Stability Assessment Using Convolutional Neural Networks Considering Data Anomalies and Localization

Short-term voltage stability of power systems is governed by load dynamics, especially the proportion of small induction motors prevalent in residential air-conditioners. It is essential to efficiently monitor short-term voltage stability in real-time by detailed data analytics on voltage measurements acquired from phasor measurement units (PMUs). It is likewise critical to identify the location of faults resulting in short-term voltage stability issues for effective remedial actions. This paper proposes a time-series deep learning framework using 1D-convolutional neural networks (1D-CNN) for real-time short-term voltage stability assessment (STVSA), which relies on a limited number of phasor measurement units (PMU) voltage samples. A two-stage STVSA application is proposed. The first stage comprises a 1D-CNN-based fast voltage collapse detector. The second stage comprises of 1D-CNN-based regressor to quantify the severity of the short-term voltage stability event. Two novel indices are presented, and their predicted future values are used to quantify the severity of short-term voltage stability events. This work also considers DB-SCAN clustering-based fault detection and physics-based fault localization for effective short-term voltage stability assessment and remedial actions by identifying the most critical PMUs. A bad data pre-processing technique is also included to mitigate the impact of missing data and outliers on short-term voltage stability assessment accuracy. The proposed framework is validated using the standard IEEE test systems and compared against other machine learning models to demonstrate the superiority of 1D-CNN-based time-series deep learning for short-term voltage stability assessment.

Analysis of the Voltage Stability of Power System with Large Wind Power Integration

Analysis of the Voltage Stability of Power System with Large Wind Power Integration

Induction motor: a new static model

Voltage stability in power system is largely determined by the characteristics of the load. In order to obtain reliable results in voltage stability, the load model must be represented as realistically as possible. The issue is even more challenging with static voltage stability techniques, because dynamic loads must be represented by static models. The commonly used static models are constant impedance, constant current, and constant power. A significant part of the load is made up of induction motors that are usually modeled as static constant power loads. Under variations of terminal voltage of the motor, this static model can approximately represent the active power, but it can commit major mistakes when representing the behavior of reactive power. Therefore, a new motor static model will be developed in this work.

Modified whale optimisation-based optimal location of UPQC in distribution system for power quality improvement

A number of researchers has studied the unified power quality conditioner (UPQC) as an eventual solution to enhance the power quality in the electrical distribution system. However, due to the high cost, the location or position of UPQC in distribution system needs to be decided with immense care and must preferably be solved as the optimisation problem. This paper presents a power quality improvement model based on a new modified optimisation algorithm, namely worst solution linked whale optimisation algorithm update (WS-WU). The proposed algorithm finds the optimal location of the UPQC device concerning the power system losses, UPQC cost, and voltage stability index as well. The experimentation is carried out in both IEEE 33 and 69 bus systems. The performance of the proposed model is compared over other conventional methods in terms of performance and convergence analysis, and proves the superiority of the proposed method.

A super-resolution perception-based incremental learning approach for power system voltage stability assessment with missing PMU measurements

This paper develops a fully data-driven, missing-data tolerant method for post-fault short-term voltage stability (STVS) assessment of power system against the incomplete PMU measurements. The super-resolution perception (SRP), based on deep residual learning convolutional neural network, is employed to cope with the missing PMU measurements. The incremental broad learning (BL) is used to rapidly update the model to maintain and enhance the online application performance. Different from state-of-the-art methods, the proposed method is fully data-driven and can fill up missing data under any PMU placement information loss and network topology change scenario. Simulation results demonstrate that the proposed method has the best performance in terms of STVS assessment accuracy and missing-data tolerance among the existing methods on the benchmark testing system.

OPTIMIZED MAXIMUM LOADABILITY OF POWER SYSTEMS USING AN ENHANCED DYNAMIC JAYA ALGORITHM

The problem of Maximum Loadability of power systems is addressed in this paper using a proposed dynamic JAYA algorithm. The maximum loadability problem is a typical optimization problem in which the maximum loadability point is to be determined optimally. Voltage stability of power systems is maintained by determining the estimated margin between the system operating point and the maximum loadability limit. The basic JAYA algorithm has been introduced to solve foremost optimization problems with small-scaled nature. However, when applied to large-scale, nonlinear and non-convex constrained problems, it showed a poor convergence characteristic. In order to deal with these weaknesses, the original algorithm has been improved by adding some dynamic features to its convergence behavior. The modified algorithm has been presented and validated when applied to well-known typical power systems. The obtained results were compared to the results achieved by other equivalent optimization techniques.

Research on power system static voltage stability considering geomagnetic disturbances effect

AbstractThe reactive power losses caused by the power grid Geomagnetically Induced Current (GIC) severely disturb the static voltage stability of power systems, and may even trigger voltage collapses. In this paper, the 1 V/km uniform induced geoelectric field is adopted to analyze how greatly geomagnetic disturbance (GMD) can influence the static voltage stability of power systems, given the features of GMD disasters hitting the power grids of China. Considering the GIC reactive power losses, a method that combines second‐order sensitivity adaptive variable step size and local curve fitting is put forth to calculate the critical point of the active power and voltage nodes (PV) curve. With the increment ratio of the curve slope set at discretion, the method enables the curve to approach its critical point with great strides, a design managing to reduce the quantity of power flow calculations remarkably. By taking into account the reactive power violation of PV nodes in the acquisition of load increment step size, the method calculates the critical point of the PV curve in a much more accurate way. The method applied to the Northwest 750 kV power grid, the calculation results suggest that the 1 V/km induced geoelectric field markedly undermines the static voltage stability, thus posing grave threats to the above grid.

Impact of Wind Farms on Power System Voltage Stability (Dept.E)

Steady state analysis of wind turbine generating units (WTGUs) interconnected with the grid is needed as the use of WTGU are getting more popular and many new systems are being planted. In this paper, probabilistic voltage stability algorithm of WTGUs interconnected with the utility grid is developed via power Moy analysis where these units are modeled as P-Q bus(es) by detecting the collapse p oint on the Q-V curves. The developed algorithm also facilitates the computation of both the real and reactive power output of the fixed speed pitch regulated wind turbine at a specific site, wind turbine characteristics, wind speed and terminal voltage. The probabilistic nature of wind is considered by introducing the expected voltage stability margin is an index that combines both of the voltage stability and the wind distribution in one index. The proposed algorithm is implemented and applied on the IEEE 26-bus, voltage stability margin (VSM), and expected voltage stability margin (EYSM) are calculated at each wind speed. The accumulation of the EVSM over a specific period, can be considered as the system voltage stability margin which is a single value that can be compared with the voltage stability margin of the all-conventional power system.

Real-time simulation of static synchronous condenser (STATCOM) for compensation of reactive power

This paper presents a real time simulation stability of power system by static synchronous condenser (STATCOM) in modern platform real-time simulator named (RT-LAB) using the latest INTEL quad-core processors to simulate a relatively large power system In our work, We have to study the problem of controlling voltage and reactive power in electric system by static synchronous condenser (STATCOM). All the simulations for the above work have been carried out using MATLAB /Simulink and RT-LAB Various simulations have given very satisfactory results and we have successfully improved the voltage by injecting a FACTS device, which is the STATCOM, the Studies and Comparisons of real-time simulation results of the power system with and without STATCOM connected illustrate the effectiveness and capability of STATCOM in improving voltage stability in power system.