System Voltage Stability Research Articles

Voltage stability assessment using PMUs and STATCOM

<p class="Abstract">Since the previous few decades, researchers and utilities have been extremely concerned about voltage instability because to the numerous instances of system blackouts caused by voltage instability that have been recorded in various regions of the world. With the development of synchro phasor technology, it appears conceivable to track and manage the system's voltage stability in real time. This study suggests using phasor measuring units (PMUs) placed strategically to monitor voltage stability margin online and to regulate it using a static synchronous compensator (STATCOM). According to the minimum reactive and real power loanability for the most of the line outages, STATCOM has been installed at the critical bus. Based on the difference between the bus voltage and its reference value, STATCOM supplies reactive power into the bus. PMU measurements are used to determine bus voltages at regular intervals, and reactive power is then added to the bus online as necessary. The increased voltage stability margin brought on by STATCOM injecting reactive power is continuously checked. Based on simulations performed on the IEEE 14-bus system and the New England 39-bus system, the effectiveness of the suggested approach for online monitoring and management of voltage stability margin (VSM) has been proven.</p>

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.

Voltage Stability Analysis of Power System with Photovoltaic Power Plant

Photovoltaic power plants usually do not provide reactive power output; hence the application of large photovoltaics in power systems will decrease the voltage stability level of the power system. Capacitor banks can provide reactive power to compensate the photovoltaic plants; therefore, capacitor banks can overcome the reactive power deficiency of photovoltaic plants. However, the effect of capacitor bank installation on the system’s voltage stability is unknown. Therefore, the research aims to investigate whether installing a capacitors bank can restore the level of system voltage stability. The study employs the method of Voltage Stability Margin and transient stability simulation to the IEEE 9 bus system. The IEEE 9 bus system is modified where one generator of the system is replaced with a photovoltaic plant, and a capacitor bank is also installed. The study results show that the modified system voltage stability level is lower than the original system. When the capacity of the capacitor bank is increased to the maximum allowable value, the voltage stability level rises. However, it is still unable to be restored to its original value.

Energy Efficiency in Modern Power Systems Utilizing Advanced Incremental Particle Swarm Optimization–Based OPF

Since the power grid grows and the necessity for higher system efficiency is due to the increasing number of renewable energy penetrations, power system operators need a fast and efficient method of operating the power system. One of the main problems in a modern power system operation that needs to be resolved is optimal power flow (OPF). OPF is an efficient generator scheduling method to meet energy demands with the aim of minimizing the total production cost of power plants while maintaining system stability, security, and reliability. This paper proposes a new method to solve OPF by using incremental particle swarm optimization (IPSO). IPSO is a new algorithm of particle swarm optimization (PSO) that modifies the PSO structure by increasing the particle size, where each particle changes its position to determine its optimal position. The advantage of IPSO is that the population increases with each iteration so that the optimization process becomes faster. The results of the research on optimal power flow for energy generation costs, system voltage stability, and losses obtained by the IPSO method are superior to the conventional PSO method.

Study on voltage stability considering unified power flow controller

The access of the unified power flow controller (UPFC) can better meet the requirements of new power system construction with a high proportion of non-fossil energy and large-scale access, and it is more intelligent than the traditional control mode. Through the sensitivity analysis of the Jacobian matrix, the voltage stability of the power system before and after the access to the unified power flow controller is compared, and the simulation analysis in MATLAB/PSAT environment is adopted to simulate the IEEE9-bus system, showing that the access of UPFC achieves the effect of flexible control and can effectively improve the voltage stability of the system.

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.

Techno-economic multi-objective reactive power planning in integrated wind power system with improving voltage stability

• Suggesting a probabilistic multi-objective framework for the RPP problem. • Proposing a novel WT model that can dynamically control reactive power. • Exploring a modified operational cost formula for wind power generation. • Introducing a new bi-level multi-objective strategy to solve the RPP. Electrical power systems encounter a variety of challenges due to load growth and technological improvement; reactive power planning (RPP) and improvement of voltage stability (VS) are the two most significant ones. The integration of wind farms (WFs) into power networks has many advantages in terms of operation cost and emissions. But leads to voltage instability if it is not optimally sized, placed, and coordinated with VAR sources. In this study, a probabilistic multi-objective RPP framework is proposed for power systems with high penetration of WFs. A novel wind turbine model that can dynamically control reactive power is suggested based on the capability curve of a double-fed induction generator. A new bi-level optimization technique is introduced to address the problem considering the uncertainties of loads and wind power. Multi-objective genetic algorithm is employed at the upper level to optimally allocate VAR sources, and select the optimal locations of WFs to improve VS and decrease VAR sources’ costs. While at the lower level, the overall operation cost is minimized. A fuzzy min-max method is modified to find the optimum compromise solution. The results show that the proposed technique is effective in improving system VS and operation costs.

Optimal Allocation of STATCOM to Enhance Transient Stability Using Imperialist Competitive Algorithm

With the daily expansion of global energy consumption, developing the power grids is of uttermost importance. However, building a new transmission line is costly and time-consuming, so utilizing the same lines with possible higher transmission capacity is very cost-effective. In this regard, to increase the capacity of the transmission lines, the flexible alternating current transmission system (FACTS) has been widely used in power grids in recent years by industrialized countries. One of the essential topics in electrical power systems is the reactive power compensation, and the FACTS plays a significant role in controlling the reactive power current in the power grid and the system voltage oscillations and stability. When a static synchronous compensator (STATCOM) is embedded in a power system to increase the bus voltage, a supplementary damping controller can be designed to enhance the system oscillation damping. Given the expansion of the grids in the power system, the complexity of their optimization and the extraordinary ability of the imperialist competitive algorithm (ICA) for solving such problems, in this paper, the ICA has been used to determine the optimal position and size of the FACTS devices.

A new line stability index for voltage stability analysis based on line loading

Voltage stability has always been a very important issue in the planning and operation of pow- er systems, but today it is much more serious. Power systems are in a transition period. The conventional centralized configuration of the power system has been transforming into a de- centralized and deregulated form. The electrification of different sectors is accelerating the increase in demand for electrical energy. Increasing energy demand, differentiating consump- tion profiles, and diversifying consumers have made power system operations more complex. All these transformations take place in the shadow of rising economic and environmental con- cerns. Therefore, a general approach has been adopted to derive the greatest possible benefit from existing systems, rather than constructing new facilities. As a result, it is aimed to operate the systems close to limit values as much as possible. The voltage stability of systems operating close to the limit values needs to be examined more precisely. There are many voltage stability indices in the literature. However, most of them are based on various ignorance or assumptions. In this study, a new index is proposed, which is based on line loading and considering multiple line parameters. It has been observed that the suggested index gives consistent results in all varying conditions and different loading types.

A two-stage bidirectional DC-DC converter system and its control strategy

With the development of more-electric aircrafts, bidirectional DC-DC converter has been widely used in this field. In order to improve the voltage regulation range and stability of the bidirectional DC-DC converter system, a two-stage bidirectional DC-DC converter with some operation modes is used and analyzed in this paper. The converter is composed of a four-switch buck-boost circuit and an isolated CLLC resonant circuit, where all MOSFETs can realize soft switching action. The four-switch buck-boost circuit regulates the output voltage in a certain range through the duty cycle control, and the CLLC resonant circuit can control the output voltage by changing its switching frequency, where the two-stage bidirectional DC-DC converter adopts voltage closed-loop control strategy to realize the stable voltage output. Due to the existence of the intermediate part conversion voltage, the converter has three-port network characteristics, which makes it applicable to the working occasions with multiple voltage levels. The feasibility of this two-stage bidirectional DC-DC converter system combined with control strategy and its three-port operation used for more-electric aircraft power system are verified by simulation analysis.

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.

Maximization of System Load-Ability and Voltage Stability Index Using Distribution Based Salp Swarm Optimization

Flexible Alternating Current Transmission Systems (FACTS) play a very prominent role in enhancing the performance of power system networks and in the quality up-gradation of power system by stabilizing the system parameters like voltage deviation, system security, power loss and system load-ability being a few to name. This work therefore handles two of the important performance parameters of a power system network namely power flow which is modeled as the System Load-ability (SL) and voltage profile which is represented as Voltage Stability Index (VSI). In this paper the maximization of VSI and SL of IEEE 30 Bus and 57 Bus networks have been exploited through the optimal placement of Thyristor Controlled Series Capacitor (TCSC), Static VAR Compensator (SVC) and Unified Power Flow Controller (UPFC) in the networks using the proposed and enhanced form of a recently developed meta-heuristic technique named as Salp Swarm Optimization (SSO). The outcomes of the simulations have been scrutinized with an established swarm-based optimization procedure.

Reactive power optimization for distribution network system with wind power based on improved multi-objective particle swarm optimization algorithm

• In the multi-objective particle swarm optimization algorithm, the adaptive mesh is introduced to reflect the density of particles, and according to the density information, the global optimal particles are selected by roulette mechanism and the scale of external repository is maintained, which effectively ensures the uniformity and diversity of Pareto frontier distribution. • The proposed IMOPSOA has faster convergence speed and shorter average computing time than NSGA-II algorithm, can get Pareto frontier with better distribution and better results, which makes the voltage stability of the distribution network system with wind power higher. Aiming at the uncertainty of the grid-connected output of wind turbines, a scenario analysis method based on probability occurrence is used to transform the uncertainty model into multi scenario problems with different occurrence probabilities, a reactive power optimization model is established with the goal of minimizing the active power network loss and voltage deviation. Aiming at the poor diversity of Pareto frontiers obtained by traditional methods, an improved multi-objective particle swarm optimization algorithm is proposed. The algorithm uses adaptive grids to obtain the density of particles in external archives, selects the global optimal particle and maintains the scale of the external repository according to the density information using a roulette mechanism, effectively ensuring the uniformity and diversity of the Pareto frontier distribution. The algorithm is used to calculate reactive power optimization of the IEEE 33-bus system with wind power, and compared with the existing NSGA-Ⅱ algorithm. The results show that the Pareto frontier obtained by the proposed algorithm is better, the voltage stability and active power loss reduction rate of the distribution network system with wind power is higher.

A novel distance‐based system reactive power index for system‐level reactive power reserve assessment

AbstractVoltage stability of the power system is of major concern with ever‐increasing stress in the transmission network. The availability of ample reactive power reserve is essential to ensure voltage stability of the power system. Voltage stability and status of reactive power reserves can be monitored in real‐time by using synchrophasor measurements at a very fast reporting rate. Although much attention has been given to online voltage stability monitoring, there has been less focus on real‐time monitoring of reactive power reserve status. In this regard, the major contributions of the study are: (i) development of a novel distance‐based generalised approach for the computation of the system reactive power index, (ii) a proactive methodology for identification and impact estimation of the nearest Q‐limit breach and (iii) formulation of an optimisation problem to identify the limited number of critical generators that need PMUs for accurately predicting the value of the proposed index. The proposed scheme looks at the reactive power reserve of the generators in the network as numerical features. The istance between the base case and nose point numerical features is computed offline. The distance between the current operating point and nose point numerical features can be computed in an online manner. The ratio of these two distance measures is proposed as a system reactive power index. Moreover, a methodology to predict the post‐Q limit breach value of the index is also introduced. The proposed approach can be used with PMUs, linear state estimators or traditional SCADA measurements. Case studies for IEEE 57 and 118 bus test systems are presented to validate the performance of the proposed index.

Voltage Profile Improvement by Integrating Renewable Resources with Utility Grid

There are three main parts of an electric power system—power generation, transmission, and distribution. For electric companies, it is a tough challenge to reduce losses of the power system and deliver lossless and reliable power from the generating station to the consumer end. Nowadays, modern power systems are more complex due to gradually increasing loads. In the electrical power system, especially in transmission and distribution networks, there are power losses due to many reasons such as overloading of the line, long distribution lines, low power factors, corona losses, and unsuitable conductor size. The main performance factor of the power system is reliability. Reliability means continuity of the power supply without any interruptions from the generating station to the demand side. Thus, due to these power losses, there are voltage stability problems and economic losses in the electrical system. The voltage stability of the power system can be increased by improving the voltage profile. In this paper, different techniques are analyzed that include the integration of wind power, the integration of photovoltaic power, and reactive power injection by integrating FACTS devices. These techniques are applied to the IEEE 57 bus system with standard data using simulation models developed in MATLAB. Thus, the results of the analysis of these techniques have been compared with each other.

Benders‐Decomposition‐Based Voltage‐Stability‐Constrained Unit‐Commitment Taking Reactive Power Limit into Account

To determine economic‐efficient and secure generation schedules, unit commitment (UC) with network and stability constraints will play an important role in the electricity market. We define a voltage‐stability‐constrained unit commitment problem taking reactive power limit into account (VSCUC‐QLIM) since the decreasing of synchronous generators may threat the voltage stability of electricity systems. This VSCUC‐QLIM problem is modeled as a mixed‐integer nonlinear programming with equilibrium constraints, which is too complex to be solved directly. Therefore, we apply Benders decomposition to solve this complex problem: the master problem consists of the UC problem to determine the commitment states for generators, and the subproblem consists of the voltage‐stability‐constrained optimal power flow with complementarity constraints problem. However, the subproblem calculation may not converge depending on the commitment states due to the following reasons: (i) any power‐flow solution cannot be obtained or (ii) the voltage stability requirement cannot be satisfied on the commitment state given by the master problem. To deal with these difficulties, two partial problems of the subproblem are added as a pre‐subproblem and post‐subproblem in the proposed method. The combination of these subproblems generate different types of Benders cut depending on the condition. The proposed method was implemented on MATPOWER, and evaluated for daily scheduling on an IEEE six‐bus test system and IEEJ standard WEST10 system. The evaluation results validated the effectiveness of the proposed method from the perspective of economic efficiency and voltage stability. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Coupled single-port method based voltage stability assessment with inverter-based generators

With the increase of inverter-based generators in the power system, the proportion of traditional generators is decreasing, and their voltage support ability to the power system is weakening, the power system operation is approaching to its voltage stability limit. It is of great significance to study on-line analysis of power system voltage stability under different control manners of inverter-based generators. Firstly, impedance matching theory and coupled single-port circuit theory are introduced. Secondly, coupled single-port method based voltage stability assessment method with inverter-based generators is proposed. Then, use the impedance matching condition and proposed method to analyze the influence of inverter-based generators on voltage stability in different control manners. The proposed method can reveal the voltage stability margin of power system with inverter-based generators in the current running state, and is suitable as an on-line voltage stability approach to evaluate the proximity of voltage collapse in real time. The various scenario simulations experiment validate the effectiveness and accuracy of the proposed method. Meanwhile, experimental analysis results show that different control manners of inverter-based generators not only affect voltage stability margin but also change the weakest bus of power system.

Many-objective optimization of real and reactive power dispatch problems

Power dispatch is one of the basic functions in power systems operation and planning activities. It involves security, performance, and economic aspects, while maintaining generation and demand balance. The Optimal Power Dispatch (OPD) and the Optimal Reactive Power Dispatch (ORPD) are formulations of the power dispatch that respectively address objectives related to efficiency, and voltage regulation and stability. Under most common approaches, both problems are independently solved, despite their strong connection. This paper addresses the problem of the simultaneous dispatch of real and reactive power considering four conflicting objectives: minimization of network power losses, maximization of system voltage stability, maximization of power factor on transmission network step-down transformers, and minimization of power dispatch economics. The mathematical model is developed based on the current regulatory framework of the Brazilian electricity sector. To solve the problem, an optimization methodology using the Non-dominated Sorting Genetic Algorithm III (NSGA-III) is proposed. This methodology is tested both on IEEE 30-bus and 57-bus systems and on a Brazilian 10351-bus system. For each system, a set of efficient solutions with good convergence and diversity is obtained. We highlight a 6.5% (30.1 MW) reduction of power losses in the Brazilian system, as well as a 2.8% reduction in the power dispatch cost and a increase of 0.6 in the power factor. The methodology showed that the simultaneous dispatch of real and reactive power is a successful approach to improving the performance of power systems in several criteria.

Enhancement of Voltage Stability by Optimal Placement of Shunt Compensation using Bus Voltage Stability Indices and Reactive Power Margin

Voltage stability problem has caused several blackouts in many countries in recent years. Impending voltage instability has been a significant threat to modern power system's security and reliability. Moreover, the operation and planning of large interconnected power systems is becoming increasingly complex as power demand rises, posing a security risk to the grid. Appropriate efforts to improve power system security and increase voltage stability margin should be planned to keep the system secure. This work investigates the voltage stability of a power system with and without a shunt capacitor. The bus voltage stability index, L index, is used to measure the distance of the power system to its stability limit in order to assign the shunt capacitor. The L-index for a particular load state is computed for all load buses, and the greatest L-index indicates the system's approach to voltage collapse. The system's load ability margin is being traced utilizing a static voltage stability evaluation approach, i.e., PV and QV curve analysis. The minimal power loss approach is used to calculate the optimal capacitor size. The effect of shunt compensation was simulated, and the results with and without compensation were compared. The IEEE-9 bus system was employed in this work, and the system was simulated using MATLAB and Power World Simulator. The result demonstrates that the shunt capacitor enhances voltage stability by injecting the appropriate reactive power.