System Voltage Stability Research Articles

Voltage stability support offered by active distribution networks

This paper investigates distributed control schemes with which an Active Distribution Network can help to increase the voltage stability loadability limit of a bulk power system. Active distribution networks with converter connected renewable energy units can improve network operation through their control and regulation resources. In this paper the aim is to enhance power system voltage stability through distributed controls, respecting at the same time the operational limits of the distribution grid. Case studies of a radial power system, as well as of a real power system snapshot are included.

Modeling of Grid-Forming and Grid-Following Inverters for Dynamic Simulation of Large-Scale Distribution Systems

Historically, distribution system planning studies mainly focused on steady state and quasi-steady state analysis, with limited attention paid to dynamic analysis. This paper develops three-phase, electromechanical models for both grid-forming and grid-following inverters, and integrates them into an open source, three-phase distribution network solver, thereby enabling dynamic simulation of large-scale, three-phase unbalanced distribution systems with high penetration of inverter-based DERs. The proposed inverter models are validated against electromagnetic simulation and field test data from the CERTS/AEP microgrid testbed, and simulated in an islanded 5252 node distribution system in the GridLAB-D simulation environment. Simulation verifies the effectiveness of the proposed inverter models for large-scale distribution system analysis. Study results show that compared to traditional grid-following inverters, the high penetration of grid-forming inverters can improve the voltage and frequency stability of islanded distribution systems.

RETRACTED ARTICLE: Multi objective dragonfly algorithm for congestion management in deregulated power systems

Congestion in transmission corridors are the major bother for deregulated power system’s operation. Generator rescheduling along with demand alteration is a traditional remedy for transmission line congestion. According to market clearing process, the system operator (SO) has to pay a certain amount of cost to the market participants for rescheduling the generation and demand. This kind of redispatch related congestion management (CM) procedure is mainly carried out to reduce the congestion cost, but they are failing to provide an attention in power systems security. The risky generator’s power shifts may diminish the voltage and transient stability of the power system. So power system security should be included in the congestion management procedure. In this proposed multi objective congestion management procedure, rescheduling of active power is carried out to improve/retain the power systems security along with a congestion cost reduction. Voltage security margin (λ) and corrected transient energy margin (CTEM) provides a measure for power system security level. Multi Objective Dragonfly Algorithm (MODA) is employed to trace the non dominated solutions for three conflicting objectives. Fuzzy decision making principle is applied to select the best Pareto solution depends on the objective’s significances. The goodness of the MODA optimization approaches is experimented in congestion alleviation of New England 39 bus systems and solutions are compared with some reputed methods.

Voltage stability of solar dish-Stirling based autonomous DC microgrid using grey wolf optimised FOPID-controller

ABSTRACT This paper proposes the maiden application of a modern meta-heuristically optimised fractional order PID (FOPID) controller for ensuring the voltage stability of a DC microgrid system having PMDC generator coupled to a solar dish-Stirling engine. A significant cost reduction and efficiency enhancement can be achieved by the proposed topology. Popular meta-heuristic optimisation algorithms such as grey wolf optimiser (GWO), mine blast algorithm (MBA) and particle swarm optimisation (PSO) are adopted for tuning the gain constants of the controllers. The major focus of this article is to keep the common DC bus voltage of the microgrid at the desired steady-state value under varying load and varying solar insolation conditions. The results demonstrate the superior performance of the proposed controller.

Quantitative short‐term voltage stability analysis of power systems integrated with DFIG‐based wind farms

With the growing penetration of doubly-fed induction generator (DFIG)-based wind farms (WFs) in power systems, short-term voltage stability problem has become more prominent. This study proposes a new approach for post-fault short-term voltage stability analysis by establishing a quantitative relationship between the system states/outputs and external disturbances. The concept of the integral-integral estimate, which is equivalent to input-to-state stability, was adopted to perform quantitative analysis at the subsystem level, and practical algorithms were developed to study the local input-to-state/output stability properties of subsystems. System-level quantitative analysis was achieved through the proposed criterion considering the stability properties of subsystems and their connections. The proposed method reveals the dynamic responses of the system under external disturbances and quantifies the size of the external disturbance that the system can tolerate, thus facilitating the operation of the power system integrated with DFIG-based WFs. The short-term voltage stability of a test power system was analysed using the proposed quantitative stability analysis approach, and the results were verified through time-domain simulations.

A hybrid bacterial foraging-particle swarm optimization technique for solving optimal reactive power dispatch problem

<div data-canvas-width="397.27351844386203">This paper presents a hybrid evolutionary computation algorithm termed as hybrid bacterial foraging-particle swarm optimization (HBFPSO) algorithm, to optimal reactive power dispatch (ORPD) problem. HBFPSO algorithm merges velocity and position updating strategy of particle swarm optimization (PSO) algorithm and reproduction and elimination dispersal of bacterial foraging algorithm (BFA). The ORPD is solved for minimization of two objective functions; system real power loss and voltage stability L-index. The objective is minimized by optimally choosing the control variables; generator excitations, tap positions of on-load tap changing transformers and switched var compensators while satisfying their constraints and also the constraints of dependent variabl</div><div data-canvas-width="98.30049385204596">es; voltages of all load buses and reactive power generation of all generators. The proposed approach has been evaluated on a standard IEEE 30 bus test system and 24 bus EHV southern region equivalent Indian power system. The results offered by the proposed algorithm are compared with those offered by other evolutionary computation algorithms reported in the recent state of the art literature and the superiority of the proposed algorithm is demonstrated.</div>

Power System Voltage Stability Enhancement Based on Line Voltage Stability Indices in Heavily Loaded and Line Outage Contingency Situations

Power System Voltage Stability Enhancement Based on Line Voltage Stability Indices in Heavily Loaded and Line Outage Contingency Situations

Model-Free Dynamic Voltage Control of Distributed Energy Resource (DER)-Based Microgrids

In this paper, we present a new control technique for sustaining dynamic voltage stability by effective reactive power control and coordination of distributed energy resources (DERs) in microgrids. The proposed control technique is based on model-free control (MFC), which has shown successful operation and improved performance in different domains and applications. This paper presents its first use in the voltage stability of a microgrid setting employing multiple synchronous generator (SG)-based and power electronic (PE)-based DERs. MFC is a computationally efficient, data-driven control technique that does not require modelling of the different components and disturbances in the power system. It is utilized as an online controller to achieve the dynamic voltage stability of a microgrid system under different disturbances and fault conditions. A 21-bus microgrid system fed by multiple DERs is considered as a case study and the overall dynamic voltage stability is investigated using time-domain dynamic simulations. Numerical results show that the proposed MFC provides improvements on the dynamic load bus voltage profiles and requires less computational time as compared to the traditional enhanced microgrid voltage stabilizer (EMGVS) scheme. Due to its simplicity and low computational requirement, MFC can be easily implemented in resource-constrained computing devices such as smart inverters.

Decision Tree for Online Voltage Stability Margin Assessment Using C4.5 and Relief-F Algorithms

In practical power system operation, knowing the voltage stability limits of the system is important. This paper proposes using a decision tree (DT) to extract guidelines through offline study results for assessing system voltage stability status online. Firstly, a sample set of DTs is determined offline by active power injection and bus voltage magnitude (P-V) curve analysis. Secondly, participation factor (PF) analysis and the Relief-F algorithm are used successively for attribute selection, which takes both the physical significance and the classification capabilities into consideration. Finally, the C4.5 algorithm is used to build the DT because it is more suitable for handling continuous variables. A practical power system is implemented to verify the feasibility of the proposed online voltage stability margin (VSM) assessment framework. Study results indicate that the operating guidelines extracted from the DT can help power system operators assess real time VSM effectively.

Design and Optimization of Multiple FACTS Devices for Congestion Mitigation Using Sensitivity Factor with Wind Integrated System

Power generation with load optimization is an extremely important process for better planning and successful operation of the electrical power system especially in the present scenario of deregulated electricity market conditions. To increase the generation share of renewable energy resources with existing supply system, it is imperative needed that the system should not suffer problems due to congestion, voltage stability, and security. This paper presents load balancing by minimization and optimization of variety of loads when applied to pool and hybrid market designs with the application of flexible alternative current transmission system (FACTS) devices for congestion mitigation with high penetration of wind power into the existing power generation systems. Designing and comparison of multiple FACTS devices like SSSC, STATCOM, UPFC, and IPFC have been done for optimal power flow with congestion derogation so as to ensure system voltage stability within the limits. The impact of FACTS devices for high level of wind penetration with (Load index) Sensitivity Factor is also implemented for load optimization using optimal power flow to increase power flow with congestion mitigation for the wind-integrated system.

Integration of solar PV into grid using a new UPQC with differential inverter control

Integrated photovoltaic (PV) distribution systems voltage stability is of great significance in supporting all connected equipment smooth functioning in the distribution network. Voltage profile maintenance is one of the challenging tasks in PV integration. To maintain a constant voltage profile to a sensitive load of 22 kVA is the main idea of this study. A single-phase PV-integrated distribution system is selected for the study. The novelty is that differential inverters are used for dynamic voltage restorer and distribution static synchronous compensator of the unified power quality conditioner (UPQC). Active power decoupling facility is the main advantage using the differential inverter. The research work objective is to synchronise a 10 kW solar PV system to the distribution system using this new UPQC. The research work discusses and derives the most suitable control strategy for the UPQC with battery energy storage system. A 20 kVA UPQC is designed for the PV integration and to increase voltage stability of the distribution system. The frequency, voltage and reactance/resistance ratio of the distribution system is assumed to be constant. A prototype model of differential UPQC is developed. Experimental and simulation results validate the main objective.

Developing a Mathematical Model for Wind Power Plant Siting and Sizing in Distribution Networks

Wind Power Plants (WPPs) are generally located in remote areas with weak distribution connections. Hence, the value of Short Circuit Capacity (SCC), WPP size and the short circuit impedance angle ratio (X/R) are all very critical in the voltage stability of a distribution system connected WPP. This paper presents a new voltage stability model based on the mathematical relations between voltage, the level of wind power penetration, SCC and X/R at a given Point of Common Coupling (PCC) of a distribution network connected WPP. The proposed model introduces six equations based on the SCC and X/R values seen from a particular PCC point. The equations were developed for two common types of Wind Turbine Generators (WTGs), including: the Induction Generator (IG) and the Double Fed Induction Generator (DFIG). Taking advantage of the proposed equations, design engineers can predict how the steady-state PCC voltage will behave in response to different penetrations of IG- and DFIG-based WPPs. In addition, the proposed equations enable computing the maximum size of the WPP, ensuring grid code requirements at the given PCC without the need to carry out complex and time-consuming computational tasks or modelling of the system, which is a significant advantage over existing WPP sizing approaches.

Multi-objective optimization of optimal capacitor allocation in radial distribution systems

Abstract The optimal size and location of the compensator in the distribution system play a significant role in minimizing the energy loss and the cost of reactive power compensation. This article introduces an efficient heuristic-based approach to assign static shunt capacitors along radial distribution networks using multi-objective optimization method. A new objective function different from literature is adapted to enhance the overall system voltage stability index, minimize power loss, and to achieve maximum net yearly savings. However, the capacitor sizes are assumed as discrete known variables, which are to be placed on the buses such that it reduces the losses of the distribution system to a minimum. Load sensitive factor (LSF) has been used to predict the most effective buses as the best place for installing compensator devices. IEEE 34-bus and 118-bus test distribution systems are utilized to validate and demonstrate the applicability of the proposed method. The simulation results obtained are compared with previous methods reported in the literature and found to be encouraging.

Maximizing Distributed Energy Resource Hosting Capacity of Power System in South Korea Using Integrated Feeder, Distribution, and Transmission System

Intermittent power generated from renewable distributed energy resource (DER) can create voltage stability problems in the system during peak power production in the low demand period. Thus, the existing standard for operation and management of the distribution system limits the penetration level of the DER and the amount of load in a power system. In this standard, the hosting capacity of the DER is limited to each feeder at a level where the voltage problem does not occur. South Korea applied this standard, thereby making it hard to achieve its DER target. However, by analyzing the voltage stability of an integrated system, the hosting capacity of DER can be increased. Therefore, in this study, the maximum hosting capacity of DER is determined by analyzing an integrated transmission and distribution system. Moreover, the fast voltage stability index (FVSI) is used to verify the determined hosting capacity of DER. For this, the existing interconnection standard of DER at a feeder, distribution system, and transmission system level is investigated. Subsequently, a Monte Carlo simulation is performed to determine the maximum penetration of the DER at a feeder level, while varying the load according to the standard test system in South Korea. The actual load generation profile is used to simulate system conditions in order to determine the maximum DER hosting capacity.

Decision tree-based classification of multiple operating conditions for power system voltage stability assessment

This paper presents a method that performs classification of thousands of operating conditions w.r.t. power system voltage stability by using decision trees. The proposed method uses a new and flexible classification criterion that allows to identify operating conditions that are near or within the region for which the system is voltage unstable, and more importantly, that can consider operational requirements. The method creates both training and test data sets when building and validating the decision trees. To minimize computational burden, a sampling method is proposed, this method exploits the Saddle Node Bifurcation conditions to explore the operational space used to train the decision trees. Case studies were performed using the IEEE 9-bus system for several operating conditions and different network configurations. This paper also proposes the use of time domain simulations to assess the prediction accuracy of decision trees. Decision trees were created for network configurations involving outage of the line were tested on test sets and also using time domain simulations results from PSS/E. The ability to classify the degree of voltage stability of a multitude of operation conditions could be useful to aid operators in selecting and applying preventive measures to steer away the system from unstable conditions or conditions that are close to breaching operational requirements w.r.t. voltage stability.

Impact of local PMU‐based equivalent methods on real‐time voltage stability assessment

This study promotes a critical discussion about the phasor measurement unit (PMU)-based equivalent methods in order to investigate the impact of the Thevenin equivalent (TE) parameters on real-time power system voltage stability assessment. Although several articles indicate good performance at impedance magnitude matching theory, they neglect the influence of TE impedance angle and voltage source magnitude, introducing inaccuracies or mathematical inconsistencies in stability evaluation. The former three parameters are highlighted in this study due to being directly used to compute active power margins and indexes, according to the maximum power transfer theorem. The approach identifies the methods’ robustness and weaknesses by the use of generic expressions. The main contribution of this study is presenting equations for directly calculating the parameters that may lead to inconsistent interpretations, particularly when measurement noise is considered. Disregarding these inconsistencies may result in an incorrect determination of the system's critical limit, increasing the risk of voltage instability. The conception of the new formulation relies on network equivalents based on the least-squares method, Tellegen's theorem and adaptive method. Following the simulations carried out in Nordic Test System, and 9, 14 and 39 Bus Test Cases available in MATPOWER, analyses substantiated in the derived expressions are given.

Photovoltaic Allocation with Tangent Vector Sensitivity

Indonesia has abundant energy potential from renewable energy resources, especially from the sun but until now, the utilization is not optimal. This paper presents a new methodology for determining the effective location of Photovoltaic (PV) integration into the power system. The proposed scheme consists of two steps: first, determining the area with good irradiance from SOLARGIS and second, calculating the PV-Tangent Vector Sensitivity (PV-TVS) to determine the area that has the greatest impact in increasing network voltage stability and minimizing losses. PV-TVS is developed based on the Continuation Power Flow (CPF) technique which is a voltage stability evaluation tool in the quasi-static analysis methodology. For effectiveness, PV-TVS will be calculated only for good exposure areas. The region that has the highest PV-TVS means that it has the best sensitivity in enhancing system voltage stability and it is recommended for PV placement. The simulation results have been carried out on the South Sulawesi power system in Indonesia, which is a priority location for PV integration in Indonesia, and the results show that this method is effective in determining the location for PV integration.

A Stochastic Voltage Stability Constrained EMS for Isolated Microgrids in the Presence of PEVs Using a Coordinated UC-OPF Framework

Microgrids are increasingly affected by volatile wind energy due to the high penetration of this kind of renewable energy sources. This study investigates the impact of wind energy uncertainty on voltage stability and energy management system (EMS) of isolated microgrids in the presence of plug-in electric vehicles (PEVs). A stochastic voltage stability constrained microgrid energy management system (SVSC-MEMS) architecture based on a coordinated unit commitment-optimal power flow (UC-OPF) methodology, which simultaneously considers the UC and OPF constraints, is proposed. The proposed model guarantees the system security from the voltage stability standpoint, considering a specific loading margin. Besides, the role of PEVs in the microgrid EMS is examined. In order to validate the performance of the introduced SVSC-MEMS, a CIGRE benchmark test system is used. The numerical results, obtained from the implementation of the proposed model in the general algebraic modeling system (GAMS) environment, demonstrate the importance of voltage stability and wind power uncertainty on the microgrid EMS, and furthermore, the key role of PEVs in the emerging microgrids.

SFCL-SMES Control for Power System Transient Stability Enhancement Including SCIG-based Wind Generators

The resolution of the environment pollution depends on renewable energy sources, such as wind energy systems. These systems face transient and voltage stability issues with wind energy employing fixed-speed induction generators to be augmented with resistive type Superconducting Fault Current Limiter (SFCL) and Superconducting Magnetic Energy Storage (SMES) devices. The use of a combined model based on SFCL and SMES for promoting transient and voltage stability of a multi-machine power system considering the fixed-speed induction generators is the primary focus of this study. Our contribution is the development of a new model that combines the advantages of SFCL and SMES. The proposed model functions assure flexible control of reactive power using SMES controller while reducing fault current using superconducting technology-based SFCL. The effectiveness of the proposed combined model is tested on the IEEE11-bus test system applied to the case of a three-phase short circuit fault in one transmission line.

Many-Objective Robust Optimization for Dynamic VAR Planning to Enhance Voltage Stability of a Wind-Energy Power System

Growing integration of wind power and increasing use of induction motor loads dramatically affect a power system's dynamic performance. To address the challenges, this paper proposes a robust dynamic VAR planning method to enhance the voltage stability of wind energy power systems under uncertainty. Firstly, two indices are developed to evaluate the steady-state and the short-term voltage stability of the system. Then, a robustness index is proposed to quantitatively evaluate the robust optimality of the solutions, considering the uncertainties from wind power output and STATCOMs initial state before a contingency. Four objectives are optimized simultaneously: 1) total planning cost, 2) short-term voltage stability index, 3) steady-state voltage stability index, and 4) robustness of the solutions. Finally, an Adaptive Non-dominated Sorting Genetic Algorithm-III based on Latin Hypercube Sampling (A-NSGA-III-LHS)is designed to solve this many-objective optimization problem with 3 improvements over the standard NSGA-III: 1) adaptive mutation rate, 2) Differential Evolution operator, 3) Latin Hypercube Sampling based initial population generation. The proposed method is tested on the New England 39-bus system with an industry-standard complex load model, showing high robust optimality and computational efficiency over conventional methods.