Voltage Instability Phenomena Research Articles

A high-frequency reduced-order model for parameters optimization of AC/DC distribution systems considering random disturbances

Accompanying the rapid development of AC/DC distribution systems, along with the random disturbances introduced by a significant number of distributed generations and loads, the difficulty of system stability analysis has increased. The phenomenon of DC bus voltage instability has become severe, affecting the safe and stable operation of power systems. This paper focuses on the research of multi-terminal AC/DC distribution systems. A reduced-order method for multi-terminal distribution systems is proposed. Through parameter equivalent transformation, the system model is simplified while maintaining its dynamic characteristics. Parameter sensitivity analysis is utilized to identify key parameters influencing the system’s dynamic behavior, achieving an analytical expression of the system’s dynamic characteristics. And stability domain analysis is applied to delineate the variations in system dynamic behavior and responses to random disturbances under different parameter settings. Then a multi-parameter optimization method is designed to enhance system stability while achieving fast system response. Finally, theoretical analysis is validated through software simulation and hardware-in-the-loop experiments.

Load shedding method aimed fast voltage recovery to prevent interference of FIDVR with UV relays

AbstractThe fault‐induced delayed voltage recovery (FIDVR) and short‐term voltage instability (STVI) phenomena appear in networks with high penetration of induction motor loads because the increase in requested reactive powers of these loads prevents the voltages from quickly returning to their pre‐fault levels. Load shedding (LS) is one of the ways to deal with FIDVR and STVI and reduce the imbalance between the generation and demand of reactive power. Under‐voltage (UV) relays that disconnect loads during voltage drop cannot effectively deal with this phenomenon because of their inability to detect the effective loads on the reduction of FIDVR and STVI severities. Therefore, the operation of UV relays during these phenomena causes unnecessary load disconnection, and the interference of their operations with FIDVR and STVI must be avoided. This paper presents two wide‐area approaches based on network and loads parameters, the first of which deals with the most critical FIDVR, and the second tries to simultaneously handle critical FIDVRs of all buses. Also, bus prioritization for LS during STVI has been addressed. Simulation results revealed the better performance of the proposed approaches than the previous ones in terms of the amount of LS and the number of selected buses for LS.

Effects of Integration of Multi Type DGs on Voltage stability and Loss Minimization in the Distribution System

In recent days in distribution system the more importance is giving to Loss minimization techniques since electricity demand is continuously increasing and utility companies are struggling to meet this rapid increase in load due constraints on energy resource to increase the generation. Furthermore, voltage instability phenomena is also playing important role in distribution systems and caused a major blackout in the network. To solve the above problem new technology that is drawing more attention is Distributed Generation (DG). Placing DG in the distribution system inherently reduces the power loss and improves the system voltage. The selection of type of DG, proper placement and sizing of DG plays an important role. This paper presents an effective methodology to identify the optimum location of multi type DG in the distribution system in order to reduce the losses and improve the voltage. In this work the IEEE 33-Bus system is simulated in Power World Simulator (PWS) and the voltage stability and system losses are analyzed with different types of DGs and combination of different types of DGs are studied. Simulation result shows that optimal placement and sizing of DG will reduce the system losses and improve the voltage profile within the acceptable limits and the loss reduction and voltage profile improvement are depending on the types of DGs and combination of DGs placed in the distribution system. Index Terms: Distributed generation, Optimum size, Optimum location, Power loss, Power world simulator, Sensitivity analysis, Types of DG, Voltage stability.

Improving performance of transmission networks using facts through continuation power flow method

Over the past 50 years, modern electrical systems have become more complex, as they overrun the geographical boundaries of neighboring countries. The problem is that the power system faces many challenges, because it is exposed to difficult operating conditions. The phenomenon of voltage instability is the most frequent phenomenon, and this can lead to the collapse of the power system. To avoid power outages in the system (especially in blackout situations), the power system must be analyzed in order to maintain voltage stability in the expected difficult operating conditions. The main objective is to determine the maximum load capacity of the system and the causes of voltage instability. The voltage instability problem is related to the nature of nonlinear loads, so different load characteristics must be taken into consideration when analyzing voltage stability. This study aims to discover the maximum load capacity required by using the continuous power flow method (CPF) in the studied network. Then, the performance of this network using a Flexible Alternating Current Transmission System (FACTS) will be utilized. FACTS systems present a promising solution in improving the voltage stability by improving the power transmission capacity and controllability of the parameters of the existing power networks. This study will be conducted on a reference network platform under normal working conditions, then installation of one of the FACTS systems will show its effect on improving voltage stability. The continuous power flow method will be used to find PV curves, which in turn will help to determine the conditions of maximum loading while maintaining stability, and identify the bus bar with the smallest voltage, on which the flexible AC systems will be installed. The software environment MATLAB/PSAT will be used for modeling and simulation.

Determining Voltage Control Areas in Large Scale Power Systems Based on Eigenanalysis of the QV Sensitivity Matrix

Bulk power systems failures caused by voltage instability phenomena have become more frequent during the last years. Voltage control schemes capable of keeping voltage magnitude within specified limits, automatically, for a specific area of the power system can prevent this problem. The identification of potential voltage control areas of the power system is an essential part of voltage control scheme design. In some European countries these schemes have being contributing significantly both for safety and for the quality of operation. Regional and coordinated voltage control schemes are powerful mechanisms to avoid or mitigate this voltage instability phenomena. These control schemes known as secondary voltage control are based on pilot nodes and control areas, and their correct identifications are fundamental to an efficient voltage profile regulation. This paper proposes a methodology to identify voltage control areas based on the eigenvalues and eigenvectors of the load flow QV sensitivity matrix. The results are compared with the traditional voltage sensitivity analysis methods.

Active and Reactive Power Joint Balancing for Analyzing Short-Term Voltage Instability Caused by Induction Motor

Short-term voltage instability has a sensational effect once it occurs with massive loss of load, possibly area instability, and voltage collapse. This paper analyzes the short-term voltage instability caused by induction motor from the viewpoint of active and reactive power joint balancing. The analysis method is based on (1) the reactive power balancing between system supply and induction motor demand, and (2) the active power balancing between air-gap power and mechanical power, which is expressed by the region of rotor acceleration and deceleration in the Q-V plane. With the region of rotor acceleration and deceleration in the Q-V plane and the reactive power balancing, the movement direction of the operating point can be visually observed in the Q-V plane, thereby achieving a clear comprehension of physical properties behind the short-term voltage instability phenomenon. Furthermore, the instability mechanisms of two kinds of grid-connected induction motor operation conditions after a large disturbance are discussed to explain the basic theory of the analysis method and to provide examples of its application. Time-domain simulations are presented for a single-load infinite-bus system to validate the analyses.

Efficient method to compute all the type‐1 low‐voltage power flow solutions in distribution systems

The power flow equations usually have multiple solutions including a high-voltage solution and many low-voltage solutions, among which only the type-1 solutions (where the power flow Jacobian matrix has only one positive real-part eigenvalue) are closely related to the voltage instability phenomenon. This study proposes an efficient method to compute all the type-1 low-voltage power flow solutions in distribution systems. First, the geometric properties of the power flow solution space of distribution systems have been studied. Second, the propositions which can guarantee to locate all the type-1 power flow solutions have been suggested and proved. Finally, the conventional implicit Z-bus method is modified to compute all the type-1 germ solutions, based on the suggested propositions; and then the Newton–Raphson method is utilised to trace all the type-1 low-voltage power flow solution branches which originate from the known type-1 germ solutions. The 7-node, 33-node, and 69-node systems are used to validate and demonstrate the proposed method.

Decentralized Load Shedding Method Based on Voltage Stability Margin Index Using Synchrophasor Measurement Technology

This study develops an analytical method for assessing the voltage stability margins of a decentralized load shedding scheme; it then examines the challenges related to the existing load shedding scheme. It also presents a practical application for implementing the proposed method, based on the synchrophasor measurement technology in modern power grid operations. By applying the concept of a continuously-computed voltage stability margin index to the configuration of the Thévenin equivalent system, the maximum transfer power could be used as an index to monitor the voltage instability phenomenon and thus determine the required load shedding amount. Thus, the calculated voltage stability margin might be a useful index for system operators in the critical decision-making process of load shedding. Dynamic simulations are performed on real Korean power systems as case studies. Simulation results, when comparing the existing and proposed methods, showed that there was a considerable reduction in the amount of load shedding in the voltage instability scenario. This indicates that the synchrophasor measurement technology has a considerable effect on the proposed load shedding method. The simulation results have validated the performance of the proposed method.

SVD-Based Voltage Stability Assessment From Phasor Measurement Unit Data

Electric power systems can display a range of undesirable dynamic phenomena by which acceptable, stable operation may be lost. Quasi-steady-state operational problems such as the voltage instability phenomena are among these. Ill-conditioning of the power flow, reflected in high sensitivity of bus voltage magnitudes to load variation is an often observed precursor to such quasi-steady state operational problems. Motivated by this insight, work here will propose a voltage stability and conditioning monitor that is model-free in real-time, based solely on phasor measurement unit (PMU) data, arguing that such an approach is well suited to near-real-time application. We review model-dependent singular value analysis in voltage stability assessment, and relate these existing approaches to our proposed model-free method in real-time application. The proposed algorithm is first applied under the idealized assumption of full measurement data at all buses. This work then extends the algorithm to apply in the more practical case for which only subset of buses have available measurement data. The proposed approach is illustrated in IEEE test cases, augmented to include heavy load conditions that stress voltage stability. Algorithms for efficient computation of small numbers of singular values, as well as means to exploit low-rank updates in data, are reviewed to demonstrate opportunities for fast computation that allow these SVD methods to operate in near-real-time in large systems.

Power Flow Study and Voltage Stability Analysis for Radial System with Distributed Generation

voltage instability phenomena occur in both transmission systems and distribution systems. The weakening of voltage stability level will limit the growth of load served by distribution companies. Voltage instability in power distribution systems could lead to voltage collapse and thus power blackouts. The integration of distributed generation (DG) in the distribution system has increased to high penetration levels. The ultimate goal of this paper is studying the impact of DG units under varied penetration level on some issues, such as voltage stability, voltage profile, power flow and PV curves for each bus. This paper analyzes and discusses the performance of static voltage stability of 15 buses a practical distribution system in the Kumamoto area in Japan by using Fast Voltage Stability Index FVSI and varying the load ability with varied DG penetrations. In this paper, two types of DG sources are used in distribution systems wind turbine and photovoltaic. KeywordsStability, Distributed Generation, Loadability, Static Voltage Stability, Power Flow, Wind Turbine and Photovoltaic.

A wide area synchrophasor-based load shedding scheme to prevent voltage collapse

Abstract This paper presents a new method based on wide area voltage stability index for optimal load shedding to prevent voltage instability phenomena. Phasor Measurement Units (PMUs) have widely been used in recent years due to their great advantages in power systems wide area monitoring, protection and control. The purpose of this paper is to provide a new optimal load shedding method, which disconnects the least possible amount of load from optimum buses. Not only the system stability is considered as main goal in this research, but also minimum load shedding is taken into account. Moreover, the problem of optimal load shedding is applied using modified Discrete Imperialistic Competition Algorithm (DICA) in mid-term and long-term voltage instability scenarios. In all investigations, certain limitations are considered to obtain practical answers. In addition, some modifications are applied to the conventional ICA, which make it proper for solving the optimal load shedding problem. New modifications result in fast convergence characteristic and less run time, which are crucial in dealing with power system instability problems.

Impact of Dynamic Behavior of Photovoltaic Power Generation Systems on Short-Term Voltage Stability

In this study, we investigate the impact of the dynamic behavior of photovoltaic (PV) power generation systems on short-term voltage stability of the transmission system. First, the impact of the fault ride-through capability of a PV model is studied by setting several recovery speeds of the active current output when the operation of the PV system is interrupted because of a voltage sag. The results are analyzed by using transient $P\hbox{-}V$ curves and a stability boundary, which has been proposed in our previous research. Further, we show that the installation of PVs severely impairs the short-term voltage stability if the PVs shut off after a voltage sag, and its recovery speed is low. Next, two countermeasures to control short-term voltage instability phenomena are tested. One is the operation of the PV system at a leading power factor in the normal state, and the other is the dynamic reactive power control by the inverters of the PV system after a voltage sag. Numerical examples are carried out for a one-load infinite-bus power system and a five-machine five-load power system. The results show that these countermeasures can play a substantial role in preventing the voltage instability phenomena caused when a PV system is suddenly interrupted because of a fault.

Analytical Method for Short-Term Voltage Stability Using the Stability Boundary in the P-V Plane

Short-term voltage stability is one of the issues of concern for power system operations. As dispersed power generation is connected to middle- and low-voltage transmission networks, the development of analytical methods will become more important. This paper describes a stability boundary line in the P-V plane of the load bus for the analysis of short-term voltage stability. By comparing the operating point of the load with the boundary line, we can visually determine the acceleration or deceleration state of the induction motor, thereby clearly explaining the short-term voltage instability phenomena. In addition, the idea of the stability boundary is applied to voltage stability assessment and emergency controls such as reactive power compensation. Numerical simulations are carried out for a single-load infinite-bus system to explain the basic theory of the proposed method and to provide examples of its application.

Accelerated degradation data of SiC MOSFETs for lifetime and Remaining Useful Life assessment

The phenomenon of threshold voltage instability has been reported to be a critical issue for the first generation of commercial SiC MOSFETs. For aeronautic mission profile, the long term reliability of such device has to be estimated prior to any integration. As far as the author knows, this paper proposes one of the first attempts to use a non-homogeneous gamma process to model the threshold voltage degradation of a commercial SiC MOSFET. Such approach allows evaluating the time to failure as well as it distribution thanks to the proposed Acceleration degradation testing methodology. All the data collected during the ageing tests will be used to model an acceleration factor and to extrapolate the Time-To-Failure in a given application. Ultimately, the use of gamma process to evaluate the Remaining Useful Life of electronic component is described as a first step toward prognostic of Remaining Useful Life in embedded power electronics.

Coordination between SC and SVC for Voltage Stability Improvement

At any point of time, a power system operating condition should be stable, meeting various operational criteria and it should also be secure in the event of any credible contingency. Present day power systems are being operated closer to their stability limits due to economic and environmental constraints. Maintaining a stable and secure operation of a power system is therefore a very important and challenging issue. Voltage instability has been given much attention by power system researchers and planners in recent years, and is being regarded as one of the major sources of power system insecurity. Voltage instability phenomena are the ones in which the receiving end voltage decreases well below its normal value and does not come back even after setting restoring mechanisms such as VAR compensators, or continues to oscillate for lack of damping against the disturbances. Reactive power limit of power system is one of the major causes of voltage instability. This paper investigates the effects of coordinated series capacitors (SC) with static VAR compensators (SVC) on steady-state voltage stability of a power system. Also, the influence of the presence of series capacitor on static VAR compensator controller parameters and ratings required to stabilize load voltages at certain values are highlighted. Keywords—Static VAR Compensator (SVC), Series Capacitor (SC), voltage stability, reactive power.

A multiagent‐based cooperative voltage and reactive power control

AbstractIn order to maintain the system voltage within the optimal range and to prevent voltage instability phenomena before they occur, a variety of phase modifying equipment are installed in optimal locations throughout the power system network and a variety of methods of voltage reactive control are employed. The proposed system divides the traditional method of controlling voltage and reactive power into two subproblems: “voltage control” to adjust the secondary bus voltage of substations, and “reactive power control” to adjust the primary bus voltage. In this system, two types of agents are installed in substations in order to coordinate voltage control and reactive power control. In order to verify the performance of the proposed method, it was applied to a model network system. The results confirm that our proposed method is able to control violent fluctuations in load. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 181(2): 20–28, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22286

Detailed modelling, implementation and simulation of an “all-in-one” stability test system including power system protective devices

This paper presents modelling and simulation results for multiple instability scenarios of the “all-in-one” test system. The test system is an alteration of the Bonneville Power Administration test system constructed to capture transient (angle), frequency and voltage instability phenomena, resulting in system collapse, within one system. The paper describes general overview of the test system and its associated individual devices modelling. These modelling are both customized and adapted from the built-in model developed by PowerFactory simulation software. The paper also provides a description of different instabilities that can be reproduced by this self-contained system. One of the case study is demonstrated in detail with the necessary initialization settings for reproducing instability scenario.

Power System Voltage and Reactive Power Control by means of Multi-agent Approach

In order to maintain system voltage within the optimal range and prevent voltage instability phenomena before they occur, a variety of phase modifying equipments are installed in optimal locations throughout the power system network and a variety of methods of voltage and reactive control are employed. The proposed system divided the traditional method to control voltage and reactive power into two sub problems: “voltage control” to adjust the secondary bus voltage of substations, and “reactive power control” to adjust the primary bus voltage. In this system, two types of agents are installed in substations in order to cooperate “voltage control” and “reactive power control”. In order to verify the performance of the proposed method, it has been applied to the model network system. The results confirm that our proposed method is able to control violent fluctuations in load.

A novel approach to deliverable power in low‐voltage DC distribution system on the basis of voltage stability

AbstractThis paper proposes that a deliverable power through a low‐voltage DC distribution system has an upper limitation. The upper limitation of the deliverable power, Plim, is explained on the basis of a voltage instability phenomenon occurring for the load with a voltage sensitivity below 1. From theoretical‐calculation results, it is pointed out that Plim diminishes with augment in the distribution‐line length. This phenomenon becomes more distinct for the higher distribution‐line inductance per unit length. Connection of the capacitor to the receiving end of the distribution line is discussed as a method for rising Plim. Measurements of the voltage waveform at the load terminals successfully support Plim derived from the theoretical calculation. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Multi-agent based Distributed Reactive Power Control Method

In order to maintain system voltage within the optimal range and prevent voltage instability phenomena before they occur, a variety of phase modifying equipment is installed in optimal locations throughout the power system network and a variety of methods of voltage reactive control are employed. In this paper, the voltage reactive control problem is considered as the two sub problems such as voltage control and reactive power control. The proposed multi-agent system intends to resolve the reactive power control sub problem. In this system, three types of agents are installed in substations in order to maintain the primary bus voltage within the operation limit by allocating the reactive power.In order to verify the performance of the proposed method, it has been applied to the model network system. The simulation results show that the proposed method is a promising approach to keep the primary bus voltage within the operational limit by changing the reactive power allocation.