Voltage Collapse Problems Research Articles

Optimal Load Shedding Based On Hybrid Energy Generation

The demand for electricity is growing at an exponential rate with no corresponding increase in the electricity production, which has led to voltage collapse in many practical power systems all over the world. This has, therefore, been a serious concern to power system engineers, investors and utilities as its effect is highly detrimental to power system operation and its reliability. Consequently, in the quest for providing solutions to this problem, integration of various renewable energy sources are deployed in recent years. This paper, therefore, presents an effective approach to solving voltage collapse problems through load shedding optimization. HOMER software was deployed due to its great features of quality design and evaluation, coupled with its technicality and economical options for both standalone and grid-connected power system. The results show that the utilization of the hybrid Hydro/PV produces 91kWh annually, whereas 88.5% of the electricity is produced by hydroelectric system while the remaining 11.5% of the electricity comes from the integrated photovoltaic system with excess electricity of 84kwh per year. The results obtained, therefore, show that there is an assurance of stable electricity with the introduction of backup battery banks even with the intermittent nature of the renewable energy systems.

Non-Iterative, Unique, and Logical Formula-Based Technique to Determine Maximum Load Multiplier and Practical Load Multiplier for Both Transmission and Distribution Systems

In recent days, due to the increasing number of electric vehicle charging stations (EVCSs) and additional power consumption by domestic, commercial, and industrial consumers, the overall power system performance suffers, which further degrades voltage profile, reduces stability, increases losses, and may also create a voltage collapse problem. Therefore, it is crucial to predetermine a maximum loadability limit for voltage collapse analysis and a practical allowable extra load for safe and secure operation, keeping the bus voltage within the security limits. To mitigate the problems, unique and innovative formulae such as the maximum load multiplier (MLM) and practical load multiplier (PLM) have been developed to consider line resistance. The determination of actual permissible extra load for a bus enables quick assessment of bus-wise suitable capacities and the number of EVs that can be charged simultaneously in the charging station. The planning engineers can easily settle on the extra load demand by domestic, commercial, and industrial consumers, while maintaining the voltage security constraint. The proposed technique is simple, non-iterative, computationally inexpensive, and applicable to both transmission and distribution systems. The proposed work is tested on a 57-bus transmission system and 69-bus radial distribution system, and the obtained results from the developed formulae are verified by comparing with conventional iterative methods.

Improvement of Voltage Collapse of MPPT Single-stage Photovoltaic Grid-connected based on Conductance Increment Method

In order to make the supply of resources meet the rapidly developing world situation, it is of great practical significance to further develop and apply renewable resources. PV power system has many advantages, such as cleanness, environmental protection, high efficiency, etc., and shows great application potential in the field of new energy. At present, solar cells are easily affected by external factors such as light intensity, temperature, etc., and can't work at the maximum power point continuously and stably, resulting in low power generation efficiency. Therefore, the introduction of Maximum power point tracking (MPPT) technology is particularly important. In this paper, a variable step conductance increment method is proposed, which can identify the current distance from the maximum power point by observing algorithm, change the tracking step and quickly identify the maximum power point, so as to solve the voltage collapse problem of single-stage photovoltaic grid-connection. Simulation results show that the new algorithm can optimize both dynamic response and steady-state oscillation, and improve the accuracy and speed of MPPT.

Voltage Stability Margin in DC Grids With CPLs: A Recursive Newton–Raphson Approximation

This express brief addresses the voltage collapse problem in direct-current (dc) networks by using a recursive heuristic search algorithm based on the Newton–Raphson method. The determinant of the Jacobian matrix in the Newton–Raphson method is used as a sensitivity index to determine the maximum power consumption of the dc network. The recursive solution approach corresponds to a sequential power flow approach by incrementing all values of the power consumptions uniformly. Simulation results validate the efficiency of the proposed method in comparison to the large-scale nonlinear solvers available in the general algebraic modeling system optimization package. The MATLAB programming environment was employed for implementing the proposed recursive Newton–Raphson method.

Application of Auto-Switched Capacitor Bank to Mitigate Voltage Collapse Problem in Distribution System; A Case Study of Osogbo South –Western, Nigeria.

Exponential demand for electrical power supply caused by increased use of electricity at both domestic and industrial level pose threat to power system stability. The need to enhance power system with adequate compensation via reactive power supply becomes a necessity. This paper therefore presents application of auto-switched capacitor bank to mitigate voltage collapse problem; a case study of Osogbo South-Western, Nigeria. The proposed approach carefully design the correct size of capacitor required to supply the reactive power needed for compensation. The obtained values were used to model the power system. The modeled system was subjected to disturbances with a view to investigate its performance. The results obtained showed that the designed capacitor bank was able to stabilize the voltage on the line despite the heavy loads on the power system.

Optimal Power Flow Using Particle Swarm Optimization of Renewable Hybrid Distributed Generation

The problem of voltage collapse in power systems due to increased loads can be solved by adding renewable energy sources like wind and photovoltaic (PV) to some bus-bars. This option can reduce the cost of the generated energy and increase the system efficiency and reliability. In this paper, a modified smart technique using particle swarm optimization (PSO) has been introduced to select the hourly optimal load flow with renewable distributed generation (DG) integration under different operating conditions in the 30-bus IEEE system. Solar PV and wind power plants have been introduced to selected buses to evaluate theirs benefits as DG. Different solar radiation and wind speeds for the Dammam site in Saudi Arabia have been used as an example to study the feasibility of renewable energy integration and its effect on power system operation. Sensitivity analysis to the load and the other input data has been carried out to predict the sensitivity of the results to any deviation in the input data of the system. The obtained results from the proposed system prove that using of renewable energy sources as a DG reduces the generation and operation cost of the overall power system.

Particle Distribution Algorithm for Solving Optimal Reactive Power Dispatch Problem

Various numerical methods like the gradient method Newton method and linear programming have been utilized to solve the optimal reactive power dispatch problem. The problem of voltage stability and collapse play a key role in power system planning and operation.

Improvement of voltage stability in power system using SVC and STATCOM

This paper deals with the problem of the static voltage stability in power systems. Basic concepts relating to the instability and voltage collapse are presented. The problem of voltage collapse is processed through the bifurcation curves voltage drawn by the continuation power flow (CPF). The optimal use of the SVC and the STATCOM in the improvement of the static voltage stability margin also retains our interest in this paper. The problem of voltage collapse has been formulated as an optimisation problem, then, a solution using particle swarm optimisation is proposed, applied on the analysis of the voltage stability of a power system. In this work, we proposed two indices to optimise the size and the location of the SVC and the STATCOM. The influence of these two FACTS on voltage stability margin of the network has been studied. Thereafter, we performed a brief comparison between SVC and STATCOM in improving the voltage stability margin of the network.

Importance Sampling Based Intelligent Test Set Generation for Validating Operating Rules Used in Power System Operational Planning

Decision tree based machine learning methods find a great deal of application in power system reliability assessment studies, wherein essential knowledge in the form of operating rules or guidelines are produced that help operators maneuver the system away from insecurity. Independent test sets are generally used to validate these rules, with the motivation of estimating their classification accuracy and error rates, apart from checking their performance against some interesting situations. This paper proposes an importance sampling based method to generate intelligent test set for validating operating rules. The method is applied for testing decision tree rules derived against voltage collapse problems in western regions of the French power system, and is seen to produce test sets at lesser computation that estimates the rule's classification errors with good accuracy. For a given computation, it also provides richer information on critical operating conditions for which the rule is vulnerable, which helps in further improving the rules.

A numerical study of the effect of degenerate Hopf bifurcations on the voltage stability in power systems

Bifurcation theory has been employed to qualitatively explain the mechanisms of voltage stability problems occurring in electric power systems by relating the voltage collapse and voltage oscillatory problems to the appearance of saddle node and Hopf bifurcations, respectively. The results obtained by bifurcation analysis have revealed the existence of degenerate Hopf bifurcations when two parameters of the system are varied simultaneously; however, the mechanisms of voltage stability problems when the system is operating near these kinds of bifurcations have not yet been investigated. Bearing this in mind, the main scope of this paper is to assess how the voltage stability of a power system is affected by the presence of codimension-2 degenerate Hopf bifurcations. From the multiparameter bifurcation analysis, the existence of degenerate Hopf bifurcation points are identified and a trajectory stability diagram is then computed for classifying the type of degenerate Hopf bifurcations. This classification is used for establishing the voltage dynamics’ behavior when the power system is operating near these bifurcations. Finally, the application of a StatCom is proposed to eliminate sustained voltage oscillations and the appearance of degenerate Hopf bifurcations.

Voltage Stability Enhancement on IEEE 14 Bus System

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. Maintaining a stable and secure operation of a power system is therefore a very important and challenging issue. A steady state analysis is applied to study the voltage collapse problem. The Modal Analysis method is used to investigate the stability of the power system. Prediction of the stability margin or distance to voltage collapse is based on the reactive power load demand. The load is connected to several selected buses. The analysis is performed for IEEE 14 Bus system. Then, the most critical mode is identified for each system. After that, the weakest bus, which contributes the most to the critical mode, are identified using the participation factor. The remedial measure is proposed to prevent the voltage collapse. SVC is used to improve the voltage profile of the system. The voltage profile obtained after the incorporation of the SVC is compared with the same before the incorporation of the SVC and the improvement is verified.

Decentralized secondary voltage control using voltage drop compensator among power plants

This paper deals with the problem of voltage collapse in power systems by presenting a decentralized secondary voltage control. For this purpose the coordination between the joint voltage control available in the generation plants is used to control the voltage level at the transmission system by adjusting a compensation impedance. By using this approach, the generation plants become more sensitive to the system operating and configuration conditions. A sensitivity-based methodology to identify the most effective plants and the impedance value associated is presented. Some examples meant to explore the potential of the methodology are presented and discussed with the help of real systems.

Progressive entropy based contingency grouping for deriving decision trees for multiple contingencies

This paper deals with decision tree based power system security assessment for multiple contingencies. In this paper, we propose a contingency grouping technique to produce good, but reduced number of decision trees for multiple contingencies. The grouping is based on the degree of overlap in class boundary regions or post-contingency performance measures of every contingency, as captured by the graphical index progressive entropy. The proposed method has been demonstrated on French EHV system for a voltage collapse problem in west France, Brittany region.

Centralized Control Algorithm for Power System Performance using FACTS Devices in the Korean Power System

This paper presents a centralized control algorithm for power system performance in the Korean power system using Flexible AC Transmission Systems (FACTS) devices. The algorithm is applied to the Korean power system throughout the metropolitan area in order to alleviate inherent stability problems, especially concerns with voltage stability. Generally, control strategies are divided into local and centralized control. This paper is concerned with a centralized control strategy in terms of the global system. In this research, input data of the proposed algorithm and network data are obtained from theSCADA/EMS system. Using the full system model, the centralized controller monitors the system conditionand decides the operating point according to the control objectives that are, in turn, dependenton system conditions. To overcome voltage collapse problems, load-shedding is currently applied in the Korean power system.In this study, the application of the coordination between FACTS and switch capacitor (SC) canrestore the solvability without load shedding or guarantee the FV margin when the margin is insufficient.Optimal Power Flow (OPF) algorithm, for which the objective function is loss minimization, isused in a stable case. The results illustrate examples of the proposed algorithm using SCADA/EMS data of the Korean power system in 2007.

Optimal reactive power dispatch in a large power system with AC–DC and FACTS controllers

With the increased loading of existing power system, the problem of voltage stability and voltage collapse has become a major concern in power system planning and operation. The dependence of the system voltage profile on reactive power distribution forms the basis for reactive power optimisation. The technique attempts to utilises fully the reactive power sources in the system to improve the voltage profile and also to meet the reactive power requirements at the AC-DC terminals to facilitate the smooth operation of DC links. The method involves successive solution of steady-state power flows and optimisation of reactive power control variables with unified power flow controllers using linear programming technique. The proposed method has been tested on a real life equivalent 96-bus AC and a two terminal DC system.

Mitigation of voltage collapse through active dynamic buffers

Power electronics continues to grow as an element of electrical loads. Most such loads, including motor drives, computer power supplies, and compact fluorescent lighting, serve to 'isolate' the load dynamics from the utility grid. The unfortunate effect is that these loads enforce local constant power behaviour. This tends to destabilise the supply system, resulting in voltage collapse. In this work, the power buffering technique is examined to mitigate the effects of constant power loads. A power buffer is a device that enforces dynamic isolation to bestow beneficial dynamic characteristics upon the grid. A review of constant-power load dynamics and weak power systems is presented. Through simulations, the generalised power buffer concept is shown to stabilise several examples of power systems. Various techniques and topologies for power buffers are then covered and related to the voltage collapse problem, including critical control methods and parameters. Finally, three experiments are presented that demonstrate the stabilising effects of buffers.

Voltage collapse in power systems: Dynamical studies from a static formulation

This paper addresses the problem of voltage collapse in power systems. More precisely, we exhibit a voltage collapse in a power system with two buses. This study is carried out with the help of two approaches. The first is a dynamical approach where a saddle‐node bifurcation is analyzed and the second is an algebraic approach. Both approaches deal with the static behavior of the power system, but some dynamic aspects may be observed. An equivalence between the algebraic and dynamical approaches is obtained. The need to use both models comes from the fact that they are usually exploited in the literature, but a deep theoretical justification is still pending. Such a justification is meant in this work.

Voltage Stability of Large Power Networks with a Large Amount of Wind Power

The article presents results of voltage stability investigations carried out on a large power network model. Presumably, around 50 per cent of electricity consumption is covered by wind turbines and by local combined heat and power (CHP) units. In investigations, a distinction is made between local wind turbines and those in a large wind farm subject to the Grid Specifications of the transmission system operator (Eltra, 2000). The main concerns of maintaining power system operation are (i) a risk of significant power loss due to tripping of local units and (ii) a risk of overvoltage at the periphery of the power network. This is contrary to previous investigations predicting that the main concern should be a risk of voltage collapse (Bruntt et al., 1999). As demonstrated, voltage collapse does not occur, because local wind turbines will trip when abnormal grid operation is indicated. This “eliminates” the problem of voltage-collapse. On the other hand, this introduces new problems with regard to (i) establishing power reserves and (ii) protecting the power network against overvoltage.

An approach for real power scheduling to improve system stability margins under normal and network contingencies

In the present day power system planning and operation, considerable interest is being shown in system security and stability analysis. Pattern of load sharing/generation scheduling that results in heavy flows tend to incur greater losses, threaten stability, security and ultimately making certain generation patterns undesirable. Generation schedules mainly based on economic criteria may lead to lower reserve margins and therefore diminished reliability is a serious concern for the systems. With increased loading of existing power transmission systems, the problem of voltage stability and voltage collapse has also become a major concern in power system planning and operation. While the voltage stability is more dependent on the reactive power sources/voltage profile in the system, it is also a function of real power flows. In this paper, network sensitivity between load voltages and source voltages to compute voltage stability index ( L), is used as the basis to evaluate desirable load sharing for improving stability margins. The proposed method has been tested on typical sample systems and also on a practical 24-bus equivalent power system, and results are presented to illustrate the proposed approach.

Control of a saddle node bifurcation in a power system using a PID controller

In this work, we present the elimination of a saddle-node bifurcation in a basic power system using a PID controller. In addition, a stability analysis of the rotor angle and its frequency, which are directly related to voltage collapse problem, is presented.