Loading Margin Research Articles

A New Approach for Finding Real Power Generation Direction to Improve Voltage Stability Margin

In this study, an efficient approach is proposed to find best real power generation participation for improving static voltage stability and reducing total generation cost. Therefore, loadability limit index is used to assess static voltage stability security margin, which is associated to the point of voltage collapse. Based on it, a toolbox is developed to recognize the loadability margin by using Lagrangian method. Finally, the mentioned problem is modeled as a non-linear and multiobjective optimization problem. In this paper, Hybrid Genetic Algorithm Particle Swarm Optimization (HGAPSO) and Particle Swarm Optimization (PSO) algorithms are applied to find out best generation direction. This problem is performed as a hierarchical optimization problem. In first stage, an algorithm is used to search possible solution area and reach tradeoff between secure and economic direction of real power generations. In second stage of proposed approach, respectively to each generation pattern, power system voltage stability margin and generation cost are evaluated during search algorithm. The simulations are performed on IEEE 14 and IEEE 30 bus test systems to find best generation direction.

Optimal Reactive Power Compensation in Power System Considering SVC

This paper introduces a method for optimal reactive power compensation considering SVC. Static load margin of each node is calculated and then sorted to determine the location of reactive power compensation. To know the optimal compensating capacity, the mathematical model of fuzzy multi-objective is established, and it can be solved by the primal-dual interior point algorithm. The proposed method is applied to a grid of Northwest China with satisfactory results.

A New Method to Optimize Locations of SVC Based on Risk and Static Load Margin

A method was proposed selecting the location of SVC, considering the power system with large wind farms interconnected. The location can be determined by risk index, which comprises credibility and global severity, and static load margin simultaneously. The method could consider the weak links and buses under both fault and normal conditions thus make better contribution to the system security. Case study shows that the correctness and effectiveness of the proposed method, comparing with the usual one.

The Effect of SVC on Gansu Hexi Grid Static Load Margin by BPA Modeling and Simulation

Wind energy is very abundant in Hexi Corridor, and inspired by government policy impetus to build “the Three Gorges on land”, total installed capacity in Hexi grid has increased sharply, and Jiuquan wind power base will become the biggest connecting wind farms in the world. However, Hexi grid has a weak grid configuration, therefore, issues such as insufficient reactive power, transient stability change, and local grid voltage level decreasing could emerge with large scale wind power integration. It’s very necessary to input SVC to implement dynamic reactive power compensation, which is helpful for improving voltage stability. This paper introduces the basic principle of SVC and SVC’s working state in three situation. Then models and simulates the effect of SVC on Gansu Hexi grid static load margin by BPA. At last, proves SVC can improve static load margin.

Risk Assessment Model of Cascading Failures in Power System Based on Danger Lines

Based on the theory of risk, a new model is proposed for cascading failure in power system. According to fault factor of power line itself and the impact of real-time power flow, the branch outage probability model is established, and then the probability of cascading failure can be calculated. The severity function of cascading failure is defined by the analysis of fault consequences including the decrease of load margin, bus voltage offset and power line overload. The use of the set of danger lines which is judged by the amount of active power increase and load margin of power line can speed the search of fault mode. The simulation and analysis of IEEE 39-node proves the effectiveness of the method.

An Efficient Margin and Sensitivity Analysis Based Method For Calculating Voltage Collapse

This paper concerns compute and exploiting the sensitivity of the loading margin to voltage collapse with respect to various parameters. The main idea of this paper is that after the loading margin has been computed for nominal parameters, the effect on the loading margin of altering the parameters can be predicted by Taylor series estimates. Loading margin is a fundamental measure of proximity to voltage collapse. Linear and quadratic estimates to the variation of the loading margin with respect to any system parameter or control are derived. The accuracy of the estimates over a useful range and the ease of obtaining the linear estimate suggest that this method will be of practical value in avoiding voltage collapse.

Voltage security constrained multi-period optimal reactive power flow using benders and optimality condition decompositions

This paper proposes a new coordinated voltage control scheme to ensure voltage security of power systems. The scheme schedules reactive power injection from VAR sources, including synchronous generators and condensers, capacitor banks, switchable reactors and FACTS devices, to ensure desired loading margin of power systems for a given horizon of time. The problem is treated as voltage security constrained multi-period optimal reactive power flow (VSC-MPORPF). To incorporate scheduling of both continuous and discrete VAR sources, the VSC-MPORPF is formulated as a mixed-integer nonlinear programming problem, and is solved using generalized Benders decomposition (GBD). Multi-period formulation ensures both optimal switching pattern of discrete voltage controllers and voltage security for a given future horizon. Also, to make the proposed method applicable for large-scale power systems, optimality condition decomposition approach is utilized, along with the GBD. The proposed methodology is examined through case studies conducted on a simple 6-bus, the IEEE 118-bus, and a 1180-bus test systems. The results demonstrate effectiveness and efficiency of the proposed framework in real-time operation of power systems.

Determination of maximum load margin using fuzzy logic

In the modern power systems, maximum load margin (MLM) plays an important role from the point of view of system stability. The knowledge of MLM helps the system operator to take proper decisions regarding load margin. In this paper, three new schemes using Fuzzy Logic (FL) is developed along with a new formation of sparse constant array. The proposed schemes are tested on IEEE 5-bus, 14-bus, 30-bus, 57-bus and 118 bus test systems under different practical security constraints. The iterative process can be started with random initialization using proposed FL schemes which is not possible using N–R technique. The results are compared with the same of Newton–Raphson (N–R) method technique and the standard fuzzy logic controllers. The comparison indicates the superiority of proposed FL schemes over traditional N–R technique.

Study of SVC for Voltage Stability Enhancement Using MATLAB

Severe and increasing strain has been observed in the power system in recent years due to incongruence between the generation and transmission infrastructure. The kind of stress developed in the system has caused concerns for voltage instability. One of the major causes of voltage instability is the reactive power limit of the system. The Modal Analysis method is used to investigate the stability of the power system and is performed for IEEE 14 Bus system. Then, the weakest bus is identified using the participation factor. Improving the system's reactive power handling capacity via Flexible AC transmission System (FACTS) devices is a remedy for prevention of voltage instability and hence voltage collapse. Here, SVC is used to improve the voltage profile of the system. The simulations are done by using PSAT and continuation power flow technique. The continuation power flow (CPF) is an accurate method for estimating the maximum loading margin.

Optimal location of interline power flow controller in a power system network using ABC algorithm

Abstract This paper proposes a methodology based on installation cost for locating the optimal position of interline power flow controller (IPFC) in a power system network. Here both conventional and non conventional optimization tools such as LR and ABC are applied. This methodology is formulated mathematically based on installation cost of the FACTS device and active power generation cost. The capability of IPFC to control the real and reactive power simultaneously in multiple transmission lines is exploited here. Apart from locating the optimal position of IPFC, this algorithm is used to find the optimal dispatch of the generating units and the optimal value of IPFC parameters. IPFC is modeled using Power Injection (PI) model and incorporated into the problem formulation. This proposed method is compared with that of conventional LR method by validating on standard test systems like 5-bus, IEEE 30-bus and IEEE 118-bus systems. A detailed discussion on power flow and voltage profile improvement is carried out which reveals that incorporating IPFC into power system network in its optimal location significantly enhance the load margin as well as the reliability of the system.

OO-Based STATCOM Installation for Power System Loading Margin Improvement

As electricity demands and power transactions continuously increase, it becomes vulnerable to voltage instability for power systems, generally incurred by over-utilized facilities or any contingency. The transmission system loading margin (LM) enhancement problem with Static Synchronous Compensator (STATCOM) installation can be formulated as a mixed discrete-continuous nonlinear optimization problem (MDCP); due to the complexity of the MDCP, the computing burden might be very heavy. In the paper, the proposed ordinal optimization (OO) based STATCOM installation method is applied to the MDCP to solve for good enough solutions rather than the best solution, so as to largely reduce the computation burden. In the method, the crude method is first used to solve the MDCP and, based on OO theory, the exact method is then used to determine the good enough solutions. Finally, the good enough solution, as uses the fewest STATCOM device units for installation and makes the power system able to provide the required LM, is recommended for network reinforcement.

Static Loadabilty Assessment Using Covariance Matrix Adapted Evolution Strategy

This paper discusses application of Covariance Matrix Adapted Evolution Strategy (CMAES) algorithm for maximizing loadability margin of power system. CMAES is a class of continuous evolutionary algorithm that generates new population members by sampling from a probability distribution that is constructed during the optimization process. IEEE 14 bus , 30 bus and 118 bus systems are considered for simulation purpose. For comparison of the results, primal dual interior point (PDIP), continuation power flow (CPF), Particle swarm optimization algorithms are considered. Statistical performance of CMAES algorithm reveals that even the mean value of maximum loadability is better than maximum loadability obtained in other methods. Even though CMAES takes higher computation time due to the determination of covariance matrix, only this algorithm gives maximum loadability margin.

Reactive Power Reserve Improvement Using Power Systems Inherent Structural Characteristics

This paper considers the use of the inherent structural characteristics of power system networks for improving the reactive power reserve margins for both topologically weak and strong networks. The inherent structural characteristics of the network are derived from the Schur complement of the partitioned Y-admittance matrix using circuit theory representations. Results show that topologically strong networks, operating close to the upper voltage limit could be made to increase their loadability margin by locating reactive power compensators close to generator sources, whereas topologically weak (ill conditioned) networks could be made to operate within the feasible operating limits by locating reactive power compensators on buses farther from generator sources.

Continuation Power Flow Method with Improved Voltage Stability Analysis in Two Area Power System

Power systems operation becomes more important as the load demand increases all over the world. This rapid increase in load demand forces power systems to operate near critical limits due to economic and environmental constraints. The objective in power systems operation is to serve energy with acceptable voltage and frequency to consumers at minimum cost. This paper studies the important power system phenomenon and voltage stability by using continuation power flow method. Voltage collapse scenario is presented which can be a serious result of voltage instability and also the parameters that affected by voltage collapse are discussed. In analysing power system voltage stability, continuation power flow method is utilized which consists of successive load flows. Case studies are carried on 11 bus network in two areas and PV curves for several buses are obtained. Simulation is done with PSAT in MATLAB. Continuation Power Flow is was implemented using Newton Raphson method. In this paper the effect of compensator, placement of generator and variation of line reactance on the voltage stability have been studied and Comparison between performance of installation shunt capacitor, adding generator and variation of line reactance for improve voltage stability has been done. Simulation results show the proper performance of installation shunt capacitor, adding generator and variation of line reactance to improve voltage control and significantly increase the load ability margin of power systems.

OPTIMAL ALLOCATION AND SIZING OF FACTS CONTROLLERS USING DIFFERENTIAL EVOLUTION ALGORITHM

This paper presents the impact of flexible AC transmission systems(FACTS) devices in increasing the loadability margin of the transmission lines without sacrificing their stability and security limits in an electrical power network.

Comprehensive comparison of FACTS devices for exclusive loadability enhancement

AbstractA complete comparison of a number of well‐known flexible alternating current transmission system (FACTS) devices for static voltage stability enhancement is presented. Various performance measures including power–voltage (P–V) curves, voltage profiles, and power losses are compared under normal and contingency conditions. The importance of proper modeling of FACTS devices, including the DC side, is emphasized because, at their limits, most of these devices behave like a fixed capacitor or inductor. A simple placement technique of series FACTS devices and unified power flow controller (UPFC) is proposed considering exclusive loading margin enhancement. A new idea of loading margin increase per cost is proposed to find the appropriate FACTS devices for investment. The paper provides a guide for utilities to have an appropriate choice of FACTS device for enhancing static voltage stability and loading margin by comparing technical merits and demerits of each of these devices in terms of system performance. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Comprehensive control framework for ensuring loading margin of power systems considering demand-side participation

This study presents a comprehensive control framework to ensure desired loading margin (LM) while minimising the corresponding control cost. The proposed framework is divided into corrective control (CC) and preventive control (PC) subproblems. The CC subproblem deals with the condition that a power system encounters voltage instability as a result of severe contingencies. This control is merely devised to restore system stability. The PC subproblem is brought up when the system operates in a stable region but its LM is insufficient. In this manner, the system-operating point is changed such that the desired LM is achieved. One of the features of the proposed methodology is to consider participation of demand-side resources as an effective control facility that reduces control costs considerably. Active and reactive redispatch of generating units and involuntary load curtailment (ILC) are employed along with voluntary demand-side participation as control facilities in CC and PC subproblems. The proposed control framework is examined through case studies conducted on the IEEE 14-bus and the IEEE 118-bus test systems. The results presented demonstrate the effectiveness and efficiency of the proposed framework.

Voltage Stability Enhancement using VSWT with Direct Drive Synchronous Generators

Th is paper investigates about the enhancement in grid voltage stability while integrating the large-scale variable speed wind turbine (VSWT) with direct drive synchronous generators (DDSG). A dynamic modeling and simulat ion of a grid connected VSWT driven DDSG with controllable power inverter strategies suitable for the study was developed, tested and verified. Th is dynamic model with its control scheme can regulate real power, maintain reactive power and generate voltage at different wind speeds. For th is paper, studies were conducted on a standard IEEE 14 bus system augmented by a rad ially connected wind power p lant (WPP) which contains 100 wind turbine generators (WTG). The studies include examin ing the voltage stability (λ-V) curves, voltage magnitude, reactive power delivered, loading margin and voltage collapse of the system. These voltage stability studies are done for the normal state as well as for line contingencies. It is found that large scale VSWT with DDSG at the transmission level has the potential to imp rove the long-term voltage stability of the grid by injecting react ive power with the help of controllable power inverter strategy.

Investigation and Comparison of the Effect of Facts Devices, Capacitors and Lines Reactance Variations on Voltage Stability Improvement and Loadability Enhancement in Two Area Power System

This paper studies the important power system phenomenon and voltage stability by using continuation power flow method. Voltage collapse scenario is presented which can be a serious result of voltage instability and also the parameters that affected by voltage collapse are discussed. In analyzing power system voltage stability, continuation power flow method is utilized which consists of successive load flows. In this paper steady-state modeling of Static VAR Compensator (SVC) and Unified Power Flow Controller (UPFC) and effect of compensator and variation of line reactance on the voltage stability have been studied and Comparison between performance of UPFC and SVC and installation shunt capacitor and variation of line reactance for improve voltage stability has been done.Case studies are carried on 11 bus network in two areas. Simulation is done with PSAT in MATLAB. Continuation Power Flow was implemented using Newton Raphson method. Simulation results show the proper performance of UPFC, SVC, installation shunt capacitor and variation of line reactance to improve voltage control and significantly increase the loadability margin of power systems. Full Text: PDF

Controlling chaos and voltage collapse using an ANFIS-based composite controller-static var compensator in power systems

Chaos and voltage collapse exist in power systems due to critical loading and disturbing of energy (DE). These phenomena cause instability in power system operation and must be avoided. In this paper, an ANFIS-based composite controller-static var compensator (CC-SVC) was proposed to control both chaotic oscillations and voltage collapse. The ANFIS-based CC-SVC was proposed because its computation was more efficient than Mamdani fuzzy logic controller. Adaptive network parameters were obtained through a training process. The controller parameters were automatically updated by off-line training. Both chaos and voltage collapse were able to control and suppress effectively by the proposed method. Furthermore, the load voltage was held to a set value by adjusting the supplied reactive power. When the reactive load was increased, the SVC susceptance and reactive power supplied by the SVC also increased. The proposed method was able to maintain the load voltage and to increase the loading margin.