Representation Of Power System Research Articles

Computational framework combining static and transient power system security evaluation using uncertainties

Abstract This paper presents a simplified but effective procedure to represent power system uncertainties that allow the development of a computational tool to tackle the power system probabilistic security problem from both the small signal stability (SSS) perspective, and the transient stability (TRS) analysis perspective. A set of examples using the New England test-system is presented and discussed. Among the advantages of the suggested method, the following points are evident: (i) the ability to discriminate between the three types of uncertainties (scenarios, fault events, and noise types) that permeate power systems and that are relevant to the system security; (ii) the capacity to use existing traditional tools from both small signal dynamic analysis and transient stability analysis to adapt them easily to the well-established concept of probabilistic adequacy assessment, without resorting to abstruse and hard-to-implement theoretical techniques; (iii) the enormous advantage of usual availability for the required statistical data (no hard-to-collect data are required); and (iv) proposal of a conceptual procedure that renders a highly combinatorial problem amenable to current state-of-the-art hardware resources, within acceptable limits of computational burden. Important practical results that one may wish to highlight are related to the effective representation of noise uncertainties through a straightforward combination of weighted histograms, and the successful performance of the new Apparent Stability Index – ASI.

Enhanced particle swarm optimisation applied for transient angle and voltage constrained discrete optimal power flow with flexible AC transmission system

Transient stability constrained optimal power flow (TSCOPF) is increasingly important as many modern power systems nowadays have been forced to operate close to their stability limits. In this study, a non-convex mixed integer non-linear program (MINLP) TSCOPF model with consideration of valve-point effects and discrete control variables is first presented, in which the energy-based transient angle and voltage constraints are simultaneously considered as an integrated stability control process. The proposed model is general and flexible with support for any complex dynamic components, including detailed generator model and flexible AC transmission system (FACTS) devices, valve-point effects and discrete control variables. An enhanced particle swarm optimisation with dynamic adjusted inertia weight and shrinking Gaussian distribution disturbance is then proposed to solve this challenging MINLP-TSCOPF problem with comprehensive testing and evaluation using a benchmarking MINLP mathematical function and two representative power systems with FACTS devices.

Determination of Whitening Filter Order for Estimation of Electromechanical Mode by Regression Model Representing Power System Damping Characteristics

SUMMARYThis paper proposes a new method of estimating accurately the modal damping of a weakly damped electromechanical oscillation in power systems. The proposed method is based on a whitening filter (finite impulse response filter) to estimate the modal damping from the system response and a regression model to express the relation between the modal damping and system state variables, such as the active and reactive power outputs of generators. The feature of the method is that an optimal order of the whitening filter is determined so as to minimize the error of the linear regression model. A simulation study using the IEEJ EAST 10 machine model shows that the proposed method is effective for accurate estimation of weakly damped oscillation modes.

Reserve from wind power potential in system economic loading

The growth of wind power in some power systems is hampered by the system requirement for emergency reserve to cover loss of the biggest infeed. The study demonstrates that reserve provision from the wind sector itself has economic and operational benefits. A heuristic algorithm has been developed that can model the relevant aspects of emergency reserve provision in a system with both thermal and wind generations. The proposed algorithm is first validated by comparing its performance with established economic scheduling methods applied to a representative power system. The algorithm is then used to demonstrate the economic benefit of reserve provision from the wind sector. It is shown that such provision reduces wind energy curtailment and thermal unit ramping. Finally, it is shown that a wind sector capable of providing emergency reserve can expand economically beyond the capacity limit that would otherwise apply.

From Each According to its Ability: Distributed Grid Regulation With Bandwidth and Saturation Limits in Wind Generation and Battery Storage

The problem addressed here is motivated by distributed control for frequency regulation in the electric power grid, and by the characteristics of new technologies contributing to this control objective: wind generation and battery energy storage. In the large scale, coupled dynamical system of the power grid, we seek a distributed control design approach that can successfully share control effort among two classes of actuators: one class having low bandwidth, but broader actuation limits (controllable power output from wind turbines); and a second class, having narrow actuation limits, essentially zero gain at dc, but much broader bandwidth actuation possible at high frequencies (power output from battery energy storage). In this context, we extend the “saturation-respecting” design methodology developed by Saberi and his co-workers, adapting their low-high gain method with partitioning of slow acting actuator input channels (e.g., wind turbine power changes) from fast acting actuators (battery power delivery). The design methodology, resulting frequency regulation performance, and characteristics of control actuation from individual wind generators and batteries is demonstrated in representative test power system models.

Low Voltage Ride Through Characterization of Wind Energy Conversion Systems

Low Voltage Ride Through (LVRT) has emerged as an essential requirement that system operators demand to wind energy conversion systems (WECS). LVRT characterization is to get the minimum grid voltage profile under which the transient stability of WECS is not possible. This paper will determine the LVRT capability of existing Egyptian WECS. The methodology for analyzing wind power systems will require the modeling of three different wind turbine generator technologies. These are the fixed speed induction generator (SCIG), variable slip IG with variable rotor resistance, and doubly-fed IG with rotor-side converter. The methodology also requires the modeling of wind power plant, and the equivalent representation of power system. Simulation results are obtained for different IG technologies. They will provide a good understanding of the dynamic behavior of existing wind farms, and how to improve the stability and LVRT capability. Moreover, the results will form a template for the requirements by wind farm developers and power utilities in Egypt when developing new wind farms.

AN EFFECTIVE DISTRIBUTED MODEL FOR XMLISED POWER SYSTEM DATA GENERATION

One of the outcomes of the continuous research on the evolution of distributed computing is the Web services. The aim of this paper is to represent Power System data effectively in XML in order to improve the interoperability and to develop an enhanced distributed model for unique XMLised Power System Data generation for solving various Power System applications in heterogeneous environment. Power System industries are now increasingly becoming privatized and hence the system data is becoming increasingly distributed, with more constrained and complex operational and control requirements. Because of the complex physical connectivity of the power systems, all levels of industry like generation, transmission, distribution and market need proper operational and equipmental data. As expected, the data to be shared between different power system applications is huge and hence it is vital to have an efficient and reliable data generation model to reduce more human efforts and to have the data in a secure and compatible form. The developed JAX-RPC-based model has the capability to generate the data dynamically in XML, fetching the power system data from various sources such as database, text file, etc. The standards such as XML and SOAP enable software design based on loose coupling which reduces restriction and eliminates similarity requirement between coordinating applications.

FTT:Power : A global model of the power sector with induced technological change and natural resource depletion

This work introduces a model of Future Technology Transformations for the power sector (FTT:Power), a representation of global power systems based on market competition, induced technological change (ITC) and natural resource use and depletion. It is the first component of a family of sectoral bottom-up models of technology, designed for integration into the global macroeconometric model E3MG. ITC occurs as a result of technological learning produced by cumulative investment and leads to highly nonlinear, irreversible and path dependent technological transitions. The model uses a dynamic coupled set of logistic differential equations. As opposed to traditional bottom-up energy models based on systems optimisation, such differential equations offer an appropriate treatment of the times and structure of change involved in sectoral technology transformations, as well as a much reduced computational load. Resource use and depletion are represented by local cost–supply curves, which give rise to different regional energy landscapes. The model is explored for a single global region using two simple scenarios, a baseline and a mitigation case where the price of carbon is gradually increased. While a constant price of carbon leads to a stagnant system, mitigation produces successive technology transitions leading towards the gradual decarbonisation of the global power sector.

Multi-area reliability evaluation including frequency and duration indices with multiple time varying load curves

The reliability evaluation of multi-area systems is part of the expansion planning process of a power system. In order to accurately estimate the system and areas reliability indices, especially the frequency and duration (F&D) indices, the dynamic behavior of system components must be adequately represented with particular attention to the variation of each area load. Nowadays, the most efficient methods for multi-area reliability evaluation do not represent the chronological aspects of the different areas loads. The method that directly considers these aspects is the sequential Monte Carlo simulation, however requiring a high computational effort. This paper presents the application of some methods that represent the chronological aspects of the load to the reliability evaluation of multi-area systems and evaluates their performance and accuracy. The main purpose is to obtain a model for multi-area reliability evaluation that represents the different load curve of each area and accurately estimates the F&D indices. Results obtained by the studied methods are presented for two systems, one composed of two areas and the other based on a representation of the Brazilian interconnected power system with four areas.

Modeling UPFC into Multi-Machine Power Systems

Modeling of unified power flow control (UPFC) into multi-machine power systems by Wang, published by IET, has been widely quoted by many researchers. However, the correctness of the derivation of its equations has not been strictly scrutinized. The model cannot properly represent power system networks in its current form and need to be corrected. In this paper, the model proposed by Wang is revisited and the equations re-derived obtaining different results. The corrected model was developed and tested on three-machine and New England power systems installed with a UPFC. The DC link capacitor voltage is controlled in UPFC by modulating the phase angle of the excitation transformer voltage. The effect of the controller in damping of the low-frequency oscillations is demonstrated by using the proposed correct model and the results are compared with model presented by Wang.

A methodology for the efficient computer representation of dynamic power systems: Application to wind parks

ABSTRACTThis contribution presents a methodology to efficiently obtain the numerical and computer solution of dynamic power systems with high penetration of wind turbines. Due to the excessive computational load required to solve the abc models that represent the behavior of the wind turbines, a parallel processing scheme is proposed to enhance the solution of the overall system. Case studies are presented which demonstrate the effectiveness and applications of the proposed methodology. Copyright © 2012 John Wiley & Sons, Ltd.

Determination of Whitening Filter Order for Estimation of Electromechanical Mode by Regression Model Representing Power System Damping Characteristics

SUMMARY This paper proposes a new method of estimating accurately the modal damping of a weakly damped electromechanical oscillation in power systems. The proposed method is based on a whitening filter (finite impulse response filter) to estimate the modal damping from the system response and a regression model to express the relation between the modal damping and system state variables, such as the active and reactive power outputs of generators. The feature of the method is that an optimal order of the whitening filter is determined so as to minimize the error of the linear regression model. A simulation study using the IEEJ EAST 10 machine model shows that the proposed method is effective for accurate estimation of weakly damped oscillation modes.

Service Oriented Architectural Model for Load Flow Analysis in Power Systems

Service Oriented Architectural Model for Load Flow Analysis in Power Systems The main objective of this paper is to develop the Service Oriented Architectural (SOA) Model for representation of power systems, especially of computing load flow analysis of large interconnected power systems. The proposed SOA model has three elements namely load flow service provider, power systems registry and client. The exchange of data using XML makes the power system services standardized and adaptable. The load flow service is provided by the service provider, which is published in power systems registry for enabling universal visibility and access to the service. The message oriented style of SOA using Simple Object Access Protocol (SOAP) makes the service provider and the power systems client to exist in a loosely coupled environment. This proposed model, portraits the load flow services as Web services in service oriented environment. To suit the power system industry needs, it easily integrates with the Web applications which enables faster power system operations.

Application of ant colony optimization for reconfiguration of shipboard power system

The shipboard power system (SPS) supplies energy to sophisticated systems of weapons, navigation, services and communication. Due to battle damage or faults, electric energy delivery may be interrupted to critical loads. Reconfiguration of electrical network in the SPS is necessary, to either restore the service to all the possible loads or to meet some of the operational requirements of the naval ship. In this research work, ant colony optimization (ACO) has been utilized to reconfigure given SPS network, satisfying the operational requirements, priorities of the loads and considering islanding operation and distributed generation. Graph theory has been applied to represent SPS electrical network to simplify the mathematical formulation to be used by ACO. Developed technique has been applied to an eight bus and thirteen bus representative shipboard power system model to reconfigure, while maximizing the load magnitude, or load priority, or load magnitude with priority. Satisfactory results have been obtained for both the test cases. Keywords: Shipboard power systems, islanding, reconfiguration, graph theory, ant colony algorithm

Novel Dynamic Representation and Control of Power Systems With FACTS Devices

FACTS devices have been shown to be useful in damping power system oscillations. However, in large power systems, the FACTS control design is complex due to the combination of differential and algebraic equations required to model the power system. In this paper, a new method to generate a nonlinear dynamic representation of the power network is introduced to enable more sophisticated control design. Once the new representation is obtained, a back stepping methodology for the UPFC is utilized to mitigate the generator oscillations. Finally, the neural network approximation property is utilized to relax the need for knowledge of the power system topology and to approximate the nonlinear uncertainties. The net result is a power system representation that can be used for the design of an enhanced FACTS control scheme. Simulation results are given to validate the theoretical conjectures.

Multi-parameter trajectory sensitivity approach for location of series-connected controllers to enhance power system transient stability

Determining suitable locations of series-connected controllers is a practical problem when it is necessary to install them in modern power systems. The aim of this paper is to find the best location of series controllers in order to reduce the proximity to instability of a current operating point of a power system, from a transient stability viewpoint. In order to achieve this goal, a general approach has been developed based on an index of proximity to instability and trajectory sensitivity analysis. An efficient way to carry out multi-parameter sensitivities is formulated analytically and solved simultaneously with the set of differential-algebraic equations representing power system's dynamics within a single-frame of reference. Simulations are performed on 9-bus and 39-bus benchmark power systems for illustration purposes. Results show that the proposed approach provides the most effective location of series-connected controllers to improve the power system's transient behavior.

A functional failure reasoning methodology for evaluation of conceptual system architectures

In this paper, we introduce a new methodology for reasoning about the functional failures during early design of complex systems. The proposed approach is based on the notion that a failure happens when a functional element in the system does not perform its intended task. Accordingly, a functional criticality is defined depending on the role of functionality in accomplishing designed tasks. A simulation-based failure analysis tool is then used to analyze functional failures and reason about their impact on overall system functionality. The analysis results are then integrated into an early stage system architecture analysis framework that analyzes the impact of functional failures and their propagation to guide system-level architectural design decisions. With this method, a multitude of failure scenarios can be quickly analyzed to determine the effects of architectural design decisions on overall system functionality. Using this framework, design teams can systematically explore risks and vulnerabilities during the early (functional design) stage of system development prior to the selection of specific components. Application of the presented method to the design of a representative aerospace electrical power system (EPS) testbed demonstrates these capabilities.

Neural networks for adaptive control coordination of PSSs and FACTS devices in multimachine power system

The paper develops a new design procedure for online control coordination which leads to adaptive power system stabilisers (PSSs) and/or supplementary damping controllers of flexible ac transmission system (FACTS) devices for enhancing the stability of the electromechanical modes in a multimachine power system. The controller parameters are adaptive to the changes in system operating condition and/or configuration. Central to the design is the use of a neural network synthesised to give in its output layer the optimal controller parameters adaptive to system operating condition and configuration. A novel feature of the neural-adaptive controller is that of representing the system configuration by a reduced nodal impedance matrix which is input to the neural network. Only power network nodes with direct connections to generators and FACTS devices are retained in the reduced nodal impedance matrix. The system operating condition is represented in terms of the measured generator power loadings, which are also input to the neural network. For a representative power system, the neural network is trained and tested for a wide range of credible operating conditions and contingencies. Both eigenvalue calculations and time–domain simulations are used in the testing and verification of the dynamic performance of the neural-adaptive controller.

Identification of coherent generators considering the electrical proximity for drastic dynamic equivalents

This paper describes an application of the coherency-based dynamic equivalent methodology to determine drastic reductions in the representation of power systems. This condition is necessary for real time power system simulator studies. The paper demonstrates that the exclusion of electrically distant generators from the coherent groups solves the convergence problems that may appear in the power flow algorithm during the calculation of drastic dynamic equivalents. This paper also demonstrates that for each fault neither the strongly coherent generators are always electrically close, nor the approximately coherent generators are always electrically distant. The New England system and two simplified configurations of the Brazilian interconnected power system are considered in the studies.

An Optimal Generation Rescheduling Approach for Transient Stability Enhancement

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper presents a new generation rescheduling approach for preventive control of power systems, which can optimally reallocate power generations for multiple unstable contingencies. The transient stability constraints used in the optimal rescheduling model are described by a heuristic stability performance index. A backward integration technique is proposed to evaluate gradient of the performance index. Using the gradient, the functional inequality constraints imposed by unstable contingencies are expressed by linear inequalities, and the rescheduling problem is solved iteratively. Effectiveness of the approach is demonstrated by numerical tests on a representation of North-China power system. </para>