Showing papers on "Power system simulation published in 2011"

MATPOWER: Steady-State Operations, Planning, and Analysis Tools for Power Systems Research and Education

Abstract: MATPOWER is an open-source Matlab-based power system simulation package that provides a high-level set of power flow, optimal power flow (OPF), and other tools targeted toward researchers, educators, and students. The OPF architecture is designed to be extensible, making it easy to add user-defined variables, costs, and constraints to the standard OPF problem. This paper presents the details of the network modeling and problem formulations used by MATPOWER, including its extensible OPF architecture. This structure is used internally to implement several extensions to the standard OPF problem, including piece-wise linear cost functions, dispatchable loads, generator capability curves, and branch angle difference limits. Simulation results are presented for a number of test cases comparing the performance of several available OPF solvers and demonstrating MATPOWER's ability to solve large-scale AC and DC OPF problems.

Simulation and Hardware Implementation of Incremental Conductance MPPT With Direct Control Method Using Cuk Converter

Abstract: This paper presents simulation and hardware implementation of incremental conductance (IncCond) maximum power point tracking (MPPT) used in solar array power systems with direct control method. The main difference of the proposed system to existing MPPT systems includes elimination of the proportional-integral control loop and investigation of the effect of simplifying the control circuit. Contributions are made in several aspects of the whole system, including converter design, system simulation, controller programming, and experimental setup. The resultant system is capable of tracking MPPs accurately and rapidly without steady-state oscillation, and also, its dynamic performance is satisfactory. The IncCond algorithm is used to track MPPs because it performs precise control under rapidly changing atmospheric conditions. MATLAB and Simulink were employed for simulation studies, and Code Composer Studio v3.1 was used to program a TMS320F2812 digital signal processor. The proposed system was developed and tested successfully on a photovoltaic solar panel in the laboratory. Experimental results indicate the feasibility and improved functionality of the system.

Efficient Modeling of Modular Multilevel HVDC Converters (MMC) on Electromagnetic Transient Simulation Programs

Abstract: The number of semiconductor switches in a modular multilevel converter (MMC) for HVDC transmission is typically two orders of magnitudes larger than that in a two or three level voltage-sourced converter (VSC). The large number of devices creates a computational challenge for electromagnetic transient simulation programs, as it can significantly increase the simulation time. The paper presents a method based on partitioning the system's admittance matrix and deriving an efficient time-varying Thevenin's equivalent for the converter part. The proposed method does not make use of approximate interfaced models, and mathematically, is exactly equivalent to modelling the entire network (converter and external system) as one large network. It is shown to drastically reduce the computational time without sacrificing any accuracy. The paper also presents control algorithms and other modelling aspects. The efficacy of the proposed method is demonstrated by simulating a point-to-point VSC-MMC-based HVDC transmission system.

Reserve Requirements for Wind Power Integration: A Scenario-Based Stochastic Programming Framework

Abstract: We present a two-stage stochastic programming model for committing reserves in systems with large amounts of wind power. We describe wind power generation in terms of a representative set of appropriately weighted scenarios, and we present a dual decomposition algorithm for solving the resulting stochastic program. We test our scenario generation methodology on a model of California consisting of 122 generators, and we show that the stochastic programming unit commitment policy outperforms common reserve rules.

Stochastic Optimization Model to Study the Operational Impacts of High Wind Penetrations in Ireland

Abstract: A stochastic mixed integer linear optimization scheduling model minimizing system operation costs and treating load and wind power production as stochastic inputs is presented. The schedules are updated in a rolling manner as more up-to-date information becomes available. This is a fundamental change relative to day-ahead unit commitment approaches. The need for reserves dependent on forecast horizon and share of wind power has been estimated with a statistical model combining load and wind power forecast errors with scenarios of forced outages. The model is used to study operational impacts of future high wind penetrations for the island of Ireland. Results show that at least 6000 MW of wind (34% of energy demand) can be integrated into the island of Ireland without significant curtailment and reliability problems.

Modeling Guidelines and a Benchmark for Power System Simulation Studies of Three-Phase Single-Stage Photovoltaic Systems

Abstract: This paper presents modeling guidelines and a benchmark system for power system simulation studies of grid-connected, three-phase, single-stage Photovoltaic (PV) systems that employ a voltage-sourced converter (VSC) as the power processor. The objective of this work is to introduce the main components, operation/protection modes, and control layers/schemes of medium- and high-power PV systems, to assist power engineers in developing circuit-based simulation models for impact assessment studies, analysis, and identification of potential issues with respect to the grid integration of PV systems. Parameter selection, control tuning, and design guidelines are also briefly discussed. The usefulness of the benchmark system is demonstrated through a fairly comprehensive set of test cases, conducted in the PSCAD/EMTDC software environment. However, the models and techniques presented in this paper are independent of any specific circuit simulation software package. Also, they may not fully conform to the methods exercised by all manufacturers, due to the proprietary nature of the industry.

A Computational Framework for Uncertainty Quantification and Stochastic Optimization in Unit Commitment With Wind Power Generation

Abstract: We present a computational framework for integrating a state-of-the-art numerical weather prediction (NWP) model in stochastic unit commitment/economic dispatch formulations that account for wind power uncertainty. We first enhance the NWP model with an ensemble-based uncertainty quantification strategy implemented in a distributed-memory parallel computing architecture. We discuss computational issues arising in the implementation of the framework and validate the model using real wind-speed data obtained from a set of meteorological stations. We build a simulated power system to demonstrate the developments.

Contingency-Constrained Unit Commitment With $n - K$ Security Criterion: A Robust Optimization Approach

Abstract: This paper presents a new approach for the contingency-constrained single-bus unit commitment problem. The proposed model explicitly incorporates an n - K security criterion by which power balance is guaranteed under any contingency state comprising the simultaneous loss of up to K generation units. Instead of considering all possible contingency states, which would render the problem intractable, a novel method based on robust optimization is proposed. Using the notion of umbrella contingency, the robust counterpart of the original problem is formulated. The resulting model is a particular instance of bilevel programming which is solved by its transformation to an equivalent single-level mixed-integer programming problem. Unlike previously reported contingency-dependent approaches, the robust model does not depend on the size of the set of credible contingencies, thus providing a computationally efficient framework. Simulation results back up these conclusions.

Incorporating Uncertainty of Wind Power Generation Forecast Into Power System Operation, Dispatch, and Unit Commitment Procedures

Abstract: An approach to evaluate the uncertainties of the balancing capacity, ramping capability, and ramp duration requirements is proposed. The approach includes three steps: forecast data acquisition, statistical analysis of retrospective information, and prediction of grid balancing requirements for a specified time horizon and a given confidence level. An assessment of the capacity and ramping requirements is performed using a specially developed probabilistic algorithm based on histogram analysis, capable of incorporating multiple sources of uncertainty - both continuous (wind and load forecast errors) and discrete (forced generator outages and startup failures). A new method called the “flying-brick” technique is developed to evaluate the look-ahead required generation performance envelope for the worst-case scenario within a user-specified confidence level. A self-validation process is used to validate the accuracy of the confidence intervals. To demonstrate the validity of the developed uncertainty assessment methods and its impact on grid operation, a framework for integrating the proposed methods with an energy management system (EMS) is developed. Demonstration through EMS integration illustrates the applicability of the proposed methodology and the developed tool for actual grid operation and paves the road for integration with EMS systems in control rooms.

Unit Commitment With Volatile Node Injections by Using Interval Optimization

Abstract: In response to the challenges brought by uncertain bus load and volatile wind power to power system security, this paper presents a novel unit commitment formulation based on interval number optimization to improve the security as well as economy of power system operation. By using full-scenario analysis, the worst-case impact of volatile node injection on unit commitment is acquired, so that the proposed model can always provide a secure and economical unit commitment result to the operators. Scenarios generation and reduction method based on interval linear programming theory are used to accelerate the solution procedure without loss of optimality. Benders decomposition is also implemented to reduce the complexity of this large-scale interval mixed integer linear programming, and prove the rationality and rigor of our proposed method. The numerical results indicate better secure and economical features of the proposed method comparing with the traditional one.

Power system and communication network co-simulation for smart grid applications

Abstract: The vision of a smart grid is predicated upon pervasive use of modern digital communication techniques to today's power system. As wide area measurements and control techniques are being developed and deployed for a more resilient power system, the role of communication network is becoming prominent. Power system dynamics gets influenced by the communication delays in the network. Therefore, extensive integration of power system and its communication infrastructure mandates that the two systems are studied as a single distributed cyber-physical system. This paper proposes a power/network co-simulation framework which integrates power system dynamic simulator and network simulator together using an accurate synchronization mechanism. The accuracy is tunable based on the time-scale requirements of the phenomena being studied. This co-simulation can improve the practical investigation of smart grid and evaluate wide area measurement and control schemes. As a case study an agent-based remote backup relay system is simulated and validated on this co-simulation framework.

A Combined State-Space Nodal Method for the Simulation of Power System Transients

Abstract: This paper presents a new solution method that combines state-space and nodal analysis for the simulation of electrical systems. The presented flexible clustering of state-space-described electrical subsystems into a nodal method offers several advantages for the efficient solution of switched networks, nonlinear functions, and for interfacing with nodal model equations. This paper extends the concept of discrete companion branch equivalent of the nodal approach to state-space described systems and enables natural coupling between them. The presented solution method is simultaneous and enables benefitting from the advantages of two different modeling approaches normally exclusive from one another.

Mosaik: A framework for modular simulation of active components in Smart Grids

Abstract: This paper presents the requirements and a concept for a modular Smart Grid simulation framework based on an automatic composition of existing, heterogeneous simulation models. The composition problem is broken down into different layers, for each of which first concepts for solving the problem are presented. A prototype showing the feasibility of the presented concept has been developed. First simulation results of a Smart Grid scenario including electric vehicles as well as renewable energy sources are presented. Finally, the limitations of the prototype and possible improvements are discussed.

Assessing the Yearly Impact of Wind Power Through a New Hybrid Deterministic/Stochastic Unit Commitment

Abstract: This paper proposes a new unit commitment (UC) formulation for a power system with significant levels of wind generation. The proposed scheme departs from existing unit commitments in that it explicitly models the day-ahead predicted residual demand probability density function (PDF) including the effect of wind power curtailment. This PDF is then used to define a constraint on the probability of the residual demand exceeding the scheduled reserve, which is imposed in addition to the standard N-1 deterministic security criterion. This hybrid probabilistic/deterministic form maintains the mixed-integer linear structure that makes the proposed UC compatible with highly efficient commercially available solvers. Numerical examples illustrate the economical and technical benefits obtained by systematically including wind curtailment as decisions variables in the UC. In addition, the paper computes the hourly day-ahead UC schedule over the course of one year for a typical power system to illustrate the impact of wind power penetration on measures such as operation costs, incremental costs, emission levels, on/off unit switching operations, and reserve levels.

MatDyn, A New Matlab-Based Toolbox for Power System Dynamic Simulation

Abstract: In this paper, we present a new Matlab-based toolbox for power system analysis, called MatDyn. It is open-source software, and available for everyone to download. Its design philosophy is based on the well-known open-source Matlab toolbox MATPOWER, but its focus is transient stability analysis and time-domain simulation of power systems, instead of steady-state calculations. MatDyn's philosophy, design criteria, program structure, and implementation are discussed in detail. A trade-off is achieved between the flexibility of the program and readability of the code. MatDyn retains overall flexibility by, for instance, allowing user defined models, and custom integration methods. The software is validated by comparing its results with those obtained by the commercial grade power system analysis package, PSS/E. Despite the fact that MatDyn is fairly new, it has already been extensively used in research and education. This paper reports interesting results obtained with MatDyn in recent research that would be hard to obtain using commercial software.

Comparison of Three Electromechanical Oscillation Damping Estimation Methods

Abstract: This paper describes three data driven methods to monitor electromechanical oscillations in interconnected power system operation. The objective is to compare and contrast the performance of the methods. The accuracy of damping ratio and frequency of oscillations are the measures of the performance of the algorithms. The advantages and disadvantages of various techniques and their limitations to measurement noise have been considered while assessing performance. The target frequency and damping are computed using the Nordic power system simulation model.

Study of battery modeling using mathematical and circuit oriented approaches

Abstract: Energy storage improves the efficiency and reliability of the electric utility system. The most common device used for storing electrical energy is batteries. To investigate power converter-based charge and discharge control of a battery storage device, effective battery models are critically needed. This paper presents a comparison study of mathematical and circuit-oriented battery models with a focus on lead-acid batteries that are normally used for large power storage applications. The paper shows how mathematical and circuit-oriented battery models are developed to reflect typical battery electrochemical properties. The relation between mathematical and circuit-oriented battery models is analyzed in the paper. Comparison study is made to investigate the difference and complexity in parameter extraction using the two different modeling approaches. The paper shows that the fundamental battery electromechanical relationship is usually built into the battery mathematical model but is not directly available in the circuit-oriented model. In terms of the computational complexity, the circuit-oriented battery model requires much expensive computing resources. Performance study is conducted to evaluate various factors that may affect the behavior of the mathematical battery models.

New Models and Concepts for Power System Reliability Evaluation Including Protection System Failures

Abstract: This paper develops new models and concepts for incorporating the effect of protection system failures into power system reliability evaluation. The two types of protection failures, i.e., undesired-tripping mode and fail-to-operate mode, and their impact on reliability modeling are discussed. A complete Markov model for current-carrying components is established and its simplified form appropriately describes the overall reliability situation of individual components. Concepts of self-down state and induced-down state are introduced and used to build the composite unit model for quantitatively assessing the influence of protection failures on modeling system states. Finally, a Markov model of power systems with protection failures is proposed for system reliability evaluation. The proposed methodology is then illustrated in detail.

An intelligent system for detecting faults in photovoltaic fields

Abstract: In this work, an intelligent system for automatic detection of fault in PV fields is proposed. This system is based on a Takagi-Sugeno-Kahn Fuzzy Rule-Based System (TSK-FRBS), which provides an estimation of the instant power production of the PV field in normal functioning, i.e, when no faults occur. Then, the estimated power is compared with the real power and an alarm signal is generated if the difference between powers overcomes a threshold. The TSK-FRBS has been trained using data collected from a PV plant simulator, during normal functioning. Preliminary tests were carried out in a simulated framework, by reproducing both normal and fault conditions. Results show that the system can recognize more than 90% of fault conditions, even when noisy data are introduced.

Real time simulation of a power system with VSG hardware in the loop

Abstract: The method to investigate the interaction between a Virtual Synchronous Generator (VSG) and a power system is presented here. A VSG is a power-electronics based device that emulates the rotational inertia of synchronous generators. The development of such a device started in a pure simulation environment and extends to the practical realization of a VSG. Investigating the interaction between a VSG and a power system is a problem, as a power system cannot be manipulated without disturbing customers. By replacing the power system with a real time simulated one, this problem can be solved. The VSG then interacts with the simulated power system through a power interface. The advantages of such a laboratory test-setup are numerous and should prove beneficial to the further development of the VSG concept.

Modeling and Simulation of Wide-Area Communication for Centralized PMU-Based Applications

Abstract: Phasor-based wide-area monitoring and control (WAMC) systems are becoming a reality with increased research, development, and deployments. Many potential control applications based on these systems are being proposed and researched. These applications are either local applications using data from one or a few phasor measurement units (PMUs) or centralized utilizing data from several PMUs. An aspect of these systems, which is less well researched, is the WAMC system's dependence on high-performance communication systems. This paper presents the results of research performed in order to determine the requirements of transmission system operators on the performance of WAMC systems in general as well as the characteristics of communication delays incurred in centralized systems that utilize multiple PMUs distributed over a large geographic area. This paper presents a summary of requirements from transmission system operators with regards to a specific set of applications and simulations of communication networks with a special focus on centralized applications. The results of the simulations indicate that the configuration of central nodes in centralized WAMC systems needs to be optimized based on the intended WAMC application.

Application of SMES Unit in Improving the Performance of an AC/DC Power System

Abstract: This paper investigates the use of a superconducting magnetic energy storage (SMES) unit to improve the performance of an ac/dc power system. In this context, investigations have been conducted on a large turbine-generator unit connected to a high-voltage direct current (HVDC) system. The impact of HVDC converter station faults on the torsional torques induced in turbine-generator shafts with and without using an SMES unit is elaborated. Faults considered are fire-through, misfire, short circuit across the inverter station, flashover, and a three-phase short circuit in the ac system. These investigations are studied using an electromagnetic transient program power system simulation/electromagnetic transients including DC (PSCAD/EMTDC) and the results are presented in the form of typical time responses as well as harmonic analysis.

The value of operational flexibility in power systems with significant wind power generation

Abstract: There is a growing body of evidence demonstrating how large penetrations of wind power generation in power systems contribute to increase the cost and the complexity of grid operations. Those costs and increased complexity are directly linked to the random nature of the wind over time, which requires system operators to carry more reserve capacity to cope with that randomness if current security and reliability standards are to be maintained. Moreover, as the frequency spectrum of the wind generation random process is relatively wide (from 10−6 to about slightly above 1 Hz), the reserves available must be capable to be deployed fast enough to counter this variability. Therefore, in systems with significant wind power penetrations the security-constrained unit commitment programs should be capable of capturing the reserve capacity deployment requirements entailed by the random wind dynamics. More fundamentally, however, what is required is that the dispatchable portion of the generation system providing reserves is flexible enough. In other words, there must be enough flexible capacity available to ramp up and down so to shadow the wind's caprices. In this paper, we formulate a modification of the classic unit commitment formulation ot assess the value of such operational flexibility in power systems with large proportions of wind capacity. We discuss some economic and technical indicators of flexibility.

Composite Reliability Evaluation Using Monte Carlo Simulation and Least Squares Support Vector Classifier

Abstract: This paper presents a fast and efficient method which combines the Monte Carlo simulation (MCS) and the least squares support vector machine (LSSVM) classifier, for reliability evaluation of composite power system. LSSVM is used to accurately pre-classify the power system operating states as either success or failure states during the Monte Carlo sampling. These pre-classified failure states are then evaluated for adequacy analysis using DC power flow to calculate reliability indices. As a result, the computing time to perform power flow analysis of the system success states is eliminated. The proposed hybrid method is applied to the IEEE Reliability Test System (IEEE-RTS-79) and simulation results obtained using LSSVM with linear and nonlinear kernels are compared with that of nonsequential MCS. These promising results demonstrate the efficacy of the proposed MCS-LSSVM based hybrid method in terms of both classification accuracy and computational time in evaluating the composite power system reliability.

A Two-Stage Stochastic Program for Unit Commitment Under Uncertainty in a Hydro-Thermal Power System

Abstract: We develop a two-stage stochastic programming model with integer first-stage and mixed-integer recourse for solving the unit commitment problem in power generation in the presence of uncertainty of load profiles. The solution methodology rests on a novel scenario decomposition method for stochastic integer programming. This method combines Lagrangian relaxation of non-anticipativity constraints with branch-and-bound. It can be seen as a decomposition algorithm for large-scale mixed-integer linear programs with block-angular structure. With realistic data from a German utility we validate our model and carry out test runs. Sizes of these problems go up to 20.000 integer and 150.000 continuous variables together with up to 180.000 constraints. Subject classifications: Programming, stochastic: Scenario Decomposition of mixedinteger programs. Natural resources, energy: Unit commitment under uncertainty. Unit commitment aims at finding a fuel cost optimal scheduling of start-up/shut-down decisions and operation levels for power generation units over some time horizon. This is a central task in reliable and efficient operation of power systems. Solution strategies for the unit commitment problem are influenced by the power mix of the generation system. In the present paper we consider a hydro-thermal system as it is met with the German power company VEAG Vereinigte Energiewerke AG Berlin. This system comprises conventional coal and gas fired thermal units as well as pumped-storage plants. The latter imply substantial coupling over time of scheduling decisions which, compared with purely thermal systems, further complicates the problem. Mathematically, unit commitment is handled as a large-scale mixed-integer optimization problem. Advances in mathematical methodology, software engineering and hardware have

From Smart Grid to Super Grid: Solutions with HVDC and FACTS for grid access of renewable energy sources

Abstract: Innovative solutions with HVDC (High Voltage Direct Current) and FACTS (Flexible AC Transmission Systems) have the potential to cope with the system planning and operational challenges of global climate developments and the call for changes in the way electricity is supplied. New power electronic technologies with self-commutated converters make advanced technical features possible, such as independent control of active and reactive power, and the capability to supply weak or passive networks. As part of the overall planning considerations, this paper presents the fundamental system planning, modeling and operational challenges of connecting large wind farms (both onshore and offshore) via long transmission systems, as well as the practical applications of traditional and new power electronic technologies.

A Comparison of Different Frequency Scanning Methods for Study of Subsynchronous Resonance

Abstract: This paper compares four different methods for determining the electrical damping of a power system seen from one generator as a function of frequency. This information is useful when the risk for subsynchronous resonance (SSR) in the system is evaluated. The study compares one frequency scanning method which is implemented in a time-domain digital simulation program with three methods of different complexity based on analytical calculations. The time-domain simulation method is easily implemented with a detailed model of the power system including complex load and generator models, whereas the analytical methods are based on simpler models of the power system. The computational effort is much larger for the time-domain method than for the analytical methods. In the study, all methods were used to determine the damping characteristics of a four-machine power system in different configurations. The study shows that fast analytical methods may provide results which closely agree with the detailed method of time-domain simulation. However, the study also shows that the level of accuracy in the analytical model is very important.