Engineering topics

Samaan, Nader A

Publications and source records attributed to Samaan, Nader A.

16 records

DOE OSTI2013

Standardized Software for Wind Load Forecast Error Analyses and Predictions Based on Wavelet-ARIMA Models - Applications at Multiple Geographically Distributed Wind Farms

Given the multi-scale variability and uncertainty of wind generation and forecast errors, it is a natural choice to use time-frequency representation (TFR) as a view of the corresponding time series represented over both time and frequency. Here we use wavelet transform (WT) to expand the signal in terms of wavelet functions which are localized in both time and frequency. Each WT component is more stationary and has consistent auto-correlation pattern. We combined wavelet analyses with time series forecast approaches such as ARIMA, and tested the approach at three different wind farms located far away from each other. The prediction capability is satisfactory -- the day-ahead prediction of errors match the original error values very well, including the patterns. The observations are well located within the predictive intervals. Integrating our wavelet-ARIMA (‘stochastic’) model with the weather forecast model (‘deterministic’) will improve our ability significantly to predict wind power generation and reduce predictive uncertainty.

uncertainty analysis, wind generation forecast, wa↗

DOE OSTI2013

Different Factors Affecting Short Circuit Behavior of a Wind Power Plant

A wind power plant consists of a large number of turbines interconnected by underground cable. A pad-mount transformer at each turbine steps up the voltage from generating voltage (690 V) to a medium voltage (34.5 kV). All turbines in the plant are connected to the substation transformer where the voltage is stepped up to the transmission level. An important aspect of wind power plant (WPP) impact studies is to evaluate the short-circuit (SC) current contribution of the plant into the transmission network under different fault conditions. This task can be challenging to protection engineers due to the topology differences between different types of wind turbine generators (WTGs) and the conventional generating units. This paper investigates the short circuit behavior of a wind power plant for different types of faults. The impact of wind turbine types, the transformer configuration, and the reactive compensation capacitor will be investigated. The voltage response at different buses will be observed. Finally, the SC line currents will be presented along with its symmetrical components.

Fault contribution, induction generator, protectio↗

DOE OSTI2012

Planning for Variable Generation Integration through Balancing Authorities Consolidation

As more and more variable generation is integrated into power grids, many challenges and concerns arise for an individual balancing authority (BA) to balance the system with limited resources. Consolidating balancing authorities provides a promising method to mitigate these problems by enabling the sharing of resources through operating different BAs as a single BA. The diversity in load and renewable generation over a wide area can be effectively leveraged, which makes it possible to achieve significant savings in balancing requirements. This paper develops a detailed procedure to compute savings in load following and regulation service requirements due to BAs consolidation. It proposes several evaluation metrics for demonstrating the benefits of BA consolidation. Several study scenarios are designed for a set of BAs in the western United States to test the proposed procedure. Results have shown significant savings in the capacity, ramp rate, and energy of balancing service requirements. Important factors affecting the savings, such as forecast accuracy and cross correlation between forecast errors, are also discussed.

Diao, Ruisheng↗

DOE OSTI2012

Overview of Common Mode Outages in Power Systems

This paper is a result of ongoing activity carried out by Probability Applications for Common Mode Events (PACME) Task Force under the Reliability Risk and Probability Applications (RRPA) Subcommittee. The paper is intended to constitute a valid source of information and references about dealing with common-mode outages in power systems reliability analysis. This effort involves reviewing published literature and presenting state-of-the-art research and practical applications in the area of common-mode outages. Evaluation of available outage statistics show that there is a definite need for collective effort from academia and industry to not only recommended procedures for data collection and monitoring but also to provide appropriate mathematical models to assess such events.

Common mode outages↗

DOE OSTI2012

Capacity Value of Solar Power

Evaluating the capacity value of renewable energy sources can pose significant challenges due to their variable and uncertain nature. In this paper the capacity value of solar power is investigated. Solar capacity value metrics and their associated calculation methodologies are reviewed and several solar capacity studies are summarized. The differences between wind and solar power are examined, the economic importance of solar capacity value is discussed and other assessments and recommendations are presented.

Duignan, Roisin↗

DOE OSTI2011

Survey of Tools for Risk Assessment of Cascading Outages

Cascading failure can cause large blackouts, and a variety of methods are emerging to study this challenging topic. In parts 1 and 2 of this paper, the IEEE task force on cascading failure seeks to consolidate and review the progress of the field towards methods and tools of assessing the risk of cascading failure. Part 2 summarizes and discusses the state of the art in the available cascading failure modeling tools. The discussion integrates industry and research perspectives from a variety of institutions. Strengths, weaknesses, and gaps in current approaches are indicated.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗

DOE OSTI2011

Assessment of Critical Events Corridors through Multivariate Cascading Outages Analysis

Massive blackouts of electrical power systems in North America over the past decade has focused increasing attention upon ways to identify and simulate network events that may potentially lead to widespread network collapse. This paper summarizes a method to simulate power-system vulnerability to cascading failures to a supplied set of initiating events synonymously termed as Extreme Events. The implemented simulation method is currently confined to simulating steady state power-system response to a set of extreme events. The outlined method of simulation is meant to augment and provide a new insight into bulk power transmission network planning that at present remains mainly confined to maintaining power system security for single and double component outages under a number of projected future network operating conditions. Although one of the aims of this paper is to demonstrate the feasibility of simulating network vulnerability to cascading outages, a more important goal has been to determine vulnerable parts of the network that may potentially be strengthened in practice so as to mitigate system susceptibility to cascading failures. This paper proposes to demonstrate a systematic approach to analyze extreme events and identify vulnerable system elements that may be contributing to cascading outages. The hypothesis of critical events corridors is proposed to represent repeating sequential outages that can occur in the system for multiple initiating events. The new concept helps to identify system reinforcements that planners could engineer in order to 'break' the critical events sequences and therefore lessen the likelihood of cascading outages. This hypothesis has been successfully validated with a California power system model.

24 POWER TRANSMISSION AND DISTRIBUTION↗

DOE OSTI2011

Model Reduction, Validation, and Calibration of Wind Power Plants for Dynamic Studies

Accurate representation of wind power plants (WPP) in both offline and online power system stability studies has gained importance because of the rapid increase in installation of wind generation around the world. On the other hand, reduced WPP representation is preferred due to computational efficiency. To improve the accuracy, other authors have proposed changes in structure of the reduced model for large WPPs. The use of model validation and calibration is an alternative to improve the accuracy of the reduced WPP model. In this paper, we compare accuracy improvements brought by changes in model structure with accuracy improvements brought by validation and calibration of the reduced WPP model with minimal changes in structure. We illustrate our findings using a 168-machine WPP connected to the IEEE-39-bus test system. The parameters of the reduced WPP model are either calculated with current equivalencing techniques or validated and calibrated against a more accurate model. The changes in structure of the reduced model are 1-machine or 2-machine reduced models connected with a 1-line or 2-line collector equivalents. We show that the most accurate response is obtained by calibrating the parameters of the reduced model with minimum changes in structure.

17 WIND ENERGY↗

DOE OSTI2011

Control Strategies for Distributed Energy Resources to Maximize the Use of Wind Power in Rural Microgrids

The focus of this paper is to design control strategies for distributed energy resources (DERs) to maximize the use of wind power in a rural microgrid. In such a system, it may be economical to harness wind power to reduce the consumption of fossil fuels for electricity production. In this work, we develop control strategies for DERs, including diesel generators, energy storage and demand response, to achieve high penetration of wind energy in a rural microgrid. Combinations of centralized (direct control) and decentralized (autonomous response) control strategies are investigated. Detailed dynamic models for a rural microgrid are built to conduct simulations. The system response to large disturbances and frequency regulation are tested. It is shown that optimal control coordination of DERs can be achieved to maintain system frequency while maximizing wind power usage and reducing the wear and tear on fossil fueled generators.

17 WIND ENERGY↗

DOE OSTI2011

Integration of Uncertainty Information into Power System Operations

Contemporary power systems face uncertainties coming from multiple sources, including forecast errors of load, wind and solar generation, uninstructed deviation and forced outage of traditional generators, loss of transmission lines, and others. With increasing amounts of wind and solar generation being integrated into the system, these uncertainties have been growing significantly. It is critical important to build knowledge of major sources of uncertainty, learn how to simulate them, and then incorporate this information into the decision-making processes and power system operations, for better reliability and efficiency. This paper gives a comprehensive view on the sources of uncertainty in power systems, important characteristics, available models, and ways of their integration into system operations. It is primarily based on previous works conducted at the Pacific Northwest National Laboratory (PNNL).

24 POWER TRANSMISSION AND DISTRIBUTION↗

DOE OSTI2011

Capacity Value of Wind Power

Power systems are planned such that they have adequate generation capacity to meet the load, according to a defined reliability target. The increase in the penetration of wind generation in recent years has led to a number of challenges for the planning and operation of power systems. A key metric for system adequacy is the capacity value of generation. The capacity value of a generator is the contribution that a given generator makes to overall system adequacy. The variable and stochastic nature of wind sets it apart from conventional energy sources. As a result, the modeling of wind generation in the same manner as conventional generation for capacity value calculations is inappropriate. In this paper a preferred method for calculation of the capacity value of wind is described and a discussion of the pertinent issues surrounding it is given. Approximate methods for the calculation are also described with their limitations highlighted. The outcome of recent wind capacity value analyses in Europe and North America are highlighted with a description of open research questions also given.

17 WIND ENERGY↗

DOE OSTI2011

Centralized and Decentralized Control for Demand Response

Demand response has been recognized as an essential element of the smart grid. Frequency response, regulation and contingency reserve functions performed traditionally by generation resources are now starting to involve demand side resources. Additional benefits from demand response include peak reduction and load shifting, which will defer new infrastructure investment and improve generator operation efficiency. Technical approaches designed to realize these functionalities can be categorized into centralized control and decentralized control, depending on where the response decision is made. This paper discusses these two control philosophies and compares their relative advantages and disadvantages in terms of delay time, predictability, complexity, and reliability. A distribution system model with detailed household loads and controls is built to demonstrate the characteristics of the two approaches. The conclusion is that the promptness and reliability of decentralized control should be combined with the predictability and simplicity of centralized control to achieve the best performance of the smart grid.

24 POWER TRANSMISSION AND DISTRIBUTION↗

DOE OSTI2010

Different Factors Affecting Short Circuit Behavior of a Wind Power Plant

17 WIND ENERGY↗

DOE OSTI2010

Wind and Load Forecast Error Model for Multiple Geographically Distributed Forecasts

The impact of wind and load forecast errors on power grid operations is frequently evaluated by conducting multi-variant studies, where these errors are simulated repeatedly as random processes based on their known statistical characteristics. To generate these errors correctly, we need to reflect their distributions (which do not necessarily follow a known distribution law), standard deviations, auto- and cross-correlations. For instance, load and wind forecast errors can be closely correlated in different zones of the system. This paper introduces a new methodology for generating multiple cross-correlated random processes to simulate forecast error curves based on a transition probability matrix computed from an empirical error distribution function. The matrix will be used to generate new error time series with statistical features similar to observed errors. We present the derivation of the method and present some experimental results by generating new error forecasts together with their statistics.

17 WIND ENERGY↗

DOE OSTI2010

Analyzing of Balancing Authorities Cooperation Methods with High Variable Generation Penetration

With the rapidly growing penetration level of wind and solar generation, the challenges of managing variability and the uncertainty of intermittent renewable generation become more and more significant. The problem of power variability and uncertainty gets exacerbated when each balancing authority (BA) works locally and separately to balance its own subsystem. The virtual BA concept is based on various forms of collaboration between individual BAs to manage power variability and uncertainty. The virtual BA will have a wide area control capability in managing its operational balancing requirements in different time frames. This coordination results in the improvement of efficiency and reliability of power system operation while facilitating the high level integration of green, intermittent energy resources. Several strategies for virtual BA implementation, such as Area Control Error (ACE) diversity interchange (ADI), variable generation only BA, BA consolidation, dynamic scheduling, and regulation and load following sharing are discussed in this paper. The objective of such strategies is to allow individual BAs within a large power grid to help each other dealing with power variability. Innovative methods have been developed to simulate the balancing operation of BAs. These methods evaluate the BA operation through a number of metrics such as capacity, ramp rate, ramp duration, energy and cycling requirements to evaluate the performance of different virtual BA strategies.

17 WIND ENERGY↗

DOE OSTI2010

Short Circuit Current Contribution for Different Wind Turbine Generator Types

An important aspect of wind power plant (WPP) impact studies is to evaluate the short circuit (SC) current contribution of the plant into the transmission network under different fault conditions. This task can be challenging to protection engineers due to the topology differences between different types of wind turbine generators (WTGs) and the conventional generating units. This paper represents simulation results for short circuit current contribution for different types of WTGs obtained through transient analysis using generic WTG models. The obtained waveforms are analyzed to explain the behavior, such as peak values and rate of decay, of the WTG. The effect of fault types and location, and the effect of the control algorithms of power converters on SC current contribution are investigated. It is shown that the response of the WPP to faults will vary based on the type of the installed WTGs. While in Type 1 and Type 2 WTGs, short circuit current will be determined by the physical characteristics of the induction generator, the contribu-tion of Type 3 and Type 4 WTG will be mostly characterized by the power converters control algorithms which are usually considered proprietary information by the wind turbine manufacturers.

17 WIND ENERGY↗