Alberto Del Rosso

Energy Storage for Relief of Transmission Congestion

Recent investigations by EPRI have focused on the application of existing technologies to reduce power system carbon footprint. Research examined the technical feasibility and potential benefits of energy storage to increase transmission capability of congested transmission networks that serve regions of the country having large renewable generation assets. The use of storage to relieve thermal constraints has not yet been explored or validated in depth. This paper summarizes the results of this research. These include a brief overview of different applications of storage, and a survey of past work by EPRI and others that investigated the application of energy storage on the transmission system. An in-depth description on the potential use of batteries storage to increase transmission capability in thermal-limited transmission paths is presented. A case study on a generic power system model illustrates the concept, with an economic analysis on benefits and costs. Conclusions and future steps are given.

Measurement-Based Real-Time Voltage Stability Monitoring for Load Areas

Summary form only given. This paper proposes a measurement-based voltage stability monitoring method for a load area fed by N tie lines. Compared to a traditional Thevenin equivalent based method, the new method adopts an N+1 buses equivalent system so as to model and monitor individual tie lines. For each tie line, the method solves the power transfer limit against voltage instability analytically as a function of all parameters of that equivalent, which are online identified from real-time synchronized measurements on boundary buses of the load area. Thus, this new method can directly calculate the real-time power transfer limit on each tie line. The method is first compared with a Thevenin equivalent based method using a four-bus test system and then demonstrated by case studies on the NPCC (Northeast Power Coordinating Council) 48-machine, 140-bus power system.

An adaptive three-bus power system equivalent for estimating voltage stability margin from synchronized phasor measurements

This paper utilizes an adaptive three-bus power system equivalent for measurement-based voltage stability analysis. With that equivalent identified online, a measurement-based approach is developed to estimate real-time voltage stability margin for a load-rich area supported by remote generation via multiple tie lines. Compared with traditional Thevenin equivalent based approach, this new approach is able to provide more accurate voltage stability margin for each individual tie line. This approach is validated on a three-bus system and the IEEE 39-bus system.

A study on fluctuations in electromechanical oscillation frequencies of power systems

This paper investigates the fluctuation phenomenon in the electromechanical oscillation frequency of a power system. Analysis on the power system swing equation explains that the oscillation frequency fluctuates around a central frequency due to the nonlinear system nature of a power system. A Phase-Plane Trajectory based method and the Prony method are used to track the real-time frequency fluctuation, based on which a realtime angular stability margin index is proposed for early warning of angular stability issues. That index is tested by case studies on a two-generator system and a 179-bus power system.

Methods to establish input-output relationship for system identification-based models

Both model-based and measurement-based methods are presented in this paper to describe the correlation between measurement locations. Transfer impedance (the model-based method) and correlation coefficient (the measurement-based method) are compared and applied to input location selection of power system dynamic modeling for dynamic response estimation. The comparison results show that both methods can describe the correlation between measurement locations effectively.

On-line transient stability analysis using high performance computing

In this paper, parallelization and high performance computing are utilized to enable ultrafast transient stability analysis that can be used in a real-time environment to quickly perform “what-if” simulations involving system dynamics phenomena. EPRIs Extended Transient Midterm Simulation Program (ETMSP) is modified and enhanced for this work. The contingency analysis is scaled for large-scale contingency analysis using Message Passing Interface (MPI) based parallelization. Simulations of thousands of contingencies on a high performance computing machine are performed, and results show that parallelization over contingencies with MPI provides good scalability and computational gains. Different ways to reduce the Input/Output (I/O) bottleneck are explored, and findings indicate that architecting a machine with a larger local disk and maintaining a local file system significantly improve the scaling results. Thread-parallelization of the sparse linear solve is explored also through use of the SuperLU_MT library.

Input signals selection for measurement-based power system ARX dynamic model response estimation

This paper proposes a measurement-based approach to optimize the inputs of Auto-Regressive with eXogenous input (ARX) model identification in large power systems. Correlation Coefficient Index (CCI) is defined in this paper and Correlation Coefficient Map (CCM) is developed for the US Eastern Interconnection (EI) to show the correlation between any two power system output measurement signals visually. This approach is verified with EI system simulation data and applied to Frequency Disturbance Recorder (FDR) measurement data to estimate system dynamic response. The verification result shows that the number of ARX model inputs can be decreased and the estimation accuracy can be ensured by using the proposed approach.

Methods and tools to estimate carbon emission savings from integration of renewable and T&D efficiency improvement

The electricity industry is moving towards the implementation of technologies options to reduce its carbon footprint. With that, the need for a consistent methodology for assessing and verify the emission reduction attributable to technology project arises. This paper first present an overview of different methodologies that are currently used for estimating CO2 emission savings from the integration of renewable generation. The strength and weaknesses of these approaches, and their suitability to asses CO2 avoided emissions from measures to improve transmission and distributing system efficiencies are addressed. A new evaluation methodology based on the EPRI calculation tool, the NESSIE model, is then presented. A simple case study is presented to illustrate its application. Finally, a summary of main conclusions and recommendation for further investigation are presented.

Measurement-based system reduction using autoregressive model

With the constantly changing power system topology and operation status, it is not yet feasible to update full power system simulation models in real time. Furthermore, the accuracy of models for dynamic simulation is a concern. In the large-scale power system dynamic simulation, usually only the dynamics of a local system need to be studied while external systems can be reduced. Thus, dynamic equivalencing is one solution for the increasing size and complexity of power systems. This paper develops a measurement-based equivalent model of the external systems in order to improve the model accuracy of the reduced system and increase the speed of dynamic simulation through system reduction. The dynamic equivalents are obtained by a system identification method and integrated to the simulation tool.

Voltage control optimization to improve transmission efficiency under near real-time conditions

This paper presents a case study on improving transmission system efficiency under near real-time conditions using voltage control optimization. In general, generator voltage schedules are developed using off-line planning models with expected system conditions, e.g., expected loads and generation. Optimal voltage schedules can be determined with Optimal Power Flow (OPF) programs to achieve certain pre-determined objectives, such as reducing active and/or reactive power losses. In addition, these optimal voltage schedules can result in a higher reactive power reserve and a more reliable power system. This case study uses Energy Management System models as proxies of near real-time operational conditions and an OPF to improve transmission efficiency while controlling the generator voltage schedule and switching on/off shunt reactive devices.