Yuri V. Makarov

Operational Impacts of Wind Generation on California Power Systems

The paper analyzes the impact of integrating wind generation on the regulation and load following requirements of the California Independent System Operator (CAISO). These requirements are simulated and compared for the study cases with and without wind generation impacts included into the study for the years 2006 and 2010. Regulation and load following models were built based on hour-ahead and five-minute ahead load and wind generation forecasts. In 2006, the CAISO system peaked at 50 270 MW. Wind generation (at the installed capacity of 2600 MW) had limited impact on the requirement of load following and regulation in the CAISO Balancing Authority. However, in 2010 (with an expected installed capacity of approximately 6700 MW), this impact will significantly increase. The results provide very useful information for the CAISO to adjust its scheduling and real-time dispatch systems to reliably accommodate future wind generation additions within the CAISO Balancing Authority.

Sizing Energy Storage to Accommodate High Penetration of Variable Energy Resources

The variability and nondispatchable nature of wind and solar energy production presents substantial challenges for maintaining system balance. Depending on the economic considerations, energy storage can be a viable solution to balance energy production with consumption. This paper proposes to use discrete Fourier transform to decompose the required balancing power into different time-varying periodic components, i.e., intraweek, intraday, intrahour, and real-time. Each component can be used to quantify the maximum energy storage requirement for different types of energy storage. This requirement is the physical limit that could be theoretically accommodated by a power system. The actual energy storage capacity can be further quantified within this limit by the cost-benefit analysis (future work). The proposed approach has been successfully used in a study conducted for the 2030 Western Electricity Coordinating Council system model. Some results of this study are provided in this paper.

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

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.

On the use of energy storage technologies for regulation services in electric power systems with significant penetration of wind energy

Energy produced by intermittent renewable resources is sharply increasing in the United States. At high penetration levels, volatility of wind power production could cause additional problems for the power system balancing functions such as regulation. This paper reports some partial results of a project work, recently conducted by the Pacific Northwest National Laboratory (PNNL) for Bonneville Power Administration (BPA). The project proposes to mitigate additional intermittency with the help of Wide Area Energy Management System (WAEMS) that would provide a two-way simultaneous regulation service for the BPA and California ISO systems by using a large energy storage facility. The paper evaluates several utility-scale energy storage technology options for their usage as regulation resources. The regulation service requires a participating resource to quickly vary its power output following the rapidly and frequently changing regulation signal. Several energy storage options have been analyzed based on thirteen selection criteria. The evaluation process resulted in the selection of flywheels, pumped hydro electric power (or conventional hydro electric power) plant and sodium sulfur or nickel cadmium batteries as candidate technologies for the WAEMS project. A cost benefit analysis should be conducted to narrow the choice to one technology.

A general method for small signal stability analysis

This paper presents a new general method for computing the different specific power system small signal stability conditions. The conditions include the points of minimum and maximum damping of oscillations, saddle node and Hopf bifurcations, and load flow feasibility boundaries. All these characteristic points are located by optimizing an eigenvalue objective function along the rays specified in the space of system parameters. The set of constraints consists of the load flow equations, and requirements applied to the dynamic state matrix eigenvalues and eigenvectors. Solutions of the optimization problem correspond to specific points of interest mentioned above. So, the proposed general method gives a comprehensive characterization of the power system small signal stability properties. The specific point obtained depends upon the initial guess of variables and numerical methods used to solve the constrained optimization problem. The technique is tested by analyzing the small signal stability properties for well-known example systems.

Computation of bifurcation boundaries for power systems: a new /spl Delta/-plane method

This paper is devoted to the problems of finding the load flow feasibility saddle node, and Hopf bifurcation boundaries in the space of power system parameters. The first part contains a review of the existing relevant approaches including not-so-well-known contributions from Russia. The second part presents a new robust method for finding the power system load flow feasibility boundary on the plane defined by any three vectors of dependent variables (nodal voltages), called the /spl Delta/ plane. The method exploits some quadratic and linear properties of the load flow equations and state matrices written in rectangular coordinates. An advantage of the method is that it does not require an iterative solution of nonlinear equations (except the eigenvalue problem). In addition to benefits for visualization, the method is a useful tool for topological studies of power system multiple solution structures and stability domains. Although the power system application is developed, the method can be equally efficient for any quadratic algebraic problem.

PMU-Based Wide-Area Security Assessment: Concept, Method, and Implementation

This paper presents a concept, method, and implementation of utilizing phasor measurement unit (PMU) information to monitor the wide-area security of a power system. The close dependency of major transmission paths requires an approach that takes that interaction into account while establishing operational transfer capability, and evaluates grid reliability and security on a system-wide basis. Thus, the concept of wide-area security region, which considers all essential constraints, including thermal, voltage stability, transient stability, and small signal stability, is proposed. This approach expands the idea of traditional transmission system nomograms to a multidimensional case, involving multiple system limits and parameters such as transmission path constraints, zonal generation or load, etc., considered concurrently. In this paper, the security region boundary is represented using piecewise approximation with the help of linear inequalities (so called hyperplanes) in a multidimensional space, consisting of system parameters that are critical for security analysis. The goal of this approximation is to find a minimum set of hyperplanes that describe the boundary with a given accuracy. Offline computer simulations are conducted to build the security region and the hyperplanes can be applied in real time with phasor information for on-line security assessment. Numerical simulations have been performed for the full size Western Electricity Coordinating Council (WECC) system model, which comprises 15 126 buses and 3034 generators. Simulation results demonstrated the feasibility and effectiveness of this approach, and proved that the proposed approach can significantly enhance the wide-area situation awareness for a bulk power system like WECC.

Revealing loads having the biggest influence on power system small disturbance stability

The paper presents a novel approach to reveal loads having the biggest impact on damping of small-disturbed oscillations in power systems. The technique is based on a quasi-optimisation procedure with the cost function reflecting shifts of selected eigenvalues along the real axis when all unknown load parameters are varied within their constraints. The cost function takes into consideration a variety of power system operating conditions. All points of the cost function steepest descent trajectory, obtained in the space of unknown load parameters, correspond locally to biggest shifts of eigenvalues. Participation factors of load parameters are computed along the steepest descent trajectory, and they give ranks of load importance. Small ranks indicate loads which have no influence on damping of selected modes. Big ranks reveal loads whose parameters cause the biggest change in damping under the most unfavourable combination of unknown parameters. Parameters with biggest ranks should be measured first of all to avoid mistakes in evaluation of damping properties and power system stability margins.

On Convexity of Power Flow Feasibility Boundary

Power flow feasibility boundaries are constraints limiting the operating transmission capability and the available stability (security) margin of the system. The convexity properties of this boundary are important to the analytical description of its shape (including the needs of approximation) and for the calculation of security margins. These analyses are significantly simplified if the boundary is convex. The conjecture that the boundary is convex in the space of system parameters has been used over a long time. However, some alarming experimental counterexamples already exist which show that this boundary is not always convex. In this letter, an analytical approach is presented to analyze the convexity properties of the power flow feasibility boundary. In particular, the approach helps to identify nonconvex parts of the boundary. Numerical case studies illustrate the effectiveness of the approach.

Wide-Area Energy Storage and Management system to Balance Intermittent Resources in the Bonneville Power Administration and California ISO Control Areas

The entire project addresses the issue of mitigating additional intermittency and fast ramps that occur at higher penetration of intermittent resources, including wind genera-tion, in the Bonneville Power Administration (BPA) and the California Independent Sys-tem Operator (California ISO) control areas. The proposed Wide Area Energy Storage and Management System (WAEMS) will address the additional regulation requirement through the energy exchange between the participating control areas and through the use of energy storage and other generation resources. For the BPA and California ISO control centers, the new regulation service will look no different comparing with the traditional regulation resources. The proposed project will benefit the regulation service in these service areas, regardless of the actual degree of penetration of the intermittent resources in the regions. The project develops principles, algorithms, market integration rules, functional de-sign and technical specifications for the WAEMS system. The project is sponsored by BPA and supported in kind by California ISO, Beacon Power Corporation, and the Cali-fornia Energy Commission (CEC).