Claudio A. Cañizares

Definition and classification of power system stability IEEE/CIGRE joint task force on stability terms and definitions

The problem of defining and classifying power system stability has been addressed by several previous CIGRE and IEEE Task Force reports. These earlier efforts, however, do not completely reflect current industry needs, experiences and understanding. In particular, the definitions are not precise and the classifications do not encompass all practical instability scenarios. This report developed by a Task Force, set up jointly by the CIGRE Study Committee 38 and the IEEE Power System Dynamic Performance Committee, addresses the issue of stability definition and classification in power systems from a fundamental viewpoint and closely examines the practical ramifications. The report aims to define power system stability more precisely, provide a systematic basis for its classification, and discuss linkages to related issues such as power system reliability and security.

Trends in Microgrid Control

The increasing interest in integrating intermittent renewable energy sources into microgrids presents major challenges from the viewpoints of reliable operation and control. In this paper, the major issues and challenges in microgrid control are discussed, and a review of state-of-the-art control strategies and trends is presented; a general overview of the main control principles (e.g., droop control, model predictive control, multi-agent systems) is also included. The paper classifies microgrid control strategies into three levels: primary, secondary, and tertiary, where primary and secondary levels are associated with the operation of the microgrid itself, and tertiary level pertains to the coordinated operation of the microgrid and the host grid. Each control level is discussed in detail in view of the relevant existing technical literature.

Point of collapse and continuation methods for large AC/DC systems

The implementation of both point of collapse (PoC) methods and continuation methods for the computation of voltage collapse points (saddle-node bifurcations) in large AC/DC power systems is described. The performance of these methods is compared for real systems of up to 2158 buses. Computational details of the implementation of the PoC and continuation methods are detailed, and the unique problems encountered due to the presence of high-voltage direct-current (HVDC) transmission, area interchange power control, regulating transformers, and voltage and reactive power limits are discussed. The characteristics of a robust PoC power flow program are presented, and its application to detection and solution of voltage stability problems is demonstrated. >

Comparison of performance indices for detection of proximity to voltage collapse

The paper proposes a new test function to be used in an existent performance index for detection of proximity to a static voltage collapse point. This test function is based on a reduction of the load flow Jacobian with respect to the critical bus of a system. The test function is compared with known singular values and eigenvalues indices, and with other previously proposed test functions. A thorough analysis of the similarities, advantages, and disadvantages of all these indices and test functions is presented. The techniques are tested and compared on the IEEE 300 bus test system, showing the effect of system characteristics and limits in these indices and functions.

Analysis of SVC and TCSC controllers in voltage collapse

This paper presents detailed steady-state models with controls of two flexible AC transmission system (FACTS) controllers, namely, static VAr compensators (SVCs) and thyristor controlled series capacitors (TCSCs), to study their effect on voltage collapse phenomena in power systems. Based on results at the point of collapse, design strategies are proposed for these two controllers, so that their location, dimensions and controls can be optimally defined to increase system loadability. A European system is used to illustrate the application of all proposed models and techniques.

Electric Energy Systems : Analysis and Operation

Electric Energy Systems-An Overview I.J. Perez Arriaga, H. Rudnick, and M. Rivier Steady-State Single-Phase Models of Power System Components E. Handschin, A. F. Otero, and J. Cidras Load Flow A. Gomez-Exposito and F. L. Alvarado State Estimation A. Gomez-Exposito and A. Abur Economics of Electricity Generation F. D. Galiana and A. J. Conejo Optimal and Secure Operation of Transmission Systems J. L. Martinez Ramos and V. H. Quintana Three-Phase Linear and Nonlinear Models of Power System Components E. Acha and J. Usaola Fault Analysis and Protection Systems J. Cidras, J. F. Minambres, and F. L. Alvarado Frequency and Voltage Control G. Andersson, C. Alvarez Bel, and C. Canizares Angle, Voltage, and Frequency Stability C. Canizares, L. Rouco, and G. Andersson Three-Phase Power Flow and Harmonic Analysis W. Xu and J. G. Mayordomo Electromagnetic Transients Analysis J. A. Martinez-Velasco and J. Marti Appendix A: Solution of Linear Equation Systems F. L. Alvarado and Antonio Gomez-Exposito Appendix B:Mathematical Programming A. J. Conejo Appendix C:Dynamic Models of Electric Machines L. Rouco Index

Optimal Operation of Distribution Feeders in Smart Grids

This paper presents a generic and comprehensive distribution optimal power flow (DOPF) model that can be used by local distribution companies (LDCs) to integrate their distribution system feeders into a Smart Grid. The proposed three-phase DOPF framework incorporates detailed modeling of distribution system components and considers various operating objectives. Phase specific and voltage dependent modeling of customer loads in the three-phase DOPF model allows LDC operators to determine realistic operating strategies that can improve the overall feeder efficiency. The proposed distribution system operation objective is based on the minimization of the energy drawn from the substation while seeking to minimize the number of switching operations of load tap changers and capacitors. A novel method for solving the three-phase DOPF model by transforming the mixed-integer nonlinear programming problem to a nonlinear programming problem is proposed which reduces the computational burden and facilitates its practical implementation and application. Two practical case studies, including a real distribution feeder test case, are presented to demonstrate the features of the proposed methodology. The results illustrate the benefits of the proposed DOPF in terms of reducing energy losses while limiting the number of switching operations.

Optimal Operation of Residential Energy Hubs in Smart Grids

This paper presents mathematical optimization models of residential energy hubs which can be readily incorporated into automated decision making technologies in smart grids, and can be solved efficiently in a real-time frame to optimally control all major residential energy loads, storage and production components while properly considering the customer preferences and comfort level. Novel mathematical models for major household demand, i.e., fridge, freezer, dishwasher, washer and dryer, stove, water heater, hot tub, and pool pumps are formulated. Also, mathematical models of other components of a residential energy system including lighting, heating, and air-conditioning are developed, and generic models for solar PV panels and energy storage/generation devices are proposed. The developed mathematical models result in Mixed Integer Linear Programming (MILP) optimization problems with the objective functions of minimizing energy consumption, total cost of electricity and gas, emissions, peak load, and/or any combination of these objectives, while considering end-user preferences. Several realistic case studies are carried out to examine the performance of the mathematical model, and experimental tests are carried out to find practical procedures to determine the parameters of the model. The application of the proposed model to a real household in Ontario, Canada is presented for various objective functions. The simulation results show that savings of up to 20% on energy costs and 50% on peak demand can be achieved, while maintaining the household owners desired comfort levels.

Point of collapse methods applied to AC/DC power systems

The authors describe an extension of the point of collapse method developed for studies of AC systems to the determination of saddle-node bifurcations in power systems including high voltage direct current (HVDC) transmission. Bus voltage profiles are illustrated for an AC/DC test system. They significantly differ from the profiles of pure AC systems for typical system models. In particular, voltage dependent current order limits are shown to affect the voltage profiles and the loadability margin of the system. It is also shown that Hopf bifurcations, which are possible in purely AC lossless systems with second-order generator models, become plausible when the dynamics for the HVDC system are included. >

On bifurcations, voltage collapse and load modeling

This paper discusses the relation between bifurcations and power systems stability through a thorough analysis of several examples, to clarify some ideas regarding the usefulness and limitations of bifurcation theory in network studies and operation, particularly in voltage stability related issues. Different types of load models are used in a sample system to analyze their effect on system stability and bifurcation. Finally, the Ecuadorian National Interconnected System is used to depict and discuss the effect of load modeling in saddle-node bifurcation analysis of real power systems. >