Graham Rogers

Bio: Graham Rogers is an academic researcher. The author has contributed to research in topics: Electric power system & Modal analysis. The author has an hindex of 3, co-authored 7 publications receiving 1297 citations.

Power System Oscillations

Abstract: 1. Introduction. 2. The Nature of Power System Oscillations. 3. Modal Analysis of Power Systems. 4. Modal Analysis for Control. 5. Power System Structure and Oscillations. 6. Generator Controls. 7. Power System Stabilizers. 8. Power System Stabilizers - Problems and Solutions. 9. Robust Control. 10. Damping by Electronic Power System Devices. A1. Model Data Formats and Block Diagrams. A2. Equal Eigenvalues. Index.

Power system structure and oscillations

Abstract: Electromechanical oscillations are inherent to interconnected power systems. However, the frequency of the oscillations and the number of generators that oscillate in any electromechanical oscillatory mode depend on the structure of the power system network. Low frequency electromechanical oscillations occur when existing generation/load areas are connected to other similar areas by relatively weak transmission lines. Weak interconnections are obvious in many interconnected systems, for example, when two independent electric grids are interconnected for the first time through one or two tie lines. However, in systems that have been interconnected for some time, such as the US/Canadian interconnected systems, and that are being stressed by increased load, weak links are less obvious. Often, the first signs of trouble are low frequency oscillations becoming unstable. The connection between loading and stability is not always obvious. It is also unclear which contingencies may lead to oscillatory instability. This tutorial examines in detail the relationship between low frequency oscillations and weak interconnections in the transmission system network. The basis of the analysis is the observation that generators in specific areas of a power system behave coherently in low frequency oscillations and that groups of coherent generators are separated from other groups of coherent generators by weak interconnections. This observation is also the starting point for dynamic system reduction.

Modal Analysis of Power Systems

Abstract: In Chapter 2, I discussed the oscillations that may occur in interconnected power systems. By looking at different models, and with different disturbances, I showed examples of the different types of oscillation that can occur. To do this, I performed a considerable number of 10-second nonlinear simulations. It is apparent that in larger systems the use of transient simulation for the analysis of system oscillations could be very time consuming. To study inter-area oscillations, it is often necessary to run simulations for longer than 10 s; 30 s is quite common in practice. Not only is the use of non-linear simulation time consuming, but also it is often difficult to interpret the results. Larger systems may have a number of interarea modes at very similar frequencies, and it can be quite difficult to separate them from a response in which more than one is excited.

Modal Analysis for Control

Abstract: In Chapter 3, I defined and applied modal analysis to understanding the nature of power system oscillations. However, it is necessary to do more than understand; controls, which modify the natural behaviour of the interconnected synchronous generators, must be designed. While power systems are essentially nonlinear, we have seen that their oscillations about an operating point can be predicted accurately from a linearized system model. For oscillation damping control design, we can use this to justify the application of linear control theory.

Power System Stabilizers — Problems and Solutions

Abstract: In Chapter 7, I showed that power system stabilizers act efficiently to damp the electromechanical oscillations in interconnected power systems. When the stabilizers are correctly tuned, the resulting damping control is robust. Power system stabilizers are cost effective when compared to the alternative, purely electronic controls, e.g., static VAr compensators - I will consider these in chapter 10. However, over the years of power system stabilizer use, a number of problems have arisen. These are often cited as reasons not to install power system stabilizers, but this is not valid. Methods to rectify the problems have been found and, in this chapter, I will discuss the problems and their solutions in some detail.

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

Abstract: 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.

Design and Stability of Load-Side Primary Frequency Control in Power Systems

Abstract: We present a systematic method to design ubiquitous continuous fast-acting distributed load control for primary frequency regulation in power networks, by formulating an optimal load control (OLC) problem where the objective is to minimize the aggregate cost of tracking an operating point subject to power balance over the network. We prove that the swing dynamics and the branch power flows, coupled with frequency-based load control, serve as a distributed primal-dual algorithm to solve OLC. We establish the global asymptotic stability of a multimachine network under such type of load-side primary frequency control. These results imply that the local frequency deviations on each bus convey exactly the right information about the global power imbalance for the loads to make individual decisions that turn out to be globally optimal. Simulations confirm that the proposed algorithm can rebalance power and resynchronize bus frequencies after a disturbance with significantly improved transient performance.

Comparison of PSS, SVC, and STATCOM controllers for damping power system oscillations

Abstract: This paper discusses and compares different control techniques for damping undesirable interarea oscillation in power systems by means of power system stabilizers (PSS), static VAr compensators (SVCs), and shunt static synchronous compensators (STATCOMs). The oscillation problem is analyzed from the point of view of Hopf bifurcations, an "extended" eigenanalysis to study different controllers, their locations, and the use of various control signals for the effective damping of these oscillations. The comparisons are based on the results obtained for the IEEE 50-machine, 145-bus test system, which is a benchmark for stability analysis.

Wide-area measurement-based stabilizing control of power system considering signal transmission delay

Abstract: Recent technological advances in the area of wide-area measurement systems (WAMS) has enabled the use of a combination of measured signals from remote locations for centralized control purpose. The transmitted signals can be used for multiple swing mode damping using a single controller. However, there is an unavoidable delay involved before these signals are received at the controller site. To ensure satisfactory performance, this delay needs to be taken into account in the control design stage. This paper focuses on damping control design taking into account a delayed arrival of feedback signals. A predictor-based H/sub /spl infin// control design strategy is discussed for such time-delayed systems. The concept is utilized to design a WAMS-based damping controller for a prototype power system using a static var compensator. The controller performance is evaluated for a range of operating conditions.

Design Aspects for Wide-Area Monitoring and Control Systems

Abstract: This paper discusses the basic design and special applications of wide-area monitoring and control systems, which complement classical protection systems and Supervisory Control and Data Acquisition/Energy Management System applications. Systemwide installed phasor measurement units send their measured data to a central computer, where snapshots of the dynamic system behavior are made available online. This new quality of system information opens up a wide range of new applications to assess and actively maintain system's stability in case of voltage, angle or frequency instability, thermal overload, and oscillations. Recent developed algorithms and their design for these application areas are introduced. With practical examples, the benefits in terms of system security are shown.