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• A reduced-order model for assessing the transient DC-link voltage oscillation stability of VSC-HVDC systems is proposed. • Lyapunov direct method is applied to assess the transient DC-link voltage oscillation stability of VSC-HVDC systems. • The conservative stabilizing conditions based on two kinds of Lyapunov functions are derived. • Limit cycle of the converter-tied DC system is found and the asymptotic stability boundary is mapped based on limit cycle theory. • The system stability can be improved by tuning the system parameters. Lyapunov direct method is utilized in this paper to reveal the transient voltage oscillation stability mechanism for VSC-HVDC systems. Firstly, a reduced analytical nonlinear model for transient voltage oscillation stability assessment is proposed, which is a Liénard system. Based on the proposed model, a novel Lyapunov function is constructed and the conservative stability boundary is depicted, which reveals that the transient voltage oscillation can be well damped when the operating points are within the domain of asymptotic stability. In addition, it is found that there exists one limit cycle for VSC-HVDC systems. Once any system operation point exceeds the limit cycle, the divergent oscillations are triggered, and the aperiodic instability will eventually appear if the perturbations failed to be cleared in time. Finally, according to the limit cycle theory, one sufficient instability condition is derived and the transient voltage instability risk of the VSC-HVDC systems can be well evaluated. [ABSTRACT FROM AUTHOR]

This paper presents a method for determining the global basin boundary of the power systems. To show the general outline of the basin, the power system is shrink to the projective space. First, a new vector field is induced according to Poincare's method. After the transformation, the structural stability of the system remains the same. The singularities at infinity are obtained by the proposed shrinking-projection method. The boundary of the basin which is extended to the infinity are complemented by the singularities at infinity in the projective space. The stability of the power system is then evaluated based on the distribution of the singularities at infinity. Finally, the proposed method is applied to the power system with perturbations to study the characteristic of the stochastic basin boundary. The validity of the proposed method is demonstrated on a 9-bus, 11-bus and 68-bus test system. • A new method is established to show the terminal points of the basin boundary. The distribution of these points is verified to indicate the stability of the power system. • Different damping factors are fully considered and the assumption of the average damping of the system is no longer necessary. • Through coordinate transformation, the geometric structure of the global basin boundary is folded into a new projective space. How the distribution of the singularities at infinity affects the stability of the system is discussed. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, equations are derived that describe the mapping of critical boundaries and characteristic curves from the three dimensional PQV-surface into the two-dimensional injection impedance plane (load impedance plane for both positive and negative resistance). The expressions derived for the critical and characteristic curves in the impedance plane form the basis for a new phasor measurement based situational awareness method, which uses the results in this paper to identify critical operational boundaries in real time and to visualize the system operating conditions in an informative way. The situational awareness method will be described in a later paper, where this paper focuses on the derivations of some system characteristics in the injection (or load) impedance plane. The critical curves from the PQV-surface that are mapped into the impedance plane are the ones representing the conditions where the partial derivatives of the variables P, Q and V in respect to each other become zero. In addition to the mapping of the critical curves, some characteristic curves are mapped as well. These include the mapping of the curves of constant P, Q, V and δ from the PQV-surface into the impedance plane. All of the mapped critical and characteristic curves appear as circles in the injection impedance plane. [Copyright &y& Elsevier]

• Results of survey to 10 transmission system operators from 8 countries. • Outline of the most important current challenges handling data in control rooms. • Description of situation with respect to artificial intelligence and machine learning applications. • Differences among utilities based on geographical, political and economic situation. • List of real needs that TSOs would like to have in operation. Nowadays, transmission system operators require higher degree of observability in real-time to gain situational awareness and improve the decision-making process to guarantee a safe and reliable operation. Digitalization of energy systems allows utilities to monitor the system dynamic performance in real-time at fast time scales. The use of such technologies has unlocked new opportunities to introduce new data driven algorithms for improving the stability assessment and control of the system. Motivated by these challenges, a group of experts have worked together to highlight and establish a baseline set of these common concerns, which can be used as motivation to propose innovative analytics and data-driven solutions. In this document, the results of a survey on 10 transmission system operators around the world are presented and it aims to understand the current practices of the participating companies, in terms of data acquisition, handling, storage, modelling and analytics. The overall objective of this document is to capture the actual needs from the interviewed utilities, thereby laying the groundwork for setting valid assumptions for the development of advanced algorithms in this field. [ABSTRACT FROM AUTHOR]