Now showing 1 - 10 of 35
  • Publication
    Validating Two Novel Equivalent Impedance Estimators
    Certain approaches to appraising voltage stability use an equivalent impedance to characterise the wider power system. This letter proposes two newways of inferring an appropriate equivalent impedance from a powersystem's admittance matrix. Continuation power flow simulations are used to validate the quality of the new estimators, and to benchmark them against some extant approaches.
  • Publication
    Robust Frequency Divider for Power System Online Monitoring and Control
    Accurate local bus frequency is essential for power system frequency regulation provided by distributed energy sources, flexible loads, and among others. This paper proposes a robust frequency divider (RFD) for online bus frequency estimation. Our RFD is independent of the load models, and the knowledge of swing equation parameters, transmission line parameters, and local Phasor Measurement Unit (PMU) measurements at each generator terminal bus is sufficient. In addition, it is able to handle several types of data quality issues, such as measurement noise, gross measurement errors, cyberattacks, and measurement losses. Furthermore, the proposed RFD contains the decentralized estimation of local generator rotor speeds and the centralized bus frequency estimation, which resembles the structure of the decentralized/hierarchical control scheme. This enables RFD for very large-scale system applications. Specifically, we decouple each generator from the rest of the system by treating metered real power injection as inputs and the frequency measurements provided by PMU as outputs; then a robust unscented Kalman filter based dynamic state estimator is proposed for local generator rotor speed estimation; finally, these rotor speeds are transmitted to control center for bus frequency estimation. Numerical results carried out on the IEEE 39-bus and 145-bus systems demonstrate the effectiveness and robustness of the proposed method.
      573Scopus© Citations 29
  • Publication
    Frequency Divider
    The paper proposes an approximated yet reliable formula to estimate the frequency at the buses of a transmission system. Such a formula is based on the solution of a steady-state boundary value problem where boundary conditions are given by synchronous machine rotor speeds and is intended for applications in transient stability analysis. The hypotheses and assumptions to define bus frequencies are duly discussed. The rationale behind the proposed frequency divider is first illustrated through a simple 3-bus system. Then the general formulation is duly presented and tested on two real-world networks, namely a 1,479-bus model of the all-island Irish system and a 21,177-bus model of the European transmission system.
      590Scopus© Citations 145
  • Publication
    Nonlinear Adaptive Excitation Control for Structure Preserving Power Systems
    The paper proposes a decentralized excitation controller to improve the stability of large power systems. Extended Lyapunov-like energy function and equivalent expressions of stator transient voltages are utilized to design a nonlinear adaptive excitation controller. The proposed controller only requires local machine measures and parameters. The performance of the designed excitation control system is evaluated on the well known IEEE 118-bus 54-unit power system and compared with conventional exciter controls.
      513Scopus© Citations 11
  • Publication
    Model-Agnostic Linear Estimation of Generator Rotor Speeds based on Phasor Measurement Units
    The paper focuses on the estimation of the rotor speeds of synchronous machines by means of phasor measurement units. This estimation is aimed at on-line monitoring of electro-mechanical transients and transient stability analysis. The proposed technique is based on the concept of frequency divider formula recently published by the first two authors in these Transactions. The dynamic state estimation is formally stated as a convex optimization problem and a thorough discussion of the sensitivity analysis of the optimal solution is provided. The case study considers a dynamic 1,479-bus model of the all-island Irish system and discusses the effect of bad data, noise and latency on the proposed estimation technique.
      524Scopus© Citations 19
  • Publication
    Primal and Dual Generalized Eigenvalue Problems for Power Systems Small-Signal Stability Analysis
    (Institute of Electrical and Electronics Engineers (IEEE), 2017-03-07) ;
    The paper presents a comprehensive study of small-signal stability analysis of power systems based on matrix pencils and the generalized eigenvalue problem. Both primal and dual formulations of the generalized eigenvalue problem are considered and solved through a variety of state-of-the-art solvers. The paper also discusses the impact on the performance of the solvers of two formulations of the equations modelling the power systems, namely, the explicit and semi-implicit form of differential-algebraic equations. The case study illustrates the theoretical aspects and numerical features of these formulations and solvers through two real-world systems, namely, a 1,479-bus model of the all-island Irish system, and a 21,177-bus model of the ENTSO-E network.
      435Scopus© Citations 25
  • Publication
    Impact of frequency estimation for VSC-based devices with primary frequency control
    This paper presents a comparison of the performance of frequency control devices considering different techniques to estimate the frequency deviation signal. We consider three estimation techniques, namely the center of inertia (COI), the frequency divider (FD) formula, and the phase-locked loop (PLL). The first two are based on the measurement of synchronous machine rotor angles and are virtually exact measures, while the latter is based on an electronic device and is affected by noise and numerical errors. The goal of the paper is first to define whether the PLL estimation is closer to the COI or to the FD. Then, the dynamic response of VSC-based wind power plants and energy storage systems providing primary frequency regulation is studied and compared using the three aforementioned signals. A comprehensive set of scenarios based on the WSCC 9-bus test system is presented in the case study.
      443Scopus© Citations 16
  • Publication
    Impact of Current Transients on the Synchronization Stability Assessment of Grid-Feeding Converters
    The synchronization instability in the presence of a fault is a main issue for the dynamic behavior and control of grid-feeding converters. In the literature, the synchronization stability assessment is carried out considering the dynamics of Phase-Locked Loops (PLL) but the transients of converter currents are neglected. The letter shows that such a simplification leads to inaccuracies and, thus, the current transients cannot be neglected. The letter proposes a model that captures the effect of such current transients on the converter synchronization. This model allows assessing the transient behavior and, hence, the stability, of power electronics converters with high accuracy, comparable, in fact, to EMT models. The fidelity of the proposed model is duly discussed in the case study.
      294Scopus© Citations 45
  • Publication
    Model Predictive Control-Based AGC for Multi-Terminal HVDC-Connected AC grids
    Multi-terminal high-voltage direct current (MTDC) grids are seen as the enabling technology in the development of massive scale international grids such as the European supergrid. It is expected that these grids can play a significant role in regulating ac system frequencies. To date, many proportional-integral (PI) controller-based techniques have been proposed for frequency regulation in ac MTDC-connected grids. In this paper, model predictive control (MPC) is proposed as a means of implementing automatic generation control, while minimizing dc grid power losses. The advantages of using MPC versus PI are highlighted with regard to improvements in both frequency and dc grid regulation, while explicitly considering both delays and dc voltage constraints.
  • Publication
    Stochastic Transient Stability Analysis of Transmission Systems With Inclusion of Energy Storage Devices
    The letter provides a thorough stochastic analysis of the impact of energy storage systems on the transient stability of transmission grids. This impact is evaluated considering the combined effect of different energy storage technologies, fault clearing times, and network topologies. The latter concerns the relative positions of faults, storage devices, and synchronous machines. The case study consists of stochastic time-domain simulations carried out for the all-island, 1479-bus model of the Irish transmission system that includes a real-world hybrid storage device. Results lead to some nonintuitive conclusions.
      491Scopus© Citations 31