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
    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.
      399Scopus© Citations 16
  • Publication
    Efficient implementation of MPC-based AGC for real-world systems with low inertia
    (Elsevier, 2018-05) ;
    The paper discusses practical implementation and computational aspects of an AGC scheme based on model predictive control (MPC) for a real-world power system, namely the all-island Irish transmission system. This system is particularly interesting from the frequency regulation point of view due to the high penetration of wind power generation. This leads to a significant reduction in system inertia, which in turn impacts on the ability of the system operator to regulate the system frequency. The paper compares the performance of the MPC-based AGC with a conventional AGC based on PI controllers and draws relevant conclusions. The case study is a high-resolution simulation of a 1479-bus model of the Irish electrical grid with significant wind penetration, stochastic loads, and controller delays.
      432Scopus© Citations 13
  • Publication
    Placement of Virtual Synchronous Generator Controlled Electric Storage combined with Renewable Generation
    The virtual synchronous generator (VSG) control of power converters has been proposed to improve the system inertia. The commonly used VSG requires an energy storage (ESS) to provide the emulated inertia power and the frequency droop power. The placement of the ESS can be either in the DC port of the power electronics generation or co-located with the power electronics generation on the AC side. In the former case, the VSG control makes the total generator behave like a synchronous generator, while in the latter one, the VSG control only regulates the ESS in response to the grid frequency. The different placement of the ESS gives rise to different performance. This paper analyzes this performance firstly by means of simple transfer function analysis and secondly by comparing their effects on the grid frequency at the system level in the IEEE 39 bus test system. The results show that the placement of the ESS has no impact on the system transient stability while it has a significant impact on the frequency dynamics especially in the low inertia situation.
      286Scopus© Citations 9
  • Publication
    Frequency Participation Factors
    This paper discusses two quantitative and complementary approaches to evaluate the participation of synchronous generators and interconnection buses on local bus frequency variations during electromechanical transients. Both approaches are based on the concept of frequency divider formula recently proposed by the authors on these transactions. A thorough comparison of the two approaches is provided considering several scenarios and three networks, namely the New England 39-bus test system, the all-island 1,479-bus Irish transmission system, and the ENTSO-E 21,177-bus transmission system.
      481Scopus© Citations 5
  • Publication
    Modeling, Simulation, and Comparison of Control Techniques for Energy Storage Systems
    This paper describes the modeling and formulation of a variety of deterministic techniques for energy storage devices, namely the PI, H-infinity, and sliding mode controllers. These techniques are defined based on a general, yet detailed, energy storage device model, which is accurate for transient stability analysis. The paper also presents a thorough statistical comparison of the performance and robustness of the considered control techniques, using stochastic dynamic models and a variety of disturbances and scenarios. The case study is based on a 1479-bus model of the all-island Irish transmission system and an energy storage device actually installed in the system.
      797Scopus© Citations 42
  • 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.
      250Scopus© Citations 38
  • Publication
    Assessment of Grid-Feeding Converter Voltage Stability
    This letter applies voltage stability analysis to grid feeding converters in the presence of the converter stability versus the grid state and its operation. By applying this analysis, it is shown that the converter may become unstable if the converter reference power or current exceeds the line capacity. This letter proposes to use a conventional PV curve to determine the stability of the dynamic response of grid-feeding converters considering both power and current limits.
      409Scopus© Citations 34
  • Publication
    Simplified Model to Study the Induction Generator Effect of the Subsynchronous Resonance Phenomenon
    This letter presents a simple model of induction machines able to appraise the induction generator effect of the subsynchronous resonance phenomenon. The proposed model is general and can be applied to induction machines utilized in wind power applications, such as doubly-fed induction generators. A rigorous stability analysis is carried out based on the proposed model. This analysis shows that the induction generator effect leads to a Neimark–Sacker bifurcation.
      645Scopus© Citations 22
  • 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.