Now showing 1 - 10 of 35
  • 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
    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
    Hardware-in-the-Loop Validation of the Frequency Divider Formula
    This paper validates a theoretical approach, namely, the frequency divider formula, recently proposed by the first and fourth authors to estimate local frequency variations based on the synchronous machine rotor speeds and on signals from phasor measurement units (PMUs). The validation is based on simulations performed in a Real-Time Digital Simulator with physical PMUs connected in the loop. The case study considers the well-known WSCC 3-machine, 9-bus test system. Simulation results show the high accuracy of the frequency divider formula to estimate the frequency at every bus of the network. Results also show that the frequency divider prevents the numerical issues due to fast variations of the voltage when measured by the PMU and indicate that such a formula can be utilized to test the fidelity of PMU implementations.
  • Publication
    Small-Signal Stability Analysis for Non-Index 1 Hessenberg Form Systems of Delay Differential-Algebraic Equations
    (Institute of Electrical and Electronics Engineers (IEEE), 2016-07-11) ;
    This paper focuses on the small-signal stability analysis of systems modelled as differential-algebraic equations and with inclusions of delays in both differential equations and algebraic constraints. The paper considers the general case for which the characteristic equation of the system is a series of infinite terms corresponding to an infinite number of delays. The expression of such a series and the conditions for its convergence are first derived analytically. Then, the effect on small-signal stability analysis is evaluated numerically through a Chebyshev discretization of the characteristic equations. Numerical appraisals focus on hybrid control systems recast into delay algebraic-differential equations as well as a benchmark dynamic power system model with inclusion of long transmission lines.
      256Scopus© Citations 43
  • 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.
      287Scopus© Citations 13
  • Publication
    The effect of time-of-use tariffs on the demand response flexibility of an all-electric smart-grid-ready dwelling
    The paper is concerned with the development and evaluation of control algorithms for the implementation of demand response strategies in a smart-grid enabled all-electric residential building. The dwelling is equipped with a 12 kW heat pump, a 0.8 m3 water storage tank, a 6 kW photovoltaic (PV) array, solar thermal collectors for domestic hot water heating and an electric vehicle. The building, located in Ireland, is fully instrumented. An EnergyPlus building simulation model of the dwelling was developed and calibrated using monitored data from the building. The developed model is used to assess the effectiveness of demand response strategies using different time-of-use electricity tariffs in conjunction with zone thermal control. A reduction in generation cost (−22.5%), electricity end-use expenditure (−4.9%) and carbon emission (−7.6%), were estimated when DR measures were implemented and compared with a baseline system. Furthermore, when the zone control features were enabled, the efficiency of the control improved significantly giving, an overall annual economic saving of 16.5% for the residential energy cost. The analysis also identified an annual reduction of consumer electricity consumption of up to 15.9%, lower carbon emissions of 27% and facilitated greater utilisation of electricity generated by grid-scale renewable resources, resulting in a reduction of generation costs for the utility of up to 45.3%.
      151Scopus© Citations 60
  • Publication
    Comparison of bus frequency estimators for power system transient stability analysis
    The paper presents a study on the dynamic response of power system frequency control devices considering different approaches to estimate bus frequencies in power system simulators. The frequency signals considered in this paper are obtained based on the center of inertia, a commonly-used washout filter that approximates the derivative of the bus voltage phase angle, and a frequency divider formula developed by the authors. The dynamic behavior of frequency control devices such as thermostatically regulated loads is compared considering the three signals above. Different scenarios are discussed based on the IEEE 14-bus and New England 39-bus, 10-machine test systems.
      315Scopus© Citations 20
  • Publication
    Comparison of the Dynamic Response of Wind Turbine Primary Frequency Controllers
    This paper presents a comparison of a variety of control strategies for the primary frequency control of wind power plants. These strategies include inertial as well as pitch angle regulators. The inertial control is sensitive to both the frequency variation through a standard droop control, and the rate of change of frequency. Since these controllers tend to counteract the operation of the Maximum Power Point Tracking (MPPT), the paper also investigates the effect of blocking the MPPT whenever the inertial control is enabled. The pitch angle control allows for a power reserve and prevents the rotor speed from exceeding the nominal value. A modified version of the WSCC 9-bus, 3-machine system with a 30% of wind penetration and a type 3 wind turbine model is considered in the case study. The behavior of these controllers are first analyzed separately. Then a compound controller, which merges together all strategies above, is proposed and discussed.
      294Scopus© Citations 7
  • 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.
      701Scopus© Citations 38
  • 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.
      373Scopus© Citations 92