Now showing 1 - 10 of 71
  • Publication
    Stochastic analysis of the impact of electric vehicles on distribution networks
    Advances in the development of electric vehicles, along with policy incentives, will see a wider uptake of this technology in the transport sector in future years. However, large penetrations of EVs could lead to adverse effects on power system networks, especially at the residential distribution network level. These effects could include excessive voltage drop and thermal loading of network components. A stochastic method is developed to take account of the uncertainties associated with EV charging and the technique is implemented on a residential test network using power system simulation software. The results show how voltage levels, component loading network losses are impacted from EV charging, taking into account the probabilistic behaviour of the EV owners.
  • Publication
    Flexible storage operation in a market environment
    (EnergynauticsGmbH, 2014-11-13) ;
    Future power systems with high penetrations of variable renewables will require increased levels of flexibility from generation and demand-side sources in order to maintain secure and stable operations. One potential source of increased flexibility is large-scale energy storage, which can provide a variety of ancillary services across multiple timescales. In order for adequate investment to take place, it is essential that the correct market signals are present which encourage suitable levels of flexibility, either from storage or alternative sources. This paper explores the changes required in operational practices for storage plant at different levels of installed wind capacity, and the challenges that private storage plant operators will face in generating appropriate bids in a market environment at high penetrations of variable renewables. The impacts on system generating costs are explored under different operating assumptions.
  • Publication
    Strategies to increase grid flexibility for an isolated system with over 80% renewable electricity in 2030
    As renewable electricity targets rise around the world, relatively isolated systems reliant on variable renewables, such as wind and solar power, are rapidly facing unresolved issues regarding system security, flexibility costs and remuneration structures for market participants. Although system service payments exist in some electricity markets, there is often insufficient incentive to invest in greater flexibility, either in the demand or supply side. Here, the economic benefits of various flexibility options are considered, leading towards a discussion of market incentives and strategies for reform. In addition to a range of traditional sources of flexibility from conventional generation, interconnection, and short duration batteries, the importance of system stability is emphasised, including synchronous condensers to supplement inertia, as well as medium-duration storage, and a more active balancing role for heat, transport and industrial loads. Each strategy alleviates the use of fossil fuel based gas plants during periods of system stress and enables the absorption of excess renewables. With over 80% of annual energy to be provided mostly by wind and solar power by 2030, Ireland provides a pertinent case for analysis.
  • Publication
    Frequency dynamics during high CCGT and wind penetrations
    Frequency stability is the paramount concern for secure and reliable operation of a power system. High wind penetration levels are reported in power systems with high thermal generation, and hence its likely to result high wind and combined-cycle gas turbine (CCGT) penetrations during system operation since CCGTs are the most preferable choice for the thermal generation. The doubly-fed induction generators (DFIGs) do not provide any inertial response while the CCGTs have unique frequency response during the system frequency disturbances. Therefore, CCGT turbine response characteristics and the zero inertial response may influence on frequency dynamics of a power network. The main objective of this study is to analyze the frequency dynamics during generator outages and three-phase short-circuit faults in a power network with high CCGT and wind penetrations. A test network model was developed based on the Northern-Ireland network in DIgSILENT Power Factory software package. It has shown that frequency stability may be threatened when three-phase short circuit faults occur in power networks during high CCGT and wind penetrations which may lead to CCGT combustor lean-blowout and ultimately results large frequency excursions in the network.
  • Publication
    Load inertia estimation using white and grey-box estimators for power systems with high wind penetration
    (Elsevier - International Federation of Automatic Control (IFAC), 2012-09-02) ; ; ;
    The increasing penetration of wind farms in power systems has increased concerns over the frequency behaviour and control of synchronous power systems due to a low contribution from modern wind turbines to overall system inertia. With this trend of conventional generators being displaced by variable speed wind turbines, the contribution from load inertia becomes more significant. The need for greater consideration towards load inertia estimation, or even on-line tracking of load inertia, seems to be required. A white-box method for estimation of load inertia is examined using system frequency and generator output power signals from previous generator forced outages. A grey-box identification method is also applied to estimate the inertia of synchronous generators. The impact of sampling rates, time shifting and signal averaging on parameter estimation is also considered. The method is shown to be robust enough to be applied for load inertia estimation in control centres.
    Scopus© Citations 22  966
  • Publication
    Unit Commitment With Dynamic Cycling Costs
    (Institute of Electrical and Electronics Engineers, 2012-11) ; ; ;
    Increased competition in the electricity sector and the integration of variable renewable energy sources is resulting in more frequent cycling of thermal plant. Thus, the wear-and-tear to generator components and the related costs are a growing concern for plant owners and system operators alike. This paper presents a formulation that can be implemented in a MIP dispatch model to dynamically model cycling costs based on unit operation. When implemented for a test system, the results show that dynamically modeling cycling costs reduces cycling operation and tends to change the merit order over time. This leads to the burden of cycling operation being more evenly distributed over the plant portfolio and reduces the total system costs relative to the case when cycling costs are not modeled.
    Scopus© Citations 52  695
  • Publication
    Wind and solar curtailment: a review of international experience
    Greater penetrations of variable renewable generation on some electric grids have resulted in increased levels of curtailment in recent years. Studies of renewable energy grid integration have found that curtailment levels may grow as the penetration of wind and solar energy generation increases. This paper reviews international experience with curtailment of wind and solar energy on bulk power systems in recent years, with a focus on eleven countries in Europe, North America, and Asia. It examines levels of curtailment, the causes of curtailment, curtailment methods and use of market-based dispatch, as well as operational, institutional, and other changes that are being made to reduce renewable energy curtailment.
    Scopus© Citations 365  3310
  • Publication
    Provision of flexibility at high wind penetration levels using modern storage heater load
    Modern storage heaters can facilitate higher levels of wind generation on the system by mitigating the effects of wind variability and uncertainty. This paper presents a coordinated control strategy for modern storage heater load to reduce conventional plant ramping and cycling requirements. Control practices and mechanisms required to utilise storage heater load for reducing system net load variability have been presented. The communication update rate to the heaters has been shown to impact conformance to the control objective. Acknowledging the impracticality of individual appliance control, a clustering scheme has been proposed to reduce the overall communication requirements. Heater load shaping mechanisms have also been presented to provide real-time system ancillary services at high wind penetration levels.  
      338Scopus© Citations 2
  • Publication
    Validating unit commitment models: A case for benchmark test systems
    Due to increasing penetration of non-traditional power system resources; e.g. renewable generation, electric vehicles, demand response, etc. and computational power there has been an increased interest in research on unit commitment. It therefore may be important to take another look at how unit commitment models and algorithms are validated especially as improvements in solutions and algorithmic performance are desired to combat the added complexity of additional constraints. This paper explores an overview of the current state of unit commitment models and algorithms, and finds improvements for both comparing and validating models with benchmark test systems. Examples are provided discussing the importance for a standard benchmark test system(s) and why it is needed to compare and validate the real world performance of unit commitment models.
      570Scopus© Citations 7
  • Publication
    Grid-forming requirements based on stability assessment for 100% converter-based Irish power system
    The fault response of a 100% converter-based system can be significantly different to that of a synchronous generator-based system, considering the lower capacity headroom, but flexible control capability, of power electronic converters. The system response is investigated for an Irish grid under balanced three-phase faults comprising of 100% converter-based generation: grid-forming (GF) and grid-following (GL). Electro-magnetic transient (EMT) simulations show that a system consisting only of GF converters (all droop control, all dispatchable virtual oscillator control, or a mix of both) is robust against three-phase faults, with little variation in performance, despite the fault location or choice of GF control methods. However, the rating and location of GF converters are critical to operating the grid securely in the presence of both GF and GL converters. Assuming that individual converter bus nodes are either GF or GL, a minimum GF requirement (by capacity) is found to be 37–40%, with these GF converters located close to the major load centres. Assuming instead that individual generation nodes consist of a mix of GF and GL converters, it is found that the GF requirement can be relaxed by 8–10%.
    Scopus© Citations 15  76