Now showing 1 - 10 of 69
  • Publication
    Evaluation of Power System Flexibility
    (Institute of Electrical and Electronics Engineers, 2012-05) ; ;
    As the penetration of variable renewable generation increases in power systems worldwide, planning for the effects of variability will become more important. Traditional capacity adequacy planning techniques have been supplemented with integration studies, which have been carried out in power systems with high targets for renewable generation. These have highlighted the increased variability that a system may experience in the future. As system generation planning techniques evolve with the challenge of integrating variable generation, the flexibility of a system to manage periods of high variability needs to be assessed. The insufficient ramping resource expectation (IRRE) metric is proposed to measure power system flexibility for use in long-term planning, and is derived from traditional generation adequacy metrics. Compared to existing generation adequacy metrics, flexibility assessment is more data intensive. A flexibility metric can identify the time intervals over which a system is most likely to face a shortage of flexible resources, and can measure the relative impact of changing operational policies and the addition of flexible resources. The flexibility of a test system with increasing penetrations of variable generation is assessed. The results highlight the time horizons of increased and decreased risk associated with the integration of VG.
      2760Scopus© Citations 437
  • 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.
      592Scopus© Citations 48
  • Publication
    Using energy storage to manage high net load variability at sub-hourly timescales
    High net load variability, driven by high penetrations of wind and solar generation, will create challenges for system operators in the future, as installed wind generation capacities increase to unprecedented levels globally. Maintaining system reliability, particularly at shorter time-scales, leads to increased levels of conventional plant starts and ramping, and higher levels of wind curtailment, with sub-hourly unit commitment and economic dispatch required to capture the increased cycling burden. The role of energy storage in reducing operating costs and enhancing system flexibility is explored, with key storage plant characteristics for balancing at this time-scale identified and discussed in relation to existing and emerging grid-scale storage technologies. Unit dispatches for the additional storage plant with varying characteristics highlight the unsuitability of energy only markets in incen-tivizing suitable levels of flexibility for future systems with high net load variability.
      433Scopus© Citations 62
  • Publication
    Impact of voltage dip induced delayed active power recovery on wind integrated power systems
    (Elsevier, 2017-04) ;
    Installed wind power capacity is increasing rapidly in many power systems around the world, with challenging penetration targets set at national, and/or regional level. Wind power, particularly at higher penetration levels, introduces various grid issues, with frequency and voltage stability being particularly critical concerns. Voltage dip induced frequency stability following a network fault in such systems is one potential risk that has so far received limited attention by the research community. With state of the art modelling, the potential impact of a delayed active power recovery from wind generation following a network fault induced voltage dip is investigated. The subsequent voltage oscillations introduced by wind turbines, exacerbating frequency stability, are also examined. Analysis is carried out for a wide range of wind penetration levels and system scenarios, with the results demonstrated on the New England benchmark system.
      526Scopus© Citations 19
  • Publication
    Efficient large-scale energy storage dispatch: challenges in future high renewables systems
    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 operation. One potential flexibility source is largescale energy storage, which can provide a variety of ancillary services across multiple time-scales. In order for appropriate levels of investment to take place, and in order for existing assets to be utilized optimally, it is essential that market signals are present which encourage suitable levels of flexibility, either from storage or alternative sources. Suboptimal storage plant dispatch due to uncertainty and inefficient market incentives are represented as operational constraints on the storage plant, and the impact of these inefficiencies are highlighted. Thus changes required in operational practices for storage plant at different installed wind capacity levels, and the challenges that private storage plant operators will face in generating appropriate bids in a market environment at high variable renewable penetrations are explored. The impacts on system generating costs and storage profits are explored under different plant operating assumptions.
      482Scopus© Citations 51
  • Publication
    RoCoF-Constrained Scheduling Incorporating Non-Synchronous Residential Demand Responsee
    Demand response has the potential to provide a multitude of operating reserve categories. However, if integrated at scale, the non-synchronous nature of most demand response sources must be recognised within the operational rules of low inertia power systems. Here, a candidate non-synchronous reserve resource is considered within the scheduling and frequency stability time frames. It is shown that a detrimental impact on the post-contingency rate of change of frequency (RoCoF) can arise, potentially requiring the development of system operator policies to ensure that security standards are not compromised, as the volume of reserve available from non-synchronous reserve resources increases. A commitment-and-dispatch RoCoF constraint within scheduling procedures is proposed, which is independently verified using time domain simulations.
      385Scopus© Citations 19
  • Publication
    Real-time System-wide Inertia Estimation in Power Systems with High Wind Penetration Levels
    Knowledge of on-line inertia in power systems with high and increasing levels of wind penetration is becoming more important for power system operators. In this paper, the basis of a real-time stored energy estimator is developed, which accounts for the inertia contribution from loads as well as generators in the system. By creating a simplified first order model of the system, power and frequency signals recorded are utilized to estimate real-time feeder stored energy by use of a linear least-squares estimator. The capability of the proposed estimator is investigated by application on a test system. The estimation error is analysed in respect of data resolution and feeder contributions to stored energy. Discussion on the requirements for applications within power systems and the communication configuration are also presented.
  • Publication
    Modelling of a Multi-purpose Commercial Building for Demand Response Analysis
    This paper examines the implementation of demand response measures, using an EnergyPlus simulation model, in a multipurpose commercial building. The simulation model, which has been developed specifically for demand response analysis, is used to assess the effectiveness of different demand response strategies, which were considered for the building. The strategies were examined for a representative zone within the building and evaluate the contribution of the building capacitance and HVAC equipment operation, as mechanisms for shifting the building electrical demand. Associated zone temperature responses and load shifts are also quantified.
  • Publication
    Voltage Dip Induced Frequency Dips for Power Systems with High Shares of Wind Energy
    (IEEE, 2022-06-29) ;
    In order to limit drivetrain mechanical stress, wind turbine generators typically implement a delayed active power recovery following a voltage dip, which may result in a substantial reduction in system frequency, if many wind farms adopt a similar strategy, due to the resulting generation-demand imbalance. Therefore, based on a modified IEEE 39-bus system, the impact of active and reactive current priority strategies, and various reactive current loop controls for wind turbine generators on voltage dip induced frequency dips (VDIFDs) are examined. The effectiveness of local voltage control with reactive current priority is validated. In addition, if synchronous-based generation is displaced by grid-forming converters (GFMs), the frequency dips are less severe and the post-fault frequency recovers more quickly. However, due to reduced overcurrent capability, the GFM virtual angle control must be carefully designed to avoid transient instability, by, for example, reducing the droop gain. Finally, if DC-link voltage control and maximum power point tracking control for the grid-side and machine-side converters are switched (to simplify fault ride through implementation) care is needed to avoid large post-fault over-frequency transients for VDIFD events.
  • Publication
    System-wide inertial response from fixed speed and variable speed wind turbines
    (IEEE, 2011-07-24) ;
    As wind penetration levels on power systems increase worldwide, the dynamic characteristics of these systems are changing due to the displacement of synchronous generation. One issue, of particular concern, is the resulting reduction in system inertia. Modern, variable speed wind turbines are controlled by power electronics and so do not inherently contribute to the inertial response of the system. Such devices can however be fitted with a control loop which provides an active power response to significant frequency deviations, similar to the inertial response of fixed speed wind turbines and synchronous generation. However, the response of variable speed turbines is dependent on local wind speeds and so cannot be quantified deterministically by system operators. This paper examines the potential for wind generation to contribute to system inertial response and considers the aggregated inertial response capabilities of fixed speed and variable speed wind generation.
      1003Scopus© Citations 30