Now showing 1 - 6 of 6
  • Publication
    Operational characteristics of non-firm wind generation in distribution networks
    (Institute of Electrical and Electronics Engineers, 2012-07) ; ;
    Distributed wind generation is growing on power systems across the world. It presents many well established technical issues in the distribution network, such as voltage rise, network reinforcement requirements or varying power output. Nonfirm generation, i.e. one to which curtailment can apply due to network infrastructure technical constraints, potentially holds certain benefits for distributed wind generation. This paper will demonstrate the operational characteristics of non-firm wind generation, without the need for network reinforcements. It also proposes an AC optimal power flow model used for evaluating the maximum capacity of wind generation and time series AC optimal power flow for time series calculation in order to determine the energy output that this type of allocation will make during the operation stage. Results show that a significant increase of energy output from non-firm wind generation connected to distribution networks can be achieved in comparison to the commonly used firm type of allocation.
      442Scopus© Citations 7
  • Publication
    Power system planning for high renewables penetration: voltage stability and system frequency aspects
    (University College Dublin. School of Electrical and Electronic Engineering  , 2016) ;
    The installed capacity and the grid access request for renewables is anticipated to continue rising in the EU and US in the coming years. The scarcity of reactive power and synchronous inertia are two inherent consequences of high penetration of renewables in the power system. This raises voltage security concerns, and may endanger rotor angle and frequency stability. In order to foresee these challenges, it is essential to carry out extensive planning and operation studies. Thus, new methodologies and innovative metrics are required to ensure secure and reliable operation of power systems.In this thesis, a multi-operating condition AC voltage stability constraint optimal power flow framework has been presented for transmission system planning. This framework captures multiple wind and demand operating conditions within an optimal power flow tool. The voltage stability constrained optimal power flow was applied to wind capacity allocation. It was shown that the capacity allocation pattern affects steady state voltage stability and the total allocated wind capacity. This indicates that a well-chosen allocation of wind capacity is not only in line with the trend of renewables integration in power systems but also enables limiting the occurrence probability of insecure operating points that may require costly remedies.A procedure for wind capacity allocation has been presented based on the finding on the effects of the pattern of wind capacity allocation on voltage stability. This benefits from the potential of an optimal wind capacity allocation for enhancing the voltage stability margin. Unit commitment was employed to take into account the reduction of the available reactive power sources at each operating condition for wind capacity allocation. By setting the wind capacity target and tracking the loadability margin, it was shown how the risk for a reduction in loadability margin may increase with allocation of wind generation. This procedure showed that specific locations in the system are favored for capacity allocation. It also identified weak areas in the network that experience a reduction in the loadability margin as a result of the allocation of the wind capacity. The methodology can help system operators prioritize network access and investment in the network to enhance the integration of renewables.Further, this thesis focused on the power system frequency aspect of renewables integration. Synchronous inertia acts as a means of immediate frequency support in power imbalances. Renewables often inject power into the network through power electronic converters. As such, synchronizing torque and synchronous inertia are not available in the power from renewables. Reduced levels of synchronizing torque raise concerns on rotor speed behavior under power imbalance events. The interaction of generators has been investigated by deriving the synchronizing torque coefficient matrix from the multi-machine Heffron-Philips model. It was shown that the reactive power output of the generators can be used to control the elements of the synchronizing torque coefficient matrix. It was identified that the varying levels of synchronizing torque affect the rate of change rotor speed of generators following a loss of generation event. Furthermore, the effect of rotor speed deviation due to synchronizing torque was presented from the system frequency perspective. This provides a foundation for system operators to establish strategies that benefit from the synchronizing torque coefficient matrix characteristics for controlling the frequency behavior.
  • Publication
    Optimal Allocation of Wind Generation Subject to Voltage Stability Constraints
    In power systems the occurrence probability of operating points close to network limits may be increased as a result of high wind penetration. Consequences of such scenarios include inefficient exploitation of both wind and economic resources. A well chosen allocation of wind capacity not only is in line with the trend of renewables integration in power systems but also allows for limiting the occurrence probability of unsafe operating points that may require costly remedies. In this work, a voltage stability constrained optimal power flow (VSC-OPF) framework is presented for transmission system planning and applied to wind capacity allocation. This framework captures multiple wind and demand scenarios within the OPF. The pattern of wind capacity allocation is studied in order to assess its impact on voltage stability and the total wind capacity allocation. The results emphasize the effect of the capacity allocation pattern on improvement of voltage stability.
      273Scopus© Citations 1
  • Publication
    Synchronizing Torque Impacts on Rotor Speed in Power Systems
    Renewables are increasingly replacing power from conventional generators. Renewable power injected through power electronic converters lacks the fundamental electric torque components. Electric torque components have an important role in determining the behavior of conventional machines in the network. The influence of this factor becomes more notable in power systems with reduced inertia. Hence, questions arise on, how can synchronizing torque basically contribute to the rotor speed deviation and eventually the system frequency and if there is a potential for using the steady state synchronizing torque coefficient (STC) to achieve acceptable frequency operating points. This paper calculates the steady state STC matrix by using the multi-machine Heffron-Philips model in conjunction with the network admitance matrix. Accordingly, it investigates the impact of the generator location and reactive power output on the STC matrix. It demonstrates how this impact manifests in the generator rotor speed deviation. Eventually, the significance of the STC from the system frequency perspective is assessed.
      971Scopus© Citations 11
  • Publication
    Allocation of Wind Capacity Subject to Long Term Voltage Stability Constraints
    Increasing wind capacity integration results in displacement of active power from conventional generators and a reduction in reactive power sources available. As such, voltage stability may become a concern in certain periods for power system operation particularly in weaker areas of the network. Thus, it is of importance to consider the AC constraints for optimal wind generation planning (long term) in order to decrease the possibility of a wind capacity allocation that requires costly remedies from the power system operation perspective (short term). In this work, a procedure is proposed for wind capacity allocation with the aim of benefiting from the potential of an optimal wind capacity allocation for enhancing the voltage stability margin. The procedure is based on a multi operating conditions voltage stability constrained optimal power flow. The wind capacity target is set and the loadability margin is tracked. The results will show the applicability of the proposed procedure and will emphasize the effects of the pattern of wind capacity allocation on the loadability margin. This will result in a wind capacity allocation that enhances the minimum loadability margin among the possible future operating conditions considered for planning. The procedure uses the Maximin concept for this purpose.
      441Scopus© Citations 16
  • Publication
    A study of operation strategy of small scale heat storage devices in residential distribution feeders
    Passive operation of thermal energy storage devices is a well established concept in Europe; this paper looks at active operation of thermal storage devices and their role in providing demand response from residential distribution feeders. It co-simulates the power system and the thermal performance of buildings to investigate the effect of operation strategy of thermal energy storage devices on the network and thermal comfort of households. A realistic residential feeder is used to demonstrate the applicability of the presented methodology. It is shown that the operation strategy of the thermal storage devices can affect the realizable reserve from these devices, house temperature and network variables such as losses and voltage. The realizable demand response found by the presented methodology can be used for market operation to avoid underestimation and overestimation of the demand response.
      328Scopus© Citations 6