Now showing 1 - 8 of 8
  • Publication
    Strategic Scheduling in Smart Grids
    With a shorter scheduling horizon, it is easier to handle the system uncertainties in distribution scheduling problem. On the other hand, due to higher cost of some control actions, e.g., tap changing operations, with a short horizon, these high cost control actions may never be justified, even though they could be necessary in the future. With a longer scheduling horizon, the operator have a wider choice and can schedule the tap changing operations to further reduce the total system cost. A multi-period scheduling scheme is proposed in this paper for cost minimization. Different scenarios are generated to model the uncertainties associated with renewable resources, upstream system and system loads. The number of scenarios is then reduced to moderate the computational burden. In the first period, the decision variables should be the same for all scenarios. Only the decisions made for the first period will be applied. For the next periods, this framework should be applied again. In this way, a long scheduling horizon is modeled, the available and forecast data are considered and future decisions are to be made when more accurate data are available. The effectiveness of the method is shown through the case studies.
      505Scopus© Citations 3
  • Publication
    Methodology for Assessment of the Impact of Smart Transformers on Power System Reliability
    The smart transformer (ST) has been proposed as an alternative to the traditional low frequency transformer as a means to provide extra control functionality in the smart power system. The ST has merits in terms of reactive power decoupling and voltage decoupling at the primary and secondary side. This provides flexibility for reactive power compensation in the transmission system and demand reduction in the distribution system. Using its ability to control demand through voltage regulation, the ST provides the possibility to reduce demand while keeping the entire load online, which can provide an alternative to load curtailment. Thus, it may provide a means to improve power system reliability. However, no of previous research has investigated these potential system reliability benefits of the ST. The paper presents a methodology which can be used to quantify the system reliability impacts of the use of STs
  • Publication
    Planning of OLTC Transformers in LV Systems under Conservation Voltage Reduction Strategy
    (IEEE, 2019-10-02) ;
    The wide voltage control capacity of on-load tap changers (OLTCs) forces them into the list of reinforcement alternatives in the expansion planning of distribution systems. Their high investment and operation cost, however, is a downside. The voltage dependent nature of loads can be deemed as an opportunity to reduce the system demand and operation cost by managing the voltage at substation level (referred to as conservation voltage reduction strategy). Here, it is shown that consideration of this strategy justifies the investment on OLTCs against the other options even for LV systems. Both short-term and long-term variations of the system parameters are taken into account, since as it will be shown, the rate of system variations affects the decision on replacing the available transformers with OLTC transformers. The proposed method embodies a prognosis of long-term future by modeling the operating conditions in a set of daily scenarios with hourly time resolution to include the cost of tap changing operations in the objective function. The oltcs' control strategy in this daily scenarios matches the industry common practice.
      8Scopus© Citations 3
  • Publication
    Stochastic network constrained payment minimisation in electricity markets
    (The Institution of Engineering and Technology, 2019-06-04) ; ;
    This study presents a novel framework to incorporate the uncertainties associated with load fluctuations and components' availability in a day-ahead joint energy-reserve payment cost minimisation (PCM). The payments are calculated based on locational marginal prices (LMPs). Considering these uncertainties, appropriate definitions are not available for energy and reserve LMPs (RLMPs) that suit the probabilistic PCM formulation and reflect the market characteristics. A tri-level optimisation framework is proposed. The optimisation variables in the first-level optimisation include commitment status. In the second-level optimisation, the production schedule and allocated reserves are the optimisation variables. The third-level problem includes different sub-problems, each of which related to optimisation of units' production in a single scenario. This tri-level optimisation is managed to be converted to a linear single-level optimisation and is solved using an off-the-shelf branch-and-cut solver. The 10-unit system is first used to show the impacts of varying the degree of uncertainties. The IEEE Reliability Test System is next analysed to validate the proposed formulation for RLMPs.
      11Scopus© Citations 7
  • Publication
    Resilient Decentralized Control of Inverter-interfaced Distributed Energy Sources in Low-voltage Distribution Grids
    (Institution of Engineering and Technology, 2019-10-29) ; ;
    Abstract: This paper shows that a relation can be found between the voltage at the terminals of an inverter-interfaced Renewable Energy Source (RES) and its optimal reactive power support. This relationship, known as Volt-Var Curve (VVC), enables the decentral operation of RES for Active Voltage Management (AVM). In this paper, the decentralized AVM technique is modified to consider the effects of the realistic operational constraints of RES. The AVM technique capitalizes on the reactive power support capabilities of inverters to achieve the desired objective in unbalanced active Low-Voltage Distribution Systems (LVDSs). However, as the results show, this AVM technique fails to satisfy the operator’s objective when the network structure dynamically changes. By updating the VVCs according to the system configuration and components’ availability, the objective functions will be significantly improved, and the AVM method remains resilient against the network changes. To keep the decentralized structure, the impedance identification capability of inverters is used to find the system configuration locally. Adaptive VVCs enable the decentralized control of inverters in an online setting. A real-life suburban residential LV-DS in Dublin, Ireland is used to showcasing the proposed method, and the effectiveness of the proposed resilient active voltage management technique is demonstrated.
    Scopus© Citations 4  274
  • Publication
    Strategic Scheduling of Discrete Control Devices in Active Distribution Systems
    The frequent actuation of discrete control devices (DCDs), e.g., on-load tap changers, drastically reduces their lifetime. This, in turn, imposes a huge replacement cost. Simultaneous scheduling of these DCDs and continuous control devices, e.g., distributed energy resources, is imperative for reducing the operating cost. This also increases the lifetime of DCDs and helps avoid the sub-optimal/infeasible solutions. Considering the high cost of discrete control actions (DCAs), they may never be justified against the other options in a short scheduling horizon (SH). With a longer SH, their benefits over a long period justify DCAs. However, a shorter SH helps to hedge against the risk impelled by uncertainties. Here, the system future is modeled as a set of multi-period scenarios. The operator exploits a long SH, but solely applies the decisions made for the first period and waits for updated data to make the next decisions. This enables cost reduction by strategically applying DCAs prior to the time that they are inevitable, while avoiding them when unneeded. The proposed branch-and-cut-based solution methodology accurately deals with DCAs while applying some expediting heuristics. During the branching process, a globally convergent trust region algorithm solves the integer relaxed problems.
    Scopus© Citations 10  9
  • Publication
    Real-Time Estimation of Support Provision Capability for Poor-Observable Distribution Networks
    An indispensable step towards coordinating the actions of distribution and transmission system operators (DSOs-TSO) is to estimate the range of flexibility that can be offered to the TSO by DSOs. Within this context, a data-driven probabilistic approach is proposed to evaluate the capability of a distribution network in providing active and reactive power support in real-time. To this end, in an offline phase, a linear discriminant analysis model, together with a piecewise linear model of the distribution network are trained to delineate the boundary of a region representing the adherence to distribution network operational constraints. In the implementation phase, this region comprises the feasible set of a series of optimization problems, formulated to determine the support provision capability. These optimization problems are of iterative linear programming type, which allows for real-time applicability. The evaluated support capability can be deemed as the available reserve in real-time transmission operation, which enables providing a coordinated response towards unexpected events, and facilitates the participation of distributed resources in the balancing market by granting an up-to-date estimation of available supports. This approach is tested on the IEEE 123-node system and verified through comparison with an AC optimal power flow technique.
    Scopus© Citations 1  21
  • Publication
    Fast Resource Scheduling for Distribution Systems Enabled with Discrete Control Devices
    This article proposes a framework for fast short-term scheduling and steady-state voltage control in distribution systems enabled with both continuous control devices, e.g., inverter interfaced distributed generators (DGs) and discrete control devices (DCDs), e.g., on-load tap changers. The voltage-dependent nature of loads is taken into account to further reduce the operating cost by managing the voltage levels. Branch and cut method is applied to handle the integrality constraints associated with the operation of DCDs. A globally convergent trust region algorithm (TRA) is applied to solve the integer-relaxed problems at each node during the branching process. The TRA subproblems are solved using interior point method. To reduce the branching burden of branch and cut algorithm, before applying TRA at each node, a simplified optimization problem is first solved. Using the convergence status and value of objective function of this problem, a faster decision is made on stopping the regarding branch. Solving the simplified problem obviates the application of TRA at most nodes. It is shown that the method converges to the optimal solution with a considerable saving in computation time according to the numerical studies.
    Scopus© Citations 5  8