This paper proposes a new approach for corrective voltage control (CVC) of power systems in presence of uncertain wind power generation and demand values. The CVC framework deals with the condition ...that a power system encounters voltage instability as a result of severe contingencies. The uncertainty of wind power generation and demand values is handled using a scenario-based modeling approach. One of the features of the proposed methodology is to consider participation of demand-side resources as an effective control facility that reduces control costs. Active and reactive redispatch of generating units and involuntary load curtailment are employed along with the voluntary demand-side participation (demand response) as control facilities in the proposed CVC approach. The CVC is formulated as a multi-objective optimization problem. The objectives are ensuring a desired loading margin while minimizing the corresponding control cost. This problem is solved using ε-constraint method, and fuzzy satisfying approach is employed to select the best solution from the Pareto optimal set. The proposed control framework is implemented on the IEEE 118-bus system to demonstrate its applicability and effectiveness.
This paper proposes a new coordinated voltage control scheme to ensure voltage security of power systems. The scheme schedules reactive power injection from VAR sources, including synchronous ...generators and condensers, capacitor banks, switchable reactors and FACTS devices, to ensure desired loading margin of power systems for a given horizon of time. The problem is treated as voltage security constrained multi-period optimal reactive power flow (VSC-MPORPF). To incorporate scheduling of both continuous and discrete VAR sources, the VSC-MPORPF is formulated as a mixed-integer nonlinear programming problem, and is solved using generalized Benders decomposition (GBD). Multi-period formulation ensures both optimal switching pattern of discrete voltage controllers and voltage security for a given future horizon. Also, to make the proposed method applicable for large-scale power systems, optimality condition decomposition approach is utilized, along with the GBD. The proposed methodology is examined through case studies conducted on a simple 6-bus, the IEEE 118-bus, and a 1180-bus test systems. The results demonstrate effectiveness and efficiency of the proposed framework in real-time operation of power systems.
The main goal of distribution network operator is to establish a balance between supply and demand at the lowest cost while considering the technical constraints. Nowadays, distribution network ...operators exploit various types of flexibilities to minimise operational costs. However, each flexibility resource has its own technical and economic characteristics. This paper proposes a day‐ahead energy dispatch model which allows the distribution network operator to minimise the energy procurement costs on an hourly basis. The developed model considers various flexibility resources such as renewable energy sources, energy storage systems, demand response, optimal distribution system reconfiguration, and on‐load tap changers optimal settings. The proposed model is formulated as a convex mixed‐integer second‐order conic programming model. It is implemented on the IEEE standard 33‐bus and 70‐bus radial systems to demonstrate its capabilities. The obtained numerical results substantiate the role of distributed energy resources in energy procurement cost reduction, while the impact of distribution system reconfiguration and on‐load tap changers on voltage profile improvement.
•A new scenario-based two-stage wind farms planning model is proposed.•The annual installation capacities of wind turbines are optimally planned.•The Levelized Cost of Energy (LCOE) of wind farms is ...minimized.•Load and wind uncertainties are modeled via scenario based approach.•A desired loading margin is satisfied in the entire planning horizon.
Recently, penetration of intermittent power sources has been increased in power systems due to an international drive for clean and sustainable energies; but these alternative sources could encounter power systems with some problems, which need planning and prevention. This paper proposes a two-stage scenario-based planning model for large-scale wind farms development, based on a project management approach. Considering a 10-year project of large wind farms development, the annual installation capacities of wind turbines are first optimally planned in order to minimize the Levelized Cost of Energy (LCOE) of wind farms. Second, as wind power penetration is consistently increasing in the grid, some stability concerns will come up such as voltage instability. To remedy this condition, the optimum dispatch of grid’s conventional power sources and control variables is determined in such a way that not only in any state of operation (taking into account wind and load uncertainties) but also in post-contingency conditions, the prescribed security margin is ensured at the lowest possible cost. This study has been conducted on an actual power system of Iran’s southeast grid, as well as IEEE 118-bus standard test system. Also, modified crow search algorithm (MCSA) is utilized to solve the developed optimization model. The numerical studies substantiate the effectiveness of the proposed method for long-term planning of wind farms.
Thermal condition monitoring of distribution transformers (DTs) as the most important and expensive equipment of the power grid is undeniable, and by accurate investigation of its thermal status, its ...failure can be prevented because the insulation condition of the transformer is directly related to the hotspot temperature (HST). In this paper, accurate and nonuniform magnetic-thermal analysis of DT is proposed for precise HST prediction. In the magnetic analysis, the DT is modeled as a 2D axial symmetry, and the losses calculation of the windings has been fulfilled as a nonuniform. In the thermal analysis, the DT is modeled as 3D and nonuniform, and the conservator and core stacking, which has a considerable effect on the HST, is precisely modeled. By taking advantage of optical fiber sensors (OFSs) in the understudied 500 kVA DT, the accuracy of the proposed nonuniform 3D CFD-based modeling during the temperature rise test (TRT) is validated. The empirical evaluation results depict that the presented nonuniform CFD-based thermal analysis for HST prediction is very precise, and there is an appropriate vicinity to the experimental values. The error percentage of the proposed 3D CFD-based thermal analysis is 0.11% (0.1 °C) compared to the OFSs measurements, which demonstrates the precision and effectiveness of the presented modeling. Also, the verification of the results of nonuniform 3D CFD-based thermal analysis in top-oil temperature (TOT) and bottom-oil temperature (BOT) during the experimental TRT is fulfilled via thermography. According to the attained evaluated results, temperatures of 3D CFD-based thermal analysis and thermography in the noted two points are in good accordance with each other. In short, the error percentage is less than 0.65%, which indicates the correctness and proper performance of the proposed nonuniform 3D CFD-based modeling. Finally, the proposed nonuniform 3D model was subjected to voltage imbalance of 0.95, 1.05, 1.1, 1.15, and 1.2 of rated voltage. The results demonstrate the HST increases by − 0.4, 0.4, 0.9, 1.3, and 1.8 °C, respectively, over the original model without voltage imbalance, which represents that this issue should be considered in the design and operation of the DT.
In this study, an operation strategy is introduced for distributed energy resources (DERs) in reconfigurable microgrids (MGs) to improve voltage profiles, minimize power losses, and boost the system ...performance. The proposed methodology aims to minimize power loss and energy not supplied (ENS) in MGs with an intelligent share of DERs and network reconfiguration in grid-connected and islanded modes. Due to the inherent uncertain nature of renewable DERs, these sources’ power output is considered as an uncertain parameter, and its effect on the system characteristics is analyzed. The state-of-the-art information gap decision theory (IGDT) approach is utilized to explore different decision-making strategies in the energy scheduling of reconfigurable MGs to deal with such uncertainty. To validate the effectiveness of the proposed method, the IEEE 33-bus radial system is utilized as the test MG. The simulation results show the importance of energy storage systems and reconfiguration in dealing with uncertainty and improving system reliability.
► A new objective function (OF) is presented for optimal reactive power dispatch. ► The proposed OF aims at improving voltage stability margin (VSM) directly. ► The proposed method acts much better ...than the previous ones in improving VSM. ► Active power loss is also decreased as a result of VSM improvement.
Management of reactive power resources is vital for stable and secure operation of power systems in the view point of voltage stability. This paper deals with the management of on-load tap changers (OLTCs) and dynamic VAR sources (including synchronous generators, synchronous condensers, and shunt reactive power compensators) to improve voltage stability margin (VSM) of power systems. This problem is usually called optimal reactive power dispatch (ORD) in the literature. The main contribution of the paper is to introduce a new objective function for the ORD problem. The proposed objective function is derived based on a local voltage stability index, called DSY, and has a strong correlation with VSM. This strong correlation makes the objective function effective for improving VSM, which is the main purpose of ORD. The proposed objective function is tested on the New England 39-bus test system and its performance is compared with some of the most common objective functions used in ORD. The obtained results show that solving ORD problem using the proposed objective function yields considerable increase in VSM.
Renewable energy sources (RESs) are becoming promising nowadays. Deploying distributed energy resources (DERs) is thus increasing accordingly, but the intermittent nature associated with RES remains ...a significant challenge. Also, the distribution grid faces technological difficulties with the large-scale integration of PV generations and EV charging loads. This paper suggests a strategy for a novel optimal voltage regulator (VR) placement model associated with the optimal placement of electric vehicle chargers (EVCs) and photovoltaic (PV) cells. Also, VRs' reference voltages are determined optimally to enhance the hosting capacity (HC) of three-phase unbalanced distribution feeders for large-scale residential/public EVCs and PVs. Two scenarios are defined to study the impact of VRs on the network's HC for DERs, namely with and without VRs in the real three-phase unbalanced feeder. The developed model determines the optimal placement of VRs and their reference voltages linked with EVCs and PVs penetration. Time-Varying Acceleration Coefficients Iteration Particle Swarm Optimization (TVAC-IPSO) algorithm has been implemented to improve the real three-phase unbalanced distribution feeder's HC for DERs. The efficiency of the proposed model and the solution method is validated on the modified IEEE 37-node medium voltage (MV) radial distribution network connected to 35 low voltage (LV) distribution feeders. The obtained results represent that installing a proper number of VRs will increase the network's HC for DERs.
The objective of the dynamic economic dispatch (DED) problem is to find the optimal dispatch of generation units in a given operation horizon to supply a prespecified demand while satisfying a set of ...constraints. In this paper, an efficient method based on optimality-condition-decomposition technique is proposed to solve the DED problem in real-time environment while considering wind power generation and pool market. The uncertainties of wind power generation, as well as the electricity prices, are also taken into account. The aforementioned uncertainties are handled using a scenario-based approach. To illustrate the effectiveness of the proposed approach, it is applied on 40 and 54 thermal generation units and a large-scale practical system with 391 thermal generation units. The obtained results substantiate the applicability of the proposed method for solving the real-time DED problem with uncertain wind power generation.
The distribution network operator is usually responsible for improvement of efficiency and reliability of the network. This paper proposes a framework to demonstrate the impact of renewable energy ...sources (RESs), energy storage systems (ESSs), demand response (DR) and reconfiguration on the optimal sharing of energy. The proposed model determines the optimal locations of RESs, ESSs and DR in the distribution network to minimize simultaneously the cost of energy procurement and energy not supplied. A multi-objective optimization problem is formulated with a mixed-integer second-order cone programming model and ε-constraint method is used to generate Pareto optimal solutions. The network reconfiguration is also considered to optimize the power flow by changing the network topology. The proposed model is implemented on the IEEE standard 33-bus radial test system, and solved by General Algebraic Modeling System (GAMS) optimization software. According to the simulation results, the proposed framework is beneficial both from the reliability and economic perspectives.
•A multi-objective energy management model is proposed.•A convex optimization model is proposed for network reconfiguration and RES, ESS and DR allocation.•Cost of energy not supplied and energy procurement cost are optimized.•The impact of various energy management tools on the reliability and energy costs is studied.
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