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The reduced inertia levels in low-carbon power grids necessitate explicit constraints to limit frequency’s nadir and rate of change during scheduling. This can result in significant curtailment of renewable energy due to the minimum generation of thermal plants that are needed to provide frequency response (FR) and inertia. Additional consideration of fast FR, a dynamically reduced largest loss and under frequency load shedding (UFLS) allows frequency security to be achieved more cost effectively. This paper derives a novel constraint from the swing equation to contain the frequency nadir using all of these services. The expected cost of UFLS is found probabilistically to facilitate its comparison to the other frequency services. We demonstrate that this constraint can be accurately and conservatively approximated for moderate UFLS levels with a second order cone (SOC), resulting in highly tractable convex problems. Case studies performed on a Great Britain 2030 system demonstrate that UFLS as an option to contain single plant outages can reduce annual operational costs by up to $\pounds $ 559 m, 52% of frequency security costs. The sensitivity of this value to wind penetration, abundance of alternative frequency services, UFLS amount and cost is explored. [ABSTRACT FROM AUTHOR]

In view of the uncertainty and intermittency of wind power, this paper proposes an optimal economical dispatch (ED) model and develops a method to estimate risk and manage hybrid power systems (traditional + wind~power~systems) for the short-term (24 h) operations. The model and the method have taken into account the large wind power penetration and the wind variability. The particle swarm optimization (PSO) refid="ref1"/ algorithm with constraints is applied to solve the ED problem. Value at risk (VaR) refid="ref2"/ and integrated risk management (IRM) refid="ref3"/ are used separately to assess the risk, so that an optimal tradeoff between the profit and risk is made for the system operations. The model and the method are tested on the standard IEEE 30-bus power system and network in Shanghai. The validity of the model and the method has been approved. [ABSTRACT FROM PUBLISHER]

In order to simplify and increase the reliability of wind generators, a new type of a direct-drive directly grid-connected wind generator known as a slip–synchronous permanent-magnet generator (SS-PMG) is proposed. It consists of two integrated generating units, i.e., a directly turbine-connected slip PMG unit and a directly grid-connected PM synchronous generator unit. The main aim of this paper is to determine if this generator is stable under transient wind turbine and grid conditions. A transfer function model is developed to evaluate the dynamic performance of the wind generator system. The transient response of a single 15-kW grid-connected system is evaluated. It is shown that the generator is very stable under transient turbine torque conditions. Furthermore, it acts as a filter to prevent voltage flickering due to oscillatory turbine pulsations. A very important design aspect to take into account is the torque ripple characteristics of the slip PM generator as torque ripple can be transferred to the grid current under certain conditions. Simulated and dynamically measured results are shown for a series of 15-kW SS-PMG prototypes. [ABSTRACT FROM PUBLISHER]

With the increasing penetration of wind power into the power grid, maintaining system reliability has been a challenging issue for ISOs/RTOs, due to the intermittent nature of wind power. In addition to the traditional reserves provided by thermal, hydro, and gas generators, demand response (DR) programs have gained much attention recently as another reserve resource to mitigate wind power output uncertainty. However, the price-elastic demand curve is not exactly known in advance, which provides another dimension of uncertainty. To accommodate the combined uncertainties from wind power and DR, we allow the wind power output to vary within a given interval with the price-elastic demand curve also varying in this paper. We develop a robust optimization approach to derive an optimal unit commitment decision for the reliability unit commitment runs by ISOs/RTOs, with the objective of maximizing total social welfare under the joint worst-case wind power output and demand response scenario. The problem is formulated as a multi-stage robust mixed-integer programming problem. An exact solution approach leveraging Benders' decomposition is developed to obtain the optimal robust unit commitment schedule for the problem. Additional variables are introduced to parameterize the conservatism of our model and avoid over-protection. Finally, we test the performance of the proposed approach using a case study based on the IEEE 118-bus system. The results verify that our proposed approach can accommodate both wind power and demand response uncertainties, and demand response can help accommodate wind power output uncertainty by lowering the unit load cost. [ABSTRACT FROM PUBLISHER]

Type 3 wind generators in series compensated networks could lead to subsynchronous resonances (SSR). Previous research focuses on balanced operation only. In this paper, impact of unbalance on Type 3 wind energy systems is investigated in two aspects: 1) impact on electric resonances and 2) impact on torsional resonances. In the first aspect, impedance models of the system in DQ domain and phase domain are developed. Particularly, negative sequence impedances are examined. Nyquist stability criterion is applied to detect possible resonances. In the second aspect, transfer functions of the electromagnetic torque versus the rotating speed due to negative sequence components are developed. The impact of negative sequence components on electromechanical damping is then analyzed. The analysis results are verified by time-domain simulation results. [ABSTRACT FROM PUBLISHER]

This paper investigates the problem of distributed energy management for both generation and demand sides in a smart grid by formulating the economic dispatch and demand response in a united framework. Our main contribution is to formulate a social welfare maximization problem for a more practical scenario by taking wind power, and temporally coupled constraints of the demands into account. The complexity lies in the nonquadratic cost function of wind power, the temporally coupled constraints of the demands, and the nonconvexity of the optimization problem. Meanwhile, a smart grid has to guarantee privacy and accommodates plug-and-play features. Aiming at these challenges, we first relax an equality constraint to obtain a new convex optimization problem. Because of the coupling in the constraint, the Lagrange duality method is then adopted to decompose the problem into subproblems for generators and demands, which are regarded as agents. As a result, each agent solves its subproblem by exchanging information with only neighbor agents, and coordinates with others using the global information discovered by a distributed finite-time consensus algorithm. We also prove the convergence and optimality of the proposed distributed energy management algorithm (DEMA). Finally, simulations are performed on the IEEE 39-bus system to illustrate the performance of our DEMA. [ABSTRACT FROM AUTHOR]

With the advent of power electronics, the size, weight, and cost of power converters have been drastically reduced while efficiency is improved. The use of variable-speed wind power generators has seen considerable growth. The use of gearboxes in the wind turbines allows for smaller size, lower weight, and higher speed generators. However, gearboxes have shown to be one of the least reliable components of the wind turbines. In this paper, we propose a method that can extend the life and reliability of wind turbine gearboxes by reducing the mechanical stress on gearbox components. Reduction of mechanical stress is achieved by the generator torque control that minimizes resonant torsional vibrations within a drivetrain caused by variations in wind velocity. A detailed model for the drivetrain of a 750-kW wind turbine, including a gearbox is presented. Experimental results are used to calculate the parameters of the gearbox. A controller is designed to adjust the generator torque at the end of the drivetrain to remove the unwanted and damaging torque variations from the drivetrain. Simulation results verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This paper analyzes fixed-speed induction generator modeling oriented to rotor speed stability studies. The single- and double-cage models are compared. The effects of symmetrical voltage sags on generator behavior are studied in detail. The rotor speed stability of the turbine is also examined and rotor speed recovery time is proposed as an indicator of system stability. Significant differences in the results obtained for both models were found, e.g., the double-cage model shows better speed and voltage stability. For some generator designs, the single-cage model can lead to erroneous stability predictions because manufacturer data of such designs can only be fulfilled with a double-cage model. The use of the latter to simulate fixed-speed wind turbines with this type of designs is therefore strongly recommended. The simulations were carried out using PSpice and PSCAD/EMTDC. [ABSTRACT FROM PUBLISHER]

In response to the challenges brought by uncertain bus load and volatile wind power to power system security, this paper presents a novel unit commitment formulation based on interval number optimization to improve the security as well as economy of power system operation. By using full-scenario analysis, the worst-case impact of volatile node injection on unit commitment is acquired, so that the proposed model can always provide a secure and economical unit commitment result to the operators. Scenarios generation and reduction method based on interval linear programming theory are used to accelerate the solution procedure without loss of optimality. Benders decomposition is also implemented to reduce the complexity of this large-scale interval mixed integer linear programming, and prove the rationality and rigor of our proposed method. The numerical results indicate better secure and economical features of the proposed method comparing with the traditional one. [ABSTRACT FROM PUBLISHER]

The feasibility study of a power system is aimed at determining whether the system can adequately satisfy the load. The study will usually include other purposes, such as estimating the life-cycle cost of the system. This paper summarizes the main capabilities of current software packages for feasibility analysis of distributed energy resources. The document presents a short description of models, dispatch strategies, and economic indicators implemented in some packages. The test cases included in this paper will illustrate the scope of a feasibility study considering off-grid and grid-connected distributed resources. [ABSTRACT FROM AUTHOR]

This paper introduces a transmission planning model for a system integrating a large amount of remote wind power. We consider uncertainties of wind availability and system load, which are represented by two dependent random variables in the optimization problem. A two-stage stochastic model and sequential approximation approach are applied to solve our total cost minimization problem, which involves a sequence of stochastic optimization problems repeatedly solved with an updated approximation of random parameters until the rate of increment of optimal cost becomes smaller than a positive target value. A wind energy integration goal is achieved by penalizing wind curtailment. As a case study, the Electric Reliability Council of Texas (ERCOT) wind and load data, and a simplified model of its transmission system, is employed. [ABSTRACT FROM PUBLISHER]

In this paper, we formulate the economic dispatch problem as a two-stage stochastic convex program for operational decision making under uncertainty. Post-contingency minimum frequency constraints are formulated as convex sets using a simplified model of frequency dynamics. The L-shaped method is used to decompose the large stochastic program into smaller sub-problems. Large-scale system examples are provided to demonstrate the computational efficiency of the proposed model formulation. Numerical results show the value of the proposed model and indicate that the proposed model is especially useful under a higher level of wind penetration. [ABSTRACT FROM PUBLISHER]

With high wind-power penetration, power-system operators require accurate wind-power output from wind farms for system operation. A more accurate four-dimension wind speed model is proposed in this paper to simulate the effects of terrain and time delay of wind speed. Two coordinate transformation matrices are proposed to easily incorporate wind direction in wind-speed simulation. The effects of random failures and wake of wind turbine generators on wind-speed distribution in a wind farm are also considered in the proposed model. A sequential Monte Carlo simulation technique is developed to evaluate adequacy of power systems with wind farms using the proposed model. The modified IEEE RTS is analyzed to illustrate the models and technique. The simulation results show that those factors have significant impact on power output of a wind farm and system reliability. [ABSTRACT FROM PUBLISHER]

Wind energy conversion systems (WECS) nowadays offer an extremely wide range of topologies, including various different types of electrical generators and power converters. Wind energy is also an application of great interest to students and with a huge potential for engineering employment. Making WECS the main center of interest when teaching power electronics and electrical machines can therefore be highly advantageous. This paper describes a novel teaching experience using wind energy as the starting point for understanding power electronics and electrical machines. The results point out the wide variety of concepts involved in the course, the numerous competences that it can enhance, and its positive reception by learners. [ABSTRACT FROM AUTHOR]

Load demand in small autonomous island systems is typically covered by Diesel Units (DU). Although a favourable renewable energy source (RES) potential might exist, the technical constraints introduced by the conventional generators result in relatively low RES penetration levels, typically up to 15%–20% of the annual energy demand. To overcome such limitations, introduction of energy storage is necessary. In the case of very small islands (less than 1 MW peak load), lead-acid battery energy storage systems (BESS) constitute a technically mature solution with considerable application potential. In this paper, the potential for achieving very high RES penetration levels with the introduction of BESS in an existing small island system is investigated. An operating policy is first introduced for the overall system, including conventional generators, RES (wind and photovoltaic) stations and storage system. Simulation results are then presented to quantify the expected energy benefits in terms of RES energy penetration and the impact on the economics of the island system. The sizing of the hybrid system components is then investigated by conducting a parametric analysis and then optimized by applying genetic algorithms. [ABSTRACT FROM PUBLISHER]

This work aims to improve the combined flow and thermal network (CFTN) accuracy for radially air-cooled generators by investigating the possible error stemming from the flow part. The nonlinear resistance characteristics of the T-junction dividing flow are first time considered for such cooling arrangement, which is achieved by employing the Gardel equations and the blend equation as the governing equations. Compared with the CFD model results as the benchmark, the nonlinear CFTN predicts an accurate flow rate in the radially extended airducts, making only 9% root mean square (rms) error for all the airducts. On the contrary, the linear CFTN fails to obtain a reliable flow distribution, as the rms error is as large as 34%. As a result, the nonlinear CFTN improves the accuracy of the maximum winding temperature by 6.4% over the linear CFTN and gives a more reasonable temperature gradient in the axial direction. Furthermore, the relative difference between the linear and nonlinear CFTNs is found to be even larger in the following conditions: large cooling air flow rate, wide airgap, low slot fill factor, and large airduct number. The proposed nonlinear CFTN modeling approach is also validated against experimental measurements for a prototype. The modeled temperatures match well with the measurements at different axial positions. According to the aforementioned findings, the nonlinear CFTN modeling approach is considered to be a reliable thermal analysis tool for the radial air-cooling arrangement. [ABSTRACT FROM AUTHOR]

In this study, a characteristic simulation method of a megawatt three-blade horizontal axis wind turbine (MW-THAWT) is proposed based on a laboratory kilowatt low-power motor system, which can realize the parameter correspondence and the rotational inertia compensation between the simulation platform and the wind turbine. First, the virtual proportional THAWT model of MW-THAWT is established to make the parameters of the motor and the wind turbine correspond. The control strategies of speed output and torque output are then designed to solve the problem that the conventional method cannot simulate the unstable region. The dynamic simulation strategy combining the shaft torque feedback rotational inertia compensation method and load characteristic simulation is proposed, which can ensure the consistency of the change time and mode between the simulation platform and the wind power system in the dynamic process. Finally, the MW-THAWT simulation experiment platform based on 1.4-KW motor is developed for theoretical verification. The experimental results verify that the proposed method can realize the characteristic simulation of static and dynamic of MW-THAWT in full speed range and is suitable for industrial production and laboratory research of wind turbine. [ABSTRACT FROM AUTHOR]

In this study, two important planning problems in power systems that are transmission expansion and reactive power are formulated as a mixed-integer linear programming taking into account the bilevel structure due to the consideration of market clearing under several load-wind scenarios. The objective of the proposed method is to minimize the installation cost of transmission lines, reactive power sources, and the annual operation costs of conventional generators corresponding to the curtailed wind energy while maintaining the reliable system operation. Lower level problems of the bilevel structure are designated for the market clearing which is formulated by using the linearized optimal power flow equations. In order to obtain mixed-integer linear programming formulation, the so-called lower level problems are represented by using primal-dual formulation. By using the proposed method, power system planners will be able to find economical investment plans by considering the balance between wind power curtailment and the installation of transmission lines and reactive power sources. [ABSTRACT FROM AUTHOR]

In this study, the design for a direct-drive permanent magnet (PM) wind power generator is presented, and its characteristics are analyzed based on analytical approach. In order to confirm their influence on the torque ripple characteristics, both the shape design and the skew effects of the PM are thoroughly studied. In particular, we performed an analytically based electromagnetic field analysis in order to investigate the influence of the AC/DC load conditions on our model. By manufacturing a model using an experimental construction setup, we validate the results of our analytical approach. [ABSTRACT FROM AUTHOR]

As power systems evolve to incorporate greater penetrations of variable renewables, the demand for flexibility within the system is increased. Combined-cycle gas turbines are traditionally considered as relatively inflexible units, but those which incorporate a steam bypass stack are capable of open-cycle operation. Facilitating these units to also operate in open-cycle mode can benefit the power system via improved system reliability, while reducing the production needed from dedicated peaking units. The utilization of the multi-mode functionality is shown to be dependent on the flexibility inherent in the system and the manner in which the system is operated. [ABSTRACT FROM PUBLISHER]